Ionic liquids (ILs) are a relatively new class of liquids that consist only of cations and anions. Some of the useful properties of typical ILs are their negligibly low vapor pressure, fire resistance, excellent chemical and thermal stability, wide liquid temperature ranges, and wide electrochemical windows. Given these excellent properties, ILs have been used or considered for use in organic synthesis, catalysis, chemical separation, and fuel and solar cells, and their applications continue to expand. Despite a plethora of emerging processes involving ILs, however, an understanding of the interfacial properties of ILs under confinement, such as rheological properties and glass transition temperatures, remain very limited compared with that of other confined material classes, such as polymers, electrolyte solutions, and liquid crystals.
The objective of the proposed work is twofold: (i) to obtain relationships describing how the structure, viscosity, and glass transition temperature of ILs depend on degree of confinement (separation) and (ii) to obtain a fundamental understanding of how the molecular parameters of confined ILs, such as the relative sizes and shapes of cations and anions and the surface properties of confining surfaces, such as surface potential and degree of hydrophobicity, affect the abovementioned properties under nanoconfinement. Our main hypothesis is that when the dimension of confinement becomes comparable to the Debye screening length of ILs, the confined glass transition temperature deviates from the bulk glass transition temperature. This hypothesis will primarily be tested with the surface forces apparatus technique, which is a unique technique that can link molecular studies to meso-scale studies and also to bulk-scale studies. This work will be first of its kind to directly measure the viscosity and glass transition temperature of ILs under dynamically controlled nanoconfined environments. From a fundamental science perspective, the proposed work represents an important step in understanding the structure/property relationships of ILs under confinement. Such an understanding may ultimately lead to new fundamental insights into a systematic method to select an ion pair(s) for the rational design of ILs operating under nanoconfined environments and with the desired physical properties.
This project will first provide pivotal guidelines to select desirable types of ILs on demand on the basis of their important interfacial properties under nanoconfinement. Such knowledge will be useful to optimize and design applications involving confined ILs, such as batteries, solar cells, and lubricants. The educational plan consists of three main components that will focus on the research supervision of students, teaching, mentoring, and outreach to interface with the research components of the project. These components include the (i) development of a new graduate course on the interfacial phenomena of soft matter to be taught by the PI, (ii) mentoring of underrepresented undergraduate students in research, and (iii) dissemination of the project outcomes to the general public in the Akron area, where the minority constitutes 25% of the total population, by reliance on the connections established with local high school teachers through an educational electronic device development grant funded by NSF.
