Capillary movement of liquid. Capillary phenomena (physics). Capillary phenomena in nature. "Study of the capillary properties of various samples of porous paper"

The existence of wetting and contact angle leads to the fact that the curvature of the liquid surface is observed near the vessel walls. If the liquid wets the walls, the surface has a concave shape; if it does not wet, it is convex. This kind of curved fluid surface is called a meniscus. (fig.10.11)

The pressure under the curved surface in the capillary will differ from the pressure under the flat surface by the value
... Such a level difference is established between the liquid in the capillary and in a wide vessel so that the hydrostatic pressure
counterbalanced capillary pressure
... In the case of a spherical meniscus

... The radius of curvature of the meniscus is expressed through the contact angle and the capillary radius r
then
,

In case of wetting
and height of liquid rise in the capillary the larger, the smaller the capillary radiusr .

The capillary phenomenon occupies an exceptional role in human life... The supply of moisture to plants and trees occurs precisely with the help of capillaries, which are in every plant. Capillary phenomena can also play a negative role. For example, in construction. The need to waterproof the foundations of buildings is caused by capillary phenomena.

Questions for self-control

1. Describe the liquid state in comparison with crystals and gases.

2.What is long-range and short-range order?

3. What can the radial distribution function do? Draw it for crystals, liquids and gases.

4.What is the surface tension coefficient?

6.What is wetting? What is the measure of wetting? Give examples of processes that require good wetting.

7. What determines the height of the liquid rise in the capillary?

Lecture number 5 (11)

Properties of solids

1. Amorphous and crystalline bodies. The structure and types of crystals. De

faults in crystals.

2. Mechanical properties of crystals. Plastic deformation mechanism

tion. Elastic tensile deformation. Hooke's Law.

Amorphous and crystalline bodies.

In amorphous bodies exists close order arrangement of atoms. Crystals possess long-range order arrangement of atoms. Amorphous body isotropic, crystalline - anisotropic.

Upon cooling and heating, the temperature versus time curves are different for amorphous and crystalline bodies. For amorphous bodies, the transition from liquid to solid state can be tens of degrees. For crystals, the melting point is constant. There are cases when one and the same substance, depending on the cooling conditions, can be obtained both in a crystalline and in an amorphous solid state. For example, glass at very slow cooling melt can crystallize... In this case, light reflection and scattering will occur at the boundaries of the small crystals formed, and the crystallized glass loses its transparency.

Crystal cell... The main property of crystals is the regularity of the arrangement of atoms in them. The set of points at which atoms are located (more precisely, atomic nuclei) are spoken of as crystal lattice, and the points themselves are called lattice nodes.

The main characteristic of the crystal lattice is spatial periodicityits structure: the crystal, as it were, consists of repeating parts (cells).

We can break the crystal lattice into exactly the same parallelepipeds containing the same number of equally spaced atoms. The crystal is set of parallelepipedsshifted parallel to each other. If the crystal lattice is displaced parallel to itself by the distance of the edge length, then the lattice will be aligned with itself. These offsets are called broadcasts, and the symmetries of the lattice with respect to these displacements are referred to as translational symmetry (parallel translation, rotation about an axis, mirror reflection, etc.).

If there is an atom in the vertex of any elementary cell, then the same atoms should obviously be in all the other vertices of this and other cells. A set of identical and identically located atoms is called lattice Bravais of this crystal. She represents as if crystal lattice skeleton, embodying all its translational symmetry, i.e. all its frequency.

Classification of different types of crystal symmetry is based primarily on the classification different types of Bravais gratings.

The most symmetric Bravais lattice is the one with the symmetry cuba (cubic system). There are three different

centers of all their faces). In addition to cubic, there are tetragonal, rhombic, monoclinic and others (we will not consider).

The Bravais lattice, generally speaking, does not include all the atoms in the crystal. Real crystal latticecan be represented as a set of several Bravais gratings pushed into one another.

Physical types of crystals.

By the kind of particles from which the crystal lattice is built, by the nature of the forces of interaction between them, ionic, atomic, metallic and molecular crystals are distinguished.

1. Ionic crystals... At the nodes of the crystal lattice, there are alternately positive and negative ions. These ions are attracted to each other by electrostatic (Coulomb) forces. Example: grate of rock salt
(fig.11.1).

