Abstract
Polydimethylsiloxane (PDMS) is one of the most widely used polymeric materials for sealants, adhesives, lubricants, and thermal as well as electrical insulation. At low temperatures, however, PDMS is subject to crystallization that can cause deterioration in mechanical function. A common way to suppress such crystallization is through the incorporation of phenylsiloxane into the backbone of polysiloxane. Nevertheless, the introduction of phenyl components, even in small quantities, could potentially change the properties of the siloxane in a significant way. In this work, a series of mechanical tests and finite element simulations were performed to study the macroscale viscoelasticity of two poly(dimethyl-co-diphenyl)siloxane formulations in order to understand the effects of a few percent diphenyl contents on the viscoelasticity of the polysiloxane material. We utilized the small-angle X-ray scattering to investigate the microscopic structures of the copolymers and broadband dielectric spectroscopy and rheology to probe the chain dynamics at the microscale. The results of these characterizations were used to inform the finite element simulations. We found that the degree of cross-linking does not significantly alter the microstructure but can profoundly affect the viscoelastic response of the copolymer networks. The corresponding hysteretic behavior is interpreted in terms of reptation-like motion and relaxation of the effective free chains in the cured polymer network. The relaxation of the copolymer chains is slowed significantly by even a small increase in the molar ratio of the diphenyl component.
Original language | English |
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Pages (from-to) | 1915-1925 |
Number of pages | 11 |
Journal | ACS Applied Polymer Materials |
Volume | 5 |
Issue number | 3 |
DOIs | |
State | Published - Mar 10 2023 |
Externally published | Yes |
Funding
The work at LLNL was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Y.L. also thanks the support from the National Science Foundation (CMMI-1762661, CMMI-1934829, CAREER-2046751). The authors thank Dr. David Pierce and Dr. Nicholas Eddy from the University of Connecticut for the help with the mechanical tests and Anton Paar USA for providing the instrument support. We also thank Dr. Lin Yang, the lead scientist for the Life Science X-ray Scattering (LiX) beamline, from Brookhaven National Laboratory for the help with the SAXS experiments. The LiX beamline is part of the Center for BioMolecular Structure (CBMS), which is primarily supported by the National Institutes of Health, National Institute of General Medical Sciences (NIGMS), through a P30 Grant (P30GM133893) and by the DOE Office of Biological and Environmental Research (KP1605010). LiX also received additional support from NIH Grant S10 OD012331. As part of NSLS-II, a national user facility at Brookhaven National Laboratory, work performed at the CBMS is supported in part by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences Program under Contract DE-SC0012704.
Keywords
- dielectric spectroscopy
- diphenylsiloxane
- mechanical test
- polydimethylsiloxane
- rheology
- viscoelasticity