Film-Stabilizing Attributes of Polymeric Core–Shell Nanoparticles

Abstract

Self-organization of nanoparticles into stable, molecularly thin films provides an insightful paradigm for manipulating the manner in which materials interact at nanoscale dimensions to generate unique material assemblies at macroscopic length scales. While prior studies in this vein have focused largely on examining the performance of inorganic or organic/inorganic hybrid nanoparticles (NPs), the present work examines the stabilizing attributes of fully organic core-shell microgel (CSMG) NPs composed of a cross-linked poly(ethylene glycol dimethacrylate) (PEGDMA) core and a shell of densely grafted, but relatively short-chain, polystyrene (PS) arms. Although PS homopolymer thin films measuring from a few to many nanometers in thickness, depending on the molecular weight, typically dewet rapidly from silica supports at elevated temperatures, spin-coated CSMG NP films measuring as thin as 10 nm remain stable under identical conditions for at least 72 h. Through the use of self-assembled monolayers (SAMs) to alter the surface of a flat silica-based support, we demonstrate that such stabilization is not attributable to hydrogen bonding between the acrylic core and silica. We also document that thin NP films consisting of three or less layers (10 nm) and deposited onto SAMs can be fully dissolved even after extensive thermal treatment, whereas slightly thicker films (40 nm) on Si wafer become only partially soluble during solvent rinsing with and without sonication. Taken together, these observations indicate that the present CSMG NP films are stabilized primarily by multidirectional penetration of relatively short, unentangled NP arms caused by NP layering, rather than by chain entanglement as in linear homopolymer thin films. This nanoscale "velcro"-like mechanism permits such NP films, unlike their homopolymer counterparts of comparable chain length and thickness, to remain intact as stable, free-floating sheets on water, and thus provides a viable alternative to ultrathin organic coating strategies.

Synthesis and characterisation of biocompatible organic–inorganic core–shell nanocomposite particles based on ureasils

“…[11][12][13] Moreover, with appropriate surface modification, CSNPs can be well-dispersed through an external medium (e.g. an emulsion 14 or polymer host 15,16 ), which affords hierarchal control over the properties.…”

Stability of Polymer Grafted Nanoparticle Monolayers: Impact of Architecture and Polymer–Substrate Interactions on Dewetting

“…The stability of polymer and nanocomposite (PNC) thin films is crucial for manufacturing and in-service performance of technologies ranging from organic electronics, photoresists, filtration membranes, and printed passives (e.g., capacitors, traces), to lubricants, coatings, and adhesives. − The thickness of the film plays a crucial role in determining stability . For thin films (<100 nm), thermal fluctuations at the air–film interface drive dewetting when the relative surface and interface interactions favor minimization of the film’s surface area. , Therefore, the surface energy of both substrate and polymer are engineered when processing or service conditions are greater than the polymer’s glass transition temperature. , For example, the inclusion of inorganic nanoparticles (NP) inhibits dewetting by segregating to the substrate.…”

Feature Size Modulation in Dewetting of Nanoparticle-Containing Ultrathin Polymer Films

“…One extremely effective generic approach in suppressing spontaneous instability is addition of nanoparticles (NPs) in trace amounts to the film, which was first demonstrated by Barnes et al in 2000 . Subsequently, a variety of NPs, such as metallic NPs, organic NPs, , surface-modified NPs, − polymer-grafted NPs, and so forth, have been utilized to enhance the stability of ultrathin films. Entropy-driven migration of the NPs toward the substrate resulting in change in the effective wettability as well as enhanced pinning is generally argued to be responsible for dewetting suppression. − Interestingly, every report on dewetting of NP-containing thin films shows stabilization of the film only beyond a critical NP concentration ( C NPC ), the precise value of which depends on the exact nature of the particles along with other parameters such as the molecular weight of the polymer, compatibility between the particles and the polymer chains, non-wettability of the substrate, and so on.…”