2. Atomic crystals... Typical representatives are graphite and diamond. Communication between atoms - covalent... In this case, each of the valence electrons is included in an electron pair that links the given atom with one of its neighbors.

3. Metal crystals... The grilles consist of positively charged ionsbetween which there are "Free" electrons... These electrons are “collectivized” and can be regarded as a kind of “electron gas”. Electrons play the role of “cement”, holding “+” ions, otherwise the lattice would disintegrate. Ions, on the other hand, hold electrons within the lattice.

4. Molecular crystals... An example is ice. At the nodes - moleculesthat are related by van der Waals, i.e. forces interactions molecular electric dipoles.

There can be several types of bonds at the same time (for example, in graphite - covalent, metallic and Van der Waals bonds).

Defects in crystals.

In real crystal lattices, there is deviations from the ideal arrangement of atoms in the lattices we have looked at so far. All such deviations are called crystal lattice defects.

Point defects - such that close order is broken:

Another type of defects - deployment - linear defects of the crystal lattice, violating the correct alternation of atomic planes... They are violate long-range order, distorting its entire structure. They play an important role in the mechanical properties of solids. The simplest types of dislocations are edge and screw. In the case of an edge dislocation, the extra crystal plane is inserted between the adjacent layers of atoms (Fig. 11.5).

In the case of a screw dislocation, part of the crystal lattice is shifted relative to another (Fig.11.6)

Mechanical properties of crystals.

Plastic deformation mechanism... The plastic deformation of metals is based on dislocation movement... The essence of plastic deformation is shear, as a result of which one part of the crystal is displaced in relation to the other due to the sliding of dislocations. In fig. 11.7 (a, b, c) shows the motion of an edge dislocation with the formation unit shift steps.

Note that in reality, atoms jump to new positions in small groups one by one. Such an alternate movement of atoms can be represented as the movement of a dislocation. Dislocations cause what plastic deformation of real crystals occurs under the action of stresses several orders of magnitude lower than those calculated for ideal crystals. But if the dislocation density and also the impurity concentration are high, then this leads to a strong deceleration of dislocations and the termination of their motion. As a result, paradoxically, the strength of the material increases.

Tensile deformation. Hooke's law.

The nature of the change in the forces that bind atoms in a solid from the distance between them is qualitatively the same as in gases and liquids (Fig. 11.8). If to the rod length and section exert force
(Figure 11.9), then under the action of this force the rod will elongate by a certain amount
... Wherein the distances between neighboring atoms along the axis of the rod will increase by a certain amount
(fig.11.8). Elongation of the entire chain of atoms
associated with
obvious relationship:

denote ... Then the total force will act in the entire rod:

,

moreover
will increase until
will not balance
.

taking into account the ratio (*):

. (**)

Let's divide both parts into then

.

Attitude
–mechanical stress tensile strain is denoted by ... The product of values \u200b\u200bconstant for a given material
denote (Young's modulus). Attitude
denote (relative extension). Taking into account these designations, equation (**) takes the form (one of the forms of Hooke's law)

Hooke's law: elongation is directly proportional to applied stress.

When
with increasing the forces of gravity decrease, and a rupture occurs.

Questions for self-control

Give a comparative description of amorphous and crystalline bodies.

Give examples of types of crystal lattices and physical types of crystals. How do they differ?

What is called a dislocation in crystals? What is a point defect?

What is the mechanism of plastic deformation? How does the dislocation density affect the strength of a material?

Derive Hooke's law by considering elastic tensile deformation.

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In our lives, we often come across familiar and ordinary things. Who among us did not use paper napkins, paper handkerchiefs and towels, did not paint in an album, did not glue paper and cardboard? Why do they absorb moisture and do it differently? What does it depend on? These questions interested me very much. This is all connected with the phenomena of wettability and non-wettability, with capillary phenomena.

Problem: What determines the different absorbency of liquid in different types of paper products? I independently decided to experimentally compare various samples of paper products in terms of the quality of liquid absorption. This can be determined by calculating the diameter of the capillaries piercing the paper and the height of the liquid rise through these capillaries. Therefore, I set the following goal for my work.

