Stable polydisperse free-standing porous films made by mechanical deformation.

Using molecular dynamics simulations, we show that the methodology of making thin stable nanoporous monodisperse films by biaxial mechanical expansion and subsequent cooling into the glassy state, also works for polydisperse films. To test this, a bidisperse polymer system of an equal number of very long (≈72 entanglements) and short (≤4 entanglements) chains with a polydispersity index of 1.80 is considered. The void formation and the development of the local morphology upon expansion, relaxation, and cooling are investigated. As for the monodisperse case, long chains in thin porous polydisperse films extend over several pores, stabilizing the whole morphology. The short chains do not fill up the pores but tend to aggregate inside the polymer matrix and to avoid surface areas and reduce conformational constraints imposed by the surrounding, a scenario very similar to strain-induced segregation between the strained long and relaxed short chains.

Entanglement-Stabilized Nanoporous Polymer Films Made by Mechanical Deformation.

We present a new simulation-guided process to create nanoporous materials, which does not require specific chemical treatment and solely relies on mechanical deformation of pure highly entangled homopolymer films. Starting from fully equilibrated freestanding thick polymer melt films, we apply a simple "biaxial expansion" deformation. Upon expansion holes form, which are prevented from growing and coalescing beyond a characteristic size due to the entanglement structure of the melt. We investigate the local morphology, the void formation upon expansion, and their stabilization. The dependence of the average void (pore) size and void fraction (porosity) on the total strain and subsequent relaxation is investigated. Furthermore, the stabilization of the porous structure of the thin expanded films through cooling below the glass transition temperature Tg is discussed.

Synthesizing Si/SiOC composites through different sol-gel reaction routes for lithium-ion battery anode materials.

Silicon oxycarbide (SiOC) exhibits good retention and a reasonable specific capacity and is an alternative to silicon used as an anode material for high-performance lithium-ion batteries. However, SiOC generally shows a low Initial Coulombic Efficiency (ICE), wasting the lithium from the cathode. This work explores different sol-gel routes to synthesize SiOC from silanes and compares their performance. We found that the crushed bulk acid-catalyzed SiOC is simple and cost-effective but with excellent performance. Adding dimethyldimethoxysilane (DMDMS) by decreasing the oxygen content further enhances the battery performance. Building upon the excellent performance of SiOC, we further embed nano-silicon into SiOC. The Si/SiOC composites achieved a significantly higher specific capacity of 2185 mAhg-1 and an impressive ICE of 77 % with acceptable battery retention.