Alkylglycoside Surfactants - Self-Assembly, Solid-State Properties and Interactions with Hydrophobic Molecules

A thorough physical-chemical characterisation of alkylglycosides has been performed. The effects of temperature, salt, concentration and deuterium exchange on the self-aggregation of n-nonyl-b-D-glucoside (b-C9G1) and n-tetradecyl-b-D-maltoside (b-C14G2) have been studied in dilute solutions by static and dynamic light scattering, neutron scattering, rheology, capillary viscometry and tensiometry. The data suggest that the aggregates grow in one dimension upon increasing concentration, addition of salting-out salts, changes in temperature and a substitution of D2O for H2O. However, the temperature effect on the micellar size is dramatically different for the two alkylglycosides. For b-C9G1, a decrease in size is observed with increasing temperature whereas the opposite is observed for b-C14G2, i.e. an increase in micellar size with increasing temperature. The effects can be rationalised as effects on unimer geometry, rather than on unimer solubility. The micelle morphology at higher surfactant concentrations was investigated by rheology and capillary viscometry. The results suggest that alkylmaltosides form entangled rod-like micelles whereas alkylglucosides have a stronger tendency to form branched aggregates and micellar networks. The thermotropic phase behaviour and phase structure of crystalline and non-crystalline alkylmaltosides as well as crystalline n-dodecyl-b-D-glucoside (b-C12G1) have been investigated by means of differential scanning calorimetry and X-ray techniques. Two different non-crystalline structures for the alkylmaltosides were identified, a gel and a glass. The gel was formed for alkylmaltosides with a hydrocarbon chain longer than 12 carbons whereas short- and medium-chained alkylmaltosides formed a glass. The results highlight the importance of intermolecular head-group interactions for the phase behaviour of alkylglycosides. Finally, the solubilisation of naphthylalkylates and the stabilisation of polypeptides by alkylglycosides were investigated. The results reveal that the unimer geometry governs both the solubilising and stabilising capacity