Division of Physical Chemistry, Ruđer Bošković Institute, Zagreb, Bijenička cesta 54, Croatia.
Langmuir. 2011 Dec 6;27(23):14118-30. doi: 10.1021/la203777c. Epub 2011 Nov 11.
A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.
一系列阳离子低聚物表面活性剂（季铵离子十二烷基二甲基，头部通过亚乙基间隔连接两条、三条或四条链，分别简写为二聚体、三聚体和四聚体）被合成并进行了特性研究。通过 X 射线衍射、偏光显微镜、热重分析和差示扫描量热法研究了低聚物聚合度对其晶型和介晶性能的影响。所有化合物均显示层状排列，具有交错的十二烷基链。低聚物聚合度的增加会增加层间距并降低固态的有序性；而二聚体样品完全结晶，具有良好的 3D 有序性，三聚体和四聚体结晶为高度有序的晶态近晶相。热相变的数量和相的顺序明显受到十二烷基链数量的影响。无水样品表现出多晶型和热致近晶型介晶性，而四聚体仅在高温下显示与分解和熔融相关的转变。所有水合化合物均形成溶致介相，在加热和冷却过程中表现出可逆的相转变。二聚体的液晶相顺序，典型的浓缩离子表面活性剂体系，包括低温下的六方相和高温下的近晶相。相比之下，三聚体和四聚体显示出六方相的纹理。
