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

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

Under a curved surface in a capillary, the pressure will differ from the pressure under a flat surface by
. Between the liquid in the capillary and in the wide vessel, such a level difference is established so that the hydrostatic pressure
balance capillary pressure
. In the case of a spherical meniscus

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

In case of wetting
and the height of the liquid in the capillary the larger, the smaller the radius of the capillaryr .

The capillary phenomenon takes important 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 for waterproofing 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 does the radial distribution function allow you to 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 rise of the liquid in the capillary?

Lecture #5 (11)

Properties of solids

1. Amorphous and crystalline bodies. Structure and types of crystals. De

effects in crystals.

2. Mechanical properties of crystals. The mechanism of plastic deformation

tions. Elastic Tensile Deformation. Hooke's law.

Amorphous and crystalline bodies.

In amorphous bodies exists short range order arrangement of atoms. crystals possess long-range order arrangement of atoms. amorphous body isotropic, crystalline - anisotropic.

During cooling and heating, the temperature versus time curves are different for amorphous and crystalline bodies. For amorphous bodies, the transition from a liquid to a solid state can be tens of degrees. For crystals, the melting point is constant. There are cases when the same substance, depending on the cooling conditions, can be obtained both in the crystalline and in the amorphous solid state. For example, glass at very slow cooling melt can crystallize. In this case, reflection and scattering of light will occur at the boundaries of small formed crystals, 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 (more precisely, atomic nuclei) are located is said to be crystal lattice, and the points themselves are called lattice nodes.

The main characteristic of a crystal lattice is spatial periodicity its 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 identically arranged atoms. The crystal is collection of parallelepipeds shifted parallel to each other. If the crystal lattice is displaced parallel to itself by a distance of the length of the edge, 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 said to be translational symmetry(parallel translation, rotation about the axis, mirror reflection, etc.).

If there is an atom at the vertex of any elementary cell, then the same atoms must obviously be located at all other vertices of this and other cells. A group of identical and equally spaced atoms is called lattice Bravais this crystal. She presents like skeleton of the crystal lattice, which embodies all of its translational symmetry, i.e. all its frequency.

Classification of different types of symmetry of crystals based primarily on the classification various 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 the cubic, there are tetragonal, rhombic, monoclinic and others (we will not consider).

The Bravais lattice, generally speaking, does not include all the atoms in a crystal. Real crystal lattice can be presented as a collection of several Bravais gratings pushed one into the other.

Physical types of crystals.

According to the type of particles from which the crystal lattice is built, according to the nature of the forces of interaction between them, ionic, atomic, metallic and molecular crystals are distinguished.

1. Ionic crystals. Alternately positive and negative ions are located at the nodes of the crystal lattice. These ions are attracted to each other by electrostatic (Coulomb) forces. Example: rock salt grate
(Fig. 11.1).

2. atomic crystals. Typical representatives are graphite and diamond. Connection between atoms covalent. In this case, each of the valence electrons is included in the electron pair that binds this atom to one of its neighbors.

3. metal crystals. The grids are made up of positively charged ions between which are “free” electrons. These electrons are 'collectivized' and can be considered as a kind of 'electron gas'. Electrons play the role of “cement”, holding “+” ions, otherwise the lattice would break up. Ions, on the other hand, hold electrons within the lattice.

4. molecular crystals. An example is ice. Molecules at the nodes, which are interconnected 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).

Defects in crystals.

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

Point Defects- those in which order is broken:

Another type of defect dislocations– linear defects of the crystal lattice, violating the correct alternation of atomic planes. They are violate the 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, an extra crystal plane is pushed between adjacent layers of atoms (Fig. 11.5).

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

Mechanical properties of crystals.

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

Note that in reality the atoms jump to new positions in small groups one by one. This successive movement of atoms can be represented as the movement of a dislocation. Dislocations cause that plastic deformation of real crystals occurs under the influence of stresses several orders of magnitude smaller than those calculated for ideal crystals. But if the dislocation density and also the impurity concentration are high, then this leads to strong deceleration of dislocations and the cessation 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 a rod of length and section apply force
(Fig. 11.9), then under the action of this force the rod will lengthen 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 ratio:

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

,

and
will increase until
won't balance
.

taking into account the ratio (*):

. (**)

Let's divide both parts into , then

.

