State of aggregation- a state of matter characterized by certain qualitative properties: the ability or inability to maintain volume and shape, the presence or absence of long- and short-range order, and others. A change in the state of aggregation can be accompanied by an abrupt change in free energy, entropy, density and other basic physical properties.
There are three main states of aggregation: solid, liquid and gas. Sometimes it is not entirely correct to classify plasma as a state of aggregation. There are other states of aggregation, for example, liquid crystals or Bose-Einstein condensate. Changes in the state of aggregation are thermodynamic processes called phase transitions. The following varieties are distinguished: from solid to liquid - melting; from liquid to gaseous - evaporation and boiling; from solid to gaseous - sublimation; from gaseous to liquid or solid - condensation; from liquid to solid - crystallization. A distinctive feature is the absence of a sharp boundary of the transition to the plasma state.
Definitions of states of aggregation are not always strict. Thus, there are amorphous bodies that retain the structure of a liquid and have low fluidity and the ability to retain shape; liquid crystals are fluid, but at the same time they have some properties of solids, in particular, they can polarize electromagnetic radiation passing through them. To describe various states in physics, the broader concept of thermodynamic phase is used. Phenomena that describe transitions from one phase to another are called critical phenomena.
The state of aggregation of a substance depends on the physical conditions in which it is located, mainly on temperature and pressure. The determining quantity is the ratio of the average potential energy of interaction of molecules to their average kinetic energy. Thus, for a solid this ratio is greater than 1, for gases it is less than 1, and for liquids it is approximately equal to 1. The transition from one state of aggregation of a substance to another is accompanied by an abrupt change in the value of this ratio, associated with an abrupt change in intermolecular distances and intermolecular interactions. In gases, intermolecular distances are large, molecules hardly interact with each other and move almost freely, filling the entire volume. In liquids and solids - condensed matter - molecules (atoms) are located much closer to each other and interact more strongly.
This leads to liquids and solids maintaining their volume. However, the nature of the movement of molecules in solids and liquids is different, which explains the difference in their structure and properties.
In solids in a crystalline state, atoms only vibrate near the nodes of the crystal lattice; the structure of these bodies is characterized by a high degree of order - long-range and short-range order. The thermal motion of molecules (atoms) of a liquid is a combination of small vibrations around equilibrium positions and frequent jumps from one equilibrium position to another. The latter determine the existence in liquids of only short-range order in the arrangement of particles, as well as their inherent mobility and fluidity.
A. Solid- a state characterized by the ability to maintain volume and shape. The atoms of a solid undergo only small vibrations around the equilibrium state. There is both long- and short-range order.
b. Liquid- a state of matter in which it has low compressibility, that is, it retains its volume well, but is not able to retain its shape. The liquid easily takes the shape of the container in which it is placed. Atoms or molecules of a liquid vibrate near an equilibrium state, locked by other atoms, and often jump to other free places. Only short-range order is present.
Melting- this is the transition of a substance from a solid state of aggregation (see Aggregate states of matter) to liquid. This process occurs when heated, when a certain amount of heat +Q is imparted to the body. For example, the low-melting metal lead changes from a solid to a liquid state if it is heated to a temperature of 327 C. Lead easily melts on a gas stove, for example in a stainless steel spoon (it is known that the flame temperature of a gas burner is 600-850 ° C, and the temperature steel melting - 1300-1500°C).
If, while melting lead, you measure its temperature, you will find that at first it increases smoothly, but after a certain point remains constant, despite further heating. This moment corresponds to melting. The temperature remains constant until all the lead has melted, and only then begins to rise again. When liquid lead is cooled, the opposite picture is observed: the temperature drops until solidification begins and remains constant all the time until the lead passes into the solid phase, and then drops again.
All pure substances behave in a similar way. The constancy of the temperature during melting is of great practical importance, since it allows you to calibrate thermometers and make fuses and indicators that melt at a strictly specified temperature.
Atoms in a crystal oscillate around their equilibrium positions. With increasing temperature, the amplitude of vibrations increases and reaches a certain critical value, after which the crystal lattice is destroyed. This requires additional thermal energy, so the temperature does not increase during the melting process, although heat continues to flow.
The melting point of a substance depends on pressure. For substances whose volume increases during melting (and these are the vast majority), an increase in pressure increases the melting point and vice versa. When water melts, its volume decreases (therefore, when water freezes, it bursts pipes), and when pressure increases, ice melts at a lower temperature. Bismuth, gallium and some brands of cast iron behave in a similar way.
V. Gas- a state characterized by good compressibility, lack of ability to retain both volume and shape. Gas tends to occupy the entire volume provided to it. Atoms or molecules of a gas behave relatively freely, the distances between them are much larger than their sizes.
Plasma, often classified as an aggregate state of matter, differs from gas in the high degree of ionization of atoms. Most of the baryonic matter (about 99.9% by mass) in the Universe is in the plasma state.
city ​​C supercritical fluid- Occurs with a simultaneous increase in temperature and pressure to a critical point at which the density of the gas is compared with the density of the liquid; in this case, the boundary between the liquid and gaseous phases disappears. Supercritical fluid has exceptionally high dissolving power.
d. Bose-Einstein condensate- is obtained as a result of cooling a Bose gas to temperatures close to absolute zero. As a result, some atoms find themselves in a state with strictly zero energy (that is, in the lowest possible quantum state). The Bose-Einstein condensate exhibits a number of quantum properties, such as superfluidity and Fischbach resonance.
e. Fermion condensate- represents Bose condensation in the BCS mode of “atomic Cooper pairs” in gases consisting of fermion atoms. (In contrast to the traditional regime of Bose-Einstein condensation of compound bosons).
Such fermionic atomic condensates are “relatives” of superconductors, but with a critical temperature of the order of room temperature and higher.
Degenerate matter - Fermi gas Stage 1 Electron-degenerate gas, observed in white dwarfs, plays an important role in the evolution of stars. 2nd stage, the neutron state, matter passes into it at ultra-high pressure, which is not yet achievable in the laboratory, but exists inside neutron stars. During the transition to the neutron state, the electrons of the substance interact with protons and turn into neutrons. As a result, matter in the neutron state consists entirely of neutrons and has a density on the order of nuclear. The temperature of the substance should not be too high (in energy equivalent, no more than a hundred MeV).
With a strong increase in temperature (hundreds of MeV and above), various mesons begin to be born and annihilate in the neutron state. With a further increase in temperature, deconfinement occurs, and the substance passes into the state of quark-gluon plasma. It no longer consists of hadrons, but of constantly being born and disappearing quarks and gluons. Perhaps deconfinement occurs in two stages.
With a further unlimited increase in pressure without increasing temperature, the substance collapses into a black hole.
With a simultaneous increase in both pressure and temperature, other particles are added to the quarks and gluons. What happens to matter, space and time at temperatures close to Planck’s is still unknown.
Other states
During deep cooling, some (not all) substances transform into a superconducting or superfluid state. These states, of course, are separate thermodynamic phases, but they can hardly be called new aggregate states of matter due to their non-universality.
Heterogeneous substances such as pastes, gels, suspensions, aerosols, etc., which under certain conditions demonstrate the properties of both solids and liquids and even gases, are usually classified as dispersed materials, and not to any specific aggregate states of matter .

