Lecture Script Polymer Sci II Colloid Stability

7/28/2019 Lecture Script Polymer Sci II Colloid Stability

1/28


2/28

A state of subdivision in

which the particles,

droplets, or bubbles

dispersed in another

phase have at least one

dimension between 1 and

1000 nm

all combinations are

possible between :

gas, liquid, and solid

W. Ostwald

Colloidal systems


3/28

Surface area of colloidal systems

Cube (1cm; 1cm; 1cm)after size reduction to an edge length of 500 nm:

surface area of 60 m2

Spinning dope (1 cm3)

after spinning to a fibre with diameter of 1000 nm:

fiber length of 1273 km

1 liter of a 0.1 M surfactant solution:

interfacial area of 40000 m2


4/28

Surface atoms [in %]

in dependence on the particle size [in nm]

0

10

2030

40

50

60

7080

90

100

20 10 5 2 1

part of surface

atoms in %%

nm


5/28

Colloidal systems

have large surface areas

surface atoms become dominant


6/28

Colloid stability

Colloidal gold: stabilized against coagulation !

Creme: stabilized against coagulation !

Milk: stabilized against coagulation !


7/28

ParticleParticle interactions

Interaction Energy ( Vtot)Distance of

Separation (d) Relationship

d


8/28


9/28

DLVO - Theory

1940 Derjaguin; Landau; Verwey; Overbeek

Long range attractive van der Waals forces

Long range repulsive electrostatic forces


10/28

DLVO Theory

Van der Waals attractive energy

a) between two plates:

b) between two spheres:

2

.

12 d

AVattr WaalsderVan

d

aAV

attr

WaalsderVan12

.


11/28

Double layer models

Helmholtz

Gouy Chapman

Stern


12/28

Gouy Chapman model

planar double layer

Ions as point charges


13/28

Electrolyte theory

kT

xez

iii

i

enezxd

xd

0

2

24

I distribution of ions in the diffuse double layer

(Boltzmann equation)

II equation for the room charge density

III Poisson relation

Aus I, II und III folgt:

Poisson

Boltzmann - relation

kT

xezenxn iii

xnezx iii

0

2

24 x

xd

xd


14/28

Solution of the P-B equation

xekx

xxd

xd

k

k

0

2

2

2

For small potentials (< 25 mV) :

Integrable form

kT

xez

i

ii

i

enezdx

xd

0

2

24


15/28

DLVO Theory

Electrostatic repulsive energy

Resulting repulsive overlap energy

a) Between two plates:

c volume concentration of the

z valent electrolyte

b) Between two spheres

drep

elektrost ekTc

V k

k

64

.

2

2

2

22

0

22

.

1

18

kT

ze

kT

ze

drep

elektrost

e

ee

ze

TkV

k


16/28

Vtot(d)= Vattr(d) + Vrep(d)

Vvan der Waals

= - A a / 12 d Velectrost.

= k e-kd

AHamaker constant

aparticle radius

d

distance between the particles

1/k - thickness of the double-layer


17/28

Electrostatic stabilization

stabilized against coagulation

Kinetically stable state

energetic metastable state in the

secondary minimum

with an energy barrier


18/28

Critical coagulation concentration (CCC)

The energy barrier disappears by adding a

critical amount of low molecular salts


19/28

DLVO Theory

(CCC)

Vtot / dd = 0 Vtot = 0

for two spheres:

2

266

3

0

3553

2

2

2

2

122

0

22

1

1

4

1039,3

121

18

kT

ze

kT

ze

kT

ze

kT

ze

e

e

Aze

Tkccc

daA

e

eeze

Tk


20/28

DLVOTheory

(CCC)

For two spheres the ccc should be related to

the valency (1 : 2 : 3) of the counterions as:

1000 : 16 : 1,3


21/28

CCC of a colloidal dispersion as a function of

the salt concentration

AlCl3

CaCl2

MgCl2

KCl

NaCl

electrolyte

1,79,3 10-5

136,5 10-4

137,2 10-4

10005,0 10-2

10005,1 10-2

Schulze-Hardy-ratioCCC of a

Arsensulfid -Dispersion


22/28

Steric stabilization

What will be happen when we add polymers

to a colloidal dispersion ?


23/28


Polymer adsorption layer


24/28


Overlap of the

polymer adsorption layer


25/28

Overlap of the adsorption layer

Osmotic repulsion

Entropic repulsion

Enthalpic repulsion


26/28

Sterically stabilized systems can

be controlled by

The thickness of the adsorption layer

The density of the adsorption layer

The temperature


27/28

Stabilization and destabilization in

dependence on the molecular

weight of the added polymer


28/28

Stabilization and destabilization in

dependence on the

polymer-concentration

Lecture Script Polymer Sci II Colloid Stability

Documents

Transcript of Lecture Script Polymer Sci II Colloid Stability