Intermolecular Interactions in Polyelectrolyte and Surfactant Complexes in Solution

Abstract

Polyelectrolytes are an important class of polymeric materials and are increasingly used in complex industrial formulations. A core use of these materials is in mixtures with surfactants, where a combination of hydrophobic and electrostatic interactions drives unique solution behavior and structure formation. In this review, we apply a molecular level perspective to the broad literature on polyelectrolyte-surfactant complexes, discussing explicitly the hydrophobic and electrostatic interaction contributions to polyelectrolyte surfactant complexes (PESCs), as well as the interplay between the two molecular interaction types. These interactions are sensitive to a variety of solution conditions, such as pH, ionic strength, mixing procedure, charge density, etc. and these parameters can readily be used to control the concentration at which structures form as well as the type of structure in the bulk solution.

Keywords: complexes; electrostatic; hydrophobic; micelle; molecular; polyelectrolyte; surfactant.

Figure 1

Schematic of how molecular interactions of polyelectrolyte and surfactant and surfactant micelle systems lead to structure, phase behavior, and rheological properties.

Figure 2

Schematic of charged polyelectrolyte conformation in good, theta, or poor solvents.

Figure 3

Depiction of binding of surfactant to polyelectrolyte chain. (A) without the presence of added salt (B) in the presence of added salt.

Figure 4

(A) Non-cooperative and cooperative binding of surfactant to polyelectrolyte (B) Illustration of the binding isotherm: degree of binding (β) versus surfactant concentration.

Figure 5

Progression of micelle-like structure formation with increasing surfactant concentration.

Figure 6

General depiction of observed enthalpy versus increasing surfactant concentration for polyelectrolyte and surfactant systems.

Figure 7

Typical micellar or micelle-like structures formed with polyelectrolytes.

Figure 8

(A) Zeta-potential versus molar ratio of surfactant to polyelectrolyte. (B) Hydrodynamic radius versus molar ratio of surfactant to polyelectrolyte. Adapted from [107,108,115,116].

Figure 9

Concentration of SDS surfactant needed to maintain a precipitated complex versus surfactant chain length. Reprinted with permission from Goddard, E.D.; Hannan, R.B. Polymer/Surfactant Interactions. J. Am. Oil Chem. Soc. 1977, 54, 561–566. Copyright 1977, John Wiley and Sons [117].

Figure 10

Experimentally reported binding strength data rescaled to SDS reference system as a function of polyelectrolyte reduced linear charge density. Solid black line is power-law regression and blue dotted line is 95% prediction interval. Points represent various studies. Reprinted with permission from Li, D.; Wagner, N.J. Universal binding behavior for ionic alkyl surfactants with oppositely charged polyelectrolytes. J. Am. Chem. Soc. 2013, 135, 17547–17555, doi:10.1021/ja408587u. Copyright 2013, American Chemical Society [98].

Figure 11

Two proposed mechanisms of the binding interaction between PVPNO and SDS at low (Model A) and high (Model B) pH values. Reprinted with permission from Wang, H.; Fan, Y.; Wang, Y. Thermodynamic association behaviors of sodium dodecyl sulfate (SDS) with poly(4-vinylpyridine N-oxide) (PVPNO) at different pH values and ionic strengths. J. Surfactants Deterg. 2017, 20, 647–657, doi:10.1007/s11743-017-1939-7. Copyright 2017, John Wiley and Sons [65].

Figure 12

Schematic of effect of salt increase on polyelectrolyte and surfactant association in excess surfactant regime where colloid is charge-stabilized. The blue represents hydrophobic cores. Reprinted with permission from Pojjaźk, K.; Bertalanits, E.; Meźszaźros, R. Effect of salt on the equilibrium and nonequilibrium features of polyelectrolyte/surfactant association. Langmuir 2011, 27, 9139–9147, doi:10.1021/la2021353. Copyright 2011, American Chemical Society [115].

Figure 13

Effect of the applied mixing protocol on the apparent mean hydrodynamic diameter versus surfactant concentration curves, Stop-flow-mixing (green); slow-mixing (red). Reprinted with permission from Pojjaźk, K.; Bertalanits, E.; Meźszaźros, R. Effect of salt on the equilibrium and nonequilibrium features of polyelectrolyte/surfactant association. Langmuir 2011, 27, 9139–9147, doi:10.1021/la2021353. Copyright 2011, American Chemical Society [115].

Figure 14

Depiction of Polyelectrolyte-Micelle Structures at low (0.3 wt%) and high (1 wt%) polyelectrolyte concentration showing that cross-links can be achieved at higher concentrations and ultimately higher viscosity. Reprinted from Hoffmann, I.; Farago, B.; Schweins, R.; Falus, P.; Sharp, M.; Prévost, S.; Gradzielski, M. On the mesoscopic origins of high viscosities in some polyelectrolyte-surfactant mixtures. J. Chem. Phys. 2015, 143, doi:10.1063/1.4928583, with the permission of AIP Publishing [134].

Figure 15

Viscosity of 1 wt% JR 400 polyelectrolyte with increasing concentration of SDS. Z represents the charge ratio between cation and anion. The dashed line is the viscosity of the polyelectrolyte solution alone. Reprinted from Hoffmann, I.; Simon, M.; Farago, B.; Schweins, R.; Falus, P.; Holderer, O.; Gradzielski, M. Structure and dynamics of polyelectrolyte surfactant mixtures under conditions of surfactant excess. J. Chem. Phys. 2016, 145, doi:10.1063/1.4962581, with the permission of AIP Publishing [133].

Figure 16

Relative Viscosity for ionene-SDS solutions versus molar ratio. Circle is 6,6-ionene, Diamond is 6,4-ionene. Reprinted from European Polymer Journal, 37, Zheng, X.; Cao, W. Interaction of main chain cationic polyelectrolyte with sodium dodecyl sulfate, 2259–2262, 2001 with permission from Elsevier [137].