State of aggregation- this is the state of a substance in a certain range of temperatures and pressures, characterized by properties: the ability (solid) or inability (liquid, gas) to maintain volume and shape; the presence or absence of long-range (solid) or short-range (liquid) order and other properties.

A substance can be in three states of aggregation: solid, liquid or gaseous; currently, an additional plasma (ionic) state is distinguished.

IN gaseous In this state, the distance between the atoms and molecules of the substance is large, the interaction forces are small and the particles, moving chaotically in space, have a large kinetic energy that exceeds the potential energy. A material in a gaseous state has neither its own shape nor volume. Gas fills all available space. This state is typical for substances with low density.

IN liquid state, only short-range order of atoms or molecules is preserved, when individual areas with an ordered arrangement of atoms periodically appear in the volume of the substance, but the mutual orientation of these areas is also absent. Short-range order is unstable and under the influence of thermal vibrations of atoms it can either disappear or appear again. Liquid molecules do not have a specific position, and at the same time they do not have complete freedom of movement. The material in the liquid state does not have its own shape; it retains only its volume. The liquid can occupy only part of the volume of the vessel, but flow freely over the entire surface of the vessel. The liquid state is usually considered intermediate between a solid and a gas.

IN hard In a substance, the arrangement of atoms becomes strictly defined, naturally ordered, the forces of interaction between particles are mutually balanced, so the bodies retain their shape and volume. The regularly ordered arrangement of atoms in space characterizes the crystalline state; the atoms form a crystal lattice.

Solids have an amorphous or crystalline structure. For amorphous bodies are characterized only by short-range order in the arrangement of atoms or molecules, a chaotic arrangement of atoms, molecules or ions in space. Examples of amorphous bodies are glass, pitch, var, which are outwardly in a solid state, although in fact they flow slowly, like a liquid. Amorphous bodies, unlike crystalline ones, do not have a specific melting point. Amorphous solids occupy an intermediate position between crystalline solids and liquids.

Most solids have crystalline a structure characterized by the orderly arrangement of atoms or molecules in space. The crystal structure is characterized by long-range order, when the elements of the structure are periodically repeated; with short-range order there is no such correct repetition. A characteristic feature of a crystalline body is the ability to maintain its shape. A sign of an ideal crystal, the model of which is a spatial lattice, is the property of symmetry. Symmetry refers to the theoretical ability of the crystal lattice of a solid body to align with itself when its points are mirrored from a certain plane, called the plane of symmetry. The symmetry of the external shape reflects the symmetry of the internal structure of the crystal. For example, all metals have a crystalline structure and are characterized by two types of symmetry: cubic and hexagonal.

In amorphous structures with a disordered distribution of atoms, the properties of the substance in different directions are the same, that is, glassy (amorphous) substances are isotropic.

All crystals are characterized by anisotropy. In crystals, the distances between atoms are ordered, but in different directions the degree of ordering may not be the same, which leads to differences in the properties of the crystal substance in different directions. The dependence of the properties of a crystal substance on the direction in its lattice is called anisotropy properties. Anisotropy manifests itself when measuring both physical and mechanical and other characteristics. There are properties (density, heat capacity) that do not depend on the direction in the crystal. Most of the characteristics depend on the choice of direction.

It is possible to measure properties of objects that have a certain material volume: sizes - from several millimeters to tens of centimeters. These objects with a structure identical to the crystal cell are called single crystals.

Anisotropy of properties manifests itself in single crystals and is practically absent in a polycrystalline substance, consisting of many small randomly oriented crystals. Therefore, polycrystalline substances are called quasi-isotropic.

Crystallization of polymers, the molecules of which can be arranged in an orderly manner with the formation of supramolecular structures in the form of packs, coils (globules), fibrils, etc., occurs in a certain temperature range. The complex structure of molecules and their aggregates determines the specific behavior of polymers when heated. They cannot go into a liquid state with low viscosity and do not have a gaseous state. In solid form, polymers can be in glassy, ​​highly elastic and viscous states. Polymers with linear or branched molecules can change from one state to another when the temperature changes, which manifests itself in the process of deformation of the polymer. In Fig. Figure 9 shows the dependence of deformation on temperature.

Rice. 9 Thermomechanical curve of an amorphous polymer: t c , t T, t p - glass transition, fluidity and onset of chemical decomposition temperatures, respectively; I - III - zones of glassy, ​​highly elastic and viscous state, respectively; Δ l- deformation.

The spatial structure of the arrangement of molecules determines only the glassy state of the polymer. At low temperatures, all polymers deform elastically (Fig. 9, zone I). Above glass transition temperature t c an amorphous polymer with a linear structure transforms into a highly elastic state ( zone II), and its deformation in the glassy and highly elastic states is reversible. Heating above the pour point t t transfers the polymer to a viscous flow state ( zone III). The deformation of a polymer in a viscous flow state is irreversible. An amorphous polymer with a spatial (network, cross-linked) structure does not have a viscous flow state; the temperature region of the highly elastic state expands to the temperature of polymer decomposition t R. This behavior is typical for materials such as rubber.

The temperature of a substance in any state of aggregation characterizes the average kinetic energy of its particles (atoms and molecules). These particles in bodies possess mainly the kinetic energy of vibrational movements relative to the center of equilibrium, where the energy is minimal. When a certain critical temperature is reached, the solid material loses its strength (stability) and melts, and the liquid turns into steam: it boils and evaporates. These critical temperatures are the melting and boiling points.

