Solvent injection for polydiacetylene particle synthesis – Effects of varying solvent, injection rate, monomers and needle size on polydiacetylene properties

ABSTRACT Polydiacetylenes (PDAs) have been widely used for sensing chemical and biological targets. The solvent injection (SI) method has been proposed as a viable alternative to the traditional thin film hydration method for large-scale PDA particle production, however the synthesis of PDA particles by SI remains understudied. The aim of the present study is to investigate the impacts of varying SI process parameters on the PDA properties. We focus on the effects of varying the solvent type, injection rate, diacetylene (DA) monomer and needle size on PDA properties, such as size, morphology, thermochromic and pH colorimetric response. Our results show that SI can produce self-assembled PDA particles and that this method does not compromise the intrinsic optical properties of PDA. Ethanol and isopropanol are suitable solvents, whereas water-immiscible solvents, such as chloroform was found to inhibit particle formation due to the poor solvent and aqueous phase mixing and the increased surface tension during self-assembly. A higher injection rate was found to produce PDA with greater color intensity due to the growth of small crystallites and the potential formation of defect sites in favor of topochemical polymerization as supported by the XRD results. We also report the relationship between synthesis flow rate and needle size as a stability cut-off point when PDA aggregation exists. Overall, we present a fully characterized alternative method to produce PDA particles and show that SI does not compromise the thermochromic and pH colorimetric sensitivity of PDA.