The innovation engine for new materials

Paul Kuhn

Paul Kuhn


University of California, Santa Barbara


Chemical Engineering

Site Abroad: 

Technical University Eindhoven, Netherlands


Ghislaine Vantomme

Faculty Sponsor(s): 

Bert Meijer

Faculty Sponsor's Department: 

Chemical Engineering
Chemistry and Biochemistry

Project Title: 

Photo-induced self-oscillating motion of azobenzene-siloxane block copolymers thin films

Project Description: 

Conversion of light into mechanical energy is a large area of interest in material research. It is known that the photo-isomerization of azobenzene units incorporated into nanostructured polymer films can induce macroscopic motion. The goal of this project is to obtain oscillatory motion of polymer films by using a continuous trans-cis-trans isomerization of azobenzenes under continuous ultraviolet irradiation. This was achieved by combining monodisperse siloxanes with azobenzene units to form a block copolymer that micro-phase separates and gives nanoscale organization. The 2-hydroxyazobenzene unit was specially selected for its ability to undergo quick thermal cis to trans relaxation. Polarized Optical Microscopy (POM) imaging and Small Angle X-ray Scattering (SAXS) were used to characterize the organization of the polymer films obtained. The films were continuously irradiated in solution and oscillating vertical motion was observed. These oscillations are likely due to continuous change in the film density, induced by creation of free volume in the film during trans-cis-trans cyclic photo-isomerization of the azobenzene units.