表面活性剂参考课件lecture9

Exam

infoDate

&

time:Form:Allowed

material:21/10

8.30-12.30

M-housequestions

-

what,

how,

why,easy

calculationsorder

of

magnitude

estimationknow

central

equations

&

discussdiscuss

&

explain

phenomenaPhysics

Handbook

(or

equivalent)Pocket

calculatorDictionaryDon’t

forget

to

register!ProjectinfoHand

in:Form:Grading:14/10

at

the

lecture3-5

pages

(longer

is

ok)references

(especially

figures)passed/not

passed(not

passed=correct

&

hand

in

again)good

report

can

help

total

course

gradeno

separate

credits

for

projectPresentation:14/10

at

the

lecturemax

2

minmax

1

slide

-

plastic“elevator

pitch”Self-assemblySelf-assemblyCharacteristics

of

self-assemblywhat,

how,

whySelf

assembly

with

surfactants

&

amphiphileswhat/typesenergiesaggregation

geometries

&

phase

behaviourSelf

assembly

with

polymersphase

separationstructures4

Characteristics

of

Soft

Matteri) Length

scales:-

Structures

of

≈10-1000

nm

determine

the

propertiesTime

scales:

processes

from

10-12

-

103

sDynamics

processes

over

a

wide

time

scales

10-12

-

103

sVery

slow

processes

in

non-equilibrium

configurationsiii)

Weak

interactions-

Interactions

between

molecules

and

molecular

structures

≈

kTSelf

assemblyHierarchical

arrangement

of

structuresCompetition

between

interaction

energy

and

entropySelf-assemblyHierarchical

arrangement

of

structuresCompetition

between

interaction

energy

and

entropyStructures

of

≈10

to

>1000

nm

formed

and

determinethe

properties

of

the

materialSurfactants

and

amphiphilesAmphiphilic

molecule:two

parts

with

very

different

affinitiesSurfactant:an

amphiphilic

molecule

with

a

tendency

to

adsorbonto

free

surfaces

and

interfacesSmall

molecules

Mw≈100-1000Surfactants

and

amphiphilesAmphiphilic

molecule:two

parts

with

very

different

affinitiesEx.

hydrophilic

head

and

hydrophobic

taila

single

molecule

is

never

really

comfortable

in

a

solvent-> aggregation

to

minimize

the

interfacial

energy->

micro-phase

separation,

thermodynamically

stableaggregates

-

micellesSurfactants

and

amphiphilesAmphiphilic

molecule:two

parts

with

very

different

affinitiesEx.

hydrophilic

head

and

hydrophobic

tailHydrophobic

tail:

CH3(CH2)n-Hydrophilic

head:

anioniccationicnon-ionicblock-copolymersSurfactants

and

amphiphilesAmphiphilic

molecule:two

parts

with

very

different

affinitiesEx.

hydrophilic

head

and

hydrophobic

tailSurfactants

and

amphiphilesEx.

hydrophilic

head

and

hydrophobic

tailSelf-assembly

of

molecules

in

order

to

minimise

free

energy-> minimising

the

contact

between

water

(solvent)

andhydrophobic

tail

while

keeping

the

hydrophilic

head

incontact

with

waterMacro

vs.

micro

phaseseparationSimple

liquids

(water

&

oil):free

energy

when

a

molecule

joins

anaggregateN

-

number

of

molecules

in

the

aggregateg-

interfacial

energy,

v

-

molecularvolumeeN

-

monotonic

decreasing

function

of

N->

infinite

aggregates

-

macroscopic

phaseseparationAmphiphiles:->

finite

size

of

aggregates

-

microscopic

phase

separationWhy?无法显示该图片。Macro

vs.

micro

phaseseparationAmphiphiles:->

micro-phase

separation->

finite

size

of

aggregates->

entropic

considerations

more

importantWhy?

