Amphiphilic block copolymer micelles : creation of functional nanocavities and their use as nanocontainers for controlled release

Block copolymers in solution can self-assemble in to a variety of morphologies, with features on the nanometer length scale. This has lead to significant recent research into this assembly process and a wide range of potential applications. The exchange of block copolymer molecules between micelles and solution is very slow compared to the exchange kinetics observed for low molecular weight surfactant micelles. A favorable result of these slow exchange kinetics is the ability to retain a micellar morphology during casting from selective solvents onto solid substrates; this morphology becomes kinetically trapped in the final thin film upon solvent evaporation, even in cases for which the copolymer composition would suggest a transition to a different equilibrium heterogeneous phase. Control of the structural parameters of the micellar thin films, including micelle core size, micelle corona size and distance between adjacent micelle cores is important for thin film applications. Here we demonstrate the ability to control these structural parameters using polystyrene-block-poly(acrylic acid) (PS-b-PAA) as a model block copolymer system that assembles into spherical micelles in toluene. Several strategies were employed: varying the block copolymer molecular weight, adding PS homopolymer into the micellar solution, and also by the combination of different micellar solutions. Patterning of micelle films on the micron length scale is accomplished via two PDMS stamp-based soft lithographic techniques. PS-b-PAA spherical micelle thin films cast from toluene can undergo rearrangement upon exposure to solvents selective for the PAA block. The solvent swells the PAA micelle core and ruptures the glassy PS corona, a process we termed cavitation. Here we have investigated the conditions required for this cavitation process to occur and the end-state polymer morphology of close-packed films of PS-b-PAA micelles following treatment with a series of short alkyl chain alcohols or aqueous solutions of varying pH and ionic strength. In addition to the effects of solvent conditions, we show that the cavitation process is influenced by the molecular weight of the PS block and is thermally reversible.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Miller, Andrew Craig

Advisor dc:contributor.advisor

• Robert E. Cohen, Paula T. Hammond and Darrell J. Irvine.

• Chemical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46027

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46027