Structuring of Polyelectrolyte (NaPSS) Solutions in Bulk and under Confinement as a Function of Concentration and Molecular Weight

Abstract

The present paper gives a deeper insight into the chain ordering in aqueous polyelectrolyte solutions under geometrical confinement as a function of degree of polymerization and polymer concentration. Colloidal probe atomic force microscopy (CP-AFM) and small-angle X-ray scattering (SAXS) are used to compare the poly(styrenesulfonate) (NaPSS) chain ordering between two solid interfaces and in bulk, respectively. Oscillatory forceÀdistance curves from CP-AFM as well as the scattering peaks from SAXS indicate a near range ordering of polyelectrolyte chains with structural parameters such as interchain distance, correlation length, and the strength of ordering. These characteristic lengths from CP-AFM (confinement) and SAXS (bulk) are in the same range. The interchain distance is up to 20% smaller and the correlation length is up to 20% higher under confinement, indicating a slight compression of the polyelectrolyte chains and a stronger counterion condensation under confinement. The interchain distance d scales with the monomer unit concentration c as d ∼ c À1/3 for a degree of polymerization N from 20 to 155 and as d ∼ c À1/2 for N = 367 and 10 690, indicating a dilute and semidilute regime, respectively. The transition from dilute to semidilute regime is in good agreement with the one found in viscosity measurements and with theoretical concepts. At a fixed monomer concentration, d depends on the chain length in the dilute regime while it is independent of the molecular weight in the semidilute regime. The experimental intercoil distance d in the dilute regime coincides well with the one calculated from the coil number density, which is based in turn on a theoretical model. Other models for calculating the interchain distance are discussed. The correlation length of the ordering increases with increasing molecular weight, indicating an increase in counterion condensation. The strength of ordering increases with the degree of polymerization due to entropic reasons.

Interplay between Depletion and Double-Layer Forces Acting between Charged Particles in Solutions of Like-Charged Polyelectrolytes

“…The phase shift θ and the amplitude A increase with concentration. Figure 4 summarizes the molecular mass dependence of the ratio λ=ξ and the power-law exponent α, and they compare favorably with values obtained from earlier direct force measurements in similar systems [13,25,26]. The fixed ratio λ=ξ decreases with the molecular mass.…”

“…The wavelength of the depletion force also increases with increasing molecular mass of the polymer and decreases with increasing concentration. Such trends were reported by researchers focusing on forces induced by charged depletants earlier [13,25,26].…”

“…More recently, the focus shifted towards charged depletants, including nanoparticles [9,10], micelles [11,12], or polyelectrolytes [13][14][15]. For a wide range of systems, these forces could be rationalized with a simple damped oscillatory profile, which follows from the large-distance asymptotics of the hard-sphere depletion potential [3,9].…”

Effect of polyelectrolytes on (de)stability of liquid foam films

“…The decay length is larger than the Debye length. 77,78 It gives the same value as the range of ordering in the bulk solution.…”

Interaction of Different Charged Polymers with Potassium Ions and Their Effect on the Yield Stress of Highly Concentrated Glass Bead Suspensions

“…It should be mentioned here that the systems containing 0.8 % PCE show higher noise in the baseline compared to that with 0.1 % PCE, which may result from the disturbance of the laser by the increased turbidity of these systems under high PCE concentration. Due to the turbidity of the solution, depletion forces were not accessible by AFM in this study, since the noise of the baseline was higher than the typical amplitudes of the depletion force [31]. The decay of the force can be described by a mono-exponential function for separations larger than 2 nm, as shown in Figure 11.…”