Attitude
–mechanical stress tensile strains are denoted . The product of quantities constant for a given material
denote (Young's modulus). Attitude
denote (relative extension). Taking into account these notations, the equation (**) will take the form (one of the forms of Hooke's law)

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

At
with increasing the forces of attraction decrease, and a break occurs.

Questions for self-control

Give comparative characteristic amorphous and crystalline bodies.

Give examples of types of crystal lattices and physical types of crystals. On what principles do they differ?

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

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

Derive Hooke's law by considering elastic tensile strain.

The text of the work is placed without images and formulas.
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In our lives, we often encounter familiar and ordinary things. Which of us has not used paper napkins, paper handkerchiefs and towels, has not painted with paints in an album, has not glued paper and cardboard? Why do they absorb moisture and do it differently? What does it depend on? These questions are of great interest to me. This is all connected with the phenomena of wettability and non-wetting, with capillary phenomena.

Problem: what determines the different absorbency of liquid in various types 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 penetrating the paper and the height of the liquid rising through these capillaries. Therefore, I set the following goal of my work.

The purpose of the project: 1. Acquaintance with the theory of wetting and non-wetting, the capillary phenomenon. 2. Substantiation 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 liquid rise height in capillaries on the effective capillary diameter. 5. Determination of the quality of liquid absorption in samples of paper products.

Project objectives: 1. To study the sources of information on the chosen topic. 2. Deepen knowledge on the theory of the capillary phenomenon. 3. Conduct a study of the capillary properties of various paper samples to compile the dependence of the height of the rise of the liquid in the capillaries on the estimated diameter of the capillary. 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 protection.

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

Subject of research: capillary properties of paper.

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, drawing public attention to the issues of using familiar things in our lives.

Novelty: measurement diagram of the dependence of the liquid rise height in capillaries on the calculated effective capillary diameter 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 pierced by many small channels (paper, yarn, leather, various building materials, soil, wood, etc.). Coming into 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. t The term "surface tension" itself implies that the substance at the surface is in a "stretched", that is, 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. So, molecules located in the inner layers of a substance experience, on average, the same attraction in all directions from 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 bordering the surface layer of the medium. For example, at the liquid-air interface, the liquid molecules in the surface layer are attracted more strongly from the neighboring molecules of the inner layers of the liquid than from the air molecules (Appendix 2). This is the reason for the difference in the properties of the surface layer of the 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 given conditions. The force acting per unit length of the interface, causing the contraction of the surface of the liquid, is called the surface tension force or simply surface tension. The coefficient is the main quantity characterizing the properties of the liquid surface, and is called surface tension.

Surface tension force is a force due to the mutual attraction of the molecules of a liquid, 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 accustomed to the effects caused by surface tension that we do not notice them unless we have fun blowing soap bubbles. The surface tension of various liquids is not the same, it depends on their molar volume, the polarity of the molecules, the ability of the molecules to form hydrogen bonds with each other, etc. As the temperature increases, the surface tension decreases, as the distances between the molecules of the liquid increase. The surface tension of a liquid is also influenced by the impurities present in it. Substances that weaken surface tension are called surface-active (surfactants) - petroleum 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, as well as 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 the given 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 nonwetting?

