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Effect of Methanol/Water Mixtures on the Lower Critical Solution Temperature of Poly(N-isopropylacrylamide)

Published online by Cambridge University Press:  10 March 2014

Sanket A. Deshmukh ,
Ganesh Kamath ,
Derrick C. Mancini  and
Subramanian K.R.S. Sankaranarayanan
Sanket A. Deshmukh
Affiliation:
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, U.S.A
Ganesh Kamath
Affiliation:
Department of Chemistry, University of Missouri-Columbia, Columbia 65211, U.S.A
Derrick C. Mancini
Affiliation:
Physical Sciences and Engineering, Argonne National Laboratory, Argonne, IL 60439, U.S.A
Subramanian K.R.S. Sankaranarayanan
Affiliation:
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, U.S.A
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Abstract

Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-sensitive polymer that exhibits a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water and above this temperature polymer chains collapse prior to aggregation. In the presence of methanol, electron paramagnetic resonance (EPR) spectroscopy suggests that, LCST of PNIPAM is depressed up to certain mole fraction of methanol (0.35 mole fraction) and it is speculated that addition of methanol affects the PNIPAM-water interactions. Above 0.35 mole fraction of methanol, LCST gets elevated to temperatures above ∼305 K (32°C) and cannot be detected up to 373 K (100 °C). The atomistic origin of this co-solvency effect on the LCST behavior is not completely understood. In the present study, we have used molecular dynamics (MD) simulations to investigate the effect of methanol-water mixtures on conformational transitions and the LCST of PNIPAM. We employ two different force fields i.e. polymer consistent force-field (PCFF) and CHARMM to study solvation dynamics and the PNIPAM LCST phase transition in various methanol-water mixture compositions (0.018, 0.09, 0.27, 0.5, and 0.98 mole fractions). Simulations are conducted at fully atomistic level for three different temperatures (260, 278, and 310 K) and radius of gyration (Rg) of PNIPAM chains was computed for determination of LCST behavior of PNIPAM.

Keywords

polymersimulationphase transformation
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1622: Symposium E – Fundamentals of Gels and Self-Assembled Polymer Systems , 2014 , pp. 25 - 30
Copyright
Copyright © Materials Research Society 2014 

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References

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