Letter pubs.acs.org/macroletters
Stability of Polymer Grafted Nanoparticle Monolayers: Impact of Architecture and Polymer−Substrate Interactions on Dewetting Justin Che,†,‡ Ali Jawaid,†,§ Christopher A. Grabowski,†,§ Yoon-Jae Yi,†,∥ Golda Chakkalakal Louis,⊥ Subramanian Ramakrishnan,⊥ and Richard A. Vaia*,† †
Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, Ohio 45433, United States ‡ National Research Council, Washington, D.C. 20001, United States § UES, Inc., Dayton, Ohio 45432, United States ∥ College of Science and Mathematics, Wright State University, Dayton, Ohio 45435, United States ⊥ College of Engineering, Florida A&M University-Florida State University, Tallahassee, Florida 32310, United States S Supporting Information *
ABSTRACT: The stability of polymer thin films is crucial to a broad range of technologies, including sensors, energy storage, filtration, and lithography. Recently, the demonstration of rapid deposition on solid substrates of ordered monolayers of polymer grafted nanoparticles (PGN) has increased potential for inks to additively manufacture such components. Herein, enhanced stability against dewetting of these self-assembled PGN films (gold nanoparticle functionalized with polystyrene (AuNP-PS)) is discussed in context to linear polystyrene (PS) analogues using high throughput surface gradients: surface energy (20−45 mN/m) and temperature (90−160 °C). PGNs exhibit a lower surface (γp) and interfacial (γsp) energy relative to linear polymers, which results in increased thermal and energetic stability by 10−25 °C and 5−15 mN/m, respectively. This enhanced wetting−dewetting transition is qualitatively consistent with the behavior of star macromolecules and depends on the architecture of the polymer canopy. Increased film stability through canopy architecture expands the manufacturability of thin film hybrids and refines postprocessing conditions to maximize local PGN order.
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properties of this canopy depend on the conformation of the tethered polymer chains, which may range from highly stretched at high graft density of low molecular weight chains, to a random-coil at low graft density of high molecular weight chains.13,14 The potential for PGN assemblies have been demonstrated for sensors, high energy storage capacitors, and high refractive lenses and filters.15−17 Recently, Che et al.18 established the rapid formation of ordered mono- and bilayer PGN assemblies directly on solid substrates, rather than via liquid interface assembly followed by film transfer.19 The correlation between quantized film thickness and processing conditions, such as concentration and deposition velocity, paralleled the slot-die deposition of ordered colloids, albeit at rates 10−100× faster. However, the local nanoparticle arrangement depended on PGN architecture and substrate surface energy. The factors determining the stability of these PGN films, especially within the context of polymer and polymer nanocomposites, are still unknown. Herein, the wetting−dewetting (stability) boundary for PGN monolayers is mapped with respect to PGN architecture via
he 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.1−4 The thickness of the film plays a crucial role in determining stability.5 For thin films (
