Bottlebrush polymers contain polymeric side-chains attached to a linear polymer backbone, and they are currently of interest for a variety of potential applications that include drug delivery, tailored surface wettability, and self-assembled photonics. These polymers are challenging to synthesize in large quantities, so for practical applications, it is of interest to study their properties as additives for low-cost linear polymers. In this work, we examine the phase behavior of bottlebrush polystyrene (PS) and linear deuterated polystyrene (dPS) in thin films. These nearly athermal systems exhibit wetting and dewetting transitions that drive bottlebrush dispersion or aggregation, respectively, and these effects depend on the relative degrees of polymerization of matrix chains N m to those of bottlebrush side-chains N sc . When N m /N sc is low (≤1.6), the bottlebrushes are dispersed throughout the film thickness with a slight excess at the free surface and substrate interfaces. When N m /N sc is high (≥8), the bottlebrushes are depleted from the interior of the film and strongly segregated at the interfaces. The interfacial excess is driven by an entropic depletion attraction effect: larger branched molecules are adsorbed (attracted) to the interfaces, and the linear chains are displaced to the film's interior where they gain conformational entropy. The bottlebrushes prefer to accumulate at the silicon substrate over the air interface, and this may be driven by the more restrictive condition of a hard boundary or weak van der Waals interactions with the underlying silicon. These studies demonstrate that low concentrations of certain bottlebrush polymer architectures can generate brushlike surfaces and interfaces in any thermoplastic material through a spontaneous, entropy-driven segregation process. ■ INTRODUCTIONBottlebrush polymers contain polymeric side-chains attached to a linear polymer backbone, and controlled polymerization techniques enable the preparation of fully grafted bottlebrush polymers with tunable backbone length, side-chain length, and side-chain composition. 1−5 This synthetic tunability has motivated a number of recent studies into the potential applications of bottlebrush polymers, including drug delivery, 6−8 polymer photonics, 9−11 lubricants and rheology modifiers, 2,12−14 and surface coatings. 15,16 These applications take advantage of unique aspects of bottlebrush polymers, including an extended backbone, densely grafted and flexible side-chains, and a very high entanglement molecular weight. 14 However, bottlebrush polymers are specialty materials that are difficult to synthesize in large quantities. Therefore, it is of interest to study their properties as additives in blends with low-cost, linear polymers.A number of recent studies have focused on a related set of materials, blends of polymer coated nanoparticles with linear polymers, as detailed in recent reviews. 17,18 Polymer-coated nanoparticles have a layer of linear polymers end-grafted to the nanoparticle surface which control...

Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 degrees C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 degrees C.

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