【作者】 原方圆；

【导师】 李孝增；

【作者基本信息】 天津大学 ， 无机化学， 2013， 博士

【摘要】 近年来随着电子信息产业的蓬勃发展，尤其是对于大功率电子器件，热管理和热发散已经变得越来越重要。新颖的轻质、高导热高分子材料越来越受到广大消费市场的青睐。酚醛树脂是世界上最早合成的树脂品种，由于其优秀的阻燃性和耐热性以及立体交联的网络结构，目前在民用、航空、建材领域仍具有无可替代的重要地位。研究导电导热酚醛树脂复合材料对于酚醛树脂的改性和功能化具有非常重要的应用价值。除了微米级陶瓷导热粒子之外，目前纳米填料也在飞速发展。石墨烯作为富勒烯家族成员，通常可以看成是单原子厚度的石墨。自从2004年被Geim和Novoselov等发现以来，备受全世界研究者们的关注。作为一种新材料，石墨烯具有独特的力学，光学，热学和电学性能，例如非整数的量子霍尔效应，超高的杨氏模量，热导率和比表面积等。然而大批量的制备石墨烯和其在复合材料中的均匀分散是目前迫切需要解决的难题。本论文主要研究内容包括：1）选用F/P摩尔比为1.32合成的甲阶PF为原料，氮化硼（BN）片和四角氧化锌晶须(T-ZnO)为填料合成了绝缘导热PF复合材料。研究发现BN填充的复合材料表现出明显的各向异性。对其进行Maxwell-Eucken方程和Nielsen方程理论模拟，高填充量时与实验值有较大程度的偏离，说明片状材料的取向特殊性。笔者首次尝试用四角状的氧化锌晶须与氮化硼混合杂化。结果证明杂化有效地提高了复合材料的热导率，协同效果明显：相比单独添加相同含量的BN，含30wt.%BN+30wt.%T-ZnO的复合材料的水平热导率提高了71.9%，垂直热导率提高了34.5%。弯曲强度比单一添加相同含量的BN提高了56.2%。一方面，立体结构的晶须易于桥连氮化硼片而形成立体的导热网络，另一方面，混合填充可以有效地提高填料在基体中的填充密度(空气中800℃燃烧后残留物的SEM照片得以证实)，因此材料的热导率和力学性能均显著提高。2）为了进一步研究混合填料的协同效果，a)用相同的方法制备片状石墨(G)/氧化锌晶须/酚醛树脂复合材料。热导率结果显示：20wt.%T-ZnO/40wt.%G的酚醛复合材料水平热导率比同体积的石墨/酚醛复合材料的热导率提高了88.6%；垂直热导率比同体积的石墨/酚醛复合材料的热导率提高了40.2%。复合材料的弯曲强度和模量均有不同程度的提高。氧化锌晶须的加入克服了片状填料层与层之间较大的热阻问题，有效形成立体的导热网络。b)制备了氮化硼/中空玻璃微球杂化填充的酚醛复合材料，取得了导热协同效果。当HGM和BN总填料为60wt.%时，1:4<HGM/BN（w/w）<3:1时，协同杂化效果最明显。此方法可以降低材料的密度和导热填料的用量，节约成本，保持材料的力学性能。综上所述，不同形状的填料混合杂化是提高复合材料热导率的有效途径，适当的配比可以协同地提高复合材料的热导率。3）研究了一种在酚醛树脂聚合反应中有效地原位还原并功能化氧化石墨烯（GO）制备酚醛导电复合材料的方法。随着反应的进行，亲水性绝缘的氧化石墨变成疏水导电的石墨烯。不同于绝缘的氧化石墨烯和酚醛树脂，由于有效地原位还原和功能化，得到的酚醛复合材料具有高的电导率。仅添加0.85vol.%的GO，复合材料的电导率达到0.2S/m。同时赋予酚醛复合材料高的热稳定性和力学强度，仅添加2.3vol.%的GO，复合材料的热分解温度提高了76℃；仅添加1.7vol.%的GO，复合材料的弯曲强度和模量分别提高了318和56%。第一，解决了石墨烯还原的问题，第二，解决了石墨烯的剥离和分散难的问题，第三，部分的功能化解决了填料与基体的相容性难的问题，制备了性能优异的石墨烯/酚醛导电复合材料，且原料廉价易得，制备工艺简单，便于工业上生产。更多还原

