剪切增稠液的优化设计及性能研究

发布时间：2018-01-31 10:49

本文关键词： 剪切增稠液 pH值电性能粘度挤压流动　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：剪切增稠液(STF)是一种高浓度的颗粒悬浮液,其分散相颗粒一般为微米或者纳米尺度的颗粒,分散介质为极性溶剂;在适当的剪切作用下,STF的粘度会随着剪切速率的增加而迅速上升。通常情况下,这种粘度的上升可以达到几个数量级。由于其力学性能变化显著,并具有非线性、响应速度快的特点,STF在软体盔甲、阻尼器、减振吸振和控制等装置的设计中引起了广泛的兴趣。近年来,随着理论研究和实验技术的发展,研究人员在关于STF的材料研发、应用开发、微观机理研究等诸多领域已经取得了显著的进展。但是,在STF的性能优化和力学性能研究等方面仍然存在许多亟待解决的问题。本文首先制备了高性能的STF,并能通过调整其pH值控制剪切增稠现象的发生;然后,研制出导电型STF(C-STF)并研究了其与剪切相关的电学性能;接着,讨论了 STF粘度的剪切时间响应特性,总结出了 STF的结构动力学模型并用结构动力学参数描述剪切过程中STF内部结构的变化;最后,研究了 STF在等体积挤压模式下的流动特性,有助于进一步开发基于STF的高性能器械。具体的内容包括以下几个方面:1.STF的制备及其pH值对性能的影响。首先研制了多种剪切增稠效应显著、性质稳定、性能可控的剪切增稠体系。采用向聚苯乙烯-丙烯酸乙酯(PSt-EA)-乙二醇(EG)悬浮液中添加酸碱溶液的方法,对STF进行性能优化,并研究了pH值对PSt-EA基STF性能的影响机理。结果表明,酸碱溶液的种类和浓度都能显著地改变STF的性能。STF的性能与分散相颗粒之间的相互斥力有着密切的关系,Zeta电位可以用来表征分散相颗粒间相互作用力。可以发现PSt-EA基STF的临界剪切速率和Zeta电位存在着线性变化的关系,临界剪切速率随Zeta电位(绝对值)的上升而上升。当STF的pH值偏离等电点较远的时候,斥力增大,粒子簇的形成受到阻碍,剪切增稠现象会被抑制。2.C-STF的研制与相关电学性能的研究。首先,通过将导电颗粒碳纳米管(CNT)分散在传统矿物Si02基STF中,开发出了新型的C-STF并研究了其与剪切相关的电学性能。随着CNT质量分数的增加,C-STF的剪切增稠效应得到加强。与传统的STF不同,由于掺杂了导电颗粒CNT,所制备的C-STF显示出独特的电学性能。当受到剪切作用的时候,C-STF的电阻会显著下降,电阻下降率△R/R的值可以达到90%以上。这种与剪切速率关系密切的电阻特性,可以用作C-STF在工程应用中工作状态的监测特征。此外,分析了 C-STF在不同剪切速率下的阻抗谱响应,提出了一种与实验结果吻合较好的等效电路模型来揭示剪切增稠过程中C-STF内部的颗粒微结构变化。将C-STF的阻抗谱响应归因于其内部的Si02颗粒链的形成、CNT网络的变化、分散相颗粒-分散介质界面以及电极-样品界面的改变。3.STF粘度的剪切时间响应特性。对于PSt-EA基STF,采用剪切速率的阶梯式变化实验来研究其粘度的剪切时间响应特性,发现STF的粘度和临界剪切速率都会受到剪切时间的影响。基于实验结果,提出有效体积分数(EVF)机理,并用这一机理对粘度进行了分析,发现其粘度的剪切时间响应特性与幂律系数有着密切的关系。当剪切速率大于临界值的时候,高幂律系数STF的粘度会迅速增长。然而,剪切时间的增加会延迟剪切增稠的发生,并降低STF的剪切增稠效应。STF的粘度变化可以看作STF内部颗粒结构形成和破坏的动态平衡过程。将实验结果与粘度的无量纲表达式进行分析,总结出关于STF结构参数的动力学模型,并引入结构动力学参数λ来描述STF内部结构的变化。EVF的变化与动力学参数λ的变化成正比,而随着EVF的增加,STF的粘度上升。4.STF在等体积挤压模式下的流动特性。将STF置于流变仪的平行板附件之间等体积径向挤压,研究了其在挤压模式下的流动特性。在挤压过程中,由于颗粒链的形成,STF的法向应力会明显增加。与剪切模式下STF的应力相比,挤压模式下的STF能提供更大的应力。因此,在挤压流动模式下开发新的STF器械可以显著提高工作效率。此外,实验结果表明,在大挤压速度,大质量分数和适当的壁面粗糙度下,STF的法向应力显著增强。此外,对挤压的STF施加恒定的剪切速率,研究了挤压模式下STF剪切粘度的变化。在移动边界的情况下,随着挤压速度的增加,STF的剪切粘度明显增加。挤压会加速STF内部颗粒链的形成,并促进剪切增稠现象的发生。
[Abstract]:Shear thickening fluid (STF) is a kind of high concentration suspension particles, the particles are generally micrometer or nanometer scale particles, the dispersion medium for polar solvent; the shear proper, STF viscosity will increase rapidly with the increase of shear rate. Usually, the rise the viscosity can reach several orders of magnitude. Due to its mechanical properties change significantly, and has a nonlinear, fast response characteristics, STF in software design of armor, damper, vibration and control device in has attracted wide interest. In recent years, with the rapid development of experimental technology and theoretical research, development and application of research personnel at about STF, many areas of materials research and development, the micro mechanism research has made significant progress. However, there are still many problems to be solved in the aspect of STF performance optimization and mechanical properties of the first. The first system of high performance STF was prepared, and by adjusting the pH value to control the occurrence of shear thickening phenomenon; then developed conductive type STF (C-STF) and to study the related electrical properties and shear; then, discusses the response characteristics of the shear viscosity of STF time, summed up the structural dynamics STF the model and structure dynamics parameters to describe the change of internal structure in the shear process of STF; finally, the study of the STF in the volume of extrusion flow characteristics under the mode, contribute to the further development of high performance devices based on STF. The specific contents include the following aspects: the preparation of 1.STF and its influence on the performance of the pH value. We developed a variety of shear thickening effect, stable properties, shear properties of controllable thickening system. Using polystyrene acrylate (PSt-EA) and ethylene glycol (EG) method of adding acid solution in suspension, the performance of STF. , and study the mechanism of the effect of pH value on the properties of PSt-EA based STF. The results show that the mutual repulsion between the performance of the type and concentration of acid solution can significantly change the performance of.STF STF and dispersed phase particles are closely related, the