surface and interfacial phenomena (2).pptx

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Surface and Interfacial Phenomena

Surface is a boundary between solidor liquid phase and a vacuum.

Interface is a boundary betweentwo phases.

Surface free energy is the workrequired to increase the area of thesurface by 1cm2.



Surface Tension is the force in dynes actingalong the surface of a liquid at right angle toany line 1 cm in length.

γ= W/ ΔA where γ is the surfacetension , W is the work in erg requiredto generate one square cm of surface

A.

The units of γ is either erg/cm2 or Dyne/ cm

As an erg is equal to a dyne.cm

urface tension is e ual numericall and



!he force of tension e"isting at the interfacebetween two immiscible liquids is known asinterfacial tension .

There are two forces that a#ect the behavior ofliquid on a solid$

1- %orce of cohesion between the molecules of aliquid.

- %orce of adhesion between the liquid and solid.

When the adhesion forces are stronger than the

cohesion forces ,the liquid spread over the solid.e.g.!ater on glass.and the angle known as

contact angle is smaller than &'.And vice versa.



"actors a#ecting Surface Tension

1( )ature of the liquid.

2( !emperature $ urface tension decreasewith increase of temp.,i.e.with anincrease of kinetic energy of the

molecules.γ = γ$%1- T/Tc&1.

'- olute

!he quantitative relationship betweensolute distribution and surface

tension is e"pressed



d

(easurement of surface Tension

1- The ca)illary *ise (ethod+

rhdg= r γ cos,

= rhdg/ or rhdg

- The ro) !eight (ethod+

mg= r γ

%or relative measurement ,it easier todetermine the )o of drops formed by agiven volume instead of determining theweight of drops.

γ1/ γ = nd1/n1d



'-*ing (ethod+

mg= 0 γ %r1 r&

preading coe0cient s.

S= Wa-Wc

S= γs- %γ2 γ2S&34am)le $ if the surface tension of water

is 32.4 dyne/cm , the surface tension of

ben5ene is 24.& and interfacial tensionbetween them is 67.8hat is the initialspreading coe0cient 9

32.4( 24.&: 67 4.& dyne/ cm.



Adsor)tion

s the accumulation of a substance over

the surface of another substance.e.g. Adsorption of alkaloid on charcoal.

A5sor)tion

!he penetration of a substance throughanother substance.

e.g.water and sponge.



The 6haracteristics of PhysicalAdsor)tion and 6hemisor)tionPhysical

Adsor)tion1( weak physical forces.

2( )on speci;c.

6( eversible.

<( =rocess ise"othermic.Amount ofadsorption decreaseswith rise of temp.

7( >ore than one layer.

?( usually rapid at alltemp.

6hemisor)tion1( nvolve sharing ofelectrons betweenadsorbent and adsorbedmolecules .

2(non speci;c .

6( rreversible.

<( urface reaction onlyproceeds above certain

temp.

7( estricted to monolayer.

?(ate increase rapidly byincrease temp.



Adsor)tion Isotherm

!he relationship between the amount of

gas adsorbate physically adsorbedon a solid and equilibrium pressure orconcentration at constant temperature.

A- freundlich Adsor)tion Isotherm.

@ "/m kc1/n

og "/m log k : 1/n log c



7- 2angmuir Adsor)tion Isotherm.

!his equation is based on the theory that

the molecules of the gas are adsorbedon active sites of the solid to form alayer one molecule thick.

!he fraction of the centers occupied bygas at pressure P is , .

!he fraction of the sites not occupied is

1- ,ate of adsorption r1 = 8 1%1- ,& P

ate of evaporation r2 B 2 C

At e uilibrium r =r



p/y 1/b ym : p/ym

"actor A#ecting Adsor)tion "rom

Solution +1- Solute concentration

Adsorption is more complete from dilute

solution than from concentrated one.- Tem)erature+- the amount of

adsorption will decrease as the temp.

increase.'- Surface area of adsor5ent+- as

surface area increased the amount of

adsorption will increase.



