The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation since the embedded nonpolar spiropyran molecules convert to their polar merocyanine isomers. The process is reversed upon green laser irradiation. Structuring of the photochromic polymeric surfaces with soft lithography enhances significantly the hydrophobicity of the system, indicating that the water droplets on the patterned features interact with air that is trapped in the microcavities, thus creating superhydrophobic air-water contact areas. Furthermore, the light-induced wettability variations of the structured surfaces are enhanced by a factor of 3 compared to those on the flat surfaces. This significant enhancement is attributed to the photoinduced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions.
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.
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