Electrostatic and Hydrophobic Interactions in NaCMC Aqueous Solutions: Effect of Degree of Substitution

Carlos G. Lopez, Ralph H. Colby, João T. Cabral

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight Mw ≃ 2.5 × 105 g/mol and varying degree of substitution (DS) as a function of polymer concentration in various solvent media: salt-free water (long-ranged electrostatic interactions), 0.5 M aqueous NaCl (screened electrostatics), and 0.5 M aqueous NaOH (screened electrostatics, diminished hydrophobic interactions) in order to selectively examine the role played by these different interactions. Decreasing DS is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5 M NaCl solution, NaCMC with DS ≃ 1.2 exhibits hydrophilic polyelectrolyte and neutral polymer in good solvent behavior, respectively. Decreasing DS to ≃0.7-0.8 leads to hydrophobic behavior in both media, becoming weak gels at high concentrations. In 0.5 M NaOH (pH = 13.5) the viscosities of solutions with different DS become identical when plotted against the overlap parameter, which we interpret as resulting from the solubilization of unsubstituted cellulose blocks. Small-angle neutron scattering (SANS) data indicate that the polymer conformation is not strongly affected by hydrophobic interactions. By varying DS, ionic strength, and pH, we demonstrate the tuning of NaCMC-solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution rheology.

Original languageEnglish (US)
Pages (from-to)3165-3175
Number of pages11
JournalMacromolecules
Volume51
Issue number8
DOIs
StatePublished - Apr 24 2018

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Electrostatics
Substitution reactions
Rheology
Polymers
Coulomb interactions
Polyelectrolytes
Cellulose
Salts
Carboxymethylcellulose Sodium
Water
Gelation
Neutron scattering
Ionic strength
Conformations
Agglomeration
Gels
Solubility
Tuning
Sodium
Molecular weight

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

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abstract = "The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight Mw ≃ 2.5 × 105 g/mol and varying degree of substitution (DS) as a function of polymer concentration in various solvent media: salt-free water (long-ranged electrostatic interactions), 0.5 M aqueous NaCl (screened electrostatics), and 0.5 M aqueous NaOH (screened electrostatics, diminished hydrophobic interactions) in order to selectively examine the role played by these different interactions. Decreasing DS is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5 M NaCl solution, NaCMC with DS ≃ 1.2 exhibits hydrophilic polyelectrolyte and neutral polymer in good solvent behavior, respectively. Decreasing DS to ≃0.7-0.8 leads to hydrophobic behavior in both media, becoming weak gels at high concentrations. In 0.5 M NaOH (pH = 13.5) the viscosities of solutions with different DS become identical when plotted against the overlap parameter, which we interpret as resulting from the solubilization of unsubstituted cellulose blocks. Small-angle neutron scattering (SANS) data indicate that the polymer conformation is not strongly affected by hydrophobic interactions. By varying DS, ionic strength, and pH, we demonstrate the tuning of NaCMC-solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution rheology.",
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Electrostatic and Hydrophobic Interactions in NaCMC Aqueous Solutions : Effect of Degree of Substitution. / Lopez, Carlos G.; Colby, Ralph H.; Cabral, João T.

In: Macromolecules, Vol. 51, No. 8, 24.04.2018, p. 3165-3175.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Electrostatic and Hydrophobic Interactions in NaCMC Aqueous Solutions

T2 - Effect of Degree of Substitution

AU - Lopez, Carlos G.

AU - Colby, Ralph H.

AU - Cabral, João T.

PY - 2018/4/24

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AB - The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight Mw ≃ 2.5 × 105 g/mol and varying degree of substitution (DS) as a function of polymer concentration in various solvent media: salt-free water (long-ranged electrostatic interactions), 0.5 M aqueous NaCl (screened electrostatics), and 0.5 M aqueous NaOH (screened electrostatics, diminished hydrophobic interactions) in order to selectively examine the role played by these different interactions. Decreasing DS is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5 M NaCl solution, NaCMC with DS ≃ 1.2 exhibits hydrophilic polyelectrolyte and neutral polymer in good solvent behavior, respectively. Decreasing DS to ≃0.7-0.8 leads to hydrophobic behavior in both media, becoming weak gels at high concentrations. In 0.5 M NaOH (pH = 13.5) the viscosities of solutions with different DS become identical when plotted against the overlap parameter, which we interpret as resulting from the solubilization of unsubstituted cellulose blocks. Small-angle neutron scattering (SANS) data indicate that the polymer conformation is not strongly affected by hydrophobic interactions. By varying DS, ionic strength, and pH, we demonstrate the tuning of NaCMC-solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution rheology.

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