闭孔泡沫铝材料十四面体模型的改进

基于对闭孔泡沫铝发泡过程更为合理的假设,提出了描述胞体结构的改进的十四面体模型,使之可以反映密度增大时质量集中于支柱和顶点的情况。采用有限元方法及耦合边界条件,研究了闭孔泡沫铝的相对弹性模量、泊松比等弹性特征与胞体参数的关系,给出了拟合的弹性模量的计算公式,并对模型在弹性压缩变形下应力分布进行了分析。通过与已有模型的比较表明,改进模型可以较好地模拟闭孔泡沫铝材料的弹性性能。     

基于原位观测的泡沫金属细观与宏观压缩实验研究

采用原位观测的方法研究了脆性泡沫铝材料在压缩载荷下细观与宏观断裂破坏规律和吸能机理。针对多孔泡沫金属材料提出一种细观原位加载实验方法,采用特别设计与制备的试件,在S570扫描电镜下研究了特定胞孔在压缩过程中孔壁的失效顺序和破坏规律,并揭示了能量吸收的细观机理。对块体材料的宏观压缩实验表明,脆性泡沫铝是以多个断裂带的形式破坏。研究发现,孔壁缺陷和胞孔形态缺陷是诱发断裂带形成与发展的重要因素。依据尺寸效应对细观与宏观实验下泡沫铝的性能进行了比较。     

Highly porous elastomer‐silsesquioxane nanocomposites synthesized within high internal phase emulsions

Highly porous elastomeric nanocomposites were successfully synthesized through copolymerization of 2‐ethylhexyl acrylate (EHA), divinyl benzene (DVB), and up to 9 mol % of a polyhedral oligomeric silsesquioxane bearing one propylmethacryl group and seven cyclohexyl groups (MACH‐POSS) within the external phase of high internal phase emulsions (HIPE). The chemical structures, morphologies, thermal properties, and mechanical properties of the polyHIPE were investigated. The mechanical loss peak temperature and full width at half maximum increased with increasing MACH‐POSS content. These changes indicate that copolymerization with MACH‐POSS limits segmental mobility and produces compositional distributions on the nanometer scale. At 9 mol % MACH‐POSS, the reduction in segmental mobility produced a glass transition temperature above room temperature and a significant increase in modulus that can be ascribed to the relatively glassy nature of the polymer. Inorganic monoliths with porosities of around 86%, O/Si of about 1.6, and less than 10% carbon were produced on pyrolysis of the nanocomposite polyHIPE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2357–2366, 2008     

A novel nanoporous structure on the surface of bubbles in polycarbonate foams

We found that novel nanoporous structures such as ellipsoidal‐ or string‐shaped nanopores were formed on the surface of the spherical bubbles in polycarbonate foams by annealing CO₂‐saturated polycarbonate. The pores were surrounded by polycarbonate nanofibrils, and birefringence with spherical symmetry was seen on the surface of the spherical bubbles. Thus, the formation of such a characteristic structure might be attributed to orientation‐induced crystallization of CO₂‐saturated polycarbonate on the surface of the bubbles and the exclusion of CO₂ from the fibrillar crystals thus obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 843–846, 2008     

Uniform foam production by turbulent mixing: new results on free drainage vs. liquid content

An apparatus is described for rapidly producing large quantities of foam via turbulent mixing of gas with a narrow jet of a surfactant solution inside a delivery tube. By controlling relative flow rates, the gas volume fraction in the resulting foam may be easily varied across . Using such foams, we present a comprehensive set of data for free drainage as a systematic function of gas fraction and sample geometry. The qualitative behavior can be understood in terms of simple theoretical considerations, emphasizing the importance of controlling the initial foam conditions. Quantitative features are compared with two approximate versions of the drainage equation, highlighting the crucial role of capillarity for very dry foams and small samples. Received 15 February 1999     

Extinction coefficient of polyolefin foams

The extinction coefficient of a collection of polyolefin foams was investigated experimentally and theoretically. Transmittance spectra were measured with Fourier transform infrared spectroscopy (FTIR) for samples of various thicknesses and different chemical compositions, densities, colors and structural characteristics. The extinction coefficients were then calculated by applying Beer's law. The results showed that the extinction coefficient decreased with the mean cell size and that this was the main structural parameter influencing the extinction coefficient of the foams under study. The experimental results agreed well with the Glicksman model. Moreover, the total thermal conductivity was calculated in terms of the Rosseland equation with an accuracy of 5%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1608–1617, 2005     

Critical parameters controlling the properties of monolithic poly(lactic acid) foams prepared by thermally induced phase separation

Monolithic poly(lactic acid) (PLA) foams were produced by thermally induced phase separation. PLA solutions with concentrations 8–22 wt % were prepared in tetrahydrofuran/methanol (THF/MeOH) solvent/nonsolvent mixtures at 55 °C. Homogenous solutions were quenched at ?20 °C to induce phase separation and gelation. Resulting gels were mechanically stabilized by solvent exchange. Subsequent supercritical CO₂ drying yielded monolithic PLA foams. Crystal structure and degree of crystallinity of the foams were obtained by x‐ray diffractometry and differential scanning calorimetry. Morphologies were determined by scanning electron microscopy. Tuning the PLA concentration and THF/MeOH ratio enabled preparation of monolithic PLA foams. Depending on the experimental conditions various morphologies, such as: interconnected networks, thin platelets, lamellar stacks, axialites, and spherulites were formed. Monoliths obtained were highly crystalline. By changing the PLA concentration monoliths with controlled average pore sizes (170–1440 nm) and porosities (80–90%) were produced. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 98–108