When a crystalline material is heated at a certain temperature, the molecules move so energetically that the rigid bonds in the polymer are broken and the crystals are destroyed - they turn into a liquid state. The temperature at which the crystals and liquid are in equilibrium is called the melting point of the crystal, or the solidification point of the liquid. For iodine, this temperature is 114 o C.

Each chemical element has an individual melting point t pl, separating the existence of a solid and a liquid, and the boiling point t kip, corresponding to the transition of liquid to gas. At these temperatures, substances are in thermodynamic equilibrium. A change in the state of aggregation can be accompanied by an abrupt change in free energy, entropy, density and others physical quantities.

To describe the various states in physics uses a broader concept thermodynamic phase. Phenomena that describe transitions from one phase to another are called critical.

When heated, substances undergo phase transformations. When copper melts (1083 o C) it turns into a liquid in which the atoms have only short-range order. At a pressure of 1 atm, copper boils at 2310 o C and turns into gaseous copper with randomly arranged copper atoms. At the melting point, the saturated vapor pressures of the crystal and the liquid are equal.

The material as a whole is a system.

System- a group of substances combined physical, chemical or mechanical interactions. Phase called a homogeneous part of a system, separated from other parts physical interface boundaries (in cast iron: graphite + iron grains; in water with ice: ice + water).Components systems are the different phases that make up a given system. System components- these are the substances that form all the phases (components) of a given system.

Materials consisting of two or more phases are dispersed systems Dispersed systems are divided into sols, whose behavior resembles the behavior of liquids, and gels with the characteristic properties of solids. In sols, the dispersion medium in which the substance is distributed is liquid; in gels, the solid phase predominates. Gels are semi-crystalline metal, concrete, a solution of gelatin in water at low temperatures (at high temperatures gelatin turns into a sol). A hydrosol is a dispersion in water, an aerosol is a dispersion in air.

Status diagrams.

In a thermodynamic system, each phase is characterized by parameters such as temperature T, concentration With and pressure R. To describe phase transformations, a single energy characteristic is used - the Gibbs free energy ΔG(thermodynamic potential).

Thermodynamics in describing transformations is limited to considering the equilibrium state. Equilibrium state thermodynamic system is characterized by the invariance of thermodynamic parameters (temperature and concentration, since in technological treatments R= const) in time and the absence of flows of energy and matter in it - with constant external conditions. Phase equilibrium- the equilibrium state of a thermodynamic system consisting of two or more phases.

To mathematically describe the equilibrium conditions of a system, there is phase rule, derived by Gibbs. It connects the number of phases (F) and components (K) in an equilibrium system with the variability of the system, i.e., the number of thermodynamic degrees of freedom (C).

The number of thermodynamic degrees of freedom (variance) of a system is the number of independent variables, both internal (chemical composition of phases) and external (temperature), to which various arbitrary (in a certain range) values ​​can be given so that new phases do not appear and old phases do not disappear .

Gibbs phase rule equation:

C = K - F + 1.

In accordance with this rule, in a system of two components (K = 2), the following degrees of freedom are possible:

For a single-phase state (F = 1) C = 2, i.e., you can change the temperature and concentration;

For a two-phase state (F = 2) C = 1, i.e., only one external parameter can be changed (for example, temperature);

For a three-phase state, the number of degrees of freedom is zero, i.e., the temperature cannot be changed without disturbing the equilibrium in the system (the system is invariant).

For example, for a pure metal (K = 1) during crystallization, when there are two phases (F = 2), the number of degrees of freedom is zero. This means that the crystallization temperature cannot be changed until the process is completed and one phase remains - the solid crystal. After the end of crystallization (Ф = 1), the number of degrees of freedom is 1, so you can change the temperature, i.e., cool the solid without disturbing the equilibrium.

The behavior of systems depending on temperature and concentration is described by a phase diagram. The phase diagram of water is a system with one component H 2 O, therefore the largest number of phases that can simultaneously be in equilibrium is three (Fig. 10). These three phases are liquid, ice, steam. The number of degrees of freedom in this case is zero, i.e. Neither the pressure nor the temperature can be changed without any of the phases disappearing. Ordinary ice, liquid water and water vapor can exist in equilibrium simultaneously only at a pressure of 0.61 kPa and a temperature of 0.0075 ° C. The point where three phases coexist is called the triple point ( O).

Curve OS separates the vapor and liquid regions and represents the dependence of saturated water vapor pressure on temperature. The OS curve shows those interrelated values ​​of temperature and pressure at which liquid water and water vapor are in equilibrium with each other, therefore it is called the liquid-vapor equilibrium curve or boiling curve.

Fig 10 Diagram of the state of water

Curve OB separates the liquid region from the ice region. It is the solid-liquid equilibrium curve and is called the melting curve. This curve shows those interrelated pairs of temperature and pressure values ​​at which ice and liquid water are in equilibrium.

Curve O.A. called a sublimation curve and shows the interrelated pairs of pressure and temperature values ​​at which ice and water vapor are in equilibrium.

A phase diagram is a visual way of representing the regions of existence of different phases depending on external conditions, such as pressure and temperature. State diagrams are actively used in materials science at various technological stages of product production.

A liquid differs from a crystalline solid by low viscosity values ​​(internal friction of molecules) and high fluidity values ​​(the reciprocal of viscosity). A liquid consists of many aggregates of molecules, within which the particles are arranged in a certain order, similar to the order in crystals. The nature of structural units and interparticle interactions determines the properties of the liquid. There are liquids: monoatomic (liquefied noble gases), molecular (water), ionic (molten salts), metallic (molten metals), liquid semiconductors. In most cases, liquid is not only a state of aggregation, but also a thermodynamic (liquid) phase.

Liquid substances are most often solutions. Solution homogeneous, but not a chemically pure substance, consists of a dissolved substance and a solvent (examples of a solvent are water or organic solvents: dichloroethane, alcohol, carbon tetrachloride, etc.), therefore it is a mixture of substances. An example is a solution of alcohol in water. However, solutions are also mixtures of gaseous (for example, air) or solid (metal alloys) substances.

When cooled under conditions of low rate of formation of crystallization centers and a strong increase in viscosity, a glassy state may occur. Glasses are isotropic solid materials obtained by supercooling molten inorganic and organic compounds.

