Nanometer-scale resolution and depth discrimination in near-field optical microscopy studies of electric-field-induced molecular reorientation dynamics
Identifieur interne : 012037 ( Main/Repository ); précédent : 012036; suivant : 012038Nanometer-scale resolution and depth discrimination in near-field optical microscopy studies of electric-field-induced molecular reorientation dynamics
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Abstract
Electric-field-induced molecular reorientation dynamics in polymer-dispersed liquid crystal (PDLC) films are characterized in detail using near-field scanning optical microscopy (NSOM) methods developed previously [Mei and Higgins, J. Phys. Chem. A 102, 7558 (1998)]. In these experiments, a modulated electric field is applied between the aluminum-coated NSOM probe and an indium-tin-oxide (ITO) substrate. The field causes reorientation of the liquid crystal within the ITO-supported PDLC film. The reorientation process is observed by near-field optical means. In this paper, it is conclusively shown that under appropriate conditions the dynamics observed occur in extremely small volumes, and are substantially confined within the near-field optical regime. The volume in which the dynamics are probed may be controlled by varying the experimental parameters (i.e., field strength and modulation frequency) employed. Conclusive evidence for confinement is obtained from both theoretical arguments and experimental results. Calculations of the electric fields in a model dielectric medium show that the largest fields occur very near the NSOM probe. Experimental observation of spatial variations in the threshold (i.e., the Frederiks transition ) for liquid crystal reorientation provide further evidence. The most direct evidence is provided by the observation of sub-diffraction-limited resolution in dynamics images of ≃ 1 μm thick samples. Spatial variations in the observed dynamics are interpreted to reflect the energetics of local liquid crystal organization, the details of the reorientation process, and also polymer/liquid-crystal interfacial interactions. Finally, important information on the local rotational viscosity and elastic force constants within individual liquid-crystal droplets is obtained. © 2000 American Institute of Physics.
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en" level="a">Nanometer-scale resolution and depth discrimination in near-field optical microscopy studies of electric-field-induced molecular reorientation dynamics</title><author><name sortKey="Mei, Erwen" uniqKey="Mei E">Erwen Mei</name><affiliation wicri:level="2"><inist:fA14 i1="01"><s1>Department of Chemistry, Kansas State University, Manhattan, Kansas 66506</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ></inist:fA14><country xml:lang="fr">États-Unis</country><placeName><region type="state">Kansas</region></placeName><wicri:cityArea>Department of Chemistry, Kansas State University, Manhattan</wicri:cityArea></affiliation></author><author><name sortKey="Higgins, Daniel A" uniqKey="Higgins D">Daniel A. Higgins</name><affiliation wicri:level="2"><inist:fA14 i1="01"><s1>Department of Chemistry, Kansas State University, Manhattan, Kansas 66506</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ></inist:fA14><country xml:lang="fr">États-Unis</country><placeName><region type="state">Kansas</region></placeName><wicri:cityArea>Department of Chemistry, Kansas State University, Manhattan</wicri:cityArea></affiliation></author></titleStmt><publicationStmt><idno type="inist">00-0179573</idno><date when="2000-05-08">2000-05-08</date><idno type="stanalyst">PASCAL 00-0179573 AIP</idno><idno type="RBID">Pascal:00-0179573</idno><idno type="wicri:Area/Main/Corpus">013644</idno><idno type="wicri:Area/Main/Repository">012037</idno></publicationStmt><seriesStmt><idno type="ISSN">0021-9606</idno><title level="j" type="abbreviated">J. chem. phys.</title><title level="j" type="main">The Journal of chemical physics</title></seriesStmt></fileDesc><profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Elastic constants</term><term>Experimental study</term><term>Liquid crystal phase transformations</term><term>Liquid films</term><term>Molecular reorientation</term><term>Polymer dispersed liquid crystals</term><term>near-field scanning optical microscopy</term></keywords><keywords scheme="Pascal" xml:lang="fr"><term>6130G</term><term>6470M</term><term>6116C</term><term>Etude expérimentale</term><term>Cristal liquide dispersé polymère</term><term>Réorientation moléculaire</term><term>Transformation phase cristal liquide</term><term>Film liquide</term><term>Constante élasticité</term></keywords></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">Electric-field-induced