Dr Cui Study Guide Daniel Judson

8/12/2019 Dr Cui Study Guide Daniel Judson

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DrCuiStudyGuide

List of things to know:

Surface tension

Surface tensionis an effect within the surface layer of a liquid that causes the layerto behave as an elastic sheet.

Surface tension = tendency of liquids to reduce their exposed surface to the

smallest possible area.

Work = g

Work required to increase the surface area of a liquid by ! area unit.

m"#m = dynes#cm

$he molecular interactions in the bulk of a liquid is very different from that on the

surface of the same liquid. %n the bulk& one molecule interaction equally in all

directions with other similar molecules. 'owever& when a molecule is located on thesurface of the same liquid& the molecule will only be attracted by other similar

molecules in the liquid& but not from above the surface. $hus& a liquid has the

tendency to reduce its exposed surface to the smallest possible area. %t is definedasthe work required to increase the surface area of a liquid by ! area unit. %ts unit is

dynes per cm or m"ewton per meter. $herefore& the surface tension is unique to each

individual liquid.

Interfacial tension

Surface tension is what happens if a liquid or solid is exposed to area. %t is a special

case of interfacial interaction. (et)s take a look at what will happen if two liquids are

put together. %f oil and water are putting together. $here will be two phases#layers&

with the oil on the top of water. $he question is that will the density of the liquidschange abruptly or gradually in the interface region. *xperimental data showed that +

is correct. $his region is called interfacial region. %n the bulk of water and oil& every

molecule will have coherent attraction from similar molecules in all directions.'owever& in the interfacial region& the water molecules will be attracted by water in

one half& and by oil in another half. $hus& the molecules in the interface region behave

differently from those in the bulk phase of both water and oil.

Surfactants Surfactants reduce the surface tension of water byadsorbingat the air,water

interface. $hey also reduce the interfacial tension between oil and water by
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adsorbing at the liquid,liquid interface. -any surfactants can also assemble in the

bulk solution into aggregates that are known as micelles.$he concentration at

which surfactants begin to form micelles is known as the critical micelleconcentration or -. When micelles form in water& their tails form a core that is

like an oil droplet& and their /ionic0 heads form an outer shell that maintains

favorable contact with water. When surfactants assemble in oil& the aggregate isreferred to as a reverse micelle. %n a reverse micelle& the heads are in the core and

the tails maintain favorable contact with oil.

%n %ndex -edicus and the "ational (ibrary of -edicine /"(-& 1S 2ept. of

'ealth and 'uman Services0& 3surfactant3 is reserved for the meaningpulmonarysurfactant /see 3alveoli3 link below0. 4or the more general meaning& 3surface

active agent3 is the heading.

Thermodynamicsof the surfactant systems are of great importance& theoretical

and practical& because surfactant systems represent a systems between ordered

and disordered state of matter,surfactant solutions may contain ordered phase/micelles0 and disordered phase /free surfactant mollecules and#or ions in the

solution0.

ny substance that when dissolved in water or an aqueous solution reduces its

surface tension or the interfacial tension between it and another liquid. lso called

surfactant

Surfactants are usually organic compounds that are amphipathic& meaning they

contain both hydrophobic groups /their 3tails30 and hydrophilic groups /their3heads30. $herefore& they are typically sparingly soluble in both organic solvents

and water.
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*ffect of surfactants on the properties of a liquid

5smotic pressure increases and reaches constant 2etergency ability increases sharply

(ight scattering becomes significant

Surface tension decreases and reaches a constant /critical micelle concentration0


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(ight scattering is a measurement of the presence of particles.

Surfactants need to form micelles to have detergency activity because any dirts haveto be solubili6ed into the micelles.

o 7equirements for a surfactant

o Soaps

o Soaps = salts of fatty acids

Soft soap 'ard soap Soft soap8 positive ion is univalent& such as "a9& :9& and "';9.

'ard soap8 positive ion is divalent& such as a99& -g99o nionic surfactants8 fatty acids& sulfate /S2S or S(S0& sulfonate& sodium

chlorate& bile saltso Sodium dodecyl sulfate/SDSor "a2S0 /'


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group& giving the molecule the amphiphilicproperties required of a

detergent.

o Sodium laureth sulfate& or sodium lauryl ether sulfate/SLES0& is a

detergentand surfactantfound in many personal care products /soaps&

shampoos& toothpasteetc.0. %t is an inexpensive and very effective foamer

o

o ll of the soaps /sodium oleate& etc0 are fatty acid salts. $hey are

characteri6ed by a long hydrocarbon chain and a carboxylate group at the

end.o

o 2ocusate sodium ?1S@A is anionic surfactant used as a stool softener and

is administered orally or rectallyB as a tablet disintegrant or as anemulsifier and dispersant in topical preparations. When sold as olace& it

is docusate sodium& or sodium salt of dioctylsodium sulfosuccinate

/2SS0.

o ationic surfactants8 $+& ben6alkonium chloride

o Benzalkonium chloride alkyl dimethyl !enzyl ammonium chloride"isan organic compoundthat is used as an antisepticand spermicide.$hisproduct is a nitrogenous cationicsurface,acting agentbelonging to the

quaternary ammonium group. +en6alkonium chloride is a mixture of

alkylben6yl dimethylammonium chloridesof various alkyl chain lengths.$he greatest bactericidal activity is associated with the !,!; alkyl

derivatives.

o %t is one of the safest syntheticbiocidesknown& and has a long history of

efficacious use. pplications are extremely wide ranging& from

disinfectant formulations to microbial corrosioninhibitionin the oilfield

sector. %t is deemed safe for human use& and is widely used ineyewashes&

hand and face washes& mouthwashes&spermicidalcreams& and in variousother cleaners& saniti6ers& anddisinfectants.$he mechanism of

bactericidal#microbicidal action is thought to be due to disruption of

intermolecular interactions. $his can cause dissociation of cellularmembranebilayers& which compromises cellular permeability controls and

induces leakage of cellular contents. 5ther biomolecular complexes within

the bacterial cell can also undergo dissociation

o Cetyl trimethyl ammonium !romide/CT#B0 & also known as

he$adecyltrimethylammonium !romideor %&he$adecanaminium'('('(&trimethyl&' !romide?!A/C!CH


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, (ecithin is extracted from plant /soy0 or eggs. $here are very biocompatible.

