The influence of surfactants on latex flocculation with poly(diallyldimethyl ammonium chloride)

Inhibition of Cationic Polymer-Induced Colloid Flocculation by Polyacrylic Acid

Although the dosage of cationic flocculants used for water treatment is well known to increase in the presence of natural organic matter (NOM), the underlying reasons for this increase are not properly understood. Herein, we studied the flocculation behavior of polystyrene latex (PSL) particles in the presence and absence of polyacrylic acid (PAA5K) as an NOM analogue using an end-over-end rotation apparatus for standardized flow mixing. In the absence of PAA5K, the initial rate of cationic flocculant (PAM5M)-induced flocculation was enhanced, as reflected by the size of flocculant in solution. Additionally, flocculation experiments were performed in the presence of 0.5 mg/L PAA5K for five concentrations of PAM5M and two ionic strengths, and the increase of the initial rate of PAM5M-induced flocculation was suppressed by PAA5K immediately after mixing, with the most pronounced suppression obtained at a PAM5M concentration similar to PAA5K. Based on the above insights and the results of viscosity measurements, the inhibitory effect of PAA on flocculation was ascribed to (1) the reduction of PAM charge and the concomitant shrinkage via electrostatic association with PAA and (2) the termination of polycation adsorption on PSL caused by polyion complex formation when the charge ratio of PAM:PAA is close to unity.

1D and 2D NMR investigations of the interaction between oppositely charged polymers and surfactants

Proton chemical shifts and two-dimensional COSY and NOE spectroscopy (NOESY) experiments have been used to examine the interaction of various oppositely charged surfactant and polyelectrolyte systems, namely, the cationic surfactant dodecyltrimethyammonium bromide (DTAB) and a series of alkanediyl-α,ω-bis(alkyldimethylammonium bromide) surfactants (Gem 12-s-12, where s is the length of the methylene spacer group) with the anionic polyelectrolyte poly(styrene sulfonate) or PSS. In all cases, we observe substantial aromatic-solute-induced chemical shifts (ASIS) in the surfactant peaks of the polymer/surfactant complexes versus that of the pure surfactant spectra. In the case of the DTAB/PSS system, the chemical-shift changes as a function of changing ratio of surfactant to polymer are interpreted in terms of structural changes that occur in the complex with increasing polymer concentration. For the Gem 12-s-12/PSS systems, the interaction of these gemini surfactants with the anionic polyelectrolyte, as deduced from the interpretation of the 1H ASIS shifts and the NOESY cross peaks, is dependent on the length of the methylene spacer. From the NOESY experiments, we observed significant NOESY cross peaks that correlated well with the expected mechanism of interaction as observed in the literature for the single-tailed surfactant/polymer system. NMR techniques are shown to provide information on the molecular arrangement of these molecules in aqueous solution.