本文關(guān)鍵詞： 剪切增稠液 pH值 電性能 粘度 擠壓流動　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：剪切增稠液(STF)是一種高濃度的顆粒懸浮液,其分散相顆粒一般為微米或者納米尺度的顆粒,分散介質(zhì)為極性溶劑;在適當(dāng)?shù)募羟凶饔孟?STF的粘度會隨著剪切速率的增加而迅速上升。通常情況下,這種粘度的上升可以達到幾個數(shù)量級。由于其力學(xué)性能變化顯著,并具有非線性、響應(yīng)速度快的特點,STF在軟體盔甲、阻尼器、減振吸振和控制等裝置的設(shè)計中引起了廣泛的興趣。近年來,隨著理論研究和實驗技術(shù)的發(fā)展,研究人員在關(guān)于STF的材料研發(fā)、應(yīng)用開發(fā)、微觀機理研究等諸多領(lǐng)域已經(jīng)取得了顯著的進展。但是,在STF的性能優(yōu)化和力學(xué)性能研究等方面仍然存在許多亟待解決的問題。本文首先制備了高性能的STF,并能通過調(diào)整其pH值控制剪切增稠現(xiàn)象的發(fā)生;然后,研制出導(dǎo)電型STF(C-STF)并研究了其與剪切相關(guān)的電學(xué)性能;接著,討論了 STF粘度的剪切時間響應(yīng)特性,總結(jié)出了 STF的結(jié)構(gòu)動力學(xué)模型并用結(jié)構(gòu)動力學(xué)參數(shù)描述剪切過程中STF內(nèi)部結(jié)構(gòu)的變化;最后,研究了 STF在等體積擠壓模式下的流動特性,有助于進一步開發(fā)基于STF的高性能器械。具體的內(nèi)容包括以下幾個方面:1.STF的制備及其pH值對性能的影響。首先研制了多種剪切增稠效應(yīng)顯著、性質(zhì)穩(wěn)定、性能可控的剪切增稠體系。采用向聚苯乙烯-丙烯酸乙酯(PSt-EA)-乙二醇(EG)懸浮液中添加酸堿溶液的方法,對STF進行性能優(yōu)化,并研究了pH值對PSt-EA基STF性能的影響機理。結(jié)果表明,酸堿溶液的種類和濃度都能顯著地改變STF的性能。STF的性能與分散相顆粒之間的相互斥力有著密切的關(guān)系,Zeta電位可以用來表征分散相顆粒間相互作用力�？梢园l(fā)現(xiàn)PSt-EA基STF的臨界剪切速率和Zeta電位存在著線性變化的關(guān)系,臨界剪切速率隨Zeta電位(絕對值)的上升而上升。當(dāng)STF的pH值偏離等電點較遠的時候,斥力增大,粒子簇的形成受到阻礙,剪切增稠現(xiàn)象會被抑制。2.C-STF的研制與相關(guān)電學(xué)性能的研究。首先,通過將導(dǎo)電顆粒碳納米管(CNT)分散在傳統(tǒng)礦物Si02基STF中,開發(fā)出了新型的C-STF并研究了其與剪切相關(guān)的電學(xué)性能。隨著CNT質(zhì)量分數(shù)的增加,C-STF的剪切增稠效應(yīng)得到加強。與傳統(tǒng)的STF不同,由于摻雜了導(dǎo)電顆粒CNT,所制備的C-STF顯示出獨特的電學(xué)性能。當(dāng)受到剪切作用的時候,C-STF的電阻會顯著下降,電阻下降率△R/R的值可以達到90%以上。這種與剪切速率關(guān)系密切的電阻特性,可以用作C-STF在工程應(yīng)用中工作狀態(tài)的監(jiān)測特征。此外,分析了 C-STF在不同剪切速率下的阻抗譜響應(yīng),提出了一種與實驗結(jié)果吻合較好的等效電路模型來揭示剪切增稠過程中C-STF內(nèi)部的顆粒微結(jié)構(gòu)變化。將C-STF的阻抗譜響應(yīng)歸因于其內(nèi)部的Si02顆粒鏈的形成、CNT網(wǎng)絡(luò)的變化、分散相顆粒-分散介質(zhì)界面以及電極-樣品界面的改變。3.STF粘度的剪切時間響應(yīng)特性。對于PSt-EA基STF,采用剪切速率的階梯式變化實驗來研究其粘度的剪切時間響應(yīng)特性,發(fā)現(xiàn)STF的粘度和臨界剪切速率都會受到剪切時間的影響�；趯嶒灲Y(jié)果,提出有效體積分數(shù)(EVF)機理,并用這一機理對粘度進行了分析,發(fā)現(xiàn)其粘度的剪切時間響應(yīng)特性與冪律系數(shù)有著密切的關(guān)系。當(dāng)剪切速率大于臨界值的時候,高冪律系數(shù)STF的粘度會迅速增長。然而,剪切時間的增加會延遲剪切增稠的發(fā)生,并降低STF的剪切增稠效應(yīng)。STF的粘度變化可以看作STF內(nèi)部顆粒結(jié)構(gòu)形成和破壞的動態(tài)平衡過程。將實驗結(jié)果與粘度的無量綱表達式進行分析,總結(jié)出關(guān)于STF結(jié)構(gòu)參數(shù)的動力學(xué)模型,并引入結(jié)構(gòu)動力學(xué)參數(shù)λ來描述STF內(nèi)部結(jié)構(gòu)的變化。EVF的變化與動力學(xué)參數(shù)λ的變化成正比,而隨著EVF的增加,STF的粘度上升。4.STF在等體積擠壓模式下的流動特性。將STF置于流變儀的平行板附件之間等體積徑向擠壓,研究了其在擠壓模式下的流動特性。在擠壓過程中,由于顆粒鏈的形成,STF的法向應(yīng)力會明顯增加。與剪切模式下STF的應(yīng)力相比,擠壓模式下的STF能提供更大的應(yīng)力。因此,在擠壓流動模式下開發(fā)新的STF器械可以顯著提高工作效率。此外,實驗結(jié)果表明,在大擠壓速度,大質(zhì)量分數(shù)和適當(dāng)?shù)谋诿娲植诙认?STF的法向應(yīng)力顯著增強。此外,對擠壓的STF施加恒定的剪切速率,研究了擠壓模式下STF剪切粘度的變化。在移動邊界的情況下,隨著擠壓速度的增加,STF的剪切粘度明顯增加。擠壓會加速STF內(nèi)部顆粒鏈的形成,并促進剪切增稠現(xiàn)象的發(fā)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.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O648.22

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