Nonequilibrium Liquid Liquid Phase Separation of Poly(N-isopropylacrylamide) in Water/Methanol Mixtures

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http://hdl.handle.net/10138/308091

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Xue , N , Qiu , X-P , Aseyev , V & Winnik , F M 2017 , ' Nonequilibrium Liquid Liquid Phase Separation of Poly(N-isopropylacrylamide) in Water/Methanol Mixtures ' , Macromolecules , vol. 50 , no. 11 , pp. 4446-4453 . https://doi.org/10.1021/acs.macromol.7b00407

Title: Nonequilibrium Liquid Liquid Phase Separation of Poly(N-isopropylacrylamide) in Water/Methanol Mixtures
Author: Xue, Na; Qiu, Xing-Ping; Aseyev, Vladimir; Winnik, Francoise M.
Contributor organization: Department of Chemistry
Polymers
Date: 2017-06-13
Language: eng
Number of pages: 8
Belongs to series: Macromolecules
ISSN: 0024-9297
DOI: https://doi.org/10.1021/acs.macromol.7b00407
URI: http://hdl.handle.net/10138/308091
Abstract: At room temperature, poly(N-isopropylacrylamide) (PNIPAM) is soluble in water and in methanol. Within intermediate mixing ratios of the two solvents, the PNIPAM coils collapse into insoluble globules, a phenomenon known as co-nonsolvency. Visual observation of mixed PNIPAM/water/methanol systems (polymer concentration >= 10 g L-1, M-n 80 000 g L-1) revealed that mixtures of methanol volume fractions (phi(M)) ranging from 0.57 to 0.65 undergo macroscopic liquid-liquid phase separation (MLLPS) at 21 degrees C. MLLPS took place over a wider composition range (0.25 <phi(M) <0.60) for water/methanol mixtures containing a polymer sample bearing n butyl end-groups (PNIPAM-45K (10.0 g L-1,M-n 44 500 g mol(-1)), but systems containing a polymer with chloroethyl end-groups (PNIPAM-CI) (10.0 g L-1,M-n 44 500 g mol(-1)) did not undergo MLLPS over the entire mixing ratio span. Observation by fluorescence microscopy of a demixed PNIPAM-45K/water/methanol sample containing trace amounts of pyrene-labeled PNIPAM revealed that the rim of the heavy phase droplets is enriched in PNIPAM, which may affect the stability/coalescence of the droplets. '1-1NMR spectroscopy analysis of the heavy and light phases formed indemixed PNIPAM-45K/water/methanol samples indicated that the heavy liquid phase is enriched in PNIPAM and in water compared to the nominal composition of mixtures as prepared. A temperature/composition map (-40 degrees C <T <+45.5 degrees C) of PNIPAM-45K/water/methanol is reported, based on visual observations of samples prepared and stabilized at 21 C. Interestingly, the macroscopically demixed samples were, never transparent: one or both liquid phases remained cloudy or opaque independently of their history over experimentally undefined long times, implying that the samples reached metastability. The equilibrium state of lowest free energy that corresponds to the coexistence of two transparent phases was never attained.
Subject: MISCIBLE GOOD SOLVENTS
PREFERENTIAL ADSORPTION
AQUEOUS-SOLUTIONS
POLYMER COLLAPSE
CO-NONSOLVENCY
MIXED-SOLVENTS
GEL PARTICLES
WATER
METHANOL
CONONSOLVENCY
116 Chemical sciences
Peer reviewed: Yes
Rights: cc_by_nc
Usage restriction: openAccess
Self-archived version: acceptedVersion


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