Mechanoresponsive Polymer Soft Materials: Synthesis, Properties And Applications

Mechanical force-induced luminescence soft materials refer to a class of materials that can generate visual optical signals such as color,fluorescence changes and chemiluminescence under the stimulation of mechanical forces.It has built a good material platform for the research in the fields of soft material mechanics,intelligent response devices and controlled drug release.In this thesis,soft materials such as hydrogels,elastomers,and nanovesicles with highly sensitive mechanical force responses were designed and prepared based on classical force-induced chromic/luminescence unit,exploring their new application as stress probe for the mechanical study in different polymer soft materials.The results can be summarized as follows:1.With the protection strategy of hydrophobic micelles,the first hydrogel of mechanical force-induced chemiluminescence was designed and prepared,which solved the low chemiluminescence efficiency problem of 1,2-dioxetane(Ad)mechanophore in a polar solvent environment.The factors affecting the chemiluminescence of hydrogels were studied,and hydrogels with different chemiluminescence wavelengths were obtained by blending different acceptor fluorescent molecules.When the Ad hydrogel with pinhole defects stretched in-situ,the scission of chemical bond around the crack tip in the hydrogel was observed in real time,and damage visualization of hydrogel-like soft materials was realized with high spatial and temporal resolution.2.Based on the micellar polymer system in the first section,using glycerol as plasticizer and rhodamine as mechanophore,a strong and tough mechanochromic elastomer was prepared.By adjusting the content of glycerin in the system,the forceinduced color change and fluorescence of the polymer from glassy to elastic state were achieved.It is found that the rhodamine in the polymer was effectively activated by fluorescence spectrum characterization.By comparing the influence of internal and external plasticizing effects on the polymer mechanochromic property,it is concluded that the main reasons for the high activation rate of rhodamine result from two respects:(1)The plasticizing effect greatly improves the toughness of the rigid polymer,which is conducive transfer of mechanical force to the rhodamine mechanophore(2)The microphase separation led to a strong stress concentration effect.In addition,due to the highly polar environment provided by glycerin,the reaction of ring-closing rhodamine is effectively inhibited.Furthermore,when the glass transition temperature of the polymer is lower,the ring closure rate of rhodamine is slower.This section provides an effective design strategy for designing strong,tough and force-responsive sensitive polymer materials.3.Based on the polymers prepared in the second section,the potential application value of this mechanochromic polymer was explored.The mechanical properties of this polymer have an obvious strain rate effect: the faster the stretching rate caused the greater fracture stress of the material and the lower fracture strain.Through the fluorescence-mechanical synchronous test system,combined with theoretical model derivation and data analysis,the fitting function relationship between the true stresschromaticity of the polymer under different stretching rates was obtained.Based on this functional relationship,the true stress mapping of polymer film under tensile conditions is obtained.It provides a powerful tool for studying the inhomogeneous stress distribution in viscoelastic soft materials Due to the polymer is sensitive to force and has high mechanical strength,it can realize visual observation of heterogeneous interface and homogeneous interface damage of composite materials.Additionally,elastomers also have birefringence effects under stretching,and have certain universality to polymers prepared from different monomers.4.Developed a force-induced color-changing group polydiacetylene based on conformational transition suitable for the study of soft-soft interface deformation,and constructed nanovesicles co-assembled with polyethylene glycol-modified polydiacetylene and polydiacetylene,the law of its mechanochromic under sonication was studied.The experimental results revealed that the color transition(blue phase to red phase)of nanovesicles was closely related to the capillary number of the vesicles.The greater the ultrasonic power,the smaller the degree of polymerization of the vesicles or the greater the viscosity of the fluid would promote the vesicles deformed easier and mechanochromic.Additionally,diacetylene molecules can be further extended to the study of nanovesicle self-assembled by commercial phospholipid molecules(dimyristoylphosphatidylcholine),which also showed mechanochromism under ultrasonic conditions.This system provides a new method for in-depth characterization of deformation and damage in nanoscale and self-assembled systems.