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

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

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.

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.

Adsorption at the gas-liquid and liquid-liquid interface

The resultant of the forces acting on a molecule in a bulk is equal to zero.

The resultant of the forces acting on the molecules in a surface layer is directed to the bulk of the liquid phase perpendicularly to its surface.

The result is a surface layer with excess of surface energy that is the surface Gibbs free energy GS.

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:

The Duclos-Traube rule:

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

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.

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.

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.

Structure of biological membranes

Structure of biological membranes

1 -carbohydrate glycoproteides moieties;

2 - lipid bilayer;

3 - integral protein;

4 - "heads" of phospholipids;

5 - peripheral protein;

6 - cholesterol;

7 - fatty acid "tails" of phospholipids