Preparation of amphiphilic SiO2 nanoparticles and investigation of interfacial dilational rheological behavior
[Objective]Amphiphilic SiO2 nanoparticles have been shown to effectively alter formation wettability and enhance emulsion and foam stability,making them promising green oil displacement materials.The interfacial dilational rheological properties of these nanoparticles are crucial as they reflect various microscale relaxation processes of active substances at and near interfaces,such as diffusion exchange,molecular orientation,and interface rearrangement.These properties are closely related to emulsion and foam stability.Therefore,it is essential to investigate the interfacial dilational rheological behavior of amphiphilic SiO2 nanoparticles.[Methods]Amphiphilic SiO2 nanoparticles were prepared using the Pickering emulsion method,grafting amino and alkyl chains on different sides of the nanoparticles.Fourier-transform infrared spectroscopy and contact angle measurements confirmed the successful preparation of amphiphilic SiO2 nanoparticles.An interfacial dilational rheometer was used to record the interfacial tension between a water droplet and n-octane in the presence of various SiO2 nanoparticles(hydrophobic,hydrophilic and amphiphilic).The water droplet was oscillated sinusoidally with a small amplitude(approximately 10% of its initial surface area).During this process,changes in interfacial tension,droplet volume,and other parameters(such as interfacial dilational modulus and phase angle)were recorded.To explore the interfacial rheological behavior of different SiO2 nanoparticles under significant deformation(approximately 80% of the initial droplet surface area),the droplets were linearly compressed at a rate of 1×10-5 mL/s after reaching equilibrium.During this compression process,changes in interfacial tension and the standard deviation of Laplace shape fitting were measured.[Results]Amphiphilic SiO2 nanoparticles with both hydrophilic and hydrophobic sides were spontaneously adsorbed at the oil/water interface to form a monolayer adsorption film,significantly reducing the interfacial tension to 40.24 mN/m.In contrast,hydrophilic and hydrophobic SiO2 nanoparticles only decreased the interfacial tension to 50.32 and 48.68 mN/m,respectively.The interfacial dilational modulus,reflecting the film's ability to resist dilational deformation,initially increased and then decreased for amphiphilic SiO2 at a fixed frequency.At a nanoparticle concentration of 1 000 mg/L and a working frequency of 0.1 Hz,the interfacial dilational modulus values were 8.85,14.54,and 22.80 mN/m for hydrophilic,hydrophobic,and amphiphilic SiO2,respectively.The phase angle of amphiphilic SiO2 nanoparticles(<5° at 1 000 mg/L)indicated the formation of an elastic film at the interface.Large-scale linear compression experiments showed that the dilational modulus of hydrophilic SiO2 nanoparticle systems remained relatively constant,whereas that of hydrophobic SiO2 nanoparticle systems initially increased and then decreased sharply to 6.83 mN/m at a surface ratio(A/A0)of 0.3.For amphiphilic SiO2 nanoparticles,the dilational modulus gradually increased from 22.35 mN/m to 23.54 mN/m and dramatically jumped to 27.12 mN/m at a surface ratio(A/A0)of 0.35.[Conclusions]This study revealed that amphiphilic SiO2 nanoparticles can form a solid-like adsorption film at the oil/water interface,with significantly higher film strength than hydrophilic and hydrophobic SiO2 nanoparticles.Amphiphilic SiO2 nanoparticles could partially overcome the long-range repulsion among them to adsorb at the interface during large-scale linear compression experiments.Additionally,the slow exchange rate between bulk-phase and interfacial particles greatly improved the film strength of amphiphilic SiO2 nanoparticles,allowing them to better to resist deformation.
amphiphilic SiO2 nanoparticlesinterface dilational modulusinterfacial tensioninterfacial film
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