Electrostatic and hydrophobic interactions in NaCMC aqueous solutions: effect of degree of substitution

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Title: Electrostatic and hydrophobic interactions in NaCMC aqueous solutions: effect of degree of substitution
Authors: Gonzalez Lopez, C
Colby, R
Cabral, JP
Item Type: Journal Article
Abstract: The rheology of water soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglements, hydrophobic and electrostatic interac- tions, whose influence is difficult to isolate. We investi- gate the rheology of semidilute solutions of sodium car- boxymethyl cellulose (NaCMC) with molecular weight M w ' 2 . 5 × 10 5 g/mol and varying degree of substi- tution (D.S.) as a function of polymer concentration in various solvent media: salt-free water (long ranged elec- trostatic interactions), 0.5M aqueous NaCl (screened electrostatics) and 0.5M aqueous NaOH (screened elec- trostatics, diminished hydrophobic interactions) in or- der to selectively probe the different interactions. De- creasing D.S. is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5M NaCl solution, NaCMC with D.S. ' 1.2 ex- hibits hydrophilic polyelectrolyte and neutral polymer in good solvent behaviour respectively. Decreasing D.S. to ' 0.7-0.8 leads to hydrophobic behaviour in both solvents, becoming weak gels at high concentrations. In 0.5M NaOH (pH = 13.5) the viscosities of samples with different D.S. become identical when plotted against the overlap parameter, which we interpret as result- ing from the solubilisation of unsubstituted cellulose blocks. Small angle neutron scattering (SANS) data in- dicate that the polymer conformation is not strongly affected by hydrophobic interactions. By varying D.S., ionic strength and pH, we demonstrate the tuning of NaCMC-solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution rheology.
Issue Date: 24-Apr-2018
Date of Acceptance: 29-Mar-2018
URI: http://hdl.handle.net/10044/1/58673
DOI: https://dx.doi.org/10.1021/acs.macromol.8b00178
ISSN: 0024-9297
Publisher: American Chemical Society
Start Page: 3165
End Page: 3175
Journal / Book Title: Macromolecules
Volume: 51
Issue: 8
Copyright Statement: © 2018 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Sponsor/Funder: Engineering and Physical Sciences Research Council
Funder's Grant Number: Ref 100087X iCASE award
Keywords: Science & Technology
Physical Sciences
Polymer Science
SODIUM CARBOXYMETHYLCELLULOSE SOLUTIONS
MULTISTICKER ASSOCIATIVE POLYELECTROLYTES
ANGLE NEUTRON-SCATTERING
RHEOLOGICAL PROPERTIES
IONIC-STRENGTH
CELLULOSE DERIVATIVES
POLYSTYRENE SOLUTIONS
POLYMER-SOLUTIONS
MOLECULAR-WEIGHT
WIDE-RANGE
03 Chemical Sciences
09 Engineering
Polymers
Publication Status: Published
Online Publication Date: 2018-04-11
Appears in Collections:Faculty of Engineering
Chemical Engineering
Faculty of Natural Sciences



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