The structure of colloidosomes with tunable particle density: simulation vs experiment

Colloidosomes are created in the laboratory from a Pickering emulsion of water droplets in oil. The colloidosomes have approximately the same diameter and by choosing (hairy) particles of different diameters it is possible to control the particle density on the droplets. The experiment is performed at room temperature. The radial distribution function of the assembly of (primary) particles on the water droplet is measured in the laboratory and in a computer experiment of a fluid model of particles with pairwise interactions on the surface of a sphere.Comment: 16 pages, 2 tables, 7 figure

Doctor of Philosophy

dissertationNumerical simulation methods, Monte Carlo simulation and phase field simulation methods were applied to the solid state sintering of unequal size particles. A geometrical model describing the solid state sintering was also developed. The numerical simulation methods and developed geometrical model were compared against results of the solid state sintering experiments. Monte Carlo simulations were performed using Kawasaki and Glauber dynamics to accurately simulate the solid state sintering. The simulation results of two unequal particles showed that sintering occurs in three subprocesses: (1) neck growth, (2) coarsening and (3) grain boundary migration. A finite overlap between the three subprocesses was also observed in the simulation results. The phase field model using conserved and nonconserved fields was applied to the sintering in solid state. The thermodynamics equations describing the energetics of the system were developed for performing the phase field simulations. An application of phased field simulations on two unequal size particle yielded results similar to those obtained by Monte Carlo simulations. The phase field simulation method was also applied to sintering of multiple particles. Realistic microstructures of multiparticle simulations were obtained. A geometric model based upon two particles simulation results was developed. The geometrical model describes the overlapping three sintering subprocesses of neck growth, coarsening and grain boundary migration. Analytical expressions for the three subprocesses were developed. These expressions were used to calculate microstructural evolution of two unequal particles and a linear array of particles. The numerical simulations and the developed geometrical model were compared with experimental data. The experimental data were obtained from sintering of nanosized tungsten powders. The geometric model successfully predicted the observed linear grain growth during sintering of tungsten

Modeling and simulation of sintering process across scales

Sintering, as a thermal process at elevated temperature below the melting point, is widely used to bond contacting particles into engineering products such as ceramics, metals, polymers, and cemented carbides. Modelling and simulation as important complement to experiments are essential for understanding the sintering mechanisms and for the optimization and design of sintering process. We share in this article a state-to-the-art review on the major methods and models for the simulation of sintering process at various length scales. It starts with molecular dynamics simulations deciphering atomistic diffusion process, and then moves to microstructure-level approaches such as discrete element method, Monte--Carlo method, and phase-field models, which can reveal subtle mechanisms like grain coalescence, grain rotation, densification, grain coarsening, etc. Phenomenological/empirical models on the macroscopic scales for estimating densification, porosity and average grain size are also summarized. The features, merits, drawbacks, and applicability of these models and simulation technologies are expounded. In particular, the latest progress on the modelling and simulation of selective and direct-metal laser sintering based additive manufacturing is also reviewed. Finally, a summary and concluding remarks on the challenges and opportunities are given for the modelling and simulations of sintering process.Comment: 45 pages, 38 figure

Grain Size Distribution and topological correlations During Ostwald Ripening: Monte Carlo Potts model simulation

Practically most polycrystalline materials such as ceramics are sintered by liquid during processing; for example, tungsten carbide applied for cutting tools. In liquid sintering, grain structure is controlled by Ostwald ripening. In this work, the Monte Carlo Potts model is employed to simulate Ostwald ripening in solid-liquid mixture. Based on the computer simulation

Conformal mapping methods for interfacial dynamics

The article provides a pedagogical review aimed at graduate students in materials science, physics, and applied mathematics, focusing on recent developments in the subject. Following a brief summary of concepts from complex analysis, the article begins with an overview of continuous conformal-map dynamics. This includes problems of interfacial motion driven by harmonic fields (such as viscous fingering and void electromigration), bi-harmonic fields (such as viscous sintering and elastic pore evolution), and non-harmonic, conformally invariant fields (such as growth by advection-diffusion and electro-deposition). The second part of the article is devoted to iterated conformal maps for analogous problems in stochastic interfacial dynamics (such as diffusion-limited aggregation, dielectric breakdown, brittle fracture, and advection-diffusion-limited aggregation). The third part notes that all of these models can be extended to curved surfaces by an auxilliary conformal mapping from the complex plane, such as stereographic projection to a sphere. The article concludes with an outlook for further research.Comment: 37 pages, 12 (mostly color) figure

Saddle-splay modulus of a particle-laden fluid interface

The scaled-particle theory equation of state for the two-dimensional hard-disk fluid on a curved surface is proposed and used to determine the saddle-splay modulus of a particle-laden fluid interface. The resulting contribution to saddle-splay modulus, which is caused by thermal motion of the adsorbed particles, is comparable in magnitude with the saddle-splay modulus of a simple fluid interface.Comment: 10 pages, 2 figure

