All-Atom Molecular Dynamics Simulations of Poly(N-isopropylacrylamide) Grafted Architectures

All-atom Molecular Dynamics Simulations of Poly(N-isopropylacrylamide) Grafted Architectures

Ganesh Kamath³, Sanket A. Deshmukh¹, Derrick C. Mancini², Subramanian K.R.S. Sankaranarayanan¹

¹Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439

²Physical Sciences and Engineering, Argonne National Laboratory, Argonne, IL 60439

³Department of Chemistry, University of Missouri-Columbia, Columbia 65211

Poly(N-isopropylacrylamide) (PNIPAM) is a thermosensitive polymer that is well-known for its lower critical solution temperature (LCST) around 305K. Below the LCST, PNIPAM is soluble in water, and above this temperature, polymer chains collapse and transform into a globule-state. In this study, we have carried out MD simulations of PNIPAM polymer chains consiting of 60 monomer units grafted on a gold nanoparticle and a planar surface to study the effect of curvature and temperature on the polymer conformations. We have also studied effect of grafting density and size of nanoparticle on the coil-to-globule collapse shown by PNIPAM above the LCST. Studied system consisted of 100 K to ~3 million atoms. All the simulations were carried out below and above the LCST of PNIPAM, namely, at 275 and 325 K. Simulation trajectories were analyzed for structural and dynamical properties such as radius of gyration of PNIPAM chains, hydrogen bond life-times, and residence time probability of water molecules.

Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.

The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.