Impact of surface hydrophilicity on the ordering and transport properties of bicontinuous microemulsions.

Microemulsions (MEs) have many industrial applications, where recent developments have shown that MEs can be utilized for electrochemical applications, including potentially in redox flow batteries. However, understanding the structure and dynamics of these systems, including at a surface, is needed to direct and rationally control their electrochemical behavior. While bulk solution measurements have provided insight into their structure, their assembly at an interface also impacts the electron (to the electrode) and ion (across the surfactant) charge transfer processes in the system. To address this shortcoming, neutron reflectivity experiments and molecular simulations have been completed that document the near surface structure of a series of deuterated water (D2O)/polysorbate-20/toluene MEs on hydrophilic and amphiphilic surfaces. These results show that the microemulsions form complex layered structures near a hard electrode surface, where most layers are not purely one component. Decreasing the D2O concentration in the ME increases the number of and purity of the layers established on the solid surface. These lamellar-type layers transition from the surface to the bulk microemulsion as a series of mixed layers (i.e., containing oil, water, and surfactant) that are consistent with perforated lamellae. Additionally, these mixed lamellae appear to become more perforated with oil and water pathways on an amphiphilic surface. The purity and thickness of these layers will influence the accessibility of an electrode by redox active species, as well as ion transport required to satisfy the electroneutrality condition.

Estimation of the hamaker coefficient for a fuel-cell-supported catalyst system.

Hamaker coefficients are estimated for various nanoparticle-support systems commonly used in polymer electrolyte membrane fuel cells. The interaction energies, cohesion between nanoparticles, and adhesion of nanoparticles on the support are also estimated from the experimental data. Comparison between the bulk properties of platinum metal, calculated from the optical spectra available in the literature, and the nanoparticles are provided. Measurements to obtain the optical properties of the systems of interest are also reported. Implications of the van der Waals forces on the supported catalyst structure properties are discussed. The algorithm used in calculation of the Hamaker coefficient using Lifshitz theory was evaluated with known materials, using the spectral parameters available in the literature, and the results are presented.