溶剂对碳系填充型导电聚合物导电性能的影响

采用基团贡献法估算了自制丙烯酸聚合物的溶解度参数,选择了合适的混合溶剂,研制出一种以自制丙烯酸聚合物为基体树脂,碳黑石墨为导电填料的新型溶液型导电聚合物。讨论了溶剂的含量、溶解度参数、混合溶剂挥发速率对碳系填充型导电高分子聚合物导电性能的影响。结果表明,所选溶剂对丙烯酸基体树脂有良好的相容性,具有合理的挥发速率曲线,在聚合物固化成膜过程中保持溶剂平衡状态,混合溶剂含量控制在35%~40%,导电聚合物方电阻(厚度为25μm)达60Ω/□.     

导电高分子复合材料的有效电导率模型

基于Maxwell理论和平均极化理论,建立了导电高分子复合材料的有效电导率模型。有效电导率描述为各组成成分的体积、形状和颗粒尺寸的函数。利用该模型,讨论了渗流阈值与导电颗粒的大小及轴长比的关系,得到了导电高分子复合材料的有效电导率随导电颗粒轴长比和半径变化的规律。用该模型计算了碳纤维聚脂树脂复合材料的有效电导率,计算结果与实验结果符合较好。     

导电高分子复合材料的有效电导率模型

基于Maxwell理论和平均极化理论，建立了导电高分子复合材料的有效电导率模型。有效电导率描述为各组成成分的体积、形状和颗粒尺寸的函数。利用该模型，讨论了渗流阈值与导电颗粒的大小及轴长比的关系，得到了导电高分子复合材料的有效电导率随导电颗粒轴长比和半径变化的规律。用该模型计算了碳纤维一聚脂树脂复合材料的有效电导率，计算结果与实验结果符合较好。     

填充氩后单壁碳纳米管的导热系数

采用平衡态分子动力学(EMD)模拟方法,计算了填充氩后的(10,10)型和(15,15)型的单壁碳纳米管分别在不同温度下的导热系数.研究了它们随温度的变化情况,并将其与相应的空的碳纳米管的导热系数进行比较,分析在相同温度下,充氩对碳纳米管导热系数的影响.模拟结果发现:在500~1 200 K的温度范围内,(10,10)型碳纳米管和(15,15)型碳纳米管在填充了氩后其导热系数值均随着温度的升高呈下降趋势,这与空的碳纳米管的导热系数随温度的变化关系相似;在相同温度下,这2种类型的碳纳米管在填充了氩后的导热系数值均比相应的空的碳纳米管的导热系数值明显高很多.     

不同形状颗粒弥散复合材料的等效导热系数

根据最小热阻力法和比等效导热系数法对不同形状颗粒弥散复合材料的等效导热系数进行预测。采用以颗粒在传热方向上的特征长度为边长的立方体体积与实际颗粒体积之比作为形状因子,对不同颗粒形状等效为立方体时的无量纲相对特征长度进行修正,基于形状因子进一步推导了适用于不同形状颗粒弥散复合材料在中低体积分数情况的等效导热系数通用计算公式。此通用计算公式与实验值及其它模型计算值吻合较好,对于导热增强型复合材料,体积分数一定时,其等效导热系数与颗粒形状因子呈正比,增加颗粒在传热方向上的尺寸能有效提高复合材料的导热性能。     

C/C-SiC复合材料的导热性能及其影响因素

以炭纤维针刺毡为预制体,采用化学气相渗透法和熔融渗硅法相结合制得C/C-SiC复合材料;研究C/C-SiC材料在室温至1300℃之间的导热性能以及预制体结构、基体炭结构和石墨化处理对其热扩散率的影响.研究结果表明:C/C-SiC材料的比热容随着温度的升高不断增大,在700℃时达到最大值2.18 J/(g·K),随后降至1300℃时的0.57 J/(g·K),其导热系数在1300℃时为3.95 W/(m·K);C/C-SiC材料的热扩散率在室温时为0.12 cm2/s,随着温度的升高不断降低并趋于常量,平行摩擦面方向的热扩散率明显比垂直于摩擦面方向的大;以全网胎为预制体的C/C-SiC材料其垂直和平行摩擦面的热扩散率相当,树脂炭质量分数增大及石墨化处理均可显著提高C/C-SiC材料的热扩散率.     

颗粒增强聚合物复合材料损伤模型

研究了颗粒增强聚合物复合材料的力学行为,研究得知:材料屈服、裂纹形核、扩展与贯通直至最终断裂是一逐渐劣化过程,而损伤理论正是这一劣化过程的良好描述.通过假设自由能和耗散势函数,导出了损伤演化规律,与实验比较,模型和试验结果基本符合.进一步采用改进的Dugdale模型,重点研究损伤对GB/PPO复合材料宏观裂纹起裂的影响,通过建立损伤模型来描述材料的劣化行为和裂纹扩展,结果表明,损伤区域严重影响裂尖的性能,材料损伤对宏观裂纹起裂影响不可忽略.     

