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Zaporizhzhya State Medical University Analytical Chemistry Department PHYSICS AND CHEMISTRY OF SURFACE PHENOMENA Lecturer: Monaykina Yulia Vitalievna 2016

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Surface phenomena are the processes that occur at the interface in heterogeneous systems. Surface phenomena are the processes that occur at the interface in heterogeneous systems. The spontaneous process of solute accumulation at the interface is called adsorption.

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The substance which adsorbs the solute is called adsorbent. The substance which adsorbs the solute is called adsorbent. The adsorbed solute is called adsorbate. The interface may be: gas – liquid, liquid – liquid, solid – liquid, solid – gas.

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Adsorption at the gas-liquid and liquid-liquid interface

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The ability of dissolved substances to change the surface tension of the solvent is called surface activity. The ability of dissolved substances to change the surface tension of the solvent is called surface activity. A measure of the surface activity is a derivative of the surface tension on the concentration, taken with an opposite sign : For narrow concentration ranges the formula is:

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The Duclos-Traube rule: The surface activity increases about 3 -3,5 times with each addition of a methylene group to the homolog.

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Molecules and atoms can attach themselves onto surfaces in two ways: Molecules and atoms can attach themselves onto surfaces in two ways: In physisorption (physical adsorption), there is a weak van der Waals attraction of the adsorbate to the surface. During this process the chemical identity of the adsorbate remains intact, i.e. no breakage of the covalent structure of the adsorbate takes place. In chemisorption (chemical adsorption), the adsorbate sticks to the solid by the formation of a chemical bond with the surface.

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Adsorption at the solid-solution interface Adsorption at the solid-solution interface Solutes adsorption by solid adsorbents is more complex as the solvent molecules can compete with adsorbate molecules for the adsorptive sites on the adsorbent surface as well as can interact with the adsorbate and adsorbent surface. Two kinds of adsorption on a solid adsorbent are distinguished: molecular and ionic adsorption.

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OTHER FACTORS AFFECTING ADSORPTION OTHER FACTORS AFFECTING ADSORPTION Surface area of adsorbent. Larger sizes of surface area imply a greater adsorption capacity. Particle size of adsorbent. Smaller particle sizes reduce internal diffusional and mass transfer limitation to the penetration of the adsorbate inside the adsorbent (i.e., equilibrium is more easily achieved and nearly full adsorption capability can be attained) Contact time or residence time. The longer the time the more complete the adsorption will be.