{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/71713"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/71713","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Phase Transitions and the Effect of External Fields in Thermotropic Main Chain Liquid Crystal Systems","abstract":"The aim of this research was to investigate the unique behavior of thermotropic main chain liquid crystal polymers with regard to phase transitions and their response to surfaces and external fields. Three different aromatic polymers were utilized in this study, including two constitutional isomers with periodic and aperiodic chemical sequences. The experimental techniques employed were x-ray diffraction, optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermally stimulated discharge (TSD). It was discovered that grooved surfaces can strongly influence the molecular orientation of macromolecular liquid crystals especially when coupled with a magnetic field. Specifically, grooves parallel to a magnetic field were found to increase both the rate and ultimate degree of molecular orientation relative to samples exposed to magnetic fields in contact with featureless surfaces. TSD spectra of one of the polymers previously crystallized from the liquid crystalline melt under the influence of an electric field revealed spontaneous repoling upon cooling which is atypical of ordinary polymers. This phenomenon was attributed to unmelted poled crystals that repole the material at lower temperatures. Optical microscopy experiments on the constitutional isomers revealed that birefringent and isotropic phases coexist over a range of 120$\\sp\\circ$C in the aperiodic isomer but only over a range of 5$\\sp\\circ$C in the periodic isomer. A computer simulation suggested that the distribution in chain flexibility in the aperiodic isomer was the source of the broad biphasic range. Finally, measurements of the kinetic rate constant for crystallization from DSC scans revealed that a medium molecular weight random sequence polymer crystallized more rapidly than the ordered sequence polymer and random sequence polymers of high and low molecular weight. This phenomenon has been attributed to an optimum balance between the molecular diffusion rate and the disruption caused by thermal agitation. Values of the relative percent crystallinity were found to monotonically increase with increasing isothermal aging time in the periodic isomer, which may be a reflection of the more facile uniaxial orientational ordering present in this system.","abstract_html":"The aim of this research was to investigate the unique behavior of thermotropic main chain liquid crystal polymers with regard to phase transitions and their response to surfaces and external fields. Three different aromatic polymers were utilized in this study, including two constitutional isomers with periodic and aperiodic chemical sequences. The experimental techniques employed were x-ray diffraction, optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermally stimulated discharge (TSD). It was discovered that grooved surfaces can strongly influence the molecular orientation of macromolecular liquid crystals especially when coupled with a magnetic field. Specifically, grooves parallel to a magnetic field were found to increase both the rate and ultimate degree of molecular orientation relative to samples exposed to magnetic fields in contact with featureless surfaces. TSD spectra of one of the polymers previously crystallized from the liquid crystalline melt under the influence of an electric field revealed spontaneous repoling upon cooling which is atypical of ordinary polymers. This phenomenon was attributed to unmelted poled crystals that repole the material at lower temperatures. Optical microscopy experiments on the constitutional isomers revealed that birefringent and isotropic phases coexist over a range of 120$\\sp\\circ$C in the aperiodic isomer but only over a range of 5$\\sp\\circ$C in the periodic isomer. A computer simulation suggested that the distribution in chain flexibility in the aperiodic isomer was the source of the broad biphasic range. Finally, measurements of the kinetic rate constant for crystallization from DSC scans revealed that a medium molecular weight random sequence polymer crystallized more rapidly than the ordered sequence polymer and random sequence polymers of high and low molecular weight. This phenomenon has been attributed to an optimum balance between the molecular diffusion rate and the disruption caused by thermal agitation. Values of the relative percent crystallinity were found to monotonically increase with increasing isothermal aging time in the periodic isomer, which may be a reflection of the more facile uniaxial orientational ordering present in this system.","abstract_has_math":true,"creators":["Martin, Philip Gene"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Ceramics Engineering","degree_department":null,"school":null,"contributors":["Stupp, Samuel I."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2014,"date_issued":"2014-12-16T19:17:00Z","date_published":"2014-12-16T19:17:00Z","updated_at":"2026-07-22T22:26:05Z","subjects":["Engineering, Materials Science"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(UMI)AAI8908770"],"render_values":[{"text":"(UMI)AAI8908770","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/71713","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Stupp, Samuel I."]