Kostko Andrei F, Cipriano Bani H, Pinchuk Olga A, Ziserman Lior, Anisimov Mikhail A, Danino Dganit, Raghavan Srinivasa R
Department of Chemical Engineering, University of Maryland, College Park, Maryland 20742-2111, USA.
J Phys Chem B. 2005 Oct 20;109(41):19126-33. doi: 10.1021/jp052575u.
Chromonic liquid crystals are formed by the addition of aromatic molecules such as disodium chromoglycate (cromolyn) to water. In this study, we investigate the addition of salts to the lyotropic nematic phase of cromolyn aqueous solutions. The addition of sodium and potassium salts shifts the isotropic-nematic phase boundary upward by more than 10 degrees C, so that samples that were isotropic at room temperature are transformed into nematic phases. Salt effects are predominantly dictated by the cation, not the anion, and appear to differ based on cation size. In contrast to small, hydrated cations like sodium, large, weakly hydrated cations such as tetraethylammonium and tetrabutylammonium shift the phase boundary downward, thus stabilizing the isotropic phase at the expense of the nematic one. The phase behavior results are highly correlated with viscosity measurements, with an upward shift in the phase boundary correlating with an increase in solution viscosity and vice versa. We also probe the microstructure in cromolyn-salt solutions, both indirectly by small-angle neutron scattering (SANS) and directly by cryo-transmission electron microscopy (cryo-TEM). The cryo-TEM images show the presence of rodlike aggregates that possibly undergo a higher order aggregation into bundles in the presence of salt.
向列型液晶是通过向水中添加诸如色甘酸二钠（色甘酸钠）等芳香分子形成的。在本研究中，我们研究了向色甘酸钠水溶液的溶致向列相添加盐的情况。添加钠盐和钾盐会使各向同性-向列相边界向上移动超过10摄氏度，从而使室温下呈各向同性的样品转变为向列相。盐效应主要由阳离子而非阴离子决定，并且似乎因阳离子大小而异。与像钠这样的小的、水合阳离子相反，大的、弱水合阳离子如四乙铵和四丁铵会使相边界向下移动，从而以向列相为代价稳定各向同性相。相行为结果与粘度测量高度相关，相边界向上移动与溶液粘度增加相关，反之亦然。我们还通过小角中子散射（SANS）间接以及通过低温透射电子显微镜（cryo-TEM）直接探测色甘酸钠-盐溶液中的微观结构。低温透射电子显微镜图像显示存在棒状聚集体，在有盐的情况下这些聚集体可能会进一步聚集成束形成更高阶的聚集体。
