Tishk International UniversityPharmacyPharmaceutics

Physical pharmacy

2nd Grade- Spring Semester 2019-2020

Colloids part 2

Instructor: Dr. Muhanad S Al Ani

Colloids. Cont.

By pharmacist Muhanad S. Al Ani

Kinetic properties of colloids Several properties of colloids which result from the

motion of the particles with respect to the dispersion medium.

The motion may be :1.thermally induced

a. Brownian movementb. Diffusionc. Osmosis

2.Gravitationally inducedsedimentation

3. Applied externallyviscosity

Brownian motionThis motion result from the bombardment of

the particles by the molecules of the dispersion medium.

The velocity increase as the particle size decrease.

The velocity decrease as the viscosity of the medium increase as by the addition of glycerin to the medium.

DiffusionParticles diffuse spontaneously from region of higher conc. To one of lower conc. Until theconc. of the system is uniform throughout.

Diffusion is a direct result of Brownian motion.

Ficks’ first lawdq = - DS dc dt

dxdq : is the amount of the substanceD : is the diffusion coefficient S : is the area of the planedc : is the change in conc.dx : is the distance traveled

Osmotic pressureWhen particles cannot diffuse through the

system because of the presence of a semipermeable membrane, the solvent molecules will move from the lower conc. of solute to the higher conc.

π = c R T Vants’ hoff equationThis equation used to measure the M.WT of a colloid in dilute solution

π = Cg RTM

Diffusion osmosis

Movement of solute movement of solventTogether with moleculesSolvent

From high to low from low to high Conc. Conc.

SedimentationStokes’ law

V = 2 r² ( P-P°) g9 η°

V : is the velocity of sedimentation of spherical particles.

P : density of particles.P°: density of medium.η°: is the viscosity of the medium.g : is the acceleration due to gravity.r : is the radius of the particle.

viscosityIt is an expression of the resistance toflow of a system under an applied stress, inwhich the more viscous the liquid, the greaterthe applied force required to make it flow at a

particular rate.Einstein equationη = ηº (1 + 2.5Ф)η : is the viscosity of the dispersion.

ηº : is the viscosity of the dispersion medium.

Ф : is the volume fraction of the colloidal particles which is equal to volume of particles

total volume of dispersion

Semi permeable membrane Semi permeable membrane

__ Colloidal particle _

_Drug particle

Colloidal particle

Drug particle

negatively charged colloidal molecule

negatively charged drug particle

Donnan membrane effect

Donnan membrane effectThe presence of charged colloids on one side of a semipermeable membraneaffects the diffusion of small ions such asdrug ions through the semipermeablemembrane .This effect is due to the electrical gradientacross the membrane in which the chargeddrug ions of the same charge as the colloidalparticles are driven to the opposite side of themembrane which alter the conc. of the drug ions.

This effect is termed Donnan effect or Donnanmembrane equilibrium

Pharmaceutical application of colloids1. colloids have a large surface area so it have a greater

efficiency for absorption and adsorption .example:a. colloidal kaolin have a good adsorption

for toxins .b. colloidal aluminum hydroxide shows a

better rate of neutralization of stomachacid.

2. Particle size reduction also alter some of the therapeutic properties of the drugs example.

a. colloidal iodine is less toxic than their ionic salts.

b. colloidal silver is a more effective as germicidal, while colloidal mercury is effective for the treatment of syphilis.

3. Hydrophilic colloids are used as asuspending agents.

4. Colloidal preparation also been used asdiagnostic agents ex. Langes’ Goldsolution is used to detect syphilis inpatients.