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Agglomeration Dynamics In Thermo-Sensitive Polymers Across The Lower Critical Solution Temperature: A Molecular Dynamics Simulation Study

Published online by Cambridge University Press:  03 February 2012

Sanket A. Deshmukh ,
Subramanian K.R.S. Sankaranarayanan  and
Derrick C. Mancini
Sanket A. Deshmukh
Affiliation:
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439
Subramanian K.R.S. Sankaranarayanan
Affiliation:
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439
Derrick C. Mancini
Affiliation:
Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
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Abstract

Poly(N-isopropylacrylamide) (PNIPAM), a classic thermo-sensitive polymer, has a lower critical solution temperature (LCST) at ∼32°C. In this work we have used molecular dynamics simulations to understand the origin of the LCST and agglomeration of PNIPAM chains of 5 and 30 monomer units (5-mer and 30-mer). Experimentally, when the concentration of PNIPAM is >1 ppm, polymer chains after undergoing coil-to-globule transition above the LCST aggregates to yield a stable colloidal dispersion.In our study two PNIPAM chains, consisting of 30 monomer units each, were placed in a cubic simulation cell and were subsequently solvated. Simulations were carried out below and above the LCST, namely at 278 and 310K for 10ns. Simulated trajectories were analyzed for structural and dynamical properties of both PNIPAM and water. We observe coil-to-globule transition in PNIPAM above the LCST. We also find that the PNIPAM chains agglomerate above the LCST. We also observe entanglement in PNIPAM chains below the LCST. We also study agglomeration of 5 PNIPAM chains each consisting of 5 monomer units. There was no significant difference in polymer agglomeration behavior across the LCST for these short chain oligomers. The agglomeration behavior is thus strongly correlated to the size of the polymer chains. These results provide fundamental insight into the atomistic scale mechanism of PNIPAM agglomeration across the LCST.

Keywords

polymerbiomedicalsimulation
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1418: Symposium LL/MM – Gels and Biomedical Materials , 2012 , mrsf11-1418-ll07-06
Copyright
Copyright © Materials Research Society 2012

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References

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