Project goal: 1. Acquaintance with the theory of wetting and non-wetting, capillary phenomenon. 2. Justification of the reasons for the movement of fluid through the capillaries. 3. Study of the capillary properties of various types of paper products. 4. Experimental proof of the dependence of the height of the liquid rise in the capillaries on the effective diameter of the capillary. 5. Determination of the quality of liquid absorption in samples of paper products.

Project objectives: 1. To study the sources of information on the selected topic. 2. To deepen knowledge of the theory of the capillary phenomenon. 3. Conduct studies of the capillary properties of various paper samples to plot the dependence of the height of liquid rise in capillaries on the calculated capillary diameter. 4. Process and analyze the results obtained during the experiment. 5. Present the results in the form of a diagram. 6. Make a conclusion that meets the goal. 7. Prepare the project for defense.

Object of research: laws and phenomena of physics in the study of the theory of capillary phenomena.

Research subject: paper capillary properties.

The relevance of the research topic is due to the advancement of knowledge on the theory of capillary phenomena in the formulation of the research problem with the attraction of society's attention to the use of familiar things in our life.

Novelty: diagram of measurements of the dependence of the height of liquid rise in capillaries on the calculated effective diameter of the capillary in various types of paper products.

Research methods: - theoretical (analysis of information sources); - practical (observation and study of the phenomenon that describes the result of the study); - experimental (measurement, presentation of measurement results in the form of a table, diagram).

Surface tension

In life, we often deal with bodies permeated with many small channels (paper, yarn, leather, various building materials, soil, wood, etc.). Coming in contact with liquids, such bodies very often absorb them into themselves (Appendix 1). Similar phenomena can also be observed in very narrow tubes called capillaries (from lat. capillus- hair). What is happening is called the phenomenon of capillarity. For a detailed study of this phenomenon, consider the forces underlying capillarity. The term "surface tension" itself implies that the substance at the surface is in a "taut", that is, a stressed state, which is explained by the action of a force called internal pressure. It pulls molecules into the liquid in a direction perpendicular to its surface. Thus, the molecules in the inner layers of a substance experience, on average, the same attraction in all directions from the side of the surrounding molecules. The molecules of the surface layer are subjected to unequal attraction from the side of the inner layers of substances and from the side adjacent to the surface layer of the medium. For example, at the liquid - air interface, liquid molecules in the surface layer are more attracted from the side of neighboring molecules of the inner layers of the liquid than from the side of air molecules (Appendix 2). This is the reason for the difference in the properties of the surface layer of a liquid from the properties of its internal volumes. Internal pressure causes the molecules located on the surface of the liquid to be drawn inward and thereby tends to reduce the surface to a minimum under these conditions. The force acting per unit length of the interface, causing the contraction of the liquid surface, is called the surface tension force or simply surface tension. The coefficient is the main quantity that characterizes the properties of the surface of a liquid, and is called surface tension coefficient.

Surface tension force is a force due to the mutual attraction of liquid molecules, directed tangentially to its surface. The action of surface tension forces leads to the fact that the liquid in equilibrium has the minimum possible surface area. When a liquid contacts other bodies, the liquid has a surface corresponding to the minimum of its surface energy. We are so used to the effects of surface tension that we do not notice them if we do not have fun blowing bubbles. The surface tension of different liquids is not the same, it depends on their molar volume, the polarity of the molecules, the ability of molecules to form a hydrogen bond with each other, etc. With increasing temperature, the surface tension decreases, as the distance between the liquid molecules increases. The surface tension of a liquid is also influenced by the impurities in it. Substances that weaken the surface tension are called surfactants - oil products, alcohols, ether, soap, etc. Some substances increase surface tension - impurities of salts and sugar, due to the fact that their molecules interact with liquid molecules more strongly than liquid molecules between themselves.

Wetting

Everyone knows that even a small drop of water spreads over the clean surface of a glass plate. At the same time, a drop of water on a waxed plate, like on the surface of the leaves of some plants, does not spread, but has an almost regular ball shape. A liquid that spreads as a thin film over a solid is called wetting that solid. A liquid that does not spread, but contracts into a drop, is called non-wetting this body (Appendix 3). How can we explain the phenomena of wettability and non-wettability?

