| Stimuli responsive material is a key topic in 21th century and is prevailing in many areas such as drug delivery, mimic biological systems and effluent treatment. Although hydrophobic associating water-soluble polymer (HAWSP) is one of the most essetntial additive in fracturing fluids, most of research about responsive HAWSP are focus on salt and temperatue and a few researchs aer related to CO2 and pH responsive HAWSP. Therefore, we prepared CO2 and pH responsive viscoelastic fluids based on HAWSP which could make them very competitive candidates for enhanced oil recovery or fracture in oil fields. The main innovative contributions of this thesis can be divided into the following sections:Cationic surfmer Octadecyl dimethyl allyl ammonium chloride (DOAC) has been synthesized by chloropropene and N, N-dimethyloctadecylamine though quaterisation reaction. Subsequently, hydrophobic associating polymer P(AM/DOAC) was synthesized under optimum reaction conditions and then characterized by FT-IR,1H-NMR, DSC and GPC. The cac of P(AM/DOAC) is about 4000 mg/L. Steady-state fluorescence experiments have showed that when concentrations are over cac, I1/I3 is tend to be constant which is marked the formation of a stable network. And the Rh of P(AM/DOAC) increases form 60-80 nm of intramolecular association to 100-800 nm of intermolecular association.At first, we utilized the unique rheology of P(AM/DOAC) to prepare a pH responsive viscoelastic fluid. The solution could present a sol-gel transition when adjust the pH of the solution:under neutral condition. G'and G" could intersect and aggrations are relatively small dispersive and the networks are loose (100 nm). In macrocosm, solution could be fluent; When pH=12, the viscosity of solution increased to 5000 mPas and G' is always higher than G". In microcosm, the size of aggrations increas and form a dense "honeycomb" network structure (800 nm). In macrocosm, the solution shows an inverted gel which could returen to sol when pH-7. Compared the effect of different counterions, all kinds of counterion could increase viscosity of P(AM/DOAC) solution but Sal-> OH-> SO42-> Cl-.This phenomeon is similar to multiple-HAWSP which contain vast ionic groups. But P(AM/DOAC) without large amount of ionic groups, thus traditional balcance of polyelectrolyte effect and hydrophobic association could not to explain it. The result of |?| confirmed the unique pH responsive behavior of P(AM/DOAC) is attributed to the shielding effects of counterions and the hydrogen bonds among surrounding water which further enhance inter-molecular hydrophobic association.Secondly, we utilized a CO2 responsive surfactant DOAPA to indirectly endow P(AM/DOAC) a CO2-responsive and prepare a CO2 responsive viscoelastic fluid. DOAPA could show a CO2-switchable behavior and in this progress the aggretation of DOAPA molecular could transform form vescicles to spherical micelles. The use of vesicle-to-micelle transition of DOAPA by bubbling CO2 to altering the pH endows the reversible gel-sol transition property to the CO2-responseless hydrophobic asssicating polymer solution. Thus, we choose DOAPA5-PAD6 as optimal system to prepare a CO2 responsive viacoelastic fluid. When pH=6.8, the viscosity of DOAPA5-PAD6 increase form 200 mPas to 1400 mPas and present a gel behavior. It has been confirmed through ESEM that vast and dense network are formed in the system. When pH=6.0 adjust by bubbing CO2, the viscosity dramatically decreases and presents a destroyed network. Proved by Cryo-TEM and DLS, the formation of gel is attributed to "vesicle bridge" between different P(AM/DOAC) molecules. Once vesicles convert into spherical micelles, "vesicle bridge" disappear and intermolecular associations are broken by micellar solubilization. The viscosity changes of DOAPA5-PAD6 adjust by CO2 is more outstanding than P(AM/DOAC) solution by pH. |
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