Preparation And Characterization Of Biomimetic Underwater Superoleophobic Coatings Based On Chitosan And Chitin

Underwater superoleophobic surfaces have been attracted considerable attention in recent years owing to their important practical applications,such as oil/water separation,antifouling or self-cleaning,fluidic devices,bio-adhesion control,liquid manipulation,etc.Generally,a combination of hierarchical micro/nano structured surfaces with high surface energy was considered as one of the most efficient strategies to achieve underwater superoleophobic surfaces.Light transmittance is very important for solar cell cover,touch screen,glass,camera lens,and goggles.To prevent the above devices from being polluted by dust,rain,oil and corrosive liquids in the environment,it is necessary to use transparent coating surface with superhydrophobicity or superoleophobicity,which can increase the using efficiency and reduce maintenance costs.However,it is very difficult to maintain high light transmittance for the coatings with superwettability.This is because that the enhancement of the surface wettability is mainly achieved by increasing micro/nanoscale structure roughness of the surface,but the increase of the surface roughness leads to severe light scattering on the surface of the coating and reduces its light transmittance.Therefore,how to prepare a coating with superwettability and excellent light transmittance has always been a huge challenge.Chitin is a natural polymer.Chitosan?CS?is obtained by deacetylation of chitin?degree of deacetylation is greater than 50%?.Chitin/CS is the second most abundant biopolymer on earth.Chitin/CS is environmentally friendly,renewable,biodegradable,biocompatible,and non-toxic.In this paper,CS and chitin were selected as raw materials to prepare underwater superoleophobic coatings owing to their hydrophilic properties.Direct film formation method was used to prepare coatings with different compositions on glass substrate.The surface roughness of the coating was adjusted by SiO₂ nanoparticles,chitin nanofibers?ChNFs?or phase separation method.Modern analytical techniques were used to observe the morphology of the coating surface,to characterize the coating surface roughness,to analyze the interaction among the coating components.The effects of coating components on the surface wettability,light transmission and swelling of the coatings were investigated.This study developed a technical method to prepare underwater superoleophobic and transparent coatings based on CS and chitin.Some coatings were applied to self-cleaning and oil/water separation to examine the application of the coating.The research contents and main conclusions are as follows:?1?CS was used as the main material for preparing the coatings.SiO₂nanoparticles were used to construct the rough surface,and a certain amount of polyvinyl alcohol?PVA?was added to enhance the film forming ability of the CS solution.Casting method was used to prepare CS/PVA/SiO₂ nanoparticles ternary composite coatings with underwater superoleophobicity.Fourier transform infrared?FT-IR?spectroscopy and swelling degree measurement results showed that cross-linking reactions took place between the components after the addition of glutaraldehyde?GA?.The results of scanning electron microscopy?SEM?and atomic force microscopy?AFM?showed that the surface roughness of CS/PVA/SiO₂nanoparticles coating increased with the increase of addition amount of SiO₂nanoparticles.At a wavelength of 458 nm,when the ratio of the mass of SiO₂nanoparticles to the total mass of CS and PVA was increased from 0.05/1 to 0.5/1 and the amount of the added GA was increased from 0 to 80?L/g,the light transmittance of the glass coated with CS/PVA/SiO₂ nanoparticles coating decreased from 68%to6%?the light transmittance of the blank glass was 91%?.The underwater oil contact angle of the CS/PVA coating was only 137°.The underwater oil contact angle of the CS/PVA/SiO₂ nanoparticles coating increased gradually with the increase of GA.Among them,the underwater oil contact angle of CS/PVA/SiO₂ nanoparticles?1/0.05?+80?L/g GA coating reached to 153.4°,the rolling angle was about 3°,showing underwater superoleophobicity with low adhesion.?2?Although the SiO₂ nanoparticles could increase the underwater oleophobicity of the coating,the light transmittance of the coating was greatly reduced.In order to improve the light transmittance of the coating,CS/PVA binary composite coating with good light transmittance was prepared by using phase separation method?simple immersing the coating into NaOH solution?combined with GA cross-linking treatment.It was critical for imparting surface roughness to the coating by immersing the CS/PVA coating into the NaOH solution.FT-IR spectroscopy and swelling degree measurement results showed that,cross-linking reaction occurred between the