;- 3#ect of Sol<ents+- adsorption of the solutewill be at ma"imum if the solvent is inert has

no a0nity for adsorbent or for solute.- *emo<al of adsor5ed im)urities+- will

increase the amount of adsorption e.g.activated charcoal .eating it at 7'(1''oc.

>- Adsor5ent - solute interaction andSol<ent com)etition+- adsorption of a solutefrom dilute solution involve breaking solutesolvent bond and adsorbent solvent bond and

formation of adsorbent Esolute bond. electiveadsorption $ charcoal will adsorb magenta dyefrom solution however,if saponin is added tothe system the dyeis released since saponin is

preferentially adsorbed.



A))lication of adsor)tion in)harmacy and allied ?eld+-

1( Decolori5ing agents. 2( Desiccantand drying agents . 6( Adsorptionchromatography.

<( >edical adsorption. 7( on e"change.Adsor5ent materials+

eavy kaolin, attapulgite ,bentonite ,

charcoal, diatomite , puri;ed talc,veegum, alumina, silica

>agnesium trisilicate Forisil.



Surface Acti<e Agents

SAA

Are solute that cause decrease in thesurface tension of the solvent.

All types of soluble AA contain$

a( ipophilic group

b( ydrophilic group

A suitable balance between two opposing

groups of AA is necessary to ensurethat surface active properties areobtained.



6ritical (icelle 6oncentration+- s theconcentration of surfactant that form

micelle and at this concentration ,dramatic changes in thephysicochemical properties of the

solution take place e.g. surface tension, conductivity, osmotic pressure.

6lassi?cation of Surfactants+

!hey classi;ed on the bases of $1( Ghemical structure

2(Hses to which they are put

6( physical propertis



6hemical classi?cation ofsurfactants+

Anionic Surface Acti<e Agents + a( oaps

b( Irganic sulfonate

c( Irganic ulfate

6ationic Surface Acti<e Agents+

a( Juaternary Ammonium alts

b( =yridinium compounds



@on Ionic Surfactants+

Are classi;ed according to the type of the

linkage between the hydrophilic groupand the lipophilic

group in the molecules into$

A( Kster Elinked surfactants.b( Kther ( linked surfactants.

c( Kster( ether linked surfactants.



Am)holytic Surface Acti<e Agents+

- :ydro)hilic 2i)o)hilic

6lassi?cation%:27& hydro)hile li)o)hile 5alance

* value is the relative e0ciency of the

hydrophilic portion of the surfactantmolecule to its lipophilic portion.

!he * system act as a guide to

quantify all non Eionic surfactants tohandful of general application.



Pharmaceutical A))lication ofSurfactants+

8etting AgentsKmulsifying Agents

olubili5ing Agents

%oaming and Antifoaming

Detergents

Antibacterial Action of AA.



issolution

Describe the process by which the drug

particles dissolve. !he dissolution of a drug is described in a

simpli;ed manner by the )oyes E8hitneyequation $

dm/ dt kAcs( c

dm/dt is the dissolution rate.

B is the dissolution rate constant .

A is the surface area of dissolving solids .Gs is the solubility of the drug .

G is the concentration of drug in the

dissolution medium at time t .



B which incorporating the drug di#usioncoe0cient

And di#usion layer thickness. !heconstant k is termed the intrinsicdissolution rate and is a characteristic of

each solid drug compound in a givensolvent under ;"ed hydrodynamicconditions.



7u#er solution and 7u#er ca)acity

8hat is a bu#er 9

8hat is the use of bu#er in the ;eld ofpharmacy9

p pka : log LA( M/ LAM

7uffer ca)acity% B& +- The ability of a bu#erto withstand the e#ect of acid and bases .

7u#er ca)acity is equal to the amount ofstrong acid or strong base, e"pressed as

moles of : or o( ions, required to changethe p of one liter of the bu#er by one punit.



• t is clear that bu#er capacity increases as theconcentrations of bu#er components increases

• !he capacity is also a#ected by the ratio of theconcentration of weak acid and its salt.

