The Assembly And Application Of Responsive Colloidal Crystals Films

Responsive photonic crystal is a smart material with dynamic tuning of electromagnetic wave propagation.It is possible to convert external stimuli into changes of optical signals and structural colors,which shows broad application prospects in green printing,photonic sensors,anti-counterfeiting materials,solar cells and photocatalysis.With the advancement of material technology and the change of actual demand,people have put forward higher requirements for responsive photonic crystal materials.It is desirable to develop large-scale synthesis method for preparation of photonic crystals with high quality,combine functional materials to expand the applications of responsive photonic crystals.What's more,it's also important to deepen the understanding of response principles,which can further improve the sensitivity,respond speed and reproducibility of responsive photonic crystals and realize the miniaturization of photonic crystal devices.Generally,there are two strategies for constructing responsive phtonic crystals.One is to fill the colloidal crystal array with responsive matrix to obtain a composite responsive material,the other is to directly prepare responsive building blocks for assembly of photonic crystals.It is shown that photonic crystals assembled by functional building blocks can take full advantages of colloidal particles,which can further improve the response performance and expand the application of responsive photonic crystals.Therefore,this paper mianly focus on the development of new building blocks with high refractive index,mesoporous or hollow structure.Based on these,we constructed responsive photonic crystal films and explored the new applications in visualized thin layer chromatography,structural color display devices and chemical sensors.Our research is as follow.In Chapter 2,CeO₂ colloidal particles with uniform size are synthesized in a large scale by the polyol method and then CeO₂@SiO₂ colloidal particles are synthesized by in-situ reaction,which can be further assembled to form liquid photonic crystals.Compared with photonic crystals assembled by traditional buiding blocks,the CeO₂@SiO₂ photonic crystal films show highly saturated structural color due to the high refractive index of CeO₂@SiO₂ particles.Furthermore,the particles also have abundant surface chage and high polarizability,which makes the liquid photonic crystal exhibite rapid electric respond speed and good electric stability.More importantly,in contrast to the reported electric filed responsive photonic crystals,the CeO₂@SiO₂liquid photonic crystals have a smaller maximal coherent periodic number and the periodic number of order structures required to show saturated structural color is also smaller.As a result,the CeO₂@SiO₂ liquid photonic crystals show a stronger resistant to the fading of colors under strong electric field,which solves the problem of electro-fading.Using the liquid photonic crystals,an electrically tunable display unit is fabricated to show dynamic patterns under programmed electric field.In Chapter 3,a hierarchically structured photonic crystal film is fabricated by using mesoporous SiO₂ as building blocks,which can be applied to a new photonic crystal based thin layer chromatography?PC-TLC?integrated separation and colorimetric detection of chemical species for the first time.The photonic crystal films contain micron-scale cracks and mesopores,which greatly accelerate the diffusion of developing solvents and improve the separation efficiency due to sufficient adsorption and desorption of analytes.Meanwhile,the chemical substances loaded on the PC film will change the refractive index and structural colors compared to the unloaded region,so that the sample spot can be recongnized directly by naked eyes.Compared with the traditional TLC technology,this new PC-TLC technology identifies chemicals by structural color,no longer requires UV irradiation or dyeing,improving the usability and safety of thin layer chromatography.In Chapter 4,in order to further improve the separation efficiency of PC-TLC,we prepare a SiO₂ photonic crystal film combined with metal-organic framework materials to develop high performance thin layer chromatography?HPTLC?,which achieves the separation of isomers.As a demonstration,o-cresol and m-cresol,which have close structures and hard to be separated by traditional TLC,are chosen as analytes to be developed on MIL-100/PC plate.The MIL-100/PC films possess large surface area and matched window size with cresols,which greatly improves the selectivity of analytes.As a result,it fully compensates for its limited development and thereby limited adsorption-desorption in TLC separation,making it possible to achieve the isomer separation within the development distance of 2 cm,where gas chromatography with long column?30 m?is as required to do the same job.In Chaper 5,a chemical sensor with high precision is fabricated using hollow polymer spheres as building blocks.The diffusion of solvents in the photonic crystal films presents a unique three-step diffusion,including the filling of the voids between spheres,swelling of the hollow sphereical polymer shell and filling of the cavity inside the hollow spheres.It is found that the swelling of polymer shell is the rate-determining step of the whole response process through experiments and silmulation.As the polarity,viscosity,size,configuration and interaction with the polymer of different solvent molecules will affect the diffusion process,precise sensing of common solvents and even isomers is realized by the optical signal changes of photonic crystal.What's more,the diffusion time of solvents can be identified through the structural color change by naked eyes directly,which greatly simplifies the detection process and removes the dependence on instruments.