Phase change materials (PCMs) are latent heat storage materials that can store or release thermal energy during phase transitions. Organic PCM nano-emulsions are formed by emulsifying oil in water in the presence of surfactants, enhancing thermal conductivity and pumpability. However, PCMs nano-emulsions can become unstable due to repeated thermal cycling and shear in heat transfer systems.
To better understand the molecular origins of phase instability in PCMs nano-emulsions, liquid-state nuclear magnetic resonance (NMR) measurements were applied to a model PCM nano-emulsion. Quantitative 1H single-pulse NMR measurements established the liquid fraction of oil within nano-emulsions as a function of temperature, providing insight into octadecane supercooling. Quantitative 13C single-pulse measurements revealed that the surfactant head groups existed in multiple environments while their signal intensities decreased upon repeated thermal cycling, leading to a loss of molecular mobility. The results explain, in part, the origin of phase instability upon thermal cycling.
To investigate the simultaneous effects of shear and thermal cycling, 1H rheo-NMR and MRI velocimetry methods were applied on the model PCM nano-emulsion in a concentric double cylinder at different rotating frequencies during thermal cycling. Double-slice selection was applied to measure the velocity profile and concentration distribution of the oil within the gap, revealing non-linear velocity profiles and the shear-induced mass transport of nano-emulsion droplets. 1H NMR Transverse relaxation times increased at higher shear rates, indicating increased molecular mobility due to shear-induced structural changes.
Overall, this dissertation presents the effective and non-invasive applications of NMR spectroscopy, rheo-NMR, and MRI velocimetry to understand and differentiate the effects of thermal cycling and shear on the phase stability of PCM nano-emulsions up from the molecular level.
","abstract_html":"<p>Phase change materials (PCMs) are latent heat storage materials that can store or release thermal energy during phase transitions. Organic PCM nano-emulsions are formed by emulsifying oil in water in the presence of surfactants, enhancing thermal conductivity and pumpability. However, PCMs nano-emulsions can become unstable due to repeated thermal cycling and shear in heat transfer systems.</p> <p>To better understand the molecular origins of phase instability in PCMs nano-emulsions, liquid-state nuclear magnetic resonance (NMR) measurements were applied to a model PCM nano-emulsion. Quantitative <sup>1</sup>H single-pulse NMR measurements established the liquid fraction of oil within nano-emulsions as a function of temperature, providing insight into octadecane supercooling. Quantitative <sup>13</sup>C single-pulse measurements revealed that the surfactant head groups existed in multiple environments while their signal intensities decreased upon repeated thermal cycling, leading to a loss of molecular mobility. The results explain, in part, the origin of phase instability upon thermal cycling.</p> <p>To investigate the simultaneous effects of shear and thermal cycling, <sup>1</sup>H rheo-NMR and MRI velocimetry methods were applied on the model PCM nano-emulsion in a concentric double cylinder at different rotating frequencies during thermal cycling. Double-slice selection was applied to measure the velocity profile and concentration distribution of the oil within the gap, revealing non-linear velocity profiles and the shear-induced mass transport of nano-emulsion droplets. <sup>1</sup>H NMR Transverse relaxation times increased at higher shear rates, indicating increased molecular mobility due to shear-induced structural changes.</p> <p>Overall, this dissertation presents the effective and non-invasive applications of NMR spectroscopy, rheo-NMR, and MRI velocimetry to understand and differentiate the effects of thermal cycling and shear on the phase stability of PCM nano-emulsions up from the molecular level.</p>","abstract_has_math":false,"creators":["Park, Jungeun"],"institution":null,"degree_name":"Doctor of Philosophy (Ph.D.)","degree_level":"Dissertation","degree_discipline":"Chemical Engineering","degree_department":null,"school":null,"contributors":["Robert J. Messinger"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-01-01T08:00:00Z","date_published":"2024-01-01T08:00:00Z","updated_at":"2026-07-24T01:57:59Z","subjects":["Thermal Energy Storage","PCM nano-emulsion","Phase stability of PCM nano-emulsion","Supercooling","NMR","Rheo-NMR","MRI Velocimetry","Chemical Engineering","Complex Fluids","Engineering"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://academicworks.cuny.edu/cc_etds_theses/1131","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Robert J. Messinger"]},{"key":"dc:creator","label":"Author","values":["Park, Jungeun"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2024-12-20T08:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (Ph.D.)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Thermal Energy Storage","PCM nano-emulsion","Phase stability of PCM nano-emulsion","Supercooling","NMR","Rheo-NMR","MRI Velocimetry","Chemical Engineering","Complex Fluids","Engineering"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://academicworks.cuny.edu/cc_etds_theses/1131"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Phase change materials (PCMs) are latent heat storage materials that can store or release thermal energy during phase transitions. Organic PCM nano-emulsions are formed by emulsifying oil in water in the presence of surfactants, enhancing thermal conductivity and pumpability. However, PCMs nano-emulsions can become unstable due to repeated thermal cycling and shear in heat transfer systems.
