Templated Synthesis of Amphiphilic Nanoparticles at the Liquid–Liquid Interface

Abstract

A simple and reliable method is described to produce inorganic nanoparticles functionalized asymmetrically with domains of hydrophobic and hydrophilic ligands on their respective hemispheres.These amphiphilic, Janus-type particles form spontaneously by a thermodynamically controlled process, in which the particle cores and two competing ligands assemble at the interface between two immiscible liquids to reduce the interfacial energy. The asymmetric surface chemistry resulting from this process was confirmed using contact angle measurements of water droplets on nanoparticle monolayers deposited onto hydrophobic and hydrophilic substrates ; particles presenting their hydrophobic face give contact angles of ∼96°, those presenting their hydrophilic face ∼19°. The spontaneous assembly process is rationalized by a thermodynamic model, which accounts both for the energetic contributions driving the assembly and for the entropic penalties that must be overcome.Consistent with the model, amphiphilic NPs form only when there is sufficient interfacial area to accommodate them; however, this potential limitation is easily overcome by mechanical agitation of the two-phase mixture. While it is straightforward to vary the ratio of hydrophobic and hydrophilic ligands, the accumulation of amphiphilic particles at the interface is maximal for ligand ratios near 1:1.In addition to gold nanoparticles and thiolate ligands, we demonstrate the generality of this approach by extending it to the preparation of amphiphilic iron oxide nanoparticles using two types of diolterminated ligands. Depending on the material properties of the inorganic cores, the resulting amphiphilic particles should find applications as responsive particle surfactants that respond dynamically to optical (plasmonic particles) and/or magnetic (magnetic particles) fields.

Communication: Re-entrant limits of stability of the liquid phase and the Speedy scenario in colloidal model systems

“…In both cases, the liquid vaporizes on cooling, but the gas phase is composed by (weakly interacting) aggregates in which particles are ordered in configurations of very low energy but also very low entropy, changing the slope of the binodal at low T. In the Janus case, the gas is indeed formed by micelles and vesicles, 47 while in the 2A9B case, the gas is composed of rings. 51 Thus, the physics that stabilizes the gas phase at low T allows the spinodal to rise back to positive P. Finally, we note that both models might be realized experimentally in the near future, [61][62][63][64] allowing for an experimental confirmation of the numerical and theoretical results reported here. The peculiar properties of these systems, while being somewhat different from those of water (for which there is no evidence of a lower gas-liquid critical point and the binodal is positively sloped), can shed light on the thermodynamics of anomalous fluids.…”

The equilibrium shape of fluid-fluid interfaces: Derivation and a new numerical method for Young’s and Young-Laplace equations

“…For example, the adsorption of colloids, nanoparticles, polymers, or proteins at fluid-fluid interfaces are highly relevant for industrial products (food, 1 Pickering Emulsion, 2-4 particle synthesis, 5 cosmetics, paints, etc.) and vital for engineering processes (washing, coating, water purification, etc.).…”

Enhanced nucleic acid amplification with blood in situ by wire-guided droplet manipulation (WDM)

“…Proteins differentially adsorb and denature at the oil-water interface depending on properties such as size, surface hydrophobicity, and surface charge (Li et al, 2012; Keerati-u-rai et al, 2012, Tubio et al, 2004). Other investigators have shown the utility of this molecular self-assembly at oil-water interfaces to specifically control aggregation of droplets in emulsion (Hadorn and Boenzli, 2012) and to create amphiphilic nanoparticles (Andala et al, 2012). …”