Colloid Definition It’s a dispersion system in which material which particle ranges from molecular size to coarse dispersion 1) Internal phase: (dispersed or discontinuous phase) 2) External phase: (dispersed or continues medium) Dispersed system can be classified according to particle size of dispersed phase into: Particle size of dispersed phase diffusion Settle down Passage Semi-perm membrane Filter paper Detection Electron Microscope Ordinary Microscope Examples Molecular dispersion < 1 um Rapid X √ √ NOT visible NOT visible O2 - ions - Glucose Colloid dispersion 1 um to 500 nm very slow By centrifugation X Coarse dispersion > 500 nm NO diffusion By gravity X X √ Detected visible NOT resolved Visible o Colloidal silver salt o RBCS o Polymers (N – S) o Emulsion , susp Colloidal types Pharmaceutical applications of colloids 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) Colloidal silver iodide , silver chloride & silver protein are effective germicides & not cause irritation Colloidal copper used in cancer Colloidal gold diagnostic agent. Colloidal mercury in syphilis. Association colloids (SAA) preparations water soluble vitamins A , D and K also essential oils and phenols colloidal form due to large surface area kaolin in adsorbing toxins from GIT and Al(OH)3 as antacid. Blood plasma substitutes as dextran, PVP & gelatin ate hydrophilic colloids à maintain volume. Iron -dextran complex form non- ionic hydrophilic à used for treatment of anemia . Artificial rain: à aggregation of minute particles of water to form large particles. Food items: milk, butter and ice creams are colloidal in nature. Dr. Amr Abdel Azeem 1 colloid Classification of colloid Lyophilic colloid (sols) Affinity Dispersed phase Stability Precipitation Preparation Sols Viscosity Effect of electrolyte Example áaffinity (solvent love) chemical or physical Organic - Higher stability (not ppt or coagulate easily) - Stability occur d.t surface charge & hydration layer Ammonium sulfate à fractional ppt of globulin (low conc) and albumin (high conc) Opposite charged à ppt (Ag-Ab reaction) Simple remixing (reconstituation) reversible or irreversible (after denaturation) - á with á conc due to particle swelling à thixotropy - Stable in â electrolyte conc - Desolvation & salt-out in á electrolyte conc Hydrophilic colloid: acacia or gelatin, insulin in water (hydrosol) Lipophilic colloid: rubber or polystyrene in org. solvent Lyophobic colloid â affinity (solvent hating) Inorganic (silver – gold - sulfur) in water Lower stability (easily ppt) Surround by charge (repulsion) Heat – shaking – low amount of electrolyte Tr benzoin + NH4Cl = coagulation Tr benzoin + NH4Cl + lyophilic colloid = protection = no coagulation Need special method (need E) Condensation irreversible Dispersion - â due to unsolvation (conc indep) Unstable in neutralization of charge à coagulation Gold particle in water Association colloid Medium affinity (amphiphile) small organic molecule or ions ------------- Spontaneous when conc > cmc á as conc á d.t á micelle No â cmc and salt out occur at á electrolyte conc ------------------- Dispersion methods 1) Ultrasonic generator: Ä Dispersion achieved by high intensity UG at frequency more than 20,000 cycles/second Ä colloidal dispersions containing graphite, mercury, metal oxides and sulphur 2) Electric arc: Ä 2 Metal Involves production of an electric arc within electrodes, the liquid and dispersion achieved by intense heat generated by the arc so some metal of the electrodes dispersed as vapor then condense to colloidal particles Ä colloidal solutions of metals as copper, gold, mercury, silver. 3) Colloidal mill: Ä Material sheared between 2 rapidly rotating close plates (in opposite directions Ä Low efficiency & reduce the size of small proportion of particles only and mix with a dispersing agent as protective colloids, peptizing agent, soap (act as a colloidal stabilizer) 4) peptization: Ä achieved by addition of electrolytes to precipitates that carry a small net charge. Ä negatively charged precipitates may be dispersed by the addition of alkali # Precipitate that contain large quantity of electrolyte may be peptized by washing with water (dialysis) to remove some electrolyt Dr. Amr Abdel Azeem 2 colloid Condensation methods 1) Change in solvent: Ä Change in solvent leading to super saturation that will result in formation & growth of nuclei. (colloidal system formation) Ä sulfur and alcohol in excess of water, simple tincture of benzoin is poured in water. 2) Oxidation: Ä Hydrogen sulfide by oxidation result in sulfur atoms that give sulfur sol Ä Colloidal iodine prepared by oxidizing sod. Iodide with sodium nitrate in acid and glucose. 3) Double decomposition: Ä Hydrogen sulfide + arsenous acid Double decomp. Arsenous sulfide sol (yellow sol transparent to transmitted light ang turbid to reflected light). 4) Reduction: Ä Colloidal silver is prepared by reduction of silver oxide with tannic acid Ä Ammonia was added drop wise to silver nitrate solution (until 1st precipitate just redissolves) then dilute water and 2% tannic solution Ä Colloidal silver is brown solution that is greenish by reflected light, can be stabilized with albumin Purification of colloids a) Dialysis Ä Depend on difference in size between colloidal particles & molecular particles (impurities). 1) use semi-permeable membrane e.g. collodion (nitrocellulose), cellophane. 