• >a"imum capacityB ma4& is obtained when the

ratio of acid to salt 1 i.e. p pka of the acid .

•

What is the characteristic of a suita5le5u#erC

pBa value of the acid should be close to prequired.

ts components must be compatible with otheringredients in the system.

!o"icity of bu#er components must be taken intoaccount if the solution is to be used for medical

purposes.



6olligati<e Pro)erties

t is any physicochemical property of a

solution which depend only on thenumber of dissolved particles andnot on the nature of those particles.

!hese include $1- Da)or )ressure lo!ering.

- 5oiling )oint ele<ation.

'- "reeEing )oint de)ression.9- Fsmotic )ressure.



• Napor pressure

• !he vapor pressure of the solution is

lower than of pure solvent. WhyC• t can be e"plained by *aoultGs la!

• = "solv " po

• Osolv mole fraction of solvent.

• =o vapor pressure of pure solvent.

•ince Osolv P 1 in any solution = P ='



7oiling Point +

8hen boiling occur9

As mentioned before the solute lower thevapor pressure of the solvent . n order toreach the atmospheric pressure boiling

point . t is necessary to increasetem)erature.

"reeEing Point+

!he presence of solute molecules will interfere

with the formation of crystals of the solvent .

!his change in the free5ing process results in adepression of the free5ing point for the

solution relative to the pure solvent.



Fsmotic Pressure+

Ismotic pressure of the solution is the e"ternal

pressure that must be applied to the solution toprevent it being diluted by the entry of solvent via aprocess that is known as Fsmosis.

!his process refers to the spontaneous di#usion ofsolvent from a solution of low solute concentration or pure solvent into a more concentrated onethrough a semi permeable membrane. Such amem5rane se)arate the t!o solutions and is)ermea5le only to the sol<ent molecules.

This process occurs spontaneously at constanttemperature and pressure.



*ate and order of reaction+

The rate of a chemical reaction orprocess is the velocity with which itoccurs.

Frder of reaction refers to the way in

which the concentration of drug orreactant inFuences the rate of achemical reaction or process.

Hero order reaction +f the amount of a drug A is decreasing

at a constant time interval t , then the

rate of disappearance of drug A is



8here B o is the 5ero order rate constant and its unit

is mass/ time e.g. mg/min.

ntegration of equation yield the followinge"pression

A B ot: Ao where Ao is the amount of drug at time

t5ero.

"irst order reaction +f the amount of the drug A is decreasing at a rate

that is proportion to the amount of drug Aremaining , then the rate of disappearance of drug

is e"pressed as follow$dA/dt= - A where k is ;rst order rate constant and

is e"pressed in unit time (1 .



6om)le4 *eactions include

1(opposite or reverse reaction

2( consecutive reaction

6( ide reaction

Along with main reaction .

*e<ersi5le reaction +

A((((((((((((((*

A((((((((((((((*: G

A:*((((((((((((( G:D this reaction ise"ample of second order reaction



e.g. is the reaction between acid and alcohol to formester and water .

G6Goo: G27I((((((((((((((G6GooG27 :2I

!he rate of reaction is proportion to the concentration oftwo reacting substance A and * in the forward reactionand G and D in the reverse reaction .

f a and 5 represent the initial concn. If two reacting

substances and if 4 denote the moles of A and * in eachliter reacting in interval of time t

The <elocity of reaction is e4)ressed 5y thiseJuation +

d4/ dt= 8 %a-4& %5-4& 1 when a not equal b

If a=5

d4/ dt= 8%a-4&2 2



ntegration of equation 1will yield $

B 2.6'6/ ta(blog ba("/ab("

B can be determined by plotting t against2.6'6/a(b log ba("/ab("

!he slope of the line equal B

!he unit for second order rate constant B is

concentration (1time(1.

ntegration of equation 2 will yield$

B 1/t."/aa(" and k can be determined by

plotting t against "/ aa(" the slope of theline k and half life t1/2 for the second

order decomposition that obey this equation

t1/2 1/aB

surface and interfacial phenomena (2).pptx

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