ABSTRACT
HYPOTHESIS: The formation of polyion complexes (PICs) comprising thermoresponsive polymers is intended to result in the formation of aggregates that undergo significant structural changes with temperature. Moreover the observed modifications might be critically affected by polymer structure and PICs composition. EXPERIMENTS: Different block copolymers based on cationic poly(3-acrylamidopropyltrimethylammonium chloride) and thermoresponsive poly(N-isopropylacrylamide) were synthesized by aqueous RAFT/MADIX polymerization at room temperature. Addition of poly(acrylic acid) in a controlled fashion led to the formation of PICs aggregates. The structural changes induced by temperature were characterized by differential scanning calorimetry, Nuclear Magnetic Resonance spectroscopy and scattering methods. FINDINGS: Thermoresponsive PICs undergo significant structural changes when increasing temperature above the cloud point of the thermoresponsive block. The reversibility of these phenomena depends strongly on the structural parameters of the block copolymers and on PICs composition.
ABSTRACT
HYPOTHESIS: Adsorption of high molar mass polymers impacts flow in porous media. In the industrially crucial case of acrylamide-based polymers in porous silicates, the very occurrence of adsorption is still debated. Thus, the present work aimed at establishing a clear correlation between adsorption of acrylamide-based polymers and injectivity loss in porous silica. EXPERIMENTS: A review of the literature revealed apparent discrepancies regarding the affinity of acrylamide-based polymers for siliceous materials having ostensibly the same chemical composition. Through a deeper analysis of the reported literature and new experimental measurements on well-defined polymers and surfaces, we investigated the relation between the silica surface properties and the acrylamide-based polymer adsorption. Our observations were confronted with water injection experiments in porous media of different surface compositions previously put in contact with polymers. FINDINGS: The polymer affinity towards the silica surface depended on the density of hydroxyl groups at the surface of the oxide, its thermal treatment, storage condition and purity. This demonstrated that the impact of adsorption on acrylamide-based polymer flow within porous silicates heavily depends on the silicate surface composition and must be carefully evaluated. In view of the continually expanding use of acrylamide-based polymers, notably in enhanced oil recovery, such considerations provide interesting insights into the effect of adsorption on their flow into porous materials.
ABSTRACT
We report the behaviour of thermoresponsive block copolymers of n-butyl acrylate and N-alkyl acrylamides in [C2mim][NTf2]. Poly(N-isopropylacrylamide) exhibits an upper critical solution temperature in [C2mim][NTf2] whereas poly(n-butyl acrylate) has a lower critical solution temperature. Consequently, these polymers exhibit double thermo-responsiveness correlated with the macromolecular structure. Moreover, a switching from micellar to reverse micellar structures was induced by a change in temperature. This property enables the development of reversible shuttles between ionic liquids and water.