There are many known substances whose transition from a crystalline state to an isotropic liquid occurs through an intermediate liquid crystalline state. It is typical for substances whose molecules have the shape of long rods (rods) with an asymmetric structure. Such phase transitions, accompanied by thermal effects, cause abrupt changes in mechanical, optical, dielectric and other properties.

Liquid crystals, like a liquid, can take the form of an elongated drop or the shape of a vessel, have high fluidity, and are capable of merging. They are widely used in various fields of science and technology. Their optical properties are highly dependent on small changes in external conditions. This feature is used in electro-optical devices. In particular, liquid crystals are used in the manufacture of electronic wristwatches, visual equipment, etc.

The main states of aggregation include plasma- partially or fully ionized gas. Based on the method of formation, two types of plasma are distinguished: thermal, which occurs when gas is heated to high temperatures, and gaseous, which is formed during electrical discharges in a gaseous environment.

Plasma-chemical processes have taken a strong place in a number of branches of technology. They are used for cutting and welding refractory metals, synthesis of various substances, plasma light sources are widely used, the use of plasma in thermonuclear power plants is promising, etc.

The most common knowledge is about three states of aggregation: liquid, solid, gaseous; sometimes they remember plasma, less often liquid crystalline. Recently, a list of 17 phases of matter, taken from the famous () Stephen Fry, has spread on the Internet. Therefore, we will tell you about them in more detail, because... you should know a little more about matter, if only in order to better understand the processes occurring in the Universe.

The list of aggregate states of matter given below increases from the coldest states to the hottest, etc. may be continued. At the same time, it should be understood that from the gaseous state (No. 11), the most “uncompressed”, to both sides of the list, the degree of compression of the substance and its pressure (with some reservations for such unstudied hypothetical states as quantum, beam or weakly symmetric) increase. After the text a visual graph of phase transitions of matter is shown.

1. Quantum- a state of aggregation of matter, achieved when the temperature drops to absolute zero, as a result of which internal bonds disappear and matter crumbles into free quarks.

2. Bose-Einstein condensate- a state of aggregation of matter, the basis of which is bosons, cooled to temperatures close to absolute zero (less than a millionth of a degree above absolute zero). In such a strongly cooled state, a sufficiently large number of atoms find themselves in their minimum possible quantum states and quantum effects begin to manifest themselves at the macroscopic level. A Bose-Einstein condensate (often called a Bose condensate, or simply "beck") occurs when you cool a chemical element to extremely low temperatures (usually just above absolute zero, minus 273 degrees Celsius). , is the theoretical temperature at which everything stops moving).
This is where completely strange things begin to happen to the substance. Processes usually observed only at the atomic level now occur on scales large enough to be observed with the naked eye. For example, if you place “back” in a laboratory beaker and provide the desired temperature, the substance will begin to creep up the wall and eventually come out on its own.
Apparently, here we are dealing with a futile attempt by a substance to lower its own energy (which is already at the lowest of all possible levels).
Slowing down atoms using cooling equipment produces a singular quantum state known as a Bose, or Bose-Einstein, condensate. This phenomenon was predicted in 1925 by A. Einstein, as a result of a generalization of the work of S. Bose, where statistical mechanics was built for particles ranging from massless photons to mass-bearing atoms (Einstein's manuscript, considered lost, was discovered in the library of Leiden University in 2005 ). The result of the efforts of Bose and Einstein was the Bose concept of a gas subject to Bose–Einstein statistics, which describes the statistical distribution of identical particles with integer spin called bosons. Bosons, which are, for example, individual elementary particles - photons, and entire atoms, can be in the same quantum states with each other. Einstein proposed that cooling boson atoms to very low temperatures would cause them to transform (or, in other words, condense) into the lowest possible quantum state. The result of such condensation will be the emergence of a new form of matter.
This transition occurs below the critical temperature, which is for a homogeneous three-dimensional gas consisting of non-interacting particles without any internal degrees of freedom.

3. Fermion condensate- a state of aggregation of a substance, similar to backing, but differing in structure. As they approach absolute zero, atoms behave differently depending on the magnitude of their own angular momentum (spin). Bosons have integer spins, while fermions have spins that are multiples of 1/2 (1/2, 3/2, 5/2). Fermions obey the Pauli exclusion principle, which states that no two fermions can have the same quantum state. There is no such prohibition for bosons, and therefore they have the opportunity to exist in one quantum state and thereby form the so-called Bose-Einstein condensate. The process of formation of this condensate is responsible for the transition to the superconducting state.
Electrons have spin 1/2 and are therefore classified as fermions. They combine into pairs (called Cooper pairs), which then form a Bose condensate.
American scientists have attempted to obtain a kind of molecules from fermion atoms by deep cooling. The difference from real molecules was that there was no chemical bond between the atoms - they simply moved together in a correlated manner. The bond between atoms turned out to be even stronger than between electrons in Cooper pairs. The resulting pairs of fermions have a total spin that is no longer a multiple of 1/2, therefore, they already behave like bosons and can form a Bose condensate with a single quantum state. During the experiment, a gas of potassium-40 atoms was cooled to 300 nanokelvins, while the gas was enclosed in a so-called optical trap. Then an external magnetic field was applied, with the help of which it was possible to change the nature of interactions between atoms - instead of strong repulsion, strong attraction began to be observed. When analyzing the influence of the magnetic field, it was possible to find a value at which the atoms began to behave like Cooper pairs of electrons. At the next stage of the experiment, scientists expect to obtain superconductivity effects for the fermion condensate.

