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Molecular Dynamics Studies on the Effects of Water Speciation on Interfacial Structure and Dynamics in Silica-Filled PDMS Composites

Conference ·
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Significant changes in materials properties of siloxane based polymers can be obtained by the addition of inorganic fillers. In silica-filled polydimethylsiloxane (PDMS) based composites the mechanism of this reinforcing behavior is presumably hydrogen bonding between surface hydroxyls and backbone siloxane species. We have chosen to investigate in detail the effect of chemisorbed and physisorbed water on the interfacial structure and dynamics in silica-filled PDMS based composites. Toward this end, we have combined molecular dynamics simulations and experimental studies employing DMA and Nh4R analysis. Our results suggest that the polymer-silica contact distance and the mobility of interfacial polymer chains significantly decreased as the hydration level at the interface was reduced. The reduced mobility of the PDMS chains in the interfacial domain reduced the overall, bulk, motional properties of the polymer, thus causing an effective ''stiffening'' of the polymer matrix. The role of the long-ranged Coulombic interactions on the structural features and chain dynamics of the polymer were also examined. Both are found to be strongly influenced by the electrostatic interactions as identified by the bond orientation time correlation function and local density distribution functions. These results have important implications for the design of nanocomposite silica-siloxane materials.

Research Organization:
Lawrence Livermore National Lab., CA (US)
Sponsoring Organization:
US Department of Energy (US)
DOE Contract Number:
W-7405-ENG-48
OSTI ID:
15004791
Report Number(s):
UCRL-JC-144790
Country of Publication:
United States
Language:
English

References (8)

Derivation of class II force fields. I. Methodology and quantum force field for the alkyl functional group and alkane molecules journal February 1994
Interactions of Elastomers and Reinforcing Fillers journal November 1965
Molecular dynamics simulations at constant pressure and/or temperature journal February 1980
Ammonia-Induced Tensile Set and Swelling in Silica-Filled Silicone Rubber journal May 1990
Structure of Chlorotrifluoroethylene/Vinylidene Fluoride Random Copolymers and Homopolymers by Molecular Dynamics Simulations journal March 2001
Derivation of force fields for molecular mechanics and dynamics from ab initio energy surfaces journal August 1988
Silica-filled polydimethylsiloxane: crystallization process of the adsorbed layer journal April 1990
Characterization of radiation-induced aging in silica-reinforced polysiloxane composites journal November 2000

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Related Subjects

08 HYDROGEN
36 MATERIALS SCIENCE
BONDING
CORRELATION FUNCTIONS
DESIGN
DISTRIBUTION FUNCTIONS
ELECTROSTATICS
FILLERS
HYDRATION
HYDROGEN
ORIENTATION
POLYMERS
SILOXANES
WATER