Influence of viologen lengths on the response time of the reflective electrochromic display prepared by monodisperse viologen-modified polymeric microspheres

To improve the response time of reflective electrochromic display (R-ECD), the distance between particle surface and viologen moiety was controlled. Firstly, cyano-functionalized polymeric microspheres were prepared by seeded polymerization and then the synthesized viologen compounds, containing alkyl chains of varying lengths, were reacted on the surface of the microspheres. Faster response time under 1 s was obtained as the viologen pendant lengths became longer. From the electrochemical and electro-optical measurements, it is reasonable to think that the redox reactions of the viologen moiety, which was derived from the electron transfer by the ions in electrolyte, could certainly be facilitated when a long chain length of viologen is used. In addition, the R-ECD device had good cyclic stability and no signs of side effects were observed since the viologen molecules were stably grafted on the surface of microspheres.