Microphase separation in maltooligosaccharide-based block co-oligomers with dominant sugar volume fractions: Toward a comprehensive understanding of the phase behavior

Block co-oligomers (BCOs) consisting of oligosaccharides and hydrophobic terpenoid blocks exhibit microphase-separated structures of various morphologies with sub-10 nm periodicity, thereby rendering them of interest for use in a range of nanotechnological applications. However, their microphase separation behaviors have yet to be fully elucidated across a broad range of sugar volume fractions, especially with regard to sugar-rich regimes. In this study, the microphase separation behaviors of sugar-rich BCOs composed of maltooligosaccharides (maltotriose, maltopentaose, and maltoheptaose) and hydrophobic terpenoid blocks (farnesol, phytol, and DL-α-tocopherol) were systematically investigated using sugar volume fractions ranging from 0.41 to 0.69. Small-angle X-ray scattering (SAXS) and grazing incidence SAXS were employed to identify a variety of nanostructures in both the bulk and thin-film states, including lamellar, sugar-rich gyroid, hexagonally perforated lamellar, and hexagonally packed cylindrical structures. Through integration of the deduced phase behaviors in the sugar-rich regime, phase diagrams were constructed to provide useful guidance for predicting the self-assembled morphologies of sugar-based block copolymer/co-oligomer systems.