Effect of Shear on Intramolecular and Intermolecular Association during Cross-Linking of Hydroxyethylcellulose in Dilute Aqueous Solutions

Abstract

Intramolecular and intermolecular associations of dilute aqueous alkali solutions of hydroxyethylcellulose (HEC) in the presence of a chemical cross-linker agent (divinyl sulfone, DVS) are studied with the aid of dynamic light scattering (DLS) and rheological methods. At quiescent state, DLS detected only interchain aggregation of HEC during the cross-linker reaction, and the magnitude and start of this effect depend on the cross-linker concentration. The growth of clusters has been investigated at various stages in the course of the cross-linking process by quenching the reaction mixture to a lower pH. After quenching, no further association of the species occurred. When the dilute reaction mixtures are subjected to shear, intrapolymer cross-linking with contraction of the molecules is observed, and at moderate shear rates this effect is followed by interpolymer cross-linking and the formation of aggregates at longer times. The rate of the growth of the multichain aggregates decreases with increasing shear rate, and at sufficiently high shear rates no cross-linking effect is observed. Depending on the shear rate, the aggregates continue to grow until they reach a certain size where an incipient breakup of interaggregate chains can be observed. The delicate interplay between intramolecular and intermolecular association effects is governed by factors such as the magnitude of the shear rate, polymer concentration, and cross-linker density.

Preparation and characterization of cross‐linked polymeric nanoparticles for enhanced oil recovery applications

“…This clearly shows that initially the larger complexes depicted by the slow relaxation mode are exposed to intrapolymer crosslinking, and this feature is strengthened under the influence of shear forces because this perturbation reduces the tendency to form interchain aggregates. This behavior is consistent with the shear viscosity results reported 15 for this system previously. At later times in the course of the cross-linker reaction, larger aggregates are formed, probably because most of the sites for intramolecular cross-linking have been consumed and the repeated collisions between the species have provoked interchain cross-linking.…”

“…The variables s f and s se are the relaxation times characterizing the fast and the slow relaxation processes, respectively. This type of bimodal relaxation process has been reported 15,18,19 from DLS studies on aggregating polymer systems of various natures. In the analysis of the correlation functions by means of eq.…”

“…The weight-average molecular weight (M w ¼ 400,000) and the overlap concentration (c* ¼ 0.25 wt %) of this HEC sample in aqueous solution have both been reported previously. 15 To remove salt and other low-molecular-weight impurities, dilute HEC solutions were dialyzed against Millipore water for 7 days and recovered by freeze drying. Regenerated cellulose with a molecular weight cutoff of % 8,000 (Spectrum Medical Industries, Rancho Dominguez, CA) was employed as dialyzing membrane.…”

“…Both cross-linking mechanisms are expected to yield particles, but the particle size and size distribution of the particles will be different. In a recent study 15 on the chemical cross-linking of hydroxyethylcellulose (HEC) in dilute aqueous solutions with divinyl sulfone (DVS) as the cross-linker agent at basic conditions (pH % 12), it was shown that interchain cross-linking is the predominant mechanism at quiescent conditions. Dynamic light scattering (DLS) experiments revealed a rapid growth of the clusters in the course of time, and no sign of compression of the molecules could be observed.…”

Nanoparticles formed by complexation of poly-gamma-glutamic acid with lead ions

“…For the ␥-PGA particles and the ␥-PGA/Pb 2+ complexes, the decays of the correlation functions were always found to be bimodal [23][24][25] initially a single exponential, followed at longer times by a stretched exponential:…”