%t)s a natural component of cell membrane. /mphoteric surfactant0

o "eutral Surfactants#"on ionic surfactants

Span

'ere is list of Spans& their chemical names& '(+ values& and other

properties. s can be seen& the '(+ values of span decrease as the

Span JJ increase. $his is because Span >G has three oleate chains&and is very lipophilic.

$ween

$ween is polyoxyethylene sorbate ester. $he polyoxyethylene groups are more

hydrophilic& and the 7 group is more lipophilic. 2ue to the many polyoxyethylenegroups& $weens are in general more hydrophilic and have larger '(+.

@oloxmers are polyoxyethylene#polyoxypropylene block copolymers.
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-icelles /structure& properties& applications& factors affecting - and si6e of

micelles0

o :rafft point,,the temperature at which an ionic surfactant becomes equal

to its -. +elow the :raft point& the surfactant precipitates instead offorming -icelles.

o micelleis an aggregate of the surfactant molecules dispersed in a liquid

colloid. olloid = a kind of dispersed system with particle si6e rangingfrom ! nm to D.G mm. ggregation number

o ritical micelle concentration

o $he concentration of surfactant at which micelles form.

o -icelle aggregation numbero $he number of surfactants that aggregate to form a micelle.

o - of the mixture of two surfactants

o !#- = f!#-! 9 f!#-

o /f = mole fraction0

o )icelles are not a solid *articles+ The indi,actors affecting C)Cand micelle size indi-idual molecules in the micelles are in dynamic

e.uili!rium with monomers in the !ulk and at the interface+

o ,actors affecting C)C and micelle size

Structure of hydro*ho!ic grou*

(ature of hydro*hilic grou*

(ature of counter ions #ddition of electrolytes to ionic surfactants decreases C)C and increase size

Effect of tem*erature

-any surfactants can also assemble in the bulk solution into aggregates that are

known as micelles. $he concentration at which surfactants begin to form micellesis known as the critical micelle concentration or -. When micelles form in

water& their tails form a core that is like an oil droplet& and their /ionic0 heads form

an outer shell that maintains favorable contact with water. When surfactantsassemble in oil& the aggregate is referred to as a reverse micelle. %n a reverse

micelle& the heads are in the core and the tails maintain favorable contact with oil.

We now know that when a surfactant is added in water& it will decrease the surface

tension. $he question is that will it decrease the surface tension to 6ero.Whensurfactants are added into water& they will preferentially absorbed on the surface of

the water. %n the end& a highly compacted surfactant monolayer will be formed. fter

reaches this point& the extra surfactants added into the water will try to dissolve intothe bulk phase of the water. t a certain concentration& the surface tension of the
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liquid won)t decrease anymore. $he extra surfactants then rearrange to form the so

called micelles.

'(+ and '(+ calculation for a blend of surfactants

'ydrophilic,lipophilic balance

$he higher the '(+& the more hydrophilic.

7equired '(+ /7'(+0 values for emulsion.

'(+ values are additive

%f D m( of an '(+ of I.D are required& what will be the ratio of two surfactants /with

'(+ values of > and !0 in the blendK

'(+ value of surfactant = >

'(+ value of surfactant + = !
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(et the weight fraction of = xB the weight fractionof + will be /!,J0.

>J 9 ! /!,J0 = IB >J 9 ! ,!J = IB ,;J = ,D blend having a '(+ value of !D.C. 'owmuch $ween >D and Span >D are neededK

Suppose we need J fraction of $ween >DB the fraction of Span >D will be !,J

!GJ 9 ;.< /!,J0 = !D.CB J = /!D.C,;.D = N D.GI = !.!> g

Weight of Span >D = N D.;! = D.> g

pplications of surfactants Detergents

Emulsifiers

@aints

dhesives

%nks

lveoli

B= 12

A = 8

9

1

3

4


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/etting

Ski Wax

Snowboard Wax

,oaming

2efoaming

(axatives8 2ocusate Sodium grochemical formulations

'erbicides

%nsecticides

ritical surface tension

*mulsions#-icroemulsion

n emulsion is a thermodynamically unstable system consisting of at least two

immiscible liquid phases& one of which is dispersed as globules in the other liquidphase& stabili6ed by the presence of an emulsifying agent.

+utter& margrine& salad dressings.

Why it is thermodynamically unstable8 creating small droplets will create large

surface area. Since the surface has the tendency to decrease due to surface tension&emulsions are unstable.

). $wo immisicble liquids& not emulsifiedB +). n emulsion of @hase + dispersed in@hase B ). $he unstable emulsion progressively separatesB 2). $he /purple0

surfactant positions itself on the interfaces between @hase and @hase +& stabili6ing

the emulsion
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%nternal vs. externalB dispersed vs. continuous phase.

o *xternal#%nternal#ontinious phase

o $hermodynamically unstableK

o $heory of emulsification

hange from to + will significantly increase of the surface area of phase.

e.g.& if ! cm< of mineral oil is dispersed into globules having diameter of D.D!

mm in ! cm< of water& how much will be the surface area increased.

