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Bulk and Adsorption Properties of Surfactant Entrapped in Polyelectrolyte Complex Nanoparticles
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With the wide application of nanotechnology in petroleum industry, transportation of nanoparticles in porous media has attracted a growing interest. This thesis focuses on investigating the bulk and adsorption properties of surfactant entrapped in polyelectrolyte complex (PEC) nanoparticles. A stable surfactant entrapped in PEC system was optimized and obtained varying parameters of the preparation protocol including pH of PEI, surfactant/PEI concentrations and surfactant to PEI weight ratio. Meanwhile, the effect of different parameters on the bulk properties of PEC was investigated. In addition, surfactant entrapment efficiency (EE) of PEC was obtained using methylene blue (MB) titration method. A TOC/TN analytical method was developed to study the static adsorption of PEC via measuring the concentration of PEI and surfactant in the PEC suspension. The prepared PEC suspension was agitated with sand grains for different time periods and analyzed using the developed TOC/TN analytical method. The TOC/TN results showed a large decrease of surfactant concentration and a small decrease of PEI concentration after shaking equilibrium. In addition, study revealed that PEC coated sand grains were more likely to adsorb surfactant than those not coated by PEC. A hypothesis of PEC adsorption model was proposed based on the observations and proved. During the PEC adsorption test, a large amount of PECs and a small amount of free PEI will be firstly adsorbed onto the sand surface and form the first layer. Then free surfactant will be adsorbed onto PEC/PEI coated surface due to the electrostatic reaction and the increasing surface area of the distorted nanoparticles on sand surface. Quartz crystal microbalance with dissipation (QCM-D) instrument and silicon sensor were used to confirm the proposed model by monitoring the real-time adsorption of PEC and surfactant in DI water. The silicon sensor was firstly flushed and incubated by PEC suspension, rinsed by DI water and then rinsed and incubated by surfactant solution. From frequency and dissipation data, the formation of the rigid PEC/PEI layer and the viscoelastic surfactant layer were detected. This observation agreed well with the proposed PEC adsorption model. Based on the proposed model, the wettability of rock surface may be changed by surfactant entrapped in PEC system through the amphiphilic properties of the surfactants adsorbed on the rock surface. The effect of salinity and sand type on PEC adsorption was investigated, too. PEC adsorbed to sand surface faster in electrolyte solution than in DI water which can be explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In addition, in DI water a faster adsorption of PEC on carbonate than sandstone was observed.
Zhou, Xilong (2016). Bulk and Adsorption Properties of Surfactant Entrapped in Polyelectrolyte Complex Nanoparticles. Master's thesis, Texas A & M University. Available electronically from