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Adsorption of Low Charge Density Polyelectrolytes to 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 13, 6585-6594 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 24, no 13, 6585-6594 p.
Keyword [en]
Adsorption; Charge density; Confocal microscopy; Electrolysis; Electrolytes; Flow interactions; Fluorescence; Glucose; Imaging techniques; Labeling; Light emission; Luminescence; Molecular mass; Painting; Polyelectrolytes; Polymers; Pore structure; Pulsed laser deposition; Substrates; Theorem proving; Volumetric analysis; Adsorption behavior; American Chemical Society (ACS); Cationic polyelectrolytes; Cellulosic fibers; Confocal laser scanning micro scopy (CLSM); Electrolyte concentrations; Electrostatic interactions; Fluorescent labeling; Free surfaces; Lateral correlation; Low charge density polyelectrolytes; Low molecular mass (LMM); Monotonically; Polyelectrolyte chains; Porous structures; Porous substrates; Staining techniques
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-8452DOI: 10.1021/la800274wISI: 000257101100029Scopus ID: 2-s2.0-47349132325OAI: oai:DiVA.org:kth-8452DiVA: diva2:13777
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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