4. Superfluid substance- a state in which a substance has virtually no viscosity, and during flow it does not experience friction with a solid surface. The consequence of this is, for example, such an interesting effect as the complete spontaneous “creeping out” of superfluid helium from the vessel along its walls against the force of gravity. Of course, there is no violation of the law of conservation of energy here. In the absence of frictional forces, helium is acted only by gravity forces, the forces of interatomic interaction between helium and the walls of the vessel and between helium atoms. So, the forces of interatomic interaction exceed all other forces combined. As a result, helium tends to spread as much as possible over all possible surfaces, and therefore “travels” along the walls of the vessel. In 1938, Soviet scientist Pyotr Kapitsa proved that helium can exist in a superfluid state.
It is worth noting that many of the unusual properties of helium have been known for quite some time. However, in recent years, this chemical element has been pampering us with interesting and unexpected effects. So, in 2004, Moses Chan and Eun-Syong Kim from the University of Pennsylvania intrigued the scientific world with the announcement that they had succeeded in obtaining a completely new state of helium - a superfluid solid. In this state, some helium atoms in the crystal lattice can flow around others, and helium can thus flow through itself. The “superhardness” effect was theoretically predicted back in 1969. And then in 2004 there seemed to be experimental confirmation. However, later and very interesting experiments showed that not everything is so simple, and perhaps this interpretation of the phenomenon, which was previously accepted as the superfluidity of solid helium, is incorrect.
The experiment of scientists led by Humphrey Maris from Brown University in the USA was simple and elegant. Scientists placed an upside-down test tube in a closed tank containing liquid helium. They froze part of the helium in the test tube and in the reservoir in such a way that the boundary between liquid and solid inside the test tube was higher than in the reservoir. In other words, in the upper part of the test tube there was liquid helium, in the lower part there was solid helium, it smoothly passed into the solid phase of the reservoir, above which a little liquid helium was poured - lower than the liquid level in the test tube. If liquid helium began to leak through solid helium, then the difference in levels would decrease, and then we can talk about solid superfluid helium. And in principle, in three of the 13 experiments, the difference in levels actually decreased.

5. Superhard substance- a state of aggregation in which matter is transparent and can “flow” like a liquid, but in fact it is devoid of viscosity. Such liquids have been known for many years; they are called superfluids. The fact is that if a superfluid is stirred, it will circulate almost forever, whereas a normal fluid will eventually calm down. The first two superfluids were created by researchers using helium-4 and helium-3. They were cooled to almost absolute zero - minus 273 degrees Celsius. And from helium-4, American scientists managed to obtain a supersolid body. They compressed frozen helium with more than 60 times the pressure, and then placed the glass filled with the substance on a rotating disk. At a temperature of 0.175 degrees Celsius, the disk suddenly began to spin more freely, which scientists say indicates that helium has become a superbody.

6. Solid- a state of aggregation of a substance, characterized by stability of shape and the nature of the thermal movement of atoms, which perform small vibrations around equilibrium positions. The stable state of solids is crystalline. There are solids with ionic, covalent, metallic and other types of bonds between atoms, which determines the diversity of their physical properties. The electrical and some other properties of solids are mainly determined by the nature of the movement of the outer electrons of its atoms. Based on their electrical properties, solids are divided into dielectrics, semiconductors, and metals; based on their magnetic properties, solids are divided into diamagnetic, paramagnetic, and bodies with an ordered magnetic structure. Studies of the properties of solids have merged into a large field - solid state physics, the development of which is stimulated by the needs of technology.

7. Amorphous solid- a condensed state of aggregation of a substance, characterized by isotropy of physical properties due to the disordered arrangement of atoms and molecules. In amorphous solids, atoms vibrate around randomly located points. Unlike the crystalline state, the transition from solid amorphous to liquid occurs gradually. Various substances are in an amorphous state: glass, resins, plastics, etc.

8. Liquid crystal is a specific state of aggregation of a substance in which it simultaneously exhibits the properties of a crystal and a liquid. It should be noted right away that not all substances can be in a liquid crystalline state. However, some organic substances with complex molecules can form a specific state of aggregation - liquid crystalline. This state occurs when crystals of certain substances melt. When they melt, a liquid crystalline phase is formed, which differs from ordinary liquids. This phase exists in the range from the melting temperature of the crystal to some higher temperature, when heated to which the liquid crystal turns into an ordinary liquid.
How does a liquid crystal differ from a liquid and an ordinary crystal and how is it similar to them? Like an ordinary liquid, a liquid crystal has fluidity and takes the shape of the container in which it is placed. This is how it differs from the crystals known to everyone. However, despite this property, which unites it with a liquid, it has a property characteristic of crystals. This is the ordering in space of the molecules that form the crystal. True, this ordering is not as complete as in ordinary crystals, but, nevertheless, it significantly affects the properties of liquid crystals, which distinguishes them from ordinary liquids. Incomplete spatial ordering of the molecules forming a liquid crystal is manifested in the fact that in liquid crystals there is no complete order in the spatial arrangement of the centers of gravity of the molecules, although there may be partial order. This means that they do not have a rigid crystal lattice. Therefore, liquid crystals, like ordinary liquids, have the property of fluidity.
A mandatory property of liquid crystals, which brings them closer to ordinary crystals, is the presence of an order of spatial orientation of the molecules. This order in orientation can manifest itself, for example, in the fact that all the long axes of molecules in a liquid crystal sample are oriented in the same way. These molecules must have an elongated shape. In addition to the simplest named ordering of molecular axes, a more complex orientational order of molecules can occur in a liquid crystal.
Depending on the type of ordering of the molecular axes, liquid crystals are divided into three types: nematic, smectic and cholesteric.
Research on the physics of liquid crystals and their applications is currently being carried out on a wide front in all the most developed countries of the world. Domestic research is concentrated in both academic and industrial research institutions and has a long tradition. The works of V.K., completed back in the thirties in Leningrad, became widely known and recognized. Fredericks to V.N. Tsvetkova. In recent years, the rapid study of liquid crystals has seen domestic researchers also make a significant contribution to the development of the study of liquid crystals in general and, in particular, the optics of liquid crystals. Thus, the works of I.G. Chistyakova, A.P. Kapustina, S.A. Brazovsky, S.A. Pikina, L.M. Blinov and many other Soviet researchers are widely known to the scientific community and serve as the foundation for a number of effective technical applications of liquid crystals.
The existence of liquid crystals was established a long time ago, namely in 1888, that is, almost a century ago. Although scientists encountered this state of matter before 1888, it was officially discovered later.
The first to discover liquid crystals was the Austrian botanist Reinitzer. While studying the new substance cholesteryl benzoate he synthesized, he discovered that at a temperature of 145°C the crystals of this substance melt, forming a cloudy liquid that strongly scatters light. As heating continues, upon reaching a temperature of 179°C, the liquid becomes clear, i.e., it begins to behave optically like an ordinary liquid, for example water. Cholesteryl benzoate showed unexpected properties in the turbid phase. Examining this phase under a polarizing microscope, Reinitzer discovered that it exhibits birefringence. This means that the refractive index of light, i.e. the speed of light in this phase, depends on the polarization.

