writer：Boualem Hammouda;* Di Jia; He Cheng
keywords：water soluble polymer, configuration, water
source：期刊
specific source：the Open Access Journal of Science and Technology
Issue time：2015年

The demixing phase behavior of Poly(N-isopropylacrylamide) (PNIPAM) aqueous solution is investigated using smallangle

neutron scattering. This polymer phase separates upon heating and demixes around 32 °C. The pre-transition temperature

range is characterized by two scattering modes; a low-Q (large-scale) signal and a high-Q dissolved chains signal. In order to get

insight into this pre-transition region, especially the origin of the low-Q (large-scale) structure, the zero average contrast method

is used in order to isolate single-chain conformations even in the demixing polymers transition region. This method consists of

measuring deuterated and non-deuterated polymers dissolved in mixtures of deuterated and non-deuterated water for which the

polymer scattering length density matches the solvent scattering length density. A fixed 4% polymer mass fraction is used in a

contrast variation series where the d-water/h-water fraction is varied in order to determine the match point. The zero average

contrast (match point) sample displays pure single-chain scattering with no interchain contributions. Our measurements prove that

the large scale structure in this polymer solution is due to a transient polymer network formed through hydrophobic segmentsegment

interactions. Scattering intensity increases when the temperature gets close to the phase boundary. While the apparent

radius of gyration increases substantially at the Lower Critical Solution Temperature (LCST) transition due to strong interchain

correlation, the single-chain true radius of gyration has been found to decrease slightly with temperature when approaching the

transition.