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Adsorption of Highly Charged Polyelectrolytes onto an Oppositely Charged Porous Substrate
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.ORCID iD: 0000-0001-8622-0386
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 15, 7857-7866 p.Article in journal (Refereed) Published
Abstract [en]

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 call 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 ill 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.

Place, publisher, year, edition, pages
2008. Vol. 24, no 15, 7857-7866 p.
Keyword [en]
Amides; Amplitude modulation; Charge density; Concentration (process); Electrolysis; Electrolytes; Electrostatics; Fees and charges; Fiber optics; Finance; Hydrogels; Labeling; Molecular mass; Polyelectrolytes; Polymers; Pore structure; Substrates; Surface charge; Titration; Volumetric analysis; Acrylamide; Adsorption behavior; Cationic polyelectrolytes; Charged polyelectrolytes; Diallyldimethylammonium chloride; Driving forces; Electrolyte concentrations; Electrolyte properties; Electrostatic driving; Electrostatic interactions; Fluorescence labeling; Kinetic processes; Persistence lengths; Porous substrates
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-8451DOI: 10.1021/la800093mISI: 000258034500034Scopus ID: 2-s2.0-49649115957OAI: oai:DiVA.org:kth-8451DiVA: diva2:13776
Note
QC 20100811. Uppdaterad från accepted till published (20100811).Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved
In thesis
1. Chemical Methods for Improving the Fracture Toughness of Paper
Open this publication in new window or tab >>Chemical Methods for Improving the Fracture Toughness of Paper
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Paper is a network material composed of a great number of fibers that interact with each other through fiber joints. In order to make a clear statement regarding observed changes being made in paper, it is vital to determine the structural level of paper that is being affected by chemical modifications. Polyelectrolytes having a wide range in molecular properties have been synthesized to investigate the adsorption behavior of cationic polyelectrolytes to cellulosic fibers. The interaction with the porous cell wall of cellulosic fibers is governed by the molecular properties of the polyelectrolyte. More specifically, polyelectrolytes having a low charge density are able to penetrate into the fiber cell wall, while high charge density polyelectrolytes are restricted to the exterior fiber surface. The molecular mass also influences the extent to which adsorption occurs within the cell wall, although this is typically only pronounced for low charge density polyelectrolytes. High charge density polyelectrolytes are generally restricted to the fiber surface due to strong Coulombic interactions between charged groups along the molecular backbone, which create a stiff molecular conformation.

These results were confirmed by fluorescent labeling techniques, which allow the polyelectrolytes to be tracked inside the cell wall by confocal laser scanning microscopy. This approach was also used to demonstrate the effect of an electrolyte, which screens the Coulombic interactions and facilitates penetration into the cell wall. However, a considerable difference in the adsorption behavior of polyelectrolytes having similar molecular mass is still observed at high electrolyte concentration, where the electrostatic contributions are negligible. These differences are a consequence of a diffusion process that occurs on a longer times scale. Although polyelectrolyte adsorption to cellulosic fibers reaches a pseudo-equilibrium at short times, a driving force into the cell wall exists due to the bulk charge of the fiber. The time scale of this diffusion process depends on the polyelectrolyte properties, and was observed to persist for over 3 months.

As the extent to which these polyelectrolytes penetrate into the cell wall has been ascertained, and the fibers can be crosslinked to different degrees in the cell wall or at the surface. Cationic acetal dextran was prepared as a model crosslinking agent, as the molecular mass, charge density and degree of acetal substitution can readily be controlled during synthesis. A considerable effect on the tensile properties and fracture toughness was observed for crosslinked paper, which could be attributed to either the fibers or the fiber joints. Crosslinking acted to stiffen the fibers and the fiber joints, which influenced the transfer of applied stresses through the paper structure. Changes in the material behavior at high relative humidity could be improved by crosslinking the fibers at the correct the structural level.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 112 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:28
Keyword
chemistry, physical chemistry
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-4752 (URN)978-91-7178-968-6 (ISBN)
Public defence
2008-05-30, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100811Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved

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