Study On Preparation And Fluorescence Control Of Carbon Quantum Dots/Shape Memory Polymer Composites

Optically adjustable shape memory polymer(SMP)materials which can realize responsive regulation of optical properties under specific stimulus conditions have important application prospects in fields of information transfer,biosensors and micro-optics.At present,the investigation on this type of SMP material mainly focuses on two aspects.One is adjusting the responsive chemiluminescence components of the material,the other is changing the microstructure.However,for the existing optically tunable SMP materials,the research on the relationship between shape memory properties and optical properties is not perfect,and the development on other functions of materials is relatively lacking,which limits the application of optically adjustable SMP.In this thesis,three types of SMP composites were prepared.The water responsive shape memory and fluorescence tunable properties,macro/micro scale shape memory and fluorescence tunable properties,shape memory microarray on fluorescence properties and wettability were studied,and their related mechanisms were analyzed.The works were listed as follows in detail:pH responsive carbon quantum dots(CQDs)were obtained by hydrothermal method,and then CQDs/polyvinyl alcohol(PVA)shape memory composites with fluorescence regulation were prepared by compounding CQDs and PVA.When the mass fraction of CQDs was 2% in the whole system,the shape fixity rate and shape recovery rate of CQDs/PVA composite could reach more than 95%.The temporary shape of CQDs/PVA composite could recover both in acid and alkaline solutions.The fluorescence properties of composites were consistent with CQDs.The water responsive shape recovery properties of the composites were mainly realized by the physical cross-linking interaction between CQDs and PVA.As a stationary phase,it could prevent the molecular chain from slipping.The fluorescence tunable properties of the composites mainly realized by protonation and deprotonation of carboxyl groups on the surface of CQDs.In acid solution,the carboxyl groups of CQDs were protonated,showing a weak fluorescence intensity.In alkaline water,the carboxyl groups of CQDs were deprotonated with strong fluorescence.CQDs/PVA/polyacrylamide(PAM)hydrogel composites with shape memory property and fluorescence modulation at both macroscopic and microscopic scales were prepared by combining pH responsive CQDs,PVA,and PAM.When the content of crosslinking agent N,N’-methylene diacrylamide(MBA)in PAM was 0.11%,the shape fixity rate and shape recovery rate of the composite could reach at least 90%.In the process of shape memory,each state of the composite corresponded to certain fluorescence intensity.The shape memory properties of composites under macroscopic or microscopic scale could be obtained by monitoring the fluorescence.The shape memory properties of CQDs/PVA/PAM hydrogel mainly depended on PAM and reversible dynamic borate bond,which helps fixing temporary shapes in alkaline conditions.When it was put into acid solution,the borate bond will be dissociated dynamically,and the composite could return to its original shape through the elastic recovery of PAM and PVA molecular chain.The fluorescence regulatory properties of the composites mainly caused from the different structures of carboxyl functional groups on the CQDs surface in acid and alkaline conditions.The superhydrophobic CQDs/epoxy composite microarrays were prepared by UV curing 3D printing,PDMS reverse template method and surface modification.The shape fixation rate and shape recovery rate of the material were 98.1% and 98.8%,respectively,which could realize the reversible regulation from vertical state to inclined state.The two sides of the microarrays were modified with fluorescent CQDs,which could control the fluorescence reversibly by switching the microarrays structure from vertical state to inclined state.The change of microarray structure could also affect its wettability.The droplet showed a non-directional rolling characteristic on the vertical microarrays with a rolling angle of 9°(width,height and spacing are 390 (?)m,2mm and775 (?)m,respectively).When the tilt angle of the microarray was 30°,the rolling angle of the droplet along the bending direction of the microarray was 42°,and it does not roll against the bending direction of the microarray,showing the characteristics of directional rolling.The shape memory effect of microarrays mainly depended on the variation of entropy in the system.The fluorescence regulation function of microarrays mainly achieved by controlling its vertical structure and inclined structure.The difference of rolling modes of droplets on vertical and inclined microarrays mainly due to the difference of rolling resistance.