Liquid crystalline nanosheet colloids with controlled particle size obtained by exfoliating single crystal of layered niobate K4Nb6O17
Liquid crystalline nanosheet colloids with controlled particle size obtained by exfoliating single crystal of layered niobate K4Nb6O17
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DOI：
10.1021/jp0363545
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发表时间：
2004-05-20
影响因子：
3.3
通讯作者：
Nakato, T
中科院分区：
文献类型：
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作者：
Miyamoto, N;Nakato, T
制备了厚度为1.8 nm且控制平均横向尺寸为0.15-7.8 μ m的胶体分散的钛酸酯纳米片，并检查了它们的液晶性。通过剥离层状铌酸盐K4 Nb 6 O 17的单晶并随后超声处理，获得了具有不同横向尺寸的纳米片状胶体。裸眼和显微镜观察的纳米片胶体之间的交叉偏振器揭示了液晶的溶胶，其特征在于作为横向尺寸和浓度的纳米片的函数的双折射。具有较小横向尺寸（0.15-1.9 μ m）的纳米片胶体随着胶体浓度的增加从各向同性变化到两相（各向同性+液晶），最后到完全液晶状态。相变浓度（从各向同性到双相和双相到液晶）随着纳米片的纵横比（横向厚度比）的增加而降低，几乎与Onsager理论的预测一致，表明液晶性基本上是由纳米片之间的排斥体积效应来解释的。另一方面，具有较大横向尺寸（6.2和7.8 μ m）的胶体即使在非常低的浓度（体积分数为5.1 × 10（-6））下也稳定地保持液晶状态，这远低于理论预期。
Colloidally dispersed niobate nanosheets with the thickness of 1.8 nm and controlled mean lateral sizes of 0.15-7.8 mum were prepared and their liquid crystallinity was examined. The nanosheet colloids with different lateral sizes were obtained by exfoliation of single crystals of layered niobate K4Nb6O17 and subsequent ultrasonication. Naked-eye and microscope observations of the nanosheet colloids between crossed polarizers revealed liquid crystallinity of the sols characterized by birefringence as functions of the lateral sizes and concentration of the nanosheets. The nanosheet colloids with smaller lateral sizes (0.15-1.9 mum) varied from isotropic to biphasic (isotropic + liquid crystalline), and finally to fully liquid crystalline states as the colloid concentration increased. The phase transition concentrations (from isotropic to biphasic and biphasic to liquid crystalline) decreased with increasing aspect ratio (lateral-to-thickness ratio) of the nanosheets, almost in accordance with the prediction by Onsager theory, indicating that the liquid crystallinity is explained basically by excluded-volume effect between the nanosheets. On the other hand, the colloids with larger lateral sizes (6.2 and 7.8 mum) stably kept liquid crystalline state even at very low concentration (5.1 x 10(-6) in volume fraction), which was much lower than that expected from the theory.