两亲SiO_(2)纳米颗粒的制备和界面扩张流变行为研究

Preparation of amphiphilic SiO_(2) nanoparticles and investigation of interfacial dilational rheological behavior

制备了一种两亲SiO_(2)纳米颗粒,借助红外光谱及接触角测量证实了相关基团在SiO_(2)纳米颗粒表面的成功接枝,探究了其界面活性和界面扩张流变行为。通过动态界面张力测量及小幅正弦振荡实验发现,两亲SiO_(2)纳米颗粒相比亲水和疏水SiO_(2)纳米颗粒能够更稳定地吸附在界面形成一层吸附膜,降低界面张力,同时由于其扩散交换速度较慢,界面扩张模量大于亲水和疏水SiO_(2)纳米颗粒。进一步的大幅线性压缩实验发现两亲SiO_(2)纳米颗粒在表面比为0.35时其界面吸附量会发生激增,扩张模量迅速增大,其形成的界面膜具有抵抗较大程度形变的能力。

[Objective]Amphiphilic SiO_(2) 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 SiO_(2) nanoparticles.[Methods]Amphiphilic SiO_(2) 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 SiO_(2) nanoparticles.An interfacial dilational rheometer was used to record the interfacial tension between a water droplet and n-octane in the presence of various SiO_(2) 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 SiO_(2) 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 SiO_(2) 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 SiO_(2) 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 SiO_(2) at a fixed frequency.At a nanoparticle concentration of 1000 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 SiO_(2),respectively.The phase angle of amphiphilic SiO_(2) nanoparticles(<5°at 1000 mg/L)indicated the formation of an elastic film at the interface.Large-scale linear compression experiments showed that the dilational modulus of hydrophilic SiO_(2) nanoparticle systems remained relatively constant,whereas that of hydrophobic SiO_(2) nanoparticle systems initially increased and then decreased sharply to 6.83 mN/m at a surface ratio(A/A0)of 0.3.For amphiphilic SiO_(2) 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 SiO_(2) nanoparticles can form a solid-like adsorption film at the oil/water interface,with significantly higher film strength than hydrophilic and hydrophobic SiO_(2) nanoparticles.Amphiphilic SiO_(2) 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 SiO_(2) nanoparticles,allowing them to better to resist deformation.