Preparation,Modulation And Performance Characterization Of Wrinkled Polyaniline Films

It is well known that unique properties of material are related to their special micro-and nanostructures.Especially,in the recent years,functional materials with well-defined structures play a more and more important role in modern technology.As a kind of potential functional materials,conducting polymer is attracting more and more interest.To satisfy the development of functional devices towards smaller and smaller scales,and multifunctional applications,the ability to pattern conducting polymers is highly important.As a nonlithographic surface patterning method,surface wrinkling has attracted considerable interest due to its simplicity,low cost,and applicability to arbitrary surface geometries.However,there are still problems in wrinkle preparation,which include how to develop a simple way to obtain wrinkle patterns,how to achieve stimuli-switchable surface wrinkling,how to obtain stabilized wrinkling patterns,and how to reprocess the wrinkling patterns for extended applications.To obtain polyaniline films with controlled microstructures,we report the large-area self-wrinkling on polyaniline(PANI)film when it is in situ grown on polydimethylsiloxane(PDMS)substrate via oxidative polymerization in an acidic medium.Based on the unique properties of PANI,we further realize unprecedented,smart,reversible modulation between the wrinkled and dewrinkled states,stabilize the wrinkling patterns,and reprocess the wrinkling patterns at micro-scale.In order to address the problems in wrinkling patterns fabricated by multistep method,such as the cost increase,stringent requirements and internal limitations in the sizes,dimensions,a new simple one-pot yet robust approach to fabricate large-scale wrinkle patterns has been developed.A novel swelling-induced self-wrinkling mechanism is responsible for the in situ growth of wrinkled PANI film on the PDMS substrate.The spontaneously formed wrinkles with controlled microstructures such as the wavelength,spatial orientation,and location have been well regulated by PANI film thickness(via polymerization time and monomer concentration)and PDMS substrate modulus as well as the boundary conditions imposed by the substrate.The results indicate that the in situ self-wrinkling is highly desirable for patterning PANI film over large areas with the instability-driven morphologies,even in the case of curved surfaces employed.Using the stimuli-response of PANI,a pH and redox-switchable surface wrinkling system based on the above self-wrinkling system is demonstrated.The rapid switch of wrinkled/dewrinkled states is obtained through a simple immersing process of acid/base or reductant/oxidant.This switch is derived from the reversible transition in different intrinsic redox and doping states of PANI that are involved in doping and dedoping,or the redox reaction,coupled with the corresponding volume expansion/shrinkage.The switching time,wrinkle wavelength,and cycle performances are depended on concentrations of acid/base or reductant/oxidant.This work paves the way to fabricate the stimuli-responsive surface patternsTo address the sensitivity to the stress field and instability of surface wrinkling pattern,a versatile strategy is demonstrated to fabricate thin free-standing crack-free PANI-based films with stable wrinkling patterns.It is based on oxidization polymerization of pyrrole inside a pre-wrinkled PANI film,in which the wrinkled PANI film is used both as a template and oxidizing agent for the first time.The subsequently grown polypyrrole(PPy)and the formation of interpenetrated PANI/PPy networks play a decisive role in enhancing the film integrity and the stability of wrinkles.This enhancing effect is attributed to the modification of internal stresses by the interpenetrated PANI/PPy microstructures.Consequently,a crack-free film with stable controlled wrinkles such as the wavelength,orientation and spatial location has been achieved.Moreover,the wrinkling PANI/PPy film can be removed from the initially deposited substrate to become free-standing.It can be further transferred onto target substrates to fabricate hierarchical patterns and functional devices such as flexible electrodes,gas sensors,and surface-enhanced Raman scattering substrates.To satisfy the development of microelectronics towards smaller and smaller scales,and desirable arbitrary shapes,we demonstrate for the first time that ultrasonic treatment can be used to fabricate the hierarchical patterns of PANI film.The PANI film can be selectively peeled off from the substrate during ultrasonic cleaning,due to the different physical and chemical properties of the oxygen plasma selectively exposed PDMS substrate,forming regular PANI arrays.The arrays can be tuned with/without surface wrinkling.This effective ultrasonic treatment method is highly expected to extend to other functional systems for surface patterning.