Interfacial Phenomena Flashcards
Mass of substance that possesses a well define boundary
Phase
Occurs when molecules at the surface of the liquid experience an inward force toward the bulk
Surface tension
Force per unit length that must be applied parallel to the surface so as to counterbalance the net inward pull
Surface tension
SI unit for surface tension
N/m
Cgs system unit for surface tension
Dynes/cm
Force per unit length existing at the interface between two immiscible liquid phases
Interfacial tension
Often used for the attractive forces between immiscible liquids
Interfacial tension
Work done against surface tension to move molecules from the inner layers to the surface
Surface Free energy
Measurement of surface and interfacial tensions
CDPSDWBO
Choice of method of measurement depends on:
SASE
T/F Inc temp inc surface tension
F
Equation for capillary rise method
Y=rpgh
T/F in capillary rise method, the force of adhesion of the liquid and the wall is less than the cohesion forces of liquid molecules
F
Principle is that the force necessary to detach a platinum-iridium ring immersed at the surface or interface is proportional to the surface or interfacial tension
DuNouy Ring Method
Equation used for the DuNuoy Ring method
Y=(dial reading/2xring circumference) x correction factor (beta)
Free energy required to separate two phases at their boundary or to break the attraction between unlike molecules
Work of Adhesion
Equation of work of adhesion
Wa=YL+Ys+ YLS
Work required to separate molecules of the spreading liquid so that it can flow over the sublayer
Work of Cohesion
When added molecules partitioned in favor of the bulk
Negative adsorption
When added molecules are partitioned in favor of the interface
Positive adsorption
Adsorbed at the interface to lower the interfacial tension between phases due to their amphiphilic nature
Surfactants
0-3 HLB
Anti foaming
7-9
Wetting agents
3-8
Water in oil emulsifying agents
8-16
Oil in water
16-18
Solubilizing agents
13-16
Detergents
Amount of amphiphile per unit area of surface in excess of that in bulk of the liquid
Surface excess
T/F the addition of amphiphile to a liquid system leads to a reduction in surface tension
T
Factors that affect the adsorption of gas by a solid
chemical nature of adsorbent and adsorbate
Surface area of adsorbent
Temp
Partial pressure of the adsorbed gas
Irreversible interface unless the bonds are broken
Chemisorption
Removal of adsorbate from adsorbent
Desorption
Describes the relationship between the amount of gas physically adsorbed on the surface of the solid and the equilibrium pressure or concentration at constant temperature
Adsorption isotherm
A plot of constant temperature
Isotherm
Aids in displacing an air phase at the surrface, and replaces it with liquid phase
Wetting agent
Angle which the liquid makes with the solid surface
Contact angle
Contact angle = 0
Complete wetting
Surfactants that are used for the removal of dirt
Detergents
Initial wetting of the dirt and of the surface to be cleaned
Detergency
Stable structure consisting of air pockets enclosed within films of liquid, the gas-in-liquid dispersion being stabilized by a foaming agent
Foam
Agents as alcohol, ether, castor oil and some surfactants that break the foam
Antifoaming agents
Other name for nernst potential
Electrothermodynamic potential
Defined as the difference in potential between the actual surface and the electroneutral region of the surface
Nernst potential
Other term for zeta potential
Electrokinetic potential
Defined as the difference in potential between the surface of the tightly bound layer and the electroneutral region of the solution
Zeta potential
Happens when the potential is reduced below a certain value, the attractive forces exceed the repulsive forces and the particles come together
Flocculation
Boundary of separation of two phases
Interface
