Rheology PDF

 Greek word – rheo “flow” logos “science”  Heraclitus (actually coming from the writings of Simplicius), panta rei, "everything flows.“  Viscosity – resistance to flow  ↑ the viscosity the greater the resistance  Use:study of paints, inks, doughs, road builidng materials, cosmetics, dair...

 Greek word – rheo “flow” logos “science”  Heraclitus (actually coming from the writings of Simplicius), panta rei, "everything flows.“  Viscosity – resistance to flow  ↑ the viscosity the greater the resistance  Use:study of paints, inks, doughs, road builidng materials, cosmetics, dairy products and other materials.  Application in the formulation  Analysis of pharmaceutical product  Emulsion  Pastes  Suppositories  Tablet coating  Medicinal and cosmetic creams  Lotion  Newtonian system  Poise- unit of viscosity  Cgs unit = for poise is dynesec/cm² or gcm-1sec-1 or g/cmsec  Centipoise (cp) plural (cps) 1 cp = 0.01 poise  Fluidity - ᶲ - reciprocal to viscosity  The USP kinematic viscosity – absolute viscosity  Kinematic viscosity = ᶯ/ᵖ  Unit:  Stoke (s)  Centistoke (cs)  Measure : arbitrary scale, Saybolt, Redwood, Engler  Acacia  Povidone  Agar  Pectin  Bentonite  Colloidal silicon  Carbomer dioxide  SCMC and CCMC  Starch  Carrageenan  Tragacanth  Dextrin  Xanthan gum  Gelatin  Gas = ↑viscosity ↑ temperature  Liquid = inversely proportional  ↑Viscosity ↓ temperature  Activation energy – energy required to initiate flow between molecules  Liquid and solid heterogeneous dispersions such as colloidal solution  Emulsions  Liquid suspension  Oitment  And other products  Analyzed in a rotational viscometer  Plasticflow  Pseudoplastic  Dilatant  Bingham bodies – modern rheology and the first investigator to study the plastic substances in a systematic manner  Those substances that exhibit a yield value as solids  substances that begins to flow at the smallest shearing stress and show no yield value are defined ad liquids Mobility – slope of rheogram – same to fluidity of Newtonian system and is reciprocal is called plastic viscosity (U)  presence of flocculated particles in concentrated suspensions.  Yield value indicate the force of flocculation  The more flocculated = the ↑ yield value  Apparent viscosity decreases with increased stress  Paper pulp in water, latex paint, ice, blood, syrup, molasses  Suspension with high percentage of dispersed solid exhibit an ↑ in resistance to flow with ↑ rate of shear  Dilatant – system that ↑ in volume when sheared  Apparent viscosity increases with increased stress  Suspensions of corn starch or sand in water  Inverse with pseudoplastic system  Shear thickening system – when stress is removed, a dilatant system return to its original state of fluidity  Invariably suspension containing ↑ concentration (about 50% or↑) of small defloculated particles  Shear stress ↑ the bulk of system expands or dilates  dilatant  Dispersion  Solid particles  high speed mixers, blenders or mils  Advantageous compare to plastic and pseudoplastic  May solidify under these condition of high shear  overloading and damaging the processing equipment  Apparent viscosity decreases with duration of stress[  Some Clays, Some Drilling Mud, many paints, synovial fluid, Honey under certain conditions  An isothermal and comparatively slow recovery, on standing of material, of consistency lost thru shearing  Shear thinning system  Gel to sol transformation and exhibit shear thinning  remove of stress  reform  Note: not instantaneous  progressive restoration of consistency  Negative thixotrophy or antithixotrophy  Magnesia magma alternately increase and decrease rate of shear  magma thickens  Not same with dilantancy or rheopexy  Dilatant system – are deffloculated and ordinarily contain greater than 50% by vol of solid dispersed phase  Antithixotrophic system – low solid content 1-10% and are flocculated  Phenomenon in which a solid forms a gel more readily when gently shaken or otherwise sheared that when allowed to form the gel while material is kept at rest  Rheopectic - Apparent viscosity increases with duration of stress (lubricant and whipped cream)  Note: rheopectic system gel – equilibrium state  Antithixotropy sol – equilibrium state  Isa desirable property in liquid pharmaceutical system  high consistency in the container  pour and spread easily  Well formulated thixotrophic susp will not settle out readily in container  fluid on shaking  will remain long enough fora dose to be dispensed  regain consistency rapidly enough (maintain particles in suspended state)  Emulsion, lotions, creams and ointnment and parenteral suspensions (IM)  Degree of thixotrophy and rate of sedimenatation  Greater thixotrophy, lower the rate of settling  Concentrated parenteral suspension containing 40-70% w/v of procaine pen G  