Fabrication of Surface Polymer Brushes Via Thin Film Crystallization and Solvent Annealing.

Polymer single crystals are used as templates to synthesize polymer brushes, known as the "polymer-single-crystal-assisted-grafting-to" (PSCAGT) approach. Polymer brushes with controlled grafting densities and spatial tethering locations are demonstrated. Previous works focused on solution crystallization, which involves large amounts of organic solvent, and the grafting density can only be tuned by varying crystallization temperatures. In this work, thin film crystallization is utilized to fabricate 2D polymer crystals on flat surfaces. Subsequent chemical tethering leads to polymer brushes that retain the original morphology of the crystals with high fidelity. Furthermore, it is shown that the grafting density of the polymer brushes fabricated using this method depends on the chain end distribution on the top/bottom surfaces of the crystal, which can be facilely controlled by annealing the crystals at various nonsolvent media. This work broadens the scope of the PSCAGT method and provides a new route to achieve polymer brushes with controlled structures.

Adaptable Multivalent Hairy Inorganic Nanoparticles.

We report a polymer brush-based approach for fabricating multivalent patchy nanoparticles (NPs) with the number of nanodomains (valency) from 6 to 10, potentially from 1 to 10, by exploiting the lateral microphase separation of binary mixed homopolymer brushes grafted on NPs with a radius comparable to the polymer sizes. Well-defined mixed brushes were grown on 20.4 nm silica NPs by two-step surface-initiated reversible deactivation radical polymerizations and microphase separated laterally upon casting from a good solvent, producing multivalent NPs on 2D surfaces. A linear relationship between valency and average core size for the corresponding valency was observed. The mixed brush NPs exhibited abilities to form "bonds" through the overlap of nanodomains and to change the valency when interacting with adjacent NPs. This method could open up a new avenue for studying patchy NPs.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method.

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Characterizing Polymer-Grafted Nanoparticles: From Basic Defining Parameters to Behavior in Solvents and Self-Assembled Structures.

Polymer-grafted nanoparticles, often called hairy nanoparticles (HNPs), are an intriguing class of nanostructured hybrid materials with great potential in a variety of applications, including advanced polymer nanocomposite fabrication, drug delivery, imaging, and lubrication. This Feature provides an introduction to characterization of various aspects of HNPs, from basic defining parameters to behavior of HNPs in solvents and self-assembled structures of multicomponent brush nanoparticles, by using a broad range of analytical tools.