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 Department of Chemical Engineering, National Chung Cheng University 1

Multiscale Measurements Phase behavior in thin films of confined colloid-polymer mixtures # Instability; Complex flows # SYSTEM STUDIED: SolventEntanglementUnder strong flow (2 types)Role of entanglements # Theory/data comparisons (terminal relaxation behavior is captured;show the 3-D Rouse model prediction; 1-D); Wen and Hua (2006) # Supported by lattice model; Impacts of CCR & tube pressure (natural) Ren, C.-L. and Y.-Q. Ma, J. Am.. Chem. Soc. 128, 2733 (2006) 2

Thin Film Formation Film Formation Evaporate Solution State 3 # Instability; Complex flows # SYSTEM STUDIED: SolventEntanglementUnder strong flow (2 types)Role of entanglements # Theory/data comparisons (terminal relaxation behavior is captured;show the 3-D Rouse model prediction; 1-D); Wen and Hua (2006) # Supported by lattice model; Impacts of CCR & tube pressure (natural) 3

Adsorption Mechanism of PEO Chains onto a Silica Particle As the silica particle surface is covered by PEO, a core-shell structure is formed Poly(ethylene oxide); PEO C-C-O C-C-O ‧ n ‧ n ‧ ‧ PEO Hydrogen bond ‧ ‧ OH OH OH OH OH OH Shell Silica Core Core Silica particle surface # Instability; Complex flows # SYSTEM STUDIED: SolventEntanglementUnder strong flow (2 types)Role of entanglements # Theory/data comparisons (terminal relaxation behavior is captured;show the 3-D Rouse model prediction; 1-D); Wen and Hua (2006) # Supported by lattice model; Impacts of CCR & tube pressure (natural) Fig 1. Hydrogen bonding between the silica surface and PEO For a hybrid suspension system consisting of fine colloidal particles (~15 nm), usual centrifugal separation for determining the adsorption isotherm becomes, however, unreliable* *Flood et al., Langmuir 22, 6923 (2006) 5

DLS analyses based on cumulants and double-exponential distribution for dilute silica/PEO suspensions (silica volume fraction φsilica=0.005 for all cases) saturation adsorption Core radius Core Core-shell PEO concentration All values compiled above are determined from simplex optimization method 6

Saturation Adsorption Concentration Determined by DLS 2 g/L PEO 4 g/L PEO Fig 2. DLS results for dilute silica/PEO suspensions with various PEO concentrations 6 g/L PEO The observed time-dependent behavior & and the detailed DLS analyses suggest that the maximum absorption of PEO should be somewhere between 2.0 g/L and 4.0 g/L. 7

Core-Shell Model* R2 ρp ρs ρm R1 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 8

Theory/Data Comparisons (a) 2.0 g/l PEO (b) 4.0 g/l PEO Fig 3. Comparisons of the SAXS data with the prediction of core-shell model for dilute silica/ PEO suspensions with various PEO concentrations (c) 6.0 g/l PEO Only at PEO concentration close to ca. 2 g/l will a homogeneous shell be formed 9

Concentrated, Non-Saturated Silica/PEO Suspensions 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 Different adsorption extent 13 Fig 2. Fitted double layer thickness δ for sample series I.

Hayter-Penfold/Yukawa Potential (HPY) HPY Potential: We use HPY to model the steric interaction between the adsorbed polymer chains on silica colloidal particles as well as the electrostatic interaction For the HPY potential, the analytical expression of the structure factor S(Q) was derived by Hayter and Penfold:* *Hayter and Penfold, Mol. Phys. 42, 109 (1981) 12

The Inferred Aggregation 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 Fig 2. Fitted double layer thickness δ for sample series I.

Electrostatic Repulsion + + + - - Potential energy + - + - - + + - - + + - - - + - + + + + Distance apart + - + - + - + - - + + - - + + - - - + - + + +

Steric Repulsion Potential energy Distance apart

Screening of Electrostatic Forces due to Adsorbed PEO Chains 24 nm 0.3 nm 0.5 nm 23 nm 1.8 nm 1.5 nm