9. Liquid- the state of aggregation of a substance, combining the features of a solid state (conservation of volume, a certain tensile strength) and a gaseous state (shape variability). Liquids are characterized by short-range order in the arrangement of particles (molecules, atoms) and a small difference in the kinetic energy of thermal motion of molecules and their potential interaction energy. The thermal motion of liquid molecules consists of oscillations around equilibrium positions and relatively rare jumps from one equilibrium position to another; the fluidity of the liquid is associated with this.

10. Supercritical fluid(SCF) is a state of aggregation of a substance in which the difference between the liquid and gas phases disappears. Any substance at a temperature and pressure above its critical point is a supercritical fluid. The properties of a substance in the supercritical state are intermediate between its properties in the gas and liquid phases. Thus, SCF has a high density, close to a liquid, and low viscosity, like gases. The diffusion coefficient in this case has a value intermediate between liquid and gas. Substances in a supercritical state can be used as substitutes for organic solvents in laboratory and industrial processes. Supercritical water and supercritical carbon dioxide have received the greatest interest and distribution due to certain properties.
One of the most important properties of the supercritical state is the ability to dissolve substances. By changing the temperature or pressure of the fluid, you can change its properties over a wide range. Thus, it is possible to obtain a fluid whose properties are close to either a liquid or a gas. Thus, the dissolving ability of a fluid increases with increasing density (at a constant temperature). Since density increases with increasing pressure, changing the pressure can influence the dissolving ability of the fluid (at a constant temperature). In the case of temperature, the dependence of the properties of the fluid is somewhat more complex - at a constant density, the dissolving ability of the fluid also increases, but near the critical point, a slight increase in temperature can lead to a sharp drop in density, and, accordingly, the dissolving ability. Supercritical fluids mix with each other without limit, so when the critical point of the mixture is reached, the system will always be single-phase. The approximate critical temperature of a binary mixture can be calculated as the arithmetic mean of the critical parameters of the substances Tc(mix) = (mole fraction A) x TcA + (mole fraction B) x TcB.

11. Gaseous- (French gaz, from Greek chaos - chaos), a state of aggregation of a substance in which the kinetic energy of the thermal motion of its particles (molecules, atoms, ions) significantly exceeds the potential energy of interactions between them, and therefore the particles move freely, uniformly filling in the absence of external fields the entire volume provided to it.

12. Plasma- (from the Greek plasma - sculpted, shaped), a state of matter that is an ionized gas in which the concentrations of positive and negative charges are equal (quasi-neutrality). The vast majority of matter in the Universe is in the plasma state: stars, galactic nebulae and the interstellar medium. Near Earth, plasma exists in the form of the solar wind, magnetosphere and ionosphere. High-temperature plasma (T ~ 106 - 108K) from a mixture of deuterium and tritium is being studied with the aim of implementing controlled thermonuclear fusion. Low-temperature plasma (T Ј 105K) is used in various gas-discharge devices (gas lasers, ion devices, MHD generators, plasmatrons, plasma engines, etc.), as well as in technology (see Plasma metallurgy, Plasma drilling, Plasma technology) .

13. Degenerate matter— is an intermediate stage between plasma and neutronium. It is observed in white dwarfs and plays an important role in the evolution of stars. When atoms are subjected to extremely high temperatures and pressures, they lose their electrons (they become electron gas). In other words, they are completely ionized (plasma). The pressure of such a gas (plasma) is determined by the pressure of the electrons. If the density is very high, all particles are forced closer to each other. Electrons can exist in states with specific energies, and no two electrons can have the same energy (unless their spins are opposite). Thus, in a dense gas, all lower energy levels are filled with electrons. Such a gas is called degenerate. In this state, electrons exhibit degenerate electron pressure, which counteracts the forces of gravity.

14. Neutronium- a state of aggregation into which matter passes at ultra-high pressure, which is still unattainable in the laboratory, but exists inside neutron stars. During the transition to the neutron state, the electrons of the substance interact with protons and turn into neutrons. As a result, matter in the neutron state consists entirely of neutrons and has a density on the order of nuclear. The temperature of the substance should not be too high (in energy equivalent, no more than a hundred MeV).
With a strong increase in temperature (hundreds of MeV and above), various mesons begin to be born and annihilate in the neutron state. With a further increase in temperature, deconfinement occurs, and the substance passes into the state of quark-gluon plasma. It no longer consists of hadrons, but of constantly being born and disappearing quarks and gluons.

15. Quark-gluon plasma(chromoplasm) - a state of aggregation of matter in high-energy physics and elementary particle physics, in which hadronic matter passes into a state similar to the state in which electrons and ions are found in ordinary plasma.
Typically, the matter in hadrons is in the so-called colorless (“white”) state. That is, quarks of different colors cancel each other out. A similar state exists in ordinary matter - when all atoms are electrically neutral, that is,
positive charges in them are compensated by negative ones. At high temperatures, ionization of atoms can occur, during which the charges are separated, and the substance becomes, as they say, “quasi-neutral.” That is, the entire cloud of matter as a whole remains neutral, but its individual particles cease to be neutral. The same thing, apparently, can happen with hadronic matter - at very high energies, color is released and makes the substance “quasi-colorless.”
Presumably, the matter of the Universe was in a state of quark-gluon plasma in the first moments after the Big Bang. Now quark-gluon plasma can be formed for a short time during collisions of particles of very high energies.
Quark-gluon plasma was produced experimentally at the RHIC accelerator at Brookhaven National Laboratory in 2005. The maximum plasma temperature of 4 trillion degrees Celsius was obtained there in February 2010.

16. Strange substance- a state of aggregation in which matter is compressed to maximum density values; it can exist in the form of “quark soup”. A cubic centimeter of matter in this state will weigh billions of tons; in addition, it will transform any normal substance it comes into contact with into the same “strange” form with the release of a significant amount of energy.
The energy that can be released when the star's core turns into "strange matter" will lead to a super-powerful explosion of a "quark nova" - and, according to Leahy and Uyed, this is exactly what astronomers observed in September 2006.
The process of formation of this substance began with an ordinary supernova, into which a massive star turned. As a result of the first explosion, a neutron star was formed. But, according to Leahy and Uyed, it did not last very long - as its rotation seemed to be slowed down by its own magnetic field, it began to shrink even more, forming a clump of “strange matter”, which led to an even more powerful during an ordinary supernova explosion, the release of energy - and the outer layers of matter of the former neutron star, flying into the surrounding space at a speed close to the speed of light.

