When 3:15 PM - 5:15 PM Dec 08, 2015
Where ACR 2, Building 10, NCRC
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Morphological Design for Block Copolymer/Homopolymer Based Thin Film Blend Systems


Junnan Zhao
Thesis Defense

Peter Green, advisor.

 

Polymer nanocomposites (PNCs) are created by incorporating nanoparticles (NPs) into polymer hosts. The properties of PNCs are determined by various intermolecular interactions and associated morphologies. The Precise control of morphologies and in particular spatial distributions of NPs in PNCs remains an important challenge; in thin films, the presence of interfaces places the additional constraint to control NP locations. These limit potential applications of PNCs. Research in this area has been devoted to bulk single polymer component PNCs: NPs in homopolymers and NPs in diblock copolymers (BCP). Research on thin films or multi polymer components PNCs remains limited despite the potential technological impact. In this dissertation, we designed nano-scale morphologies for thin film BCP/homopolymer blend based systems: (1) applying morphology design rules to create various NP spatial distributions in thin film BCP/homopolymer blends; (2) investigating phase behaviors of potential PNC polymer hosts, thin film BCP/star-shaped homopolymer blends.

 

 

We achieved the control of NP distributions in a mixture of BCP polystyrene-b-poly (2- vinylpyridine) (PS-b-P2VP) with homopolymer polystyrene (PS), in which PS-b-P2VP formed micelles composed of an inner core of P2VP block and an outer corona of PS block. P2VP grafted NPs (P2VP-NPs) were encapsulated within P2VP micelle cores and each micelle contained one or no NP. In the case of PS grafted NPs (PS-NPs), prudent choices of grafted chain lengths and NP sizes enabled us to control NP locations, ranging from preferentially segregating to interfaces (free surface or/and substrate) to primarily locating on the surface of micelle cores. The competing enthalpic and entropic interactions dictate the various morphological structures that are not achievable in the single polymer component PNCs.

 

 

Following that we showed phase behaviors of thin film PS-b-P2VP/star-shaped PS blends could be tailored by the functionality and arm length of star-shaped PS due to its topology and associated entropy effects. The system, in which PS-b-P2VP also formed micelles, exhibited miscibility or phase separation of micelles in star-shaped PS. In the soft colloid-like star PS, close-packed micelles segregated toward the substrate, which is not achieved in the linear PS hosts. The BCP/star-shaped polymer system would increase the “template” available to organize NPs.