hydroxyl groups or the amine groups of the CS and GA,as well as the hydroxyl groups of the PVA and GA.The results of SEM and AFM showed that the surface roughness of the coating increased gradually with increase of CS content and the addition of GA in the coating,but the light transmittance of the CS/PVA coating coated glass decreased gradually.When the CS content was increased from 0%to100%,the surface roughness of the coating increased from 1.93 nm to 79.2 nm.At a wavelength of 458 nm,when the mass ratio of CS/PVA was increased from 1/3 to 3/1and the amount of the added GA was increased from 0 to 80?L/g,the light transmittance of the coating coated glass decreased from 73%to 57%?the light transmittance of the blank glass was 77%?.By adjusting the coating components and the preparation process,the CS/PVA coating could be imparted with low adhesion underwater superoleophobicity.The underwater oil contact angle of the CS/PVA?1/1?+80?L/g GA coating reached to 161°,and the rolling angle was only 3°.The superoleophobicity of the CS/PVA coating remained stable in aqueous solutions of HCl?1 mol/L?,NaCl?10 wt%?and NaOH?1 mol/L?.In addition,the coating exhibited underwater self-cleaning property against oil staining.Copper mesh coated with CS/PVA coating could be used to separate oil/water mixture efficiently.?3?The surface roughness of the coating could also be achieved by using nanofibers.ChNFs with a mean diameter of approximately 15 nm,mean equivalent size of approximately 203.1 nm,were successfully prepared from commercially available chitin powder via esterification modification using maleic anhydride and ultrasound treatment?500 W/45 min,0.5s/4s on/off pulses?.Light transmittance of the film prepared using ChNFs with mean diameter of 15 nm was up to 92%at a wavelength of 458 nm.?4?The CS/ChNFs coating with underwater oleophobicity was prepared by using ChNFs to improve the surface roughness of the CS coating.However,floccules appeared in the CS/ChNFs mixed solution?the compatibility between ChNFs dispersion and CS solution was poor?;The film formation ability of CS/ChNFs mixed solution was not good and the the CS/ChNFs coating didn't adhere well to the glass substrate.This may be due to the electrostatic interaction of the amino groups on the CS and the carboxylate groups on the esterified ChNFs.The light transmittance of the glass coated with CS/ChNFs coating was less than 20%in the wavelength range of400 nm to 800 nm?the light transmittance of the blank glass was 90%?.The underwater oil contact angle of the CS/ChNFs coating was less than 150°.?5?ChNFs are hydrophilic,and ChNFs film showed excellent light transparency.Since nanofibers with certain size can be used to construct rough surfaces,the ChNFs/PVA binary composite underwater superoleophobic coating with high transparency was prepared by adding an appropriate amount of PVA into ChNFs dispersion,its film formation ability was improved,and adhesion of ChNFs with glass substrate was enhanced.The swelling of the coating in water was reduced after adding GA.The swelling degree measurement results showed that the swelling degree of the ChNFs/PVA coating increased with increase of the content of ChNFs and decreased with increase of the amount of added GA.The results of AFM roughness characterization showed that the surface roughness of ChNFs/PVA coating increased from 1.96 nm to 155.7 nm as the content of ChNFs in the coating increased from 0%to 100%.At a wavelength of 458nm,the light transmittance of the glass coated with ChNFs/PVA was between 64%and 47%?the light transmittance of the blank glass was 90%?.The underwater oil contact angle of ChNFs/PVA?1/1?+40?L/g GA coating was 159.2°,the rolling angle of the coating was about 3°,showing low adhesion underwater superoleophobicity.?6?In order to further improve the surface roughness of the ChNFs/PVA coating,SiO₂ nanoparticles were used.The ChNFs/PVA/SiO₂ nanoparticles ternary composite coating with underwater superoleophobicity was prepared by direct film formation method.The results of AFM observation showed that the surface of the ChNFs/PVA/SiO₂ nanoparticles coating had micro/nano composite structure,and the surface roughness of the coating increased with increase of the content of SiO₂nanoparticles.When the mass ratio of SiO₂ nanoparticles to ChNFs/PVA increased from 0.1/1/1 to 0.2/1/1,the surface roughness of ChNFs/PVA/SiO₂ nanoparticles coating increased from 742nm to 988nm.At a wavelength of 458nm,the light transmittance of the glass coated with ChNFs/PVA/SiO₂ nanoparticles was between53%and 22%?the light transmittance of the blank glass was 90%?.After the addition of SiO₂ nanoparticles,underwater oleophobicity of the ChNFs/PVA coating was improved.The underwater oil contact angle of ChNFs/PVA/SiO₂ nanoparticles?1/1/0.2?+40?L/g GA coating was up to 160.2°,and the rolling angle was about 2°.