Ernesto C. Cortés-Morales

We explore an idealized theoretical model for ion transport within highly asymmetric ionic liquid mixtures. A primitive model-inspired system serves as a representative for asymmetric ionic materials (such as liquid crystalline salts) which quench to form disordered, partially arrested phases. Self-consistent generalized Langevin equation theory is applied to understand the connection between the size ratio of charge-matched salts and their average mobility. Within this model, we identify novel glassy states where one of the two charged species (without loss of generality, either the macro-cation or the micro-anion) is arrested, while the other retains liquid-like mobility. We discuss how this result is useful in the development of novel single-ion conducting phases in ionic liquid-based materials, for instance, conductors operating at low temperature or the technology associated with ionic liquid crystals.

In this work, we present a first-principles theoretical framework for the description of structural and dynamical behaviors of ionic liquids. This framework applies the self-consistent generalized Langevin equation (SCGLE) theory, which predicts the dynamically arrested states of several physical systems, including charge and size asymmetric ionic liquids. In its current form, the SCGLE is a particularly useful framework for predictions of arrested and partially arrested states in both classical and room-temperature molten salts, electrolytic solutions, and superionic conductors. Some illustrative examples of the predictive power of our framework are presented in this work, showing its potential application in design and development of novel conducting materials.

The recently developed non-equilibrium self-consistent generalized Langevin equation theory of the dynamics of liquids of non-spherically interacting particles [2016 J. Phys. Chem. B 120 7975] is applied to the description of the irreversible relaxation of a thermally and mechanically quenched dipolar fluid. Specifically, we consider a dipolar hard-sphere liquid quenched (at t _w = 0) from full equilibrium conditions towards different ergodic–non-ergodic transitions. Qualitatively different scenarios are predicted by the theory for the time evolution of the system after the quench (t _w > 0), that depend on both the kind of transition approached and the specific features of the protocol of preparation. Each of these scenarios is characterized by the kinetics displayed by a set of structural correlations, and also by the development of two characteristic times describing the relaxation of the translational and rotational dynamics, allowing us to highlight the crossover from equilibration to aging in the system and leading to the prediction of different underlying mechanisms and relaxation laws for the dynamics at each of the glass transitions explored.

Although macromolecules such as polymers are in widespread industrial use, pure formulations rarely have precisely the properties new applications demand. Pure polymer is often too brittle and inflexible, necessitating plasticizers to soften or toughen films and bulk polymer materials. In practice, new formulations are developed by extensive trial-and-error methods, as no general molecular explanations exist for the mechanism of plasticization to aid in determining the optimal structure and concentration of plasticizers. Here, through atomistic molecular simulations augmented with advanced sampling techniques, we develop an atomic-level picture of the processes in plasticization by directly calculating free energies that govern the interaction between polymers and small-molecule plasticizers. This work focuses on the influence of two common plasticizer molecules—glycerol and sorbitol—interacting with polyvinyl alcohol (PVA), a frequently used component of polymer films. In particular, we focus on conformational and hydrogen bond structure changes induced in globules of PVA by the plasticizer molecules, with the hypothesis that hydrogen bonding plays a role in the incorporation of these plasticizers into PVA and, thus, in the observed mechanical properties. While we focus on nanoscopic systems, we observe distinct preferences in the conformational free energy that can be connected to the performance of polymer materials at laboratory and industrial scales. This work presents a new molecular perspective from which effective plasticizers can be developed and presents a firm basis from which important analyses of plasticization in complex chemical environments relevant to industry may be developed.