Preparation Of Revealable Photonic Prints With High Visibility And Their Applications In Visual Sensing

Invisible photonic prints show uniform color under normal conditions,and the hidden pattern of the invisible photonic prints can be revealed when being exposed to an external stimulus,so as to realize the storage and transformation of information,which can be widely used in the fields of anti-counterfeiting,recognition,sensing,and dynamic display.In general,photonic prints can be obtained by selectively patterning the photonic crystal materials with stimuli-responsive polymer.However,due to the limited contrast between the patterned region and the background region,the visibility and sensitivity of photonic prints for visual sensing are still not satisfactory.In this thesis,we proposed a novel strategy to realize the high visibility of invisible photonic prints by patterning the photonic hydrogel matrix with two oppositely responsive polymers to one stimulus.Under external stimuli,the maximum reflection peaks of the pattern region and the background region of the photonic prints shifted in the opposite directions,which improved the detection range,visibility,and sensitivity of the invisible photonic prints for visual sensing.Superparamagnetic Fe₃O₄@C colloidal nanoparticles were chosen as the assembly block and poly(hydroxyethyl methacrylate)(PHEMA)was used as the polymer matrix.Under the magnetic field,the Fe₃O₄@C colloidal nanoparticles can self-assemble into one-dimensional(1D)chain-like structure,which can be further immobilized within PHEMA hydrogel by the UV-triggered polymerization of hydroxyethyl methacrylate.The as-obtained PHEMA-based photonic hydrogels were then used as the substrate for the selective modification of two oppositely responsive polymers to achieve the invisible photonic prints with high visibility.(1)pH-responsive photonic prints with high visibility:in the presence of patterned mask,two monomers of acrylic acid(AA)and 2-(dimethylamino)ethyl methacrylate(DMAEMA)comprising weak acidic and weak basic groups were selectively polymerized on the PHEMA-based photonic hydrogel substrate to obtain pH-responsive photonic prints(PHEMA-PAA/PHEMA-PDMAEMA).Its performance in pH sensing is studied,including the color detection range,repeatability,and contrast.Out results show that the maximum reflection peak of the different regions of the photonic prints moves in opposite directions when the pH value of the solution changed,and the pattern is hidden under certain pH conditions.Compared with the photonic hydrogel modified with only one pH-responsive monomer,the color range and contrast are obviously improved.(2)Solvent-responsive photonic prints with high visibility in sensing:in the presence of patterned mask,two monomers with different solubility parameters(poly(ethylene glycol)methacrylate(PEGMA)and acrylamide(AM))were selectively polymerized on the PHEMA-based photonic hydrogel substrate to obtain the solvent-responsive photonic prints(PHEMA-PEGMA/PHEMA-PAM).The contrast and optical repeatability of the photonic prints in three solvents with different solubility parameters were studied.Results show that in the process of transferring PHEMA-PEGMA/PHEMA-PAM solvent-responsive photonic prints from deionized water to acetone or glycol,the maximum reflection peak in different regions of the photonic prints moves in the opposite directions,and the pattern is hidden in glycol.Such photonic prints exhibited better optical repeatability and contrast than the photonic hydrogel patterned with only one monomer.