Nonlinear Optical Properties and Structural Characteristics of Ionically Self-Assembled Nanoscale Polymer Films Influenced by Ionic Concentration and Incorporation of Monomer Chromophores

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dc.contributor.authorNeyman, Patrick J.en
dc.contributor.committeechairHeflin, James R.en
dc.contributor.committeememberMarand, Hervé L.en
dc.contributor.committeememberGuido, Louis J.en
dc.contributor.departmentMaterials Science and Engineeringen
dc.date.accessioned2014-03-14T20:38:19Zen
dc.date.adate2002-05-29en
dc.date.available2014-03-14T20:38:19Zen
dc.date.issued2002-04-30en
dc.date.rdate2003-05-29en
dc.date.sdate2002-05-23en
dc.description.abstractIonically self-assembled monolayer (ISAM) films are typically an assemblage of oppositely charged polymers built layer by layer through coulombic attraction utilizing an environmentally friendly process to form ordered structures that are uniform, molecularly smooth, and physically robust. ISAM films have been shown to be capable of the noncentrosymmetric order requisite for a second-order nonlinear optical response. However, films fabricated with a nonlinear optical (NLO) polymer result in significant cancellation of the chromophore orientations. This cancellation occurs by two mechanisms: competitive orientation due to the ionic bonding of the polymer chromophore with the subsequent polycation layer, and random orientation of the chromophores within the bulk of each polyanion layer. A reduction in film thickness accompanied by an increase in net polar ordering is one possible avenue to obtain the second-order nonlinear optical susceptibility chi(2) necessary for electro-optic devices. In this thesis, we will discuss the structural characteristics of ISAM films and explore three novel approaches to obtain the desired characteristics for nonlinear optical response. One approach involves the variation of solution parameters of several different cationic polymers separately from the polyanion solution in order to reduce the competitive chromophore orientation at the layer interfaces and to reduce the thickness of the inactive polycation layer. We have found that the complexity of ISAM films does not allow large chi(2) values in polyion-based films, and that the selection of the polymer cation is vital to achieve second harmonic generation (SHG) at all. The second approach involves the incorporation of dianionic molecules into ISAM films in order to eliminate both competitive chromophore orientation and random chromophore orientation inherent with polymer chromophores. We have also studied the effects of complexing dianionic chromophores with beta-cyclodextrin in order to increase solubility and improve chromophore orientation. This approach fails because the outermost monolayer of dianionic chromophore is only tethered to the preceding polycation layer by a single ionic bond for each molecule, so each chromophore can by dissociated during the following immersion into the cation solution. Finally, we have introduced a novel approach of hybrid covalent / ionic self-assembly which overcomes these disadvantages and yields a substantial increase in chi(2) due to the chromophore being locked in place to the preceding polycation layer by a covalent bond. The films fabricated in this manner yield a chi(2) that rival any polymer-polymer films despite the very low first-order molecular hyperpolarizability beta of the incorporated monomer. This suggests that incorporation of high beta molecules may result in significant improvement of chi(2), holding high promise for the hybrid covalent / ionic self-assembly technique.en
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-05232002-161046en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05232002-161046en
dc.identifier.urihttp://hdl.handle.net/10919/33137en
dc.publisherVirginia Techen
dc.relation.haspartPat_Neyman_Master_Thesis.pdfen
dc.relation.haspartPat_Neyman_Vita.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectsecond harmonic generationen
dc.subjectisamen
dc.subjectpolymeren
dc.subjectionically self assembled monolayersen
dc.subjectnanotechnologyen
dc.subjectthin filmen
dc.subjectchromophoreen
dc.subjectnonlinear opticsen
dc.titleNonlinear Optical Properties and Structural Characteristics of Ionically Self-Assembled Nanoscale Polymer Films Influenced by Ionic Concentration and Incorporation of Monomer Chromophoresen
dc.typeThesisen
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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