Zeta potential can be used to characterize the interaction between a dispersed phase particle. Found that the relationship between the critical shear rate and Zeta potential of PSt-EA based STF has a linear variation of the critical shear rate with Zeta potential (absolute value) of the rose. When the STF pH value, deviation from the isoelectric point far repulsion increases, the formation of particle cluster is hindered, the research of shear thickening phenomenon by inhibition of.2.C-STF development and related electrical properties. Firstly, the conductive particles of carbon nanotubes (CNT) dispersed in traditional mineral Si02 based STF, developed a new type of C-STF and to study the related electrical properties and shear with CNT. The increase of the content of C-STF, the shear thickening effect has been strengthened. Unlike traditional STF, because the conductive particles doped CNT, C-STF prepared by showing the unique electrical properties. When when subjected to shear, the resistance of C-STF will significantly decrease the resistance rate of decline Delta R/R value can reach above 90% this close relationship between resistance characteristics. With the shear rate, monitoring features can be used as C-STF in the application state. In addition, analysis of the impedance of the C-STF under different shear rates of spectral response, internal C-STF proposed an equivalent circuit model of good agreement with the experimental results to reveal the shear thickening process of micro particles the formation of C-STF structure change. The impedance spectra of Si02 particles due to its internal chain response, changes of the CNT network, the dispersed particle dispersion medium interface and the electrode sample interface changes.3.STF viscosity The response characteristic of the shearing time. For PSt-EA based STF, response time to study the shear viscosity using a step change experiment of shear rate, the viscosity of STF and found that the critical shear rate is affected by the shearing time. Based on the experimental results, put forward the effective volume fraction (EVF) mechanism, and this mechanism the viscosity was analyzed, found that the viscosity shear time is closely related to the response coefficient and power law. When the shear rate is greater than the critical value, high power coefficient STF viscosity will increase rapidly. However, the increase of shear time will delay the occurrence of shear thickening, dynamic balance process and reduce the viscosity the change of STF shear thickening effect of.STF can be regarded as STF internal grain structure formation and destruction. The experimental results and the viscosity of the dimensionless expressions are analyzed, summed up the dynamics of the structure parameters of STF The model, and the introduction of structural dynamics parameter changes to describe changes in the kinetic parameters and lambda.EVF changes the internal structure of the STF is proportional to, and with the increase of EVF, the viscosity of STF increased at.4.STF volume extrusion flow characteristics under the mode of STF is placed in a parallel plate rheometer. The attachment between the volume of radial extrusion. The flow characteristics in the extrusion mode. In the extrusion process, due to the formation of particle chains, STF normal stress will be significantly increased. Compared with the shear stress under the mode of STF, the extrusion mode of STF can provide greater stress. Therefore, the development of new instruments can significantly improve STF the work efficiency in squeeze flow mode. In addition, the experimental results show that the extrusion speed, large mass fraction and proper surface roughness, STF normal stress significantly enhanced. In addition, constant applied shear rate of extruded STF, research With the increase of extrusion speed, the shear viscosity of STF increased significantly. Extrusion accelerated the formation of particle chains inside STF and promoted the shear thickening phenomenon under the moving boundary condition. The shear viscosity of STF increased significantly with the increase of extrusion speed.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O648.22

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