Microphase coexistence in polymeric brushes

A collapse of polymeric brushes in a solvent can be induced by a change in external conditions, for example, solvent quality or its temperature. The systems with following specific interactions are considered in this paper, namely, polyelectrolyte brushes, amphiphilic brushes in a mixture of incompatible solvents, and brushes with possibility of liquid-crystalline ordering of polymer segments. For all the systems it is shown that the brush collapse can be observed under certain conditions, and it occurs through a microphase segregation. There are two microphases of different densities that coexist in the brush. The effect is caused by general properties of the swollen phase of polymeric brush and hence appears at all types of the interactions that can induce a phase transition of the brush into collapsed state.     

Properties of optically addressed liquid crystal spatial light modulators studied by mach-zehnder interferometry

In this work optically addressed liquid crystal spatial light modulators are experimentally investigated. Local reorientation of molecules in the modulator and local changes of effective refractive index n_eff (x,y) are induced by modulated light intensity I (x,y). We present preliminary results of measurements of phase shifts in optically addressed liquid crystal panels using a Mach-Zehnder interferometer. Experiments were performed for the panels filled with nematic and dye-doped nematic liquid crystals. Optical addressing was realized by Ar+ laser beam (λ = 514.5 nm) while the reading beam was supplied by He-Ne laser (632.8 nm). The operation voltage was in the range 4 - 20 V. The total phase shift under the influence of addressing light for the studied systems was 2 - 6 pagr;, sensitivity to the addressing light ∼ μW/cm² per 2π phase change and speed of response to the light was 20 ms - 30 s with total recovery time 0.5 - 120 s.     

On the Uniaxial–Biaxial Nematic Phase Transition in Liquid‐Crystalline Polymers and Elastomers

We study how the uniaxial–biaxial nematic phase transition changes its nature when going from a low‐molecular‐weight liquid crystal to a liquid‐crystalline elastomer or polymer (the latter above the Maxwell frequency) and find a qualitative change due to the presence of a coupling to the strain field in these materials. While this phase transition can be of second‐order in low‐molecular‐weight materials, as is also experimentally observed, we show here that the order of this phase transition is changed generically to no phase transition at all or to a first‐order phase transition in mean‐field approximation. We analyze the influence of an external mechanical stress field above the uniaxial–biaxial nematic phase transition and find that either biaxial nematic order is induced, which is linear or quadratic in the stress intensity, or no response to an external stress results at all, depending on the relative orientation of the applied shear with respect to the director of the uniaxial nematic phase.     

原子吸收光谱法测定铸铝铜合金拉伸断口毫克级样品中主成分

研究了铸铝铜合金拉伸断口毫克极样品中主成分铜、锰、镉的火焰原子吸收光谱法（FAAS）和钛的石墨炉原子吸收光谱法（GFAAS）。其中铜、锰、镉、钛的相对标准偏差分别为0.53%,0.79%,2.57%,5.5%。其加标回收率分别为95%,95%-97%,101%,90%。通过对铸铝铜合金拉伸断口的化学分析研究,发现铜偏析是该合金位伸断裂的主要因素。     

Computing a flattest, undercut-free parting line for a convex polyhedron, with application to mold design

A parting line for a polyhedron is a closed curve on its surface, which identifies the two halves of the polyhedron for which mold-boxes must be made. A parting line is undercut-free if the two halves that it generates do not contain facets that obstruct the de-molding of the polyhedron. Computing an undercut-free parting line that is as “flat” as possible is an important problem in mold design. In this paper, algorithms are presented to compute such a parting line for a convex polyhedron, based on different flatness criteria.     

LCP aromatic polyesters by esterolysis melt polymerization

Polyarylates have previously been synthesized from acetate esters via esterolysis (loss of methyl acetate). This polycondensation can be extended to p‐substituted aromatic monomers for liquid crystal polyesters (LCPs). For AB‐type polymers, methyl p‐acetoxybenzoate and methyl 6‐acetoxynaphthoate were copolymerized to an LCP with reasonable molecular weights. Benzoate esters, methyl 4‐benzoyloxybenzoate (MBB) and methyl 6‐benzoyloxy‐2‐naphthoate (MBN), are also investigated. Several tin and antimony oxide catalysts were effective. The rate of esterolysis polymerization of MBB and MBN is slower than that of the corresponding acidolysis melt polymerization, but fast enough to give relatively high‐molecular‐weight polymers and similar thermal stability as commercial LCP prepared by acidolysis. Using these alternative benzoyloxy groups significantly reduced the color problem, because ketene loss cannot occur. Esterolysis melt polymerizations leading to AB/AABB‐type LCPs were performed using either dimethyl 2,6‐naphthalene dicarboxylate (DMND) or dimethyl terephthalate (DMT) with methyl 4‐acetoxybenzoate and phenylhydroquinone diacetate with tin and antimony catalysts. DMT‐based monomer compositions show much faster polymerization than DMND‐based compositions using antimony oxide catalyst. All these LCPs show a T_g in the 140–170 °C range as a result of the inclusion of the naphthalene and/or phenyl hydroquinone units in the polymer chain. Compositions completely off‐balanced on either side still lead to relatively high‐molecular‐weight copolyesters because either excess monomer can be removed during polymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3586–3595, 2000     