$he surface area will become CDD m /greater than a basketball court0B thesurface free energy will increase by > calories. $herefore& emulsions are

thermodynamically unstable& and the droplets have the tendency to coalesce.

*mulsifying agents are needed to decrease the surface tension and to stabili6e

the droplets.

*mulsifying agents can prevent coalescence or at least reduce its rate to

negligible. %t will form a film around the dispersed globules. $he strength of

an emulsifying agent lies in its ability to form a firm film.

o *mulsifying gents /surfactants& hydrocolloids& particles0

cacia& tragacanth& veegum& pectin& bentonite& etc.

Surface active agents /monomolecular film0

'ydrophilic colloids /multimolecular film0 4inely divided solid particles /@articulate film0


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o 0hysical sta!ility of emulsions

reaming

reaming is the upward movement of dispersed droplets of emulsion relative to the

continuous phase /due to the density difference between two phases0

Stoke)s law8 dx#dt = d /i,e0g#!>h

dx#dt = rate of setting

2 = diameter of particles


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= density of particles and medium

g = gravitational constant

h = viscosity of medium

7eversible. "eed to be shaken well prior to use. %t does not look good. lso& if not

uniformally distributed& required amount of the active ingradient might not be achieved.

+reaking& coalescence& aggregation

+reaking is the destroying of the film surrounding the particles.

oalescence is the process by which emulsified particles merge with each to formlarge particles.

ggregation8 dispersed particles come together but do not fuse.

$he maOor fact preventing coalescence is the mechanical strength of the interfacialfilm.

@hase inversion

n emulsion is said to invert when it changes from an o#w to w#o or vice versa.

ddition of electrolyte

ddition of al into o#w emulsion formed by sodium stearate can be inverted to

w#o.

hanging the phase8volume ratio

hanging from a soft soap into a hard soap& a hydrophilic surfactant into lipophilic

surfactant.

o )ethods of emulsion *re*aration ontinental -ethod /2ry Pum0

$he continental method is used to prepare the initial or *rimary emulsionfrom

oil& water& and a hydrocolloid or 3gum3 type emulsifier /usually acacia0. $he

primary emulsion& or emulsion nucleus& is formed from ; parts oil& parts water&and ! part emulsifier. $he ; parts oil and ! part emulsifier represent their total

amounts for the final emulsion.

%n a mortar& the ! part gum /e.g.& acacia0 is levigated with the ; parts oil until the

powder is thoroughly wettedB then the parts water are added all at once& and themixture is vigorously and continually triturated until the primary emulsion formed

is creamy white.

dditional water or aqueous solutions may be incorporated after the primary

emulsion is formed. Solid substances /e.g.& active ingredients& preservatives&

color& flavors0 are generally dissolved and added as a solution to the primary

emulsion. 5il soluble substance& in small amounts& may be incorporated directly

into the primary emulsion. ny substance which might reduce the physical
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stability of the emulsion& such as alcohol /which may precipitate the gum0 should

be added as near to the end of the process as possible to avoid breaking the

emulsion. When all agents have been incorporated& the emulsion should betransferred to a calibrated vessel& brought to final volume with water& then

homogeni6ed or blended to ensure uniform distribution of ingredients.

*xample of @rep -ethod8 od liver oil GD m(

cacia !.G g

Syrup !D m(

4lavor oil D.; m(

@urified water& qs ad !DD m(

ccurately weigh or measure each ingredient

@lace cod liver oil in dry mortar

dd acacia and give it a very quick mix

dd 12 mLof water and immediately triturate to form the thick& white&

homogenous primary emulsion dd the flavor and mix

dd syrup and mix

dd sufficient water to total !DD m(

Cod li-er oil& as its name suggests& is an oilextracted fromcodlivers. %t is a

nutritional supplement&in the past commonly given to children.od liver oil is

one of the most effective providers ofomega,


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itQs possible for dietary excess /well above the 720 to accumalate and become

harmful.

+ecause the body naturally produces vitamin 2 when exposed tosunlight&a

common way to benefit from both oils while avoiding a vitamin 2 overdose is to

take cod liver oil during latefallthrough winter& and fish oil during spring

through summer. $he ideal dosage and timing of consumption depends on yourseasonal sun exposure /and therefore natural vitamin 2 production0. $he only way

to be certain of any possible vitamin 2 deficiencies or overdosing /from

supplements0 is to have your levels checked.

5n the other hand& the 72 of vitamin 2 is considered by many to be strongly

understated. -ost adults donQt even meet the 72. %n DDG researchers at the

1niversity of aliforniareported that Ritamin 2 can dramatically lower the risk

of developing different types of cancers& cutting in half the chances of gettingbreast& ovarian& or colon cancer

$riturate /$richerat08 $o rub& crush& grind& or pound into fine particles or a

powderB pulveri6e.

*nglish -ethod /Wet Pum0 %n this method& the proportions of oil& water& and emulsifier are the same /;88!0&

but the order and techniques of mixing are different. $he ! part gum is triturated

with parts water to form a mucilageB then the ; parts oil is added slowly& inportions& while triturating. fter all the oil is added& the mixture is triturated for

several minutes to form the primary emulsion. $hen other ingredients may be

added as in the continental method. Penerally speaking& the *nglish method is

more difficult to perform successfully& especially with more viscous oils& but mayresult in a more stable emulsion.

