Processing And Application Of Janus Micropillars Based On Femtosecond Laser

As a new bottom-up processing method,femtosecond laser two-photon polymerization(TPP)technology,has the advantages of simple working environment,high resolution and flexibility,which is widely used in the fields of micro-optical devices,micro-mechanical devices and micro-fluid devices.In the long process of evolution,many organisms in the nature have the ability to deform with the change of the external environment,which make them gain more survival advantage in the cruel environment.Many researchers are inspired by the deformation of organisms and develop various deformable structures controlled by the external environment.Janus is a two-faced god in Roman mythology.His head has two faces at the front and back,one looking at the past and the other looking at the future.It represents contradiction and opposition.In contrast,structures with different chemical or physical properties on either side are called Janus structures.In particular,when there is difference in expansion coefficient between the two sides of the Janus structure in different external environments,the structure as a whole will show shape changes controlled by the external environment,so processing Janus structure is an important way to achieve structural deformation.This thesis focuses on the fabrication of deformable Janus micropillars by femtosecond laser two-photon polymerization.At first,we present a simple and flexible method to produce geometry-switchable Janus micropillars by focusing controllable femtosecond laser into a pH-sensitive hydrogel.These micropillars are polymerized from pH sensitive hydrogel,and its volume varied with the pH value.When the pH value is less than 9,the hydrogel structure shrinks,otherwise it expands.By controlling the scanning path,the two sides of these Janus micropillars expand differently when the pH value changes,resulting in the reversible bending of the whole micropillar.Benefited from the high flexibility of the laser printing technique,the spatial arrangements,pillar heights,and bending directions of micropillars are readily controlled,enabling a variety of switchable ordered patterns and complex petal-like structures.At last,potential applications of this method in information encryption/decryption,and microtarget capturing are explored,which shows its good application value in intelligent display,information security,drug transportation and other fields.The key to prepare the Janus structure is the uniformity of the diprosopic structure itself.In this thesis,after the photoresist micro-column was processed by femtosecond laser,vacuum evaporation technology is used to transform the ordinary micropillars into Janus micropillars by steaming metal on one side of the micropillars by tilting the sample at 45 degrees.These Janus micropillars will have a directional bending towards the side of coating metal.This phenomenon is analyzed theoretically and simulated numerically,and verified by experiments.