high inherent thixotrophy and shear thinning  caused to pass thru hypodermic needle  Formation of depot of drug at the site of injection in the muscle from which drug was slowly removed and made available to the body  Thixotrophy – pen – specific surface  Newtonian system – shearing stress  single rate of shear called as “one point” instrument  Non Newtononian system – variety of rates of shear called as “multipoint” instrument  Note : all viscometer – Newtonian  Only those with variable shear stress control can be used for Non Newtonian  Tackiness,stickiness, “body”, “slip” and spreadability  difficult to measure using conventional apparatus  no precise meaning  Pseudoplasticmaterials – instrument caplable of a wide range shearing rates  Ostwald viscometer  Ubbelohde viscosimeters  Newtonian liquid – measuring time required for a liquid to pass between two marks as flows by gravity thru a vertical tube  USP suggest capillary apparatus for determining the viscosity of high viscosity types of methyl cellulose solution A glass or steel ball rolls down an almost vertical glass tube containing the test liquid at a known constant temp.  Hoeppler viscometer  Variety of glass and steel ball of different diameter – can be used over range 0.5 to 200,000 poise  Best result ball used NLT 30 sec  The sampled is sheared in the space between the outer wall of a bob and the inner wall of a cup into which the bob fits  Couette – cup is rotated  Searle – stationary cup and rotating bob  20-50 ml sample  Disadvantage: variable shear stress across the sample between the bob and the cup  Brookfield viscometer is a rotational viscometer of a Searle type – QC  Newtonian and Non- Newtonian liquid and empirical viscosity measurement on paste and other semisolid materials  Gap between the cup and the bob  Largest bob with a cup of a definite circumference so to reduce the gap and minimize the chance of plug flow  Important in paste and concentrated suspension thru an orifices  Extrusion of toothpaste in tube  The sample is placed at the center of the plate which is then raised into position under the cone  The cone angle generally ranges from 0.3⁰ to 4⁰ smaller angle is being preferred.  Advantage :  time save in cleaning and filling  Temperature stabilization of the sample during a run  0.1 to 0.2 ml sample  Semisolids  Kelvin material - "Parallel" linear combination of elastic and viscous effects  Anelastic - Material returns to a well-defined "rest shape”  Based on the mechanical properties of materials that exhibit both viscous properties of liquid and elastic properties of solid  Creams  Lotion  Ointments  Suppositories  Suspension  Colloidal dispersing  Emulsifying and suspending agent  Biologic material : blood, sputum and cervical fluid  Organoleptc evaluation  Feel, spreadability, color, odor and other psychologic and sensory characteristics  Dermatologist three classes  Class I – soft and are for ophthalmic use  Class II – commonly medicated ointmentof intermediate consistency  Class III – involved stiff protective products use for moist ulcerative condition  USPbacitracin ointment decreased when temperature was raised from 20⁰ to 35⁰C  Three attributes:  Smoothness – coefficient of friction  Thinness – Non Newtonian  Warmth  Fluids  Mixing  Particle size reduction or disperse system with shear  Passage thru orifices, including pouring, packaging in bottles and passage thru hypodermic needle  Fluid transfer, including pumping and flow thru pipes  Physical stability of disperse system  Quasisolids  Spreading and adherence on the skin  Removal from jars or extrusion from tubes  Capacity of solids to mix with miscible liquids  Release of drug from the base  Solids  Flow of powders from hoppers and into die cavities in tabletting or into capsules during encapsulation  Packagability of powdered or granular solids  Processing  Production capacity of the equipment  Processing efficiency  Poloxamers (Pluronics) – dermatologic bases or topical ophthalmic preparation because of its low toxicity and ability to form clear water based gel  Polymer solution – ophthalmic preparation as wetting solution for contact lensand as tear replacement solution “dry eye syndrome”  dextran (natural) and polyvinyl alcohol (synthetic) + preservatives  High MW preparation of Na hyaluronate at 0.1 to 0.2% - dry eye syndrome  Torque – is the force acting to produce rotation of a body  1Nm= 1 joule  Pendular state – lenses of liquid at contact point of the particles  Funicular state – mixture of air and liquid between particles  Capillary state – pores filled with liquid  Liquid droplet state – envelop particles  The approximate viscosity in centistokes at room temperature of ether is 0.2; of water, 1; of kerosene, 2.5; of mineral oil, 20 to 70; and of honey, 10,000.