self-assembling amphiphilic...

University of Cologne

Self-Assembling Amphiphilic Systems

Dr. Helge Klemmer Physical Chemistry, University of Cologne, D-50939 Köln,

Germany

Funktionen & Anwendungen

Sommersemester 2014


Low surfactant content, low energy input: emulsions

(usually micrometer size, very instable)

Low surfactant content, high energy input: nanoemulsions

(usually nanometer size, slightly kinetically stable)

High surfactant content, just thermal energy: microemulsions

(lower nanometer size, thermodynamically stable)

Non-amphiphile systems: e.g. Pickering emulsions

2

It‘s the amphiphile content that matters


3

Microemulsions

hydrophililic —hydrophobic—amphiphilic

component

(A) — (B) — (C)

thermodynamically stable, macroscopically homogeneous

but nano-structured phases of at least 3 components

water glycerol

monomers

n-alkanes triglycerides, monomers

super-critical fluids

non-ionic & ionic

surfactants


4

Binary Water – Surfactant Systems / Surfactant types

non-ionic surfactants

ethylene glycol monoalkyl ether (CiEj)

alkylpolyglucoside (CiGj)

ionic surfactants

sodium bis(2-ethylhexyl) sulphosuccinate (AOT) anionic

dodecyl trimethylammonium bromide (DTAB) cationic


5

Binary side-systems


6

Water (A) – CiEj (B) Systems / upper miscibility gap

a

A C

2

cp

CA

C

mm

m

T

tie-line

critical point cp


7

Water (A) – C12Ej (B) / Variation of j


8

Water (A) – CiEj (B) / Micelle formation - cmc

c

1e-7 1e-6 1e-5 1e-4 1e-3 1e-2

/

mN

m-1

0

10

20

30

40

50

60

70

80

H2O - Tensid

cmc

TpdA

dE

,

Gibbs adsorptions isotherm:

Tpcd

d

RT ,ln

1

Surfactant head group area:

ANa

1

Surface tension:


9

Water – CiEj Systems / Liquid crystalline phases

micellar cubic (I1):

hexagonal (H1):

bicontinuous cubic (V1):

lamellar (La):

+ inverted liquid crystalline phases:

V2, H2, I2


10 0.001 0.01 0.1 1

T /

°C

0

10

20

30

40

50

60

70

80

90

2

1

spheres

cylinders

networks

Water – C12E6 / more self-assembly

wB

T /

°C

1

2

32_

T1 T1

T2

T2

T3

T3

H2O / C

iE

j

oil


11

Water – C12E5 System / dilute self-assembled phases

/ wt%

0.001 0.01 0.1 1 10 1000

20

40

60

80

100

C12E6

C12E5

C12E4

2

1

/ wt%

0.001 0.01 0.1 1 10 100

T /

°C

0

20

40

60

80

100

L1

L1'+L3

L3

La

L2

H1

cmc

L1'+L1''

L1'+L2

wB

T /

°C

1

2

32_

T1 T1

T2

T2

T3

T3

H2O / C

iE

j

oil

L2: reversed micelles

dilute lamellae

L3: isotropic bi-

layer sponge-

phase


12

Ternary microemulsion systems / Gibbs phase triangle

water (A) oil (B)

non – ionic surfactant (C)

T, p = constant


13

Gibbs phase prism

p = constant


14

Sections through the phase prism

BA

B

mm

m

a

CBA

C

mmm

m


15

Isothermal sections - phase inversion


16

Sections through the phase prism

BA

B

mm

m

a

CBA

C

mmm

m


17

Isoplethal T()-section I

~

Measure of

Efficieny:

Phase inversion:

Monomeric

solubility:

T~

0

F = 0.50 = const.


18

Isoplethal T()-section II

F = 0.50 = const.

H2O - n-octane - CiEj

= 0.5

0.0 0.1 0.2 0.3 0.4 0.5

0

20

40

60

0

20

40

60

T / °C

0

20

40

60

0

20

40

60

80

C10E4

C8E3

C6E2

1

1

13

32

2

23

C12E5

T / °C

T / °C

T / °C

La3

La

La

2_

2_

2_

1

2_

V

H2O – n-octane – CiEj


19

Efficiency – Phase inversion temperature

F = 0.50 = const.

