The adsorption of block copolymers of poly(ethylene oxide) (PEO) and poly(lactide) (ExLy) at silica and methylated silica was investigated with in situ ellipsometry and AFM. It was found that at the former substrate, the adsorbed layer consists of adsorbed micelles, whereas at the latter, the polymers form a brush structure. With increasing packing density of the polymer molecules, their capacity to prevent protein adsorption increases. However, the effect of the copolymer composition on both the adsorption and the protein rejecting capacity is found to be minor within the composition range investigated. The effect of chemical degradation of E39L5 and E39L20 on their adsorption was investigated in some detail. Due to decreased hydrophobic anchoring the adsorption of both copolymers at hydrophobic methylated silica decreased with an increased degree of degradation. Also at silica, a monotonic decrease in the adsorbed amount was found for E39L5, but not for E39L20. In the latter case, a pronouced deposition at intermediate degradation degree resulted from aggregation in solution. At extensive degradation, however, also this system displayed the expected decrease in the adsorption, approaching that of the corresponding poly(ethylene oxide) homopolymer. The effects of the degradation of the poly(lactide) block on the adsorption properties of these polymers correlate with the performance of these polymers in protein rejection and steric stabilization. Comparison is also made between the experimental findings and results from mean-field calculations.
The results from a study regarding wettability alteration (oil-wet to water-wet) in low permeability chalk using water-soluble surfactants are presented. Fourteen different surfactants were tested for spontaneous imbibition into oil-wet chalk cores. Cationic surfactants of the type R-N+(CH3)3 were able to desorb organic carboxylates from the chalk surface in an irreversible way, and 70% of the oil in place was recovered within 30 days by a spontaneous imbibition of the aqueous surfactant solution at 70 oC. The fluid distribution inside the core was studied by cleaving the core and taking pictures. The mechanism for the wettability alteration is supposed to take place by an ion-pair formation between the cationic surfactant and adsorbed negatively charged carboxylates from the oil. The efficiency of the surfactant is related to properties including CMC-value, hydrophobic property, IFT-value, and steric effects close to the N-atom. Anionic surfactants were not able to desorb anionic organic carboxylates from the crude oil in an irreversible way. Ethoxylated sulfonates with high EO-numbers did, however, displace oil spontaneously in a slow process. The brine imbibed non-uniformly, and the mechanism is suggested to involve the formation of a water-wet bi-layer between the oil and the hydrophobic chalk surface. At a very low IFT-value, 0.08 mN/m, oil is displaced spontaneously from the core by gravity forces.