The Structure and Thermodynamics of a Heteropolymer Chain in Confinement – Computer Simulation Studies

A coarse‐grained model of heteropolymer (polypeptide) chains in a slit was designed in order to study the folding process in confinement. The idealized chains represented heteropolymers consisted of hydrophobic and hydrophilic united atoms, which were restricted to vertices of a (310) lattice. The force field consisted of the excluded volume, the long‐distance potential between pairs of segments and the local helical potential. Monte Carlo simulations were performed using the algorithm with micromodifications of the chain's conformation and employing the Replica Exchange technique. The influence of the size of the slit, the temperature and the force field on the dimension and the structure of chains were studied. It was shown that a moderate confinement stabilizes folded chains while a strong confinement does not.

     

Three‐Dimensional Fluorescence Image Patterning of Network Aliphatic Polyester via Microtransfer Molding and Thermal Treatment

This paper describes that three‐dimensional (3‐D) fluorescence image patterning of a network aliphatic polyester was successfully conducted by microtransfer molding (µTM) of the prepolymer and subsequent thermal treatment. A highly sticky, aliphatic ester prepolymer, containing a malonate moiety in the main chain, was obtained by a two‐step reaction, quantitatively. The 3‐D micropattern of the prepolymer was fabricated by µTM using polydimethylsiloxane (PDMS) as elastomeric mold. The patterns showed a clear shape without any residual layer. When the molded prepolymer was thermally treated, the patterns exhibited very distinct fluorescence images in a full color range of sky‐blue, yellowish green and red regions when excited at wavelengths of 325, 488, and 580 nm, respectively.

     

针对注塑成型随形冷却的流热力耦合拓扑优化方法研究

注塑成型在塑料工业生产中占据重要地位,注塑模具的散热能力影响着塑料制品的生产效率以及产品质量.本文基于变密度拓扑优化方法,以最小化结构平均温度为目标,研究了注塑模具冷却管道的拓扑优化问题.由于在注塑成型过程中模具会受到注塑机施加的克服塑件胀模力的巨大锁模力,故本文还将模具结构承载性能作为优化的评价指标.最终基于开源平台...     

硅表面CS/BSA复合微图形的制备及表征

采用微加工方法在硅表面成功地制备出壳聚糖/牛血清白蛋白(CS/BSA)复合微图形. 借助光镜和荧光显微镜对复合微图形进行形貌分析. 利用大肠杆菌和白色葡萄球菌定量考察了CS/BSA复合微图形的抗菌性能, 结果表明, 硅表面沟槽交叉状CS/BSA复合微图形对两种细菌都具有较好的抗菌效果. 通过MC3T3-E成骨细胞培养考察了复合微图形的细胞相容性, 结果表明, CS/BSA复合微图形对于细胞的生长方向具有较强的诱导性, 可促进细胞在材料表面的黏附、铺展及增殖分化. 结果表明, 采用微转移模塑法制备的CS/BSA复合微图形具有较好的抗菌性和细胞相容性.     

聚(L-乳酸)的成纤模压增强

用成纤模压法制备了弯曲强度和剪切强度分别为 2 50～ 2 80MPa和 1 70～ 1 85MPa的聚 (L 乳酸 )(PLLA)园棒 .由于PLLA对热的不稳定性 ,在模坯制备过程中 ,PLLA的分子量下降 65%～ 70 % ,但模压过程对分子量影响较小 .扫描电子显微镜 (SEM)显示PLLA模坯在模压过程中发生了取向形变并形成纤维结构 ,这是PLLA棒材的力学性能得以增强的主要原因 .差示扫描量热 (DSC)分析和X 射线衍射 (XRD)分析表明PLLA模压成棒后 ,PLLA的结晶熔点下降 ,微晶尺寸变小 ,而结晶度增大 .     

