Research And Application Of Evaporative Self-assembly Of Halloysite Nanotubes And Chitin Nanocrystals

Halloysite nanotubes(HNTs)and chitin nanocrystals(Ch NCs)are natural one-dimensional nanomaterials with tubular nanostructures.The potential of materials can be effectively used and their applications range can be expanded by studying their special nanostructure and self-assembly behavior.This article explored the evaporative self-assembly behavior of HNTs in an open environment,and prepared HNTs coffee rings firstly.Glass slides are used to construct a sandwich structure with restricted space allows HNTs to evaporate and self-assemble in the restricted space,forming a unique worm-like structure.Ch NCs with similar morphology to HNTs are prepared into environmentally friendly nano-adhesives by confined evaporation-induced self-assembly.Specifically:(1)HNTs were purified by physical purification methods and formulated into HNTs aqueous dispersions of different concentrations.The glass slide was used as the base of the open space to explore the evaporation and self-assembly process of HNTs aqueous dispersion.The circular pattern(coffee ring)formed by the assembly of HNTs was characterized by polarizing microscope,scanning electron microscope,etc.The results showed that HNTs were highly ordered in the coffee ring.Through the method of controlling variables,it was found that the diameter,height and area of the coffee ring pattern depend on the concentration of the HNTs dispersion and the droplet volume.In addition,the formation of coffee rings could be suppressed by raising the evaporation temperature or adding surfactant.(2)A special worm-like micro/nano pattern was obtained by drying the HNTs liquid film between two parallel glass slides.The confined space generated by the device can change the direction of water evaporation so that HNTs occurred a unique self-assembly process and form a worm-like pattern on the surface of the glass slide.The formation of a worm-like pattern is recorded visually and videoed by optical microscopy,and a model is proposed to depict the formation process.Birefringence phenomenon of the worm-like pattern is observed within all experimental halloysite concentrations(from 1-16 wt%).The stripe width and height of the worm-like pattern increases with halloysite dispersion concentration,drying temperature,and confined space height.The pattern area on the substrates also increases with halloysite concentration,liquid film volume and decrease with confined space height.The formed worm-like patterns can be transferred to produce PDMS stamp,and the worm-like morphology of styrene butadiene rubber can be precisely obtained by using the PDMS stamp.The worm-like patterns of halloysite show promising applications in nanotechnology,electronics,photonics,and biotechnology.(3)In order to solve the damage to environment and human body caused by organic solvent adhesive in the utilization process,Ch NCs suspension is explored as strong anisotropic adhesive which is an eco-friendly and water-based adhesive with high adhesive strength.Ch NCs extracted from crab shells are rod-like nanoparticles with high aspect ratios,which are mainly employed as reinforcing polymer nanocomposites and biomedicine nanomaterials.Ch NCs suspension sandwiched between substrates form a long-range orderly superstructure by self-assembly process.Ch NCs nanoglue exhibits high anisotropy adhesion strength,i.e.,in-plane shear strength(5.26 MPa)and out-of-plane shear strength(0.46 MPa)for glass substrates.Moreover,the Ch NCs nanoglue is suitable to many substrates,such as glass,plastic,wood,metal,paper,etc.The Ch NCs nanoglue shows high biocompatibility towards the fibroblast cell and rat skin,proving their excellent biosafety.As an eco-friendly and high-performance adhesive,Ch NCs nanoglue shows promising applications in daily life and industrial fields.