Physics and chemistry of surface phenomena

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

2.

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.

3.

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.

4. 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.

5.

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 :
dσ
g
dC
For narrow concentration ranges the formula is:
Δσ
g
ΔC

6.

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

7.

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.

8.

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.

9.

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.

10.

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