To better understand the molecular origins of phase instability in PCMs nano-emulsions, liquid-state nuclear magnetic resonance (NMR) measurements were applied to a model PCM nano-emulsion. Quantitative 1H single-pulse NMR measurements established the liquid fraction of oil within nano-emulsions as a function of temperature, providing insight into octadecane supercooling. Quantitative 13C single-pulse measurements revealed that the surfactant head groups existed in multiple environments while their signal intensities decreased upon repeated thermal cycling, leading to a loss of molecular mobility. The results explain, in part, the origin of phase instability upon thermal cycling.
To investigate the simultaneous effects of shear and thermal cycling, 1H rheo-NMR and MRI velocimetry methods were applied on the model PCM nano-emulsion in a concentric double cylinder at different rotating frequencies during thermal cycling. Double-slice selection was applied to measure the velocity profile and concentration distribution of the oil within the gap, revealing non-linear velocity profiles and the shear-induced mass transport of nano-emulsion droplets. 1H NMR Transverse relaxation times increased at higher shear rates, indicating increased molecular mobility due to shear-induced structural changes.
Overall, this dissertation presents the effective and non-invasive applications of NMR spectroscopy, rheo-NMR, and MRI velocimetry to understand and differentiate the effects of thermal cycling and shear on the phase stability of PCM nano-emulsions up from the molecular level.
"]},{"key":"dc:title","label":"Title","values":["Molecular Origins of Phase Stability in Phase-Change Nano-Emulsions for Thermal Energy Storage by NMR Spectroscopy"]}]}],"canonical_facts":{"dc:contributor":["Robert J. Messinger"],"dc:creator":["Park, Jungeun"],"dc:date.available":["2024-12-20T08:00:00Z"],"dc:description.abstract":["Phase change materials (PCMs) are latent heat storage materials that can store or release thermal energy during phase transitions. Organic PCM nano-emulsions are formed by emulsifying oil in water in the presence of surfactants, enhancing thermal conductivity and pumpability. However, PCMs nano-emulsions can become unstable due to repeated thermal cycling and shear in heat transfer systems.
To better understand the molecular origins of phase instability in PCMs nano-emulsions, liquid-state nuclear magnetic resonance (NMR) measurements were applied to a model PCM nano-emulsion. Quantitative 1H single-pulse NMR measurements established the liquid fraction of oil within nano-emulsions as a function of temperature, providing insight into octadecane supercooling. Quantitative 13C single-pulse measurements revealed that the surfactant head groups existed in multiple environments while their signal intensities decreased upon repeated thermal cycling, leading to a loss of molecular mobility. The results explain, in part, the origin of phase instability upon thermal cycling.
To investigate the simultaneous effects of shear and thermal cycling, 1H rheo-NMR and MRI velocimetry methods were applied on the model PCM nano-emulsion in a concentric double cylinder at different rotating frequencies during thermal cycling. Double-slice selection was applied to measure the velocity profile and concentration distribution of the oil within the gap, revealing non-linear velocity profiles and the shear-induced mass transport of nano-emulsion droplets. 1H NMR Transverse relaxation times increased at higher shear rates, indicating increased molecular mobility due to shear-induced structural changes.
Overall, this dissertation presents the effective and non-invasive applications of NMR spectroscopy, rheo-NMR, and MRI velocimetry to understand and differentiate the effects of thermal cycling and shear on the phase stability of PCM nano-emulsions up from the molecular level.
"],"dc:identifier":["https://academicworks.cuny.edu/cc_etds_theses/1131"],"dc:subject":["Thermal Energy Storage","PCM nano-emulsion","Phase stability of PCM nano-emulsion","Supercooling","NMR","Rheo-NMR","MRI Velocimetry","Chemical Engineering","Complex Fluids","Engineering"],"dc:title":["Molecular Origins of Phase Stability in Phase-Change Nano-Emulsions for Thermal Energy Storage by NMR Spectroscopy"],"thesis:degree_discipline":["Chemical Engineering"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (Ph.D.)"]},"updated_at":"2026-07-24T01:57:59Z"}