A Numerical Study of Phase Transitions Inside the Pores of Aerogels

Phase transitions inside the pores of an aerogel are investigated by modelizing the aerogel structure by diffusion-limited cluster-cluster aggregation on a cubic lattice in a finite box and considering $q$-states Potts variables on the empty sites interacting via nearest-neighbours. Using a finite size scaling analysing of Monte-Carlo numerical results, it is concluded that for $q=4$ the transition changes from first order to second order as the aerogel concentration (density) increases. Comparison is made with the case $q=3$ (where the first order transition is weaker in three dimensions) and with the case $q=4$ but for randomly (non correlated) occupied sites. Possible applications to experiments are discussed.Comment: RevTex, 12 pages + 10 postscript figures compressed using "uufiles", To appear in J. of Non-Cryst. Solid

Optimization of the Hot Embossing Parameters and Sintering Characterization for Alumina/Berea Sandstone Sintering

The purpose of this study is to investigate the process of hot embossing on alumina based ceramics as a cost-efficient procedure for manufacturing microfluidic testing components. Alumina ceramics were used as an exploratory phase for the final objective of the project, manufacturing of Berea sandstone based ceramic samples. Previous research has shown potential in using hot embossing on Alumina based ceramics; however, complications with extrusion and micro-structure quality were observed. For this reason, the research performed aimed to produce Berea Sandstone based components by first improving upon the embossing quality of alumina ceramics. The thesis first investigates changes in the extrusion ratio and the subsequent effects observed on the quality of extrudate. Next, improving the quality of embossed microstructures is examined. This is done by varying the MFI as well as changing the embossing speed and temperature. Finally, a preliminary study into the effectiveness of Berea sandstone based ceramics is reported. The improved ram extruder demonstrated improved surface quality in post-extrusion samples which can be attributed to a greater extrusion ratio, enhanced temperature uniformity, and changing the extruder stock material to stainless steel. Alumina samples extruded from the new extruder had an average surface roughness of compared to reported for the previous design. Comparisons of optical scan data showed that a lower MFI provided sharper edges along the testing section; however, demolding from the embossing plate was a challenge often rendering samples unusable. The higher MFI was very easy to demold from the embossing plate and the resolution of the imprinted microstructures improved; therefore, the higher MFI was chosen and other embossing parameters were examined: embossing temperature and speed. It was concluded that low viscosity and slow embossing speeds provide higher quality embossed samples. After inspection of several embossing parameters on microstructure quality, an introductory study into Berea sandstone ceramics was conducted. During sintering, a properly densified sample was not obtained and SEM results indicated a loss of iron oxide on the periphery of the sample. However, this initial step in manufacturing sandstone samples provides invaluable insight into the future of the project

Optimization of the Hot Embossing Parameters and Sintering Characterization for Alumina/Berea Sandstone Ceramics

The purpose of this study is to investigate the process of hot embossing on alumina based ceramics as a cost-efficient procedure for manufacturing microfluidic testing components. Alumina ceramics were used as an exploratory phase for the final objective of the project, manufacturing of Berea sandstone based ceramic samples. These testing components are vital to the growth of various fields ranging from the retrieval of oil and natural gas to studying the water purification process of aquifers. Previous research has shown potential in using hot embossing on Alumina based ceramics; however, complications with extrusion and micro-structure quality were observed. For this reason, the research performed aimed to produce Berea Sandstone based components by first improving upon the embossing quality of alumina ceramics. The thesis first investigates changes in the extrusion ratio and the subsequent effects observed on the quality of extrudate. Next, improving the quality of embossed microstructures is examined. This is done by varying the MFI as well as changing the embossing speed and temperature. Finally, a preliminary study into the effectiveness of Berea sandstone based ceramics is reported. The improved ram extruder demonstrated improved surface quality in post-extrusion samples which can be attributed to a greater extrusion ratio and enhanced temperature uniformity, as well as a changing the extruder stock material to stainless steel. Alumina samples extruded from the new extruder had an average surface roughness of; this was compared to reported for the previous design. Comparisons of optical scan data showed that a lower MFI provided sharper edges along the testing section; however, demolding from the embossing plate was a challenge often rendering samples unusable. The higher MFI was very easy to demold from the embossing plate and the resolution of the imprinted microstructures improved; therefore, the higher MFI was chosen and other embossing parameters were examined: embossing temperature and speed. It was concluded that low viscosity and slow embossing speeds provide higher quality embossed samples. After a thorough inspection of several embossing parameters on microstructure quality, introductory study into substituting Berea sandstone for alumina was conducted. The analysis showed a loss in microstructure resolution when compared to alumina ceramics due to an increase in the average particle size of the sandstone powder. During sintering, a properly densified sample was not obtained and SEM results indicated a loss of iron oxide on the periphery of the sample. However, this initial step in manufacturing sandstone samples provides invaluable insight into the future of the projec