Surfactant Composition Dependent Evolution of Electronic/Structural Properties of P3HT Nanoparticle Colloids Synthesized via Mini-Emulsion Technique

Abstract

This study investigates the influence of surfactant (sodium dodecyl sulfate, SDS) concentration onthe size and optoelectronic properties of poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) synthesized viathe mini-emulsion technique. P3HT NPs were fabricated with varying SDS concentrations. The sizedependent optoelectronic properties, including the highest occupied molecular orbital (HOMO) and the lowestunoccupied molecular orbital (LUMO) levels, were analyzed through photoelectron spectroscopy in air, UVVisabsorption spectroscopy and cyclic voltammetry. A clear trend of decreasing NP size with increasing SDSconcentration was observed. Higher SDS levels resulted in smaller NPs with enhanced pi-pi stacking andshorter conjugation lengths. This structural change led to a noticeable shift in HOMO and LUMO levels,indicating a direct correlation between surfactant concentration and the electronic properties of the P3HTNPs. The absorption spectra revealed a decrease in the A0-0/A0-1 ratio with smaller NP size, suggesting atransition towards more pronounced H-aggregate characteristics. As the size of the P3HT NPs decreases,there is a notable increase in H-aggregate formation. This increase can be attributed to enhanced interchaininteractions between the polymer chains. In smaller NPs, the surface area-to-volume ratio is higher, leadingto more significant interactions between adjacent polymer chains. These interactions promote the formationof H-aggregates, characterized by their interchain pi-pi stacking, which differs from the intrachain couplingobserved in J-aggregates.