Single-polymer adsorption in shear: Flattening vs. hydrodynamic lift and surface potential corrugation effects

Abstract

PACS 82.35.Gh -Polymers on surfaces; adhesion PACS 83.50.-v -Deformation and flow PACS 82.37.Gk -STM and AFM manipulations of a single moleculeAbstract. -The adsorption of a single polymer to a flat surface in shear is investigated using Brownian hydrodynamics simulations and scaling arguments. Competing effects are disentangled: in the absence of hydrodynamic interactions, shear drag flattens the chain and thus enhances adsorption. Hydrodynamic lift on the other hand gives rise to long-ranged repulsion from the surface which preempts the surface-adsorbed state via a discontinuous desorption transition, in agreement with theoretical arguments. Chain flattening is dominated by hydrodynamic lift, so overall, shear flow weakens the adsorption of flexible polymers. Surface friction due to smallwavelength surface potential corrugations is argued to weaken the surface attraction as well.

Shear-induced dynamics of polymeric globules at adsorbing homogeneous and inhomogeneous surfaces

“…Although this reduces the hydrodynamic lift force, the effective surface adhesion strength is reduced so that adsorption is disfavored when compared to the limit of no shear. This is similar to the analysis of a simple model of a monomer dragged along a corrugated potential [17].…”

“…Since the stretched chain shows reduced fluctuations in the perpendicular direction to the surface, it is more easily adsorbed leading to state (D) where the center-ofmass height is reduced compared to the globular state. This stretching-induced adsorption mechanism has been previously discussed in the absence of hydrodynamic interactions and is typically overwhelmed by hydrodynamic drag effects [34,17], in the present situation it seems to be operative since the chain is inhomogeneous and consists of a stretched protrusion and a globular section that acts as an anchor. Once adsorbed, the shear forces are reduced and the polymer can refold into a globular state (E), this transformation is assisted by the rolling motion of the chain, and leads back to the starting configuration of a globule adsorbed at the surface, state (A).…”

“…6, the rescaled velocity V /γz COM , measured along the adsorption transition line, decreases with decreasing interaction range σ W as a result of enhanced surface friction, while the extension in flow direction R S /2N , also measured along the transition line, increases strongly due to internal shear effects in the globule. This means that the inhomogeneous surface enhances unfolding of the FD polymer in shear flow but suppresses adsorption; in other words, the stretching of the chain, which by itself weakens entropic repulsion from the surface and therefore promotes adsorption [34], is overwhelmed by the weakened energetic attraction to the surface since the monomers are constantly pulled away from the surface binding sites [17,14].…”

“…When considering non-equilibrium effects, e.g. by inclusion of simple shear-flow [12][13][14], it has been shown that hydrodynamic interactions and the presence a e-mail: radtkem@physik.fu-berlin.de of a no-slip boundary is crucial and therefore has to be taken into account [15][16][17][18].…”

Von Willlebrand Adhesion to Surfaces at High Shear Rates Is Controlled by Long-Lived Bonds

“…Simultaneous research into fluorescently labeled DNA molecules has elucidated the driving forces governing the adsorption and desorption of molecules in shear flows near surfaces; specifically, a powerful lift force drives the desorption and subsequent depletion of molecules that are stretched by shear flow (17)(18)(19)(20)(21). This lift force is a hydrodynamic effect seen in flow-stretched polymers that produces a force perpendicular to the applied shear flow, and it is due to local induced flows interacting with the no-slip boundary condition at the surface (17)(18)(19)(20)(21).…”