High density polyethylene-grafted-maleic anhydride low-k porous films prepared via thermally induced phase separation

Low dielectric constant (low-k) porous films of high density polyethylene-grafted-maleic anhydride were prepared via thermally induced phase separation (TIPS) using di-n-octyl phthalate as the solvent and methanol as the extractant. The results show that, for the process of TIPS, cellular structures of spherical pores were obtained. Lower polymer concentration and lower cooling rate induced larger pores and higher porosity. For the dielectric constant, the introduction of pores considerably reduced the dielectric constant from 2.60 to 1.56 at most. Pore size showed little effect on dielectric constant in our experiment, but porosity was found to be the key influential factor. The relationship between dielectric constant and porosity was found to be best fit to Rayleigh model.     

染料敏化太阳电池用聚合物电解质

综述了本研究小组近年来用于染料敏化太阳电池中聚合物电解质的研究概况.设计合成了几类性能优良的聚合物电解质,较好地改进了液体电解质染料敏化太阳电池(DSSC)的使用稳定性,研究结果具有实际应用的价值,并提出了此领域研究今后的发展方向.     

双峰聚合物分子刷的层化机理

建立了用于模拟双峰聚合物分子刷相结构的自洽场理论. 模拟结果表明, 良溶剂条件能够促使双峰聚合物分子刷裂分为内外两个亚分子层, 其中短链居于内分子层, 而长链伸展到外分子层. 体系溶解性的加强不仅使聚合物的密度分布逐渐趋近强分凝理论的解析结果, 而且加大了分子链的伸展和链段的局部取向程度. 分子链接枝密度的增加能够促使分子刷的层化, 并且在良溶剂区域, 不同接枝密度的分子链密度分布可以回归到同一条主线. 在良溶剂条件下, 长链的聚合度对短链的密度分布影响不大, 但能够导致长链向外分子层扩展.     

光漂白全过程中聚合物薄膜折射率和厚度的实时分析

在基于衰减全反射原理的基础上提出一种新的测量方法, 动态研究漂白动力学过程, 即利用波导的衰减全反射吸收峰对聚合物材料的折射率和厚度敏感的特性, 实时测量聚合物材料的折射率和厚度. 实验系统采用CCD摄像头将标志波导模式的一组暗线显示在计算机屏幕上, 然后根据暗线的移动, 可以精确测量每一时刻波导薄膜的折射率和膜厚. 利用这种技术, 对聚合物薄膜的光漂白过程进行了实时监控. 发现在光漂白全过程中, 聚合物薄膜的折射率和厚度的变化同时存在化学和物理两种变化过程.     

A Subtle Change in the Flexible Achiral Spacer Does Matter in Supramolecular Chirality: Two-Fold Odd-Even Effect in Polymer Assemblies

Precise control over the chirality and morphologies of polymer assemblies, a remaining challenge for both chemists and materials scientists, is receiving ever-increasing attention in the recent years. Herein, we report the subtle manipulation of the achiral spacers from the chiral stereocenter to the azobenzene (Azo) unit, of which the chiroptical consistency or chiroptical inversion of self-assemblies could be successfully controlled and present “two-fold” odd-even effect. Furthermore, morphological transitions from 0D spherical micelles, 1D worms, and nanowires to 3D vesicles, spindle- and dumbbell-shaped vesicles were also unexpectedly found to exhibit odd-even correlations. These observations were collectively elucidated by mesomorphic properties, stacking modes, chiroptical dynamics, and stimuli-responsive behaviors. Negligible modifications to the spacer structures can enable remarkable modulation of supramolecular chirality and anisotropic topologies in polymer assemblies, which is of great significance for the design of complex chiral functional polymers.     

Novel ferrocene-containing amphiphilic block copolymer nanoparticles as high-capacity charge carriers in aqueous redox flow systems

