コレステロール誘導体/鎖状アミンから成るイオン錯体の相挙動および液晶ガラスのエンタルピー緩和特性

Abstract

カルボン酸モノコレステリル(フタレートCHP，サクシネートCHS)と鎖状アミン(Cn-amine，n＝4–18)から成るイオン錯体(CHP/Cn-amine，CHS/Cn-amine)とそれらの混合試料(コレステリル一種と二種のCn-amineから成る鎖長分布型，ならびに二種のコレステリルと一種のCn-amineとの連結基混在型)について，サーモトロピック液晶性と液晶ガラスのエンタルピー緩和挙動を調査した．対象試料のほとんどは液晶性を有し，結晶化することなく液晶ガラスを形成した．長鎖Cn-amine (n≥10)との錯形成ではコレステリル単独体よりも高秩序な液晶相となり，アルキル鎖長nの低下とともに漸次その秩序性は低下した．混合試料はすべて単一のガラス転移と液晶–等方相転移を示し，相分離のない均一な分子凝集構造をとることが示された．さらに，Kohlrausch-Williams-Watts式によるエンタルピー緩和解析から，分子配列様式の秩序低下に伴って緩和時間の分布が広がる傾向が明らかとなった．分子量分布を有する混合試料では緩和の均一性は低下し，その効果は鎖長分布型でより顕著であった．

Through DSC and polarized optical microscopy measurements, thermotropic phase behavior was examined for ionic complexes of cholesterol hydrogen phthalate (CHP) or succinate (CHS) with normal aliphatic amines (Cn-amines; carbon number n = 4–18), and for two types of complexes; one was composed of one cholesterol derivative and two different alkyl amines [i.e., CHP/(Cm, Cn)-amine and CHS/(Cm, Cn)-amine, m ≠ n] and the other consisted of two cholesteryls and one Cn-amine [(CHP, CHS)/Cn-amine]. Except for the cholesteryl complexes with shorter Cn-amine (n ≤ 6), all the complex salts easily formed a liquid-crystalline glass (smectic or cholesteric type) without crystallization and phase-separation after passing through the mesomorphic fluid state, when they were cooled from the respective isotropic melts. Enthalpy relaxation of these glassy materials, occurring during physical aging below their Tg, was followed as a function of the aging time and temperature, and the obtained data was analyzed in terms of a Kohlrausch-Williams-Watts function. Uniformity of the relaxation mode was quite high for the aged samples of CHP/Cn-amine (n = 10–18) forming a smectic liquid-crystalline glass, and a slow relaxation with diverse modes was observed for the mixed complexes, particularly for CHP/(Cm, Cn)-amine and CHS/(Cm, Cn)-amine.