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Microstructure and Rheology of Concentrated Colloidal Suspensions with Varying Nanotribological Interactions

機(jī)譯：具有不同納米摩擦學(xué)相互作用的濃縮膠體懸浮液的微觀結(jié)構(gòu)和流變學(xué)

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The shear thickening of dense colloidal suspensions is an active area of research to understand the non-linear flow response relevant to various processing conditions, such as high-speed coating, spraying, printing, pumping, and other industrial applications. Efforts in theoretical models and simulations seek to examine the underlying physical forces acting between particles in the suspension, including nanotribological forces such as lubrication hydrodynamics and frictional contact forces, to predict suspension shear rheology. However, few experimental investigations directly measure the nanotribological forces acting between particles or measure the associated suspension microstructure under flow, despite these being essential for connecting colloidal forces to the measured bulk rheology. Thus, there is a scientific need to perform direct nanotribological and microstructural measurements to resolve the origins of this complex rheological behavior. Such research has technological value for improving the processing of high solid dense suspensions, which is often limited by shear thickening, and commercial products that benefit from the shear thickening behavior, such as door stops and speed bumps and armor movement reactive fabrics. Thus, the overarching goal of this thesis is to systematically investigate how the nanotribological interactions affect the microstructure and rheology of concentrated colloidal suspensions.This thesis is divided into two research aims: The first aim, presented in Chapters 3 and 4, is to test the theoretical framework of friction contact models with rheological and nanotribological measurements on model suspensions with controlled surface properties. In Chapter 3, we first present comprehensive experimental tests of a friction contact model based on correlating simulation results against rheological measurements for both model and industrial colloidal dispersions complemented by independent estimates of the particle-scale friction coefficients from literature surveys. The comparisons emphasize the sensitivity of the first normal stress difference can distinguish between states of shear thickening dominated by hydrodynamic friction or contact friction. Based on the findings in Chapter 3, a systematic exploration of nanotribological measurements using lateral force microscopy (LFM) is presented in Chapter 4. Our systematic studies qualitatively agree with the Stribeck relationship regardless of the solvent environment. It is also confirmed that the friction coefficient obtained from the bulk rheology lies in the high Sommerfeld number regime, suggesting that directly applying the friction coefficient obtained from the nanotribological measurements for predicting the rheology using the friction contact model is not quantitative.The second aim of this thesis presented in the remaining chapters is to investigate the underlying relationship between suspension microstructure and shear rheology relationship with the aid of small angle