Phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) by differential scanning calorimetric and spectrophotometric methods |
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Authors: | W S Cai L H Gan K C Tam |
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Institution: | (1) School of Science, Nanyang Technological University, Singapore, SG;(2) School of Mechanical and Production Engineering Nanyang Technological University Singapore, SG |
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Abstract: | The phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) (DEAAm–AA) is studied by differential scanning calorimetry (DSC) and UV–vis spectrophotometry. The copolymer
aqueous solutions are shown to have well-defined lower critical solution temperatures (LCSTs). The LCST values obtained from
the maximum of the first derivatives of the DSC and optical transition curves agree well. DSC can be used to measure the phase-transition
temperature of more dilute polymer solutions. On increasing the AA composition in the copolymers, the LCST values of the copolymer
increase, then decrease at higher AA composition. For the aqueous solution of the copolymers, the transition curve obtained
by the spectrophotometric method is highly wavelength dependent. The LCST values are found to be concentration-dependent.
The changes in the heat of the phase transition of the copolymer solutions measured from DSC are lower than that of the homopolymer
PDEAAm solution. This is consistent with the suggestion that the polymer chains of the copolymers collapsed only partially
at temperatures above the LCST. The added salt (sodium chloride) decreases the transition temperature of the polymer solution.
Received: 14 November 2000 Accepted: 15 January 2001 |
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Keywords: | Phase transition N N-Diethylacrylamide Acrylic acid Differential scanning calorimetry |
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