For ionomers, unfavorable interaction between highly polar ion pairs and the low polarity polymer medium leads to ion aggregation. In contrast, for polyelectrolytes, the counterions prefer solvation in the polar medium to leave the chain charged and accordingly stretched due to the charge repulsion. In this study, linear viscoelastic and dielectric properties of mixtures of two ionomers with high dielectric constant low volatility plasticizers were examined. The ionomer chains having bulky side chains are not entangled. Upon increasing the plasticizer content, the terminal relaxation is significantly accelerated due to two effects: (1) a plasticizing effect lowering the T g and (2) a higher dielectric constant that softens the ionic interactions, leading to ionic dissociation into isolated pairs that further boosts the static dielectric constant at low frequency/long time. A model incorporating these two mechanisms and utilizing a dielectric constant εC, after the nonionic segmental α relaxation as the relevant dielectric constant for ion dissociation, predicts quantitatively the accelerated dynamics, as ionomers transition to polyelectrolytes on dilution.

We report a combined theoretical and experimental effort to elucidate systematically for the first time the influence of anions of transition metal salt-decorated surfaces on the orientations of supported films of nematic liquid crystals (LCs) and adsorbate-induced orientational transitions of these LC films. Guided by computational chemistry predictions, we find that nitrate anions weaken the binding of 4'-n-pentyl-4-biphenylcarbonitrile (5CB) to transition metal cations, as compared to perchlorate salts, although binding is still sufficiently strong to induce homeotropic (perpendicular) orientations of 5CB. In addition, we find the orientations of the LC to be correlated across all metal cations investigated by a molecular anchoring energy density that is calculated as the product of the single-site binding energy and metal cation binding site density on the surface. The weaker single-site binding energy caused by nitrate also facilitates competitive binding of adsorbates to the metal cations, leading to more facile orientational transitions induced by adsorbates. Finally, our analysis suggests that nitrate anions recruit water via hydrogen bonding to the metal binding sites, modulating further the relative net binding energies of 5CB and adsorbates to surfaces decorated with metal nitrates. After accounting for the presence of water, we find a universal exponential relationship between the calculated displacement free energies and measured dynamic response of LCs to adsorbates for all metal salts studied, independent of the metal salt anion.

Surface-supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox-triggered changes in the strength of binding to nitrogen-based LCs upon exposure to Cl gas. Guided by these predictions, μm-thick films of nitrile- or pyridine-containing LCs were prepared on surfaces decorated with Mn binding sites as perchlorate salts. Following exposure to Cl , formation of Mn (in the form of MnO microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl gas. The response was also selective to Cl over other oxidizing agents such as air or NO and other chemical targets such as organophosphonates.