薄毡叠层炭/炭复合材料的高温导热性能

对薄毡叠层结构的炭纤维预制体采用化学气相沉积（CVD）和沥青浸渍增密工艺,制备具有粗糙层热解炭结构和光滑层热解炭与沥青炭复合结构的2种炭／炭复合材料;用JR-3型热物性测试仪测试垂直炭纤维叠层方向室温至800℃的导热性能,并对其导热机制进行分析。研究结果表明：具有粗糙层热解炭结构的样件A的导热系数随温度升高先下降,在400℃后导热系数变化平缓;具有光滑层热解炭及少量沥青炭结构的样件B的导热系数随温度升高先上升,在300℃后导热系数变化平缓;样件A较样件B的导热系数高。2种炭／炭复合材料的导热机理主要由声子导热决定,不同基体炭结构使得2种声子散射机理对导热性能的贡献不一样,粗糙层热解炭结构的样件A的高温导热性能主要由声子间散射路程和比热容的综合作用所决定;光滑层热解炭和少量沥青炭复合结构的样件B的高温导热性能主要由结构不均匀引起的卢子散射和比热容的共同作用所决定。     

纳米SiO2改性UHMWPE性能的研究

文中研究了纳米SiO₂填充改性超高相对分子质量聚乙烯(UHMWPE)塑料的耐热性能。结果表明：在UHMWPE中添加少量经偶联剂表面处理的纳米SiO₂对材料的耐热性能有较显著影响。用DSC法研究了UHMWPE/纳米SiO₂复合材料在不同纳米粒子含量时的熔融结晶行为。纳米SiO₂的加入，起到了结晶成核剂作用。通过偏光显微镜观察了复合材料结晶结构，同时和纯UHMWPE进行了比较。发现较低含量纳米SiO₂在UHMWPE中有成核作用，使UHMWPE以异相成核方式结晶，UHMWPE的结晶度提高，球晶颗粒变小。     

Autonomic healing of polymer composites

Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).     

碳纳米管复合材料的有效热导率

考虑到碳纳米管的空间取向分布特征，建立了碳纳米管复合材料的有效热导率模型。根据Maxwell理论，推导出了计算碳纳米管复合材料有效热导率的简单公式。应用实例表明，该模型能够很好地解释在碳纳米管纳米流体中观察到的热导率异常增加现象，还可以用来分析纳米管复合材料的渗流性质，而且理论计算结果与实验结果吻合较好。     

碳纳米管复合材料的有效热导率

考虑到碳纳米管的空间取向分布特征,建立了碳纳米管复合材料的有效热导率模型。根据Maxwell理论,推导出了计算碳纳米管复合材料有效热导率的简单公式。应用实例表明,该模型能够很好地解释在碳纳米管纳米流体中观察到的热导率异常增加现象,还可以用来分析纳米管复合材料的渗流性质,而且理论计算结果与实验结果吻合较好。     

Ionic conductivity in crystalline polymer electrolytes

Polymer electrolytes are the subject of intensive study, in part because of their potential use as the electrolyte in all-solid-state rechargeable lithium batteries. These materials are formed by dissolving a salt (for example LiI) in a solid host polymer such as poly(ethylene oxide) (refs 2, 3, 4, 5, 6), and may be prepared as both crystalline and amorphous phases. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass transition temperature, Tg, where polymer chain motion creates a dynamic, disordered environment that plays a critical role in facilitating ion transport. Here we show that, in contrast to this prevailing view, ionic conductivity in the static, ordered environment of the crystalline phase can be greater than that in the equivalent amorphous material above Tg. Moreover, we demonstrate that ion transport in crystalline polymer electrolytes can be dominated by the cations, whereas both ions are generally mobile in the amorphous phase. Restriction of mobility to the lithium cation is advantageous for battery applications. The realization that order can promote ion transport in polymers is interesting in the context of electronically conducting polymers, where crystallinity favours electron transport.     

Increasing the conductivity of crystalline polymer electrolytes

Polymer electrolytes consist of salts dissolved in polymers (for example, polyethylene oxide, PEO), and represent a unique class of solid coordination compounds. They have potential applications in a diverse range of all-solid-state devices, such as rechargeable lithium batteries, flexible electrochromic displays and smart windows. For 30 years, attention was focused on amorphous polymer electrolytes in the belief that crystalline polymer:salt complexes were insulators. This view has been overturned recently by demonstrating ionic conductivity in the crystalline complexes PEO6:LiXF6 (X = P, As, Sb); however, the conductivities were relatively low. Here we demonstrate an increase of 1.5 orders of magnitude in the conductivity of these materials by replacing a small proportion of the XF6- anions in the crystal structure with isovalent N(SO2CF3)2- ions. We suggest that the larger and more irregularly shaped anions disrupt the potential around the Li+ ions, thus enhancing the ionic conductivity in a manner somewhat analogous to the AgBr(1-x)I(x) ionic conductors. The demonstration that doping strategies can enhance the conductivity of crystalline polymer electrolytes represents a significant advance towards the technological exploitation of such materials.     

