Self-Assembly of Rod-Terminally Tethered Three-Armed Star-Shaped Coil Block Copolymer: Investigation of the Presence of the Branching in the Coil to the Self-Assembled Behavior

Self-assembled behavior of rod-terminally tethered three-armed star-shaped coil block copolymer melts was studied by applying self-consistent-field lattice techniques in three-dimensional (3D) space. Similar to rod-coil diblock copolymers, five morphologies were observed, i.e., lamellar, perforated lamellar, gyroidlike, cylindrical and sphericallike structures, while the distribution of the morphologies in the phase diagram was dramatically changed with respect to that Of rod-coil diblock copolymers.

AFM study of the self-assembly behavior of hexa-armed star polymers with a discotic triphenylene core

The size-armed polystyrenes and poly-(methyl methacrylate)s with a triphenylene core showed different self-assembling patterns, isolated cylinders for polySt on mico and highly ordered cylindrical pores for polyMMA on a silicon water. With a decrease of polymer concentration in tetrahydrofuran (HHF), the size and height of cylinders decreased for polySt, but fur polyMMA, the size and depth of the cylindrical pores increased. Slow evaporation of the solvent and a low molecular weight favored the formation of regular patterns.

Pulse self-compression in normally dispersive bulk media

We experimentally demonstrate that high-power femtosecond pulses can be compressed during the nonlinear propagation in the normally dispersive solid bulk medium. The self-compression behavior was detailedly investigated under a variety of experimental conditions, and the temporal and spectral characteristics of resulted pulses were found to be significantly affected by the input pulse intensity, with higher intensity corresponding to shorter compressed pulses. By passing through a piece of BK7 glass, a self-compression from 50 to 20 fs was achieved, with a compression factor of about 2.5. However, the output pulse was observed to be split into two peaks when the input intensity is high enough to generate supercontinuum and conical emission. (c) 2005 Elsevier B.V. All rights reserved.

Self-assembly of rod-coil-rod ABA-type triblock copolymers

Self-assembled behavior of symmetric ABA rod-coil-rod triblock copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. The phase diagram is constructed to understand the effects of the chain architecture on the self-assembled behavior. Four stable structures are observed for the ABA rod-coil-rod triblock, i.e., spherelike, lamellar, gyroidlike, and cylindrical structures. Different from AB rod-coil diblock and BAB coil-rod-coil triblock copolymers, the lamellar structure observed in ABA rod-coil-rod triblock copolymer melts is not stable for high volume fraction of the rod component (f(rod)=0.8), which is attributed to the intramolecular interactions between the two rod blocks of the polymer chain.

Self-assembly of T-shaped rod-coil block copolymer melts

Self-assembled behavior of T-shaped rod-coil block copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. Compared with rod-coil diblock copolymers with the anchor point positioned at one end, the copolymers with the anchor point at the middle of the rod exhibit significantly different phase behaviors. When the rod volume fraction is low, the steric hindrance of the lateral coils prevents the rods stacking into strip or micelle as that in rod-coil diblock copolymers. The competition between interfacial energy and entropy results in the formation of lamellar structures and the increasing thickness of the lamellar layer with increasing rod volume fraction.

Preparation and layer-by-layer self-assembly of positively charged multiwall carbon nanotubes

The report described a method of more stably dispersing oxidized carbon nanotubes (CNTs) by forming complex with polycation and the layer-by-layer self-assembly behavior of the complex with polyanion was studied. The properties of the self-assembled multilayer film containing carbon nanotubes were studied. Cyclic voltammetry, UV-vis-NIR spectroscopy, electrochemical impedance spectroscopy and scanning electron microscopy were used for characterization of film assembly. UV-vis-NIR spectroscopy and cyclic voltammetry study indicated the uniform growth of the film. Electrochemical impedance spectroscopy results showed that incorporating of carbon nanotubes in the polyelectrolyte multilayers; decreased in the electron-transfer resistance R, indicating more favorable electrochemical reaction interface. The electrocatalytic property of the multilayer modified electrode to NADH was investigated mainly with different numbers of the bilayers; and the results showed that along with the increase of the assembled bilayers the overpotential of NADH oxidation decreased. The detection lit-nit Could reach 6 mu M at a detection potential of 0.4 V.

Self-assembled monolayers of novel surface-bound dendrons: Peripheral structure determines surface organization

The synthetic and functional versatility of dendrimers and their well-defined shapes make them attractive molecules for surface modification. We synthesized six structurally very similar surface-bound dendrons and used them as building blocks for the preparation of self-assembled monolayers (SAMs) on a gold surface. We studied the effects of the surface-bound dendron's main structure, peripheral substituents, and the coadsorption process on its self-assembling behavior. Using scanning tunneling microscopy (STM), we observed nanostripes for SAMs of the surface-bound dendron consisting of symmetrical benzene rings. When we changed the symmetrical dendron's structure slightly, by increasing or decreasing the numbers of benzene rings at one wedge, we found no ordered structures were formed by the asymmetrical dendrons. We also introduced two kinds of substituents, heptane chains and oligo(ethylene oxide) chains, to the symmetrical dendron's periphery. Heptane chains appear to enhance the interaction between symmetrical backbones, leading to the formation of stripes, while oligo(ethylene oxide) chains appear to weaken the interaction between symmetrical backbones, resulting in a homogeneous structure. Dendrons with both heptane and oligo(ethylene oxide) chains exhibit nanophase separation in a confined state, leading to the formation of a honeycomb structure.