High-gain W-band-printed antenna on flexible substrate

This article demonstrates a novel type of series-fed planar antenna array for a W-band (70 GHz) application. The proposed architecture is a 5-element antenna array with 10 numbers of gap-coupled parasitic patches in microstrip configuration over a thin, flexible and bio-compatible substrate named LCP (liquid crystal polymer). A detailed design methodology with all fabrication constraints has been elaborated on here. Full wave analysis of the whole structure has been carried out in the FEM-based 3D electromagnetic (EM) solver ANSYS HFSS Suite V.19.2. Parametric simulations were studied to achieve the optimized values of all design parameters. Further, an empirical electrical equivalent circuit model is proposed for the antenna array, and it was validated with the simulation results obtained from the FEM solver. Two prototypes have been fabricated, and measurements were carried out to fetch all the designed antenna parameters. The proto version of the antenna offers peak directive gain of about 19 dBi with better than 22 dB of return loss and 80% radiation efficiency for the frequency range of 67–85 GHz. Experimental and simulated results closely match each other. Small deviations are attributed to practical imperfections incurred by fabrication tolerances, measurement inaccuracies, testing, assembly-related issues and so forth. Finally, the current research work is compared with the recently reported literature.     

Synthesis and chiroptical properties of optically active polymer liquid crystals containing azobenzene chromophores

A series of optically active methacrylic homopolymers, poly[(4‐{4′‐[(S)‐2‐methyl‐1‐butyloxycarbonyl]phenylazo}phenoxyl)x‐methylene methacrylate] (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, ¹H NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260–360 nm) of azobenzene chromophores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3210–3219, 2006     

Linear and A2+B3‐type hyperbranched polyesters comprising phenylbenzothiazole unit: Preparation,liquid crystalline,and optical properties

Novel liquid crystalline (LC) hyperbranched (HB) polyesters comprising phenylbenzothiazole (PBT) unit as mesogen in the interiors were prepared at various feed mole ratios (A₂/B₃) by solution polycondensation of a dioxydiundecanol derivative of PBT (A₂ monomer) with trimesic acid trimethyl ester (B₃ monomer) via A₂+B₃ approach and their LC and optical properties were investigated. Analogous linear polyesters containing the PBT unit in the main chains were also prepared by the solution polycondensation of A₂ monomer with aromatic or aliphatic dimethyl esters. FTIR and ¹H‐NMR spectroscopies indicated that the HB polyesters are produced without gelation during the polycondensation and have degree of branching (DB) of 7–46%. The structures of HB polymers changed depending on the feed mole ratios and the polymer prepared in the mole ratio of A₂/B₃ = 3/2 had the highest inherent viscosity and DB. Acetylation of terminal OH group‐having HB polyesters prepared in excess mole ratios of A₂/B₃ afforded ones bearing acetoxy groups in the terminals. DSC measurements, polarizing microscope observations of textures, and X‐ray analyses suggested that only the terminal OH group‐having HB polymer prepared in the mole ratio of A₂/B₃ = 3/1 form smectic C phase. In the linear polymers, the polymers derived by using the aromatic dimethyl esters had no LC melt, but those from the aliphatic dimethyl esters formed LC smectic C phase. The acetoxy group‐bearing HB polymers showed more stable smectic A or C phase than those with the OH terminals. Solution UV‐vis and photoluminescent (PL) spectra indicated that the linear and the HB polymers have analogous optical properties and display maximum absorbances and blue‐light emission on the basis of the PBT unit, where the Stokes shifts were observed because of intermolecular aggregation effects, but there is a large difference between the optical behaviors of the linear and the HB polymers in film, whose E_g values of the linear polymers decreased and those of the HB polymers vice versa. Quantum efficiencies (Φ) had a tendency of increase in the linear polymers and the HB polymers forming LC phases. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6688–6702, 2008     

Preparation and characterization of nematic polyazomethine/single‐walled carbon nanotube composites prepared by in situ polymerization

The synthesis and characterization of a series of nematic SWNT‐polyazomethine composites are described. The composites were prepared by in situ polymerization in the presence of 1 wt % of chemically modified SWNTs in such a way that they were either dispersed or covalently bonded to the polymeric matrix. The presence of the SWNTs did not alter the thermal behavior of the polymer matrix and, therefore, highly oriented fibers could be melt‐extruded from the composites at moderate temperatures, as revealed by structural and morphological studies. Preliminary tests on tensile properties indicate that strength and stiffness were improved when compared with fibers without CNTs, particularly when SWNTs were covalently bonded to the polymeric matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2361–2372, 2009