利用小角度 X 光散射、動態光散射探討二氧化矽／聚環氧乙烷 懸浮液之結構與作用力

利用小角度利用小角度 XX 光散射、動態光散射探討二氧化矽／聚環氧乙烷光散射、動態光散射探討二氧化矽／聚環氧乙烷懸浮液之結構與作用力懸浮液之結構與作用力

Structure and Particle Interaction of Hybrid Silica/Poly(ethylene oxide) Structure and Particle Interaction of Hybrid Silica/Poly(ethylene oxide) Suspensions Characterized bySuspensions Characterized by

Small Angle X-ray Scattering and Dynamic Light ScatteringSmall Angle X-ray Scattering and Dynamic Light Scattering

化 學 工 程 學 系化 學 工 程 學 系Department of Chemical Engineering, National Chung Cheng UniversityDepartment of Chemical Engineering, National Chung Cheng University

李淳毅、陳致中、溫玉合、李淳毅、陳致中、溫玉合、華繼中華繼中 ** 、李岱洲、李岱洲 **

1

Multiscale MeasurementsMultiscale Measurements

Ren, C.-L. and Y.-Q. Ma, J. Am.. Chem. Soc. 128, 2733 (2006)

Phase behavior in thin films of confined colloid-polymer mixtures

2

Thin Film FormationThin Film Formation

3

Solution StateSolution StateEvaporateEvaporate

Film FormationFilm Formation

Adsorption Mechanism of PEO Chains onto a Adsorption Mechanism of PEO Chains onto a Silica ParticleSilica Particle

Fig 1. Hydrogen bonding between the silica surface and PEO

Silica particle surface

OH

OH

OH

OH

OH

OH

C-C-On

‧‧‧

Poly(ethylene oxide); PEO

Hydrogen bond

C-C-On

‧‧‧

As the silica particle surface is covered by PEO,a core-shell structure is formed

5

Core

PEO

Silica

Core

Shell

For a hybrid suspension system consisting of fine colloidal particles (~15 nm), usual centrifugalseparation for determining the adsorption isotherm becomes, however, unreliable*

*Flood et al., Langmuir 22, 6923 (2006)

DLS analyses based on cumulants and double-exponential distribution for dilute silica/PEO suspensions (silica volume fraction φsilica=0.005 for all cases)

Core radius

Core Core-shell

saturationadsorption

(s)

100 101 102 103 104 105 106

|g(1

) ()|

0.0

0.2

0.4

0.6

0.8

1.0 12.0 g/L silcia12.0 g/L silica; 0.5 g/L PEO12.0 g/L silica; 1.0 g/L PEO12.0 g/L silica; 2.0 g/L PEO12.0 g/L silica; 4.0 g/L PEO12.0 g/L silica; 6.0 g/L PEO12.0 g/L silica; 10.0 g/L PEO

All values compiled above are determined from simplex optimization method

PEOconcentration

6

7

The observed time-dependent behavior &and the detailed DLS analyses suggest that themaximum absorption of PEO should be somewhere between 2.0 g/L and 4.0 g/L.

(s)

100 101 102 103 104

|g(1

) ()|

0.0

0.2

0.4

0.6

0.8

1.0

Upon mixing1-day after mixing2-day after mixingCumulantsDouble-exponential distribution

(a)

(s)100 101 102 103 104

|g(1

) ()|

0.0

0.2

0.4

0.6

0.8

1.0

Upon mixing1-day after mixing2-day after mixingCumulantsDouble-exponential distribution

(c)

2 g/L PEO

6 g/L PEO

(s)100 101 102 103 104

|g(1

) ()|

0.0

0.2

0.4

0.6

0.8

1.0

Upon mixing1-day after mixing2-day after mixingCumulantsDouble-exponential distribution

(b)4 g/L PEO

Fig 2. DLS results for dilute silica/PEO suspensionswith various PEO concentrations

Saturation Adsorption Concentration Determined by DLSSaturation Adsorption Concentration Determined by DLS

