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Blockcopolymers are attractive building blocks for designing micelleshaving complex shapes and functionality, but experimental investigationsinto the detailed thermodynamics of block copolymer micellizationhave been constrained. In this work, we take advantage of the favorablesolvent properties of ionic liquids to study the thermodynamics ofblock copolymer micelle formation. Specifically, we investigate theeffects of solvent quality and degree of polymerization on the criticalmicelle temperature (cmt) of poly(ethylene oxide-b-n-butyl methacrylate) (PEO-b-PnBMA)in mixtures of two ionic liquids: 1-butyl-3-methylimidazolium:bis(trifluoromethylsulfonyl)imide([BMIm][TFSI]) and 1-ethyl-3-methylimidazolium:TFSI ([EMIm][TFSI]).The solvent quality for the core-forming block of the block copolymer,PnBMA, is varied over a wide range by blending the two ionic liquidsin different ratios, resulting in a large variation in the cmt ofPEO-b-PnBMA. It is shown that the interaction parameterbetween the solvent and PnBMA atthe cmt is approximatelyconstant for all of the ionic liquid mixtures. The enthalpies andentropies of micelle formation also do not vary with ionic liquidcomposition, suggesting that the nature of the polymer/solvent andsolvent/solvent interactions do not change much as the ionic liquidcomposition is varied despite the large change in solvent quality.Furthermore, the cmt is shown to depend on the degree of polymerizationof PnBMA as predicted by theory. [ABSTRACT FROM AUTHOR]

Ionic liquids feature a combinationof properties that make them very interesting solvents for polymers,but many questions remain regarding the thermodynamics of polymer/ionicliquid 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-angleneutron scattering measurements. Several relevant thermodynamic parametersare easily tuned by varying the ionic liquid composition. In particular,the cloud point, spinodal, and Θ temperatures are all foundto increase linearly with [BMIm] content. The interaction parameters, χ,are determined as a function of temperature and concentration usingthree 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 theionic liquid, increasing and decreasing, respectively. The increasein the enthalpic driving force for mixing with increasing [BMIm] contentdominates over the decrease in the entropic penalty for mixing, leadingto improved solubility. This result is discussed in terms of molecularinteractions and oriented solvation. This work characterizes the solutionthermodynamics of one representative system in a very interestingclass of polymer solutions, and provides insight into the molecularmechanisms underlying its LCST phase behavior. [ABSTRACT FROM AUTHOR]

The management of proton conductivity in the protic ionic liquidimidazolium bis(trifluoromethylsulfonyl)imide ([Im][TFSI]) is investigatedvia the use of quasi-elastic neutron scattering (QENS) and pulsed-fieldgradient NMR. The introduction of excess neutral imidazole to [Im][TFSI]leads to enhanced conductivity. We find that proton dynamics in [Im][TFSI]with excess imidazole are characterized by proton hopping that isencompassed in the slower of two translational processes, as identifiedby QENS. This relatively slow process contributes to long-range diffusionmore than the faster process. NMR diffusion measurements show thatproton hopping decreases with increasing temperature, but significantproton hopping persists even at the maximum experimental temperatureof 120 °C. This, in combination with minimal ion aggregation,leads to high proton conductivity and a high proton transference numberover a wide temperature range. [ABSTRACT FROM AUTHOR]

Highly transparent and effective encapsulating materials have become increasingly important for photovoltaic (PV) modules to prevent water vapor molecules from permeating PV cells. The composite consists of block copolymer (PS- b -P2VP), comprised of hydrophobic and hydrophilic parts, and hygroscopic nanocrystals (Magnesium Oxide, MgO) incorporated to enhance water vapor blocking by both presenting obstacles for mass transport and also scavenging water molecules. The water vapor transmission rate (WVTR) values were reduced ∼3000 times, compared to homopolymer (PS), for both polymer and composite samples. Achieving both high transparency and low WVTR, it is expected that the composite materials can function as an excellent water vapor blocking layer for PV modules.

To optimize the properties of membranes composed of mixtures of block copolymers with ionic liquids, it is essential to understand universal scaling relationships between composition, structure, temperature, and ionic conductivity. In this work, we demonstrate the universality of relationships developed to describe the temperature and concentration dependence of ionic conductivity in such membranes by comparing the conductivity behavior of mixtures of ionic liquid with two block copolymer chemistries. The conductivities of all the mixtures are described by a single expression, which combines percolation theory with the Vogel-Tamman-Fulcher (VTF) equation. Percolation theory describes the power law dependence of conductivity on the overall volume fraction of ionic liquid, while the VTF equation takes into account the effect of the glass transition temperature of the conducting phase on the temperature dependence. The dominance of the overall volume fraction of ionic liquid in determining conductivity indicates that there is incredible flexibility in designing highly conductive block copolymer/ionic liquid membranes.