The phenomenon of wettability and non-wettability

Consider a drop of liquid on the surface of a solid (Appendix 4). The line bounding the surface of the drop on the plate is the boundary of the surfaces of three bodies: liquid, solid and gas. Therefore, in the process of establishing the equilibrium of a liquid droplet on the boundary of these bodies, three forces will act: the force of the surface tension of the liquid at the boundary with the gas, the force of the surface tension of the liquid at the boundary with the solid, and the force of the surface tension of the solid at the boundary with the gas. Whether the liquid will spread over the surface of a solid, displacing gas from it, or, conversely, will collect in a drop, depends on the ratio of the magnitudes of these forces. Any liquid, freed from the action of gravity, takes on its natural shape - spherical. Falling, raindrops take the form of balls, pellets are frozen drops of molten lead. It should be noted that it is the rate of change in the diameter of the spot formed by a drop of liquid applied to the clean surface of the material that is used as the main characteristic of wetting in capillaries. Its value depends both on surface phenomena and on the viscosity of the liquid, its density, and volatility. A more viscous liquid with other identical properties spreads over the surface longer and flows more slowly through the capillary channel.

Wetting value

We know that it is better to wash your hands with warm water and soap. The water has up to a hundred-point-but-large co-ef-fi-chi-ent on-top-no-na-ty-ze-niya, which means that cold water will be bad vat la-do-no. In order to reduce the co-ef-fi-chi-ent of the top-nost-but-th-th-th-th of water, we increase-li-chi-va-va-we-to-ra-tu -with water (with an increase in the temperature of water, co-ef-fi-chi-ent over-the-top-no-go na -sha-et-sya), and we use soap, which-that-swarm contains top-no-active substances, strongly reduce ko-ef-fi-tsi-ent on-top-nost-th-th-th-th-nia-niya Ef-fek-you sma-chi-va-nia also work-bo-ta-yut when gluing-and-va-nii de-re-vyan-ny, re-zi-new, bu-mazh and other on-top-no-stays and os-no-va-ny on the connection between the mo-le-ku-la-mi liquid and the mo-le-ku -la-mi solid body. Any glue, first of all, should smear the glue-and-va-si-ness. Soldering is also connected with the properties of sma-chi-va-nia. So that the melted pri-sing (an alloy of tin and lead) is good-ro-sho ras-te-kal-Xia on the top of the spa-and-va-e-me Tal-li-che-items, these surfaces must be carefully cleaned of fat, dust and oxides. An example of the use of sma-chi-va-nia in a living environment can be the feathers of water-to-pl-va-yu-shih birds. These feathers are always smack-zhi-ro-you-mi you-de-ni-i-mi from the glands, which leads to the fact that the feathers of these birds are not sma-chi-va -sya water and do not get wet (Appendix 5).

Capillary phenomena

The action of the top-nost-no-na-ty-ze-niya and the ef-fek-tov sma-chi-va-nia is manifested in the capillary phenomena -le-ni-yah - the movement of the liquid along the thin pipes. Capillary phenomena are the phenomena of the rise or fall of a liquid in capillaries, consisting in the ability of liquids to change the level in small-diameter tubes, narrow channels of arbitrary shape and porous bodies.

Capillaries

About-ra-ti-te attention to how ras-pre-de-la-is-sya liquid in so-sous-dakh of different thickness: in tone kih co-su-dakh the liquid is sub-ni-ma-et-sya higher (Appendix 6). Let us note that sma-chi-va-yu-yu-yu-yu-yu-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-r will be, and nesma-chi-va-yu-s-chaya-omit -sya (Appendix 7). It is known that in cases of full smack-chi-va-nia or not-chi-chi-va-nia, men-nisk - a curved surface of a liquid - in narrow tubes of representations la-is a half-sphere, the diameter of which is equal to the diameter of the ka-na-la of the tube (Appendix 8). Along the border of the top of the liquid, having the shape of a circle, on the liquid from the side of the walls of the tube to the action -there is the power of the top-nost-no-go na-tya-niya, right-flax-naya up, in the case of sma-chi-va-yu-yu-ko-sti, and down , in the case of nesma-chi-va-yu-shchey. This force puts the liquid underneath (or down) in a narrow tube.

