Pentaerythritol particles covered by layer-by-layer self assembled thin films with stereocomplex of isotactic poly(methyl methacrylate) and syndiotactic poly(methyl methacrylate)

In this paper, we present a different approach of coating a phase change material (PCM) for a possible use in thermal energy storage. We focused on layer-by-layer coating of pentaerythritol (PE) particles, which was achieved through stereocomplex formation of isotactic (it-)poly(methyl methacrylate) (PMMA) and syndiotactic (st-)PMMA as coating materials. As a model system, a quartz crystal microbalance (QCM) was covered by PE and subsequently coated by alternated dipping into solutions of it-PMMA and st-PMMA in hexane/acetonitrile (1/9, v/v). Frequency shifts in each step were calculated using Sauerbrey’s equation and specific peaks of PE, PMMA, and PMMA stereocomplex were detected by FT-IR. The results indicate a stepwise formation of PMMA stereocomplex onto the PE substrate covering the QCM. Furthermore, PE particles were prepared by homogenization and coated by alternating submersion in solutions of it-PMMA and st-PMMA in hexane/acetonitrile (1/9, v/v). After 20 cycles resulting in 40 PMMA layers, IR measurements of the particles showed the specific peaks for PE, PMMA, and PMMA stereocomplex. SEM pictures of uncoated PE particles and of residues of the coated particles after washing out the PE by water/methanol (water/MeOH) were compared to confirm the successful coating. With this basic demonstration of the processes feasibility for the abovementioned materials, the enhanced PCMs could be developed for the use in thermal energy storage.