H2O – n-octane – CiEj


20

Microstructure

Techniques:

direct: Transmission Electron Microscopy (TEM)

indirect: Scattering Techniques

• Small Angle Neutron Scattering (SANS)

• Small Angle X-Ray Scattering

• Dynamic Light Scattering

Diffusion NMR

Electric Conductivity


21

o/w droplets

FFEM FFDI

L. Belkoura, C. Stubenrauch, and R. Strey, Langmuir (2004)

H2O – n-octane - C12E5

Microstructure – TEM I


22

L. Belkoura, private communication

=0.3

T=31.3°C, =0.04 T=32.2°C, =0.06 T=30.5°C, =0.01

=0.5 =0.1

From networks to bicontinuous microemulsions


Microstructure – TEM II


23

w/o droplets

FFEM FFDI

L. Belkoura, C. Stubenrauch, and R. Strey, Langmuir (2004)


Microstructure – TEM III


24

R. Strey, Colloid Polym. Sci., 272 (8), 1005 (1994).

Microstructure – Overwiew

F = 0.50 = const.


25

Microstructure – Length Scales I

Small angle neutron scattering (SANS)

q / Å-1

10-3 10-2 10-1 100

I(q

) /

cm-1

10-1

100

101

102

103

D2O - n-C8D18 - C12E5

a=0.0707, wB=0.0561, T=18°C

S(q)

P(q)

I(q)

r = 61.2 Å

= 9.7 Å

t = 6.0 Å

Iincoh= 0.125 cm-1

o/w

q / Å-1

10-3 10-2 10-1 100

I(q

) /

cm-1

10-1

100

101

102

103

D2O - n-C8D18 - C12E5

b=0.1260, wA=0.0959, T=46°C

S(q)

P(q)

I(q)

r = 50.0 Å

= 12.0 Å

t = 6.0 Å

Iincoh= 0.16 cm-1

w/o

M. Gradzielski, D. Langevin, L. Magid, and R. Strey, J. Phys. Chem. 99, 13232 (1995)

bicontinuous

D2O - n-octane - C12E5

q / Å-1

10-3 10-2 10-1

I ( q

) /

cm-1

10-1

100

101

102

103

104

105

106

107

108

109

1010

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.9

M. Teubner and R. Strey, J. Chem. Phys. 87, 3195 (1987)


26

Lichtstreuung set-up

thermostatisierbare, mit Toluol

gefüllte Probenkammer

Korrelator PC

Laserlichtquelle

Glasküvette mit Probe

Ausgangsoptik +

Photomultiplier auf drehbarem

Goniometer-Arm

Umlenk- und Fokussieroptik


27


Lichtquelle: - Laser (P > 70 mW) Vorteile: Strahlen parallel, polarisiert,

monochrom, kohärent, Leistung konstant

- Hg-Dampflampe (früher)

Umlenk- und Fokussieroptik: nicht zwingend erforderlich

Probe: - in zylindrischer Glasküvette (D=10-25 mm)

- Küvette ist in einem Brechungsindex “gematchten“ Bad

nToluol = nGlas: Vermeidung von Oberflächenreflexion

Detektion: - Photonenmultiplier (IStrom = I Lichtintensität) Spitzenbelastung

- Photodiode

Korrelator: - Für dynamische Lichtstreuung (DLS)

Goniometer: - Küvette und einfallender Strahl genau im Drehmittelpunkt

konstanter Abstand Probe - Detektor r, keine Strahlenversetzungen

Ausgangsoptik: nur paralleles Licht wird detektiert


28


He/Ne-Laser (632nm)

Probe

Photomultiplier


29

Proben-Umgebung

Glaszelle, gefüllt mit Toluol

Probe

Thermometer


30

R. Strey, Colloid Polym. Sci., 272 (8), 1005 (1994).

Microstructure – Overwiew

F = 0.50 = const.


31

Phase behaviour – Interfacial tensions

Microemulsions, T. Sottmann and R. Strey in Fundamentals of Interface and Colloid Science,

Volume V, edited by J. Lyklema, Academic Press (2005)


32

Variation of oil/water-interfacial tension

T. Sottmann and R. Strey, J. Chem. Phys. 106, 8606 (1997)

T / °C

0 10 20 30 40 50 60 70

ab /

mN

m-1

10-4

10-3

10-2

10-1

100

H2O - n-C8H18 - CiEj

C12E5

C10E4

C8E3

C6E2

C4E1


33

Theoretical background

T. Sottmann and R. Strey, J. Chem. Phys. 106, 8606 (1997)

Thermodynamic stability:

Structure size approximation:

Specific internal interface:

Droplet radius approximation:

²TkB

VSa

/

)1(

c

cic

v

aVS ,/

iC

Ac

iC

A

c

c la

vR

,,

33

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