The phenomenon of wettability and non-wetting

Consider a drop of liquid on the surface of a solid body (Appendix 4). The line limiting 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 drop 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 into a drop, depends on the ratio of the magnitudes of these forces. Any liquid, freed from the action of gravity, takes 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 a spot formed by a drop of liquid deposited on a clean surface of a 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 washing hands is best with warm water and soap. The water has a hundred-accurate-but-big co-ef-fi-ci-ent in the top-nost-no-go on-the-s-th-zhe-niya, which means, cold water it will be bad to sm-chi-vat la-do-ni. In order to reduce the co-ef-fi-ci-ent on the top-nost-no-go on the water, we increase-whether-chi-va-em so-pe-ra-tu -ru of water (with increase-whether-che-ni-em te-pe-ra-tu-ry water co-eff-fi-ci-ent on-top-nost-but-go on-tya-zhe-niya reduce -sha-et-sya), and we use soap, some-swarm contains top-of-the-nost-but active substances, greatly reduce co-ef-fi-ci-ent on top-of-nost-no-go on-heavy-water. Ef-fek-you sma-chi-va-nia also work with gluing-and-va-ni de-re-vyan-nyh, re-zi-no-vyh, boo-mazh-nyh and other top-no-stay and os-no-va-ny on the inter-and-mo-action between mo-le-ku-la-mi liquid-to-sti and mo-le-ku -la-mi solid-to-th body. Any glue, first of all, should lubricate the glue-and-va-yu-sche-top-no-sti. Soldering is also connected with the properties of sma-chi-va-nia. To melt-melted flax solder (an alloy of tin and lead) ho-ro-sho spreads-te-kal-sya on top-no-sti spa-and-va-e-my- tal-li-che-th objects, you need to carefully clean these top-but-sti from grease, dust and oxides. As a measure of application, sma-chi-va-nia in living nature can serve as feathers of water-to-pla-va-u-ing birds. These feathers always lubricate us with fat-ro-you-mi you-de-le-ni-i-mi from the glands, which leads to the fact that the feathers of these birds are not sma-chi-va -yut-sya with water and do not get wet (Appendix 5).

Capillary phenomena

The action of the top-nost-no-go on-the-zhe-zhe-niya and the effects of sma-chi-va-niya appear-la-et-sya in capillary-nyh -le-ni-yah - move-same-nii liquid-to-sti through thin pipes. Capillary phenomena are phenomena of the rise or fall of liquid in capillaries, which consist in the ability of liquids to change the level in small-diameter tubes, narrow channels of arbitrary shape and porous bodies.

capillaries

Ob-ra-ti-te-attention to how the liquid is dispersed in co-su-ds of different thicknesses: in tons kih so-su-dah liquid under-no-ma-et-sya above (Appendix 6). For-me-tim that sma-chi-va-yu-shaya liquid will go down-no-mother-sya on ka-pil-la-ru, and nesma-chi-va-yu-shaya - drop -sya (Appendix 7). It is known that in cases of full sma-chi-va-nia or non-ma-chi-va-nia, the meniscus - the curved surface of the liquid - in narrow tubes is represented by la-et itself in a lu-sphere, the diameter of some-swarm is equal to the diameter of the can-on-la pipe (Appendix 8). Along the border on the top of the liquid, having the shape of a circle, on the liquid from the side of the walls of the tube -there is a force of over-the-top-nost-no-th-on-gravity, on-right-len-up, in the case of sma-chi-va-yu-schey liquid, and down , in the case of nesma-chi-va-yu-schey. This force makes the liquid drop down (or drop 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 Ft causes the liquid to fall down; The surface tension force Fn moves the water upwards. The substance will stop rising provided that Ft = Fn. The ascent / lowering of the liquid along the cap-pil-la-ru stops-but-wit-sya when the force of the top-of-the-no-th-on-gravity equation - sits by the force of gravity, acting on a column of under-thrown-that liquid (Appendix 9). You-with-the one on which the sma-chi-va-u-th liquid in the capillary tube rises, overcoming gravity, is calculated by the formula (3.2.1 ):

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

The formula for you-with-you, on which the non-smoking liquid capillary is lowered, will be the same. Liquids that wet the material of which the capillary is made will rise in it (water / glass). And vice versa: liquids that do not wet the capillary will sink 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 affected 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 rise of the liquid 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 branches), the height of the liquid rise 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 that surround us. The most common example of a ka-pil-lyar-no-go yav-le-niya is the principle of working as usual ten-tsa or boo-mazh-noy napkin-ki. Water leaves the hands on a lo-ten-tse or a paper napkin due to the rise of the liquid along thin fibers, from something ryh they co-hundred-yat. Without capillary phenomena, the existence of living organisms is simply impossible. Climb nutrient along the stem or trunk of a plant 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 penetrated by many small 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 located inside the bee proboscis.

