Preparation and Characterization of Cross-Linked Polymeric Nanoparticles for Enhanced Oil Recovery Applications

Chemically cross-linked nanoparticles from dilute aqueous alkali Solutions of hydroxyethylcellulose (HEC) in the presence of a cross-linker agent (divinyl sulfone, DVS) were prepared from a reaction mixture, which was exposed to different stirring speeds during the cross-linking process. At various stages during the cross-linking procedure, the reaction was terminated and the species were characterized by means of turbidimetry, asymmetric flow field-flow fractionation (AFFFF), dynamic light scattering (DLS), and rheo-small-angle light scattering (rheo-SALS) methods. During the cross-linking of a dilute polymer solution, the competition between intrapolymer and interpolymer is a prominent feature. The DLS results show that at early times in the cross-linking process, intrachain cross-linking with contraction of the complexes is promoted by high stirring speeds; at later times the growth of aggregates is inhibited by high stirring speeds. The results from the rheo-SALS measurements disclosed that at early times during the cross-linker reaction, the complexes are fragile against shear forces if the reaction mixture had been subjected to low stirring speeds. At a later state of cross-linking, more cross-links lead to better stability of the species, even for solutions that have been exposed to low stirring speeds during the cross-linking process. This study shows that the sizes of the particles can be tuned by exposing the solutions to different stirring speeds during the cross-linker reaction and to terminate the reaction at desired reaction times. The strategy discussed in this work for the preparation of particles of various sizes is of special interest in connection with enhanced oil recovery applications. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1916-1924, 2009