{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/140812"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/140812","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Diffusiophoresis and Auto Stratification in Rapidly Drying Colloidal Suspensions","abstract":"Because of the coupled effects of diffusion, advection, and phoretic transport under non-equilibrium conditions, polydisperse colloidal suspensions exhibit interesting auto-stratification phenomena during rapid drying, where particles of different sizes segregate into layered structures. The physical mechanism responsible for these phenomena is believed to be diffusiophoresis, which refers to the phoretic motion of a particle driven by the concentration gradients of other solutes in the suspension. Although molecular diffusiophoresis, where salts with a molecular size much smaller than the phoretic particles serve as the solutes, is well documented, colloidal diffusiophoresis in polydisperse suspensions displays new features that are not well understood. In this dissertation, a model is developed to enable a systematic study of colloidal diffusiophoresis with molecular dynamics simulation, where the solutes are also colloidal particles with sizes comparable to or even larger than the phoretic particles. The results reveal the effects of the strength of the concentration gradient and the size of the phoretic particles on their diffusiophoretic mobility, which provides a foundation to understand the auto-stratification phenomena in rapidly drying colloidal suspensions featuring size dispersity. Further simulations show that mixtures of particles with similar mass but different shapes also stratify upon rapid drying, alluding to the potential effect of particle shape on diffusiophoresis. Also, analytical interaction potentials are developed for disks in two dimensions (2D) based on the Lennard-Jones 12-6 potential. These potentials are used to study the behavior of 2D suspensions of disks, including their equilibrium and drying properties. Auto-stratification is found to also occur in 2D suspensions of bidisperse disks that are rapidly dried. This points to new features of colloidal diffusiophoresis in 2D suspensions. Finally, a facile strategy is proposed to use a binary mixture of solvents to induce and control the stratification of a binary mixture of colloidal particles suspended in the solvent mixture upon solvent evaporation. Overall, this dissertation provides a molecular understanding of colloidal diffusiophoresis and its relation to auto-stratification phenomena in rapid drying by revealing the effects of particle size and shape, system dimensionality, and solvent composition on diffusiophoresis.","abstract_html":"Because of the coupled effects of diffusion, advection, and phoretic transport under non-equilibrium conditions, polydisperse colloidal suspensions exhibit interesting auto-stratification phenomena during rapid drying, where particles of different sizes segregate into layered structures. The physical mechanism responsible for these phenomena is believed to be diffusiophoresis, which refers to the phoretic motion of a particle driven by the concentration gradients of other solutes in the suspension. Although molecular diffusiophoresis, where salts with a molecular size much smaller than the phoretic particles serve as the solutes, is well documented, colloidal diffusiophoresis in polydisperse suspensions displays new features that are not well understood. In this dissertation, a model is developed to enable a systematic study of colloidal diffusiophoresis with molecular dynamics simulation, where the solutes are also colloidal particles with sizes comparable to or even larger than the phoretic particles. The results reveal the effects of the strength of the concentration gradient and the size of the phoretic particles on their diffusiophoretic mobility, which provides a foundation to understand the auto-stratification phenomena in rapidly drying colloidal suspensions featuring size dispersity. Further simulations show that mixtures of particles with similar mass but different shapes also stratify upon rapid drying, alluding to the potential effect of particle shape on diffusiophoresis. Also, analytical interaction potentials are developed for disks in two dimensions (2D) based on the Lennard-Jones 12-6 potential. These potentials are used to study the behavior of 2D suspensions of disks, including their equilibrium and drying properties. Auto-stratification is found to also occur in 2D suspensions of bidisperse disks that are rapidly dried. This points to new features of colloidal diffusiophoresis in 2D suspensions. Finally, a facile strategy is proposed to use a binary mixture of solvents to induce and control the stratification of a binary mixture of colloidal particles suspended in the solvent mixture upon solvent evaporation. Overall, this dissertation provides a molecular understanding of colloidal diffusiophoresis and its relation to auto-stratification phenomena in rapid drying by revealing the effects of particle size and shape, system dimensionality, and solvent composition on diffusiophoresis.","abstract_has_math":false,"creators":["Liu, Binghan"],"institution":"Virginia Tech","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Physics","degree_department":"Physics","school":null,"contributors":[],"advisors":[],"committee_chairs":["Cheng, Shengfeng"],"committee_members":["Nguyen, Vinh","Kaplan, Cihan Nadir","Liu, Guoliang","Tauber, Uwe C."],"year":2026,"date_issued":"2026-01-14","date_published":"2026-01-14","updated_at":"2026-07-22T22:19:01Z","subjects":["Stratification","Evaporation","Colloidal Suspension","Diffusiophoresis","Molecular Dynamics"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45094"],"render_values":[{"text":"vt_gsexam:45094","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/140812","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Cheng, Shengfeng"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Nguyen, Vinh","Kaplan, Cihan Nadir","Liu, Guoliang","Tauber, Uwe C."]