+ottle -ethod /4orbes +ottle0

$his method may be used to prepare emulsions of volatile oils& or oleaginous

substances of very low viscosities. $his method is a variation of the dry gummethod. 5ne part powdered acacia /or other gum0 is placed in a dry bottle and

four parts oil are added. $he bottle is capped and thoroughly shaken. $o this& therequired volume of water is added all at once& and the mixture is shaken

thoroughly until the primary emulsion forms. %t is important to minimi6e the

initial amount of time the gum and oil are mixed. $he gum will tend to imbibe theoil& and will become more waterproof.

uxiliary -ethod

n emulsion prepared by other methods can also usually be improved by passing

it through a hand homogeni6er& which forces the emulsion through a very smallorifice& reducing the dispersed droplet si6e to about G microns or less.

"ascent Soap -ethod /%n situ soap0 %n situ soap method

alcium soaps8 w#o emulsions contain oils such as oleic acid& in combination with limewater /calcium hydroxide solution& 1S@0. @repared by mixing equal volumes of oil and

lime water.
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%n situ soap method is also called nascent soap methods. "ascent means beginning to

exist or to develop. $he emulsifier is formed as the emulsions are made.

5il phase8 olive oil#oleic acidB olive oil may be replaced by other oils& but oleicacid must be added

(ime water8 a/5'0 should be freshly prepared. *qual volume of oil and lime water

$he emulsion formed is w#o or o#wK -ethod of preparation8

+ottle method8

-ortar method8 when the formulation contains solid insoluble such as 6inc oxide and

calamine.

o @rimary or initial emulsion KKK

o Incor*oration of drugs in emulsionso ddition of drug during emulsion formation

o

o ddition of drugs to a preformed emulsion

o !. ddition of oleaginous materials into a w#o emulsion

o . ddition of oleaginous materials to an o#w emulsion

o


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3heology45iscosity4Thi$othro*y 7heo = flow

Riscosity /h& poise0 is an expression of the resistance of a fluid to flow /! p = D.!

@a.s0

4luidity /f0 = !#h

"ewton)s theory

When a shear stressis applied to a solidbody& the body deforms until the deformation

results in an opposing force to balance that appliedB forming an equilibrium.'owever&when a shear stress is applied to a fluid& such as a windblowing over the surface of the

ocean& the fluid flows& and continues to flow while the stress is applied. When the stressis removed& in general& the flow decays due to internal dissipation of energy. $he

3thicker3 the fluid& the greater its resistance to shear stress and the more rapid the decay

of its flow.

%n general& in any flow& layers move at different velocitiesand the fluidQs 3thickness3arises from the shear stress between the layers that ultimately opposes any applied force.

(aminar shear of fluid between two plates. 4riction between the fluid and the moving

boundaries causes the fluid to shear. $he force required for this action is a measure of thefluidQs viscosity.

(aminar shear& the non,linear gradient& is a result of the geometry the fluid is flowingthrough /a pipe0.
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%saac "ewtonpostulated that& for straight&paralleland uniform flow& the shear stress& &

between layers is proportional to the velocitygradient& Tu#Ty& in the direction

perpendicularto the layers& in other words& the relative motion of the layers.

'ere& the constant U is known as the coefficient of viscosity& viscosity& or dynamic

viscosity. -any fluids& such as waterand most gases& satisfy "ewtonQs criterion and areknown as"ewtonian fluids."on,"ewtonian fluidsexhibit a more complicated

relationship between shear stressand velocitygradientthan simple linearity.

$he relationship between the shear stress and the velocity gradient can also be obtained

by considering two plates closely spaced apart at a distance t. ssuming that the plates

are very large& with a large areaA& such that edge effects are neglected and that the lowerplate is fixed& let a forceFbe applied to the upper plate. %ncidentely& if this force causes

the plate to move& the substance is concluded to be a fluid. $he velocity of the moving

plate and the top of the fluid must have the same velocity U. "ow& by experimentation&

the applied force is proportional to the area and velocity of the plate and inversely

proportional to the distance between the plates. ombining these three relations results inthe equation 4 = mu/1#t0. Where mu is the proportionality factor called the absoulte

viscosity/with units @a,s or slugs#s,ft0. $he equation can be expressed in terms of shearstressB rho = 4# = mu/1#t0. 1#t is the rate of angular deformation and can be written as

an angular velocity& du/dy. 'ence& through this method& the relation between the shear

stress and the velocity gradient can be obtained.

%n many situations& we are concerned with the ratio of the viscous force to the inertialforce& the latter characterised by the fluiddensityV. $his ratio is characterised by the

kinematic viscosity& defined as follows8

ames lerk -axwellcalled viscosityfugitive elasticitybecause of the analogy thatelasticdeformation opposes shear stressin solids&while in viscous fluids& shear stressisopposed by rateof deformation.

Riscosity is the principal means by whichenergyis dissipated influidmotion& typically

as heat.

4)# = h dn#drB h = 4#PB

P = dn#dr = velocity gradient#rate of shear

4 = 4)# = shear stress

7ate of shear is directly proportional to shearing stress.

:inematic viscosity = h# /is density0

*ffect if temperature on viscosity
http://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Non-Newtonian_fluidhttp://en.wikipedia.org/wiki/Non-Newtonian_fluidhttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/Elastichttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Non-Newtonian_fluidhttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Gradienthttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/Elastichttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Heat


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h = e *v7$ / is a constant& *v is the activation energy required to initiate flow

between molecules

onsider a block of liquid consisting of parallel plates of molecules& similar to a deck ofcards. $he bottom layer is fixed& the top layer is moved at a constant velocity& each lower

layer will move with a velocity directly proportional to ints distance from the bottomlayer. $he velocity different between two different layers& dv#dr& is called shear rate.

force per unit area& 4)#& required to bring about flow is called shear stress. "ewtonrecogni6ed that the higher the viscosity of a liquid& the greater a certain force per unit

area required to produce a certain rate of shear.

