Adhesion of Spherical Polyelectrolyte Brushes on Mica:  An in Situ AFM Investigation

Abstract

We demonstrate that the adsorption of cationic spherical polyelectrolyte brushes (SPB) on negatively charged mica substrates can be controlled in situ by the ionic strength of the suspension. The SPB used in our experiments consist of colloidal core particles made of polystyrene. Long cationic polyelectrolyte chains are grafted onto these cores that have diameters in the range of 100 nm. These particles are suspended in aqueous solution with a fixed ionic strength. Atomic force microscopy (AFM) in suspension as well as in air was used for surface characterization. In pure water the polymer particles exhibit a strong adhesion to the mica surface. AFM investigations of the dry samples show that the particles occupy the identical positions as they did in liquid. They were not removed by the capillary forces within the receding water front during the drying process. The strong interaction between the particles and the mica surface is corroborated by testing the adhesion of individual particles on the dried surface by means of the AFM tip: after a stepwise increase of the force applied to the surface by the AFM tip, the polymer particles still were not removed from the surface, but they were cut through and remained on the substrate. Moreover, in situ AFM measurements showed that particles which adsorb under liquid in a stable manner are easily desorbed from the surface after electrolyte is added to the suspension. This finding is explained by a decreasing attractive particle-substrate interaction, and the removal of the particles from the surface is due to the significant reduction of the activation barrier of the particle desorption. All findings can be explained in terms of the counterion release force.

Salt-regulated attraction and repulsion of spherical polyelectrolyte brushes towards polyelectrolyte multilayers

“…While this has been demonstrated for hard particles 39 and soft shells,40 the present system could allow for annealing structures beca use of the stimuli-responsive nature of the brush layer, whieh avoids an irreversible hit-stick behaviour. 19 In addition, numerous chemical modifications have been reported for SPB particles ls . ' S .…”

“…Intriguingly, the force of adhesion could be adjusted by the ionic strength of the surrounding medium. 19 We extend these studies to substrates coated with charged polymers. Polyelectrolyte multilayers are applicable to almost any solid support and the layer-by-Iayer technique is compatible with 'a wide selection of polymers 21 The assembly process even allows the incorporation of charged particles opening avenues to highly functional surfaces.…”

“…Preceding studies using negatively charged mica surfaces demonstrated distinct differences in the adsorption behaviour of cationic and anionic SPB. 19,20 Whereas anionic SPB exhibited a high lateral mobility during drying resulting in hexagonally packed arrangements, cationic SPB were strongly affixed to the surface, which resulted in open structures. Intriguingly, the force of adhesion could be adjusted by the ionic strength of the surrounding medium.…”

Adsorption of Spherical Polyelectrolyte Brushes: from Interactions to Surface Patterning

“…Understanding the interaction of SPB with solid substrates is a prerequisite for their technological application in functional coatings. Studies with mica surfaces demonstrated distinct differences in the adsorption behavior of cationic and anionic SPB [34,35]. While anionic SPB exhibited a high lateral mobility on the negative substrates and Fig.…”

Nanoparticles in the Water Cycle

“…Two approaches are chosen to investigate the adsorption of the two different types of SPB: In a first approach the negatively and positively charged particles adsorbed on mica were investigated by ex situ AFM techniques. In the second, in situ AFM experiments were carried out to investigate the adsorption and desorption of cationic particles on mica substrates in an aqueous environment (Gliemann et al, 2006;Mei et al, 2003). Table 6.1 summarizes the characteristic data of both SPB.…”