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Title: Uncovering and exploiting cucurbit[8]uril host-guest dynamics in bulk mechanical behaviour
Author: Hoogland, Dominique
ISNI:       0000 0004 7961 8523
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Understanding the contribution of small molecule dynamics to bulk mechanical properties is of increasing importance in progressing the field of smart materials from benchtop curiosity to a design-based approach with myriad application. Hydrogels based on cucurbit[8]uril (CB[8]) supramolecular interactions are ideal candidates to study this relationship due to the variability in guests and binding modes it accommodates. In the first chapter earlier studies on pressure-induced changes in CB[8] hetero-ternary complexes, where the association rate was found to increase with external pressure, are extended to hydrogels harnessing these interactions. It appears that changes observed in the complexes are too small to be translated into viscosity changes of the bulk material, but unlike other systems used commercially, this system is unaffected by pressure. In an attempt to design a stimuli responsive, reversible system, dicationic azobenzene derivatives with various binding modes to CB[8] are studied in the second chapter. The isomerisation rates of the various derivatives are studied as a function of temperature, irradiation, presence of CB[8] and pH. Finally, a polymer bearing one of the azobenzenes is studied via rheometry for it's light-responsiveness. As pressure did not perturb the association event to a large enough extend to allow for studies on bulk mechanical behaviour as a function of association rate, several first guests were synthesised in an effort to amplify these differences. N,N -Dimethyl-4,4-bipyridine, N,N -dimethyl-2,7-diazaphenantrene and N,N -dimethyl-2,7-diazapyrene were synthesised in a systematic study based on increase in surface area of the first guest. Through use of complexation techniques as isothermal titration calorimetry (ITC) and stopped-flow fluorescence, the kinetics of complexation between these auxiliary guests in CB[8] and four second guests were studied. To translate the results of the small molecule techniques to bulk mechanical properties, functional derivatives of these first guests were prepared. Through semi-batch RAFT polymerisation these reactive first guests created branched polymers with CB[8] rotaxanes, which formed gels upon mixing with hydroxyethyl cellulose (HEC) bearing pendant second guests. Lastly, the effect of different binding modes between guest molecules and CB[8] on gel behaviour was studied for systems based on two different polymers, HEV and poly(vinyl alcohol) (PVA). These polymers were chosen to be of similar molecular weight but differ in rigidity. Through looking at the relaxation spectrum of gels composed of one or both of these polymers with either hetero or homo-ternary guests, the contribution of both polymer and host-guest chemistry is further elucidated.
Supervisor: Scherman, Oren Alexander Sponsor: Schlumberger
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Supramolecular chemistry ; Host-Guest chemistry ; Cucurbit[n]uril ; Rheology ; Kinetics ; Polymer chemistry ; Polymer Physics ; Organic chemistry