Some newtonian flows8 castor oil& chloroform& ethyl alcohol& glyerin& olive oil& water.

4or newtonian

flows& the plot of shear rate vs. shear stress is a linear line. -aOority of pharmaceuticalsystems are non,newtonian flow. $he relationship between shear stress and shear rate is

not linear.


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$his can be divided

into three categories.

Simple plastic flow or bingham plastic. %n plastic flow& the liquid does not flow onlywhen the shear stress is above a certain value& which is called the Xield Ralue. 5nce

above the yield value& the flow behaves Oust like a newtonian flow. +elow the yield value&

the substance acts as an elastic material. 7heologists classify bingham bodies as a solid.4locculated particle suspensions usually behave like this. yield stress has to be appliedto break the structure formed between two adOacent particles. $he frictional forces

between moving particles can also contribute to yield value.

@seudoplastic like natural and synthetic gums /tragacanth& "aalginate& -& "a-0. %t

is typically exhibited by polymers in solution. "o yield value exists. $he viscosity of thepseudoplastic material cannot be expressed by a single value. Riscosity decreases as the


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shear rate increase. Shear,thinning. s shear stress increases& normally disarranged

molecules begin to align their long axes in the direction of flow. $his orientation reduce

the internal resistance and allows great shear rate at each successive shear stress. %"addition& some of the solvent associated with the polymers may be released& resulting in

the lowering of the concentration and si6e of the polymer dispersion.


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ertain suspensions with a high Y of dispersed solids exhibit an increase in resistance to

flow with increased rate of shear. $he volume of the system increase when sheared& thus

called dilatant flow. Riscosity increase at shear rate increases. Shear thickening flow.

ertain suspensions with a high Y of dispersed solids exhibit an increase in resistance to

flow with increased rate of shear. $he volume of the system increase when sheared& thuscalled dilatant flow. Riscosity increase at shear rate increases. Shear thickening flow.

"on,newtonian systems

!. +ingham plastic flow

does not begin to flow until a shear stress corresponding to the yield value is

exceeded.

4locculated colloid particles

. @seudoplastic flow

$ypically exhibited by polymers in solution /tragacanth& sodium alginate&methylcellulose& "a-0

Riscosity decreases with the increase of shear rate#shear thinning

aused by the re,alignment of polymer and#or the release of solvents associatedwith the polymers.


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We have shown that the shear rate progressively increased when plotted against the

resulting shear stress. 5ne may wondering what will happen if the rate of shear is reduced

once the desired maximum shear stress is reached. Will the down curve overlays theupcurveK $his is only true for newtonian flow. 4or non,newtonian flows& the downcurve

is usually displaced relative to the upcurve. 4or shear,thinning systems& the downcurve is

usually displaced to the left of the upcurve. $his indicates the breakdown of structure thatdoes not immedidately reform when stress is removed or reduced. $his phenomena is

called thixotropy. $hixotropy can only be applied to shear,thinning materials. 'ow do

you explain itK symetric particles& when stand& can form some loose associations toconfer some degree of rigidity to the system. When stress is applied& the contact is

broken& and a gel,to,sol transition occurs. 5n removal of the stress& the structure starts to

reform& but this process is not instantaneous.

Some times& one may observed a totally different phenomena. $hat represents an increasein consistency in the downcurve& which is in the right of the upcurve. -agnesia magma at

shear rate above


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$homas Praham discovered /!>CD0 that certain substances /e.g.& glue& gelatin& or

starch0 could be separated from certain other substances /e.g.& sugar or salt0 by

dialysis. 'e gave the name colloidto substances that do not diffuse through asemipermeable membrane /e.g.& parchment or cellophane0 and the name

crystalloidto those which do diffuse and which are therefore in true solution.

olloidal particles are larger than molecules but too small to be observed directlywith a microscopeB however& their shape and si6e can be determined by electron

microscopy. %n a true solution the particles of dissolved substance are of

molecular si6e and are thus smaller than colloidal particlesB in a coarse mixture/e.g.& a suspension0 the particles are much larger than colloidal particles. lthough

there are no precise boundaries of si6e between the particles in mixtures& colloids&

or solutions& colloidal particles are usually on the order of !D,F to !D,G cm in

si6e. Classification of Colloids5ne way of classifying colloids is to groupthem according to the phase /solid& liquid& or gas0 of the dispersed substance and

of the medium of dispersion. gas may be dispersed in a liquid to form a foam

/e.g.& shaving lather or beaten egg white0 or in a solid to form a solid foam /e.g.&

styrofoam or marshmallow0. liquid may be dispersed in a gas to form anaerosol /e.g.& fog or aerosol spray0& in another liquid to form an emulsion /e.g.&

homogeni6ed milk or mayonnaise0& or in a solid to form a gel /e.g.& Oellies orcheese0. solid may be dispersed in a gas to form a solid aerosol /e.g.& dust or

smoke in air0& in a liquid to form a sol /e.g.& ink or muddy water0& or in a solid to

form a solid sol /e.g.& certain alloys0. ! further distinction is often made in thecase of a dispersed solid. %n some cases /e.g.& a dispersion of sulfur in water0 the

colloidal particles have the same internal structure as a bulk of the solid. %n other

cases /e.g.& a dispersion of soap in water0 the particles are an aggregate of small

molecules and do not correspond to any particular solid structure. %n still othercases /e.g.& a dispersion of a protein in water0 the particles are actually very large

single molecules. different distinction& usually made when the dispersing

medium is a liquid& is between lyophilic and lyophobic systems. $he particles in alyophilic system have a great affinity for the solvent& and are readily solvated

