The document discusses the electrical properties of interfaces and the electrical double layer. When solids are dispersed in a liquid, they develop a charged interface due to adsorption of ions or functional groups. This forms an electrical double layer consisting of a tightly bound layer and diffuse second layer. The zeta potential, which is the potential at the boundary between these layers, governs particle interactions and stability of dispersions. An optimum zeta potential is desired for maximum stability.
Surfactants and their applications in pharmaceutical dosage formMuhammad Jamal
This presentation is very much helpful for the medical students,pharmacists, researchers and other health care providers. i hope it will provide important information regarding surfactants and their applications in pharmaceutical dosage forms.
INCLUDES SPREADING COEFFICIENT AND ITS THEORY AND ALSO FEW OF ITS APPLICATION IN PHARMACEUTICAL FIELD
WILL BE HELPFUL FOR B PHARMACY STUDENTS
INCLUDES HOW IT IS DERIVED AND ALSO HOW IT IS RELATED TO SPREADING OF A CREAM OR OINTMENT ON OUR SKIN
IMPORTANCE OF SPREADING COEFFICIENT
Surfactants and their applications in pharmaceutical dosage formMuhammad Jamal
This presentation is very much helpful for the medical students,pharmacists, researchers and other health care providers. i hope it will provide important information regarding surfactants and their applications in pharmaceutical dosage forms.
INCLUDES SPREADING COEFFICIENT AND ITS THEORY AND ALSO FEW OF ITS APPLICATION IN PHARMACEUTICAL FIELD
WILL BE HELPFUL FOR B PHARMACY STUDENTS
INCLUDES HOW IT IS DERIVED AND ALSO HOW IT IS RELATED TO SPREADING OF A CREAM OR OINTMENT ON OUR SKIN
IMPORTANCE OF SPREADING COEFFICIENT
EXPLAINS WHAT IS AN ELECTRICAL DOUBLE LAYER AND HOW IT FORMS
INCLUDES DISTRIBUTION OF IONS AROUND A PARTICLE OF SUSPENSION
HOW THE IONS GET ADSORBED ON THE SURFACE OF SUSPENDED PARTICLE AND HOW IT AFFECTS DISTRIBUTION OF REST OF THE IONS IN THE LIQUID PHASE
EXPLAIN DIFFERENT POTENTIALS ACROSS
ZETA POTENTIAL NERNST POTENTIAL ETC.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
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1. ELECTRICAL PROPERTIESOF INTERFACES The studyof electrical propertiesof interfacesfinds
applicationsin
the formulationof dosage formsregarding:
1. Stabilizationof colloidal dispersions
2. Preparationof flocculatedsuspensions
3. Stabilization of emulsions
Whensolidsare dispersedinaliquid,alarge solid/liquidinterface isobtained,whichmaybecome
charged.The originof charge on such an interface canbe accountedas follows.
1. Electrolytes(ions)presentinthe solutionmaygetadsorbedonthe solidsurface.If ionsare absent,
the vehicle,(water),maydissociate intohydronium(H3O)+andhydroxyl,(OH)- ionsandgetadsorbed.
Adsorptionof hydroxyl ionsismostcommonbecause of the asymmetricnature of the hydroxyl ions
2. Functional groups(suchas carboxyl group) presentonthe surface of the particlesmaygetdissociated
and imparta charge.Forexample, -COOH, -NH2groupsonproteinsgetionised.
3. Differencesinthe dielectricconstantsbetweenthe particlesanddispersionmedium are responsible
for the originof charge thougha lesscommonsource.
The charge on the solidparticle impartscertainchangestoitsenvironmentregardingthe distributionof
ions
ELECTRICAL DOUBLE LAYER:
The concept of the electrical double layeratthe interface canbe
illustratedwiththe helpof .Figure 5-20.The solidparticles are dispersed inanaqueous solution
containinganelectrolyte
2. The interface :aa' isthe solid/liquidinterface.The cationsare assumedtobe presentinsolution.These
are adsorbedonthe solidinterface andimpartapositive charge.These cationsare referredaspotential
determiningions.
TIGHTLY BOUND LAYER: Immediatelyadjacenttothisinterface(aa')isaregionof tightlyboundlayer.This
layerextends uptobb'.Once the adsorptioniscomplete,the cationsattracta tew anionsandrepel the
approachingcations.Further,thermal motiontendstoproduce equal distributionof ioninsolution.
Thus,at equilibrium,some excess
anionsare e presentinthis region.However,theirnumberislessthanthe adsorbedcations.Therefore,
bb' still possessescharge. Anionsare normallytermedascounterionsorgegenions.When
particlesmove relative tothe liquid,thistightlyboundlayeralsomovesalong.Thus,the particlesurface
nowextendsuptobb'ratherthan aa'.The boundarybb'is termedasshearplane
DIFFUSE SECONDLAYER: This regionisboundbylinesbb'and cc'. In thislayer,excessnegative ionsare
present
At andbeyondcc' the distributionof ionsisuniform.Onthe whole the systemiselectricallyneutral,
eventhoughthe distributionof ionsinunequal indifferentregions.
Thus,the electrical double layerconsistsof
(1) Tightlyboundlayer
3. (2) Diffuse secondlayer
n the above example (Figure 5-20),bb'may possessnegativecharge.Itindicatesthatthe numberof
anionsismore comparedto that of cationsadsorbedon the interface.However,cc'still maintains
electrical neutralityasmentionedearlier.
Whenthe interface isadsorbedby negative ions,thenaa'assumesnegative charge,bb'possesses
negative charge andcc' will be neutral.Theargumentscanbe appropriatelysequenced.Onsimilarlines
dependingonthe distributionof ions,aa'can be negative,bb'maybe positive andcc' will be neutral.
Whenwe move fromthe interface (aa') towardsthe bulkof dispersion(dd'),the potentialchangesare
representedinFigure5-21.These changesare characterizedandexpressedbydifferentways.
NERNSTPOTENTIAL:It isthe potential of the solidsurface itself,aa'owingtothe presence of potential
determiningions.
Nernstpotential,E,orelectrothermodynamicpotentialisdefinedasthe differenceinpotential between
the actual surface andthe electroneutral regionof the solution.
ZETA POTENTIAL:It isthe potential observedatthe shearplane,i.e.,bb'line (Figure 5-20).
Zetapotential,orelectrokineticpotential isdefinedasthe difference inthe potential betweenthe
surface of the tightlyboundlayer(shearplane) andthe electroneutralregionof the solution
Zetapotential canalsobe definedasthe workrequiredtobringa unitcharge frominfinitytothe surface
of the particles.
4. From Figure 5-21, itcan be inferredthatthe potential energydecreasesrapidlyin the initialstage,
followedbya gradual decrease
towardsthe boundarycc'. The counterions,whichare presentclose tothe surface bb'and inthe region
of bb' tocc', may reduce the particle-
particle interactions.Hence,the potential energydecreasesmore graduallyinthisregion.Ingeneral,
zetapotential ismore importantinthe fieldof
pharmacycomparedto Nernstpotential,becausethe electrical double layeralsomoves,whenthe
particle isundermotion.
APPLICATIONS:Zeta potential governs the degree of repulsions between the adjacent ions of like charges.
Hence,itis usedtopredict
Particle-particle- interaction.Suchinformationprovidesinsightsaboutthe stabilityof systems
containingdispersedparticles.Anoptimumzetapotential desirable forthe maximumstability.
If zeta potential fallsbelowaparticularvalue,the attractive forcesexceedthe repulsive forces.
Thisresultsinthe aggregationof particles.