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Spectroscopic studies of the optical and structural properties of nano-engineered polymer opals

Spectroscopic studies of the optical and structural properties of nano-engineered polymer opals
Spectroscopic studies of the optical and structural properties of nano-engineered polymer opals

The results of the spectroscopic studies of the optical and structural properties of polymer-based thin film photonic crystals are presented in this thesis. The 3D polymer opal material system is created through the shear-induced self-assembly of core-shell polymer particles leading to the ordering of the polymer spheres into an /ce-lattice. The polymer sphere size can be tuned in the precursor manufacturing polymerization process so that these opals have their optical response in the visible wavelength range. Furthermore, the polymer opal can be straightforwardly doped with nanoparticles en- abling the tailoring of the optical features. The structural ordering of the polymer opal was studied using UV-laser diffraction revealing opal superdomains extending over tens of square-centimetres. UV-diffraction was also used to analyze the unit cell changes of the opal under strain and the results show significant anisotropy depending on the mutual orientation of the opal director and the strain vector. The reflection, transmis- sion and scattering characteristics in the visible wavelength range were studied both by simulations and in experiments. Angle-, strain-, and wavelength-dependent charac- teristics were measured for both undoped and doped opals. The results show that the reflectivity is minimized at the bandgap conditions and at the same time the scattering is maximized. The opals also show colour-scattering features that can be tuned with the inclusion of nanoparticles. The effect of the nanoparticles is to widen the bandgap colour viewing angle and to prune the non-resonant scattering from the opals. Thus the overall colour appearance of the opals is enhanced significantly. These features cannot be understood in the traditional Bragg scattering regime, but new models com- bining nanoparticle-induced multiple scattering and the underlying low-refractive index contrast opal have to be developed. Coherent backscattering studies reveal that the scattering mean free path length is maximized in the vicinity of the bandgap and can be tuned with the nanoparticle doping level. Furthermore, the coherent backscattering spectroscopy results suggest that the opal scattering is most likely a combination of Mie and Rayleigh type contributions and their balance can be affected by the nanoparticle doping level. Finally, the polymer opal thin film photonic crystal shows substantial industrial potential in decorative, sensing, and security applications.

University of Southampton
Pursiainen, Otto Lauri Juhana
b7705c7e-e88c-4031-91ea-9aa4e03acc86
Pursiainen, Otto Lauri Juhana
b7705c7e-e88c-4031-91ea-9aa4e03acc86

Pursiainen, Otto Lauri Juhana (2008) Spectroscopic studies of the optical and structural properties of nano-engineered polymer opals. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The results of the spectroscopic studies of the optical and structural properties of polymer-based thin film photonic crystals are presented in this thesis. The 3D polymer opal material system is created through the shear-induced self-assembly of core-shell polymer particles leading to the ordering of the polymer spheres into an /ce-lattice. The polymer sphere size can be tuned in the precursor manufacturing polymerization process so that these opals have their optical response in the visible wavelength range. Furthermore, the polymer opal can be straightforwardly doped with nanoparticles en- abling the tailoring of the optical features. The structural ordering of the polymer opal was studied using UV-laser diffraction revealing opal superdomains extending over tens of square-centimetres. UV-diffraction was also used to analyze the unit cell changes of the opal under strain and the results show significant anisotropy depending on the mutual orientation of the opal director and the strain vector. The reflection, transmis- sion and scattering characteristics in the visible wavelength range were studied both by simulations and in experiments. Angle-, strain-, and wavelength-dependent charac- teristics were measured for both undoped and doped opals. The results show that the reflectivity is minimized at the bandgap conditions and at the same time the scattering is maximized. The opals also show colour-scattering features that can be tuned with the inclusion of nanoparticles. The effect of the nanoparticles is to widen the bandgap colour viewing angle and to prune the non-resonant scattering from the opals. Thus the overall colour appearance of the opals is enhanced significantly. These features cannot be understood in the traditional Bragg scattering regime, but new models com- bining nanoparticle-induced multiple scattering and the underlying low-refractive index contrast opal have to be developed. Coherent backscattering studies reveal that the scattering mean free path length is maximized in the vicinity of the bandgap and can be tuned with the nanoparticle doping level. Furthermore, the coherent backscattering spectroscopy results suggest that the opal scattering is most likely a combination of Mie and Rayleigh type contributions and their balance can be affected by the nanoparticle doping level. Finally, the polymer opal thin film photonic crystal shows substantial industrial potential in decorative, sensing, and security applications.

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Published date: 2008

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Local EPrints ID: 466516
URI: http://eprints.soton.ac.uk/id/eprint/466516
PURE UUID: 4e506080-be4c-448c-8af2-4b9c748b6c0a

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Date deposited: 05 Jul 2022 05:33
Last modified: 16 Mar 2024 20:45

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Author: Otto Lauri Juhana Pursiainen

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