molecular reorientation dynamics in polymer-dispersed liquid crystal (PDLC) films are characterized in detail using near-field scanning optical microscopy (NSOM) methods developed previously [Mei and Higgins, J. Phys. Chem. A 102, 7558 (1998)]. In these experiments, a modulated electric field is applied between the aluminum-coated NSOM probe and an indium-tin-oxide (ITO) substrate. The field causes reorientation of the liquid crystal within the ITO-supported PDLC film. The reorientation process is observed by near-field optical means. In this paper, it is conclusively shown that under appropriate conditions the dynamics observed occur in extremely small volumes, and are substantially confined within the near-field optical regime. The volume in which the dynamics are probed may be controlled by varying the experimental parameters (i.e., field strength and modulation frequency) employed. Conclusive evidence for confinement is obtained from both theoretical arguments and experimental results. Calculations of the electric fields in a model dielectric medium show that the largest fields occur very near the NSOM probe. Experimental observation of spatial variations in the threshold (i.e., the Frederiks transition ) for liquid crystal reorientation provide further evidence. The most direct evidence is provided by the observation of sub-diffraction-limited resolution in dynamics images of ≃ 1 μm thick samples. Spatial variations in the observed dynamics are interpreted to reflect the energetics of local liquid crystal organization, the details of the reorientation process, and also polymer/liquid-crystal interfacial interactions. Finally, important information on the local rotational viscosity and elastic force constants within individual liquid-crystal droplets is obtained. © 2000 American Institute of Physics.</div></front></TEI><inist><standard h6="B"><pA><fA01 i1="01" i2="1"><s0>0021-9606</s0></fA01><fA02 i1="01"><s0>JCPSA6</s0></fA02><fA03 i2="1"><s0>J. chem. phys.</s0></fA03><fA05><s2>112</s2></fA05><fA06><s2>18</s2></fA06><fA08 i1="01" i2="1" l="ENG"><s1>Nanometer-scale resolution and depth discrimination in near-field optical microscopy studies of electric-field-induced molecular reorientation dynamics</s1></fA08><fA11 i1="01" i2="1"><s1>MEI (Erwen)</s1></fA11><fA11 i1="02" i2="1"><s1>HIGGINS (Daniel A.)</s1></fA11><fA14 i1="01"><s1>Department of Chemistry, Kansas State University, Manhattan, Kansas 66506</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ></fA14><fA20><s1>7839-7847</s1></fA20><fA21><s1>2000-05-08</s1></fA21><fA23 i1="01"><s0>ENG</s0></fA23><fA43 i1="01"><s1>INIST</s1><s2>127</s2></fA43><fA44><s0>8100</s0><s1>© 2000 American Institute of Physics. All rights reserved.</s1></fA44><fA47 i1="01" i2="1"><s0>00-0179573</s0></fA47><fA60><s1>P</s1></fA60><fA61><s0>A</s0></fA61><fA64 i1="01" i2="1"><s0>The Journal of chemical physics</s0></fA64><fA66 i1="01"><s0>USA</s0></fA66><fC01 i1="01" l="ENG"><s0>Electric-field-induced molecular reorientation dynamics in polymer-dispersed liquid crystal (PDLC) films are characterized in detail using near-field scanning optical microscopy (NSOM) methods developed previously [Mei and Higgins, J. Phys. Chem. A 102, 7558 (1998)]. In these experiments, a modulated electric field is applied between the aluminum-coated NSOM probe and an indium-tin-oxide (ITO) substrate. The field causes reorientation of the liquid crystal within the ITO-supported PDLC film. The reorientation process is observed by near-field optical means. In this paper, it is conclusively shown that under appropriate conditions the dynamics observed occur in extremely small volumes, and are substantially confined within the near-field optical regime. The volume in which the dynamics are probed may be controlled by varying the experimental parameters (i.e., field strength and modulation frequency) employed. Conclusive evidence for confinement is obtained from both theoretical arguments and experimental results. Calculations of the electric fields in a model dielectric medium show that the largest fields occur very near the NSOM probe. Experimental observation of spatial variations in the threshold (i.e., the Frederiks transition ) for liquid crystal reorientation provide further evidence. The most direct evidence is provided by the observation of sub-diffraction-limited resolution in dynamics images of ≃ 1 μm thick samples. Spatial variations in the observed dynamics are interpreted to reflect the energetics of local liquid crystal organization, the details of the reorientation process, and also polymer/liquid-crystal interfacial interactions. 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