共查询到19条相似文献,搜索用时 140 毫秒
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采用本体聚合技术合成全氘代聚苯乙烯(DPS),所得聚合物分子量约250000,分散度约3,氘代率为98.7%。采用热诱导相分离技术制备全氘代聚苯乙烯泡沫。在室温溶解DPS于溶剂中,然后转入轴向冷却模具,进行单向冷却,直到溶剂完全冷冻,最后取出冷冻样置于冷冻干燥仪中进行冷冻干燥,待溶剂完全脱出后即得泡沫。通过对二恶烷/环己烷混合溶剂相图,以及PS一混合溶剂体系的相图的测定, 相似文献
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为有效制得Z箍缩氘代聚苯乙烯/纳米铝(DPS/AlNPs)导电丝阵材料,采用PS中掺入AlNPs制备PS/AlNPs复合材料纤维进行模拟研究。研究了温度及剪切速率等因素对PS/AlNPs复合材料流变性能的影响、复合材料熔体的结构变化及流动状态与可纺性能的关系,以及PS/AlNPs纤维的形貌、热稳定性能和力学性能。结果表明:PS/AlNPs熔体属于典型剪切变稀型非牛顿流体,熔体的表观粘度与温度呈现负相关,240~260 ℃时复合材料的非牛顿指数介于0.462~0.546,结构黏度系数介于1.8~2.1,黏流活化能介于77.2~104.6 kJ·mol-1,具有良好的可纺性。PS/AlNPs纤维表面光滑,对AlNPs粒子包覆良好且对其抗氧化非常有利,其中当AlNPs质量分数为1%时纤维的断裂伸长率突出、掺量为5%时其断裂强度较高。 相似文献
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采用聚苯乙烯(PS)催化氘化技术,在使苯环被氘化饱和的基础上,成功地制备出了部分氘化的聚环己基乙烯(D-PVCH,C8H8D6)。用傅里叶红外光谱仪、核磁共振仪对D-PVCH的结构进行了表征,结果表明与目标产物吻合,即苯环被氘饱和转化为环己基,氘代率为41.5%。采用差式扫描量热仪和热重分析仪分析了D-PVCH的热性能,结果表明D-PVCH的玻璃化转变温度为125 ℃,5%失重温度为403 ℃。另外,D-PVCH可溶于常见溶剂,如石油醚、环己烷和甲苯等。与PS相比,D-PVCH具有较好的热稳定性和良好的溶解性能。 相似文献
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靶用氘代聚合物的合成与性能研究一直是ICF领域的研究热点。采用聚苯乙烯(PS)经氢化反应制备出非氘代聚环己基乙烯(PVCH),利用傅里叶红外光谱仪、核磁共振仪和凝胶渗透色谱对PVCH结构进行了表征,表征结果与目标结构吻合良好,同时摸索出最优合成条件,并通过差式扫描量热仪和热重分析仪对其热性能进行分析。结果表明:PVCH相对于PS的玻璃化转变温度和初始分解温度都有所提高,分别达到146℃和345℃;PVCH在溶解度方面也得到改善,可以完全溶于石油醚和环己烷中。 相似文献
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介绍使用计算机模拟软件,建立的聚苯乙烯和溴代聚苯乙烯非晶态高分子模型.选择适于有机高分子的DREIDING分子力场,根据模型的原子类型,参照文献数据修改其力场参数.在此力场下对模型进行能量优化,使模型尽量符合实际材料.然后,使用分子模拟法中的机械特性模拟,选择一定的计算方法和力学参量,模拟玻璃态物质在外张力下的形变,并计算出其力学特性参数,如体积模量、杨氏模量、泊松比等,给出了PS的应力-应变曲线以及各力学特性随溴代量变化情况. 相似文献
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利用高速CCD 可见光相机系统研究了EAST 上的边缘局域模(ELMs)细丝动力学特性。采用Tsai 两步标定法对CCD 相机进行标定,以实现将CCD 图像坐标转换为真实空间坐标。选取CCD 图像中与边缘局域模细丝垂直方向上的图像灰度值,绘制了灰度分布图。灰度分布图中的一个凸起的尖峰代表了一条边缘局域模细丝结构,细丝的位置坐标由尖峰顶点确定。运用Sobel 边缘检测算子检测细丝边缘轮廓,从而得到细丝的宽度。通过对边缘局域模细丝宽度特性的分析,发现边缘局域模细丝在从最外层封闭磁面向外传播的过程中宽度不断减小。这表明细丝在向外传播的过程中其能量和粒子不断耗散。I-型边缘局域模的细丝宽度比III-型边缘局域模细丝的宽度更大。 相似文献
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Measurements of current-carrying filaments associated with Type-III edge localized mode (ELM) have recently been made in the Experimental Advanced Superconducting Tokamak by direct probing of the edge plasma using an advanced, fast-moving electrostatic and magnetic probe system. Contrary to expectations, no current filaments were detected near the separatrix. However, a clear signature of current filament has been observed in the far scrape-off layer (SOL) where the difference of the voltage between the divertor plates connecting a filament is sufficiently large, thus strongly suggesting that the current-carrying filaments form in the SOL, rather than being ejected from the plasma inside the separatrix. These findings provide, for the first time, information on the formation and sustainment of current filaments during type-III ELMy H-modes. 相似文献
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In this paper we have studied the mechanisms of so-called ‘indentation creep’ in a zirconium alloy. Nanoindentation was used to obtain strain rate data as the sample was indented at room temperature, at a homologous temperature below that for which creep behaviour would be expected for this material. A high value of strain rate was obtained, consistent with previous work on indentation creep. In order to elucidate the mechanism of time-dependent deformation, a load relaxation experiment was performed by uniaxial loading of a sample of the same alloy. By allowing relaxation of the sample from a peak load in the tensile test machine, a similar stress exponent was obtained to that seen in the nanoindentation creep test. We conclude that for metals, at temperatures below that at which conventional creep will occur, nanoindentation ‘creep’ proceeds through deformation on active slip systems that were initiated by prior loading beyond the plastic limit. It is therefore more appropriate to describe it as a viscoplastic process, and not as creep deformation. 相似文献
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A. T. Kosilov V. A. Mikhailov V. V. Sviridov V. A. Khonik 《Physics of the Solid State》1997,39(11):1796-1802
A generalized theoretical model is proposed for the structural relaxation of metallic glasses under load. Structural relaxation
is treated as a set of irreversible, uncorrelated, two-stage atomic displacements in some regions of the structure, the “relaxation
centers.” In loaded samples structural relaxation acquires a directional character, leading to the buildup of plastic deformation
in accordance with the magnitude and orientation of the applied mechanical stress. General equations are obtained for creep
kinetics including a continuous statistical distribution of the principal activation parameters. These equations are compared
with the results of a special experiment. The model is found to provide an adequate interpretation of the observed creep kinetics,
except for the first 101–102 seconds after loading. It is argued that the initial stage of creep is determined by reversible atomic realignments in relaxation
