SALS,WAXS and mechanical properties of heat‐treated thermotropic polymers

The influence of heat treatment on the texture, microstructure and tensile mechanical properties of extruded thin films of a series of high‐performance thermotropic liquid crystal polymers (LCPs) was investigated. LCPs based on random units of hydroxybenzoic acid (B), hydroxynaphthoic acid (N), terephthalic acid (TA) and biphenol (BP) were kindly supplied by the former Hoechst Celanese Corp as 50 µm thick extruded tapes. The LCPs, denoted B‐N, COTBP and RD1000, have B and N as common comonomers and vary the other comonomers. Thus, this study also enables the investigation of the influence of monomer composition on microstructure and mechanical properties. Heat treatments were carried out at temperatures close to the solid‐to‐nematic transition (T_s→n) for periods up to 5 h, under dry air conditions. The thermal treatment produced either two endotherms or a small increase of T_s→n (B‐N and RD1000), or increased significantly T_s→n (COTBP). Moreover, when heat treatment was carried out approximately 40°C below the respective T_s→n, the mechanical Young's modulus, E, along the extrusion axis, increased for all LCPs. Strikingly, for COTBP, E increased over 100% relative to the as‐extruded film. The results also showed that the optimum treatment time for improving the Young modulus, under dry air atmosphere, was between 3 and 4 h. Wide‐angle X‐ray scattering showed a significant sharpening of crystalline reflections and concentration of the 002 meridional reflection as a result of thermal treatment, suggesting the elimination of defects and a better alignment of the molecular chains along the extrusion axis. This would explain the increase in tensile modulus. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

大豆油煎炸过程理化指标与LF-NMR弛豫特性的相关性研究

在对大豆油无料/薯条煎炸过程[温度:(180±5)℃,持续36 h]中的酸价(AV)、粘度(V)、吸光值(A)及总极性化合物(TPC)含量等及低场核磁共振(LF-NMR)弛豫特性(峰起始时间T21、T22、T23、相应的峰面积比例S21、S22、S23、单组份弛豫时间T2W)变化规律研究的基础上,利用多元回归分析建立了理化指标与其LF-NMR检测结果的相关性模型,并进行验证。结果表明:大豆油的酸价、TPC含量及S21峰面积均随煎炸时间的延长而线性增大,T21、T22峰起始时间及T2W则随煎炸时间的延长而线性减小(r2>0.90),粘度、吸光值随煎炸时间的延长逐渐增加并符合二项式关系(r2>0.90),而T23峰起始时间及S22、S23与煎炸时间之间无明显规律性变化。煎炸薯条后,油样的酸价、粘度、TPC含量、吸光值及S21均较无料煎炸显著增大(P<0.05),而T21、T22峰起始时间及T2W显著缩短。多元回归分析表明,酸价及TPC含量与T2W、T21,粘度与T2W,吸光值与S21间均可建立良好的相关性模型(R2>0.93)。模型验证合理可靠,可通过油样的LF-NMR检测结果有效预测其理化指标的变化。     

Performance of density functional theory in computing nonresonant vibrational (hyper)polarizabilities

A set of exchange‐correlation functionals, including BLYP, PBE0, B3LYP, BHandHLYP, CAM‐B3LYP, LC‐BLYP, and HSE, has been used to determine static and dynamic nonresonant (nuclear relaxation) vibrational (hyper)polarizabilities for a series of all‐trans polymethineimine (PMI) oligomers containing up to eight monomer units. These functionals are assessed against reference values obtained using the Møller–Plesset second‐order perturbation theory (MP2) and CCSD methods. For the smallest oligomer, CCSD(T) calculations confirm the choice of MP2 and CCSD as appropriate for assessing the density functionals. By and large, CAM‐B3LYP is the most successful, because it is best for the nuclear relaxation contribution to the static linear polarizability, intensity‐dependent refractive index second hyperpolarizability, static second hyperpolarizability, and is close to the best for the electro‐optical Pockels effect first hyperpolarizability. However, none of the functionals perform satisfactorily for all the vibrational (hyper)polarizabilities studied. In fact, in the case of electric field‐induced second harmonic generation all of them, as well as the Hartree–Fock approximation, yield the wrong sign. We have also found that the Pople 6–31+G(d) basis set is unreliable for computing nuclear relaxation (hyper)polarizabilities of PMI oligomers due to the spurious prediction of a nonplanar equilibrium geometry. © 2013 Wiley Periodicals, Inc.     

Skin Constituents as Cosmetic Ingredients. Part II: A Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Dynamic Mode

This work aims at presenting the viscoelastic behavior of bio‐mimetic monoglycerides used as emulsifier in a mixture made of two non‐miscible liquids, squalene and water. The measurement of the interfacial tension, carried out by the “pendant drop” method in “dynamic” mode, made it possible to characterize these amphiphilic molecules according to the value of their elastic modulus, ?, as well as their relaxation time, τ_R.

The analysis of these parameters, as well as those developed in the previous publication [L. Blasco et al. (2006) Skin constituents as cosmetic ingredients. Part I: A Study of bio‐mimetic monoglyceride behavior at the squalene‐water interface by the “pendant drop” method in a static mode. J. Dispers. Sci. Technol., 27(6).] shows that the hydrocarbon chain structure, such as its length, the presence of one or more unsaturations, hydroxyl function, affects the behavior of surfactant molecules at the squalene/water interface.     

Laterally dibenzyloxy-branched nematogens with large nematic range and rich solid polymorphism

Mesogenic compounds containing four rings in the core usually have very high melting points. However, when two identical lateral benzyloxy groups are introduced on the same side of one of the central rings, the melting point is lowered dramatically and a large nematic range is retained. This range is affected by the bulkiness of the para-substituents in the lateral rings. Methyl groups can be introduced in the ortho- or meta-positions with a consequent decrease in the melting temperature without much affecting the nematic range. These compounds exhibit a rich solid polymorphism which is certainly related to the effect of the conformations of the lateral substituent on the molecular arrangment in the solid phase. Some preliminary NMR experiments on the nematic phase indicate that the molecular long axis coincides with the core axis, whereas the para-axis of the lateral fragment makes an angle close to the magic angle with respect to the molecular long axis.     

Dielectric behaviour of binary dual-frequency nematics with low crossover frequencies

Binary dual-frequency nematic liquid crystals synthesised at the Military University of Technology were measured by dielectric means. All the investigated materials exhibit low crossover frequency. They were composed of only two molecules with longitudinal and transverse dipole moments. The main difference is the molecular weight of the molecules. Results of relaxation parameters of detected mode and crossover frequency are shown. The influence of structure on ion conductivity is discussed. The broad phase transition from an isotropic phase to a nematic one was observed.