Core-Shell Model*Core-Shell Model*

8

p( ) ( ) ( )I q n P q S q

R2

R1

ρsρp ρm

2 21( ) (2 )

p 1 2 1

1( ) ( , , )

2

RI q e n P q R R dR

3 31 c 1 1 1 1

3 32 t 2 2 2 2

3 (sin cos ) ( )

3 (sin cos ) ( )

A V qR qR qR q R

A V qR qR qR q R

p 1 2

2

p s m 2 1 p m 1

( ) ( , , )

( )( ) ( )

I q n P q R R

n A A A

The scattered intensity is

For a dilute core-shell particle suspension ( S(q)~1 ) I(q) becomes

with

Since the silica particles are slightly polydisperse, I(q) may be better evaluated by

p

c

t

( ) : Form factor

( ) :Structure factor

:Scattering vector

: Number of particles per unit volume

: Coherent scattering length density

: Volume of the core

: Volume of the core-shell particle

: Mean cor

P q

S q

q

n

V

V

e radius

:Standard deviation

*Markovic et al., , 648 (1984)Colloid Polym. Sci. 626

Theory/Data ComparisonsTheory/Data Comparisons

9

Only at PEO concentration close to ca. 2 g/lwill a homogeneous shell be formed

(b) 4.0 g/l PEO(a) 2.0 g/l PEO

(c) 6.0 g/l PEOFig 3. Comparisons of the SAXS data with theprediction of core-shell model for dilute silica/PEO suspensions with various PEO concentrations

Sample Series ηsilica PEO (g/L)

I 0.005 0.063 0.188 0.313

II 0.041 0.500 1.500 2.500

III 0.083 1.000 3.000 5.000

IV 0.165 2.000 6.000 10.000

13

Different adsorption extent

Concentrated, Non-Saturated Silica/PEO Suspensions

Hayter-Penfold/Yukawa Potential (HPY)Hayter-Penfold/Yukawa Potential (HPY)

1

( )1 24 ( )

S Qa K

0 0 00

2 exp ( )( ) ,

R U w RU w w R

w

HPY Potential:

0

0

1

: Distance from the center of a reference particle

: Mean radius of the particle

: Depth of the potential

: Decay constant of the potential

w

R

U

For the HPY potential, the analytical expression of the structure factor S(Q) was derived by

Hayter and Penfold:*

0

: Scattering vector

: Volume fraction

( ), where , is as defined in the

original paper of Hayter and Penfold

Q

a K K QR

*Hayter and Penfold, Mol. Phys. 42, 109 (1981)

We use HPY to model the steric interaction between the adsorbed polymer chains on silica colloidal particles as well as the electrostatic interaction

12

PEO [g/L]0.1 0.2 0.3 0.4

(A

ngs

trom

)

15.0

15.5

16.0

16.5

17.0

17.5

18.0

18.5

19.0

Distance from a reference particle surface (Angstrom)

0 20 40 60 80 100

Rep

uls

ion

inte

ract

ion

pot

enti

al

k BT

0

2

4

6

8

Q (Angstrom-1)0.02 0.03 0.04 0.05 0.06

S(Q

)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

The Inferred The Inferred AggregationAggregation of Suspended PEO Chains of Suspended PEO Chains

PEO concentration

For all sample series investigated, our results revealed that, as the thickness of the grafted chains (<1 nm) remains substantially smaller than that of the electrical double layer (~1.5 nm), an increasing PEO adsorption leads to an unexpected decrease in the interparticle repulsion.

14

Electrostatic Repulsion

Pot

entia

l ene

rgy

Distance apart

- +

++

+

+

+

+

++ +

+

+

+

--

-

-- -

-

-

-

-

- +

++

+

+

+

+

++ +

+

+

+

--

-

-- -

-

-

-

-

Steric Repulsion

Pot

entia

l ene

rgy

Distance apart

Screening of Electrostatic Forces due to Adsorbed PEO Chains

24 nm

1.8 nm

0.3 nm

23 nm

1.5 nm

0.5 nm