Height of liquid rise in capillary tubes

Capillary phenomena are caused by two oppositely directed forces: the force of gravity Fт makes the liquid go down; the surface tension force Fн moves the water upward. The substance will stop rising, provided that Ft \u003d Fn. The rise / fall of the liquid along the ca-pill-la-ru remains-but-whit-Xia when the force is top-nost-no-go na-cha-ze-nia-no-ve -sit-sya force of gravity, acting on the pillar of the under-nyaty liquid (Appendix 9). You-so-that, on which the sma-chi-va-yu-yu-si-chi-va-yu-chi-chi-va-yu-chi-chi-chi-va-yu-yu-yu-yu-yu-yu-yu-chi-chi-chi-va-yu-yu-yu-si-ka-pillar-ka, overcoming gravity, is calculated by the formula ):

N / m; - density of liquid, kg / m 3 9.8 m / s 2 m; - capillary radius, m; d - capillary diameter, m.

The form-mu-la for you-so-you, on which the capillary will go down, will be the same. Liquids that wet the material from which the capillary is made will rise in it (water / glass). And vice versa: liquids that do not wet the capillary will go down in it (glass / mercury). In addition, the height of the rise or fall of the liquid depends on the thickness of the tube: the thinner the capillary, the greater the height of the rise or fall of the liquid. The height is also influenced by the density of the liquid and its coefficient of surface tension (Appendix 10). It is important that if the capillary is inclined to the surface of the liquid, then the height of the liquid rise does not depend on the value of the angle of inclination. No matter how the capillaries are located in the structure (strictly vertically, at an angle to the vertical or with ramifications), the height of the rise of the liquid will depend only on ------, and (or d ) (Appendix 11).

The role of capillary phenomena in nature, everyday life and technology

The phenomenon of capillarity plays a huge role in a wide variety of processes around us. The most common example of a ca-pylar-no-go phenomenon is the principle of work-bo-you habit-no-ven-no-lo ten-tsa or bu-mazh-noy sal-fet-ki. Water from the hands leaves on a lo-ten-tse or bu-mazh-ny sal-fet-ku due to the rise of liquid along the thin fibers, from rykh they co-stand. The existence of living organisms is simply impossible without capillary phenomena. The rise of a nutrient along the stem or stem of a plant is due to the phenomenon of capillarity: the nutrient solution rises through thin capillary tubes formed by the walls of plant cells.

The capillarity of the soil should also be taken into account, because it is also permeated by many shallow channels through which water rises from the deep layers of the soil to the surface. Bees, butterflies extract nectar from the depths of the flower through a very thin capillary tube inside the bee's proboscis.

The majority of plant and animal tissues are penetrated by an enormous number of capillary vessels. It is in the capillaries that the main processes associated with the nutrition and respiration of the body take place. Blood vessels are the capillaries through which blood flows. Moreover, the further the vessels go from the heart, the thinner they become.

Straw-and-te-lyam comes to learn to raise moisture from the soil through the pores of construction-and-tel ma-te-ri-a-lov. If this is not taken into account, then the walls of the buildings are from-sy-re-eut. To protect the fun-da-ment-that and the walls from such waters, they use a hydro-isolation. Fuels and lubricants rise through the capillaries of the wick. Top-l-in-st-pa-e-e-t-e-t-l due to the movement along the fibers of the fi-t-la, as on c-pylar pipes. The wetting of clothes in the rain, for example, trousers to the very knees from walking in puddles, is also due to capillary phenomena. There are many examples of this natural phenomenon around us (Appendix 12).

Experiment

"Study of the capillary properties of various samples of paper products"

The purpose of the experiment: to prove that the height of the liquid rise in the capillaries depends on the diameter of the capillary. Equipment and materials: a container with water, a thermometer, a measuring ruler, a pencil, a clamp, a set of paper samples: a single-layer paper handkerchief, a paper napkin, a notebook sheet, office paper, parchment paper, a paper towel, a watercolor sheet (Appendix 13). Work progress: 1. Prepared samples for research from a set of paper products. To do this, I cut out strips 10 cm and width 2 cm and numbered (Appendix 14). Distance 2 cm drew a line from one end of the sample. 2. I took a container with water and in turn lowered the samples into the water, so that the water level coincided with the drawn line (Appendix 15). 3. As soon as the rise of water stopped, the sample was taken out and the height of the rise of the liquid from the drawn line to the dry area was measured. I conducted such an experiment with each sample (Appendix 16). 4. The obtained analysis data was entered in the table (Appendix 17). 5. The diameter of the capillaries of each of these samples was determined by calculation. For this, from the formula for the height of the liquid rise in the capillaries (4.1), I expressed the formula for finding the diameter of the capillary (4.2):

where ------- ko-ef-fi-chi-ent on-top-no-go na-ty-zh-niya, N / m; - density of liquid, kg / m 3 ; - acceleration of gravity, 9.8 m / s 2 ; - the height of the column of the raised liquid, m; - capillary radius, m; d - capillary diameter, m.

