Preparation And Characterization Of Silver Nanowhisker/Polydopamine Electrothermal Composite

In recent years,electrothermal composite materials have attracted widespread attention due to its active heating property and generate Joule heating effects in extremely harsh environments.Light weight,low-voltage drive,flexibility,environmental protection,fast response and wearability are the ultimate goals of current electrothermal composite.As the most popular nano-conductive filler,silver nanowhisker?AgNW?have the advantages of excellent electrical conductivity,low cost,controllable formation,and non-entanglement.Many researches have shown that the AgNW on electrothermal composite materials can achieve high electrothermal efficiency,fast response speed and thermal stability under low voltage.In this paper,silver nanowhisker/polydopamine/cotton-based?AgNW/PDA-C?electrothermal composites were prepared by the dip-coating method.The surface morphology,electrical properties,electrothermal properties of the composites were studied.On this basis,in order to further enhance the durability and practicality,an electrothermal composite material with polydimethylsiloxane?PDMS?as a protective layer was coated on its surface.Further,its electrothermal performance and the electrothermal model of the new system were studied.The specific research content and analysis are as follows:?1?AgNW were prepared by a one-step polyol method,and the effects of silver nitrate,polyvinylpyrrolidone,and sodium chloride on the morphology of AgNW were investigated.Then,scanning electron microscopy,X-ray diffraction analysis,and ultraviolet-visible absorption spectroscopy were used to analyzed AgNW.The study found that AgNW with good morphology can be formed under the preparation conditions of 0.2g AgNO3,0.4g PVP and 0.2ml NaCl(0.1mol L^-1).Through the electron micrograph,AgNW with an average diameter of 94.84 nm,a length of9.61um,and an aspect ratio of about 100 were observed.X-ray diffraction analysis and ultraviolet-visible absorption spectrum analysis can confirm that the prepared AgNW have high purity and excellent linear structure.?2?AgNW/PDA-C composites were prepared by dip-coating method by preparing polydopamine modified cotton fabrics?PDA-C?.Infrared spectroscopy,contact angle,multimeter,scanning electron microscope,and infrared imager were used to study the surface properties,electrical properties,morphology,and electrothermal properties.The results show that polydopamine can maintain the surface properties of cotton fabrics and adsorb the AgNW through its unique adhesion effect,so that the composite material can quickly reach a lower resistance value.AgNW can form a good conductive circuit on the surface of cotton fabrics,and can provide them with excellent electrical heating performance.Composite can exhibit excellent electrothermal performance at low voltages below 1.6V.The electrothermal properties can match well with the classic power conservation model.The steady-state temperature has a quadratic relationship with voltage and a linear relationship with electrical power.The average total heat transfer coefficient reaches 15.04 W·?^-1·m^-2,and the average characteristic time parameter is 15.92,which exhibit excellent electrothermal conversion rate and fast response time.The composite can maintain good static electrothermal performance under constant voltage and gradient voltage,but the dynamic electrothermal performance decreases after 2000 repeated bending,and need further strengthen.?3?In order to further enhance the durability and usability of the composite,a silver nanowhisker/polydopamine/cotton/polydimethylsiloxane?AgNW/PDA-C-PDMS?composite was prepared by coating the outer layer with polydimethylsiloxane as a protective layer,and study their surface properties,morphology,mechanical properties and electrothermal properties.The results show that PDMS can provide good hydrophobicity,and well protect the internal heating elements.Compared with cotton fabrics,the tensile properties have a decrease in breaking strength,but the elongation at break remains unchanged.It can still maintain good tensile properties and can meet the requirements for wearable use.At a voltage of 1.6V,the composite still has excellent electrothermal properties.The actual electrothermal curve can better match the modified power balance model.The steady-state temperature of composite materials increases with increasing voltage or electrical power.The average total heat transfer coefficient of the composite material is25.20 W·?^-1·m^-2,the average temperature characteristic time parameter is 20.33,and the average temperature characteristic time parameter reaches 21.17.It also has excellent electrothermal conversion rate and fast response time,which can meet requirement for wearable devices at low voltages.In the static and dynamic electrothermal test,the composite has a stable electrothermal curve and a small amount of steady state temperature change,showing excellent electrothermal stability.In comparison,the composite material can better meet the use needs in the wearable field.