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| - Photothermal Patterning of Microgel/Gold NanoparticleComposite Colloidal Crystals
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| - We present a new method for laser direct writing in self-assembled hydrogel microparticle colloidalcrystals via photothermal excitation of co-assembled colloidal Au particles. Close-packed colloidal crystalsare assembled from ∼224 nm diameter, thermoresponsive, poly-N-isopropylacrylamide hydrogel microparticles (microgels); these crystals display sharp Bragg diffraction peaks in the mid-visible region of thespectrum due to the periodic dielectric function of the assembly. Raising the temperature of the crystalabove the characteristic volume phase transition temperature of the microgel particles results in a reversiblemelting of the crystalline material due to the particle-based deswelling event. This transition can be usedeither to anneal defects from the crystalline material or to controllably and reversibly convert the assemblyfrom the colored, crystalline state to a nondiffracting glassy material. Crystal-to-glass transitions are similarlyaccomplished via photothermal excitation when 16 nm diameter colloidal Au particles are co-assembledwith the responsive microgels. Excitation of the colloidal Au plasmon absorption with a frequency doubledNd:YAG laser (λ = 532 nm) results in optically directed conversion of either glasses to crystals or crystalsto glasses, depending on the initial state of the assembly and the illumination time. These results representa fundamentally new method for the patterning of self-assembled photonic materials.
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