Computational analysis of smart soft hydrogels subjected to pH-electrical coupled stimuli: Effects of initial geometry

A chemo-electro-mechanical formulation, referred to as the multi-effect-coupling pH-stimulus (MECpH) model, is presented in this paper for the analysis of the effects of the initial geometrical size on the responsive behavior of pH-sensitive hydrogels subject to the coupled stimuli of environmental solution pH and externally applied electric voltage. The model is composed of coupled nonlinear partial differential equations, and it accounts for the diffusion of ionic species, distributive electric potential and large mechanical deformation. In addition, the correlation between the diffusive hydrogen ion within the hydrogel and charge groups fixed to the polymeric network chains is incorporated quantitatively into this MECpH model. For the simulation of the response characteristics of the smart hydrogel, we solve the one-dimensional steady-state problem using the Hermite–Cloud meshless technique. For the MECpH model, the present numerical simulations were compared with experimental data available from literature to validate the accuracy and robustness of the model, and good agreement was observed. Several parameter studies were then carried out in the analysis of the hydrogel swelling when immersed in solution, and it was observed that the initial geometrical size has significant influence on the volume variations of these pH-responsive hydrogels.     

Numerical study of surface agglomeration of ultraviolet-polymeric ink and its control during 3D nano-inkjet printing process

There is a pressing need in very small scale three-dimensional (3D) inkjet printing to control and reduce agglomeration, as agglomeration often leads to nozzle clogging. While agglomeration within ultraviolet ink has been studied, there has been, to our knowledge, no extensive studies conducted for surface agglomeration of the ink on nozzle's wall. This numerical study therefore focuses on investigating if surfactants can effectively control surface agglomeration during nanodroplet formation. Many-body dissipative particle dynamics is the numerical method of choice here. We found that small amount of surfactant of about 1 wt % is sufficient to effectively reduce ink deposition on the nozzle's wall. However, by using the properties of a commercially available surfactant, sodium dodecyl sulfate, it was found that the maximum reduction achieved by its addition is only 60%. Thus, further physical or chemical deagglomeration techniques are required, and we show that by considering these other techniques, reduction of surface agglomeration to nearly 92% can be achieved. Finally, we found that adding surfactants has the additional benefit of improving total kinetic energy of the ink compositions, lowering possibility of agglomerations within the ink. It also raises the nanodroplet velocity while reducing nanodroplet breakup time, which can help speed up the process of 3D printing process. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1615–1624     

Quantifiable correlation of ToF-SIMS and XPS data from polymer surfaces with controlled amino acid and peptide content

Peptide-coated surfaces are widely employed in biomaterial design, but quantifiable correlation between surface composition and biological response is challenging due to, for example, instrumental limitations, a lack of suitable model surfaces or limitations in quantitatively correlating data from different surface analytical techniques. Here, we first establish a reference material that allows control over amino acid content. Reversible addition-fragmentation chain-transfer (RAFT) polymerisation is used to prepare a copolymer containing alkyne and furan units with well-defined chain length and composition. Huisgen Cu(I)-catalysed azide-alkyne cycloaddition reaction is used to attach the model azido-polyethyleneglycol-amide-modified pentafluoro-l -phenylalanine to the polymer. Different compositional ratios of the polymer provide a surface with varying amino acid content that is analysed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Nitrogen-related signals are compared with fluorine signals from both techniques. Fluorine and nitrogen signals from both techniques are found to be related to the copolymer compositions, but the homopolymer data deviate from this trend. The approach is then translated to a heparin-binding peptide that supports cell adhesion. Human embryonic stem cells cultured on copolymer surfaces presenting different amounts of heparin-binding peptide show strong cell growth while maintaining pluripotency after 72 h of culture. The early cell adhesion at 24 h can be correlated to the logarithm of the normalised CH₄N⁺ ion intensity from ToF-SIMS data, which is established as a suitable and generalisable marker ion for amino acids and peptides. This work contributes to the ability to use ToF-SIMS in a more quantitative manner for the analysis of amino acid and peptide surfaces.     