Size-exclusion polymer electrolytes are promising charge carriers to diminish the crossover and allowing commercially available low-cost porous membranes in redox flow batteries. Boosting the solubility in water and maximizing the number of redox sites to enhance the capacity of these polymeric systems is challenging. New highly water dispersed amphiphilic diblock copolymers are reported here, with an average concentration value of 1.7 10^?3 mmol of Ferrocene (Fc)-linked moieties per mg of polymer, determined by total X-ray reflection fluorescence. These redox amphiphilic block copolymers are stabilized in water as spherical nanoparticles (20 nm) by using a simple phase solvent inversion procedure. We evidence a maximum polymer dispersibility value of 6 g/L in water, for long-term stable polymer nanoparticle suspensions, yielding a theoretical capacity value of 4.78 mAh at 10.5 mM Fc. Further adjustment of the ionic conductivity and pH of these stable redox block copolymer suspensions has rendered a conductivity value of 44.5 mS/cm at pH values close to a neutral one, by adding a variety of salt supports. Studies using a 3-electrode configuration cell reveal an efficient charge transport between each of the Fc motifs in the polymer nanoparticle. A capacity value of 3.1 mAh with no transient of the polymer nanoparticles crosswise the cheap porous membrane is evidenced when cycled as polycatholyte material in a Zn hybrid aqueous redox flow battery. The particle size and electronic changes of these novel amphiphilic redox block copolymer electrolytes during consecutive redox cycles have also been monitored by dynamic light scattering and ultraviolet-visible spectroscopy, respectively. The analysis of the results enables the understanding of the main mechanisms behind their non-fully reversible capacity. Among them, aggregation and sedimentation, along with retention inside the graphite felt electrode acting the latter as a filter. These insights will aid the design of future polymer electrolyte materials and redox flow battery components with better performance and cost.     

Study of polymer-stabilised blue phase liquid crystal on a single substrate

One outstanding feature of the polymer-stabilised blue phase (PSBP) is that it is unnecessary to form an alignment film, which requires a high-temperature baking process. Therefore, PSBPs may enable flexible liquid crystal displays (LCDs) on plastic substrates. In this study, polymer stabilisation of a blue phase (BP) on a single substrate was performed without using a conventional sandwich-type cell, and the electro-optical properties are demonstrated to be similar to those of a sandwich-type PSBP LCD cell. It was experimentally shown that the oxygen which inhibits radical polymerisation is required to be excluded in order to complete the polymer stabilisation in blue phase.     

Evaluation of image sticking property on liquid crystal displays with polymer layers produced from phenanthrene-carrying monomers

As a model of polymer-sustained-alignment liquid crystal display (PSA-LCD), the liquid crystal (LC) cells having the polymer layers produced from monomers of phenanthrene (Phen)-carrying monomers, 2,7-, 3,8-, 1,8- and 3,6-dimethacryloyl-oxy-phenanthrene (DMAPhen), were prepared and investigated image sticking phenomenon with evaluations of residual direct current voltage (V_rDC) and difference in pretilt angle before and after application of alternate current voltage (Δtilt). The V_rDC values were small for the LC cells with the polymer layers produced from the Phen-carrying monomers used in this study. On the other hand, Δtilt depends on the molecular structure of the Phen-carrying monomer. The Δtilt values became small with increasing the linearity of the monomer structure for the Phen-carrying monomers. The findings would be useful for obtaining the small level of image sticking in the PSA-LCDs produced from the Phen-carrying monomers.     

Highly accurate excited-state energies from direct computation of the 2-electron reduced density matrix by the anti-Hermitian contracted Schrödinger equation

ABSTRACT

Directly solving for the 2-electron reduced density matrix (2-RDM) via the anti-Hermitian contracted Schrödinger equation (ACSE) enables computations for excited states energies without the N-electron wave function. Of particular interest are excitations and dissociation curves that exhibit strong multi-reference correlation effects. The ground and excited states of the molecules HF, H₂O, and N₂ are examined at both equilibrium and non-equilibrium geometries to compare the ability of the ACSE and widely used ab initio techniques to treat strong multi-reference electron correlation. Calculations are performed with double-ζ basis sets for calibration with full configuration interaction (FCI). Multi-reference second-order perturbation theory (MRPT2) and the ACSE both provide qualitative precision with respect to FCI data, although the ACSE's capability to include higher order correlation effects permits near-FCI accuracy for ground and excited states and excitation energies.     

Statistically and Computationally Efficient Estimating Equations for Large Spatial Datasets

For Gaussian process models, likelihood-based methods are often difficult to use with large irregularly spaced spatial datasets, because exact calculations of the likelihood for n observations require O(n³) operations and O(n²) memory. Various approximation methods have been developed to address the computational difficulties. In this article, we propose new, unbiased estimating equations (EE) based on score equation approximations that are both computationally and statistically efficient. We replace the inverse covariance matrix that appears in the score equations by a sparse matrix to approximate the quadratic forms, then set the resulting quadratic forms equal to their expected values to obtain unbiased EE. The sparse matrix is constructed by a sparse inverse Cholesky approach to approximate the inverse covariance matrix. The statistical efficiency of the resulting unbiased EE is evaluated both in theory and by numerical studies. Our methods are applied to nearly 90,000 satellite-based measurements of water vapor levels over a region in the Southeast Pacific Ocean.