Temperature Dependence of a Thermosensitive Nanogel: A Dissipative Particle Dynamics Simulation of PNIPAM in Water

Thermosensitive nanogels undergo a volume phase transition in response to temperature changes, making them promising candidates for applications, such as water pollutant remediation and drug delivery. In this study, we investigated the thermosensitive volume phase transition of a neutral poly(N-isopropylacrylamide) (PNIPAM) nanogel using coarse-grained dissipative particle dynamics (DPD) simulations conducted using ESPResSo software with varying bead volumes. Langevin dynamics simulations were employed to compare the results. In DPD simulations, water is explicitly treated, whereas in Langevin dynamics, it is treated implicitly, and hydrophobic interactions are represented by an attractive potential between monomer beads. Our results, including the radius of gyration and various radial distribution functions, revealed a clear volume phase transition as the temperature varied, transitioning from an expanded state to a collapsed state. Notably, the volume phase transition observed in Langevin simulations is attributed to the attractive potential between the PNIPAM monomers, whereas in the DPD simulations, it arises from implicit hydrophobic interactions, obviating the need for an additional attractive potential between the monomer beads. This implicit hydrophobic effect originates from the temperature dependence of the Flory-Huggins interaction parameter.