Pick up, move and release of nanoparticles utilizing co-non-solvency of PNIPAM brushes

Abstract

A critical complication in handling nanoparticles is the formation of large aggregates when particles are dried e.g. when they need to be transferred from one liquid to another. The particles in these aggregates need to disperse into the destined liquid medium, which has been proven difficult due to the relatively large interfacial interaction forces between nanoparticles. We present a simple method to capture, move and release nanoparticles without the formation of large aggregates. To do so, we employ the co-non-solvency effect of poly(N-isopropylacrylamide) (PNIPAM) brushes in water-ethanol mixtures. In pure water or ethanol, the densely end-anchored macromolecules in the PNIPAM brush stretch and absorb the solvent. We show that under these conditions, the adherence between the PNIPAM brush and a silicon oxide, gold, polystyrene or poly(methyl methacrylate) colloid attached to an atomic force microscopy cantilever is low. In contrast, when the PNIPAM brushes are in a collapsed state in a 30-70 vol% ethanol-water mixture, the adhesion between the brush and the different counter surfaces is high. For potential application, we demonstrate that this difference in adhesion can be utilized to pick up, move and release 900 silicon oxide nanoparticles of diameter 80 nm using only 10 × 10 μm PNIPAM brush.

Cononsolvency Transition of Polymer Brushes: A Combined Experimental and Theoretical Study

“…Although previous experimental studies [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] claimed that the cononsolvency transition of polymer brushes show features of a phase transition, so far, direct experimental evidence is missing. In order to check whether the cononsolvency transition of polymer brushes is an equilibrium transition, we measured swollen brush thickness as a function of time.…”

“…By using an extended surface forces apparatus, R. Espinosa-Marzal et al [ 18 ] studied the impact of solvation on equilibrium conformation of dextran brushes in aqueous dimethyl sulfoxide mixtures. By combining the methods mentioned above, cononsolvency effects of polymer brushes have been related to applications for nanomaterials [ 19 ], tunable friction [ 20 , 21 ] and adhesive [ 22 ] properties of surfaces, as well as response of polymer brushes in liquid fluid media [ 23 , 24 ].…”

Many-chain effects on the co-nonsolvency of polymer brushes in a good solvent mixture

“…When raising the methanol fraction by more than 40 mol%, the brush gradually re-swell to form the conformation in the pure water. This asymmetric change as the solvent composition has emerged also in the dynamic, 12,29 synthetic, 30 mechanical properties, 9,31,32 extending the notion of the co-nonsolvency beyond the structural response.…”

Effect of Architecture of Thermoresponsive Copolymer Brushes on Switching of Their Adsorption Properties

“…They are also able to demonstrate switchable properties due to the stimuli‐responsive behavior of the polymer chains that were grafted onto the surface . The responsiveness of these brushes was utilized to design surfaces with tunable wetting properties with regard to adhesion, adsorption, friction, and other properties . In one approach for the design of stimuli‐responsive brushes, the switching is provided by changing the properties (charge and hydrophobicity) of the polymer themselves .…”