Browsing by Subject "kinetic theory"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Theory and simulation of polymer adsorption in flowing fluids(2014-09) Dutta, SaritAdsorption and desorption of polymers in the presence of flowing fluids lies at the heart of many technological applications such as thin film deposition via layer-by-layer fabrication, development of surface coatings and responsive interfaces, stabilization of colloidal suspensions, and rheology modifiers. Adsorption under flow also constitutes a key step in many physiological mechanisms, e.g., formation of a platelet plug during hemostasis. Moreover, flow induced adsorption/desorption offers a rich source of problems from the point of view of fundamental polymer physics. However, despite its importance little is understood about the behavior of adsorbed polymers under flow, in contrast to the well-developed field of adsorption from a quiescent solution. Some experimental observations regarding the effect of flow on adsorption/desorption exist in the literature, but they are mutually conflicting and the underlying physics involved is yet to be explained. In this work, we provide new insight into the mechanism of adsorption/desorption under shear flow near a single planar wall using kinetic theory and Brownian dynamics (BD) simulations. We show that in the presence of shear flow accounting for hydrodynamic interactions (HI) between the polymer molecules and the wall is crucial to observe the experimentally obtained trends of the amount of adsorbed polymer with respect to shear rate and molecular weight. The amount adsorbed is governed by a balance between HI-induced repulsion and polymer-wall attraction. At a fixed molecular weight increasing shear rate increases HI, causing a reduction in the amount adsorbed. Moreover, if the shear rate is fixed the amount adsorbed decreases with an increase in molecular weight. These trends are in qualitative agreement with prior experimental observations of Lee and Fuller [J. Colloid Interface Sci. 103, 569 (1985)]. In the case of desorption, the trend for the amount adsorbed with respect to molecular weight depends on the polymer-wall interaction energy. We show that when adsorption is weak, desorption increases with an increase in molecular weight, but for strong adsorption the trend is reversed. We provide an explanation for this reversal in terms of the change in polymer conformations with increase in the interaction energy, thereby resolving the apparently conflicting experimental observations of Lee and Fuller and Soga and Granick [Langmuir 14, 4266 (1998)].Item Thermodynamics of Hot Hadronic Gases at Finite Baryon Densities(2015-11) Albright, MichaelIn this thesis we investigate equilibrium and nonequilibrium thermodynamic properties of Quantum Chromodynamics (QCD) matter at finite baryon densities. We begin by constructing crossover models for the thermodynamic equation of state. These use switching functions to smoothly interpolate between a hadronic gas model at low energy densities to a perturbative QCD equation of state at high energy densities. We carefully design the switching function to avoid introducing first-, second-, or higher-order phase transitions which lattice QCD indicates are not present at small baryon chemical potentials. We employ three kinds of hadronic models in the crossover constructions, two of which include repulsive interactions via an excluded volume approximation while one model does not. We find that the three crossover models are in excellent agreement with accurate lattice QCD calculations of the equation of state over a wide range of temperatures and baryon chemical potentials. Hence, the crossover models should be very useful for parameterizing the equation of state at finite baryon densities, which is needed to build next-generation hydrodynamic simulations of heavy-ion collisions. We next calculate the speed of sound and baryon number fluctuations predicted by the crossover models. We find that crossover models with hadronic repulsion are most successful at reproducing the lattice results, while the model without repulsion is less successful, and hadron (only) models show poor agreement. We then compare the crossover models to net-proton fluctuation measurements from the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC). The comparisons suggest baryon number fluctuations freeze-out well below the chemical freeze-out temperature. We also search for signs of critical fluctuations in the STAR data, but we find no evidence for them at this time. Finally, we derive kinetic theory formulas for the shear and bulk viscosity and thermal conductivity of hot hadronic matter. This generalizes previous works by incorporating baryon chemical potential and a vector mean field into the formalism. We show that the theory is thermodynamically self-consistent and it obeys the Landau-Lifshitz conditions of fit. The formulas should be very useful for predicting transport coefficients in future heavy-ion collision experiments at RHIC and other colliders.