Fabrication Of Photonic Crystals And Application Of Photonic Crystal Sensors

Photonic crystal（PhC）is a periodic material composed of high and low dielectric constants.This regular repeating structure has a stop band,and satisfies the Bragg’s law of diffraction.When the diffraction wavelength meets the visible spectrum,the PhC is able to present different colors.With the remarkable advantages of well defined physical properties and visual detection mode,the PhC has been widely used as chemical and biological sensors.The color of PhC could be tuned by changing a series of parameters,such as lattice constant,effective refractive index and titling angle.After embedded PhC into other substrates,like hydrogels,or modified the constitutional unit of PhC,the color switching can be simulated by various external chemical or physical stimuli,and provide visual determination of the concentrations of specific chemical species.In order to further expand the application of PhC,it’s important to fabricate the PhC with larger surface and lower defeat in a more simplified way.Thus the improvement of response speed,mechanical strength,selectivity,sensitivity,reversibility and stability of PhC sensors by integrating other techniques has become another research hotspot.In this thesis,we are focusing on the fabrication and application of PhC sensing materials to overcome the problems of complex preparation process,long response time and low selectivity.The efficient and economic preparation method of PhC was achieved by self-assembling from the spherical colloidal particles on the interface.Meanwhile,the high selectivity of PhC sensors was also obtained by combining molecular imprinted technique（MIT）.Subsequently,the eco-friendly sensing materials with high mechanical strength were applied in the real time visual detection of nitroaromatics,organic solvent and volatile organic compounds（VOCs）.The main contents and results are summarized as following:1)The integration of ion mobility spectrometry（IMS）and molecular imprinted polymers（MIPs）was explored in the on-site detection of nitrobenzene compounds in industrial waste water and surface water,respectively.The high selectivity of the individual IMS to the nitrobenzene compands in these real samples was theoretically elucidated with the transformation energy.The limit of detection（LOD）of 2,4,6-trinitrotoluene（TNT）was 0.1mg/L with a response time of few seconds.What’s more,the adsorption on MIPs could reach up to more than 87%,with 90–105%of recovery with the MIP-IMS system,presenting an excellent adsorption capacity of the nitrobenzene compounds with trace amount in surface water.The real-time on-site detection was achieved without any sample pretreatment.2)The visual detection of TNT was obtained by combining molecular imprinted technology（MIT）and PhC.Monodisperse molecularly imprinted colloidal particles（MICs）for TNT adsorption were prepared by the emulsion polymerization.And then,the MICs were self-assembled into close-packed three-dimensional（3D）PhC.The color of the molecularly imprinted colloidal array（MICA）sensor changed from green through yellow green,to yellow,to orange,and finally to red with an 84 nm diffraction red shift when the TNT concentration increased from 0 to 20 mM.The sensor response time was 3 min with a LOD of 1.03μg.Besides,the MICA sensor has excellent selectivity,stability and reversibility.Subsequently,a colorimetric sensor array of TNT,2,6-dinitrotoluene（2,6-DNT）,2,4-dinitrotoluene（2,4-DNT）and 4-nitrotoluene（4-MNT）templated MICA was constructed to further improve the selectivity and practicalbility of individual sensor.With the assistance of principal component analysis（PCA）,the sensor array can generate a separate response region of nitroaromatics for pattern recognition with 95.25%of significant characteristics by the first three principal components（PCs）.3)By encapsulating a 3D PMMA PhC into an elastic nano-composite hydrogel（NC gel）,an optical nanocomposite hydrogels（ONHs）sensor with high mechanical strength was easily achieved.The ONHs showed instant optical response to the uniaxial tension,and the color changing can cover the entire visible spectrum within 50%strain following Bragg’s law.The mechanical and optical properties can be adjusted via changing the ratio of the co-monomers.And the reversibility could reach up to more than 10 times without any deterioration.Besides,the fast response of ONHs was observed with varying pH values.Owing to the high biocompatibility and self-healing ability of NC gels,and water-stability of ONHs,the optical sensor has high potential to be applied in biomedical field as the implanted materials.After combining the N-Isopropylacrylamide,the ONHs could obtain the thermodynamical response at the same time.4)We embedded the 3D and two-dimensional（2D）PhC into cellulose respectively,to obtain the opal and inverse opal cellulose photonic crystal films（CPCFs）.The CPCFs can be stored and used in without water.And the influence of the particle spacing and average refractive index changing to the optical properties was discussed.By alternately exposed to different organic solvents,like methanol,the 3D inverse opal CPCFs displayed an excellent sensing performance with instantaneously reversible color changes from violet to red in the order of increasing effective refractive index.Besides,the visual detection application of CPCFs for sensing benzene,acetone,ammonia,SO₂ and hydrogen chloride in gas phase was also discussed,which promised a new opportunity for visual gas sensing materials.As a degradable substrate of celluse,the material is eco-friendly.5)A convenient and fast approach to preparing close-packed 3D PhC at the air/water interface was descriped.The self-assembly period could be decreased from one week to three minutes.By blowing N₂ smoothly to the heated PMMA suspension composed of mono-dispersed particles at a certain concentration,the self assemble process could be started and kept going with the lateral capillary force and electrostatic repulsion between the particles.The influence of the N₂ blowing-rate,the microspheres size was discussed,and the floating mechanism was calculated.By applying the p-nitrophenol（p-NP）imprinted colloidal microspheres,a MICA sensor for p-NP sensing could be easily constructed.After embedding it into the NC gels,the visual detection results could be obtained in 3min with a high reversibility of more than 10 times.In conclusion,the functionaliztion and extensive application of PhC sensing materials have attracted considerable interest due to its unique optical property.We expect this work may provide a novel and efficient strategy for the construction of PhC sensors and its application in self-reporting sensing materials.