colloidal stability, dvlo theory Flashcards
what are consequences of instability in disperse systems and describe the diagram of it
coagulation- small aggregates form, surface area decreases so surface tension experienced by less molecules, strong attractive forces, cant be redispersed by shaking
-cluster of circles
coalescence- droplet structure is gone, impossible to reform emulsion (called cracking in emulsions)
-solid block at bottom
what is brownian motion
random motion of small particles suspended in a fluid
particles less than 2 microns diameter are constantly moving due to brownian motion
what is the kinetic energy of a particle dependent on
temperature and external forces (shaking)
what do particles experience as they approach each other
forces of repulsion due to electrostatic interactions, forces of attraction due to VDW forces, steric forces if they have non ionic surfactant on surface
equation for overall potential energy when particles approach each other
Vt=Vr+Va+Vs
Vt= overall potential energy
Vr= energy of electrostatic repulsive interaction
Va= energy of attractive interaction due to VDW
Vs= energy of steric interactions
what is the DVLO theory
theory of balance between electrostatic repulsion and attractive forces
Vt=Vr+Va
what does a potential diagram look like
graph of the force (V) against particle separation (H)
what is the source of charge in particles
ion adsorption- surfactants
or
ion dissolution- ionic substances like drugs acquire charge by uneven dissolution of oppositely charged ions
what is a stern layer/ gouy chapman layer
electrical double layer formed when ions attract/repel charged surface of a particle
result of primary maximum in a total potential energy of interaction graph
repulsive barrier to aggregation, high Ke, coagulation
result of secondary minimum in a total potential energy of interaction graph
weak attraction causes flocculation, low Ke, particle has insufficient energy to continue its path to neighbouring particle and escape secondary min
effects of electrolyte
