Zhang Jie, Luan Lingyu, Zhu Wenxia, Liu Shangying, Sun Dejun
Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, 250100, Shandong, P. R. China.
Langmuir. 2007 May 8;23(10):5331-7. doi: 10.1021/la0625300. Epub 2007 Apr 17.
Birefringence observations and rheological measurements were used to monitor the phase behavior of Mg/Al (the molar ratio of Mg(2+) to Al(3+) being 2:1) layered double hydroxide (LDH) suspensions. The suspensions of concentration lower than 16% (w/w) appear isotropic (I) between crossed polarizers. In contrast, the suspensions of concentration between 16% and 30% (w/w) showed an isotropic (I)-nematic (N) biphasic coexistence. Detailed observations led us to divide the suspensions in the gap into three groups according to their behaviors: the suspensions with concentration between 16% and 25% (w/w) experienced an I-N phase transition and particle sedimentation simultaneously, while the suspensions of 25% to 27% (w/w) showed I-N transition after particle sedimentation, and in the suspension of 30% (w/w), a critical sol-gel transition appeared with an I-N transition. Above 33% (w/w), the gel network hindered a complete I-N separation in the suspensions. Upon raising the NaCl concentration, the liquid crystalline phase transition and the sol-gel transition shifted to higher particle concentrations. The facts demonstrate that the phase behavior of aqueous LDH suspensions is controlled by the competition among liquid crystal phase transition, sedimentation, and gelation.
利用双折射观测和流变学测量来监测Mg/Al（Mg²⁺与Al³⁺的摩尔比为2:1）层状双氢氧化物（LDH）悬浮液的相行为。浓度低于16%（w/w）的悬浮液在正交偏振器之间呈现各向同性（I）。相反，浓度在16%至30%（w/w）之间的悬浮液呈现各向同性（I）-向列相（N）双相共存。详细观测使我们根据其行为将间隙中的悬浮液分为三组：浓度在16%至25%（w/w）之间的悬浮液同时经历I-N相变和颗粒沉降，而25%至27%（w/w）的悬浮液在颗粒沉降后呈现I-N转变，在30%（w/w）的悬浮液中，出现临界溶胶-凝胶转变并伴有I-N转变。高于33%（w/w）时，凝胶网络阻碍了悬浮液中I-N的完全分离。随着NaCl浓度的升高，液晶相变和溶胶-凝胶转变向更高的颗粒浓度移动。这些事实表明，水性LDH悬浮液的相行为受液晶相变、沉降和凝胶化之间的竞争控制。
