【作者】 方茜；

【导师】 袁学锋；

【作者基本信息】 广州大学 ， 机械工程（专业学位）， 2022， 硕士

【摘要】 氧化石墨烯是一种具有大长径比的二维颗粒材料,由于其优异的力学、电学和热学性能,与石墨烯相比更具有易合成、易加工和较廉价等特点,在材料科学、工程应用中引起了极大的关注。氧化石墨烯在极性溶剂中容易分散,随颗粒在分散液中浓度的增加,会形成各向同性、两相共存、向列相液晶等相结构,氧化石墨烯悬浮液的流变学性质对于各种溶液法加工和制造技术的发展至关重要。本文通过系统流变学实验表征,结合其相结构特征,进一步实验数据分析为建立普适性的氧化石墨烯悬浮液非平衡态相图奠定基础,对胶体流变学和氧化石墨烯悬浮液的材料成型技术有一定理论意义及实用价值。本文主要研究内容和结果如下:（1）通过交叉偏振器观察氧化石墨烯悬浮液的平衡态相结构,浓度低于0.05 wt%时为各向同性相,高于0.25 wt%时形成完全向列相,中间浓度范围则为两相共存区。通过线性黏弹区的频率扫描实验,验证了相转变行为。（2）通过稳态剪切速率扫描,发现氧化石墨稀悬浮液存在明显的应力滞后现象,其与氧化石墨烯悬浮液的黏弹性老化性质和相结构密切相关,松弛时间达到数万秒;蠕变实验测量出不同浓度氧化石墨烯悬浮液的屈服应力,与浓度呈幂率关系,指数为2.32;通过应力增长实验,发现应力在一个区间内跳动,应力增长的瞬态结果与剪切速率扫描的稳态结果都在同一区间,从动力学角度证明了剪切带的存在。（3）通过Maxwell模型对频率扫描结果进行拟合,得出零剪切黏度,并且零剪切黏度与浓度呈现两个幂率,对应两种相结构。使用时间-浓度等效原理,模量和复合黏度能够叠加成一条主曲线,呈现出普适性。由于液晶相结构的存在导致复杂的非线性行为,平移剪切黏度和剪切应力曲线,发现剪切速率低于10 s^-1时曲线难以很好的叠加,对浓度有很强的依赖性,这与其流动不稳定性密切相关,高于10 s^-1时可以叠加成一条主曲线,具有普适性。更多还原

【Abstract】 Graphene oxide is a two-dimensional granular material with a large aspect ratio.It has attracted great attention in materials science and engineering applications,due to its excellent mechanical,electrical and thermal properties,which is more easy to synthesize,easy to process and cheaper than graphene.graphene oxide is easy to disperse in polar solvents,and with the increase of the concentration of particles in the dispersion liquid,it will form isotropic,two-phase coexistence,nematic liquid crystal and other phase structures.The rheological properties of graphene oxide suspensions are crucial for the development of various solution processing and manufacturing technologies.Through the systematic rheological experimental characterization,combined with its phase structure characteristics,the further experimental data analysis lays the foundation for the establishment of the universal graphene oxide suspensions non-equilibrium phase diagram,which has certain theoretical significance and practical value for the colloid rheology and the material forming technology of graphene oxide suspensions.The main research contents and results are as follows:(1)The equilibrium phase structure of graphene oxide suspensions were observed by cross-polarizer.The isotropic phase concentration was below 0.05 wt%,a complete nematic phase was formed above 0.25 wt%,and the intermediate concentration range is a two-phase coexistence zone.The phase transition behavior was verified by frequency scanning experiments in the linear viscoelastic region.(2)Through the scanning of steady-state shear rate,it was found that there was a significant stress lag phenomenon in the dilute suspensions of graphene oxide,which were closely related to the viscoelastic aging properties and phase structure of the graphene oxide suspensions,and its relaxation time reached tens of thousands of seconds.Creep experiments measured the yield stress of graphene oxide suspensions at different concentrations,with a power-law relationship with the concentration and an exponentof 2.32;Through the stress growth experiments,the stress was found to beat within an interval,and the transient result of the stress increase was in the same interval as the steady-state result of the shear rate scan,so the existence of the shear band was proved in terms of dynamics.(3)The frequency scanning results were fitted by the Maxwell model to obtain the zero shear viscosity,and the zero shear viscosity and the concentration showed two power-law,corresponding to the two phase structures.Using the time-concentration equivalence principle,the modulus and composite viscosity could be superimposed into a main curve,showing universality.Due to the existence of liquid crystal phase structure leads to complex nonlinear behavior,translation shear viscosity and shear stress curve,It was found that the shear rate curve was difficult to superposition well below 10s-1,and had a strong dependence on the concentration,which was closely related to its flow instability,and could be superimposed above 10s-1 into a main curve with universality.更多还原