Doped conjugated polymers are making a comeback as the enabling components in a variety of technologies some of which include flexible integrated circuits, hybrid supercapacitors, tissue-compatible biosensors and neural network simulants. In addition to that is the fact that for long they have been the material of choice for conductive channels in ion sensors, color modulators in electrochromic devices and also used as actuating materials in artificial muscles.
In doped conjugated polymers two things occur. They are counterion transport and film swelling or deswelling due to ion and/or solvent diffusion into or out of the films, respectively. There has been Innovations in film deposition routines and doping protocols which have resulted in huge leaps in the electronic conductivities of doped conjugated polymer films. However insights on correlation into how these processing conditions affect the swelling behavior and ion transport in doped conjugated polymer films is lacking. Knowing this is important for optimizing the performance of polymer-based hybrid supercapacitors and enabling accurate data interpretation from electrochemical transistors, among other applications.
Dr. Lushuai Zhang and Professor Trisha Andrew from the University of Massachusetts used simultaneous electrochemical and electro gravimetric measurements to probe the swelling behavior, perm selectivity and electrochemical cycling stabilities of a model material, p-doped poly (3,4-ethylenedioxythiophene), in selected electrolytes. They paid attention to the effects of deposition method on the electrochemical and electro gravimetric properties of resulting films. The result of their findings is published in a peer reviewed publication Advanced Materials Interface.
Using electrochemical quartz crystal microbalance the researchers tried to understand ion transport across a polymer/electrolyte interface in poly (3,4-ethylenedioxythiophene) films. This was prepared by making use of two widely used vapor deposition methods, which are Oxidative Chemical Vapor Deposition (oCVD) and vapor phase polymerization (VPP). They confirmed that poly (3,4-ethylenedioxythiophene) films deposited using vapor phase polymerization displays detrimental mass trapping with electrochemical cycling. Information that was derived from their results was that changing the method of film deposition to Oxidative Chemical Vapor Deposition oCVD creates films with comparatively minimal redox-associated mass trapping.
Lushuai Zhang and Trisha Andrew findings are significant because previously little distinction has been made between vapor phase polymerization and Oxidative Chemical Vapor Deposition. Their research has been able to point out that subtle differences between vapor deposition methods can have significant ramifications on the ultimate performance and longevity of charge storage devices. The study is also provided useful empirical information about the transport of ions across a polymer/electrolyte interface were presented.
“Chemical vapor deposition allows real-time control of the nanoscale morphology of the polymer film that is produced and also allows uniform doping throughout the bulk of the film, which is fundamentally important for prohibiting charge and ion trapping and destructive redox reactions when conjugated polymers are used in electrochemical devices. Identifying a processing technique that promises electrochemical fatigue resistance will be immensely and broadly useful for creating industrially-viable technologies.” said Professor Trisha Andrew.
Trisha L. Andrew, Lushuai Zhang. Deposition Dependent Ion Transport in Doped Conjugated Polymer Films: Insights for Creating High-Performance Electrochemical Devices. Advanced Material Interfaces , 2017, 4, 1700873.
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