/combined& chemically or physically& with the solvent0 and dispersed& even at high

concentrations. %n a lyophobic system the particles resist solvation and dispersionin the solvent& and the concentration of particles is usually relatively

low. ",ormation of Colloids$here are two basic methods of forming a colloid8

reduction of larger particles to colloidal si6e& and condensation of smaller

particles /e.g.& molecules0 into colloidal particles. Some substances /e.g.& gelatinor glue0 are easily dispersed /in the proper solvent0 to form a colloidB this

spontaneous dispersion is called pepti6ation. metal can be dispersed by

evaporating it in an electric arcB if the electrodes are immersed in water& colloidalparticles of the metal form as the metal vapor cools. solid /e.g.& paint pigment0

can be reduced to colloidal particles in a colloid mill& a mechanical device that

uses a shearing force to break apart the larger particles. n emulsion is oftenprepared by homogeni6ation& usually with the addition of an emulsifying agent.

$he above methods involve breaking down a larger substance into colloidal

particles. ondensation of smaller particles to form a colloid usually involves

chemical reactions\typically displacement& hydrolysis& or oxidation and
http://www.bartleby.com/65/di/dialysis.htmlhttp://www.bartleby.com/65/di/dialysis.html


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reduction. #0ro*erties of Colloids5ne property of colloid systems that

distinguishes them from true solutions is that colloidal particles scatter light. %f a

beam of light& such as that from a flashlight& passes through a colloid& the light isreflected /scattered0 by the colloidal particles and the path of the light can

therefore be observed. When a beam of light passes through a true solution /e.g.&

salt in water0 there is so little scattering of the light that the path of the lightcannot be seen and the small amount of scattered light cannot be detected except

by very sensitive instruments. $he scattering of light by colloids& known as the

$yndall effect& was first explained by the +ritish physicist ohn $yndall. When anultramicroscope /see microscope0 is used to examine a colloid& the colloidal

particles appear as tiny points of light in constant motionB this motion& called

+rownian movement& helps keep the particles in suspension. bsorptionis

another characteristic of colloids& since the finely divided colloidal particles havea large surface area exposed. $he presence of colloidal particles has little effect on

the colligative properties/boiling point& free6ing point& etc.0 of a solution. $$he

particles of a colloid selectively absorb ions and acquire an electric charge. ll of

the particles of a given colloid take on the same charge /either positive ornegative0 and thus are repelled by one another. %f an electric potential is applied to

a colloid& the charged colloidal particles move toward the oppositely chargedelectrodeB this migration is called electrophoresis. %f the charge on the particles is

neutrali6ed& they may precipitate out of the suspension. colloid may be

precipitated by adding another colloid with oppositely charged particlesB theparticles are attracted to one another& coagulate& and precipitate out. ddition of

soluble ions may precipitate a colloidB the ions in seawater precipitate the

colloidal silt dispersed in river water& forming a delta. method developed by 4.

P. ottrell reduces air pollution by removing colloidal particles /e.g.& smoke&dust& and fly ash0 from exhaust gases with electric precipitators. @articles in a

lyophobic system are readily coagulated and precipitated& and the system cannot

easily be restored to its colloidal state. lyophilic colloid does not readilyprecipitate and can usually be restored by the addition of solvent. %$hixotropy is

a property exhibited by certain gels /semisolid& Oellylike colloids0. thixotropic

gel appears to be solid and maintains a shape of its own until it is subOected to ashearing /lateral0 force or some other disturbance& such as shaking. %t then acts as

a sol /a semifluid colloid0 and flows freely. $hixotropic behavior is reversible&

and when allowed to stand undisturbed the sol slowly reverts to a gel. ommon

thixotropic gels include oil well drilling mud& certain paints and printing inks& andcertain clays. ]uick clay& which is thixotropic& has caused landslides in parts of

Scandinavia and anada.

$ype of colloid systems

!. (yophilic colloids /solvent,loving0
http://www.bartleby.com/65/mi/microsco.htmlhttp://www.bartleby.com/65/br/Brownian.htmlhttp://www.bartleby.com/65/ab/absorpti.htmlhttp://www.bartleby.com/65/ab/absorpti.htmlhttp://www.bartleby.com/65/co/colligat.htmlhttp://www.bartleby.com/65/co/colligat.htmlhttp://www.bartleby.com/65/mi/microsco.htmlhttp://www.bartleby.com/65/br/Brownian.htmlhttp://www.bartleby.com/65/ab/absorpti.htmlhttp://www.bartleby.com/65/co/colligat.html


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Systems containing colloidal particles that interact to an appreciable extend with

the dispersion medium.

cacia in water or celluloid in amyl acetate lead o the formation of asol. Solvation& hydration& hydrophilic sols /gelatin& acacia& insulin& albumin in water0&

lipophilic sols /rubber& polystyrene in non,aqueous solvents0

. (yophobic colloids /solvent,hating0

olloids are composed of materials that have little attraction& if any& for thedispersion medium.

"o solvent sheath around the particles

Pold& silver& arsenous sulfide& silver oxide in water


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7intment Bases e$am*les' *ro*erties" 'ydrocarbon 5leaginous bases

*mollient effect8 hydrates skin due to sweat accumulation

5cclusive dressing

2ifficult to wash,off#remove

Small amount of water can be incorporated into it with difficulty and can be

protective to water labile drugs such as tetracycline and bacitracin.

