Electric Field-assisted Construction Of Chitin Nanofiber Antireflection Coatings

Antireflection coating is a common method to reduce optical loss,which can increase the luminous flux and sensitivity of optical system,and improve the performance and efficiency of light-emitting devices.It is of great significance to use natural polymer materials as raw materials of antireflective coatings for expanding the application field of natural polymer materials and preparing green antireflective coatings.Chitin nanofibers(Ch NFs)are widely present in shrimp and crab shells,have good film-forming properties,and as the only positively charged natural polymer in nature,they are easily assembled and arranged by an electric field during the preparation of coatings.In this paper,using chitin as raw material,chitin nanofibers were prepared by partial deacetylation modification pretreatment combined with ultrasonic mechanical treatment.The concentration of Na OH solution,reaction time and subsequent ultrasonication conditions in the pretreatment process were studied by using a nanoparticle size potential analyzer.Effects on nanofiber size and potential values.Then,the obtained chitin nanofibers were used as raw materials,and the coating was constructed by means of an external DC electric field.Aiming at the problems of partially deacetylated chitin nanofibers,a combination of esterification pretreatment and partial deacetylation pretreatment was selected to prepare a coating solution for chitin nanofibers,and the coating was assisted by a DC electric field.The transmittance and geometric parameters of the obtained coating were analyzed by atomic force microscope,transmission spectrometer,ellipsometer,scanning electron microscope and other instruments,and the reflectance of the coating was estimated and verified by the vector method.The specific research contents and results are as follows:(1)The deacetylation degree of chitin was changed by changing the concentration of Na OH solution and the reaction time,and chitin nanofibers of different sizes were obtained.When the reaction time was 4 h,the chitin nanofibers could not be fully exfoliated by ultrasonication after treatment with 35% and 38% Na OH solutions;the chitin nanofibers were completely dissolved by Na OH solutions with a concentration of more than 42%.The chitin nanofibers obtained by sonicating the 35% Na OH solution and chitin for 5 h have a width of about 15 nm and a length between 100 nm and 200 nm;the zeta potential values are all above 35 m V,which can be Disperses stably in water for a long time.(2)Partially deacetylated chitin nanofibers are used as raw materials,and the coating is assisted by applying a DC electric field.The size of the chitin nanofibers had the greatest effect on the transmittance of the coating.The light transmittance of the slide substrate at a wavelength of 550 nm is 89%.The transmittances of the substrates coated with PD-35-4-Ch NFs(average particle size: 392 nm)at wavelength of 550 nm were all below 85%;those coated with PD-38-4-Ch NFs(average particle size: 392 nm)The transmittance of the substrates coated with 328 nm)at the wavelength of 550 nm was between 85% and 89%,which was slightly lower than that of the glass slide substrates;)The transmittance of the coated substrate is about 89%.The regulating effect of the electric field is limited by the viscosity of the coating solution,and too high viscosity will inhibit the mobility of the nanofibers under the electric field.(3)In view of the problem of excessively high viscosity of the partially deacetylated chitin nanofiber coating solution,esterification modification and esterification-partial deacetylation double-modified chitin nanofibers were selected as the coating solution to construct the coating.The Zeta potential of the chitin nanofibers after esterification modification was-38 m V,and the adjustment effect of the electric field was weak.The zeta potential of chitin nanofibers after esterification-partial deacetylation double modification reached 48 m V,and the coating solution with a concentration of 0.5 wt% applied a voltage of 55 V for 5 min to obtain a coating with a thickness of 400 nm at a wavelength of 550 nm.The transmittance increased from 89%to 91%,and the porosity reached 28.55%.The coating solution with a concentration of0.05 wt% was applied with a voltage of 55 V for 5 min to obtain a coating with a thickness of 132 nm.The highest light transmittance at the wavelength of 550 nm reached 94%,which was 5% higher than that of the glass slide substrate.