},{"key":"dc:contributor.department","label":"Department","values":["Physics"]},{"key":"dc:creator","label":"Author","values":["Liu, Binghan"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-01-15T09:00:47Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-01-15T09:00:47Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-01-14"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Stratification","Evaporation","Colloidal Suspension","Diffusiophoresis","Molecular Dynamics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45094"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/140812"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Because of the coupled effects of diffusion, advection, and phoretic transport under non-equilibrium conditions, polydisperse colloidal suspensions exhibit interesting auto-stratification phenomena during rapid drying, where particles of different sizes segregate into layered structures. The physical mechanism responsible for these phenomena is believed to be diffusiophoresis, which refers to the phoretic motion of a particle driven by the concentration gradients of other solutes in the suspension. Although molecular diffusiophoresis, where salts with a molecular size much smaller than the phoretic particles serve as the solutes, is well documented, colloidal diffusiophoresis in polydisperse suspensions displays new features that are not well understood. In this dissertation, a model is developed to enable a systematic study of colloidal diffusiophoresis with molecular dynamics simulation, where the solutes are also colloidal particles with sizes comparable to or even larger than the phoretic particles. The results reveal the effects of the strength of the concentration gradient and the size of the phoretic particles on their diffusiophoretic mobility, which provides a foundation to understand the auto-stratification phenomena in rapidly drying colloidal suspensions featuring size dispersity. Further simulations show that mixtures of particles with similar mass but different shapes also stratify upon rapid drying, alluding to the potential effect of particle shape on diffusiophoresis. Also, analytical interaction potentials are developed for disks in two dimensions (2D) based on the Lennard-Jones 12-6 potential. These potentials are used to study the behavior of 2D suspensions of disks, including their equilibrium and drying properties. Auto-stratification is found to also occur in 2D suspensions of bidisperse disks that are rapidly dried. This points to new features of colloidal diffusiophoresis in 2D suspensions. Finally, a facile strategy is proposed to use a binary mixture of solvents to induce and control the stratification of a binary mixture of colloidal particles suspended in the solvent mixture upon solvent evaporation. Overall, this dissertation provides a molecular understanding of colloidal diffusiophoresis and its relation to auto-stratification phenomena in rapid drying by revealing the effects of particle size and shape, system dimensionality, and solvent composition on diffusiophoresis."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["A liquid suspension is a heterogeneous mixture where particles are dispersed in a fluid but do not dissolve. For example, mud is a suspension of fine soil particles like clay, silt, and sometimes fine sand that have sizes varying from microns ($10^{-6}$ meter) to millimeters ($10^{-3}$ meter). Similarly, colloidal suspensions contain particles of sizes from nanometers ($10^{-9}$ meter) to microns. Recent experiments and simulations show that when a colloidal suspension containing small and large particles dries, the particles often do not stay even mixed. Instead, they can develop a layered distribution as the solvent evaporates, and the so-called stratified structure can persist in the final dry film formed by packing particles. These findings point to a cost-effective approach to making multilayered coating films. In this dissertation, I use molecular dynamics simulations, where the motion of each particle and each solvent atom is tracked, to study the drying process of colloidal suspensions. My results help elucidate the molecular mechanisms underlying the stratification phenomena. I further show that stratification occurs not only in suspensions containing spherical particles of different sizes but also in suspensions containing particles of similar sizes but different shapes. Additionally, like 3-dimensional suspensions of spheres, 2-dimensional suspensions of disks of assorted sizes exhibit stratification upon solvent evaporation as well. Finally, I propose a strategy to use a binary solvent mixture, where a solvent of low volatility is mixed with one of high volatility, to induce and control the stratification of a mixture of colloidal particles that have contrasting interactions strengths with the two solvent components. Overall, these results provide a detailed study on stratification of colloidal systems and suggest new ways to design coatings and nanomaterials with precisely controlled internal layering created naturally through drying."