centers having symmetric two-well potential.
Fiz. Tverd. Tela (St. Petersburg) 39, 2008–2015 (November 1997) 相似文献
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Comparative investigation of the resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air 下载免费PDF全文
A comparative investigation of the resistance and ability to trigger high voltage(HV) discharge for a single filament(SF) and multiple filaments(MFs) has been carried out.The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance,but this is not the case for the MF.The MF’s resistance is much smaller than the SF’s.However,the MF shows a slightly higher HV breakdown threshold than the SF.The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path. 相似文献
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Comparative investigation of resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air 下载免费PDF全文
A comparative investigation of resistance and ability to trigger high voltage (HV) discharge for single filament (SF) and multiple filaments (MF) has been carried out. The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance, but this is not the case for the MF. The MF's resistance is much smaller than SF's. However, the MF shows a bit higher HV breakdown threshold than the SF. The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path. 相似文献
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In former investigations it has been shown that creep (constant stress, altering strain) and relaxation (constant strain, decreasing stress) can be observed with dry bulk solids. Both effects are covered when investigating the time dependent behaviour of bulk solids where time dependence can also mean an increase of the deformation resistance with increasing deformation rate. In this paper the investigated time dependent effects do not include time consolidation. The effects of creep and relaxation are often neglected for bulk solids because in many applications the influence of these time dependent behaviours is of minor importance. A deeper insight into the bulk solids flow characteristics and mechanisms can only be obtained when time dependence is taken into consideration. 相似文献
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L. P. Myasnikova V. A. Marikhin E. M. Ivan'kova P. N. Yakushev 《Journal of Macromolecular Science: Physics》2013,52(5-6):859-868
To clarify whether the interfibrillar slippage occurs on plastic deformation of oriented polymers, flow creep of ultrahigh molecular weight polyethylene (UHMW PE) samples with various connectedness of microfibrils has been studied in a dead load mode at room temperature. The flow creep rate of melt-crystallized and gel-cast UHMW PE films drawn to various draw ratios, as well as of modified gel-crystallized samples (cross-linked/grafted or washed free of low molecular weight fraction) has been measured with the help of a unique laser interferometric technique (Doppler creep rate meter). The technique allows one to measure creep rates for deformation increments as small as 0.3 μ within an accuracy 1%. The interferometric technique enabled us to observe an extremely high variability of flow creep rate. It was recognized that the creep process accelerates or slows from time to time. A length of a loaded sample increased by multiple consecutive deformation jumps (or steps). The size distribution of the steps appeared to be controlled by the structure of interfibrillar regions. The influence of the latter on the variability of creep rate confirms a hypothesis that suggests a contribution of interfibrillar slippage to plastic deformation of oriented polymers. The observed phenomenon has been attributed to stick-slip motion of microfibrils and their aggregates sliding on each other under the action of applied stress. It was found that the creep rate decreases with increasing interfibrillar interaction. 相似文献
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Modulation of terahertz generation in dual-color filaments by an external electric field and preformed plasma 下载免费PDF全文
Terahertz generation driven by dual-color filaments in air is demonstrated to be remarkably enhanced by applying an external electric field to the filaments. As terahertz generation is sensitive to the dual-color phase difference, a preformed plasma is verified efficiently in modulating terahertz radiation from linear to elliptical polarization. In the presence of preformed plasma, a dual-color filament generates terahertz pulses of elliptical polarization and the corresponding ellipse rotates regularly with the change of the preformed plasma density. The observed terahertz modulation with the external electric field and the preformed plasma provides a simple way to estimate the plasma density and evaluate the photocurrent dynamics of the dual-color filaments. It provides further experimental evidence of the photo-current model in governing the dual-color filament driven terahertz generation processes. 相似文献