| Photochromic materials,have many important applications in the fields of optics,chemical sensing,storage and anti-counterfeiting because of their significant and reversible color change under UV light.Over the years,related research has emerged in large numbers.Especially in recent years,the application of photochromic soft materials such as gels and functional films in information storage,inkless printing and rewritable paper has attracted the interest of researchers.The current photochromic units are mainly represented by organic molecular typified by azobenzene,diarylethene and spiropyran,and inorganic materials such as a polyoxometalate?POM?or transition metal oxide.These two types of color-changing units have their own advantages and disadvantages:photochromic materials based on organic color-changing units have fast response speed and various colors,but their stability are still insufficient,and they are easily interfered by other molecules or atoms;the inorganic photochromic units have good stability and can withstand multiple discoloration fading cycles,but the response speed is slow and the color is relatively simple.Inorganic materials exhibit certain advantages over organic materials in stability,but many inorganic color-changing units based on metal oxides such as tungsten trioxide have poor solubility,and the preparation methods when combined with other materials are complicated.Among the inorganic photochromic materials,POM has stable negative charges on the surface.So,its solubility is good,and it is easy to combine with a positively charged material to become an excellent choice for inorganic photochromic materials.It can tolerate certain electron gains and losses without causing significant changes in the molecular structure,which is beneficial to achieve a stable reversible photochromic process.Importantly,it is widely used and relatively inexpensive,which is beneficial to the large-amount industrial production of such photochromic materials in the future.Therefore,we have designed a series of photochromic soft materials with low-cost,widely used ammonium molybdate[?NH4?6Mo7O24]?Mo7?as photochromic unit.In this thesis,we use the negative charge of Mo7 surface to combine with different positively charged polymer materials and obtain a series of photochromic gels and film materials and explore their applications.The specific research contents are as follows:First,we introduced Mo7 into a polyacrylamide?PAAm?hydrogel to obtain a hydrogel material with fast photochromic properties.This hydrogel had good transparency and rapid photochromism.The degree of photochromism could be precisely controlled by controlling the time and intensity of UV light irradiation.It could fade under the action of oxygen,and the increased in temperature and oxygen concentration could speed up the fading process.The temperature control allowed precise control of the fading time.The hydrogel material could be used to display and store traditional information such as images and texts and could also be used to store digital information such as two-dimensional QR codes and binary data.The hydrogel had flexibility and stretchability and was resistant to stress fatigue.The mechanical behavior did not change after 1000 cycles of continuous cyclic stretching at 50%strain,and the hydrogel itself did not deform.This made it impossible for information to be lost due to deformation.The stored information could be erased and rewritten and could be preserved for long-term storage by drying or freezing.Through the precise control of the photochromic process,the storage density could be doubled when storing binary data.This hydrogel also had application in optical protective materials and adjustable optical filters.Second,based on the previous work,we obtained a high strength photochromic hydrogel by using a hydrophobically-associated PAAm network and gelatin.Compared with the previous work,the strength of this hydrogel was 16 times higher than that of the previous work,and its resistance to continuous compression was good.It was continuously compressed 5 times under 90%strain,and its mechanical properties and shape did not change significantly.We studied the principle of high mechanical strength of hydrogel by cyclic stretching,which showed that gelatin played an important role in the high strength of the hydrogel.This hydrogel had good photochromic properties and was capable of forming text or patterns on the surface.A variety of color writings could be written on the surface of the hydrogel with appropriate reducing reagents.This hydrogel exhibited applications in inkless printing and had potential as a writing and printing medium in the future.Third,we introduced Mo7 into gelatin to prepare a series of photochromic films,and the properties of the films could be controlled by the addition of triethylene glycol?TEG?.These films had high mechanical strength,good transparency and fast photochromic ability.The addition of TEG reduced the mechanical properties while improving the transparency and photochromic performance,and the change in TEG content could also affect the color of the films.After photochromism,the films would slowly fade in an indoor enviro nment,and heating in a humid enviro nment could accelerate the fading process.This film could be used as a daily writing medium and was compatible with common oil-based inks and water-based inks.At the same time,the use of different reducing reagents to write on the film could achieve daily writing,anti-counterfeiting and encryption.The film was compatible with a wide range of common printers and enabled high-resolution"light printing"processes that display information such as patterns on micron scales.The film was erasable,self-healable,recyclable,and offers advantages in terms of recyclability.This film could be used like traditional paper and had the functions that traditional paper did not have.It had a significant advantage in replacing traditional papers as a new generation of writing and printing media.Fourth,based on the previous work,we have tried to find a strategy to achieve both rewritability and stable color display of the film.The introduction of polyvinyl alcohol?PVA?could interact with Mo7 through hydrogen bonding,which might be the main reason for reducing the photochromic performance while prolonging the coloring time of the film.As shown in the previous section,heating in a humid enviro nment could significantly accelerate the fading process.This part of the work provided a new strategy for the design of photochromic materials with both rewritable and long-term coloring properties and would be helpful for the development of future rewritable paper.In this thesis,we have obtained a series of low-cost,fast-responding photochromic gel and film materials based on Mo7.These materials have application prospects in fields such as information storage and inkless printing.It also shows advantages in replacing the traditional paper into a new writing and printing medium in the future.The research work of this thesis further promotes the research progress of POM materials in the field of photochromism,and it also helpful to the design of future rewritable smart materials. |
PDF Full Text Request