Date of Degree

9-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

George John

Committee Members

Charles Maldarelli

Ruth E. Stark

Rein Ulijn

Subject Categories

Materials Chemistry

Keywords

molecular gel, low molecular weight gelator, self-assembly, bio-based, biomass, bio-synthesis

Abstract

The interest in molecular gels has been gaining momentum as evident from being developed for a broad spectrum of applications. This impetus stems from several reasons that include: (i) molecular gels are highly stimuli responsive as they easily respond to thermodynamic changes, disintegrating into well-defined chemicals/building blocks because of the purely physical (in contrast to chemically cross-linked) nature of the interactions holding their 3D networks together; (ii) the sheer abundance of simple small molecules to choose starting materials from and the vast potential of tunability of the low molecular weight gelators (LMWGs) make the LMWGs and the molecular gels highly diverse and versatile; and (iii) one fascinating aspect of molecular gels is the demonstration of how properties and events could be controlled at the molecular level to effect specific physical and/or chemical properties at the macroscopic level, with one such remarkable event being self-assembly that eventually give rise to the solid-like properties of the gel. The most common type of gels is polymeric in nature and usually derived from non-renewable resources such as petroleum. In contrast, the precursor LMWGs of molecular gels are derived from natural resources that are readily available, renewable and bio-based, rendering this class of gels with desirable features such as being biocompatible, biodegradable, safer and sustainable. However, most molecular gels have been discovered by serendipity and thus prompting the need to develop new molecular gels, improve their mode of synthesis and better understand the process of gelation. In this research, efforts were made to develop LMWGs for molecular gelation in both organic and aqueous media and to correlate the gelation behavior of certain gel-forming seeds with that of synthetic gelators.

Sugar alcohols are abundant, renewable and structural diverse, with extensive usage in commercial products. Conveniently, they have distinct primary hydroxyl groups which could be regioselectively targeted to afford the LMWGs via biocatalysis - a simple, single-step and GRAS synthesis. The sugar alcohol-based LMWGs were systematically studied for three different applications. During each application, hydrophobicity was systematically fine-tuned by varying fatty acid chain length. The first application was phase-selective gelation for crude oil spill remediation using mannitol, sorbitol and xylitol-base amphiphiles. Correlation between subtle structural differences and efficiency of phase-selective gelation was systematically studied. The second and third applications involved exploring the multifunctionality of oleogels (edible oil gels). The aim was to uncover LMWGs with potentials to impart additional properties like aesthetic and low-calorie effect in addition to structuring.

Sucralose is another molecule with intriguing features like being noncaloric, noncariogenic, extremely sweet and derived from renewable biomass. Various derivatives were systematically synthesized, characterized and studied for their hydrogelation capability and efficiency in polar and nonpolar solvents and selected beverages.

Finally, since assimilating inspirations from nature requires studying and understanding nature, one of our undertakings has been to study the gelation process of gel-forming seeds in order to correlate with that of synthetic gelators. Chia and basil seeds spontaneously undergo hydrogelation, which is concomitant with moisture-retention and proposed health benefits. The work aimed to elucidate and corroborate the involvement of nanoscale 3D-network. The influence of several conditions on fiber extrusion were systematically tested before using various microscopic techniques to establish nanoscale fiber formation.

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