Preparation And Properties Of Polyoxometalate Based Hydrogel Chromotropic Materials

Color changing material is a kind of material that can change color reversibly under external stimulation.This feature makes it have many applications in the field of people's production and life,such as the intelligent window made by electrochromic phenomenon,antiglare rearview mirror.Inkless printing materials,image information storage materials and erasable paper made of photochromic phenomenon.Previous studies on color changing materials mostly focused on rigid materials.With the development of the times,a variety of flexible color changing materials are emerging in recent years.Flexible materials have tensile and bending properties,so they can be better applied in some scenes.According to the different chemical composition,color changing materials can be divided into organic color changing materials and inorganic color changing materials.The advantages and disadvantages of the two are complementary.For example,the former has a variety of color changes,while most of the latter can only change one color.The former has fast response to stimulation,but poor long-term stability.The latter has a slow response to stimulation,but good long-term stability.If we can combine the advantages and disadvantages of the two,it is possible to prepare color changing materials with excellent properties.However,most of the common inorganic color changing materials are mainly WO₃,Ti O₂ and other metal oxides,which are difficult to disperse and dissolve in water or various solvents.Therefore,it greatly limits its development in the field of composite materials.Cheap and easily available polyoxometalates(POM)are one of the inorganic color changing materials.POM has good solubility in water and most organic solvents,and its molecular structure will not change due to the gain and loss of electrons,so it has good stability in the color changing process.They have stable negative charge on the surface,and are easy to composite with positive charge materials.Therefore,it is an ideal inorganic color changing material.Hydrogel,as a polymer material,has a positive charge on its surface.It can be regarded as an ideal carrier for POM.Therefore,in this thesis,we prepared two functional POM hydrogels with electrochromic properties and photochromic properties by compounding two different hydrogels.The specific research contents are as follows:First,we use ionic crosslinking and covalent crosslinking to prepare negatively charged tungstate(P₂W₁₈)as electrochromic unit in polyacrylamide(PAAm)hydrogel by a simple preparation method,and prepare a new electrochromic hydrogel.The hydrogel has simple preparation and low cost.It has both flexibility and transparency,and is also environmental-friendly.The electrochromic degree of hydrogels can be precisely controlled under different voltages.The above characteristics enable electrochromic hydrogels to be applied to display systems,flexible smart windows and wearable devices.Meanwhile,the design strategy of this hydrogel electrochromic material opens up a new direction for the manufacture of electrochromic flexible devices.Second,we used acrylamide(AAm)and sodium alginate(SA)to prepare PAAm/SA double network hydrogels via radical polymerization,and then used them as substrates to load the photochromic unit ammonium molybdate(Mo7)to prepare PAAm/SA-Mo7 strong and tough photochromic hydrogels.Compared with pure PAAm and Mo7,the hydrogel has a great improvement in mechanical properties.The fracture stress and strain are increased by 7 and 30 times respectively.Considering the mechanical properties,the hydrogel also has good optical properties.The initial transmittance of hydrogel with different Mo7concentration reaches over 87%.Photochromic hydrogels can fade under the action of air,and the coloring and fading degree under various conditions can be precisely controlled,and the purpose of controlling fading and speed can be achieved by controlling the ambient temperature.The good transmittance enables the hydrogel to record the image information clearly.Excellent mechanical properties make the hydrogel not damage the information due to external force after recording information.Moreover,the hydrogel also has the function of erasing information and recycling.The above characteristics make it have a broad application prospect in the field of flexible information storage.