Most plant and animal tissues are permeated with 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 capillaries through which blood flows. Moreover, the farther from the heart the vessels go, the thinner they become.

Build-and-te-lyam at-ho-dit-sya teach-you-wat-eat moisture from the soil through the pores of building materials-te-ri-a-fishing. If this is not taken into account, then the walls of the buildings are from-sy-re-yut. To protect the fun-da-men-ta and walls from such waters, use hydro-iso-la-tion. Combustibles and lubricants rise through the capillaries of the wick. Top-whether in-stu-pa-et on fi-ti-lu due to the movement along fi-ti-la, as in capillary tubes. Wetting clothes during rain, for example, trousers up to the knees from walking through puddles, is also due to capillary phenomena. There are many examples of this natural phenomenon around us (Appendix 12).

Experiment

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

The purpose of the experiment: to prove that the height of liquid rise in capillaries depends on the diameter of the capillary. Equipment and materials: a container with water, a thermometer, a measuring ruler, a pencil, a clip, 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). Progress of work: 1. I prepared samples for research from a set of paper products. To do this, I cut out strips 10 long. cm and width 2 cm and numbered (Appendix 14). At a distance of 2 cm draw a line from one end of the sample. 2. She took a container with water and lowered the samples in turn 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 measured the height of the rise of the liquid from the drawn line to the dry area. I carried out such an experiment with each sample (Appendix 16). 4. The obtained data of the analysis entered into the table (Appendix 17). 5. The diameter of the capillaries of each of these samples was determined by calculation. To do this, from the formula for the height of the rise of liquid in capillaries (4.1), she expressed the formula for finding the diameter of the capillary (4.2):

where - N/m; - density of the liquid, kg/m 3 ; - acceleration of gravity, 9.8 m/s 2 ; is the height of the liquid column, m; - capillary radius, m; d - capillary diameter, m.

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

Paper absorbency

But are the calculated values ​​of diameters in the samples plausible? The dry paper thickness of the presented samples is from 0.1 mm up to 0.3 mm. In water, the capillaries will straighten out and fill with water - the paper will become thicker, but even in this case its thickness will become no more than 0.5 mm. What does this discrepancy indicate? Capillaries are not continuous, but interrupted (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 a strict constancy of the diameter of the capillaries. Therefore, one speaks of the effective (average) diameter of the capillaries. Many types of paper are characterized by increased absorbency to 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 refers to the class of blotting and filter papers for various purposes, such as samples numbered 1,2,6. This paper has the thinnest capillaries and absorbs water the best. Giving paper limited absorbent properties in relation to liquids (water, ink) is called sizing.

Such paper is made from very carefully milled paper pulp, where the formation of partially soluble, degraded cellulose products begins to affect, giving varying degrees of monolithic films that block the pores and have 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 papers for writing and drawing, as sample numbers 3,4,7. Therefore, in this experiment, I only consider the capillary effect of samples numbered 1,2,6, the products of which have an increased absorbency.

Measurement chart

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

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

Conclusion

As a result of my research work, I:

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

2. I learned how to derive the formula for the diameter of a capillary by the height of the rise of the liquid and calculate the effective (average) diameter of the capillary using the formula.

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

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

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

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

perseverance;

observation;

the ability to work with a large amount of information;

desire for self-development.

Bought:

focus on results;

systematic thinking;

analytic skills.

7. Achieved a solution to the problem with the help of the set 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 questions about capillary phenomena in the human body, as well as in improving knowledge of chemistry in studying condensation or colloidal chemistry.

