exist between the molecules of the liquid adhesive force, for different surface and subsurface (inner) layers.Molecules on the surface layer, get a one-sided attraction from the deep layers and in the deep layers of the attractive forces between the molecules are mutually balanced.The molecules of the surface layer air molecules are attracted to and less steam, their resultant force is directed downward, and a surface layer of molecules as it is pulled deep layers.Surface tension, in turn, depends on the nature of the liquid and the boundary environments, ambient temperature, presence of impurities in liquids, and so on. D.
To increase the liquid surface should do some work against surface tension forces.From the value of the surface tension depends on the droplet size, the meniscus, the amount of gas bubbles passing through the liquid wettability and nesmachivaemost liquid solid surface and others.
surface tension force is also dependent on the vapor pressure of a liquid, more steam, the lessthe amount of internal fluid pressure.If the fluid is bordered with the air, the molecules of the surface soil is almost not subjected to the forces of gravity from the gaseous phase.In those cases where the vapor pressure above a liquid increases, its surface tension will be less.Thus, the molecules of the surface layer are not balanced, and therefore the system at the interface is always a certain excess free energy.For all other identical conditions this excess is greater than the largest surface.According to the second law of thermodynamics, the system aims to reduce internal energy.Therefore, the process of reducing the interface is a separate process.It is therefore a liquid to which no force forms a spherical shape, because this shape when a certain volume has a minimum surface.
On the surface tension effect and the magnitude of the hydrocarbon radical substance.Thus, if we take more carboxylic acids of the same homologous series (HCOOH, CH3COOH, S2N5SOON, S3N7SOON), the surface tension decreases as their carboxylic chain elongation - 3.2 times per group CH2.
presence of impurities of various substances in body fluids affects the value of the surface tension.Many substances, mainly organic, lower the surface tension.Such compounds are called surfactants (proteins, bile acids, soaps, alcohols, aldehydes, esters, ketones, tannins, etc.).Substances whose presence does not significantly affect surface tension are called surface-inactive (fructose, glucose, starch, etc.).Reduction of the surface tension is of great importance in the process of absorption of liquid nutrients epithelium of intestinal mucosa.Thus, fats and other lipids in the food channel received in the form of droplets.These droplets are emulsified with bile into the small intestine, and thereafter become available to the hydrolytic cleavage lipase and other lipolytic enzymes.Adding to liquids surfactants increases their ability to wet the surface.When used insecticides are often added to the soap that allows them to contact the surface of the body and provide insects insecticidal effect.
surface tension of the liquid: the methods of determining
There are several methods for determining the surface tension: stalagmometrichesky, raising the height of the liquid in the capillary, the maximum pressure in the bubbles on the separation of the ring.
stalagmometrichesky most commonly used method is based on using a special device - stalagmometry.It is a capillary tube having upper and lower marks and extension.In stalagmometry recruited to the mark with water, after which it is produced, and count the number of drops.Then the same thing is done with the test liquid.Under the action of surface tension forces flowing liquid and the water takes the form of spherical droplets.
surface tension in the life of organisms
Surface tension is one of the factors determining the shape of the cell and its parts.Cage - an elementary particle of living matter that makes up the human body, animals and plants.For cells that have a strong and rigid surface (plants, microorganisms), the value of the surface tension is small.Most of the cells of the animal has a shape close to spherical.Low surface tension allows the cells easily isolated from one another.Form cells attached to other cells or the substrate, depends on other factors - of the cytoskeleton complexed membranes, contact structures and others. Certain types of cells (e.g., leukocytes and egg) Upon release from the action of surface tension take the form of a ball and lose activity.Local changes the surface tension plays an important role in the perception and transmission of nerve impulses in phagocytosis, pinocytosis, gastrulation, amoeboid movement, and especially in the permeability of cell membranes.
