Preparation Of PPy Nanotube Aerogels By LCA Template Method And Research Of Their Properties

Polypyrrole(PPy)nanotube aerogels are a new type of conductive polymer materials with hierarchical porous micro-nano structure,large surface area,good environmental stability and other excellent properties,making it to have potential applications in many areas,such as energy storage,adsorbent,sensors and antirot materials.Preparation of PPy nanotubes is a prerequisite for the synthesis PPy aerogels.Based on the current research results,there are different ways to prepare PPy nanotubes,However,the large-scale assembly of PPy nanotubes into interconnected three-dimensional(3D)structures is challenging.The topic of this dissertation is that PPy nanotube aerogels with different shapes can be prepared on a large scale via lithocholic acid(LCA)self-assembly at room temperature to form nanotubes as a soft template.The effect of the concentration of LCA and the amount of pyrrole(Py)monomer in the reaction on the morphology and propertity of PPy nanotube aerogels was investigated.Meanwhile,the preparation mechanism of PPy nanotube aerogels was discussed.And it is of importance to study the morphology,structure,water absorption,mechanical properties and electrical properties of PPy nanotube aerogels with specific components.Compared with other reported substances as templates to prepare PPy gel,LCA template method is more simple,effective and environmentally friendly.First,we have studied the self-assembly of LCA into a hollow nanotube structure at room temperature.Scanning electron microscopy(SEM)shows that LCA nanotubes could interconnect to form a network structure.Transmission electron microscopy(TEM)demonstrates that self-assembly of LCA forms hollow nanotubes with a wall thickness of about 13 nm,while the LCA molecule has a length from the carboxyl group to the hydroxyl group of about 1.5 nm,so the wall thickness of the LCA nanotube is 8 times the length of the LCA molecule.This indicates that the walls of the LCA nanotubes are stacked by multiple LCA molecules.Secondly,this paper uses LCA as a soft template to synthesize PPy nanotube gel with hierarchical porous structure.The effects of different concentrations of LCA as soft template and different concentration of Py on the morphology,elasticity and electrical conductivity of the prepared PPy nanotube aerogels were investigated.As the concentration of LCA increases,the diameter of PPy nanotubes enlarges,the surface of PPy nanotubes smoothens,making them easier to adhere to one another.When the concentration of LCA is 50 mM,with the increased addition of Py,PPy nanotube network has more PPy particles,rougher surface,better conductivity and higher stiffness.Next,the mechanism of preparation of PPy nanotube aerogels by soft template method was analyzed.The-NH of Py and the-COO~-of the surface of the LCA nanotube forms hydrogen bonding so that Py can adsorb on the surface of the LCA nanotube.The Py monomers adsorbed on the surface of LCA nanotubes are oxidatively polymerized to form PPy nanotubes,and the PPy nanotubes intersect each other to form a three-dimensional network structure.Finally,the best composition of PPy nanotube aerogel was selected to study its morphology,structure,elasticity and electrical properties.Compared with hydrogels,PPy nanotube aerogels have a weight reduction of 96%,a density of only 38 mg/cm~3,and better elasticity.The aerogel can withstand up to 70%of the compressive strain and spontaneously returns to the original state.It also exhibits excellent recyclability.The G'of PPy nanotube aerogel is almost an order of magnitude larger than G".PPy nanotube aerogel has excellent electrical properties.Under its loose aerogel structure,the conductivity is 1.13 S/m,which is higher than most template conductive polymer gels.In addition,PPy nanotube gel exhibits a negative strain-dependent resistance behavior,while the electrical resistance of the PPy nanotube aerogel remains constant for multiple compression loading-unloading cycles.The elastic PPy nanotube hydrogel can also be sliced.It can be bent to 90°without damaging the internal transmission channel.