Shape anisotropy induced jamming of nanoparticles at liquid interface: A tensiometric study

Abstract

The intersection of nanotechnology and interfacial science has opened up new avenues for understanding complex phenomena occurring at liquid interfaces. The assembly of nanoparticles at liquid/liquid interfaces provides valuable insights into their interactions with fluid interfaces, essential for various applications, including drug delivery. In this study, we focus on the shape and concentration effect of nanoscale particles towards interfacial affinity. Using pendant drop tensiometry, we monitor the real-time interfacial tension between an oil droplet and an aqueous solution containing nanoparticles. We measure two different types of nanoparticles: spherical gold nanoparticles (AuNPs) and anisotropic gold nanorods (AuNRs), each functionalized with surfactants to facilitate interaction at the interface. We observe that the interface equilibrium behaviour is mediated by kinetic processes, namely, diffusion, adsorption and rearrangement of particles. For anisotropic AuNRs, we observe shape-induced jamming of particles at the interface, evidenced by their slower diffusivity and invariant rearrangement rate. In contrast, the adsorption of spherical AuNPs is dynamic and requires more time to reach equilibrium, indicating weaker interface affinity. By detailed analysis of the interfacial tension data and interaction energy calculations, we show that anisotropic particle shape acquires stable equilibrium inter-particle separation as compared to the isotropic particles. Our findings demonstrate that anisotropic particles are a better design choice for drug delivery applications as it provides better affinity for fluid interface attachment, a crucial requirement for efficient drug transport across cell membranes. Additionally, anisotropic shapes can stabilize interfaces at low particle concentrations as compared to isotropic particles, thus minimizing side effects associated with biocompatibility and toxicity.