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Lower Critical Solution Temperature Phase Behavior of Poly(n‑butyl methacrylate) in Ionic Liquid Mixtures
journal contribution
posted on 2013-12-10, 00:00 authored by Megan L. Hoarfrost, Yanpu He, Timothy P. LodgeIonic liquids feature a combination
of properties that make them very interesting solvents for polymers,
but many questions remain regarding the thermodynamics of polymer/ionic
liquid solutions. In this work, the lower-critical-solution-temperature
(LCST) phase behavior of poly(n-butyl methacrylate)
(PnBMA) in mixtures of the ionic liquids 1-butyl-3-methylimidazolium:bis(trifluoromethylsulfonyl)imide
([BMIm][TFSI]) and 1-ethyl-3-methylimidazolium:TFSI ([EMIm][TFSI])
is characterized by transmittance, light scattering, and small-angle
neutron scattering measurements. Several relevant thermodynamic parameters
are easily tuned by varying the ionic liquid composition. In particular,
the cloud point, spinodal, and Θ temperatures are all found
to increase linearly with [BMIm] content. The interaction parameters, χ,
are determined as a function of temperature and concentration using
three different methods, and the results from each method are compared.
The entropic and enthalpic components of the interaction parameter,
χ, are also found to vary linearly with [BMIm] content in the
ionic liquid, increasing and decreasing, respectively. The increase
in the enthalpic driving force for mixing with increasing [BMIm] content
dominates over the decrease in the entropic penalty for mixing, leading
to improved solubility. This result is discussed in terms of molecular
interactions and oriented solvation. This work characterizes the solution
thermodynamics of one representative system in a very interesting
class of polymer solutions, and provides insight into the molecular
mechanisms underlying its LCST phase behavior.
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polymer solutionsinteraction parametersphase behaviorinteraction parameterΘ temperaturesmethacrylaterepresentative systemIonic Liquid MixturesIonic liquids featurecontentmethodcloud pointenthalpic componentssolution thermodynamicsentropic penaltyBMImLCST phase behaviorCritical Solution Temperature Phase Behavior
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