Molecular Dynamics and Structure of Poly(Methyl Methacrylate) Chains Grafted from Barium Titanate Nanoparticles

Core−shell nanocomposites comprising barium titanate, BaTiO₃ (BTO), and poly(methyl methacrylate) (PMMA) chains grafted from its surface with varied grafting densities were prepared. BTO nanocrystals are high-k inorganic materials, and the obtained nanocomposites exhibit enhanced dielectric permittivity, as compared to neat PMMA, and a relatively low level of loss tangent in a wide range of frequencies. The impact of the molecular dynamics, structure, and interactions of the BTO surface on the polymer chains was investigated. The nanocomposites were characterized by broadband dielectric and vibrational spectroscopies (IR and Raman), transmission electron microscopy, differential scanning calorimetry, and nuclear magnetic resonance. The presence of ceramic nanoparticles in core–shell composites slowed down the segmental dynamic of PMMA chains, increased glass transition temperature, and concurrently increased the thermal stability of the organic part. It was also evidenced that, in addition to segmental dynamics, local β relaxation was affected. The grafting density influenced the self-organization and interactions within the PMMA phase, affecting the organization on a smaller size scale of polymeric chains. This was explained by the interaction of the exposed surface of nanoparticles with polymer chains.     

On the primary thermal decomposition pathways of hydroxycinnamic acids

Valorization of pyrolytic lignin to fuels and chemicals is still poorly understood due to its ill-defined structure and the complexity of the decomposition chemistry. To shed some light on the dominant reaction pathways of lignin thermolysis, novel experimental and first-principles based calculations of its building blocks have been carried out. Pyrolysis chemistry of hydroxycinnamic acids is investigated in this work using a unique Py-GC × GC-FID/TOF-MS coupled with a customized GC to detect water and gases, to gain an understanding of the role of the branching ratios in lignin and its linkages with hemicellulose. Mean residence times of cinnamic and ferulic acids were estimated to be 12 and 21 s at 573 K, based on time-resolved experiments. Cinnamic acid undergoes a CO₂ elimination reaction at temperatures higher than 873 K without an intermediate liquid phase. At temperatures as low as 573 K, –OH and –OCH₃ substituted cinnamic acids underwent decarboxylation despite bearing similar BDEs for Cβ–Cγ scission. At these temperatures, p-coumaric and ferulic acids were converted into 4-vinylphenol and 4-vinylguaiacol by 40 wt% and 30 wt%, respectively. On the other hand, sinapinic acid converted nearly by 80 wt% at temperatures below its boiling point of 676 K. In conjunction with novel quantum chemical calculations, it could be ruled out that decarboxylation was not occurring via concerted unimolecular reactions at low temperatures. Instead, water-catalyzed reactions of hydroxycinnamic acids seem to be the primary cause for the CO₂ elimination in the intermediate liquid phase via a 6-centered transition state.     

Synthesis and characterization of PVA-based binary-gel electrolytes including massive ions

Journal of Solid State Electrochemistry - The motion of the ion pairs under the applied electric field is an important phenomenon in the storage properties of the capacitive devices. In this study,...