Coatings for Light-Actuated Nanoscale Topography

Intellectual Merit. Nature presents us with many examples of how a simple contractile motion can be harnessed for applications as varied as motion, adhesion, superhydrophobicity, and directed fluid flow. In each application, the temporal control of contraction is paired with a unique geometry of actuation to enable real time control of phenomena on nano to macro size scales. This work leverages recent progress made in bulk actuatable materials to develop new chemistry enabling the translation of light-actuated films to new geometries and evaluate the underpinnings of current material limitations. While the basic concept of utilizing light responsive polymers for actuation is not new, these materials are almost exclusively restricted to two-dimensional structures of limited applicability. We propose to rationally design a coating system capable of selective and specific growth of a photo-contractile motion in the complex geometries required of simple actuation modes. The proposed coatings are based on a pairing of ring opening metathesis polymerization (ROMP) with a cyclic azobenzene molecule. This unique chemistry enables 1) growth of conformal coatings on geometrically complex surfaces, 2) growth of polymer bridges across gaps for actuation, 3) direct photopatterning of the coating, and 4) investigation into coating and substrate deformation during actuation in application-relevant geometries. Our approach is targeted to overcome the two most significant challenges to advanced, actuated geometries: Improved control over rational actuator design and uniform coating deposition over complex patterned surfaces. We propose to rationally design monomeric species for the facile, rapid formation of light actuated coatings. Based on ring strain being established as the major driving force for ROMP, we expect to use a computationally guided approach to design azobenzene-containing monomeric species capable of photo-mediated polymerization. We will employ control over azobenzene cis-trans isomerization in the ROMP monomer to actively switch polymerization on and off by modulating monomer ring strain. Density functional theory calculations of molecular conformation free energy will guide experimental efforts through computational evaluation of proposed structures and through investigation into the structural hallmarks of actuatable ring strain. We propose to evaluate the deposition kinetics and coating structure of this new class of material. Based on the active control of monomer ring strain, we expect irradiation dependent growth kinetics enabling topographical patterning. Based on previous results, we expect the formation of light responsive microdomains resulting from a precise repeat structure and dissimilar solubility coefficients. We will deposit photoactive coatings in nanostructured, bridged, and vertically oriented geometries, and we will evaluate the influence of photo-actuation on the responsive coatings and the underlying substrate. We expect analysis of the mechanical response to provide insight into the uniformity of actuation across nanoscale geometries. The development of nanoscale actuation theory will support the integration of these adaptable materials into the next generation applications. Broader Impacts. Research findings will be disseminated to undergraduate students through contributions to lab work, projects and homework in Dr. Berron’s Materials Engineering course. Dr. Berron has a strong commitment to service to the automotive coatings community, and impactful findings will be disseminated through scientific talks at conferences including a keynote address at the Painting Technology Workshop. The computational effort will integrate into ongoing outreach activities at non-PhD granting institutions. Finally, The PIs will continue to attract and retain undergraduate and graduate researchers from underrepresented minorities for the advancement of the proposed work.