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Information about Rheology

Published on March 24, 2009

Author: amitmgupta31



Slide 1: Introduction to polymers Definition, classifications, chemical/physical properties, some structures, applications Rheology Viscosity, newtonian and non-newtonian flow, rheograms, application in pharmaceutics Colloids Lyophilic, lyophobic, association Introduction to polymers : Introduction to polymers Poly = many, mer = unit, many units Classification: Homochain polymers Heterchain polymers Polymerization : Polymerization Addition Condensation Initiation: R-CO-O-O-CO-R ? 2 R-CO-O* R-CO-O* + H2C=CH-C6H5 ? R-CO-O-CH2-C*H-C6H5 Propagation: Mn-CH2-CHR* + H2C=CHR ? Mn-CH2-CHR-CH2-CHR* Termination: Mn-1-CH2-CHR* + Mm-1-CH2-CHR* ? Mn-1-CH2-CHR-CHR-CH2-Mm-1 Polymers : Polymers Homopolymers (A-A-A-A-A-A) Copolymers -- Random copolymer A-A-B-A-B-B-B-A-A-B-A-B- -- Alternating copolymer A-B-A-B-A-B-A-B -- Block copolymer A-A-A-A-B-B-B-B-B-A-A-A Types of polymers : Types of polymers Thermoplastics (material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently), polystyrene, polyethylene Thermosets (cannot be melted and remolded) phenolic resins, urea-formaldehyde resin Elastomers Rubbers Chemical, physical properties : Chemical, physical properties Molecular weight: Number average Mw = ? Xi Mwi Weight average Mw = ? wi Mwi Conformation of polymers dissolved in solutions (molecular interactions) -- Randomly coiled linear polymer -- Very dilute polymer solution -- Gel state of polymers (elastmers) Intramolecular interactions : Intramolecular interactions Diluted polymer solution and gel : Diluted polymer solution and gel Polymer blend : Polymer blend Poly (Vinyl alcohol)-(vinyl pyrrolidone), PVA-PVP Structures of selected polymers : Sodium alginate methylcellulose Sodium carboxylmethycellulose hydroxypropylmethylcellulose Carbopol Structures of selected polymers Pharmaceutical applications : Pharmaceutical applications Pharmaceutical excipients Drug delivery (PLGA microparticles) Hydrogels Adhesive biomaterials Pharmaceutical excipients : Pharmaceutical excipients Coat tablets: Microcrystalline cellulose (MCC), sodium carboxylmethylcellulose (NaCMC), hydroxypropylmethycellulose (HPMC), hydroxyethylcellulose (HEC), Hydroxypropylcellulose (HPC), PEG, povidone Binder: acacia, gelatin, sodium alginate Disintegrants: Starch, carboxymethylstarch, povidone Plasticizer, PEG Thickening agents: xanthan gum (a natural gum polysaccharide used as a food additive and rheology modifier ) PLGA microparticles : PLGA microparticles Prolonged release : Prolonged release Leuprolide release from PLGA microparticles Treat endometeriosis Prostate cancer Treat growth deficiency Rheology : Rheology Rheo = flow Viscosity (h, poise) is an expression of the resistance of a fluid to flow (1 p = 0.1 Pa.s) Fluidity (f) = 1/h Newton’s theory Newton’s theory : Newton’s theory F’/A = h dn/dr; h = F/G; G = dn/dr = velocity gradient/rate of shear F = F’/A = shear stress Rate of shear is directly proportional to shearing stress. Kinematic viscosity = h/? (? is density) Effect if temperature on viscosity h = A e EvRT (A is a constant, Ev is the activation energy required to initiate flow between molecules Newtonian and non-newtonian systems : Newtonian and non-newtonian systems Slide 20: Rheograms of different fluids Viscosity vs. Shear rate : Viscosity vs. Shear rate Non-newtonian systems : Non-newtonian systems 1. Bingham plastic flow does not begin to flow until a shear stress corresponding to the yield value is exceeded. Flocculated colloid particles 2. Pseudoplastic flow Typically exhibited by polymers in solution (tragacanth, sodium alginate, methylcellulose, NaCMC) Viscosity decreases with the increase of shear rate/shear thinning Caused by the re-alignment of polymer and/or the release of solvents associated with the polymers. Dilatant flow Volume increases when sheared Shear-thickening Suspension containing a high concentration of small, deflocculated particles Thixothropy and anti-thixotropy : Thixothropy and anti-thixotropy :  Procaine benzylpenicillin Procaine benzylpenicillin, also known as procaine penicillin, is a combination of benzylpenicillin with the local anaesthetic agent procaine. Following deep intramuscular injection, it is slowly absorbed into the circulation and hydrolysed to benzylpenicillin – thus it used used where prolonged low concentrations of benzylpenicillin are required. This combination is aimed at reducing the pain and discomfort associated with a large intramuscular injection of penicillin. It is widely used in veterinary settings. Thixotropy in formulation Colloids : Colloids a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. Size: 1 nm to 0.5 mm Visible under electron microscope Not resolved by ordinary microscope Do not pass through semipermeable membrane Type of colloid systems : Type of colloid systems 1. Lyophilic colloids (solvent-loving) Systems containing colloidal particles that interact to an appreciable extend with the dispersion medium. Acacia in water or celluloid in amyl acetate lead o the formation of a sol. Solvation, hydration, hydrophilic sols (gelatin, acacia, insulin, albumin in water), lipophilic sols (rubber, polystyrene in non-aqueous solvents) Lyophobic colloids (solvent-hating) Colloids are composed of materials that have little attraction, if any, for the dispersion medium. No solvent sheath around the particles Gold, silver, arsenous sulfide, silver oxide in water 3. Association colloids Classification of colloids : Classification of colloids

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