基于表征体元的空心型回填多孔结构导热模型

合理开发与利用地热能,可以有效推动绿色低碳发展、改善环境质量、实现多能互补及提高资源利用效率等。一般地,热能从地下到地上的采集和输送由地埋管来实现,管外回填结构存在散热损失,对地热能的有效利用影响较大。为研究回填结构在微观层面的导热机理,通过建立表征体元的方法,建立了2种导热分析模型：二维模型和三维模型。以硅酸钙为例,通过自主研发的实验装置对模型的准确性进行了验证,并分析了相关参数(水气比、孔隙率)对三维模型导热系数的影响。结果表明：当温度变化时,串联模型曲线变化较为平缓,更接近真实值;当水气比变化时,串联模型曲线变化较为平缓,更接近真实值。可见,建立的三维串联模型更加精准,为其他多孔材料导热系数的测定提供了一种可供参考的数值计算方法。     

高耐磨聚四氟乙烯复合材料的实验研究

利用MM-200摩擦磨损试验机考察了填充聚丙烯腈的聚四氟乙烯复合材料在干摩擦条件下的摩擦学性能．用扫描电子显微镜对样品的磨损面和转移膜进行了观察和分析．结果表明，聚丙烯腈的加入，使聚四氟乙烯的耐磨损性大幅提高，摩擦系数有所降低；填充聚丙烯腈的聚四氟乙烯样品的对磨面有完整而且不易脱落的转移膜，这是其具有良好耐磨性的主要原因；在复合材料中，聚丙烯腈与聚四氟乙烯有很好的相容性．     

Thermal conductivity of nanoscale thin nickel films

The inhomogeneous non-equilibrium molecular dynamics (NEMD) scheme is applied to model phonon heat conduction in thin nickel films. The electronic contribution to the thermal conductivity of the film is deduced from the electrical conductivity through the use of the Wiedemann-Franz law. At the average temperature of T=300 K, which is lower than the Debye temperature ΘD=450 K, the results show that in a film thickness range of about 1?11 nm, the calculated cross-plane thermal conductivity decreases almost linearly with the decreasing film thickness, exhibiting a remarkable reduction compared with the bulk value. The electrical and thermal conductivities are anisotropic in thin nickel films for the thickness under about 10 nm. The phonon mean free path is estimated and the size effect on the thermal conductivity is attributed to the reduction of the phonon mean free path according to the kinetic theory.     

碳纤维水泥基复合材料导电机理的探讨

通过研究水泥基体的导电性能和不同纤维掺量、外力作用下及掺入骨料后的碳纤维水泥基复合材料的导电性能,探讨碳纤维水泥基复合材料的导电机理.研究表明,水泥基体的电阻随水化时间显著增加,其导电机理是强电解质溶液的离子导电;碳纤维水泥基复合材料的电阻率随纤维掺量增加而显著降低,其电导由接触导电、隧道导电和离子导电3种机制共同决定;碳纤维水泥基复合材料在压力作用下,电阻率因界面接触的改善和纤维搭接概率的增加而降低,在拉力作用下,电阻率因纤维的拔出、折断而提高;骨料的引入增加了复合材料的电阻,这是由于骨料增加了纤维分散的难度和折断的概率,同时阻碍了纤维的搭接并提高了隧道势垒.     

颗粒增强复合材料机械性能细观分析模型研究

假设立方体颗粒均匀分布于树脂基体材料中，借助于单元串联、并联和Halpin-Tsai模型算法导出了复合材料杨氏模量的计算公式。利用三维有限元数值方法对立方体和球体颗粒增强复合材料代表性体积元进行了数值模拟，得到了应力分量σ33及von MiseS应力的分布规律，阐述了应力分布和材料破坏之间的联系。研究结果发现，颗粒的几何形状对复合材料杨氏模量的影响甚微，由分析预测模型、有限元数值模拟和实验测量所得到的结果符合良好。     

氮化硼纤维填充聚乙烯醇导热复合材料的制备

以聚乙烯醇(PVA)为基体,选用六方氮化硼纤维(BN fiber)作为导热填料,通过溶液共混的方法制备导热复合材料。结合X射线衍射仪(XRD)、扫描电子显微镜(SEM)以及导热测试结果,探究填料的微观形貌以及与基体的界面相容性对于提升复合材料导热性能的影响。结果表明:BN fiber对于提升复合材料的面内导热率有很好的效果,而且采用过氧化氢(H₂O₂)溶液进行表面改性,可以有效改善界面相容性;当经过1 400℃热处理再经过表面改性的BN fiber(BN fiber-1400-H₂O₂)的填充量为5%(质量分数)时,复合材料的面内导热率达到了1.32 W·m^-1·K^-1,为纯PVA体系的629%,相比于表面改性前提升了60%。