【Abstract】 As heat management and dissipation are becoming more and more crucial for highlyintegrated electronic devices with high-power output, novel heat releasing packagematerials are highly desired and the thermal conductivity of most polymers should besubstantially improved. Currently, Inorganic fllers, such as metal, ceramic and nanofillerwere used to improve thermal and electrical conductivities of polymers. In addition,graphene has attracted the attentions from the researches in the world since2004.As amember of fullerenes family, graphene is usually regarded as the single-atom-thick graphite,which possessed distinct properties, such as mechanical, optical, thermal and electricalproperties. However, there are many obstacles in the mass production and homogenousdispersion in host polymers need to be addressed. Graphene oxide (GO) is treated as theprecursor of graphene for its similarity to graphene. By thermal treatment or chemicalmethods, GO can be reduction to graphene, Amounts of oxygen-containing groups attachedon the surface of GO sheets provided active sites for the covalent modification.The detailsand results in this paper are as follows:1) PF/BN composites and PF/T-ZnO were prepared by a solution blending and curingmethod. With the addition of BN flakes, the thermal conductivity of PF is improvedaccompanying with an anisotropic thermal conductance, which is attributed to the naturaltendency for platelet fillers to align parallel with one another especially at high contents.Itis seen that Maxwell-Eucken model and Nielsen model are suitable to evaluate the thermalconductivity at low loadings of BN flakes. At a constant filler loading of60wt.%, thepartial replacement of BN with T-ZnO results in a striking synergistic effect on thermalconductivity of PF. With30wt.%BN and30wt.%T-ZnO, the in-plane thermalconductivity of composite shows71.9%higher than that of the PF composite with thesame BN content. The flexural strength of the PF composite is56.2%higher than that ofthe PF composite with60wt.%BN. Due to its stereo structure with four needles, T-ZnOplays an important role in bridging the BN flakes in through-plane and in-plane directions,thus facilitating the formation of heat conductance.2) In order to study synergetic effect of tetrapod-shaped ZnO whiskers and graphiteflakes, an similiar method is developed. A maximum in-plane thermal conductivity of9.2Wm-1K-1is observed with a T-ZnO/G mass ratio of1/2, which is88.6%higher than that ofPF/G composite with the same filler content. The flexural strength and elongation at break are also improved with filler content. The hollow glass microsphere (HGM) and BN flakewere filled into PF matrix with the same method. The results show that a striking synergiceffect on thermal conductivity with different HGM/BN mass ratio (1:4<HGM/BN（w/w）<3:1). The synergetic effect may originate from the size exclusion effect of rigid HGM.3）An efficient one-step approach to reduce and functionalize graphene oxide (GO)during the in situ polymerization of phenol and formaldehyde was reported. Thehydrophilic and electrically insulating GO is converted to hydrophobic and electricallyconductive graphene with phenol as the main reducing agent. Simultaneously,functionalization of GO was realized by the nucleophilic substitution reaction of epoxidegroups of GO with hydroxyl groups of phenol or phenol prepolymer in the alkali condition.The electrical conductivity of PF composite with0.85vol.%of GO is0.2S/m, nearly nineorders of magnitude higher than that of neat PF. Moreover, the efficient reduction andfunctionalization of GO endows the PF composites with high thermal stability and flexuralproperties. A striking increase in decomposition temperature is achieved with2.3vol.%ofGO. The flexural strength and modulus of the PF composite with1.7vol.%GO areincreased by318and56%, respectively.更多还原