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<meta http-equiv="Content-Type" content="text/html; charset=koi8-r"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif; "><div><b style="text-align: center; "><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></div><span id="OLK_SRC_BODY_SECTION"><div xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Rahul Pandey-
</span></b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">PhD Defense<b><o:p></o:p></b></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">DATE:
</span></b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Friday, April 17, 2015<b><o:p></o:p></b></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">TIME:
</span></b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">12:30 pm<b><o:p></o:p></b></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">PLACE:
</span></b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Civil Engineering Conference Room-N137<b><o:p></o:p></b></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">DISSERTATION CHAIR:
</span></b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Dr. Jacinta Conrad<b><o:p></o:p></b></span></p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></b></p><div class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><hr size="2" width="100%" align="center"></span></b></div><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">TITLE:
<o:p></o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><span style="font-size: 14pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Confined Flow of Attractive Colloidal Suspensions<o:p></o:p></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><span style="font-size: 14pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); "><o:p> </o:p></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal"><b><i><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Abstract<o:p></o:p></span></i></b></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Attractive particulate fluids flowing through complex confined geometries are frequently used in technological applications, such as drilling and fracturing fluids in exploration
and production services or colloidal inks in inkjet printing and three-dimensional printing (or rapid prototyping). While the flow properties of hard-sphere suspensions in micro-scale geometries have been studied extensively, the effects of interparticle attractions
and particle size dispersity on the confined flow properties of particulate suspensions are not well understood. We used confocal microscopy, particle tracking, and bulk rheology to study the confined structure, dynamics, and flow properties of colloid-polymer
mixtures, which serve as simple models of attractive particulate suspensions. We employed poly(methyl-methacrylate) spheres that were suspended in a refractive-index and density- matched solvent, and induced a controlled short-range depletion attraction between
particles by adding non-absorbing linear polystyrene.<o:p></o:p></span></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">First, we investigated the effects of particle size dispersity on confinement-induced solidification of colloid-polymer mixtures. We formulated mixtures of polymer and bidispersed
colloids with particle size ratio a<sub>S</sub>/a<sub>L</sub> — 0.49 at a constant total volume fraction
</span><span style="font-size: 12pt; color: rgb(34, 34, 34); ">f</span><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">T and measured the dynamics of the large particles as a function of the volume fraction of large
particles. The dynamics of large particles became slower as the volume fraction of large particles r=</span><span style="font-size: 12pt; color: rgb(34, 34, 34); ">f</span><sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">L</span></sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">/</span><span style="font-size: 12pt; color: rgb(34, 34, 34); ">f</span><sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">T</span></sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">
was decreased or the confinement thickness was decreased, indicating increasingly solid-like behavior. The slowest dynamics appeared at minimum confinement thickness and minimum volume fraction of large particles.<o:p></o:p></span></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Second, we investigated the effects of variation in particle size dispersity r on the rheology and microstructure of mixtures of polymer and bidispersed colloids. Significant
changes in rheology and microstructure were observed only at high concentration of large particles. By contrast, dense suspensions
</span><span style="font-size: 12pt; color: rgb(34, 34, 34); ">f</span><sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">T</span></sub><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">
= 0.40 were strong gels at all concentration of large particles and exhibited only modest rheological and microstructural changes as volume percent of large particles was varied. These results suggested that the effect of particle size dispersity on the dynamics
and flow properties of colloid-polymer mixtures are most pronounced near the gelation boundary.<o:p></o:p></span></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Third, we investigated the effects of variation in interparticle attractions on the microchannel flow of colloid-polymer mixtures. In suspensions with weak interparticle attractions,
the number density of particles increased downstream in the channel due to shear-induced migration and consolidation by compression. In suspensions with stronger interparticle attractions, an interconnected network of particles suppressed these mechanisms
and prevented the increase in density downstream.<o:p></o:p></span></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Finally, we quantified the effects of particle size dispersity on the confined flow properties of attractive bidispersed suspensions. As the concentration of large particles
was decreased the flow became increasingly non Newtonian at all flow rates. The shear induced migration of large particles increased with increase in flow rate for monodispersed suspension of large particle and decreased when the concentration of large particles
was decreased at all flow rates. These results show that particle size dispersity can be tuned to control and optimize the segregation due to shear migration of a species of particles during microchannel flow.<o:p></o:p></span></p><p class="MsoNormal" style="mso-margin-top-alt:3.0pt;margin-right:0in;margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:normal"><span style="font-size: 12pt; font-family: 'Times New Roman', serif; color: rgb(34, 34, 34); ">Together, our results indicate that the confined structure, dynamics, and flow properties of attractive colloidal suspensions can be controllably tuned from fluid-like to solid-like
by varying the interparticle attractions and the particle size dispersity. Our results establish a platform for development of fundamental understanding for the rational design of suspensions with phase behavior and flow properties for technological applications.<o:p></o:p></span></p></div></div></div></span><style><!--
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