Colloids Flashcards
What are colloids???
Dispersions in which the size of the dispersed particles is within the range of 1 nm to about 1μm.
What are the 2 classifications of colloids???
Lyophobic (solvent hating)
Lyophilic (solvent liking)
What are types of dispersion methods???
Colloid mills
Ultrasonic treatment
What are types of condensation methods???
Colloidal silver iodide
Changing the solvent, for example, sulfur in acetone into water.
What are some of the properties of colloids???
Shape and size of colloid particles
e.g. spherical, ellipsoid.
Kinetic properties
e.g. Brownian motion, diffusion, sedimentation.
Optical properties
Electrical properties
What are Micelles???
They are colloidal dimensions.
What is the formation of Micelles???
A means of shielding the hydrophobic group of the surfactant from the aqueous environment.
What are the 2 parts of a Micelles???
Shell/corona
Core
What is the shape of Micelles???
They are not static structures.
They are unstable structures with two times, relaxation time (t1 - microseconds) and slow relaxation time (t2 - milliseconds to minutes).
What are the roles of Micelles in drug formation???
Solubilization
Hydrolytic degradation may be reduced
Increases stability of drug
Taste masking
Release rates
Immunology
Medical diagnostic imaging
The study of cell membranes and micellar catalysis
What are some properties of micelles???
CMC decreases with the addition of electrolytes.
CMC decreases with an increase in the hydrophobic chain length of a surfactant.
CMC tends to decrease with increasing temperature.
What is the electrical double layer (EDL)???
A particle surface with a negative charge with a layer of positive ions that are attracted to the surface form the stern layer.
What is zeta potential???
The potential at the stern plane (the plane of the closest approach of ions to the particle
surface).
What are suspensions???
They are dispersions of an insoluble drug in a aqueous or non aqueous continuous phase.
Why is surfactants used as wetting agents???
They can be used to lower S/L interfacial tension which reduces the contact angle.
What is some oral uses of wetting agents???
Polysorbates (Tweens) Sorbitan esters (Spans)
What is some external uses of wetting agents???
Sodium lauryl sulphate
Sodium dioctylsulphosphate
What is some parenteral uses of wetting agents???
Polysorbates
Polyoxyethylene/polyoxypropylene co-polymers
What are hydrophilic colloids???
It’s a multi-molecular coat around the particles.
It accumulates at the surface because its hydrophobic and this build-up reduces S/L interfacial tension.
Also promotes wetting.
How can sedimentation be reduced???
Reducing the particle size.
Increasing viscosity of continuous phase.
Decreasing the density diff. between the two phases.
What is a Flocculate???
A cluster of particles held together in a loose open structure.
Flocculated systems can be formulated to achieve formulated suspensions to
minimise caking.
What are the possible forces interaction between suspended particles???
Electrostatic repulsion. Van der walls attraction forces. Short-range attraction forces. Steric forces. Solvation forces.
What is the DLVO theory???
The theory states that between colloidal particles the only interactions are;
Electrostatic repulsion and Van der waals attraction forces
What is electrostatic repulsion???
Charged particles will repel each other because electrical double layers inhibit
close contact, which inhibits flocculation.
How do the particles becomes charged???
Ionisation of groups on the surface of the particles.
Adsorbed ions which will confer charge onto the particle surface.
Why do particles flocculate???
At a certain distance of separation, an approaching particle become trapped in the 2o
min energy region - flocculated. To move away again enough energy must
be supplied to the system so that the particle can escape the 2o min region
and act as a discrete particle again with no forces of attraction acting on it.
What are some examples of flocculating agents???
Electrolytes -
Controls double layer thickness and VR.
Surfactants -
Ionic surfactants controls VR
Non-ionic surfactants cause steric repulsion.
Polymeric agents -
Can bridge particles together or cause steric repulsion.
