PPAR Lec Colloidal Systems and Coarse Dispersions

Pharmaceutical dispersions

• These are systems where one substance is dispersed within another substance (homogenous and heterogenous)

• In heterogenous system, the dispersed phase is physically distinguishable from the medium in which it is dispersed.

  • Examples ranges from very large molecules like Macromolecules (albumin and polysaccharides), to liquid suspensions of “nano-” sized crystals, and of “micro” –sized droplets, to coarse suspensions and emulsions.

suppositories and medication sticks, solid drug suspensions

classification based on phases

• dispersion medium: solid

• dispersion phase: solid

gels

classification based on phases

• dispersion medium: solid

• dispersion phase: liquid

solid foam, marshmallow, whipped candy

classification based on phases

• dispersion medium: solid

• dispersion phase: gas

crystal suspensions

classification based on phases

• dispersion medium: liquid

• dispersion phase: solid

smoke, aerosolized spray powder, inhalation dry powder

classification based on phases

• dispersion medium: gas

• dispersion phase: solid

emulsions

classification based on phases

• dispersion medium: liquid

• dispersion phase: liquid

foams

classification based on phases

• dispersion medium: liquid

• dispersion phase: gas

mist, unevaporated liquid sprays

classification based on phases

• dispersion medium: gas

• dispersion phase: liquid

none

classification based on phases

• dispersion medium: gas

• dispersion phase: gas

pearls, opals

solid + solid = solid sol

cheese, butter

solid + liquid = solid emulsion

pumice, marshmallow

solid + gas = solid foam

jelly, paint

liquid + solid = sol, gel

milk, mayonnaise

liquid + liquid = emulsion

whipped cream, shaving cream

liquid + gas = foam

smoke, dust

gas + solid = solid aerosols

clouds, mist, fog

gas + liquid = liquid aerosols

discontinuous or internal

dispersed particles (dispersed phase)

continuous or external

dispersing medium (dispersing phase)

molecular, colloidal and coarse dispersions

• Dispersed particles (dispersed phase) = discontinuous or internal

• Dispersing medium (dispersing phase) = continuous or external

true solutions <1nm

defined as a mixture of two or more components that form a homogenous molecular dispersion or one-phase system.

ex: glucose, oxygen, and ordinary ions

colloidal dispersions 1nm-0.5um

represents a systems having a particle size intermediate between that of a true solution and a coarse dispersion.

ex: colloidal silver soln, natural and synthetic polymers, cheese, butter, jelly, paint, milk, shaving cream

coarse dispersions

• diameter of particles being larger than 0.5 µm.

• examples: emulsions and suspensions, grains of sand

colloidal dispersions

• defined as the intermediate between solutions and precipitates

• a colloid, also called a colloidal dispersion, is a two-phase heterogenous mixture made up of a dispersed phase of tiny particles that are distributed evenly within a continuous phase.

colloid

also called as colloidal dispersion, is a two-phase heterogenous mixture made up of a dispersed phase of tiny particles that are distributed evenly within a continuous phase.

1-1000nm

because of thier size, _____, colloidal particles may be separated from molecule and ion particles by dialysis

types of colloidal system

• this classification is based on the interation of particles, molecules or ions of the dispersed phase with the molecules of the dispersion medium.

  • lyophilic and lyophobic colloids

  • association colloids

lyophilic colloids

• colloidal particles that interact to an appreciable extent with the dispersion medium referred to as lyophilic (solvent-loving) colloids.

• since for most pharmaceutical dispersions the medium is water, the terms hydrophilic and hydrophobic are used.

  • thermodynamically stable

  • method of production: hydration and solvation

acacia or gelatin

• most lyophilic colloids are organic molecules of gelatin, acacia, insulin, albumin, rubber, and polystyrene.

  • ____ in water or celluloid in amyl acetate leads to the formation of a sol.

hydrophilic colloids

these colloids have polar regions that enable them to become hydrated in contact with aqueous environments

ex: macromolecules (proteins and polysaccharides)

second class of colloids

• is composed of materials that have little attraction, if any, for the dispersion medium.

hydrophobic colloids

• do not have sufficient surface hydrophilicity to enable them to interact well with water.

  • thermodynamically unstable

  • condensation

  • deffloculation/peptization

lyphobic colloids

• these are generally composed of inorganic particles dispersed in water namely: gold, silver, sulfur, arsenous sulfide, and silver iodide.

association colloids

• are formed by the association of dissolved molecules of a substance to create particles of colloidal dimensions.

  • includes micelles and the CMC Association, or amphiphile colloids

amphiphiles or surface-active agents

• characterized by having surface-active agents are characterized by having two distinct regions of opposing solution affinities within the same molecule or ion.

amphiphiles, subcolloidal

when present in a liquid medium at low concentrations, the _____ exist separately and are of such a size as to be _____

increased, micelles

• as a concentration is _____, aggregation occurs over a narrow concentration range.

• these aggregates, which may contain 50 or more monomers, are called _____

association colloids

critical micelle concentration

• the monomers interact so as to minimize contact between the lipophilic portion of the amphiphile and water, usually resulting in spherical shape.

• the concentration of monomer at which micelles form is term the ______, or CMC.

aggregation number

• the number of monomers that aggregate to form a micelle is known as the _____ of the micelle.

microemulsion

• another example of association colloids is ____, which are dispersion of oil droplets in water.

• difference form conventional emulsion is that the droplets of ____ (1) have a diameter of 10-100nm, the dispersions are transparent, and thermodynamically stable.

properties of colloids

1. Optical Properties

• Faraday Tyndall Effect

2. Kinetic Properties

• Brownian Motion, Diffusion, Osmotic pressure, Sedimentation, Viscosity, Electrokinetic phenomena

3. Electrostatic Properties

• Nernst Potential, Zeta Potential

Faraday Tyndall Effect

when an intense converging beam of light is passed through a colloidal solution kept in dark, the path of the beam gets illuminated with a bluish light.

• a solution, on the other hand, will appear clear even when a light is shown through it.

6 kinetic properties of colloids

1. Brownian motion

2. Diffusi

brownian motion

• describes the random and irregular movement of colloidal particles caused by the momentum induced by being bombarded with molecules of the dispersion medium.

• the erratic motion, which may be observed with particles as large as about 5um, was explained as resulting from the bombardment of the particles by the molecules of dispersion medium.

brownian motion

• this type of particle movemenr depend on many factors: temperature, medium viscosity, and dispersed particle size.

  • decrease in temperature will decrease Brownian motion

  • increase in dispersed particle size and viscosity of the medium can also decrease Brownian motion

diffusion

• particles diffuse spontaneously from a region of higher concentration to one lower concentration until the concentration of the system is uniform throughout.

• this can be thermally induced.

osmosis

• movement of solvent accross a semi-permeable membrane

• but does not allow passage from the pure solvent. this can be thermally induced.