Week 5 Lecture - Disperse Systems Dosage Forms-4 cut.pptx PDF

Solutions Dissolving a solute into a solvent Molecular dispersion Contain small particles (ions or molecules) Transparent Do not separate Water Sugar solution Cannot be filter...

Solutions Dissolving a solute into a solvent Molecular dispersion Contain small particles (ions or molecules) Transparent Do not separate Water Sugar solution Cannot be filtered Sugar Do not scatter light Dissolving sugar in water Disperse systems One phase (a disperse phase) is distributed throughout a second phase (a continuous phase or dispersant) Two immiscible phases in contact Continu Dispers ous e phase phase Solutions Saline solution Multi-purpose contact lens solutions Hydrogen peroxide contact lens solutions Disperse systems Droplets of pine oil containing dissolved active germ‐killing ingredient (para‐chloro‐meta‐ xylenol or PCMX), held dispersed in water by a layer of surfactant molecules Pharmaceutical solutions Pharmaceutical disperse systems Colloids A colloid or colloidal dispersion = a two-phase system of matter; a type of mixture intermediate between homogeneous mixtures and heterogeneous mixtures (size < 1 μm) In a phase colloid, small droplets or particles of one substance (the disperse phase) are dispersed in another (the continuous phase) In a molecular colloid, macromolecules are dispersed in a continuous phase Properties of colloids Tyndall effect Brownian motion Adsorption Dialysis Electrophoresis Thixotropy Tyndall effect Colloids scatter light Light beam path through colloid is visible due to light scatter Soluti on Colloids Dynamic Light Scattering. (2021). Retrieved September 24, 2021, from https://www.sympatec.com/en/particle-measurement/glossary/dynamic -light-scattering/ Brownian motion Under a microscope, the molecules of the liquid are in motion Because of the motion, the larger particles of the colloid are being constantly bombarded by the smaller particles of the liquid This motion and bombardment keeps the colloid particles suspended Brownian motion in a colloid | Britannica. (2021). Retrieved September 24, 2021, from https://www.britannica.com/video/200465/Brownian-motion-colloid- Adsorption A chemical is associated to the surface of a second Gas agent molecules Often reversible (adsorbate ) Can lead to conformational changes Activated charcoal Manipulate physicochemical properties (Adsorbe Examples: nt) Adsorption of gases on solids Adsorption of surfactants, polymers or proteins Dialysis Separation of suspended colloidal particles from dissolved ions or molecules of small dimensions By means of their unequal rates of diffusion through the pores of semi-permeable membranes Electrophoresis Migration of charged particles Surface dependent Ionotec - beta alumina supplier-Electrodeposition and electrophoretic deposition. (2013). Retrieved September 24, 2021, from http://www.ionotec.com/electrodeposition.html Thixotropy Exhibit stable form at rest Becomes fluid with shear/agitated Types of colloids (1) Disperse Continuous Colloidal system Examples phase phase Liquid Gas Liquid aerosol Fog, mist Solid Gas Solid aerosol Smoke Gas Liquid Foam* Soap foam Liquid Liquid Emulsion* Milk, mayonnaise Solid Liquid Sol, suspension* Toothpaste Gas Solid Solid foam Expanded polystyrene Liquid Solid Solid emulsion Pearls Solid Solid Solid suspension Pigmented plastic Types of colloids (2) Based on the nature of the interaction between the dispersed phase and the continuous phase Lyophobic – solvent hating (hydrophobic when the solvent is water) Lyophilic – solvent liking (hydrophilic when the solvent is water) Lyo means solvent, philic means loving, phobic means hating. Lyopho bic Lyophilic protecting particles particle s Types of colloids (2) (for info) Lyophobic Lyophilic Large organic molecules in colloidal size Inorganic molecules or particles (insoluble) range Little or no interaction Solvated by medium (H2O – this is hydrated) between particles and dispersion medium Do not disperse spontaneously, Disperse spontaneously special procedures needed Increase viscosity, forming gels at higher No effect on viscosity unsolvated concentrations Electrolytes: low concentrations may Electrolytes: generally stable but “salted stabilise, out” by very high concentrations due to higher concentration causes instability desolvation Examples: calcium phosphate Examples: starch, gelatin Self-check Can you distinguish