Microphase separation in RIM polyureas as studied by solid-state NMR

The microphase separation (MPS) in polyureas based on methylene diphenyl diisocyanate (MDI) hard segment, diethyltoluenediamine chain extender, and amino-terminated polypropylene glycol soft segment prepared by reaction injection molding (RIM) was studied by advanced solid-state NMR spectroscopy. Incomplete microphase separation leads to the presence of mobilized hard segments dispersed in the soft segment domains as well as immobilized soft segments residing in the hard domains. This is detected by ¹H-NMR spectra recorded under spinning at the magic angle (MAS) as well as two-dimensional wide-line separation (WISE) NMR spectra. The sizes of the various domains as well as the interfaces between them are quantified by spin diffusion measurements. In this way the impact of annealing, method of polymerization, and hard segment content on MPS is studied. Whereas annealing at temperatures up to 170°C results in improving the MPS, major changes are observed after annealing at higher temperatures (190°C), where the system changes from “soft-in-hard” to “hard-in-soft” behavior. The MPS decreases with increasing hard segment content. The highest MPS is observed for solution polymerized samples. The various NMR experiments clearly reveal the nonequilibrium nature of RIM systems. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 693–703, 1998     

常压动态保压注塑自增强高密度聚乙烯的结构与性能

研究了常压动态保压注塑自增强高密度聚乙烯的结构和力学性能的关系,自增强高密度聚乙烯的抗张强度和杨氏模量分别从原来的23MPa和1.0GPa提高到93MPa和5.0GPa。DSC、TEM和X射线衍射研究结果表明:力学性能的显著改善主要归因于串晶的产生、高分子链沿流动方向的轴取向和结构更加完善的球晶的生成。和高压保压法相比,本法具有现实的工业应用前景。     

不饱和聚酯树脂的减收缩研究(Ⅱ)——几种饱和聚酯的减收缩作用

饱和聚酯作为减缩剂的优点是制品表面光洁,所得低收缩UP-树脂透明度较好,往往为半透明,使制品外观与原UP-树脂差不多,从而扩大了制品的用途。我们在酸和醇的种类及比例上进行了探索,合成了7种低分子量饱和聚酯并测试了它们的减收缩效果。发现芳香族聚酯具有更好的减收缩性能,其中具有封端结构的效果更佳。此外,制备了几种无填料浇     

RTM充模过程数值模拟的隐式有限元算法

建立了基于欧拉方法描述树脂传递模塑(RTM)工艺充模过程的基本数学方程,并采用有限元隐式时间积分方法对基本方程进行了数值求解．编制了基于隐式有限元算法及传统有限元控制体算法的程序,通过具体算例比较了这两种算法的优缺点．与传统的有限元控制体法相比,该文提出的隐式有限元算法能节省计算时间,特别适合于单元、节点数目多的情况．隐式有限元算法是一种纯有限元方法,不需要使用控制体积技术,采用该算法计算出的流动前沿与时间步长无关。     

Flame retardant poly (lactic acid) biocomposites based on azo‐boron coupled 4,4′‐sulfonyldiphenol and its combination with calcium lignosulfonate—Crystalline and mechanical properties

Poly (lactic acid) (PLA) has become an important biopolymer with excellent properties but has limited engineering applications where fire safety is ultimate. An efficient flame retardant (FR) for PLA biocomposites based on azo‐boron coupled with 4,4′‐sulfonyldiphenol‐(((1E,1′E)‐(sulfonylbis(6‐hydroxy‐3,1‐phenylene))bis (diazene‐2,1‐diyl))bis(3,1‐phenylene))diboronic acid (SBDA) was synthesized and characterized by FTIR, ¹H and ¹³C NMR spectra. SBDA was combined with calcium lignosulfonate (Calig) and compounded with PLA, and the FR, crystallization, and mechanical properties were investigated. The addition of 15 wt% FR (10 wt% Calig and 5 wt% SBDA) into PLA led to important reductions in peak heat release rate (PHRR) approximately 54%, total heat release (THR) approximately 28.6%, and the average effective heat of combustion (AEHC) approximately 29.4%. The fire performance index and fire growth index improved by approximately 56.4% and 33.1%, respectively. A V‐0 rating (vertical burning test) and a limiting oxygen index value of 28.8% were achieved for the FR PLA biocomposites. The combinatory SBDA/Calig reduced the segmental mobility of PLA in the organic‐inorganic interface with insignificant changes in the elongation at break and the Young Modulus. TG‐IR study showed significant reductions in pyrolysis gaseous products for the composites compared with PLA. This research work will expand the frontiers of knowledge on use of boron and calcium functionalized polyaromatic polyols for reducing the flammability of PLA.