Adsorption of Low Charge Density Polyelectrolytes to an Oppositely Charged Porous Substrate

Abstract

The adsorption behavior of a low charge density cationic polyelectrolyte to cellulosic fibers has been studied. Cationic dextran served as a model polyelectrolyte, as it can be prepared over a range in molecular mass and charge density. The adsorption behavior of the cationic dextran was measured in electrolyte-free conditions using polyelectrolyte titration techniques. By fluorescent labeling the cationic dextran, the extent to which adsorption occurs inside the porous structure was further determined by fluorescent confocal laser scanning microscopy. Cationic dextran having a sufficiently low charge density adsorbed into the pores, although the extent the cationic dextran adsorbed was governed by the molecular mass. The adsorption behavior of the cationic dextran was also studied in various electrolyte concentrations. The adsorbed mass monotonically decreased with increasing electrolyte, as the electrostatic interaction with the substrate was more effectively screened. This behavior also suggests that the interactions between adsorbed polyelectrolyte chains, i.e. lateral correlation effects, are negligible for low charge density polyelectrolytes. Finally, the effect of having a preadsorbed layer of cationic dextran on the adsorption behavior was determined in electrolyte-free conditions using fluorescent double staining techniques. The preadsorbed cationic dextran had almost no effect on the adsorption of low molecular mass fractions. Low molecular mass fractions directly adsorbed into the pore structure, as opposed to adsorbing to a free surface and diffusing into the pores. It was also shown that cationic dextran can be selectively adsorbed to different locations, such that the surface of a porous substrate can be treated uniquely from the bulk.

Adsorption of cationized barley husk xylan on kraft pulp fibres: influence of degree of cationization on adsorption characteristics

“…In the cases of HPTMA-GAX H and HPTMA-GAX M adsorption, the number of introduced charges exceeds the fibre surface charge. This finding along with the research by Horvath et al (2008) on the adsorption of cationic dextrans on pulp fibres, make it plausible to assume that adsorption of HPTMA-GAX not only occurs on the outer fibre surface, but also inside the fibre wall.…”

Analytical staining of cellulosic materials: A review

“…A cationic fluorescent labeled dextrin of various molecular mass was used to study diffusion into cell walls. Horvath et al 2008 A cationic fluorescent labeled polyallylamine was used to study diffusion into cell walls and resulting paper strength.…”

“…Charge phenomena appear especially evident in the case of cationic dyes, which would reasonably have an affinity for the negatively charged (acidic) groups present on a wide range of cellulosic materials when wet (Thomaneck et al 1991;van de Ven et al 2007;Horvath et al 2008;Gimaker and Wågberg 2009). For instance, Drnovsek and Perdih (2005a) observed that cationic dyes, as a group, generally have a preferential affinity for lignin.…”

“…The same colorant, when added in the absence of salt, remained mainly on the outsides of the fibers and did not stain them deeply. According to Horvath et al (2008), the uptake of the polyelectrolyte (a cationic dextran with fluorescent labeling) increased monotonically with increasing salt concentration. Likewise, Goodrich and Winter (2007) soaked cellulose and chitin nanocrystals in salt buffer to neutralize the charge sites (sulfated cellulose) on the nanocrystals to focus the adsorption of Congo red.…”

Adsorption of paper strength additives to hardwood fibres with different surface charges and their effect on paper strength

“…entropic gain of counter ions being released (Wågberg 2000). Due to their high molecular weights (> 10 5 g/mole), the additives will predominantly interact with the fibre surface as they are too large to penetrate the fibre walls (Horvath et al 2008). The surface charge of the fibres is therefore of utmost importance when it comes to defining the properties of the final packaging material.…”