Colloids Flashcards
Particle size range for colloids
less than 0.5 microns or 500 nm
Colloid drug delivery systems that improve performance of dosage forms
Large surface area
drive to decrease surface energy
tendency for aggregation
unequal distribution of phases
consideration of surface and interfacial phenomena for colloids
if a cube is subdivided in smaller particles, volume will stay the same but surface area will increase by 10^5 fold.
Lyophillic colloids
solvent liking, hydrophillic
strong extensive interactions between dispersed phase and dispersion medium
thermodynamically stable
Lyophobic colloids
solvent hating, hydrophobic
little interaction of the dispersed phase and medium. low adhesion forces. thermodynamically unstable
assoication colloids (detergents)
Thermodynamically stable. Dispersed phase consists of aggregates of amphiphilic molecules or ions (micelles), lower concentration, they exist in true solution. At higher concentrations, Micelles.
Tyndall effect
light may be absorbed, scattered, polarized or reflected by the dispersed phase of a colloid.
Brownian Motion
how colloids are small enough to be influenced by the collision with molecules of the dispersion system. When observed, seem to be in a random manner.
Ficks Law
D is diffusion coefficient K- Boltzmann Constant T- absolute temperature N- viscosity of the solution R- hydrodynamic radius of the particle
Strokes einstein equation calculates
ficks law in how far a particle will travel per a certain amount of time
If size increases, what does it do to the diffusion coefficent?
Inversely proportional to D
If temperature increases, what does it do to the diffusion coefficent?
Proportional to D
If viscosity increases, what does it do to the diffusion coefficent?
Inversely proportional to D
Counterions
cations in solution
similions
anions in a solution
Which electrical region next to the particle surface neutralizes the charge on the particle?
The diffuse layer: with excess of counterions will neutralize surface charge. This would also be the adsorbed ions on the surface of the colloid.
What does the zeta potential measure and how is it important for stability of colloidal systems
Zeta potential measures the voltage difference between double diffuse layer and the neutral region of the soln. measurement degree of attraction/ repulsion between adjacent particles.
Steric Stabilization
Polymers adsorbed to the surface make it difficult for particles to approach each other.
Polymer bridging
adsorbed polymers at very low concentrations promote the opposite effect of steric stabilization. instead of stablizing particles, promotes flocculation ( loosely clumped mass of fine particles)
Hydrogels
water dispersion in the medium. Primary used in wound healing, tissue engineering and drug delivery systems
Microparticles
0.2 to 0.5 microns loaded with drug, usually contain polymers and used in vaccines, chemotherapy, improve release profiles and drug targeting.
Liposomes
consist of an outer membrane and liquid core. Can be filled with lipophilic drugs or hydrophilic drugs.
Micelles
similar to liposomes but do not have inner fluid structure. Used as microcontainers for poorly soluble hydrophobic drugs. The surface can be modified such like liposomes.
Nanoparticles
particles that are less than 1 nanometer.