Preparation And Characteristic Of MWNTs/PANI And MWNTs/PTh Electrochromic Composite Films

Electrochromic is a phenomenon that the material changes its color with the influence of an external electric field, in the oxidation and reduction process which occurs in the system of the material. The color of the electrochromic material changes by the change of the external voltage, and the changing process is reversible, the new feature can be used to manufacture electrochromic devices, and also be used in the building windows, flat panel displays, industrial controlling panels, energy-saving materials, electronic information and so on.Recently, it was discovered that the conductive polymer such as polyaniline(PANI), polythiophene(PTh) and derivatives thereof, also has a great electrochromic phenomenon, and the conductive polymer material has low cost, simple preparation process, low operating voltage, long cycle life, and the color contrast which material changes with the change of the external electric field is significant, and the device corresponding speed is fast, it has better prospect than other types of electrochromic materials. However, how to combine or compound the polymer and the contemporary nanomaterials or a variety of new materials, how to develop the new electrochromic composite material, how to enhance the physical and chemical properties of the conductive polymer electrochromic material further, has also been the hot research problem in the field of the electrochromic materials.Therefore, this paper uses multi-walled carbon nanotubes(MWNTs) as an additive, makes it respectively composite with two kinds of conductive polymers, polyaniline(PANI) and polythiophene(PTh), and then prepares MWNTs/PANI, MWNTs/PTh electrochromic composite films with different adding proportions, and assembles MWNTs/PANI, MWNTs/PTh composite film electrochromic device at last. This paper probes whether adding different proportions of MWNTs to prepare the MWNTs/PANI, MWNTs/PTh electrochromic thin film has an influence on the microstructure, morphology and electrochromic properties of the thin film. The results have a certain value for the development of the new electrochromic film and devices. The main contents of this paper are as follows:(1) With the solution mixing techniques, make 1-methyl-2-pyrrolidone as solvent, add the MWNTs with different amounts to the conductive PANI, and prepare the MWNTs/PANI electrochromic film devices on the ITO glass substrate by spin-coating process. It probes the effect of different amounts of MWNTs on the conductivity, microstructure and electrochromic properties of the PAIN/MWNTs film. Compare the color contrast and response time situation of the PANI electrochromic device and the PANI/MWNTs electrochromic device under the changing external electric field. The study found that after adding MWNTs, the MWNTs/PANI composite film electrochromic device shows a stronger electrochromic property, with increasing levels of carbon nanotubes, the conductivity of the composite film device will also be improved, compare with the pure PANI electrochromic thin film device, the external voltage that the composite film desires obviously drops, it is very favorable to improve the response time and the device lifetime; The study also found that, after addition MWNTs, due to the cluster particles which is produce by MWNTs’ entanglement, the surface roughness of the prepared PANI/MWNTs composite film is increased, but the carbon tubes which are dispersed uniformly in the PANI polymer may form a series of electronic transmission paths by cross-linking, it’s helpful to improve the conductivity of the composite film.Therefore, so long as the MWNTs disperse uniformly in the MWNTs/PANI composite film, in the case that the addition amount of the carbon tube is less than 5% by weight, MWNTs/PANI composite film electrochromic properties can be enhanced or improved.(2)The different amounts of MWNTs are added directly into PTh conductive solution, after powerful ultrasonic agitation dusting, by spin-coating process, the MWNTs/PTh composite electrochromic thin film device is prepared on the ITO glass substrate. By scanning electron microscopy(SEM), it researches that whether the different amounts of MWNTs which is added into the PTh has influence on the conductivity, microstructure and electrochromic properties of the composite film; Test the conductivity diversification of the composite film with a four-probe technique; Analyze the characteristics of the composite film under the external field by UV-visible spectroscopy(UV-vis); It is found that after doping a small amount(<5% by mass) of MWNTs, the conductivity of MWNTs/PTh composite electrochromic thin film device increases, and its electrochromic performance and response time also improve. However, with the increase of the adding amount of the carbon nanotubes, although the outside voltage which is needed by the composite thin film device’s discoloration decreases significantly, but the color uniformity of the device’s discoloration region has a certain deviation. The study found that the uniform distribution of the carbon nanotubes in the composite films has differences, when the amount of the carbon tube is large, local conductivity increases significantly, and the discolored response time in the region improves significantly. But in some areas, the density of the carbon tube is less, its color response can not keep up with the areas which have more carbon nanotube density, it leads the electrochromic properties of the MWNTs/PTh composite thin film device to change. But after adding carbon nanotubes, there is a significant improvement of the MWNTs/PTh composite electrochromic thin film device lifetime, because carbon nanotubes provide some more one-dimensional conductive channels. It will be very favorable to improve the response time and the lifetime of the device.This paper makes the conductive polymer and carbon nanotubes uniformly mix and then spin-coat, the operation is simple, cheap, safe and reliable, and it has a certain reference value in the electrochromic device practical applications.