(216ar) Phase Transition in HPMC Hydrogel
The rearrangement of the polymer molecules within the film matrix during film drying, which defines its internal and surface structure, has an important role in the control release, optical and mechanical properties of the therapeutical oral films. Via a coarse-grained Molecular Dynamics-based simulation technique called Dissipative Particle Dynamics we investigate changes in the molecular conformational dynamics and morphology of polymer chains in films during the drying process. Dissipative Particle Dynamics is a multiscale mesoscopic simulation method that simultaneously captures the molecular details of the components through soft-sphere coarse-grained models and reproduces the hydrodynamic behavior of the system over extended time scales. We have developed a bead-spring model of individual polymer molecules where each bead or soft sphere is a coarse-grained representation of a group of atoms with two consecutively bonded beads along a polymer chain linked by a spring. The solvent is modeled by soft spheres which are coarse-grained representation of multiple solvent molecules. To capture the drying process, we simulate the polymer chain dynamics for different concentrations of the polymer, for a constant number of solvent and polymer soft spheres in the system. We characterize the polymer chain dynamics and conformation at the various stages of the drying process, or solvent concentration, via the correlation between measurements of the radius of gyration and end-to-end distance with the inter- and intra-polymer chain interactions. Obtained computational data are in good agreement with experimentally observed conformation changes in the polymeric matrix determined by means of Raman spectroscopy and diffusing wave spectroscopy. It is also confirmed that DPD methodology can provide a good prediction for the critical points of drying process.