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Diffusiophoresis and Auto Stratification in Rapidly Drying Colloidal Suspensions"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Cheng, Shengfeng"],"dc:contributor.committeemember":["Nguyen, Vinh","Kaplan, Cihan Nadir","Liu, Guoliang","Tauber, Uwe C."],"dc:contributor.department":["Physics"],"dc:creator":["Liu, Binghan"],"dc:date.accessioned":["2026-01-15T09:00:47Z"],"dc:date.available":["2026-01-15T09:00:47Z"],"dc:date.issued":["2026-01-14"],"dc:description.abstract":["Because of the coupled effects of diffusion, advection, and phoretic transport under non-equilibrium conditions, polydisperse colloidal suspensions exhibit interesting auto-stratification phenomena during rapid drying, where particles of different sizes segregate into layered structures. The physical mechanism responsible for these phenomena is believed to be diffusiophoresis, which refers to the phoretic motion of a particle driven by the concentration gradients of other solutes in the suspension. Although molecular diffusiophoresis, where salts with a molecular size much smaller than the phoretic particles serve as the solutes, is well documented, colloidal diffusiophoresis in polydisperse suspensions displays new features that are not well understood. In this dissertation, a model is developed to enable a systematic study of colloidal diffusiophoresis with molecular dynamics simulation, where the solutes are also colloidal particles with sizes comparable to or even larger than the phoretic particles. The results reveal the effects of the strength of the concentration gradient and the size of the phoretic particles on their diffusiophoretic mobility, which provides a foundation to understand the auto-stratification phenomena in rapidly drying colloidal suspensions featuring size dispersity. Further simulations show that mixtures of particles with similar mass but different shapes also stratify upon rapid drying, alluding to the potential effect of particle shape on diffusiophoresis. Also, analytical interaction potentials are developed for disks in two dimensions (2D) based on the Lennard-Jones 12-6 potential. These potentials are used to study the behavior of 2D suspensions of disks, including their equilibrium and drying properties. Auto-stratification is found to also occur in 2D suspensions of bidisperse disks that are rapidly dried. This points to new features of colloidal diffusiophoresis in 2D suspensions. Finally, a facile strategy is proposed to use a binary mixture of solvents to induce and control the stratification of a binary mixture of colloidal particles suspended in the solvent mixture upon solvent evaporation. Overall, this dissertation provides a molecular understanding of colloidal diffusiophoresis and its relation to auto-stratification phenomena in rapid drying by revealing the effects of particle size and shape, system dimensionality, and solvent composition on diffusiophoresis."],"dc:description.abstractgeneral":["A liquid suspension is a heterogeneous mixture where particles are dispersed in a fluid but do not dissolve. For example, mud is a suspension of fine soil particles like clay, silt, and sometimes fine sand that have sizes varying from microns ($10^{-6}$ meter) to millimeters ($10^{-3}$ meter). Similarly, colloidal suspensions contain particles of sizes from nanometers ($10^{-9}$ meter) to microns. Recent experiments and simulations show that when a colloidal suspension containing small and large particles dries, the particles often do not stay even mixed. Instead, they can develop a layered distribution as the solvent evaporates, and the so-called stratified structure can persist in the final dry film formed by packing particles. These findings point to a cost-effective approach to making multilayered coating films. In this dissertation, I use molecular dynamics simulations, where the motion of each particle and each solvent atom is tracked, to study the drying process of colloidal suspensions. My results help elucidate the molecular mechanisms underlying the stratification phenomena. I further show that stratification occurs not only in suspensions containing spherical particles of different sizes but also in suspensions containing particles of similar sizes but different shapes. Additionally, like 3-dimensional suspensions of spheres, 2-dimensional suspensions of disks of assorted sizes exhibit stratification upon solvent evaporation as well. Finally, I propose a strategy to use a binary solvent mixture, where a solvent of low volatility is mixed with one of high volatility, to induce and control the stratification of a mixture of colloidal particles that have contrasting interactions strengths with the two solvent components. Overall, these results provide a detailed study on stratification of colloidal systems and suggest new ways to design coatings and nanomaterials with precisely controlled internal layering created naturally through drying."],"dc:description.degree":["Doctor of Philosophy"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:45094"],"dc:identifier.uri":["https://hdl.handle.net/10919/140812"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Stratification","Evaporation","Colloidal Suspension","Diffusiophoresis","Molecular Dynamics"],"dc:title":["Diffusiophoresis and Auto Stratification in Rapidly Drying Colloidal Suspensions"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:19:01Z"}