},{"key":"dc:creator","label":"Author","values":["Martin, Philip Gene"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2014-12-16T19:17:00Z","10000-01-01","1988"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Ceramics Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Engineering, Materials Science"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/71713","(UMI)AAI8908770"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The aim of this research was to investigate the unique behavior of thermotropic main chain liquid crystal polymers with regard to phase transitions and their response to surfaces and external fields. Three different aromatic polymers were utilized in this study, including two constitutional isomers with periodic and aperiodic chemical sequences. The experimental techniques employed were x-ray diffraction, optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermally stimulated discharge (TSD). It was discovered that grooved surfaces can strongly influence the molecular orientation of macromolecular liquid crystals especially when coupled with a magnetic field. Specifically, grooves parallel to a magnetic field were found to increase both the rate and ultimate degree of molecular orientation relative to samples exposed to magnetic fields in contact with featureless surfaces. TSD spectra of one of the polymers previously crystallized from the liquid crystalline melt under the influence of an electric field revealed spontaneous repoling upon cooling which is atypical of ordinary polymers. This phenomenon was attributed to unmelted poled crystals that repole the material at lower temperatures. Optical microscopy experiments on the constitutional isomers revealed that birefringent and isotropic phases coexist over a range of 120$\\sp\\circ$C in the aperiodic isomer but only over a range of 5$\\sp\\circ$C in the periodic isomer. A computer simulation suggested that the distribution in chain flexibility in the aperiodic isomer was the source of the broad biphasic range. Finally, measurements of the kinetic rate constant for crystallization from DSC scans revealed that a medium molecular weight random sequence polymer crystallized more rapidly than the ordered sequence polymer and random sequence polymers of high and low molecular weight. This phenomenon has been attributed to an optimum balance between the molecular diffusion rate and the disruption caused by thermal agitation. Values of the relative percent crystallinity were found to monotonically increase with increasing isothermal aging time in the periodic isomer, which may be a reflection of the more facile uniaxial orientational ordering present in this system.","Made available in DSpace on 2014-12-16T19:17:00Z (GMT). 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Three different aromatic polymers were utilized in this study, including two constitutional isomers with periodic and aperiodic chemical sequences. The experimental techniques employed were x-ray diffraction, optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermally stimulated discharge (TSD). It was discovered that grooved surfaces can strongly influence the molecular orientation of macromolecular liquid crystals especially when coupled with a magnetic field. Specifically, grooves parallel to a magnetic field were found to increase both the rate and ultimate degree of molecular orientation relative to samples exposed to magnetic fields in contact with featureless surfaces. TSD spectra of one of the polymers previously crystallized from the liquid crystalline melt under the influence of an electric field revealed spontaneous repoling upon cooling which is atypical of ordinary polymers. This phenomenon was attributed to unmelted poled crystals that repole the material at lower temperatures. Optical microscopy experiments on the constitutional isomers revealed that birefringent and isotropic phases coexist over a range of 120$\\sp\\circ$C in the aperiodic isomer but only over a range of 5$\\sp\\circ$C in the periodic isomer. A computer simulation suggested that the distribution in chain flexibility in the aperiodic isomer was the source of the broad biphasic range. Finally, measurements of the kinetic rate constant for crystallization from DSC scans revealed that a medium molecular weight random sequence polymer crystallized more rapidly than the ordered sequence polymer and random sequence polymers of high and low molecular weight. This phenomenon has been attributed to an optimum balance between the molecular diffusion rate and the disruption caused by thermal agitation. Values of the relative percent crystallinity were found to monotonically increase with increasing isothermal aging time in the periodic isomer, which may be a reflection of the more facile uniaxial orientational ordering present in this system.","Made available in DSpace on 2014-12-16T19:17:00Z (GMT). No. of bitstreams: 1 8908770.pdf: 8652893 bytes, checksum: 32224620d2e23bb38271c007abc589d4 (MD5) Previous issue date: 1988","Embargo set by: Seth Robbins for item 71879 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","301 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988."],"dc:identifier":["http://hdl.handle.net/2142/71713","(UMI)AAI8908770"],"dc:subject":["Engineering, Materials Science"],"dc:title":["Phase Transitions and the Effect of External Fields in Thermotropic Main Chain Liquid Crystal Systems"],"dc:type":["text"],"thesis:degree_discipline":["Ceramics Engineering"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:26:05Z"}