Bibliography

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

2. Peryshkin A.V. Course of physics: A textbook for high school / In three parts. - M .: Uchpedgiz, 1965

3. Paper, its structure, composition, classification, applications 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

Annex 3

Appendix 4

Annex 5

Appendix 6

Appendix 7

Mercury Water

Appendix 8

Appendix 9

Annex 10

Appendix 11

Appendix 12

Appendix 13

Appendix 14

Numbering of samples of paper products

Appendix 15

Annex 16

Annex 17

Estimated data of paper samples

Appendix 18

Appendix 19

Capillaries continuous and discontinuous

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 include phenomena in liquids caused by the curvature of their surface, bordering on another liquid, gas, or proper. ferry. K. Ya. is a special case of surface phenomena. In the absence of a liquid, the surface is always curved. Under the influence, a limited volume of liquid tends to take the form of a ball, i.e., to occupy a volume with min. surface. Gravity forces 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 adjacent to the walls of the vessel) in the case of sufficiently large masses of liquid and a large area of ​​the free surface 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 crushing a liquid in a gas (or a gas in a liquid), droplets (bubbles) spherical are formed. 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. They also play in nucleation during vapor condensation, liquid boiling, and crystallization. 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 on this surface. If it takes place, i.e., the molecules of liquid 1 (Fig. 1) interact more strongly with the surface of a solid body 3 than with the molecules of other 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 body, 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- pressure difference 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 zones of curvature will overlap and a meniscus is formed - a completely curved surface. In such a capillary, under conditions of wetting under a concave meniscus, the pressure is lowered, the liquid rises; weight of the liquid column. h 0 balances the capillary pressure Dр. In equilibrium

Let the liquid be in any 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 that occur in capillaries are called capillary phenomena . The capillaries are capillary rise liquids and capillary adhesion between wetted surfaces.

The simplest and most commonly used capillaries are cylindrical capillaries (Fig. 10.10). The liquid surface 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 is the acceleration of gravity, h is the height of the capillary rise. The radius of curvature of the liquid surface is conveniently expressed in terms of 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 o, cos θ \u003d 1, r = R and the formula for the height of capillary rise is:

With complete wetting θ=180 o, cos θ = - 1, and the height of the capillary rise will be negative, that is, the surface of the liquid will fall 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 (Fig. 10.12).

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

With an increase in temperature, the surface tension coefficient 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 expressed the stronger, the greater the density of the liquid and the less it molar mass. To determine the surface tension coefficient, you can use the semi-empirical formula:

Here B is a constant coefficient, almost the same for all liquids, Tc is the critical temperature, ρ is the density of the liquid, μ is its molar mass, τ is a small temperature dimension. Formula (10-14) is not applicable near the critical temperature. Surface tension coefficient aqueous solutions depends on the type of solute. Some substances, for example, such as alcohol, soap, washing powders, dissolved in water, having a density lower than that of water, lead to a decrease in the surface tension coefficient and are called surfactants . Surfactants are used as wetting agents, flotation reagents, foaming agents, hardness dispersants, plasticizers, 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, such as 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 Rehbinder 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 seen 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 wetting liquid has a concave meniscus (Fig. 1, a), while a non-wetting liquid has a convex one (Fig. 1, b).

Since the surface area of ​​the meniscus is greater than the cross-sectional area of ​​the tube, the curved surface of the liquid tends to straighten out 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, we assume that the surface of the liquid has the shape of a sphere of radius R (Fig. 2. a), from which a spherical segment is mentally cut off, based on a circle of radius .

Each infinitesimal element of the length of this contour is affected by a surface tension force tangent to the surface of the sphere, the modulus of which is . We decompose 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 perpendicular to the sectional plane inside the liquid (Fig. 2, c) and its modulus is equal to

The overpressure created by this force

where is the area of ​​the base of the spherical segment. That's why

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

where are the radii of curvature of any two mutually perpendicular normal sections 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 a cylindrical surface overpressure .

If we place a narrow tube ( capillary) at one end into a liquid poured into a wide vessel, then due to the presence of the Laplacian pressure force, the liquid in the capillary rises (if the liquid is wetting) or falls (if the liquid is not wetting) (Fig. 3, a, b), since under the flat surface of the liquid in there is no excess pressure in a wide vessel.