Functionalized Polymers for Modifying the Interfacial Properties of Polymers and Inorganic Nanoparticle
Bumjoon Kim
Department of Chemical Engineering
UCSB Doctoral Candidate
Date:
Thursday, June 15, 2006
Time: 4:00 p.m.
Place: Engineering II, Room 3361
ABSTRACT
Diblock copolymers formed by the reaction of end-functional polymers at an interface between immiscible homopolymers lead to a dramatic reduction in the size of dispersed phase droplets and an enhancement of interfacial adhesion. The fundamentals of such reactions were investigated using a model system of amine end-functional deuterated polystyrene (dPS-NH2) and anhydride end-functional poly (2-vinylpyridine) (P2VP-ah). The normalized interfacial excess (ξ) of dPS-NH2 was determined using dynamic secondary ion mass spectrometry. The experimental data for reaction kinetics were fit by the reaction-controlled model. As the molecular weight (Mn) of dPS-NH2 increases, the forward reaction rate coefficient (k+) decreases as Mn-0.68 in reasonable agreement with theoretical predictions. As more diblock copolymers are formed, the interfacial tension decreases to zero, where the interface becomes unstable. The onset of interface roughening as a function of ξ was detected using SFM and TEM for end-functional chains of different Mn. This onset coincides roughly with ξc at which the interface tension vanishes as predicted by SCMFT. At still higher values of ξ > ξc, dPS-b-P2VP polymers are emitted from the interface.
End-functional polymers are also a versatile material for modifying the properties of interfaces between inorganic nanoparticles and polymers. Short thiol terminated PS-SH, P2VP-SH homopolymers and PS-r-P2VP-SH random copolymers were synthesized to prepare polymer-coated gold nanoparticles. The polymer coating enabled these particles to be incorporated into PS-b-P2VP templates with precise control over particle location. Such control was achieved by three different methods producing Au surfaces consisting of: 1.) PS-SH and P2VP-SH with different PS fractions, 2.) PS-r-P2VP with different PS fractions and 3.) PS-SH with different areal chain densities. Polymer-coated particles whose location can be precisely controlled can also induce changes in the block copolymer morphology. Block copolymer films with Au particles located in one domain exhibit phase transitions, caused by their swelling that domain selectively as the particle volume fraction increases. On the other hand an increase in the volume fraction of particles strongly bound to the interface causes a transition to a bicontinuous morphology with domain spacings well below 100 nm, a desirable morphology very difficult to achieve by other means.