17. Strongly symmetrical substance- this is a substance compressed to such an extent that the microparticles inside it are layered on top of each other, and the body itself collapses into a black hole. The term “symmetry” is explained as follows: Let’s take the aggregative states of matter known to everyone from school - solid, liquid, gaseous. For definiteness, let us consider an ideal infinite crystal as a solid. There is a certain, so-called discrete symmetry with respect to transfer. This means that if you move the crystal lattice by a distance equal to the interval between two atoms, nothing will change in it - the crystal will coincide with itself. If the crystal is melted, then the symmetry of the resulting liquid will be different: it will increase. In a crystal, only points remote from each other at certain distances, the so-called nodes of the crystal lattice, in which identical atoms were located, were equivalent.
The liquid is homogeneous throughout its entire volume, all its points are indistinguishable from one another. This means that liquids can be displaced by any arbitrary distances (and not just some discrete ones, as in a crystal) or rotated by any arbitrary angles (which cannot be done in crystals at all) and it will coincide with itself. Its degree of symmetry is higher. Gas is even more symmetrical: the liquid occupies a certain volume in the vessel and there is an asymmetry inside the vessel where there is liquid and points where it is not. Gas occupies the entire volume provided to it, and in this sense, all its points are indistinguishable from one another. Still, here it would be more correct to talk not about points, but about small, but macroscopic elements, because at the microscopic level there are still differences. At some points at a given moment in time there are atoms or molecules, while at others there are not. Symmetry is observed only on average, either over some macroscopic volume parameters or over time.
But there is still no instant symmetry at the microscopic level. If the substance is compressed very strongly, to pressures that are unacceptable in everyday life, compressed so that the atoms are crushed, their shells penetrate each other, and the nuclei begin to touch, symmetry arises at the microscopic level. All nuclei are identical and pressed against each other, there are not only interatomic, but also internuclear distances, and the substance becomes homogeneous (strange substance).
But there is also a submicroscopic level. Nuclei are made up of protons and neutrons that move around inside the nucleus. There is also some space between them. If you continue to compress so that the nuclei are crushed, the nucleons will press tightly against each other. Then, at the submicroscopic level, symmetry will appear, which does not exist even inside ordinary nuclei.
From what has been said, one can discern a very definite trend: the higher the temperature and the greater the pressure, the more symmetrical the substance becomes. Based on these considerations, a substance compressed to its maximum is called highly symmetrical.

18. Weakly symmetrical matter- a state opposite to strongly symmetrical matter in its properties, present in the very early Universe at a temperature close to Planck's, perhaps 10-12 seconds after the Big Bang, when the strong, weak and electromagnetic forces represented a single superforce. In this state, the substance is compressed to such an extent that its mass turns into energy, which begins to inflate, that is, expand indefinitely. It is not yet possible to achieve the energies for experimentally obtaining superpower and transferring matter into this phase under terrestrial conditions, although such attempts were made at the Large Hadron Collider to study the early universe. Due to the absence of gravitational interaction in the superforce that forms this substance, the superforce is not sufficiently symmetrical in comparison with the supersymmetric force containing all 4 types of interactions. Therefore, this state of aggregation received such a name.

19. Ray substance- this, in fact, is no longer matter at all, but energy in its pure form. However, it is precisely this hypothetical state of aggregation that a body that has reached the speed of light will take. It can also be obtained by heating the body to the Planck temperature (1032K), that is, accelerating the molecules of the substance to the speed of light. As follows from the theory of relativity, when a speed reaches more than 0.99 s, the mass of the body begins to grow much faster than with “normal” acceleration; in addition, the body elongates, heats up, that is, it begins to radiate in the infrared spectrum. When crossing the threshold of 0.999 s, the body changes radically and begins a rapid phase transition up to the ray state. As follows from Einstein’s formula, taken in its entirety, the growing mass of the final substance consists of masses separated from the body in the form of thermal, x-ray, optical and other radiation, the energy of each of which is described by the next term in the formula. Thus, a body that approaches the speed of light will begin to emit in all spectra, grow in length and slow down in time, thinning to the Planck length, that is, upon reaching speed c, the body will turn into an infinitely long and thin beam, moving at the speed of light and consisting of photons that have no length, and its infinite mass will be completely converted into energy. Therefore, such a substance is called ray.

In order to understand what the state of aggregation of a substance is, remember or imagine yourself in the summer near a river with ice cream in your hands. Wonderful picture, isn't it?

So, in this idyll, in addition to receiving pleasure, you can also carry out physical observation. Pay attention to the water. In the river it is liquid, in ice cream it is solid, and in the sky in the form of clouds it is gaseous. That is, it is simultaneously in three different states. In physics, this is called the aggregate state of matter. There are three states of aggregation - solid, liquid and gaseous.

Changes in aggregate states of matter

We can observe changes in the aggregate states of matter with our own eyes in nature. Water from the surface of reservoirs evaporates and clouds form. This is how the liquid turns into gas. In winter, water in reservoirs freezes, turning into a solid state, and in the spring it melts again, turning back into liquid. What happens to the molecules of a substance when it transitions from one state to another? Are they changing? Are ice molecules, for example, different from steam molecules? The answer is clear: no. The molecules remain absolutely the same. Their kinetic energy changes, and, accordingly, the properties of the substance. The energy of the vapor molecules is high enough to fly apart in different directions, and when cooled, the vapor condenses into liquid, and the molecules still have enough energy to move almost freely, but not enough to break away from the attraction of other molecules and fly away. With further cooling, water freezes, becoming a solid, and the energy of the molecules is no longer enough even to move freely inside the body. They vibrate around one place, held by the attractive forces of other molecules.

The nature of the movement and state of molecules in various states of matter can be reflected in the following table:

State of matter	Properties of matter	Particle distance	Particle interaction	Nature of movement	Arrangement order
	Does not retain shape or volume	Much larger than the size of the particles themselves		Chaotic (disorderly) continuous. They fly freely, sometimes colliding.	Messy
Liquid	Does not retain shape, retains volume	Comparable to the size of the particles themselves		They oscillate around the equilibrium position, constantly jumping from one place to another.	Messy
Solid	Maintains shape and volume	Small compared to the size of the particles themselves	Very strong	Continuously oscillates around the equilibrium position	In a certain order

Processes in which there is a change in the aggregate states of substances, six in total.

