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

## TL;DR

This paper uses simulations to study how a thermosensitive nanogel changes size with temperature, revealing different mechanisms in two simulation methods.

## Contribution

The study demonstrates that DPD simulations capture hydrophobic effects implicitly, unlike Langevin simulations requiring explicit attractive potentials.

## Key findings

- DPD simulations show a volume phase transition due to implicit hydrophobic interactions.
- Langevin simulations require an attractive potential to observe the phase transition.
- The transition is linked to the temperature-dependent Flory–Huggins interaction parameter.

## Abstract

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.