Nakato Teruyuki, Watanabe Tsuyoshi, Harada Takumi, Shintaku Mahito, Mouri Emiko, Tani Seiji, Suzuki Yasutaka, Miyata Hirokatsu, Breu Josef, Kawamata Jun
Department of Applied Chemistry, Kyushu Institute of Technology, Fukuoka 804-8550, Japan.
Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8512, Japan.
Langmuir. 2024 Aug 12;40(34):18297-304. doi: 10.1021/acs.langmuir.4c02246.
Colloidal clay nanosheets obtained by the delamination of layered crystals of smectite-type clay minerals in water form liquid crystals because of their shape anisotropy. Loading of organic dyes onto the liquid crystalline clay nanosheets will enable novel photonic materials, where photofunctions of the loaded dye are controlled by the liquid crystallinity of the clay nanosheets. However, adsorption of organic dyes onto the nanosheets renders the nanosheet surfaces hydrophobic, and consequently, colloidal stability of the nanosheets is lost. In this study, this drawback is overcome by sandwiching cationic stilbazolium dyes between a pair of synthetic fluorohectorite nanosheets. This is realized by the preparation of stilbazolium-clay second-stage intercalation compounds characterized by intercalation of dye cations into every other interlayer space of the hectorite clay, where nonintercalated interlayer spaces are occupied by Na ions. The second-stage intercalation compounds are obtained by partial ion exchange of mother clay mineral incorporating Na ions in all of the interlayer spaces and delaminated from the Na-containing interlayer spaces to form clay nanosheets sandwiching the dye molecules. Aqueous colloids of the dye-sandwiching clay nanosheets form colloidal liquid crystals, and the dye-sandwiching liquid crystalline clay nanosheets respond to an applied AC electric field to be aligned parallel to the electric field. The assembled structure of the dye-sandwiching clay nanosheets under the electric field is characterized by aligned discrete clay platelets, which is somewhat different from that of a colloidal liquid crystal of clay nanosheets without dye loading characterized by macroscopic liquid crystalline domains up to submillimeters. The electric alignment of the clay nanosheets induces alteration of light absorption of the sandwiched stilbazolium molecules, which verifies a strategy of constructing stimuli-responsive photonic materials of clay-organic hybrids.
通过在水中对蒙脱石型粘土矿物的层状晶体进行剥离而获得的胶体粘土纳米片，由于其形状各向异性而形成液晶。将有机染料负载到液晶粘土纳米片上可制备新型光子材料，其中负载染料的光功能由粘土纳米片的液晶性控制。然而，有机染料在纳米片上的吸附使纳米片表面具有疏水性，因此，纳米片的胶体稳定性丧失。在本研究中，通过将阳离子二苯乙烯基苯并噻唑染料夹在一对合成氟锂蒙脱石纳米片之间克服了这一缺点。这是通过制备二苯乙烯基苯并噻唑-粘土二级插层化合物来实现的，其特征在于染料阳离子插入锂蒙脱石粘土的每隔一层的层间空间，其中未插层的层间空间被钠离子占据。二级插层化合物是通过对在所有层间空间中都含有钠离子的母粘土矿物进行部分离子交换，并从含钠的层间空间中剥离形成夹着染料分子的粘土纳米片而获得的。夹有染料的粘土纳米片的水胶体形成胶体液晶，并且夹有染料的液晶粘土纳米片响应施加的交流电场而平行于电场排列。电场作用下夹有染料的粘土纳米片的组装结构的特征是离散的粘土薄片排列，这与未负载染料的粘土纳米片的胶体液晶有所不同，后者的特征是具有高达亚毫米级的宏观液晶域。粘土纳米片的电场排列导致夹在其中的二苯乙烯基苯并噻唑分子的光吸收发生变化，这验证了构建粘土-有机杂化的刺激响应光子材料的策略。