2) pore size of used semi-permeable membrane prevent passage of colloidal particles & permit passage of small molecules & ions (impurities) such as urea, glucose, and sodium chloride Ä A type of dialysis equipment; "Neidle dialyzer" At equilibrium, the colloidal material is retained in one compartment, while the sub-colloidal material is distributed equally on both sides of the membrane. B) Electro dialysis Ä An electric potential may be used to increase the rate of movement of ionic impurities through a membrane and so provide rapid purification. Ä Electrodialysis is carried out in a three-compartment vessel with electrodes in the outer compartments containing water and the sol in the center compartment. Ä Application of electrical Crystalloids potential causes cations to migrate to the negative electrode compartment and anions to move to the positive electrode compartment c) Ultra filtration Ä Apply pressure (or suction) result in, Solvent & cm particles forced across a membrane while colloidal particles are retained. Ä The membrane must be supported on a sintered glass plate to prevent rupture due to high pressure Ä Pore size of the membrane can be increased by soaking in a solvent that cause swelling Ä Cellophane swell in zinc chloride solution. And Collodion (nitrocellulose) swell in alcohol. Artificial kidney machine Ä patient's blood (arterial) pass through record las cellophane coils (ideal SPM for hemodialysis) Ä cellophane pass urea, glucose, electrolytes but don't pass plasma proteins & blood cells Ä pure dialyzed blood enter the body again through a vein à ability to reduce blood urea Ä Cellophane coils are supported on a drum rotating in electrolyte solution (rinsing fluid). Importance of the rinsing solution: (1) Substances present in excess in blood (e.g. urea) diffuse from blood to the rinsing solution (2) Substances which are deficient in blood (e.g. bicarbonate) diffuse from the rinsing solution to blood (3) Substances which are present in normal amounts in blood are kept unaltered have the same conc. Dr. Amr Abdel Azeem 3 colloid To destroy a colloid (coagulation) Heat the colloid Ä heating increases velocities of particles à knock off the ion barriers à aggregate and precipitate out. Add an electrolyte Ä the electrolyte will neutralize the ion layers Ä deposition of clay where a river reaches the ocean. T Ä he high salt content of the seawater causes the suspension of clay particles to coagulate Optical properties of colloids 1. Faraday Tendall effect ý True solution do not scatter the light and appear clear but colloidal dispersion contain opaque particles that scatter the light and appear turbid (Tendall effect) ý Light scattering important to estimate and study: size, shape and interactions of the particles 2. Electron microscope ý Give actual picture of the particles (up to 5A) ý Used to observe size, shape and structures of the sols ý High energy electron beams are used (greater resolving power) ý Disadvantages: used only for dried samples, and not give information for solvation 3. Ultra-microsopic ý Particles appears as bright spots of light against dark background of the microscope ý Used as technique of microelectrophoresis for measuring particle charge Kinetic properties of colloids Brownian motion § 1827: Robert brown see pollen gran in water § It is erratic [zigzag] motion § bombardment of particles [random] with dispersion medium molecule § Called random motion Motion depend on particle size and viscosity Diffusion o particle diffuse [éconc èêconc] Sedimentation o Stock Law until equilibrium o According to fick’s first law dm dc = − DA dt dx 2r ! (ρ − ρ" )g V= 9η o This equation for suspension and § -ve charge mean that diffusion take place in direction of ê conc § é viscosity è ê diffusion rate Viscosity Donnan membrane Effect § Linear > spherocolloids § Diffusion of small ions through membrane affected by presence of Because long molecule form network within dispersion medium charged macromolecule that’s can’t penetrate due to its size § colloid col up to spherical shape § Na.CMC is macromolecular anion + change è êviscosity K. benzyl penicillin is small anion § viscosity gives allow calculation of Mwt and information for shape è enhance diffusion of penicillin due to repulsion Dr. Amr Abdel Azeem 4 emulsion only because colloid particle [< 0.5 um] have Brownian motion so we need stronger force to ppt by ultracentrifugation Osmotic pressure P = osmotic pressure T = absolute temperature C = solute molar conc M = molecular wt This equation valid only for true & very diluted solution è molecule not interact mutually as egg albumin and glycogen colloid Electric properties of colloids Ä The charger port is a surrounded by an ionic cloud containing a chance of opposite sign to that of the particle development of a net charge at the bottom surface affect the distribution of irons and the surrounding interfacial region Ä As a result concentration of counter ions increase of the surface that's an electrical double layer exist around each particles Ä Does not believe may be considered to consist of two parts and in a region which includes iron bound Inn strong to the surface and an author or did he was region in which the vines distribution is determined by a balance of electro static forces and random thermal motion Ä The potential in this region therefore decays with the distance from the surface until a certain distance it becomes zero Ä Electrokinetic zeta potential is a difference in potential between the dispersion medium and the surface of tightly bound portion of the diffuse double layer surrounding the particles Ä The reduction of zetapotential below certain value result in the attractive force exceeded the repulsive leading to floculation and precipitation Electrophoresis Ä The movement of colloidal particles under the influence of I electric Geld is called Electrophoresis. Ä When an electric field is applied across the colloidal solution, the colloidal particles migrate to oppositely charged electrode where they get neutralized. Ä colloidal particles move with respect to liquid upon maintaining potential difference across the sol. Ä Used generally for separation of protein using paper Ä movement rate of protein is dependent on zeta Potential, Molecular size and Potential gradient where a mixture of proteins can be resolved into separate of mobilities of individual proteins ore different . Ä The electrophoretic mobility of a protein at the iso- electric point is Zero . Dr. Amr Abdel Azeem 5 colloid
