Oppositely Charged, Stimuli-Responsive Anisotropic Nanoparticles for Colloidal Self-Assembly

Anisotropic nanoparticles (ANPs) composed of distinct compartments are of interest as advanced materials because they offer unique physicochemical properties controlled by polymer composition, distribution of functional groups, and stimuli responsiveness of each compartment. Furthermore, colloidal self-assembly of ANPs via noncovalent interactions between compartments can create superstructures with additional functionality. In this study, ANPs with two compartments composed of oppositely charged and thermally responsive ternary copolymers were prepared using electro-hydrodynamic cojetting. One compartment was composed of poly(N-isopropylacrylamide-co-stearyl acrylate-co-allylamine), which is positively charged in aqueous solution at pH 7, and the other compartment was composed of poly(N-isopropylacrylamide-co-stearyl acrylate-co-acrylic acid), which is negatively charged. The ANPs were stabilized in aqueous solution by physical cross-linking because of hydrophobic interactions between the 18-carbon alkyl chains of their stearyl acrylate moieties and self-assembled into supracolloidal nanostructures via electrostatic interactions. Colloidal self-assembly and thermal responsiveness were controlled by compartment charge density and solution ionic strength. The supracolloidal nanostructures exhibited both the intrinsic temperature-responsive properties of the ANPs and collective properties from self-assembly. These multifunctional, stimuli-responsive nanostructures will be useful in a variety of applications, including switchable displays, drug delivery carriers, and ion-sensitive gels.