Preparation and characterization of self-assembled monolayers of trichlorogermanyl propanoic acid and its derivatives

Self-assembled monolayers(SAMs) of trichlorogermanyl propanoic acid derivatives on hydroxylated silicon substrates are prepared for the first time. Contact angle measurement, ellipsometry and X-ray photoelectron spectrometry(XPS) are used to characterize these SAMs, It is demonstrated that a quasi-2D network is formed on the surface of the substrate after molecules adsorbed on it. The molecular chains have certain tilt angles to the substrate surface, The wettabilities of the SAMs are various,because the molecules adsorbed and liquids used in the experiments are different. It can be concluded that trichlorogermanes have similar self-assembly behavior as trichlorosilanes, Four SAMs are studied together: they are acid, ethyl, butyl and hexyl surfaces whose results are of good consistency.

飞秒激光脉冲在正色散固体材料中的自压缩

实验研究了正色散固体介质中的激光脉冲自压缩现象，证明了无需任何外加色散补偿情况下，固体透明介质中的自聚焦传输过程可使高功率飞秒激光脉冲实现时域脉冲压缩，并详细研究了输出脉冲的时域和频域特性随入射脉冲强度的演化规律．实验结果表明脉冲自压缩量随入射脉冲强度的增加呈递增趋势，然而当入射光强增大到足以引起超连续谱及锥形辐射产生时，脉冲时域形状会发生分裂．此外还发现发散光束入射情况下同样可以观察到脉冲自压缩现象．

SrF2 hierarchical flowerlike structures: Solvothermal synthesis, formation mechanism, and optical properties

We present a solvothermal route to the synthesis of SrF2 hierarchical flowerlike structures based on thermal decomposition of single source precursor (SSP) of strontium trifluoroacetate in benzylamine solvent. These flowerlike superstructures are actually composed of numerous aggregated nanoplates, and the growth process involves the initial formation of spherical nanoparticles and subsequent transformation into nanoplates. which aggregated together to form microdisks and finally flowerlike superstructures. The results demonstrate the important role of benzylamine in the formation of well-defined SrF2 superstructures, not only providing size and shape control to form nanoplates but also contributing to the self-assembly behavior of nanoplates to build into flower-like superstructures. Additionally, the photoluminescence properties of the obtained SrF2 superstructures are studied.

Vesicles Formed by Oligostyrene-block-Oligoaniline-block-Oligostyrene Triblock Oligomer

Novel pi-conjugated coil-rod-coil triblock oligomers containing optoelectronic active oligoaniline segments were synthesized. The block oligomer can self-assemble into diverse aggregating morphologies including spherical micelles and thin-layer vesicles in THF, which is found associated with the removing of the protecting groups of oligoaniline segments. A possible mechanism was proposed to explain the self-assembly behavior changes in which chain conformation variation of the aniline segments initiated from deprotection of the nitrogen atoms is pointed to be the key factor that dominates the transition process.

Theoretical study on the mechanism for the addition reaction of SiH3 with propylene and acetic acid

To explore the reactivities of alkene (-CH=CH2) and carboxy (-COOH) group with H-Si under UV irradiation, the addition mechanism for the reactions of SiH3 radical with propylene and acetic acid was studied by using the B3LYP/6-311++ G(d,p) method. Based on the surface energy profiles, the dominant reaction pathways can be established; i.e., SiH3 adds to the terminal carbon atom of the alkene (-CH=CH2) to form an anti-Markovnikov addition product, or adds to the oxygen atom of the carboxy group (-COOH) to form silyl acetate (CH3-COOSiH3). Because the barrier in the reaction of the carboxy group (39.9 kJ/ mol) is much larger than that of alkene (11.97 kJ/mol), we conclude that the reaction of bifunctional molecules (e.g., omega-alkenoic acid) with H-Si under irradiation condition is highly selective; i.e., the alkene group (-CH= CH2) reacts with SiH3 substantially faster than the carboxyl group (-COOH), which agrees well with the experimental results. This provides the possibility of preparing carboxy-terminated monolayers on silicon surface from omega-alkenoic acids via direct photochemical reaction.

基于循环抑制CPG模型的蛇形机器人控制器

依据生物利用中央模式发生器(Central pattern generator,CPG)的自激行为产生有节律的协调运动适应多种环境,基于循环抑制CPG建模理论设计了蛇形机器人CPG控制器模型,分析了单个神经元、循环抑制CPG以及该控制器模型的稳定性,并把该控制器应用到一个结合蛇形机器人“勘查者-Ⅰ”动力学特性的仿真模型,得到了实现蜿蜒运动的CPG控制器参数,进而研究了调节S波个数、身体构形曲率、蜿蜒运动速度以及运动轨迹曲率的CPG控制器参数设定策略。此外,“勘查者-Ⅰ”应用该CPG控制器的输出成功实现了蜿蜒运动。该研究结果为设计人工CPG控制器提供了一个可行的方法。