In this case, the samples were each time dipped into tap water, the temperature of which was 20 0 С (Appendix 18), that is, the liquid had a constant density \u003d 1000 kg / m3, surface tension coefficient \u003d 0.073 N⁄m... The data obtained was entered in the table (Appendix 17). Conclusion: it follows from the table that all paper samples absorb water, which indicates the presence of capillaries.

Paper absorbency

But are the calculated values \u200b\u200bof the diameters in the samples plausible? Dry paper thickness of the presented samples from 0.1 mm up to 0.3 mm... In water, the capillaries will straighten and fill with water - the paper will become thicker, but in this case its thickness will be no more than 0.5 mm... What is the evidence of this discrepancy? The capillaries are not continuous, but discontinuous (Appendix 19).

An important property of paper is absorbency. Paper is a capillary-porous body consisting of solid particles or aggregates of particles, the space between which is capillaries. Since paper is a product of industrial processing of cellulose, it is impossible to ensure strict constancy of the diameter of the capillaries. Therefore, they talk about the effective (average) diameter of the capillaries. Many types of paper are highly absorbent for various liquids. The liquid is absorbed into the thickness of the sheet, diverges and passes to its reverse side. Such paper has bright hydrophilic properties. First of all, this applies to the class of blotting and filter papers for various purposes, such as samples numbered 1,2,6. This paper has the finest capillaries and absorbs water best. The imparting of limited absorbency to paper with respect to liquids (water, ink) is called sizing.

Such paper is made of very carefully ground paper pulp, where the formation of partially soluble, degraded cellulose products begins to affect, giving in varying degrees of monolithic films, blocking the pores and having a higher resistance to liquid penetration. This applies to the class of wrapping paper, as sample number 5, as well as to the class of writing and drawing paper, as sample numbers 3,4,7. Therefore, in this experiment, I consider the capillary effect of only samples numbered 1, 2, 6, the products of which have an increased absorbency.

Measurement chart

Based on the data obtained, I built a diagram of measurements of the dependence of the height of liquid rise in capillaries on the calculated effective diameter of the capillary (Appendix 20).

Conclusion: wetting liquids rise through the capillaries, overcoming the force of gravity, to a height that depends on the coefficient of surface tension of the liquid, the density of the liquid and the diameter of the capillary. The smaller the capillary diameter, the higher the liquid rises through the capillary. Best absorption quality for a sample with a smaller capillary diameter. A paper handkerchief has the best absorption quality.

Conclusion

As a result of my research work, I:

1. Deepened my knowledge of the phenomena of wettability and non-wettability, capillary phenomena, which are widespread both in our daily activities and in nature.

2. Learned to derive the formula for the capillary diameter by the height of the liquid rise and calculate the effective (average) capillary diameter by the formula.

3. Proved the dependence of the height of the liquid rise in the capillaries on the calculated capillary diameter.

4. I learned that capillary phenomena depend on the strength of the interaction of molecules inside the liquid and on the strength of the interaction of molecules of a solid with molecules of a liquid; the smaller the capillary diameter, the higher the water rises through the capillary.

5. Compared samples of paper products for the quality of liquid absorption and noted that the best absorption quality was in the sample with a smaller capillary diameter.

6. Improved personal qualities in the process of her work:

perseverance;

observation;

the ability to work with a lot of information;

striving for self-development.

Acquired:

focus on results;

systematic thinking;

analytic skills.

7. Has reached a solution to the problem with the help of the goal and objectives.

I liked my work, I am satisfied with my result. My research can be used in physics lessons when studying the topic "Capillary phenomena", in biology classes in matters of capillary phenomena in the human body, as well as in improving knowledge of chemistry in the study of condensation or colloidal chemistry.

