Morphological and transport characteristics of swollen chitosan‐based proton exchange membranes studied by molecular modeling

Abstract

Chitosan biopolymer has been extensively applied in direct methanol fuel cells (DMFCs) as a potential replacement to conventional Nafion membrane for its considerably reduced methanol crossover. Here, we computationally explored the influences of methanol concentration, temperature, and pH parameters upon the nanostructure and dynamics, particularly the methanol crossover, in chitosan proton-exchange membrane (PEM) through molecular dynamics simulations. Theoretical results demonstrated the increased swelling and radius of gyration of chitosan chains at higher concentrations. Structural examinations further revealed that an increase in methanol loading weakened the water interactions with chitosan functionalities (amineNH , hydroxylOH, and methoxyCH OH) whereas improved the methanol affinities toward chitosan, reflecting higher methanol sorption capability of chitosan at enhanced concentrations. Additionally, it was found that interactions between solvents and chitosan strengthened under acidic pH conditions on account of amine protonation. The water diffusivity inside the swollen chitosan diminished by increasing CH OH uptake, and in contrast diffusivity of methanol was noted to enhance. Furthermore, it was observed that an enhancement in temperature or a decrease in pH intensified solvent mobility. These insights imply that supplying methanol-concentrated and/or acidic feed solutions into DMFCs based on chitosan PEMs could lower membrane performance due to the significant methanol transport dynamics.

Polyserotonin Nanoparticles as Multifunctional Materials for Biomedical Applications

“…As shown in Figure c, the RDFs for DOX oxygen atoms with respect to serotonin monomer, dimer, and tetramer oxygen atoms showed heightened first peaks, particularly for serotonin and dimer-1 at 2.62–2.97 Å. These peak positions are within the distances required for hydrogen-bonding interactions between oxygenated sites in DOX and serotonin species.…”

“…Both the potential energy and temperature of all simulated cells stabilized with negligible fluctuations, indicating that equilibria had been reached. 82–84 The final structures of DOX on the surfaces of serotonin and its dimers and tetramers are shown in Figure 6b, which were obtained from the last step of the MD simulations. When these snapshots were compared with the corresponding initial cells (Figure S8), we found that DOX distances relative to all serotonin substrates were significantly reduced, which suggests the tendency of DOX molecules to adsorb on all investigated surfaces.…”

“…Radial distribution functions (RDFs, also called paired correlation functions, g(r)) were analyzed 84 to elucidate DOX interactions with polyserotonin nanoparticle surfaces further. The RDF analysis was carried out for the oxygen atoms in DOX with regard to oxygen and nitrogen heteroatoms in serotonin monomers, dimers, and tetramers (Figure 6c,d).…”

Rheological Study and Molecular Dynamics Simulation of Biopolymer Blend Thermogels of Tunable Strength

“…The visual examinations simply exhibit that Chs polymers are more stretched in pure system compared to those blended with HEC. This structural change was quantified through radius of gyration ( R g ) prediction, as used in an earlier study Figure b displays the time evolution of R g for Chs and HEC chains.…”

“…The intermolecular interactions between Chs and HEC chains likely occur among their functional moieties. For this purpose, to gain a deeper understanding of the underlying interactions of the bindings between Chs and HEC, radial distribution function (RDF, also called g ( r )) analyses were done for various Chs and HEC functional groups responsible for their interactions . RDFs were calculated for amine −NH 2 , backbone hydroxyl (−OH1), and hydroxyl in hydroxymethyl group (−OH2) in Chs and backbone hydroxyl (−OH1) and side chain hydroxyl (−OH2) in HEC chains.…”