title: Contactless, photoinitiated snap-through in azobenzene-functionalized polymers.
abstract: Photomechanical effects in polymeric materials and composites transduce light into mechanical work. The ability to control the intensity, polarization, placement, and duration of light irradiation is a distinctive and potentially useful tool to tailor the location, magnitude, and directionality of photogenerated mechanical work. Unfortunately, the work generated from photoresponsive materials is often slow and yields very small power densities, which diminish their potential use in applications. Here, we investigate photoinitiated snap-through in bistable arches formed from samples composed of azobenzene-functionalized polymers (both amorphous polyimides and liquid crystal polymer networks) and report orders-of-magnitude enhancement in actuation rates (approaching 10(2) mm/s) and powers (as much as 1 kW/m(3)). The contactless, ultra-fast actuation is observed at irradiation intensities <<100 mW/cm(2). Due to the bistability and symmetry of the snap-through, reversible and bidirectional actuation is demonstrated. A model is developed to elucidate the underlying mechanics of the snap-through, specifically focusing on isolating the role of sample geometry, mechanical properties of the materials, and photomechanical strain. Using light to trigger contactless, ultrafast actuation in an otherwise passive structure is a potentially versatile tool to use in mechanical design at the micro-, meso-, and millimeter scales as actuators, as well as switches that can be triggered from large standoff distances, impulse generators for microvehicles, microfluidic valves and mixers in laboratory-on-chip devices, and adaptive optical elements.
authors.affiliation: Department of Industrial Engineering, University of Pittsburgh, Pittsburgh, PA 15261.
authors.forename: M Ravi
authors.initials: MR
authors.lastname: Shankar
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Smith
authors.forename: Vincent P
authors.initials: VP
authors.lastname: Tondiglia
authors.forename: Kyung Min
authors.initials: KM
authors.lastname: Lee
authors.forename: Michael E
authors.initials: ME
authors.lastname: McConney
authors.forename: David H
authors.initials: DH
authors.lastname: Wang
authors.forename: Loon-Seng
authors.initials: LS
authors.lastname: Tan
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: White
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D004738:Engineering / Q000379:methods*; D050866:Liquid Crystals / Q000737:chemistry; D008956:Models, Chemical; D010777:Photochemistry / Q000379:methods*; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D001391:Azo Compounds; D011108:Polymers; C009850:azobenzene
keywords: elastic instability; photochemistry