Preparation And Properties Of Structural Colored Carbon Fibers With Gradient Structure And Thermochromic Properties

Carbon fiber materials are widely used in aerospace,military,chemical and other fields due to its excellent mechanical properties,high electrical conductivity,heat resistance and corrosion resistance.For years,however,the monotonous black color of carbon fibers does not satisfy our aesthetic needs for a colorful world,thus limiting their development in textile and other fields.Therefore,researchers have been working on a simple and efficient way to endow carbon fiber materials brilliant color.However,the surface of carbon fiber is highly crystalline and lacks highly reactive groups,so it is very hard to color this material by conventional dyes.At present,most methods for coloring carbon fibers are self-assembly of photonic microspheres on the surface of the fibers.The structural colored carbon fibers prepared by this method have the problems of single color,unable to realize color dynamic regulation and unstable mechanical properties.Therefore,it is a big problem to prepare structural colored carbon fibers with rich color,dynamic regulation and stable mechanical properties.In this paper,we proposed two strategies to construct structural colored carbon fibers with dynamic color regulation and stable mechanical properties.Firstly,a photonic coating with gradient structure was prepared on the surface of the fiber,and its thickness decreases gradually along the top of the fiber to both sides,which can endow the carbon fiber with dynamically regulated structural color.We used magnetron sputtering to alternately sputter Ti O₂ and Al₂O₃ nanometer layers on the surface of the carbon fiber to construct photonic crystal nanometer layers with gradient structure.By controlling the thicknesses of Ti O₂,a series of blue,green,orange and purple-red carbon fibers were prepared.The reverse reflection spectral further shows that the gradient structure enriches the color of the carbon fiber and gives the carbon fibers a dynamically tunable structural color.For example,the original purple color of CF transforms to red,orange,green,blue,and finally purple as the incline angle increases from 0° to 50°.In addition,taking advantage of the electrothermal conversion properties of the base carbon fiber material,the integration of it with the bluetooth module and control chip allows accurate temperature control through the smartphone,which provides a good development opportunity for the next generation of wearable electronic products.Secondly,we deposited a thermochromic VO₂ film on the surface of the fiber.By using the reversible metal-insulator transformation behavior of the functional film at the critical temperature,the dynamic color control of the structural colored carbon fiber can be realized under external stimuli(electricity,heat).By controlling the thicknesses of VO₂,a series of brightly structural colored carbon fibers were prepared according to the principle of film interference.The VO₂ after thermal reduction treatment gives the fiber a thermochromic function.For example,when the annealed yellow sample is heated to 68 °C,its original color transforms to green and the corresponding reflection peak position shifts from 625 nm blue to553 nm,thus realizing the dynamic color control of structural colored carbon fibers.