%s greasy and can stain clothing.

!. @etrolatum& 1S@

Xellow petrolatum#petrolatum Oelly

Raseline /hesebrough,@onds#1nilever0 /vahser,elaion0

-elts at ,CDo

. White petrolatum& 1S@

2ecolored petrolatum&

White petroleum Oelly#white vaseline


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White wax#white petrolatum

-ineral oil

(iquid petrolatum

%s a mixture of refined liquid saturated hydrocarbons obtained from petroleum (evigating agent to incorporate lipiphilic solids

n excipient in topical formulations where its emollient properties are exploited

as an ingredient in ointment bases.

5leaginous bases

!. Synthetic esters8

glyceryl monostearate& isopropyl myristate& isopropyl palmitate& butyl stearate&

butyl palmitate& and long,chain alcohol /cetyl alcohol& stearyl alcohol& @*P0

. (anolin derivates8

(anolin oil& hydrogenated lanolin

#!sor*tion !ases

$hose that *ermit the incorporation of aqueous solution resulting in he formation

of w#o emulsions

,,hydrophilic petrolatum& 1S@

holesterol CD g

,,quaphor8 gentle healing ointment to help heal dry& cracked skin

/@etrolatum. &t'er (ngredients)-ineral 5il& eresin& (anolin lcohol& @anthenol&

Plycerin& +isabolol0

$hose that arew#o emulsion

'ydrous lanolin8 w#o emulsion containing GY of water

lanolin 1S@8 nhydrous& contains ^ D.GY of water& absorbs twice its weight inwater& also called wool wa$& wool fat& or wool grease& a greasy yellow substance from

wool,bearing animals& acts as a skin ointment& water,proofing wax& and raw material

/such as in shoe polish0.


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@roperties____

bsorption bases /anhydrous0

*mollient

5cclusive

bsorbs water

Preasy

W#5 emulsion

*mollient

5cclusive

ontains water& absorbs additional water

Preasy

/ater&remo-a!le !ases

Water,washable bases& 5#W emulsion

'ydrophilic ointment& 1S@

-ethylparaben D.G g

@ropylparaben D.!G

S2S !D

@ropylene alcohol !D

Stearyl alcohol GD

White petrolatum GD

Water


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@roperties__..

Water,washable& easier to remove

"on#less greasy an be diluted with water

"on#less occlusive +etter cosmetic appearance

+etter compliance

/ater&solu!le !ases

@*P ointment& "4

, @*P


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synthetic high -W polymers of acrylic acid cross,linked with either allysucrose

or allyl ethers of pentaerythritol

@roperties___

Water soluble and washable "on,greasy

"on#less occlusive

(ipid free Synthetic base

7elatively inert

2oes not support mold growth

(ittle hydrolysis& stable

-ay dehydrate skin and hinder percutaneous absorption.

Le-igating #gents

spatula with a long& broad blade should be used

%nsoluble substances should be powdered finely in a mortar and mixed with an

equal amount of base until a smooth mixture is obtained. $he rest of the base isadded in increment.

(evigation of powders into small portion of base is facilitated by the use of

levigating agents.

(evigating agents8

-ineral oil for oily bases or bases where oil are the external phase

Plycerin for bases where water is the external phase.

(evigating agent should be equal in volume to the solid material.

When liquid is added into an ointment& care must be taken to consider thecapacity of the ointment in accepting the liquid. When it is necessary to add an

aqueous preparation to a hydrophobic base& the solution should be added into

minimal amount of the hydrophilic base first. $he mixture should be then addedinto the hydrophobic base.

*xample

)edication order

Sulfur /


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White petrolatum&


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Pels8 semisolids consisting of dispersions of small or large molecules in an

aqueous liquid vehicle rendered Oelly,like through the addition of a gelling agent.

Single,phase gel8

arbomers8 high -w water soluble polymers of acrylic acid cross,linked with

allyl ethers of sucrose or pentaerythritol.

$wo,phase system8 magma#milk of magnesia#magnesia magma& a gelatinousprecipate of magnesium hydroxide

Skin anatomy /Stratum corneum& stratum corneum& stratum corneum. 2id %

mention stratum corneumK0

,i-e main target regions4sites in dermatology

Surface treatment

,, amouflage& protective layer& insect repellent& antimicrobial#antifungal&

Sunscreen

Stratum corneum

,, *mollient& keratosis

Skin a**endage

,, cne& antibiotics& depilatory& antiperspirant& vaccine

5ia!le e*idermis4dermis

,, antiinflammation& anesthetics& antihistamine& antipruritic

Systemic treatment

,, transdermal

#cne cne vulgaris is a disorder of the pilosebaceous units.

plug of the pilosebaceous duct and follicle opening.

2rugs have to get into the hair follicles and pilosabaceous units

cne is a disorder of the pilosebaceous units& mainly in face& hest& and back. $helesions usually start as open or closed comedones& and evolves into inflammatorypapules and pustules that can evolve into nodules and cysts. $he definitions of all this

terms are rather confusing. @lease refer to the above website if you would like to get

more information.

cne is common in young people in the age of !,;. %n fact& over >GY of all peoplein the age of !,; are affected. %t does occur in adults too.
http://oregonstate.edu/~williate/p1wiki/index.php/Acnehttp://oregonstate.edu/~williate/p1wiki/index.php/Acne


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@ustule\ dome,shaped& fragile lesion containing pus that typically consists of a

mixture of white blood cells& dead skin cells& and bacteria. pustule that forms over a

sebaceous follicle usually has a hair in the center. cne pustules that heal withoutprogressing to cystic form usually leave no scars. $his photo shows pustules& papules

and comedones on the face of an acne patient8

@apule\ papule is defined as a small /G millimeters or less0& solid lesion slightly

elevated above the surface of the skin. group of very small papules andmicrocomedones may be almost invisible but have a 3sandpaper3 feel to the touch.

papule is caused by locali6ed cellular reaction to the process of acne. $his photo

shows papules and comedones on the face of an acne patient8

omedo /plural comedones0\ comedo is a sebaceous follicle plugged with sebum&

dead cells from inside the sebaceous follicle& tiny hairs& and sometimes bacteria.

