Confined soft-templating of gold nanoparticles within reverse wormlike micelles

Nanoreactors with limited space can enhance aqueous reaction conditions by restricting reactant mobility, influencing both the kinetics and thermodynamics of the process¹. In this study, we employ reverse wormlike micelles (RWLMs) as quasi-one-dimensional nanoreactors for nanoparticle formation. RWLMs are elongated, self-assembled structures with narrow aqueous channels, creating confined spaces ideal for controlling chemical reactions, particularly nanoparticle nucleation and growth. By adjusting the system's composition, we can modify the channel diameter, which in turn affects viscosity and molecular mobility within the channels².

We focused on reduction reactions to explore how these nanoreactors influence the shape of gold nanoparticles (AuNPs). Using chloroauric acid as the precursor and hydroquinone as the reducing agent, AuNP formation was successfully achieved by confining the reactants within the nanoreactors, as indicated by the characteristic red-colored gel. Notably, the system's optical properties changed with water content (W₀). At low levels, the solution looked red, while more water shifted the color to blue. This was due to AuNP elongation, reflected in a transverse plasmon resonance band near 613 nm in UV/vis. SAXS experiments also confirm an increase in AuNP aspect ratio at a higher W₀. By that, this study demonstrates that RWLMs provide a stable and controlled environment for nanoparticle formation and their ability to modulate the shape of nanoparticles.