Bibliography

1. Vasyukov V.I. Physics. Basic formulas, laws: A reference guide. - M .: Landmark, 2006

2. Peryshkin A.V. Physics course: Textbook for secondary school / In three parts. - M .: Uchpedgiz, 1965

3. Paper, its structure, composition, classification, fields of application and properties (http://material.osngrad.info)

4. Capillary effects (http://www.studopedia.ru)

5. Capillary phenomena (http://www.booksite.ru)

6. Surface tension (http://www.mirznanii.com)

7. Wetting and capillarity (http://phscs.ru)

Applications

Attachment 1

Sheet plate Blood vessels Filter paper

Appendix 2

Appendix 3

Appendix 4

Appendix 5

Appendix 6

Appendix 7

Mercury Water

Appendix 8

Appendix 9

Appendix 10

Appendix 11

Appendix 12

Appendix 13

Appendix 14

Numbering of samples of paper products

Appendix 15

Appendix 16

Appendix 17

Calculated data of paper samples

Appendix 18

Appendix 19

Capillaries are solid and interrupted

Appendix 20

CAPILLARY PHENOMENA - a set of phenomena caused by the action of interfacial surface tension at the interface of immiscible media; to K. i. usually refers to the phenomenon in liquids caused by the curvature of their surface, bordering on other liquid, gas or proper. ferry. K. Ya. Is a special case of surface phenomena. In the absence, the surface of the liquid is always curved. Under the influence of a limited volume of liquid tends to take the shape of a ball, that is, to occupy a volume with min. surface. The forces of gravity significantly change the picture. A liquid with a relatively low viscosity quickly takes the form of a vessel, into which it is poured, and its free surface (not bordering on the walls of the vessel) in the case of sufficiently large masses of liquid and a large free surface area is practically flat. However, as the mass of the liquid decreases, the role of surface tension becomes more significant than the force of gravity. So, for example, when a liquid in a gas (or a gas in a liquid) breaks up, drops (bubbles) are spherical. forms. The properties of systems containing a large number of drops or bubbles (emulsions, liquid aerosols, foams), and the conditions for their formation are largely determined by the curvature of the surface of these formations, that is, K. i. The big role of K. I. play in nucleation during vapor condensation, boiling of liquids, crystallization. The curvature of the surface of a liquid can also occur as a result of its interaction with the surface of another liquid or solid. In this case, the presence or absence of wetting liquid of this surface. If it takes place, that is, molecules of liquid 1 (Fig. 1) interact more strongly with the surface of a solid body 3 than with molecules of another liquid (or gas) 2, then under the influence of the difference in the forces of intermolecular interaction, the liquid rises along the wall of the vessel and the adjacent to a solid, a section of the surface of the liquid will be curved. Hydrostatic the pressure caused by the rise in the liquid level is balanced capillary pressure - the difference in pressure above and below the curved surface, the value of which is related to the local curvature of the liquid surface. If you bring the flat walls of the vessel closer to the liquid, then the curvature zones overlap and a meniscus is formed - a completely curved surface. In such a capillary, under wetting conditions under the concave meniscus, the pressure is reduced, the liquid rises; the weight of the liquid column is high. h 0 balances the capillary pressure Dp. In equilibrium

Let the liquid be in a vessel. If the distances between the surfaces bounding the liquid are comparable to the radius of curvature of the liquid surface, then such vessels are called capillaries ... The phenomena occurring in the capillaries are called capillary phenomena ... Capillary phenomena include capillary rise liquids and capillary coupling between wetted surfaces.

The simplest and most commonly used capillaries are cylindrical capillaries (Figure 10.10). The surface of the liquid in such capillaries is spherical. Let r be the radius of curvature of the liquid surface, R - the radius of the capillary, θ - the contact angle. In the case of partial wetting, the liquid will rise through the capillary under the action of the Laplace pressure, until it is compensated by the hydraulic pressure of the liquid:

Where ρ is the density of the liquid, g - acceleration of gravity, h - the height of the capillary rise. It is convenient to express the radius of curvature of the liquid surface through the radius of the capillary, which can be easily measured:. Substituting the Laplace pressure for a spherical surface expression (10-12), we get:

In case of complete wetting θ \u003d 0 о, cos θ \u003d 1, r \u003d R and the formula for the height of capillary rise is:

With complete non-wetting θ \u003d 180 о, cos θ \u003d - 1,and the height of capillary rise will be negative, that is, the surface of the liquid will drop by an amount h (fig.10.11).

