|Superstructures fabricated from carbohydrates and their derivatives hold an immense promise for the application in diverse fields. However, still many understudied problems challenge us, such as the roles of backbones and side chains during the formation of superstructures, precise control of their morphologies and the application of these unique structures.
In this thesis, I first fabricated hydrophobic and superhydrophobic surfaces on wood by using cellulose stearoyl ester (CSE) and glycerol stearoyl ester (GSE). CSE was used for dip-coating (1st layer) the wood, leading to a hydrophobic surface and GSE was used for brush-coating (2nd layer) the wood, leading to a hierarchical superhydrophobic surface. Both hydrophobic and superhydrophobic woods exhibit better anti-fungal properties comparing with non-treated wood. Furthermore, superhydrophobic wood could thoroughly prevent fungal attachment to treated wood, while fungi could still be found inside hydrophobic wood after anti-fungal test. This study shows that both CSE and GSE can form hydrophobicity due to the full substitution of the hydroxyl groups by fatty side chains with 18 carbons. However, the backbone of cellulose and the monomer structure of glycerol result in the formation of membrane by CSE and hierarchical porous structure by GSE, respectively.
The most commonly introduced microparticles from carbohydrates all hold conventional filled morphology. Nevertheless, microparticles with chiral and porous morphology are rarely mentioned from carbohydrates. Moreover, the formation of tunable chiral and porous flower-like microparticles using the same materials, especially monosaccharides without applying external stimuli, is still highly understudied. In this study, the formation of chiral, solid, and flower-like microparticles by only using monosaccharide stearoyl esters (MSSEs) were reported for the first time. Chiral, hierarchical superstructures can be obtained from D/L-glucose stearoyl esters (D/L-GlcSE). Chiral ‘left-handed’ (counterclockwise) spiralling morphology can be obtained by D-GlcSE, while ‘right-handed’ (clockwise) morphology can be induced by L-GlcSE. The formation of microparticles with chirality can only be achieved when the α/β ratio of anomer in D/L-GlcSE is 20/80, the concentration is 1 mg/mL from 60°C to 25°C with the aging time of 20 min. The α configuration leads to irregular aggregates, which show worse thermal and crystallization properties, while mature round smooth microparticles with better thermal and crystallization properties are beneficial from β configuration. Axially stretched α configuration improves the difficulties of stacking of MSSE molecules during self-assembly, while better stacking is beneficial from equatorially stretched β configuration. These results can be explained by the displacement during molecular stacking via self-assembly and chirality amplification in the hierarchical superstructures.
In addition to the effects of configurations as D/L-configuration and α/β-anomers, the effect of the monosaccharides that contain more structural difference was further studied by using four different D-monosaccharide stearoyl esters (D-MSSEs), which are D-glucose stearoyl esters (D-GlcSE), D-xylose stearoyl esters (D-XylSE), D-galactose stearoyl esters (D-GalSE) and D-mannose stearoyl ester (D-ManSE). Based on the 1H NMR spectra, the α/β ratios at C1 for D-GlcSE, D-XylSE, D-GalSE and D-ManSE are 20/80, 15/85, 27/73 and 35/65, respectively. Besides, they also have diverse number of side chains and the bonds stretching axially/equatorially at C2, C4 and C6. By adjusting the number of side chains and the bonds stretching axially/equatorially, diverse microparticles with solid and porous flower-like morphologies can be adapted. More sidechains lead to lower precipitation temperature, worse thermal and crystallization properties. With the same side chains, axially instead of equatorially stretched bond configuration results in lower precipitation temperature, worse thermal and crystallization properties. This conclusion can be explained by the increased obstacles during the stacking of molecules from more side chains and more bonds stretched axially. Thus, both the number of side chains and the number of bonds stretching axially/equatorially play the pivotal rules when tuning the sugar-based superstructures from solid to chiral and porous morphology.
This thesis is a cumulative work including 3 publications. One of them was already published and two are under submission. The background, the objective of the study, results and discussion of these three publications and the conclusion are presented in Sections 1-4.