Research Of Roll-to-roll Thermal Curing Process For Fabrication Of Superhydrophobic Film

Superhydrophobic functional surface（with a water contact angle more than 150°and a sliding angle less than 10°）is widely used in aerospace,medical devices,flexible electronics and other fields due to its excellent performance of anti-icing,micro-liquid transportation,antifouling and oil removal^[1-7].The high efficiency and high precision preparation of superhydrophobic surface with micro-nano composite structures has always attracted great interest in the field of micro-forming.Early scholars replicated lotus leaf’s surface by template method in order to realize the superhydrophobic performance.Then,lots of methods such as chemical vapor deposition,spray coating,laser etching and 3D printing were put forward,but the current methods can’t take the efficiency and forming precision into account as well so that the large area superhydrophobic film can’t be prepared.In this paper,combined with the roll-to-roll（R2R）continuous forming method,a new technology called roll-to-roll thermal curing was proposed.Low surface energy thermosetting resin materials were cured to realize the high-efficiency and high-precision preparation of large-area microstructures.However,due to the small size of the microstructure,it is difficult for the resin material to flow and fill the mold so that bubble defects are easy to occur.As a result,the forming precision of the microstructure is not high,which ultimately affects the surface superhydrophobic performance.Therefore,deep analysis of the bubble defect mechanism during the R2R thermal curing filling process and exploration of the R2R thermal curing process rules are of great significance for the high-efficiency and high-precision preparation of the large-area superhydrophobic film.In this paper,the new technology of superhydrophobic film called R2R thermal curing process was studied by simulation modeling analysis and process experiments to realize the preparation of large-area superhydrophobic film.First of all,based on the existing R2R forming system in the laboratory,the equipment was upgraded so as to be suitable for polymer resin materials.At the same time,the feasibility verification experiment was carried out and the formation rule of bubble defect was explored experimentally.Secondly,a simulation model of thermal curing filling process based on two-phase flow was established to explore the influence law of process parameters on filling results which can optimize the experimental parameters.Finally,based on the micro-pyramid array mold,the micro-nano composite characteristic mold was prepared by chemical etching method and R2R thermal curing experiments of resin materials were carried out.And the polymer film with large area,superhydrophobicity,corrosion resistance and light resistance was finally prepared.The research of this paper mainly includes the following aspects:（1）Feasibility of R2R thermal curing process and analysis on the forming defectsBy upgrading and modifying R2R hot embossing system,a new process called R2R thermal curing suitable for thermosetting resin materials was proposed.Micro-pyramid array structures mold was chosen to explore the curing rule of the polydimethylsiloxane and the feasibility of preparing the superhydrophobic film by R2R thermal curing was verified experimentally.Finally,the forming mechanism of bubble defects was analyzed and the effect on the hydrophobic properties of the film was studied.（2）Simulation and process research of filling processThe rheological properties of the polymer resin were determined by testing the flow mechanical properties and surface contact behavior parameters of PDMS.Secondly,the two-phase flow free interface simulation method based on the level set method was used to simulate and analyze the filling process of thermal curing.Based on the N-S equation,the process of modeling is described in detail by tracing the filling results of gas-liquid two-phase interface by the level set method,as well as the viscosity curve of materials in the simulation was fitted by using the Carreau rheological model.In addition,the simulation model was used to analyze and discuss the process parameters（including surface tension,viscosity model,residual layer thickness,velocity and wall wettability）to determine the influence law of each parameter on the filling result,which can provide guidance for the subsequent process experimental prototype.（3）Preparation and performance evaluation of the superhydrophobic filmThe surface morphology of the micro-pyramid mold was modified by chemical etching method,and the nickel mold with micro-nano composite structures was prepared,which stood for the preparation of super-hydrophobic film.Then,the influence of process parameters on the forming accuracy and surface hydrophobicity was analyzed by single factor experiment,which provided guidance for the process optimization of preparing large area superhydrophobic film.Finally,based on the as-prepared micro-nano composite mold and the optimized process parameters,a large-area PDMS superhydrophobic film was prepared by R2R thermal curing.Its superhydrophobic performance was verified,and the properties of the surface such as wear resistance,corrosion resistance and light resistance were evaluated.In this paper,considering superhydrophobic films prepared by R2R thermal curing,a new method called R2R thermal curing system suitable for forming polymer resin is established.The feasibility of the new process is studied and the formation mechanism of bubble defects is analyzed.A two-phase flow model based on the level set method is established to describe the filling process of the resin.The influence factors of filling results are analyzed to optimize process parameters.R2R thermal curing parameter experiments are carried out and the forming law and hydrophobic characteristics of superhydrophobic films are explored.To sum up,the research results and analysis methods in this paper are beneficial to the preparation of large-area superhydrophobic films.