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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013., Some pages printed landscape orientation. Cataloged from PDF version of thesis., Includes bibliographical references (pages 365-399)., We combine pressure, velocimetry and birefringence measurements to study three phenomena for which the fluid rheology plays a dominant role: 1) shear banding in micellar fluids, 2) extension-dominated flows in microfluidic devices, and 3) flow-induced particle migration in microchannels. Firstly, worm-like micellar solutions are model non-Newtonian fluids having a single relaxation time [beta]. At shear rates larger than ... however, these systems exhibit shear banding and non-linear rheological behavior, whose importance is characterized by the Weissenberg number ... We develop a stability criterion for the onset of a purely viscoelastic instability for shear-banding fluids, to establish the limitations of conventional rheometric techniques for studying these fluids. A second challenge for conventional rheometers is inertially-driven secondary flows. The onset of these flows is governed by the Reynolds number ... where U is the velocity, D is the flow geometry length and v is the fluid kinematic viscosity. We develop microfluidic devices to impose shear and extensional deformation rates up to ...at low Re. These experiments combine pressure measurements, micro-particle image velocimetry ([mu]-PIV) and birefringence measurements. We develop a microfluidic chip that enables applied rheologists to quantitatively differentiate between fluid formulations intended for applications at high deformation rates. Finally, we study the interplay between fluid inertia and elasticity on particle migration. The inertially-dominated case is governed by the channel Reynolds number Re, and particle Reynolds number ... where a is the particle diameter. In a microfluidic device, the particle and channel size are on the same order, and hence migration occurs at ... in the so-called 'inertial focusing' regime which may have applications in clinical medicine. However, most physiological fluids are viscoelastic and therefore particle migration in these fluids occurs at high Reynolds and We, by Thomas Joseph Ober., Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010., Cataloged from PDF version of thesis., Includes bibliographical references (p. 203-213)., Worm-like micellar solutions are model non-Newtonian systems on account of their well understood linear viscoelastic behavior. Their high deformation rate, non-linear rheological response, however, remains inadequately characterized and poorly understood. In this study, two worm-like micellar systems composed of either cetylpyridinium chloride (CPyCl) with sodium salicylate (NaSal) or cetyltrimethylammonium bromide (CTAB) with NaSal have been characterized across several orders of magnitude of deformation rate (10-2 < i6 < 104 s- 1 ). This range enables us to span both the linear and non-linear regimes of rheological behavior for both systems. The low deformation rate rheology was characterized using conventional rheometer fixtures. The high deformation rate rheology was determined using microfluidic rheometric devices, which may be exploited to observe the response of a fluid undergoing very large deformation rates at moderate volumetric throughputs, on account of the small lengthscales associated with microfluidic devices. In these experiments, micro-particle image velocimetry (p-PIV) was used to measure the flow kinematics and a commercial birefringence microscopy instrument (ABRIOTM System, CRi., Inc.) was adapted for making full-field measurements of flow-induced birefringence (FIB) in order to obtain high-resolution measurements of the evolution of the average stress and molecular conformation in the fluids undergoing strong deformations. First, the shear banding response of the CPyCl:NaSal system and shear thinning response of the CTAB:NaSal system were observed in Poiseuille flow through a rectilinear microchannel. Then the corresponding behavior in an extension-dominated flow through a converging microchannel was characterized. Qualitative as well as quantitative features of the flow kinematics and conformation were assessed in order to understand how the linear rheological properties of these systems effect their respective constitutive responses in high r, by Thomas J. Ober., S.M.