Hydrophobic Collapse Initiates the Poly( N-isopropylacrylamide) Volume Phase Transition Reaction Coordinate

The Journal of Physical Chemistry. B
Tsung-Yu WuSanford A Asher

Abstract

The best-known examples of smart, responsive hydrogels derive from poly( N-isopropylacrylamide) (PNIPAM) cross-linked polymer networks. These hydrogels undergo volume phase transitions (VPTs) triggered by temperature, chemical, and/or environmental changes. PNIPAM hydrogels can undergo more than 50-fold volume changes within ∼1 μs intervals. Studies have tried to elucidate the molecular mechanism of these extraordinarily large responses. Nevertheless, the molecular reaction coordinates that drive the VPT remain unclear. Using visible nonresonance Raman temperature-jump spectroscopy, we determined the molecular ordering of this VPT. The PNIPAM hydrophobic isopropyl and methylene groups dehydrate with time constants of 109 ± 64 and 104 ± 44 ns, initiating the volume collapse of PNIPAM. The subsequent dehydration of the PNIPAM amide groups is significantly slower, as our group previously discovered (360 ± 85 ns). This determination of the ordering of the molecular reaction coordinate of the PNIPAM VPT enables the development of the next generation of super-responsive materials.

References

Dec 26, 2001·Chemical Reviews·Pavel Hobza, Zdenek Havlas
Feb 5, 2004·Journal of the American Chemical Society·Chad E ReeseSanford A Asher
Jul 23, 2004·The Journal of Chemical Physics·Katsunori TakahashiToshiro Masuda
Nov 28, 2006·Advanced Drug Delivery Reviews·Dirk Schmaljohann
Mar 6, 2009·The Journal of Physical Chemistry. B·Zeeshan AhmedSanford A Asher
Apr 2, 2009·Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology·Jan Kubelka
Jul 30, 2010·The Journal of Physical Chemistry. B·Shengtong SunPeiyi Wu

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Citations

May 18, 2019·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Iwona StanislawskaEwelina Zabost
Sep 26, 2019·Small·Hang ZhangMartin Möller
Apr 24, 2021·ACS Applied Materials & Interfaces·Jonguk YangSanghyun Ju
Sep 18, 2021·Langmuir : the ACS Journal of Surfaces and Colloids·Anastasia FrolovaSvetlana Kotova

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