Browsing by Author "Lee, Ming-Tao"

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Shape and Confinement Effects of Various Terminal Siloxane Groups on Supramolecular Interactions of Hydrogen-Bonded Bent-Core Liquid Crystals
(2015-07-14)
Chiang, I-Hung
;
Chuang, Wei-Tsung
;
Lu, Chia-Lin
;
Lee, Ming-Tao
;
Lin, Hong-Cheu
To investigate the shape and confinement effects of the terminal siloxane groups on the self-assembled behavior of molecular arrangements in hydrogen-bonded (H-bonded) bent-core complexes, four H-bonded bent-core complexes Si, P1, C4, and P8 with string-, ring-, and cagelike siloxane termini (i.e., linear siloxane unit -Si-O-Si-O-Si, cyclic siloxane unit (Si-O)(4), and silsesquioxane unit PUSS, respectively) were synthesized and investigated. By X-ray diffraction measurements, different types of SmCG (B8) phases and leaning angles were controlled by the shape effect of the string- and cage-like siloxane termini for Si and P1 (with only one arm of H-bonded bent-core), respectively. In addition, the confinement effect of Pi, C4, and P8 (accompanied by increasing the numbers of attached H-bonded bent-core arms) resulted in higher transition temperatures and the diminishing of mesophasic ranges (even the disappearance of mesophase in P8). Moreover, AFM images showed the bilayer smectic CG phases of Si and P1 were aligned to reveal highly ordered thread-like structures by a DC field. By spontaneous polarization measurements within the mesophasic ranges, Si and P1 showed ferroelectric transitions but C4 displayed antiferroelectricity. Finally, the electro-optical performance of B8 phases could be optimized through binary mixtures of Si and P1, and a well aligned modulated ribbon phase could be formed via specific molar ratios of the binary mixtures.
Using in-situ synchrotron x-ray diffraction to investigate phase transformation and lattice relaxation of a three-way piezo-phototronic soft material
(2017-07-01)
Ko, Wen-Ching
;
Hsu, Yu-Hsiang
;
Weng, Shih-Chang
;
Chang, Chung-Kai
;
Lee, Ming-Tao
A poly(vinylidene fluoride-co-trifluoro-ethylene) piezoelectric polymer is blended with nano particles of titanium oxide phthalocyanine to bridge photoconductive and piezoelectric effects. In this study, a system is examined by in situ synchrotron x-ray to test a three-way piezo-phototronic soft-material design. The sample is heated for in situ phase transformation characterization. The semi-crystalline poly (vinylidene fluoride-co-trifluoro-ethylene) polymer gradually transforms to an amorphous structure. A complementary piezoelectric experiment before and after the heating experiment shows that the piezoelectric performance is proportional to the phase ratio. Secondly, the system is examined to test its phototronic effect. Piezoelectric responses are measured by controlling the light illumination. The positive and negative controls of light illumination which validate this newly-designed system can be modulated by a three-way piezo-phototronic effect. In-situ synchrotron x-ray diffraction experiments are employed to measure the microstructure evolution as a function of applied voltage up to 800 V. We then turned off both the light and the applied voltage to examine the kinetic behavior of the system. There is orientation-dependent anisotropic relaxation. We compared the lattice-strain evolutions. Piezo-phototronic creep is found in the (110), but not the (310) planes.