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A supercritical carbon dioxide(Sc CO2) assisted phase inversion was developed to produce microporous poly(vinylidene fluoride)(PVDF) membranes whose morphology characteristics arise from both liquid-liquid demixing and solid-liquid demixing(crystallization). This result was confirmed by Fourier transform infrared spectroscopy(FTIR), from which both α and β crystals were found. As revealed by contact angle experiment, the PVDF membranes prepared via Sc CO2 assisted phase inversion were more hydrophobic compared with the control membrane produced via conventional immersionprecipitation technique. In particular, the sample with 15 wt% PVDF prepared at 45 °C and 13 MPa exhibited a contact angle of 142°, which was mainly caused by the multilevel micro- and nano- structure. The effects of polyethylene glycol(PEG), polyvinyl pyrrolidone(PVP) and lithium chloride(Li Cl) on the structures and crystal form were investigated. PVP promoted the formation of β phase crystal form, while PEG boosts the evolution of α phase. Li Cl restrained the crystallization degree of PVDF membrane under Sc CO2. 相似文献
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刚刚落幕的2017年上海市春季高考数学考试,与高中数学学业水平考试分开命题,是首次与6月秋季高考在试卷布局、题型结构以及分值分配等方面均保持一致的一次大规模选拔性考试.今年的上海高考又是高考制度改革后实施的首次高考,不区分文理科,其意义和影响不言而喻.
无论是教师教,还是学生学,都要重视基础知识和基本技能,即“双基”,改革后的高考,“双基”考查呈现什么样的特点呢?本次春季高考数学卷又透露出怎样的信息呢?笔者以2017年春考中的一道中等难度试题和一道压轴题为例进行剖析. 相似文献
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Sunshine等在Bi-Sr-Ca-Cu-O体系中掺入少量Pb~(2+)后,可获得T_(c(0))=110K以“2223”相为主的样品.其后,Shun-ichi、卢伟京等也得到同样的结果,但都需要长达300~500小时烧结,所得到的样品仍含有少量“2212”相、我们拟对Bi(Pb)-Sr-Ca-Cu-O体系掺入高价离子,M~(n+)(n≥4),如Sn~(4+),Sb~(5+),Mo~(6+),W~(6+),研究它们对“2223”成相和结构的影响。 相似文献
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