Nanostructured block copolymer films with responsive photonic band gap and nonlinear optical properties
Restricted (Penn State Only)
- Author:
- Xu, Yifan
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 27, 2022
- Committee Members:
- Robert Hickey, Chair & Dissertation Advisor
Enrique Gomez, Outside Unit & Field Member
Venkatraman Gopalan, Major Field Member
Ralph Colby, Major Field Member
John Mauro, Program Head/Chair - Keywords:
- Block copolymer
Photonic band gap property
Nonlinear optical property
Responsive materials - Abstract:
- New materials are highly desired for developing next-generation photonic devices, which can transfer and process information by manipulating light. Two properties are usually involved - photonic band gap and nonlinear optical response - allowing one to guide and modulate light. Although many studies have demonstrated these two properties separately, it is still relatively unexplored if one can fabricate a single material exhibiting both properties with organic materials. Therefore, the primary scope of this dissertation work is to study the optical properties of block copolymers that form self-assembled morphology and the resulting nanostructure aid in orienting nonlinear optical active crystals, with the goal of using this material in future photonic devices. This dissertation starts with two independent studies on photonic band gap and nonlinear optical properties in nanostructured polymer materials. Firstly, a fundamental study on the necessary parameters tuning the resulting photonic band gap properties is designed by using solvent molecules as swelling additives in the self-assembled block copolymer nanostructure, resulting in a responsive and reversible photonic film. Both simulation and experimental results reveal that nanostructure size, size distribution, effective refractive indices, and polymer crystallinity are crucial parameters governing the photonic band gap properties of polymer films. Secondly, an innovative method is developed to configure dipole moment in the semi-crystalline polymer/chromophore co-crystalline film, resulting in significant second-order nonlinear optical responses. By aligning nonlinear optical-active chromophores inside the co-crystalline unit cell, the dipole moment randomization is avoided, leading to a stable material with long-term nonlinear optical properties. Lastly, chromophores are further blended and co-crystallized with block copolymers, which are expected to form self-assembled nanodomains where the optical nonlinearities change alternatingly, providing a model material exhibiting photonic band gap and nonlinear optical properties simultaneously. Additionally, the nanostructure morphology, length scale, and chemical compositions studied in this dissertation are highly tunable. As a result, the optical properties of the targeted block copolymer/chromophore materials are responsive or even reversible, which is yet challenging for inorganic materials. Overall, introducing polymer materials with both photonic band gap and nonlinear optical properties makes it possible to guide and modulate light simultaneously, which would be of interest to apply in future photonic devices and benefit the development of telecommunication networks.