neutron scattering (SANS) to further explore consequences of these different nanotribological forces on suspension rheology. In Chapter 5, these effects of nanotribological interparticle interactions are explored via Flow-SANS to identify the microstructural differences in the nearest neighbor distribution under flow between two model colloidal suspensions with very different levels of surface contact friction. We find quantitative differences in the non-equilibrium microstructure resulting from differences in the nanotribological interactions operative in the shear thickened state, demonstrating that microstructural measurements can distinguish between micromechanical mechanisms and that simulations are not accurate enough to statistically predict this. The extent of structure formation in shear thickening is measured in Chapter 6 for showing that hydroclusters are very localized for continuous shear thickening suspensions, with qualitative differences with simulation predi
機(jī)譯：致密膠體懸浮液的剪切增稠是一個(gè)活躍的研究領(lǐng)域，旨在了解與各種加工條件相關(guān)的非線性流動(dòng)響應(yīng)，例如高速涂層、噴涂、印刷、泵送和其他工業(yè)應(yīng)用。理論模型和仿真方面的工作旨在檢查作用在懸浮液中顆粒之間的潛在物理力，包括納米摩擦力，例如潤(rùn)滑流體動(dòng)力學(xué)和摩擦接觸力，以預(yù)測(cè)懸浮液的剪切流變學(xué)。然而，很少有實(shí)驗(yàn)研究直接測(cè)量作用在顆粒之間的納米摩擦力或測(cè)量流動(dòng)下相關(guān)的懸浮微觀結(jié)構(gòu)，盡管這些對(duì)于將膠體力連接到測(cè)量的體流變學(xué)至關(guān)重要。因此，科學(xué)需要進(jìn)行直接的納米摩擦學(xué)和微觀結(jié)構(gòu)測(cè)量，以解決這種復(fù)雜流變行為的起源。此類(lèi)研究對(duì)于改進(jìn)高固體致密懸架的加工具有技術(shù)價(jià)值，高固體致密懸架通常受到剪切增稠的限制，以及受益于剪切增稠行為的商業(yè)產(chǎn)品，例如門(mén)擋和減速帶以及裝甲運(yùn)動(dòng)反應(yīng)織物。因此，本論文的首要目標(biāo)是系統(tǒng)地研究納米摩擦學(xué)相互作用如何影響濃縮膠體懸浮液的微觀結(jié)構(gòu)和流變學(xué)。本論文分為兩個(gè)研究目標(biāo)：第一個(gè)目標(biāo)，在第 3 章和第 4 章中介紹，是在具有受控表面特性的模型懸架上通過(guò)流變學(xué)和納米摩擦學(xué)測(cè)量來(lái)測(cè)試摩擦接觸模型的理論框架。在第 3 章中，我們首先介紹了摩擦接觸模型的綜合實(shí)驗(yàn)測(cè)試，該測(cè)試基于將模擬結(jié)果與模型和工業(yè)膠體分散體的流變測(cè)量相關(guān)聯(lián)，并輔以文獻(xiàn)調(diào)查中對(duì)顆粒級(jí)摩擦系數(shù)的獨(dú)立估計(jì)。比較強(qiáng)調(diào)了第一法向應(yīng)力差的敏感性，可以區(qū)分由流體動(dòng)力摩擦或接觸摩擦主導(dǎo)的剪切增稠狀態(tài)?；诘?3 章中的發(fā)現(xiàn)，第 4 章介紹了使用側(cè)向力顯微鏡 （LFM） 進(jìn)行納米摩擦學(xué)測(cè)量的系統(tǒng)探索。我們的系統(tǒng)研究在定性上同意 Stribeck 關(guān)系，無(wú)論溶劑環(huán)境如何。還證實(shí)了從體流變學(xué)獲得的摩擦系數(shù)位于高 Sommerfeld 數(shù)區(qū)，這表明直接應(yīng)用從納米摩擦學(xué)測(cè)量中獲得的摩擦系數(shù)來(lái)使用摩擦接觸模型預(yù)測(cè)流變學(xué)不是定量的。其余章節(jié)介紹的本論文的第二個(gè)目標(biāo)是借助小角中子散射 （SANS） 研究懸浮微觀結(jié)構(gòu)和剪切流變關(guān)系之間的潛在關(guān)系，以進(jìn)一步探索這些不同的納米摩擦力對(duì)懸浮流變的影響。在第 5 章中，通過(guò) Flow-SANS 探討了納米摩擦學(xué)顆粒間相互作用的這些影響，以確定表面接觸摩擦水平非常不同的兩個(gè)模型膠體懸浮液在流動(dòng)下最近鄰分布的微觀結(jié)構(gòu)差異。我們發(fā)現(xiàn)，在剪切增稠狀態(tài)下，納米摩擦學(xué)相互作用的差異導(dǎo)致了非平衡微觀結(jié)構(gòu)的定量差異，這表明微觀結(jié)構(gòu)測(cè)量可以區(qū)分微觀力學(xué)機(jī)制，并且模擬不夠準(zhǔn)確，無(wú)法對(duì)此進(jìn)行統(tǒng)計(jì)預(yù)測(cè)。第 6 章測(cè)量了剪切增稠中結(jié)構(gòu)形成的程度，以表明水團(tuán)簇對(duì)于連續(xù)剪切增稠懸浮液非常局部，與模擬預(yù)測(cè)存在定性差異

著錄項(xiàng)

  • 作者

    Lee, Yu-Fan.;

  • 作者單位

    University of Delaware.;

    University of Delaware.;

    University of Delaware.;

  • 授予單位 University of Delaware.;University of Delaware.;University of Delaware.;
  • 學(xué)科 Chemical engineering.;Physics.
  • 學(xué)位
  • 年度 2022
  • 頁(yè)碼 314
  • 總頁(yè)數(shù) 314
  • 原文格式 PDF
  • 正文語(yǔ)種 eng
  • 中圖分類(lèi)
  • 關(guān)鍵詞

    Chemical engineering.; Physics.;

    機(jī)譯：化學(xué)工程。;物理。;
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