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...
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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 Structure and Particle Interaction of Hybrid Silica/Poly(ethylene oxide) Suspensions Characterized by Small Angle X-ray Scattering and Dynamic Light Scattering. 李淳毅、陳致中、溫玉合、 華繼中 * 、李岱洲 *. 化 學 工 程 學 系 - PowerPoint PPT PresentationTRANSCRIPT
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
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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