It is interesting to note that in communicating capillaries the height of the liquid level is not the same. The largest capillary rise is observed in the narrowest capillary, and the smallest - in the widest capillary (Figure 10.12).

For complete wetting. Capillary phenomena are observed when water rises to the soil surface, when using blotting paper, rags, when kerosene rises in wicks, etc.

With increasing temperature, the coefficient of surface tension of liquids decreases, and at a critical temperature it is equal to zero. The surface tension coefficient of liquids also depends on the density and molar mass of the liquid. Moreover, the dependence of the surface tension coefficient on temperature is more pronounced, the higher the density of the liquid and the lower its molar mass. A semi-empirical formula can be used to determine the surface tension coefficient:

Here B is a constant coefficient, practically the same for all liquids, T to is the critical temperature, ρ is the density of the liquid, μ is its molar mass, τ is a small value of the dimension of temperature. Formula (10-14) is not applicable near the critical temperature. The surface tension coefficient of aqueous solutions depends on the type of solute. Some substances, for example, such as alcohol, soap, washing powders, dissolved in water, having a lower density than water, lead to a decrease in the surface tension coefficient and are called surfactants ... Surfactants are used as wetting agents, flotation reagents, foaming agents, dispersants, hardness reducing agents, plasticizing additives, crystallization modifiers, etc. An increase in the concentration of such substances leads to a decrease in the surface tension coefficient. Other substances dissolved in water, for example, sugar, salt, lead to an increase in the density of the solution and increase the surface tension coefficient. An increase in the concentration of such substances leads to an increase in the surface tension coefficient. For the experimental determination of the surface tension coefficients, several measurement methods are used: the Rebinder method, the capillary wave method, the drop and bubble method, etc.

The curvature of the surface of the liquid at the edges of the vessel is especially clearly visible in narrow tubes, where the entire free surface of the liquid is curved. In tubes with a narrow cross-section, this surface is part of a sphere, it is called meniscus... A concave meniscus is formed in a wetting liquid (Fig. 1, a), and in a non-wetting one, a convex one (Fig. 1, b).

Since the surface area of \u200b\u200bthe meniscus is greater than the cross-sectional area of \u200b\u200bthe tube, the curved surface of the liquid tends to straighten under the action of molecular forces.

Surface tension forces create additional (Laplace) pressure under the curved surface of the liquid.

To calculate the excess pressure, let us assume that the liquid surface has the shape of a sphere of radius R (Fig. 2. a), from which a spherical segment is mentally cut off, resting on a circle of radius.

Each infinitesimal element of the length of this contour is acted upon by a surface tension force tangential to the surface of the sphere, the modulus of which. Let's split the vector into two components of the force. From Figure 2, a we see that the geometric sum of forces for two selected diametrically opposite elements is equal to zero. Therefore, the surface tension force is directed perpendicularly to the section plane inside the liquid (Fig. 2, c) and its modulus is

The excess pressure created by this force

where is the area of \u200b\u200bthe base of the spherical segment. therefore

If the surface of the liquid is concave, then the surface tension force is directed from the liquid (Fig. 2, b) and the pressure under the concave surface of the liquid is less than under the flat surface by the same amount. This formula determines the Laplace pressure for the case of a spherical shape of the free surface of a liquid. It is a special case of the Laplace formula, which determines the excess pressure for an arbitrary surface of a liquid of double curvature:

where are the radii of curvature of any two mutually perpendicular normal sections of the liquid surface. The radius of curvature is positive if the center of curvature of the corresponding section is inside the fluid, and negative if the center of curvature is outside the fluid. For cylindrical surface overpressure .

If you place a narrow tube ( capillary) with one end into a liquid poured into a wide vessel, then due to the presence of the Laplace pressure force, the liquid in the capillary rises (if the liquid is wetting) or descends (if the liquid is non-wetting) (Fig. 3, a, b), since under the flat surface of the liquid in there is no excess pressure in a wide vessel.