Design of Molecular Gels with Exceptional Structural, Dynamic and Mechanical Properties

Georgetown University, Washington DC

Investigators

Abstract

In this project funded by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professor Richard G. Weiss of Georgetown University is developing 'molecular gelators' (small molecules that aggregate into 3-dimensional networks which immobilize large amounts of a liquid) with special properties, such as the ability to transform reversibly into free-flowing liquids. A primary objective of this research is to develop fundamental relationships between the shapes and functionalities of structurally simple molecular gelators and the properties of their gels. To do so, two fundamental scientific questions are being addressed: "What constitutes an efficient molecular gelator?" and "How can the gelator structures be designed to provide materials with rather unique structural and mechanical properties?" The results from this research are expected to contribute information that is important to both basic and applied science and to fill current large gaps of understanding between molecular structure and self-assembly that lead to a wide range of self-organized materials in addition to gels. Several of the gels may be useful in applications that include art conservation, oil recovery, and food chemistry. Another very important impact is the training of young scientists, including those in under-represented groups and from developing countries. Students at all levels--postdoctoral to high school- are given opportunities to become integrated within the scientific community by attending and presenting their research results at conferences and by interacting directly with students in other collaborating labs throughout the world. The gelators selected are commercially available (e.g., ethylenediaminetetraacetic acid, Ethomeen surfactants, and polyethylenimines) or naturally occurring (e.g., sphingosine, glucamine, and 12-hydroxystearic acid) molecules. Alternatively, the gelators are easily synthesized from related molecules. Solvents that are most appropriate complements to the gelators are pre-selected using Hansen or other parameter sets that dissect liquid properties. The gels are designed to provide 'exceptional' properties, such as high degrees of thixotropy with variable recovery rates after destructive shear, gel-to-gel transitions initiated by thermally and photochemically induced changes of the molecular packing within gel fibers, and isothermal sol<->gel transitions induced by adding or removing a neutral triatomic gas (such as CO2). Several spectroscopic, thermodynamic and kinetic techniques are available for characterizing the structural/functionality relationships for this study.