(376au) An Accurate Coarse-Grained Model of Poly(acrylic acid) with Explicit Solvent Models of DMF and Water

Understanding the role of solvents in altering the conformations of biomaterials, polymers, and other soft matters is of fundamental interest in materials science and engineering. Here, we have developed a coarse-grained (CG) model of poly(acrylic acid) (PAA) to study its configuration in the presence of explicit solvent models of water, dimethylformamide (DMF), and their binary mixtures. The CG PAA model was developed based on the propionic acid model, and then validated by comparing its density and glass transition temperature with corresponding experimental data. The CG PAA 30-mer (30-monomer) in pure water and pure DMF exhibited a globule-like and a coil-like state, respectively. This is consistent with results from AA molecular dynamics (MD) simulations. The averaged radius of gyration (Rg) of globule-like and coil-like CG PAA 30-mer chains was ~9 Å and ~13.8 Å, respectively. In binary solvent mixtures, the averaged Rg values increased gradually from ~9 to ~13 Å with the mass fraction of DMF increasing from 2.6 wt% to 80.2 wt%. Moreover, the radial distribution function of solvents around the polymer chain suggests that there is an enhanced ordering of DMF molecules at the polymer-solvent interface even at a low mass fraction of DMF. The coordination number of DMF molecules within the first solvation shell of PAA increases with increasing the DMF mass fraction. This indicates that DMF molecules form a shielding layer and protect PAA from water molecules.