methods of formulation 1 Flashcards
what is the size difference between colloid and coarse dispersions?
colloid: 1nm - 1um
coarse: >1um
what property must a colloid have in order for it to be classified as a colloid?
it must NOT settle under gravity
what properties do lyophilic sols exhibit?
high viscosity
asymmetrical particles
stable in presence of electrolytes
what properties do lyophobic sols exhibit?
low viscosity
symmetrical particles
unstable in presence of electrolytes
How are lyophilic sols formed?
by surfactants forming into micelles
How are lyophobic sols formed?
by dispersions of oil in water
Lyophilic colloids form spontaneously, but how do you form lyophobic colloids?
by dispersion (breakdown of coarse materials by colloid mills or by ultrasonic treatment) or by condensation (rapid production of a supersaturated solution by lowering temp)
What 3 ways can be used to purify colloids?
- dialysis
- electrodialysis (electrodecantation)
- ultrafiltration
Other than spherical, what shape can colloidal particles be?
prolate ellipsoids (rugby ball shape) oblate ellipsoids (discus shape)
Below what size will particles sediment?
0.5um (any lower, and they have to be sedimented by centrifugation)
What is the difference between coagulation and flocculation?
Coagulation: irreversible aggregation
Flocculation: reversible aggregation
How are gels formed?
by aggregation of colloidal sol particles
A gel rich in liquid is called a …
jelly
A gel with no liquid is called a …
zerogel e.g. sheet gelatin, tragacanth flakes
What are gels from lyophobic sols made from and what is their structure?
- clays (e.g. bentonite)
- the face of the particle is -ve and the edge is +ve so the structure is a ‘card floc’ shape
Lyophobic gels show thixotropy, what is this?
gel-sol-gel due to the weak forces holding the particles together
shaking the gel –> sol
upon standing –> gel again
What are the 2 types of gels from lyophilic sols?
type I: irreversible, covalent bonds, have a cross linking agent, swell in water but don’t dissolve due to the cross links
type II: reversible, weak H bonds, thixotropy, form micelles (the higher the temp, the more micelles)
What is the relation between CMC and length of hydrophobic chains?
CMC decreases with increasing lengths of hydrophobic chains
How many surfactants make up a micelle and what is the diameter of a micelle?
50-100
diameter = 2.5nm
what is a suspension and what is it used for?
coarse dispersion of insoluble particles >1um
- for the admin of poorly soluble drugs
What 3 things should suspensions show?
- shouldn’t settle too quickly
- shouldn’t aggregate and should be easily re-suspended
- viscosity should allow for pouring/admin through a syringe needle
are emulsions stable?
no - only if globules retain initial character and remain uniformly distributed
what is separation of an emulsion called?
cracking/breaking
what is creaming?
when disperse phase in emulsions sinks or floats due to density differences between the 2 phases
