Master of Science (M.S.), University of Dayton, 2022, Chemical Engineering

Nanoparticle additives increase the thermal conductivity of conventional heat transfer fluids like water at low concentrations, which could lead to improved heat transfer fluids and processes. In this study, lignin-based Fe₃O₄ nanoparticles (lignin@Fe₃O₄ ) are investigated as a novel bio-based magnetic nanoparticle additive to enhance the thermal conductivity of aqueous-based fluids. Kraft lignin was used to encapsulate the Fe₃O₄ nanoparticles to increase the dispersion rate and prevent agglomeration and oxidation of the magnetic nanoparticles. Lignin@Fe₃O₄ nanoparticles were prepared using a co-precipitation method and characterized by various experimental techniques, including Transmission Electron Microscopy (TEM) and Vibrating Sampling Magnetometry (VSM). Once fully characterized, lignin@Fe₃O₄ nanoparticles were dispersed in aqueous 0.1 % w/v agar-water solutions at five low concentrations: 0.001 %w/v, 0.002 %w/v, 0.003 %w/v,0.004 %w/v and 0.005 %w/v. Thermal conductivity was measured using METER Group's KD-3 Tempos and the transient line heat source method was used at five different temperature conditions: 25 °C, 30 °C, 35 °C, 40 °C, and 45 °C. Additionally, at room temperature, the thermal conductivity of aqueous-based lignin@Fe₃O₄ suspensions was characterized at the following magnetic fields of 0 Gauss, 100 Gauss, 200 Gauss, 300 Gauss, and 400 Gauss. This study shows an increment of thermal conductivity by about 10% in the highest concentrations and temperature conditions. Additionally, the study also demonstrated the increment of thermal conductivity up to 5% in 200 Gauss magnetic field strength in the highest concentrations at a constant room temperature of 21 °C. This work establishes that lignin-based Fe₃O₄ nanosuspension increases the thermal conductivity of aqueous-based fluids and has the potential to enhance the thermal conductivity of conventional heat transfer fluids.

Committee: Eric Vasquez Ph.D (Committee Chair); Soubantika Palchoudhury Ph.D (Committee Member); Kevin Myers D.Sc (Committee Member) Subjects: Chemical Engineering; Materials Science; Nanoscience

Doctor of Philosophy (PhD), Wright State University, 2019, Engineering PhD

Drop on demand (DOD) inkjet printing has been widely investigated for its low cost, noncontact, high throughput, and reproducible process advantages. This dissertation research sought to capitalize on these advantages for use in micro solid oxide fuel cells (micro SOFCs). Understanding the important variables underpinning the inkjet process, including ink formulation, jet kinematics, and process settings was essential. These variables were evaluated for their impact on drop deposition quality, resolution, microstructure, and electrochemical functionality, with the end goal of making submicron to micron scale ceramic features. Initially, the fluid kinematics of single pass printing was investigated using a dilute, solid-solvent, colloidal, ink suspension of of La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) and α-terpineol. Favorable process conditions were identified that attained uniform, well-shaped, circular dots ~ 0.1 μm thick and ~ 80 μm in diameter. Multiple, sequential ink passes were employed to increase feature dimensions on the x/y/z axes. This required additional process constraints to control deposition quality and resolution of micro features including micro-dots (0-D), micro-lines (1-D) and micro-planes (2-D). Using optimal conditions, 0-D dots and 1-D lines with x/y dimensions < 100 μm and z axis dimensions < 1 μm with dense, open or networked microstructures were demonstrated; in addition 2-D planes having smooth surface and continuous intra-planar ceramic coverage with dimensions as small as ~ 100 μm by ~ 100 μm were achieved. Sintering the inkjetted submicron prototypes produced consolidated submicron films that were uniform, smooth and void of defects such as cracks or delamination. Thermal treatments resulted in grain growth from an average crystallite size of ~158 nm to ~ 356 nm. Heat treatments < 800°C were essential to avoid deleterious effects on electrochemical activity. Electrochemical characterizations of prototypes produced tolerable peak power (open full item for complete abstract)

Committee: Hong Huang Ph.D. (Advisor); Sharmila Mukhopadhyay Ph.D. (Committee Member); Jason Deibel Ph.D. (Committee Member); Lei Kerr Ph.D. (Committee Member); Thomas Reitz Ph.D. (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering

Advancement in computational capacity combined with the emergence of efficient algorithms has made the computational studies very powerful and desirable. Despite the great importance of complex fluids such as emulsions, colloidal suspensions, and gels in many applications, some of their physical and mechanical properties remain poorly understood. To understand rheological and mechanical properties of such systems, one needs to understand their properties at different time and length scales through careful multiscale analysis. To answer these questions, we use Dissipative Particle Dynamics as a versatile coarse-grained method to gain a better understanding of different scales and bridge the gap between the microscopic and macroscopic worlds in particulate multicomponent complex fluids. In Chapter 1, briefly, we introduce the DPD mathematical and physical formalism. In Chapter 2, we examine different algorithms to measure the transport properties of a simple DPD fluid and introduce the new computational method to measure the viscosity of DPD liquids under non-equilibrium conditions to account for the numerical instabilities. In Chapter 3, we discuss the properties of multiphasic systems mainly liquids in liquids. We investigate the effect of molecular composition, configuration, and conformability of surface active molecules in stabilizing immiscible mixtures for flat interfaces as well as curved interfaces. The final section of chapter 3 is dedicated to studying the effect of shear deformation on the geometrical evolution of surfactant covered nanodroplets. In chapter 4, we mainly focus on colloidal suspensions and their rheological responses in nonlinear deformation. Through network analysis, we show that the frictional bonds form a percolated network at volume fractions close to jamming while at volume fractions well below jamming the frictional networks are transient and unstable. Measuring viscosity and normal stresses show the discontinuous (open full item for complete abstract)

Committee: Joao Maia (Committee Chair); Gary Wnek (Committee Member); Michael Hore (Committee Member); Daniel Lacks (Committee Member) Subjects: Engineering; Molecular Physics; Morphology; Physical Chemistry; Physics