剪切和拉伸流动下类硬球模型胶体致密悬浮液的剪胀性
Dilatancy in dense suspensions of model hard-sphere-like colloids under shear and extensional flow
AI总结：
本研究实验探究了玻璃态类硬球胶体致密悬浮液的剪切与拉伸流变行为，发现了剪胀效应，构建了包含多种流变响应的状态图，并对比了两种流动下的剪切增稠特性。
摘要：
本研究通过实验考察了玻璃态下具有不同粒径的类硬球模型胶体致密悬浮液在剪切和拉伸流变学行为下的特性。在稳态剪切流动中，我们检测到高于临界剪切速率时会出现不连续剪切增稠（Discontinuous Shear Thickening, DST）。启动剪切实验显示，在DST起始点附近存在应力过冲现象，这与微观形貌的变化相关，此时样品表现出剪胀效应。对法向应力的分析结合高速相机对样品的直接观察表明，在剪切增稠起始点出现了正的第一法向应力差N1和膨胀行为。在拉伸流动中也检测到了剪胀效应。我们通过毛细管破裂和细丝拉伸实验装置对拉伸流动进行了研究，结果显示：当应变速率低于临界应变速率时，样品表现出类液体响应；当应变速率高于临界值时，表现出类固体行为。通过监测不同条件（体积分数和应变速率）下的细丝变细过程，我们构建了一张状态图，展示了硬球悬浮液的所有响应类型（牛顿型、剪切稀化、剪切增稠、剪胀）。最后，我们比较了这些类硬球悬浮液和玻璃态体系在剪切流动与拉伸流动中的剪切增稠响应。
英文摘要：
Dense suspensions of model hard-sphere-like colloids, with different particle sizes, are examined experimentally in the glass state, under shear and extensional rheology. Under steady shear flow we detect Discontinuous Shear Thickening (DST) above a critical shear rate. Start-up shear experiments show stress overshoots in the vicinity of the onset of DST related with a change in microscopic morphology, as the sample shows dilatancy effects. The analysis of the normal stress together with direct sample observation by high speed camera, indicates the appearance of positive N1 and dilation behavior at the shear thickening onset. Dilatancy effects are detected also under extensional flow. The latter was studied through capillary breakup and filament stretching experimental setups, where liquid-like response is seen for strain rate lower than a critical strain rate and solid like-behavior for higher strain rates. Monitoring the filament thinning processes under different conditions (volume fractions and strain rates) we have created a state diagram where all responses of a hard-sphere suspension (Newtonian, shear thinning, shear thickening, dilatant) are shown. We finally compare the shear thickening response of these hard-sphere-like suspensions and glasses in shear with that in extensional flow.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
