Heterogeneous photosensitizers: Super-efficient dual functional polydopamine nanohybrid for epoxy photopolymerization

Abstract

The photosensitivity of nanoparticulate polydopamine (PDA) and polydopamine coated multiwalled carbon nanotubes (PDA/MWCNT) and their effect on the photopolymerization of epoxy monomers were systematically investigated. PDA/MWCNT nanohybrid at only 0.625 wt% has been shown to photo-catalyse the polymerization speed and conversion when compared with the commercial free radical photoinitiator, BAPO or non-free radical enhanced cationic photoinitiating resin systems. More importantly, it substantially increased the conversion by more than 140% over the unfilled free radical promoted cationic photoinitiating resin system. Covalent coated PDA/MWCNT nanohybrids were fabricated by oxidative polymerization of dopamine on the surface of acid treated MWCNTs. The modified MWCNT nanofiller has a dual role as photosensitizer/co-initiator in the FRPCP photoinitiating system and as mechanical reinforcement for the epoxy matrix. The use of PDA nanoparticles also led to the improvement in the polymerization process, albeit a limited one. Further evaluation of the observation suggests that the increase in the polymerization speed could be due to the photoinduced electron transfer effect in the polydopamine domain of the hybrid. The super efficiency effect has been explained through the heterojunction formation at the interface of dissimilar semi-conductive/conductive materials, polydopamine, a bio conjugated molecule with UV sensitivity and MWCNT hybrids, in the curing of epoxy monomers. This type of hybridized sensitizers/co-initiators have the potential to be applied in vat type 3D printing technologies such as SLA and DLP enabling printing with light blocking additives which otherwise pose a challenge in UV–Vis enabled curing and printing.