The transition of a substance from solid to liquid is called melting, reverse process - crystallization. When a substance changes from a liquid to a gas, it is called vaporization, from gas to liquid - condensation. The transition from a solid state directly to a gas, bypassing the liquid state, is called sublimation, reverse process - desublimation.

• 1. Melting
• 2. Crystallization
• 3. Vaporization
• 4. Condensation
• 5. Sublimation
• 6. Desublimation

Examples of all these transitions You and I have seen this more than once in our lives. Ice melts to form water, water evaporates to form steam. In the opposite direction, the steam, condensing, turns back into water, and water, freezing, becomes ice. And if you think that you do not know the processes of sublimation and desublimation, then do not rush to conclusions. The smell of any solid body is nothing more than sublimation. Some molecules escape from the body, forming a gas that we can smell. An example of the reverse process is patterns on glass in winter, when steam in the air, freezing, settles on the glass and forms bizarre patterns.

>> Aggregate state of matter

• Have you ever been on the banks of a fast mountain river in winter? Look at the figure below (Fig. 2.23). There is snow all around, the trees are frozen on the bank, covered with frost, which shines in the sun's rays, and the river does not freeze. Extremely clean, clear water crashes against frozen rocks. Why did frost appear? What is the difference between water and ice? Are there any similarities between them? In this paragraph you will definitely find answers to these questions.

1. We observe different states of matter

You already know that water and ice (snow, frost) are two different physical states of water: liquid and solid. The appearance of frost on trees is explained simply: water from the surface of the river evaporates, turning into water vapor. The water vapor, in turn, condenses and settles as frost. Water vapor is the third state of water - gaseous.

Let's give another example. You are certainly aware of the danger of breaking a medical thermometer: it contains mercury - a thick, silver-colored liquid that, when evaporated, forms a very poisonous vapor. But at temperatures below -39 ° C, mercury turns into a solid metal. Thus, mercury, like water, can be in solid, liquid and gaseous states.

Almost any substance, depending on physical conditions, can be in three states of aggregation: solid, liquid and gaseous.

Rice. 2.23 Various physical states of water

In our example with a mountain river (Fig. 2.23), all three aggregate states of water are present.

2. Observe and explain the physical properties of solids

Look carefully at fig. 2.24. All the solids depicted on it differ from each other: in color, appearance, etc., they are made of different substances. At the same time, they also have common properties inherent in all solids.

Solids retain volume and shape. This is explained by the fact that the atoms and molecules of solids are located in equilibrium positions. The forces of attraction and repulsion between molecules (atoms) in these positions are equal to each other. If an attempt is made to increase or decrease the distance between particles (that is, to increase or decrease the size of the body), intermolecular attraction or repulsion occurs, respectively (see § 14).

You know that according to the atomic-molecular theory, atoms (molecules) are always in motion. Particles of solid bodies practically do not move from place to place - they constantly move around a certain point, that is, they oscillate. Therefore, solids retain not only volume, but also shape.

Rice. 2.24. Despite external differences, any solid body retains its shape and volume.

Rice. 2.25 Models of crystal lattices: o - diamond, 6 - graphite. The balls represent the centers of atoms; lines connecting atoms do not actually exist; they are drawn only to explain the nature of the spatial arrangement of atoms

3. Distinguish between crystalline and amorphous substances

In the course of studying the structure of solids using modern methods, it was possible to find out that the molecules and atoms of most substances in the solid state are arranged in a strictly defined order; physicists say: they form a crystal lattice. Such substances are called crystalline. Examples of crystalline substances include diamond, graphite (Fig. 2.25), ice, salt (Fig. 2.26), metals, etc.

The arrangement of atoms in the crystal lattice of a substance determines its physical properties. For example, diamond and graphite consist of the same atoms - carbon atoms, but these substances are very different from each other, since the atoms in them are located differently (see Fig. 2.25).

Rice. 2.26. Models of crystal lattices: a - ice b - table salt (small balls - Sodium atoms, large ones - Chlorine atoms)

Rice. 2.27. In a liquid state, a substance retains its volume, but takes on the shape of the vessel in which it is located.

Rice. 2.28. The molecules of the liquid are located almost close to each other. In a small volume of liquid, mutual orientation of neighboring molecules is observed (short-range order exists). In general, the molecules of the liquid are arranged chaotically

There is a group of solids (glass, wax, resin, amber, etc.), the molecules (atoms) of which do not form a crystal lattice and are generally arranged randomly. Such substances are called amorphous.

Under certain conditions, solids melt, that is, they turn into a liquid state. Crystalline substances melt at a certain temperature. For example, ice usually turns into a liquid state if the temperature is 0 °C, naphthalene - if it reaches 80 °C, mercury - if it drops to -39 °C. Unlike crystalline substances, amorphous substances do not have a specific melting point. If the temperature increases, they gradually turn into a liquid state (melting of a wax candle).

4. Observe and explain the physical properties of liquids

Liquids easily change their shape and take on the shape of the vessel in which they are contained, however, the volume of the liquid remains unchanged (Fig. 2.27). Moreover, if we try to compress the liquid, we will not succeed. To prove the incompressibility of liquids, scientists conducted an experiment: water was poured into a lead ball, which was sealed, and then compressed with a powerful press. The water did not shrink, but leaked through the walls of the ball.

The ability of liquids to maintain their volume is explained by the fact that, as in solids, the molecules in liquids are located close to each other (Fig. 2.28). The molecules of a liquid are quite tightly packed, but they not only vibrate in the same place surrounded by their closest “neighbors,” but can also move quite easily throughout the volume occupied by the liquid. Therefore, liquids retain volume, but do not retain shape - they are fluid.

Rice. 2.29 Movement and arrangement of molecules in gases: a - the direction of movement of molecules changes as a result of their collision with other molecules; b - approximate trajectory of an air molecule at normal pressure (a million times increase)

5. Explain the physical properties of gases

• Experimental tasks

1. Using a glass of water, prove that there is air in the rubber bulb.

2. Amorphous bodies are called very viscous liquids. Using a candle and, for example, a marker, prove that the wax, albeit very slowly, flows. To do this, place a marker on the windowsill, place a candle on top - perpendicular to the marker - and leave it there for several days. Explain the results of your experiment.