Molecular Dynamics Simulations of Alkane-Functionalized Polyhedral Oligomeric Silsesquioxanes (POSS). Oligomeric Silsesquioxanes (POSS).

POSS;Simulation;Nano-composite;Materials Science and Engineering;Engineering;Materials Science and Engineering

Zhou, JinhuaVan Der Ven, Anton ;

University of Michigan

关键词: POSS;    Simulation;    Nano-composite;    Materials Science and Engineering;    Engineering;    Materials Science and Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/62346/zhouj_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Polyhedral oligomeric silsesquioxanes (POSS) is an inorganic cubic-shaped molecule withchemical formula R8Si8O12, where R can be hydrogen atoms or complex organic molecules.Due to the nano-size and because it can be functionalized with disparate materials, POSS constitutes the elementary building block of novel nano-composites.This thesis provides a comprehensive analysis of alkane-functionalized POSS hybrids using computer simulation.A force field was developed for the accurate description of mixed covalent-ionic interactions in the POSS hybrids.Parameters of the force filed were optimized to reproduce the structure and infrared spectrum of mono-functionalized C6-POSS crystal at 291 K. The crystal melts at 430 K, undergoing a distinctive two-step melting process.First, hydrocarbons depart from their lattice sites and entangle with neighboring hydrocarbons.Then POSS cages rotate, shift and eventually evolve into an amorphous configuration. Comparing POSS structures mono-functionalized with 5-, 9-, or 20-membered alkane chains shows that the spacing between nearest POSS cubes is independent of the length of the hydrocarbon chain.A similar phenomenon is observed in pendent and di-functionalized POSS systems of of varying chain length.POSS nano-composites were also explored for their potential application as battery electrolytes. For this purpose POSS was functionalized with two different Li+ cation-donating groups, either a siloxy group at the corner of the cube or a carboxyl group at the end of the alkane chain.In the carboxyl-based systems, Li and O form a continuous band structure in which lithium can migrate via a hopping mechanism and are thus capable of long-range transport.Conversely, in the siloxy-based systems Li gets trapped inside the cavities formed by clustered POSS cubes, and is not free to diffuse.In all cases does the association of ionic species act as an anchor for the molecular building blocks.Species on the opposite end, i.e., hydrocarbons in the siloxy-based systems and POSS in the carboxyl-based systems, appear to have higher mobility.These species do not migrate in a diffusive regime because they are anchored.