Mediating conducting polymer growth within hydrogels by controlling nucleation

Abstract

This study examines the efficacy of primary and secondary nucleation for electrochemical polymerisation of conductive polymers within poly(vinyl alcohol) methacrylate hydrogels. The two methods of nucleation investigated were a primary heterogeneous mechanism via introduction of conductive bulk metallic glass (Mg64Zn30Ca5Na1) particles and a secondary mechanism via introduction of “pre-polymerised” conducting polymer within the hydrogel (PEDOT:PSS). Evidence of nucleation was not seen in the bulk metallic glass loaded gels, however, the PEDOT:PSS loaded gels produced charge storage capacities over 15 mC/cm2 when sufficient polymer was loaded. These studies support the hypothesis that secondary nucleation is an efficient approach to producing stand-alone conducting hydrogels.

Mechanisms for Imparting Conductivity to Nonconductive Polymeric Biomaterials

“…[ 213 ] Spontaneous nucleation (homogeneous) typically occurs at a surface, for example the electrodeposition of a CP on a metallic substrate. [ 213,214 ] However, if there is no surface, or it is required that a material forms away from a surface-effectively suspended within a polymer, as is the case for in situ growth-this nucleation mechanism can be extremely problematic and is largely unsuccessful. [ 214,215 ] The type of nucleation used to create a conductive composite affects the resulting properties in the longer term.…”

“…It is thought that this is primarily through the introduction of an additional phase that creates both a defect and an existing CP chemistry with which the CP monomer solution can react to readily polymerize. [213] Ultimately, this enables the nucleation and growth process of the CP to be driven by secondary growth mechanisms, rather than primary spontaneous nucleation. The latter is by far the lower energy cost solution when driving electropolymerization such that it occurs away from the underlying electrode.…”

“…In this study a loading of 5 wt% PEDOT:PSS was required to reach a percolation threshold and impart a small conductivity (≈0.16 mS cm −1 ). However Patton et al [213] were able to load PVA at 0.5 wt% PEDOT:PSS and used this dispersion to electrochemically grow additional PEDOT from the dispersed PEDOT:PSS chains within the hydrogel (see Figure 7). It was shown that conductivity could be increased from 0.04 to 1.48 mS cm −1 when electrodeposition was undertaken in situ.…”

Incorporation of Conductive Materials into Hydrogels for Tissue Engineering Applications

“…It is important to generate sites in the hydrogel for nucleation support and the subsequent growth of conductivity elements [144]. Since these elements have the property of forming at the lowest energy-cost position [144][145][146], spontaneous homogeneous nucleation can generally be precipitated on one side of a substrate as it is, affected by gravity during the heat or photopolymerization process or by electrical adsorption.…”

“…Since these elements have the property of forming at the lowest energy-cost position [144][145][146], spontaneous homogeneous nucleation can generally be precipitated on one side of a substrate as it is, affected by gravity during the heat or photopolymerization process or by electrical adsorption. Therefore, when the conductive polymer nuclei are formed and synthesized at the lowest energy cost, the process is necessary to grow a continuous long polymer chain homogeneously to form a conductive film [147].…”