"元素化学实验"中的热致变色现象(一)——部分Co(Ⅱ)化合物的热致变色现象及其变色机理探讨

2021年沃尔夫化学奖颁给了Leslie Leiserowitz和Meir Lahav两位教授,以此来表彰他们在证明三维分子结构与有机晶体结构之间相互影响中的贡献。他们的研究成果,极大地补充了科学界对于有机大分子自组装的相关机理的理解,为有机晶体化学领域的发展做出了杰出的贡献。本文以此为契机简要介绍了两位2021年沃尔夫化学奖获得者及沃尔夫奖的历史与地位。     

标准化降水蒸发指数的改进与适用性评价

针对标准化降水蒸发指数中Thornthwaite方法对干旱区估算误差较大的问题, 采用FAO Penman-Monteith方法计算潜在蒸发, 改进标准化降水蒸发指数计算方法. 应用1961–2013 年全国541个气象站点逐日观测资料, 从分布检验以及与标准化降水指数、Palmer干旱指数、实测土壤湿度等常用干旱指标一致性校核等方面, 评估改进前后标准化降水蒸发指数在区域和季节上的适用性. 结果表明: 改进蒸发能力计算方法能够显著提高标准化降水蒸发指数的区域和季节适用范围, 使标准化降水蒸发指数能够应用于全国不同季节的干旱评估, 改进了干旱区标准化降水蒸发指数冬季适用性不高的不足, 改进后的标准化降水蒸发指数在年尺度及月尺度上的干旱评估能力均得到改善, 满足我国以季节性干旱为主的干旱评估需求.     

Polyhedral study of the connected subgraph problem

In this paper, we study the connected subgraph polytope which is the convex hull of the solutions to a related combinatorial optimization problem called the maximum weight connected subgraph problem. We strengthen a cut-based formulation by considering some new partition inequalities for which we give necessary and sufficient conditions to be facet defining. Based on the separation problem associated with these inequalities, we give a complete polyhedral characterization of the connected subgraph polytope on cycles and trees.     

基于光纤叠栅的全光纤声光可调谐滤波器的特性分析

本文提出了一种基于光纤叠栅的全光纤声光可调谐滤波器, 与普通光纤布拉格光栅型全光纤声光可调谐滤波器相比, 该滤波器能够对光纤叠栅的两个中心波长进行同步调制. 理论分析了声波频率和声致应变幅度对基于光纤叠栅的全光纤声光可调谐滤波器的传输光谱的影响, 结果表明, 各阶次反射峰分别以两个主反射峰为中心呈对称关系, 且主反射峰与其所调制出的次反射峰之间的波长间隔与声波频率成正比, 而两个主反射峰所调制出的同阶次反射峰之间的波长间隔与声波频率无关; 声致应变幅度主要影响主反射峰及次反射峰的反射率的变化. 实验中, 分别测试声波频率为390 kHz和710 kHz的基于光纤叠栅的全光纤声光可调谐滤波器的传输光谱, 实验结果的变化趋势与仿真分析结果相一致.     

二维电子光谱仪器研制与指标分析

介绍了一种利用光栅分光,光子回波矩阵构型的二维光谱实验装置．利用快速,高灵敏度的EMCCD对信号进行外差单脉冲测量．并对仪器的指标进行了检测,30 min内12路相干光的相位抖动均方差达到λ/200,19 min内染料IR140溶液外差回波信号的稳定性达到λ/90,通过移动平移台测量了仪器的光谱准确性,相移偏差均方差为λ/90,对平移台移动不均匀导致的光谱失真进行了数值模拟．另外在位相调整时为解决样品泵浦探测信号有干涉的问题,提出了相位移动的方法．将散射信号扣除,大大提高了位相调整的准确性．对染料IR144溶液,光合蛋白色素复合体B820的测量与文献一致．