研究目的
To investigate the structure and properties of polyimide/silica hybrid materials using molecular dynamics simulation, focusing on the effects of SiO2 doping content on mechanical and thermodynamic properties.
研究成果
The study demonstrates that embedding SiO2 in PI through chemical bonding improves mechanical properties (e.g., Young's modulus, shear modulus, tensile strength up to 568.15 MPa at 9% doping) and increases density and cohesive energy density. The trends in Tg and tensile strength align with experimental results, validating molecular dynamics simulation as an effective tool for material design and performance prediction of hybrid composites.
研究不足
The simulation may not fully capture all real-world complexities, such as accurate energy calculations for chemical bonding in the model structure, potential deviations in Tg predictions due to molecular chain flexibility and hydrogen bonding effects, and the assumption of isotropic properties which might not hold for all composite structures.
1：Experimental Design and Method Selection:
A PI/SiO2 copolymer model was established by chemically bonding tetraethyl orthosilicate (TEOS) molecules to a silane coupling agent (ICTOS) and dehydrating them to form SiO2 embedded in the polyimide (PI) matrix. The mass fraction of SiO2 was controlled by adjusting the number of TEOS molecules. Molecular dynamics simulations were performed using the Forcite module in Material Studio software with the COMPASS force field for optimization and property calculations.
2：Sample Selection and Data Sources:
Models were created for pure PI and PI/SiO2 hybrids with SiO2 mass fractions of 5%, 7%, 9%, 11%, and 13%, based on chemical reactions involving PMDA, ODA, ICTOS, and TEOS.
3：List of Experimental Equipment and Materials:
Software: Material Studio (Forcite module). Materials: Tetraethyl orthosilicate (TEOS), silane coupling agent (isocyanate propyl triethoxysilane, ICTOS), pyromellitic dianhydride (PMDA), diaminodiphenyl ether (ODA).
4：Experimental Procedures and Operational Workflow:
- Establish structural units of PI (PMDA-ODA) and bond ICTOS to end groups. - Dehydrate TEOS and bond to ICTOS to form PI/SiO2 copolymer. - Adjust TEOS molecule number to control SiO2 content. - Perform geometric optimization and molecular dynamics optimization in canonical (NVT) and isothermal-isobaric (NPT) ensembles at 298 K and 1 atm, with 500 ps simulation steps, using Andersen and Berendsen methods for temperature and pressure control. - Calculate properties such as density, cohesive energy density, hydrogen bonds, Young's modulus, shear modulus, tensile strength, and glass-transition temperature.
5：Data Analysis Methods:
Used Forcite module for mechanical properties calculation (stiffness matrix, Lame's constants), cohesive energy density, solubility parameters, and Tg estimation from specific volume and mean-squared displacement curves.
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