Molecular Dynamics Investigation of the Thermo-Responsive Polymer Poly(N-isopropylacrylamide)

Using molecular dynamics simulations with an OPLS force field, the lower critical solution temperature (LCST) of single- and multiple-chain PNIPAM solutions in water is investigated. The sample containing ten polymer chains shows a sudden drop in size and volume at 305?K. Such an effect is absent in the single-chain system. Large fluctuations of the physical properties of a short single-chain prevent any clear detection of the LCST for the chosen model system, at least on the time scale of 200?ns. The results provide evidence that a critical number of PNIPAM monomer units must be present in the simulated system before MD simulations are capable to detect conformational changes unambiguously.