The Research Of Thermotropic Liquid Crystals Built From Polyoxometalates And Simple Surfactant

By ion metathesis reactions, the dimethyldioctadecylammonium (DODA+) was used asthe surfactant to encapsulate polyoxometalates (POMs), resulting in foursurfactant-encapsulated clusters (SECs) with characteristic thermotropic liquid-crystallinebehavior. The chemical composition of the obtained SECs was determined by IR spectra,elemental analysis, TG analysis and1H NMR spectra. Also, polarized optical microscopy,differential scanning calorimetry (DSC), variable temperature X-ray Diffraction (VT-XRD)and TEM of the samples were also performed, which revealed that both SECs showthermotropic liquid crystal behavior.1.Two organic–inorganic hybrid polyoxometalates (POMs)(NH4)6{Mo2VO4[(Mo2VIO6)NH3CH2CH2CH2C(O)(PO3)2]2}10H2O (POM-1) and(NH4)8{Mo2VO4[(Mo2VIO6)CH3C(O)(PO3)2]2}14H2O (POM-2) were enwrapped bydimethyldioctadecylammonium to construct liquid crystal materials, and the chemicalformulas are as follows,[DODA]6{MoV2O4[(MoVI2O6)NH3CH2CH2CH2C(O)(PO3)2]2}16H2O （1）[DODA]8{Mov2O4[(MoVI2O6)CH3C(O)(PO3)2]2}8H2O （2）For1, According to the results of DSC, upon the second heating process, we can clearlysee two peaks corresponding to the phase transition between two kinds of solids and thetransition from solid state to liquid crystal phase, respectively. During the firrst cooling run,the phase transition between liquid crystal phase and solid state and the transition betweentwo kinds of solids can be observed. For2, during its first cooling and second heatingprocesses, we observed the transitions between the solid state and liquid ctystal phase. Theresults of VT-XRD indicates the formation of well-ordered layer structures of1and2. Thefan-shaped textures of1and2were observed from the polarized optical microscopy with ahot stage. The liquid crystal phase of1and2can be assigned to smectic A phase.2. Waugh-type and Silverton-type POMs (K3(NH4)3[MnMo9O32] and H8[CeMo12O42]) werefirstly encapsulated by simple surfactant DODA+forming the surfactant-encapsulatedcomplex (DODA)6[MnMo9O32]·16H2O (3) and (DODA)8[CeMo12O42]·9H2O (4), whichexhibited typical thermotropic liquid crystalline properties. Waugh-type and Silverton-typePOMs K3(NH4)3[MnMo9O32] and H8[CeMo12O42] contained metal centers MnO6octahedronand CeO12icosahedron as the heteroatoms instead of the typical XO4(X=P, Si, Ge, As)tetrahedron in the POM system. We observe three phase transitions of3during its firstcooling process and second heating process. For4, the phase transition between isotropic phase and liquid crystal phase and the transition from liquid crystal phase to solid state wereobserved during its first cooling process. Upon the second heating, we observe the reversibleprocess. The results of VT-XRD indicates the formation of lamellar structures of3and4. Thefan-shaped textures of1and the grain texture of2were observed from the polarized opticalmicroscopy with a hot stage. The above results confirm the smectic mesomorphic behaviorsof3and4.