We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.
The purpose of the present paper is twofold. First, the projective Riccati equations (PREs for short) are resolved by means of a linearized theorem, which was known in the literature. Based on the signs and values of coeffcients of PREs, the solutions with two arbitrary parameters of PREs can be expressed by the hyperbolic functions, the trigonometric functions, and the rational functions respectively, at the same time the relation between the components of each solution to PREs is also implemented. Second, more new travelling wave solutions for some nonlinear PDEs, such as the Burgers equation, the mKdV equation, the NLS^+ equation, new Hamilton amplitude equation, and so on, are obtained by using Sub-ODE method, in which PREs are taken as the Sub-ODEs. The key idea of this method is that the travelling wave solutions of nonlinear PDE can be expressed by a polynomial in two variables, which are the components of each solution to PREs, provided that the homogeneous balance between the higher order derivatives and nonlinear terms in the equation is considered. 相似文献
In a series of poly[di(alkyl) vinylterephthalates] (PDAVTs) synthesized via radical polymerization, fine-tuning the size and shape of the side groups manipulated the supramolecular self-assembly and led to control over the formations between amorphous and 2D ordered hexagonal phases. To introduce the 2D long-range ordered structure, the size of the ester side groups at the 2- and 5-positions of the phenyl rings laterally attached to the backbones had to be in the range of propyl/isopropyl to hexyl. The relatively extended backbones observed in these polymers were attributed to steric effects from the side groups. When the n-alkyl groups were larger than hexyl, the ability to form the liquid crystalline phase gradually decreased. A completely disordered phase could be observed by substituting dodecyl groups as side groups. 相似文献
Spherical micelles of a polystyrene-b-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer with the number-average molecular weight of 193 000 g/mol for PS and 39 000 g/mol for PDMS were obtained by using n-dodecane or n-octane as the selective solvent for the PDMS block. The drying process of micelle solution drops with relatively high polymer concentration on solid substrates and the resultant drying patterns were studied using optical microscopy and atomic force microscopy. The drying drops exhibited an inner solution "cap" connecting with an outer gelled "foot" through a transition zone. A crust was first formed on the surface of the transition zone and remained on the top of the foot region. An inhomogeneous stress perpendicular to the radial direction within the crust, which was due to the solvent evaporation accompanied by the receding of the solution cap, induced regular 45 degrees -tilted stripes (pleats) in the transition zone and main radial cracks in the foot region. The stripes and cracks have periods of a few and tens of microns, respectively. Concave micelle "bricks" were also observed between cracks. In addition to micelle close packing, these patterns demonstrate that drying micelle solution drops may provide a potential means to manipulate fine and multiscale structures for technological applications. 相似文献
The bounded and smooth solitary wave solutions of 10 nonlinear evolution equations with a positive fractional power term of dependent variable are successfully obtained by homogeneous balance principle and with the aid of sub-ODEs that admits a solution of sech-power or tanh-power type. In the special cases that the fractional power equals to 1 and 2, the solitary wave solutions of more than 10 important model equations arisen from mathematical physics are easily rediscovered. 相似文献
Recently, polymer crystallization in ultrathin films (thickness less than 100 nm) on solid substrates has attracted increased attention. As it can be considered to be a quasi-two-dimensional (2D) system with one-dimensional (1D) confinement along the substrate normal, ultrathin polymer film offers unique possibilities for testing the theories of crystallization and for studying the effects of confinement and interface which may invoke new mechanisms other than those applied in bulk crystallization of polymers. In this article, we will summarize the important results of ultrathin film crystallization of polymers obtained in the past decades. The morphologies, the crystallization kinetics, and the transformation between monolayer crystals with various metastabilities are reviewed in depth, with an attempt at discussing the ultrathin polymer film crystallization in the general framework of thermodynamics and kinetics of crystallization. 相似文献
Using poly(5-{[(4'-heptoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne) as an example, we demonstrate the incorporative accommodation of the rigid polyacetylene backbones and the mesogenic pendants, which leads to a highly ordered smectic (Sm) phase with a frustrated structure. The polymer exhibits a recognizable sheetlike molecular shape due to its rigid backbone and relatively short spacer (three methylene units), and the building block of the liquid crystalline (LC) phase is the whole molecule. In the LC phase, five layers of the molecules stack as a smectic A (SmA) block, and adjacent SmA blocks glide halfway of the molecular width from one to another. In scanning tunneling microscopy (STM) experiments, the STM tip scrape is found to generate a regular nanopattern with periodic electron conductivity, of which the spacing is determined by the side-chain length. 相似文献