Maito Koga

Phase separation and self-assembly of cyclic amphiphilic block copolymers with a main-chain liquid crystalline segment

A series of linear and cyclized amphiphilic block copolymers consisting of poly(acrylic acid) (AAm) and main-chain liquid crystalline (LC) poly(3-methylpentamethylene-4,4′-bibenzoate) (BBn) segments were newly synthesized. Solid state morphology was investigated by X-ray scattering. Linear AA21BB9AA21, cyclic AA33BB10, and cyclic AA51BB18 formed lamellar microdomains, where the BBn segment of cyclic AA51BB18 formed a smectic CA phase. On the other hand, cylinder-type microdomains were formed by linear AA44BB9AA44 and cyclic AA100BB9. These amphiphilic block copolymers were self-assembled in water to form vesicles or cylindrical micelles, depending on the polymer concentration of the initial THF solution. The response of these nanostructures against an electric field demonstrated that the vesicles formed from linear AA25BB14AA25 and cyclic AA51BB18 turned into substantially larger aggregates, likely due to the reorganization of the LC segment in the bilayer.

Transition of liquid crystal anchoring at the microdomain interface observed for main-chain nematic polyester segments of block copolymers

The microdomain structures and liquid crystal (LC) orientations of ABA triblock copolymers comprising poly(styrene) (PS) A blocks and a main-chain LC polyester B block were examined via small-angle X-ray scattering and electron microscopy in the form of fibrous samples. The LC polyester blocks were segregated from the PS blocks to form a nematic LC in the lamellar microdomains of the copolymers, with the PS volume fraction (φ) ranging from 13 to 38%. As φ decreased, the nematic director was always positioned along the fiber axis, but the microdomain lamellae changed their direction from parallel to perpendicular with respect to the fiber axis and began to adopt a zigzag configuration. These lamellar orientations were attributed to the main-chain nematic LC segments lying along the microdomain interface but extending perpendicularly to the interface as the occupying interface area was reduced. The lamellar microdomains parallel to the nematic director increased the LC and PS lamellar thicknesses reversibly by 48 and 16%, respectively, at the same time as the isotropization of the nematic LC. Such changes in lamellar thickness suggest that both the PS and LC segments were elongated along the direction of the LC orientation.Lamellar microdomain and liquid crystal (LC) orientations in a fibrous sample were investigated for a series of ABA triblock copolymers comprising poly(styrene) (PS) A blocks and a main-chain nematic LC polyester B block. As the PS volume fraction decreased from 38 to 13%, the lamellae changed their direction from parallel to perpendicular with respect to the fiber axis and began to adopt a zigzag configuration, although the LC mesogens always lay along the fiber axis. At the microdomain interface, the LC mesogens exhibited an anchoring transition from planar to homeotropic.

Effect of freeze–thaw treatment on the precipitation of octyl β-D-Galactoside hemihydrate crystal from the aqueous solution

Cryogenic treatment, like the freeze-thaw process, has been reported to be effective in modifying the physicochemical properties of polymeric hydrogels. However, not much attention has been paid to this process in terms of the precipitation of surfactant-water systems. In this study, two effective cryogenic methodologies were successfully reported to alter the physicochemical properties of a precipitate of an octyl β-D-galactoside (Oct-Gal)-water system. First, hyperrapid cooling (i.e., cooling at 30°C/min) was found to be an effective type of cryogenic treatment: the phase transition temperature (TK) and enthalpy at the phase transition (∆HK) between the crystal-dispersed phase and the sol (micelle) phase significantly decreased. In addition, cryogenic treatment in the presence of electrolytes, such as NaCl, NaBr, and CsCl, was effective even in the absence of the hyperrapid cooling condition. The hyperrapid cooling or the addition of certain electrolytes was considered to prevent the precipitation of the Oct-Gal hemihydrate crystals prior to the complete freezing of ice and the electrolyte/ice eutectic. Hence, the size of the aggregated crystals prepared by the above-mentioned effective cryogenic treatments seemed to be decreased compared with that of the normal precipitated crystals, thereby changing TK and ∆HK. Thus, two basic methodologies for the modification of the physicochemical properties of the crystal-dispersed phase of surfactant-water systems are discussed.