Adsorption of Highly Charged Polyelectrolytes onto an Oppositely Charged Porous Substrate

Abstract

The adsorption behavior of highly charged cationic polyelectrolytes onto porous substrates is electrostatic in nature and has been shown to be highly dependent on the polyelectrolyte properties. Copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) were synthesized to have a range of macromolecular properties (i.e., charge density and molecular mass). Traditional titration methods have been complemented by fluorescence labeling techniques that were developed to directly observe the extent that fluorescently labeled poly(AM- co-DADMAC) adsorbs into the pore structure of a cellulosic substrate. Although contributing to the electrostatic driving force, the charge density acts to limit adsorption to the outermost surface under electrolyte-free conditions. However, adsorption into the pores can occur if both the molecular mass and charge density of poly(AM- co-DADMAC) are sufficiently low. Adsorption initially increases as the electrolyte concentration is increased. However, the electrostatic persistence length of poly(AM- co-DADMAC) restricts the polyelectrolyte from entering the pores. Therefore, changes in the adsorption behavior at moderate electrolyte concentrations have been attributed to swelling of the polyelectrolyte layer at the fiber exterior. The adsorption behavior changes again at high electrolyte concentrations such that poly(AM- co-DADMAC) could adsorb into the pore structure. This occurred when the electrolyte concentration was sufficient to screen the electrostatic persistence length of poly(AM- co-DADMAC), provided that the entropic driving force for adsorption still existed. It is suggested that adsorption into the pore structure is a kinetic process that is governed by localized electrostatic interactions between poly(AM- co-DADMAC) and the charges located within the pores.

Nanocomposite-based lignocellulosic fibers 3: polyelectrolyte adsorption onto heterogeneous fiber surfaces

“…A kinetic factor was previously suggested to influence PDDA adsorption at high ionic strength (Horvath et al 2008a, b). High electrolyte concentration is sufficient to screen the electrostatic interactions of PDDA, which significantly reduces the persistence length of polymer in the solution (Horvath et al 2008a). As a result, polyelectrolyte chains become more coiled and are able to penetrate into the pore structure at very high electrolyte conditions (Gimaker and Wagberg 2009;Horvath et al 2008b).…”

Structural and Ecofriendly Holocellulose Materials from Wood: Microscale Fibers and Nanoscale Fibrils

“…It is well known that the wood fiber surface can be altered by polymer adsorption [ 72 ] and chemical modification. [ 73,74 ] The porosity of the wood fiber cell wall also allows for diffusion of molecules into the fiber cell wall, [ 75 ] and this has for instance been used for calcium carbonate functionalization, [ 76 ] also performed in the central wood fiber pore space (lumen). [ 77 ] The modification of individual fibrils inside the fiber cell wall is challenging, yet chemical functionalization in the form of acetylation has been carried out, [ 78 ] in order to improve optical transmittance of polymer matrix biocomposites.…”

Inverse Emulsion Polymerization of Dimethyl Diallyl Ammonium Chloride and Acrylamide for Water Treatment

“…The organic flocculant PDA was grafted by free radical polymerisation of acrylamide monomer (AM) onto the cationic monomer dimethyl diallyl ammonium chloride (DMDAAC), which widely used in the field of oil exploration, paper making, textile printing, industrial wastewater treatment and sludge dewatering, etc. 3,4 .…”