Summery ofSurface and interfacial phenomenon and Rheology
Surface and interfacial phenomenonInterphase: - the boundary between two immiscible phases is known asInterphase. The region between two immiscible phases is known as interphasialregion.Classification of Interphase:-Phase Example of InterphaseGas to gas Not possibleGas to liquid Liquid surfaceGas to solid Solid surfaceLiquid to liquid EmulsionLiquid to solid SuspensionSolid to solid Powder particle in contactInterfacial tension: - force of tension per unit length existing at the surface isknown as interfacial tension. Unit: dyne/cmSurface: - this is boundary between solid or liquid and vacuum.Surface tension: - force of tension per unit length existing at the surface is knownas surface tension. V= W/∆A W= surface free energy in watt. ∆A= area in cm.Surface free energy:-it is defined as a work required to extend the surface by unitarea. W= ν (∆A)Surfactants or surface active agent: - some molecules or ions of a substancesthat are adsorbed at interface or surface and reduce the interfacial tension orsurface tension is known as surface active agents.Example Oleic acid. Sorbitan mono oleate ( span80) Sorbitan mono laurate(span 20)
Polyoxyethylene sorbitan mono oleate(tween80) Polyoxyethylene sorbitan mono laurate (tween80)Adhesive force: - the force of attraction between molecules of different phases isknown as adhesive force.Cohesion force: - the force of attraction between molecules of same phases isknown as Cohesion force.Work of adhesion: - It is defined as energy per cm² required separating the twounlike molecules. Wa=Vx+ Vy-Vxy Vx= surface tension of x phase Vy= surface tension of y phase Vxy= interrfacial tension of xyWork of Cohesion: - It is defined as energy per cm² required producing twoseparate phases containing same molecules.Wc= 2(surface tension of same molecules) = 2VxSpreading co efficient: - it is defined as deficiency between the work of adhesionand word of cohesion. S=Wa - WcHLB value: - it is a number which is used to measures the hydrophilic andlipophilic nature of surface active agents. HLB= 20(1- S/A) S= saponification number A = acid numberSaponification number: - number of mg of KOH needed to saponify one gm offat.Acid number: - - number of mg of KOH required to neutralize one gm of thesubstances.Methods of measurement of surface tension:- 1. Capillary rise method.
2. Drop weight method. 3. Du-nowy method.Solubilization: - Solubilization is the process in which water insoluble substancesare dissolved in aqueous solution in the presence of surfactant.Micelles: - the surfactants molecules in solution begin to associates into smallaggregates are called micelles.Critical micelle concentration: - while the concentration of non associatedsurfactant molecules remain nearly constant, this concentration at which allsolution properties changes abruptly, is called the Critical micelle concentration.Mechanism of Solubilization:- 1. Dissolving the solute in micelle. 2. Adsorption of solute on the micelle. Tetracycline is solubilized in anionic surfactant (sodium lauryl sulphate) at pH 2.1Zeta potential: - it is the potential difference between the surface of tightly boundlayer and electro neutral region of the bulk phases (solution).Electrical double layer: - the surface of colloidal particles acquire a positivecharges by a relative adsorption of a layer of positive ions around it, this layerattracts counter ions from the medium which from a second layer of negativechargesMore recent considerations have shown that double layer is made of compact layer(inner) and diffused layer(outer).
RheologyDefinition: - it is the science which is concerned with the deformation of matterunder the influence of stress which may be applied perpendicularly to the surfaceof a body tangentically to the surface or at any other angle to the surface.Viscosity (η): - the resistance of a fluid to flow, the higher the viscosity higher theresistance.Fluidity (Ǿ): - the property of a fluid to exist as a fluid. It is reciprocal ofviscosity, higher the fluidity lowers the viscosity and vise versa. Ǿ=1/η, unit: time/minShear stress(S): - it may be defined as forces per unit area create in thedeformation of the matter.Rate of shear (D):- it may be defined as the ratio of velocity (V) differencebetween two planes of liquid to distance traveled by the liquid (x). D= V/xNewtonians law of fluid: - Newtonian’s was recognized the characteristics of thefluid and derived a loe which is known a Newtonian’s law.It can be expressed as “shearing stress is directly proportional to the rate of shear.” Shearing stress, S ∞ rate of shear D, S ∞ D, S=η D (viscosity co efficient) η = S/DUnit: - poise (gm/cm/sec) If an ointment is rubbed into the skin with a relative rate of motionbetween two surface 15 cm/s and the film thickness is 0.01cm and shearing stress15dyne/cm², then calculate the viscosity of ointment Given, rate of motion, V is 15 cm/s Film thickness is 0.01cm and Shearing stress, S 15dyne/cm²Rate of shear, D= V/X=15/0.01=1500/sViscosity, η = S/D= 15/1500=0.01 poise
Rheogram :- graphical representation of shear stress(S) versus rate of shear (D)which express the viscosity (η) as well as flow characteristics of substances iscalled rheogram.Kinetic viscosity (ν) - it is the viscosity divided by the density (d) liquid, ν= η/d.unit:-stokes.Newtonian’s fluid/ system/ flow: the flow characteristics of Newtonian’s liquid iscalled Newtonian’s flow. In case of Newtonian’s flow there is direct relationshipbetween shear stress and rate of shear.Example – simple organic solvent - dilute solution - true solution( the solution in which the solute is dissolved homogeneously)Non Newtonian’s fluid/ system/ flow;- the fluid which does not follow theNewtonians law is called Non Newtonian’s fluid/ system/ flow. There is no directrelationship between shear stress and rate of shear. Example –most of pharmaceutical product(suspension, emulsion). Based on flow characteristics the non Newtonian.s fluid are three types-. 1. plastic flow 2. pseudo plastic flow 3. dilatants flowRelative viscosity: - it is defined as the ratio of viscosity of dispersion to theviscosity of liquid concentration medium.Specific viscosity :- relative increase of viscosity caused by the presence ofdispersed phase.Reduced viscosity :- the ratio of specific viscosity to the concentration ofdispersed phase.Intensive viscosity: - it is the intercept obtain by extrapolation of graph of reducedviscosity versus concentration.Thixotropy: - Thixotropy means change by touch. It is usually defined as reversibleisothermal transition from gel to solution. In the Thixotropy system viscosity isdecreased from the break down of structure.