When a comedo is open& it is commonly called ablackheadbecause the surface of the

plug in the follicle has a blackish appearance. closed comedo is commonly called a

whiteheadB its appearance is that of a skin,colored or slightly inflamed 3bump3 in theskin. $he whitehead differs in color from the blackhead because the opening of the

plugged sebaceous follicle to the skin)s surface is closed or very narrow& in contrastto the distended follicular opening of the blackhead

*tiology

%ncreased sebum production

ndrogens regulate sebum production. $estosterone converted to 2'$& which induces

sebaceous glands to increase in si6e and activity& resulting in increased amount of sebum.

bnormal clumping of epithelial horny cells in the pilosebaceous unit

'orny cells usually sloughed off from epithelial lining of the pilosebaceous duct.

7etention hyperkeratosis /increased adherence and production of follicular epithelial

cells0

@resence of*ropionibacterium acnes

*+ acnes lipases break triglyceride to fatty acids& which are irritating& cause comedones&

and result in inflammation.

cne $x Strategies___

(ncreased sebum production ,decrease t'e sebum production-
http://www.skincarephysicians.com/acnenet/glossary.html#Pustulehttp://www.skincarephysicians.com/acnenet/glossary.html#Papulehttp://www.skincarephysicians.com/acnenet/glossary.html#Sebumhttp://www.skincarephysicians.com/acnenet/glossary.html#Blackheadhttp://www.skincarephysicians.com/acnenet/glossary.html#Whiteheadhttp://www.skincarephysicians.com/acnenet/glossary.html#Pustulehttp://www.skincarephysicians.com/acnenet/glossary.html#Papulehttp://www.skincarephysicians.com/acnenet/glossary.html#Sebumhttp://www.skincarephysicians.com/acnenet/glossary.html#Blackheadhttp://www.skincarephysicians.com/acnenet/glossary.html#Whitehead


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Androgens regulate sebum production+ .estosterone converted to H.0 'ic' induces

sebaceous glands to increase in si2e and activity0 resulting in increased amount of

sebum+

Abnormal clumping of epit'elial 'orny cells in t'e pilosebaceous unit ,t'en

unblock sebaceous duct-

Horny cells usually sloug'ed off from epit'elial lining of t'e pilosebaceous duct+

3etention 'yperkeratosis ,increased ad'erence and production of follicular epit'elial

cells-

*resence of *ropionibacterium acnes ,4ill t'e bacteria-

*+ acnes lipases break triglyceride to fatty acids0 'ic' are irritating0 cause

comedones0 and result in inflammation+

5$ $x)s

+en6oyl peroxide

,, .GY to !DY

,, -ost effective 5$

,, :ill*+ acnesand irritant to increase epithelial cell turnover rate.

,, gel& cream& or lotion

Salicylic acid

,, D.G,Y& irritant keratolytic agent& lotion& creams

Sulfur& Y combined with resorcinol Y& or resorcinol monacetate


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-ore effective agent for acne

%ncrease hair growth

5thers8 dapalene /2ifferin0& $a6arotene gel and cream /$a6orac0& antibiotics/tetracyline& erythromycin& clindamycin& etc0

%sotretinoin /ccutane0

4or severe racalcitrant nodulocytic acnes

2ecrease sebum and keratini6ation 7educe population of*+ acnes

+irth defect

Contact Dermatitis

%rritant contact dermatitis

aused by direct contact with the irritant

bsolute primary irritants8 acids& alkalis& industrial chemicals&

7elative primary irritants8 soaps& detergent& ben6oyl peroxide& etc0

llergic contact dermatitis8

$he result of direct contact with a contact allergen& such as poison ivy and nickel.

llergic contact dermatitis is considered a $,cell mediated delayed,response immunereaction& because elicitation of an allergic reaction typically takes ;> to F hours to

occur after reexposure to the same allergen.

llergic 2

5ne of the most common dermatological conditions encountered in clinical practice.

!. =a*tencontacts skin epidermis. 'apten com*le$eswith protein


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1rushiol from poison ivy& poison oak& and sumac.

$x)s

Severe eruptions8 systemic corticosteriods

(ess severe eruptions8

7elieve itching

(ocal anesthetics /ben6ocaine0

ntihistamines /oral or topical& mainly sedative effect0

$opical hydrocortisone

$reatment

$opical hydrocortisone.

4or information about the transdermal drug delivery section& please see previous exams.Xou do not need to remember the equations for (og @ and log S calculations. 2o not

need to remember the polymeric composition of different transdermal patches. @eneration

enhancers /2-S5& water& 6one. 2o not need to remember the types of transdermaldevice the transdermal patches mentioned.

@ay attention to 4ickQs (aw and parameters in the equation /:oct#'5 diffusion

coefficient& permeability coefficient& solubility and the relationship between them.
http://oregonstate.edu/~maxwellr/Mid%20term%20exams.dochttp://oregonstate.edu/~maxwellr/Mid%20term%20exams.doc

Dr Cui Study Guide Daniel Judson

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