All‐Optical Reversible Actuation of Photochromic‐Polymer Microsystems

Abstract

The morphology of the precursors and end products (crystals) were characterized by scanning electron microscopy (SEM) using a LEO Gemini 1530. The particle size and its distribution were determined from the SEM images with the help of the image measuring software ImageJ (Image Processing and Analysis, Wayne Rasband, National Institutes of Health, Bethesda, MD). Statistical analysis was performed using Origin (Origin Version 6.0, Microcal, Northampton, MA).Electrochemical Testing: Cathode samples were prepared by mixing 20 wt.-% acetylene black and 20 wt.-% wt poly(tetrafluoroethylene) with 60 wt.-% of our LiCoO 2 as an active material. The mixture was pressed with 10 5 kPa onto aluminum foil as a current collector. The complex cathode was punched into 1 cm 1 cm sized pieces.The half cells were prepared by assembling the complex LiCoO 2 cathode, a polyethylene separator, and a lithium-metal foil as a counter electrode. All cells were assembled in an Ar-filled glove box. As liquid electrolyte, a 1 M LiPF 6 solution in a 1:1 mixture of ethylene and dimethyl carbonate was used. The electrochemical tests were conducted at 25.0 C with a 20 h charging and discharging rate (C/20 rate). The ªC-rateº defines the rate at which the battery is charged or discharged per hour relative to its total charge capacity; e.g., a battery rated at 180 mA h g ±1 provides 180 mA g ±1 for one hour if discharged with C/1, while the same battery discharged with C/20 provides 9 mA g ±1 for twenty hours.

Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks

“…Photomechanical effects in polymeric materials have been examined by researchers for more than four decades [1]. Photochromic molecules (primarily azobenzene, although other molecules have been employed [2]) predominately are covalently bonded into the polymer network but at times have been added as a guest molecule [3,4]. The photomechanical response of these materials is strongly dictated by the structure of the polymer network.…”

Photoinduced variable stiffness of spiropyran-based composites

“…The MC aggregates, compared to the initial SP stereoisomers, have less effective partial molar volume. For this reason the polymer chains move closer to each other, 8 forming stronger inter-chain bonds and causing thus an increased stiffness of the sample. Upon VIS light and SP recovery there are no more MC isomers to form aggregates and the composite reverts to the original stiffness.…”

“…A proper choice of the polymer and PMs is necessary in order to tailor effectively the mechanical properties of the material, due to the usually quite low efficiency of the photomechanical effect. So far the photochromic blends of SP and polymers were proposed for applications in rather few papers, e.g., the works of Athanassiou et al 8,9 and Fragouli et al, 10 where it was shown that SP-polymeric films (5 to 10% wt.) can change reversibly their volume due to the isomeric transformations of the embedded photochromic molecules, acting as light-controlled mechanical actuators or as optical gratings with reversible diffraction efficiency.…”

“…The second scenario involves aggregates formation as proposed by Athanassiou et al 8 The colored MC, due to its high polarity, forms dimers or aggregates of zwitterionic character upon UV irradiation in solutions 14 and in polymeric matrices. 8 The latter case was proven by measuring fluorescence spectra of the metastable MC photoisomers responsible for aggregate formation.…”

“…8 The latter case was proven by measuring fluorescence spectra of the metastable MC photoisomers responsible for aggregate formation. The MC aggregates, compared to the initial SP stereoisomers, have less effective partial molar volume.…”