Folding of a single polymer chain and phase transition |
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Authors: | YanWei Ding GuangZhao Zhang |
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Institution: | (1) Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, 230026, China |
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Abstract: | Using an ultra-sensitive differential scanning calorimetry (US-DSC), we have investigated the folding and aggregation behaviors
of poly(N-isopropylacrylamide) (PNIPAM) chains in dilute and semidilute solutions. In the heating process, the intrachain
folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases
with decreasing concentration. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated
temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an extremely dilute solution,
PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration
to zero, we have obtained the phase transition temperature (T
S
) and enthalpy change (ΔH
S
) of the single chain folding. ΔH
S
is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single
chain folding can not be taken to be a macroscopic phase transition.
Supported by the National Natural Science Funds for Distinguished Young Scholar (Grant No. 20474060) and Major State Basic
Research Development Program of China (Grant No. 2007CB936401) |
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Keywords: | Ultra-sensitive differential scanning calorimetry interchain aggregation single chain folding |
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