Solution rheology of a hydrophobically modified alkali-soluble associative polymer

Abstract

Rheological and photophysical data are presented for a hydrophobically modified alkali-soluble copolymer, of a constitution similar to materials currently employed as rheology modifiers in water-borne coatings. The copolymer comprises a polyelectrolyte backbone bearing ethoxylate side chains capped with complex alkylaryl groups of a high molar volume. In aqueous alkaline media, the hydrophobes associate dynamically, the topology of the network so formed being dependent on the polymer concentration. Photophysical studies, employing pyrene as a hydrophobic fluorescent probe, indicate the presence of hydrophobic associations. At concentrations below the coil overlap concentration, c*, these associations are predominantly intramolecular. At higher polymer concentrations, intermolecular interactions become more probable. This change in network topology is in qualitative agreement with previous theoretical considerations of associative polymer systems and is reflected in an unusually high concentration dependence of the zero shear viscosity, with η0∼c8. Evidence for shear-induced structuring in steady shear, large amplitude oscillatory shear, and parallel superposed steady and dynamic shear is presented. Such structuring is more pronounced at lower polymer concentrations, consistent with the formation of intermolecular associations at the expense of intramolecular. In contrast to the simple linear telechelic associative polymers considered in a number of previous studies, the network dynamics of the polymer are no longer represented by a single characteristic time. This deviation from a classical Maxwellian response in oscillatory shear is interpreted as a broadening of the relaxation spectrum, arising from the coexistence of both hydrophobic associations and topological entanglements. Mechanistically, stress relaxation is better envisaged in terms of “hindered reptation” [Liebler et al. (1991)] of the chains, rather than Rouse-like behavior moderated purely by the hydrophobe disengagement rate [Annable et al. (1993)].

Rheological Study of Aqueous Solutions of Hydrophobically-Associating Derivatives of Propylene Glycol Alginate (Pga)

“…As suggested by Aubry and Moan [7], we determined a mean hydrophobic association lifetime as the inverse of the shear rate at which a catastrophic drop in viscosity is observed, as shown in Figure 1. We found a value of 0.08 s, which is consistent with other values reported in literature [7], [12] and [13].…”

Amphiphilic derivatives of sodium alginate and hyaluronate for cartilage repair: Rheological properties

“…This leads to the formation of a more and more compact network, which provokes the increase in 0 and c . 26 The mechanical spectra of the AA derivative solutions (Fig. 3) confirmed the network densification.…”

Synthesis, physicochemical, structural and rheological characterizations of carboxymethyl xanthan derivatives

“…These findings may be explained in two ways: i) the first possible explanation is the presence of two different populations of particles consisting of CMXG particles with a smaller average size that are less aggregated compared to the second population formed by the residual fractions of native XG particles that are more entangled, where region I is attributed to the flow of smaller particles and regions II and III correspond to the flow of XG particles; ii) the second speculation is the presence of weak intermolecular and intramolecular hydrophobic associations due to the presence of -CH2-on the carboxymethyl group (-CH2-COO -). The first region describes the flow resulting from the destructuring phenomenon initiated by the rupture of intermolecular bonds where the predominant interaction mode is intramolecular(English at al., 1997), while the second region corresponds to the breaking of intramolecular bonds that present a certain resistance expressed here by the presence of the transition equilibrium plateau Ballard et al (1988). attributed this effect to associative polymers and postulated that such intra-intermolecular interactions are responsible of the shear thickening region (when the interactions are very strong) or the Newtonian plateau appearance at intermediate shear stress, as is the case here.…”