Balance

between

protecting

the

hydrophobictailand

keeping

the

head

in

contact

with

the

waterassociating

tails

vs.

repulsion

of

head

groupsShape

of

aggregatesBasic

shapes:spherescylindersbilayersvesiclesSuperstructures:micellar

crystalslamellar

phasesbicontinuous

networks-

…micellesShape

of

aggregatesFactors

determining

the

shapeOptimum

head

group

are,

a0Critical

chain

length,

lcHydrocarbon

volume,

vlc

- length

of

fully

extended

tailv

- volume

of

the

tail#

of

tails,

side

groups,

…vlcOptimum

head

group

area,

a0a0

controlled

byrepulsive

forces:electrostatic

or

steric

repulsion(can

be

altered

by

e.gsalt

concentration)attractive

forces:protecting

the

tailShape

of

aggregatesSpheres

-

smallest

area/volumeVolume:4pr3/3=Nv(N

-

#

of

molecules

in

aggregate)Surface

area:4pr2=Na0->

r=3v/a0but

rmax≤lcv/lca0

≤

1/3

for

spherical

micellsShape

of

aggregatesSpheres:v/lca0

≤

1/3Cylinders:1/3≤

v/lca0

≤

1/2Bilayer:v/lca0

>

1/2Spherical

micellesSpheres

formed

when:v/lca0

≤

1/3Size

of

micelles

finite

->eN

has

a

minimum

value

at

anoptimum

number

MXN

-

volume

fraction

of

micelleswithNmolecules无法显示该图片。size

distributionCritical

Micelle

Concentrationf

-

volume

fraction

of

amphiphilef

<

fc

-

monomersf

>

fc

-

micelles

of

average

size

Mfc

=

exp(-∆e/kBT)-

CMC无法显示该图片。Cylindrical

micellesSpheres

formed

when:1/3<v/lca0

≤

1/2Size

of

micelles

finite

but

eN

has

a

no

minimum

-energy

of

a

molecule

in

thecylinder

is

independent

ofthe

size

->

only

2∆Eend->

forming

larger

micelles

leads

toenergy

gain,

but

a

loss

in

entropy无法显示该图片。Cylindrical

micellesIf

∆Eend

is

large

->

very

longcylinder >µmPolymer-like

system

but:Polymer

length

fixedMicelles

form

and

breakMicellar

size

varies

withexternal

conditionsChange

in

dynamicpropertiesBilayersBilayers

formed

when:v/lca0

>

1/2A1/2∆Eedge(A) (A

-

area

of

a

layer)dependent

on

the

size

of

the

bilayer->

formation

of

infinite

layersVesicles

-

closed

surface

by

a

bilayer->

model

for

cell

membranes->

drug

delivery

systems->

colloidal

behaviourBilayersCell

membranes

-

phospholipid

bilayersTwo

tails

give

a

largevolume,

vv/lca0

>

1/2BilayersBilayers

are

not

flat

-

highly

crumpledPersistence

length:k

-

bending

modulus

of

membraneFor

r

>

x

direction

in

membrane

is

lostLamellar

phases

can

anyway

be

obtainedwith

very

large

d

->

confinement

betweentwo

adjacent

planes

leads

to

loss

in

entropy无法显示该图片。BilayersLamellar

phase

can

be

distorted

by

fluctuationsforming

complex

geometriesPhase

behaviourSelf

assembled

structuresare

rich

in

phases->

response

by

changingsize

and

shape

andarrangement

of

micelles->

dramatic

change

inpropertiesSelf-assemblyMore

complexity

from:several

types

of

amphiphilesmixed

solventschanging

pH,

temperature,

…Self

assembly

inpolymersMixingpolymersGenerally

polymers

don’t

mix

-

why?Free

energy

of

mixing:(two

molecular

liquids)无法显示该图片。entropicinteraction

energyInteraction

parameter

c:

c

<

2

always

single

phasec

>

2

phase

separationregular

solution

modelMixingpolymers(Flory-Huggi