Agra-Kooijman Dena M, Singh Gautam, Lorenz Alexander, Collings Peter J, Kitzerow Heinz-S, Kumar Satyendra
Department of Physics, Kent State University, Kent, Ohio 44242, USA.
Department of Chemistry, Berlin Institute of Technology, Strasse des 17. Juni 124, 10623 Berlin, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Jun;89(6):062504. doi: 10.1103/PhysRevE.89.062504. Epub 2014 Jun 12.
Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 Å between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from ∼35 to 42 Å in the orientationally ordered nematic (N) phase and from 27 to 32 Å in the columnar or middle (M) phase having long range lateral positional order. The assemblies' length depends on concentration and consists of ∼23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values ∼7.19 ± 0.14 k_{B}T (15 wt %), 2.73 ± 0.4 k_{B}T (20 wt %), and 3.05 ± 0.2 k_{B}T (25 wt %). Solutions of all concentrations undergo a spinodal decomposition at temperatures above ∼40 °C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases.
此前曾有人提出，水溶液中色甘酸钠（DSCG）聚集体的结构为堆叠状、烟囱状和线状组装体。本文报道的同步加速器X射线散射研究结果表明，DSCG分子之间以3.4 Å的间距形成了具有π-π堆积的简单柱状组装体。组装体之间的横向间距取决于浓度和温度，在取向有序的向列相（N相）中为35至42 Å，在具有长程横向位置有序的柱状相或中间相（M相）中为27至32 Å。组装体的长度取决于浓度，在N相中由约23个分子组成，在M相中则增大三至十倍。在N相中，断裂能取决于浓度，其值分别为7.19 ± 0.14 kBT（15 wt%）、2.73 ± 0.4 kBT（20 wt%）和3.05 ± 0.2 kBT（25 wt%）。所有浓度的溶液在温度高于约40°C时都会发生旋节线分解，形成富含DSCG的M相区域以及N相和各向同性相的富水区域。
