Investigation On The Interactions Between Surfactants And SiO₂ Nanoparticles With Different Surface Affinity

Due to their special physicochemical properties,silica nanoparticles（SiO₂ NPs）offer great opportunities to address the challenges confronted by traditional enhanced oil recovery methods.SiO₂ NPs are usually employed in combination with surfactants,and the interactions between the NPs and surfactants have crucial effects on the performance of the compound systems.These interactions are closely connected with the hydroxyl density on the NPs surfaces,which determines the affinity of the NPs surfaces.Many researchers have reported the interactions between the NPs and surfactants,while most of the investigations were carried out in dilute surfactant systems and only for one type of surfactant or NPs.Herein,the interfacial activity and viscoelasticity of the surfactant/SiO₂ NPs systems were regarded as the research objects.The interfacial tension and rheological measurements were conducted to investigate the effects of SiO₂ NPs with different surface affinitiy on the performance of various surfactant systems,and the corresponding effect mechanisms were explored.The effects of both hydrophilic and hydrophobic SiO₂ NPs on the interfacial activity of sodium dodecyl sulfate（SDS）,dodecyltrimethylammonium bromide（DTAB）,and Triton X-100（TX-100）were investigated in first part.The results indicated that the electrostatic repulsion between SDS molecules and hydrophilic SiO₂ NPs facilitated the SDS molecules in the aqueous phase migrate to the oil/water interface and increased the concentration of SDS molecules at the interface.In other surfactant/SiO₂ NPs systems,the addition of NPs hindered the diffusion of surfactant molecules to the oil/water interface.Under the electrostatic attraction,hydrophobic interaction,and hydrogen bonding,a large amount of surfactant molecules were adsorbed on the surfaces of NPs and formed surfactant-coated nanoparticles（SCNPs）,which decreased the number of surfactant molecules at the oil/water interface.The migration of amphiphilic SCNPs to the oil/water interface decreased the interfacial coverage of surfactant molecules and further weakened the interfacial activity of various surfactant systems.Subsequently,the effects of both hydrophilic and hydrophobic SiO₂ NPs NPs on the viscoelasticity of stearyltrimethylammonium bromide（STAB）/sodium salicylate（Na Sal）and sodium oleate（Na OA）/sodium carbonate（Na₂CO₃）wormlike micelles（WLMs）solutions were investigated.In the STAB/Na Sal system,STAB molecules were adsorbed on the surfaces of NPs via electrostatic attraction and hydrophobic interaction to construct SCNPs.The crosslinking of SCNPs and WLMs effectively increased the contour length and network strength of WLMs,which greatly enhanced the viscoelasticity of the solution.In addition,the stronger hydrophobic interaction in WLMs/hydrophobic NPs system guaranteed a better viscoelasticity promoting effect to the hydrophobic SiO₂ NPs.For the Na OA/Na₂CO₃ system,the electrostatic repulsion prevented Na OA molecules from adsorbing to the surfaces of hydrophilic NPs,and the exposed NPs unabled crosslink with WLMs.Therefore,the hydrophobic NPs could effectively enhanced the viscoelasticity of the system,while the hydrophilic NPs had almost no effect.