If you increase the temperature, the kinetic energy increases, and the liquid is likely to become less viscous and more willing to flow
o If you decrease the temperature, the kinetic energy decreases as well, and the liquid becomes more viscous Interpret pseudoplastic and dilatant rheograms and identify shear-thinning and shear-thickening behaviors Explain the significance of rheology in biological and pharmaceutical systems Rheology – study of deformation and flow of matter o When a liquid is flowing, it’s deforming o To pharmacy, Formulate desired flow properties Formulate a product of desired viscosity Understand the aspects of bio-rheology o i.e. blood thins out and based on temperature, you’ll see more or less blood on the surface Discuss the important of thixotropy in pharmaceutical systems. Thixotropy is the breakdown of structure that doesn’t come back to normal quickly o Applicable to non-Newtonian fluids only o DESIRABLE property for pseudoplastic and plastic fluids so that you can pour them o i.e. ketchup, shampoo, conditioner o The longer a fluid undergoes shear stress (force of deformation), the lower its viscosity (easier to flow, thinner)
Pharmaceutical Emulsions Define emulsions and identify types of emulsions Emulsion – dispersed system containing at least 2 immiscible liquid phases o Must have 3 major components: Dispersed phase (internal phase; 0.1-100 micron) Make this so small to ensure below IV max Dispersion medium (external phase) Emulsifying agent – homogenous mixture between disperse phase and dispersion medium Necessary for stability o Can have other excipients, such as sweeteners and flavors Ensure they are soluble in your external phase Most are water-soluble, and you will need an O/W emulsion to mask the oily taste o Used if drug isn’t soluble in water i.e. TPN’s are a source of calorie but are lipids so they can’t be administered alone IV Turn them into an emulsion with an external water phase and you can give them to the patient o Purposes/advantages: Homogenous mixture of two or more immiscible liquids Masks objectionable taste and odor Permits administration of liquid drug in the form of small globules Elegant preparation Water washable drug bases IV administration of lipids Cost-effective over using a single-phase preparation o Disadvantages: Separation over time Minimum free energy of an emulsion is settled and separated o Every preparation works to achieve minimum free energy oer time STABILITY Not very stable o If administered while separated, will clog arteries o “Thermodynamically semi-stable system” Semi-stable because there are 2 competing processes – dispersion of one immiscible liquid into another increases the free energy, but combination of droplets to reform the initial liquid reduces the free energy Combination of droplets is a spontaneous process o Reduced by emulsifiers reducing the interfacial tension and therefore decreasing free energy
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- Fall '09
- Colloid, Emulsion, Stratum Corneum, Formulate