ブックタイトル高分子　POLYMERS　62巻12月号

概要

高分子　POLYMERS　62巻12月号

高分子科学最近の進歩Front-Line Polymer Science1D gratings, 2D gratings can also be achieved bylithography or etching. 34）The monolayer CCAs areusually composed of latex nanoparticles. 35）Thesenanoparticles tend to assemble into a close-packedmonolayer on a water surface; thus, the monolayerCCAs can be achieved by transferring them ontosubstrates. Because 2D PhCs are all simply constructedof single monolayer nanostructures, they are easy toreplicate by some methods, such as soft lithography.Thus, 2D PhC hydrogels can be achieved easily.Multilayer CCAs are typical 3D PhCs. They are highlyordered arrays of nanoparticles and are versatile 3Dmaterials for generating responsive PhC hydrogels. 36）Several methods have been developed to assemblethese colloidal nanoparticles into an ordered crystallinestructure. Natural sedimentation is one of the simplestapproaches. 37）Monodispersed nanoparticles slowlyprecipitate under the influence of gravity and packinto a hexagonal arrangement. Although this methodis simple, there is little control over the morphology ofthe prepared colloidal PhCs. To fabricate high qualitycolloidal PhCs, vertical deposition methods providethe most promising approach. 38）The thickness of thePhCs can be controlled by the concentration of thecolloidal suspension. The PhCs prepared by the methodsdescribed above are usually close packed. Although thekinds of colloidal particles are relatively limited, thechoice of dispersion mediums for filling the gaps inthe colloidal particles is extensive. Thus, based on selfassembledCCA templates, diverse PhCs with extremelybroad space-sensitive materials could be made.The non-close-packed colloidal PhCs also belongto 3D class of PhCs. These PhCs are commonly selfassembledelectrostatically from highly chargedmonodispersed nanoparticles. Because the particlesare unconnected, they could be immobilized withinresponsive hydrogels directly to realize their sensingability. 39）3.2 Responsive PhC hydrogels for biosensingAs described above, with the development ofnanofabrication techniques and colloidal self-assemblymethods that are available for PhCs, responsive PhCsensors that undergo structural changes in response toa given stimuli have attracted considerable attention.There are a lot of studies focusing on colored PhCsensors. In the following section, we will describeresponsive PhC sensors that have been developedbased on hydrogels responsive to physical, chemicaland biochemical stimuli.3.2.1 PhC hydrogels responsive to physical stimuliTemperature-responsive PhC hydrogels were firstprepared by Lyon et al. by centrifugation of wellknowntemperature-sensitive PNIPAM hydrogelnanospheres. 31）Thermally induced phase changes of thehydrogel were associated with substantial changes inthe lattice and the refractive index, which altered thePBGs. At present, various strategies have been studiedto create temperature-responsive PhC hydrogels. Yanget al. 30）demonstrated a direct approach to fabricatingtemperature-responsive hydrogel PhCs usinginterference lithography. They used a single refractingprism with a triangular pyramidal frustum shape togenerate 3D interference patterns. By combining prismholographic lithography and hydrogel photoresists, 3Dhydrogel PhCs can be fabricated directly. By usinghydroxyethyl methacrylate（HEMA）-based hydrogels,the viscoelasticity driven temperature-responsivenessin the hydrogel system was explored for the first time.Light-responsive hydrogels have also been usedas the basis for PhC fabrications. Our group 40）hasdemonstrated a photo-responsive PhC with a mixtureof malachite green carbinol base, which can be ionizedinto two charged fragments by UV light. Photo-inducedphase transitions in CCAs were realized by controllingthe delicate balance of interaction forces. The researchgroup led by Asher has achieved the construction oflight-responsive PhCs by polymerizing non-close-packedCCAs in azobenzene-linked hydrogels. After irradiationby UV light, these light-responsive molecules changetheir forms, increasing the free energy of thehydrogel polymer network, and consequent hydrogelswelling. A similar light-responsive hydrogel has beendemonstrated in an inverse opal structure by Takeokaet al. 41）They achieved changes of the structural colorsby using light to induce a controlled temperature.Pressure-responsive PhC hydrogels were first fabricatedby locking the ordered structures of non-close-packedCCAs in a polyacrylamide hydrogel. The diffraction peakwavelengths of the PhC hydrogels were blue-shiftedin response to increased pressure. Flexible polymershave also been used as pressure-responsive PhCs. Kolleet al. 42）built 1D PhC films with a layered structureusing two polymer rubbers. When the PhC films wereunder pressure, the decrease of the layer thicknesscould blue-shift the PBG, and shifts in wavelength acrossthe entire visible spectrum were achieved. Elastomershave also been incorporated into PhCs to developpressure-sensitive materials. Arsenault et al. reported anelastomer inverse opal PhC film by photopolymerization高分子62巻12月号（2013年）c2013 The Society of Polymer Science, Japan745