Core-shell structured microgels and their behavior at oil and water interface
MetadataShow full item record
Oil is still the prime energy resource that the world relies on. With the expectation of the global economic growth, the oil consumption will grow faster over the coming decades. The oil extraction technology influences the oil price and usage efficiency, drawing lots of attention of both researchers and engineers. Interface and colloids play an important role in this multidisciplinary field. This thesis mainly introduces colloid promoted oil extraction with two focuses on enhance oil recovery (EOR) and oil well cement. As one type of colloidal particles, microgels exhibit unique properties among others. The solvent-microgel interaction can respond to the environmental stimulation such as temperature, pH, and so on. Due to the synergy between core and shell, strong functionalities are accessible for core-shell microgels. In this thesis, we developed microgels with hydrophobic, rigid poly-2,2,2-trilfuoroethyl methacrylate (PTFMA) core and tunable thickness of the hydrophilic, soft Poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)) shell. The behavior of the microgels at oil/water and oil/water/solid interfaces have been explored towards the application of the oil extraction technology. The core-shell microgels are able to stabilize oil-in-water Mickering emulsion. Capsule with dual-level controlled permeability can be fabricated from as-formed emulsion, which has the potential to be used in controlled gelation. The distribution of fluorescent microgels in the vicinity of the oil/water/solid three-phase contact line (TPCL) is then quantitatively investigated for a better understanding of the particles initiated wettability alteration. There are close packed microgel (CPM) layers around the TPCL of the oil droplet with an acute contact angle. Since no wedge film is observed to form at oil and solid interface, the microgel-initiated wettability alteration is attributed to the force imbalance caused by the adsorption of microgels at interfaces rather than the disjoining pressure. The behavior of core-shell microgels has been investigated at the oil/water interface under compression and expansion. Typical core-shell microgels undergo viscoelastic and then elastic deformation which corresponds to the mechanical characteristics of shell and core, respectively. The stability of core-shell microgels at oil/water interface is mainly determined by the deformability of surrounding part of microgels.