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Unsteady Shear Flows of Monodisperse Colloidal Suspensions Using Discrete Particle Simulations
Başlık:
Unsteady Shear Flows of Monodisperse Colloidal Suspensions Using Discrete Particle Simulations
Yazar:
Marenne, Stephanie, author.
ISBN:
9780438002685
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (180 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Jeffrey M. Morris Committee members: James F. Gilchrist; Ilona Kretschmar; Charles M. Maldarelli; Raymond Tu.
Özet:
We study freely-flowing monodisperse colloidal suspensions in time-dependent shear flows: by examining the microstructure and stress simultaneously in this complex fluid, we elucidate the time scales and length scales governing the dynamics of the suspension. The volume fraction of particles in the suspension is in the range 0.3< ф < 0.56, with most results presented at ф =0.4, a volume fraction where particle interactions are important, yet still far from the glassy state. We vary the shear rate: 0.1 < Pe < 1000, where Pe =6pietaya3/ kT represents the balance of hydrodynamic forces to thermal forces. Here, eta is the viscosity of the suspending fluid, y is the shear rate, a is the particle radius and kT is the thermal energy. Most results are computed with Accelerated Stokesian dynamics (ASD), a simulation tool which includes Brownian motion and hydrodynamic interactions (HI) between particles.
We also present results from Brownian dynamics (BD), which include Brownian motion but no HI, and LF DEM simulations, which include Brownian motion, near-field HI and allow for contact and friction between particl We use start-up and cessation of shear flows and oscillatory shear flows to determine the correlations between certain features of the microstructure and the stress tensor. During start-up of shear flow, the shear stresses have an overshoot before reaching steady state, and the strain at which this overshoot happens increases with Pe. The concept of the particle cage, which is popular for interpreting the dynamics of glassy suspensions and directly relates the evolution of the stress to the microstructure, is useful for understanding the origin of this overshoot (the particle breaking its neighbor cage) and predicting the evolution of the strain at the overshoot with Pe. We use the nearest neighbors of the particle as a statistical representation of the particle cage.
Observing the microstructure and stress after cessation of shear flow for suspensions with HI leads to the conclusion that the second normal stress difference has a fast relaxation, which corresponds to the time scale needed for the thin boundary layer of pair distribution function in the compressional quadrant to diffuse after cessation of shear flow, while the first normal stress difference has a slow relaxation, as it involves the angular diffusion of particles on the order of the particle size. The particle cage idea also proves helpful for interpreting the difference between oscillatory shear flows at intermediate strain amplitudes, where the particle does not leave its cage at each reversal, and large strain amplitudes, where it does.
Notlar:
School code: 1606
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(677992.1) | 677992-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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