between a solution and a colloidal dispersion? Can you tell the different types of colloids? Phase colloids Lyophobic and lyophilic colloids Sol and gel Sol = a colloidal suspension of small solid particles in a continuous liquid medium Gel = a colloidal suspension in which the liquid medium has become viscous enough to behave more or less as a solid Solid particles will arrange themselves into a 3D structure within the liquid solvent, giving the solution a rigid, definite shape as in a jelly Sol Gel Think time Three types of everyday products which are gels Three types of pharmaceutical gels Gels Pharmaceutical gels Gels Two-phase system One-phase system (lyophobic) (lyophilic) Gels Two-phase system One-phase system (lyophobic) (lyophilic) (if the gel contains small discrete (if the gel does not appear to have particles) discrete particles) Clear or translucent, with no definite Usually opaque, not as stable as boundaries between the dispersed single phase macromolecules and the liquid Can be dispersed in water to provide a range of bases from mobile Colloidal particles aggregate to form liquids to solids a 3D sponge like network Matted fibres Flocculated small particles Crystalline and amorphous regions Network for elongated molecules e.g. held by van de Walls forces e.g. Gels Two-phase system One-phase system (lyophobic) (lyophilic) a) Flocculated particles in a two- c) Matted fibres as found in soap phase gel structure gels b) Network of elongated particles d) Crystalline and amorphous or rods forming a gel structure regions in a gel of carboxymethylcellulose Gels Formulation contains: Gelling agents Natural Gums Tragacanth, carrageen, pectin, agar, alginic acid Semisynthetic Materials Methylcellulose, Carboxymethylcellulose, hydroxyethylcellulose Synthetic Carbopol Humectants (to prevent drying out) Glycerol, sorbitol, propylene glycol Preservatives Water Self-check Can you distinguish between a two-phase and one- phase gel? Can you link the excipients of a gel to their functions? Foams Foams = gases dispersed in a liquid/solid Formed by trapping many gas bubbles (a 3D network of surfactants in air) Used for the delivery of enemas and topical drugs Foaming cleanser Budesonide rectal (sodium foam to treat lauryl ulcerative colitis sulphate as foaming Also produced as an often unwanted by-productagent) in manufacture Troublesome, especially if the foam forms on shaking  Defoamers/antifoaming agents Foam breakers and preventers Act as small droplets forming in the foam lamellae Displaces surfactants (which stabilise the thin films) at the air- water interface Example: Silicone fluids Yazhgur, P., Langevin, D., Caps, H. et al. How antifoams act: a microgravity study. npj Without With Microgravity 1, 15004 (2015). https://doi.org/10.1038/npjmgrav.2015. defoamer defoamer  Disperse system – dosage forms Colloids Properties of colloids Sol Foam Emulsion Gel Defoamer Emulsions (1h lecture) A ‘pseudo-stable’ dispersion of at least two immiscible liquids, one of which is dispersed throughout the other in the form of fine droplets (generally oil and water) stabilised by the presence of an emulsifying agent (known as emulsifier) Fish oil in water emulsified by Oil propylene glycol alginate Emulsified oil droplet Water Suspensions (not a colloid; 1h lecture) Course dispersion in which insoluble particles, generally > 1 μm, are dispersed within a liquid medium which is usually aqueous Settle out Shake to stay suspended Paracetamol in water/propylene glycol (co- solvent) stabilised by xanthan gum as suspending agent Solution vs colloid vs suspension Property Solution Colloid Suspension Less than 1 nm (10-9 1 nm to 1 µm 1 µm to 1 mm Particle Size m) (10-9 m to 10-6 m) (10-6 m to 10-4 m) Cloudy, Clear, transparent, Cloudy, but uniform heterogeneous, at Appearance homogeneous and homogeneous least two substances visible Particles will Separation None None eventually settle out Filtration Passes through filter Passes through filter Particles filtered out Variable – generally Effect of light None Scatters light can not pass through Particles not visible Particles visible Particles visible to Visibility even under under microscope naked eye Solution vs colloid vs suspension 10-9 m 10-6 m True solution Colloid Suspension Self-check Can you describe the types of colloid when the continuous phase is a liquid? Can you tell the differences between a solution, colloid and suspension?