Self-Regulated Nanoparticle Assembly at Liquid/Liquid Interfaces: A Route to Adaptive Structuring of Liquids

Abstract

The controlled structuring of liquids into arbitrary shapes can be achieved in biphasic liquid media using the interfacial assemblies of nanoparticle surfactants (NP-surfactants), that consist of a polar nanoparticle "head group" bound to one or more hydrophobic polymer "tails". The nonequilibrium shapes of the suspended liquid phase can be rendered permanent by the jamming of the NP-surfactants formed and assembled at the interface between the liquids as the system attempts to minimize the interfacial area between the liquids. While critical to the structuring process, little is known of the dynamic mechanical properties of the NP-surfactant monolayer at the interface as it is dictated by the characteristics of the component, including NP size and concentration and the molecular weight and concentration of polymers bound to the NPs. Here we provide the first comprehensive understanding of the dynamic mechanical character of two-dimensional NP-surfactant assemblies at liquid/liquid interfaces. Our results indicate that the dynamics of NP-polymer interactions are self-regulated across multiple time scales and are associated with specific mesoscale interactions between self-similar and cross-complementary components. Furthermore, the mechanical properties of the NP-surfactant monolayer are tunable over a broad range and deterministic on the basis of those component inputs. This control is key to tailoring the functional attributes of the reconfigurable structured liquids to suit specific applications.

Reconfigurable Printed Liquids

“…The presence of multiple functional groups on the polymers gives rise to cross‐linked NPS films and, hence, tunable mechanical properties of the constructs . Typically, increasing polymer concentration results in prints with fewer defects, more consistent thread diameters, and reduced structural evolution after printing (Figure S11, Supporting Information), in agreement with recent results on NPS assembly kinetics . For silica particle concentration, c p < 0.5 mg mL −1 stable prints were not formed.…”

Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants

“…The pH of the aqueous dispersions was adjusted to ∼6 using 1.0 M NaOH or HCl. Monoamino-terminated polydimethylsiloxanes (PDMS-NH 2 , M w = 1,000, 3,000, 5,000 or 10,000 g mol -1 ) were synthesized using organocatalytic ring-opening polymerization with a procedure reported in our previous work 28 . Monoamino-terminated polystyrenes (PS-NH 2 , M w = 1,000 or 5,000 g mol…”

Nanoparticle Assembly at Liquid–Liquid Interfaces: From the Nanoscale to Mesoscale

“…For this in situ formation of the NP‐surfactants via electrostatic interactions, the final number of polymer chains anchored to the NPs at the interface is self‐regulated, so as to maximize the reduction in interfacial energy . If the number is too small, NP‐surfactants would eventually be drawn into the aqueous phase; if the number of anchored chains is too large, the NP‐surfactants would be drawn into the oil phase (known as phase transfer) .…”