【作者】 姜秋艳；

【导师】 李秋红；

【作者基本信息】 山东理工大学 ， 材料科学与工程， 2020， 硕士

【摘要】 近年来,随着纳米技术飞速发展,由固体纳米颗粒作为乳化剂代替传统表面活性剂稳定的Pickering乳液引起了广泛的关注。固体纳米颗粒乳化剂吸附在两种不相混溶液体的界面上形成固体粒子膜,有效阻止了液滴之间的聚结,故Pickering乳液具有强稳定性。Pickering乳液开发的关键在于选择具有合适表面润湿性的固体颗粒乳化剂,除了人工合成的功能性高分子聚合物纳米颗粒,一般天然无机纳米颗粒不具备这样的性质。但通常高分子聚合物纳米颗粒的化学合成步骤复杂,如果能通过非共价键疏水改性无机纳米颗粒制备固体颗粒乳化剂,就可避免合成困难的问题。在Pickering乳液的应用中,如在石油输送和乳液聚合反应时,超稳定Pickering乳液的破乳是一个巨大的挑战。因此,通过适当的环境触发调控乳液的稳定性,即刺激响应型Pickering乳液的研究引起了相当大的关注。.基于上述讨论,本文探索了非共价表面改性无机纳米颗粒的可行性,并将其作为固体颗粒乳化剂构建稳定Pickering乳液,研究此种类型Pickering乳液稳定机理、乳液刺激响应性的触发机制。具体研究结果如下:1. 制备了核壳结构Fe₃O₄@SiO₂纳米颗粒,采用双亲染料分子罗丹明B对其进行疏水改性,并将改性后的纳米颗粒作为稳定剂制备Pickering乳液。研究表明,随着乳化剂颗粒浓度增加,乳液液滴粒径减小。另外,所得Pickering乳液具有良好的磁场响应性,可通过外加磁场实现对乳液稳定性的可逆调控,且此过程可重复三次以上。2. 将合成的具有电化学活性的乙酰基二茂铁-9-蒽醛吖嗪荧光分子（Fc A）与SiO₂纳米颗粒非共价结合作为固体颗粒乳化剂,构建一种新型氧化还原响应型Pickering乳液,研究发现油水相体积比、乳化剂颗粒浓度、转速均能影响乳液性能。当油水比为6:4,乳化剂质量分数为0.3 wt%,均质搅拌器乳化5 min（10000 r/min）后可获得粒径均匀,稳定性最佳的Pickering乳液。常温下向Pickering乳液中交替添加氧化剂和还原剂,由于SiO₂表面上Fc⁺A的吸附和Fc A的解吸,SiO₂纳米粒子的亲疏水性发生变化,乳液的稳定性在常温下可通过氧化还原触发调控,该调控过程可以重复至少三次。此外,Fc A分子的荧光强度可以通过氧化还原刺激来调节,因此在氧化还原循环调控中可以观察到乳液液滴的荧光行为变化。这项工作有助于深入了解氧化还原刺激型Pickering乳液的调控机理,同时在不额外引入荧光分子条件下为Pickering乳液的荧光标记开辟了新的途径。3. 采用电化学阻抗谱法（EIS）研究非共价表面改性SiO₂无机纳米颗粒制备水包油（O/W）Pickering乳液的稳定性,观察到乳液在Nyquist图中的特征是一个半圆,乳液液滴的平均粒径随着转速的增加而减小,表明乳液的稳定性越高。通过对EIS获得的乳液频率响应数据模拟分析,发现不同转速制备的乳液拟合阻抗值(R_O/W)随粒径减小而减小。此外,随着乳液储存时间的增长,乳液平均粒径增大且稳定性较差,乳液的拟合阻抗值R_O/W与粒径变化趋势一致。研究表明EIS可用于实时表征改性SiO₂颗粒制备的O/W型Pickering乳液稳定性,对乳液的贮存和使用具有重要意义。更多还原

【Abstract】 In recent years,based on the rapid development of nanotechnology,the use of solid nanoparticles as emulsifiers instead of traditional surfactant-stabilized Pickering emulsions has attracted widespread attention.The solid nanoparticle emulsifier is adsorbed on the interface of two immiscible solutions to form a solid particle film,which effectively prevents coalescence between droplets,so Pickering emulsion has strong stability.The key to the development of Pickering emulsions is to select solid particle emulsifiers with suitable surface wettability.In addition to artificially synthesized functional polymer nanoparticles,natural inorganic nanoparticles do not possess such properties.However,the chemical synthesis steps of high molecular polymer nanoparticles are usually complicated.If solid particle emulsifiers can be prepared by hydrophobically modifying inorganic nanoparticles with non-covalent bonds,the problem of difficult synthesis can be avoided.In the application of Pickering emulsions,such as in petroleum transportation and emulsion polymerization,the demulsification of ultra-stable Pickering emulsions can be a huge challenge.Therefore,switching the stability of the emulsion through proper environmental triggering,the stimulating responsive Pickering emulsion has attracted considerable attention.Based on the above discussion,the feasibility of non-covalent surface-modified inorganic nanoparticles and the stabilization mechanism of Pickering emulsions as solid particle emulsifiers,the triggering mechanism of emulsion stimuli are studied.The specific research results are as follows:1. Fe₃O₄@SiO₂ nanoparticles with core-shell structure were prepared.The amphiphilic dye molecule rhodamine B was used for hydrophobic modification,and the modified nanoparticles were used as stabilizer to prepare Pickering emulsion.As the mass concentration of the emulsifier particles increases,the particle size of the prepared emulsion droplets decreases.In addition,the obtained Pickering emulsion has good magnetic field response,and the stability of the emulsion can be controlled reversibly by applying a magnetic field,and this process can be repeated more than 3 times.2. A novel redox-responsive oil-in-water Pickering emulsion was constructed by non-covalently combining the synthesized acetylferrocene-9-anthaldehyde azine fluorescent molecule（Fc A）with SiO₂ nanoparticles as a solid particle emulsifier.It is found that the volume ratio of oil-water phase,the concentration of emulsifier particles,and the speed can affect the performance of the emulsion.When the oil-water ratio is 6:4 and the emulsifier mass fraction is 0.3 wt%,a homogeneous mixer can be emulsified for 5 min（10000 r/min）to obtain Pickering emulsion with uniform particle size and best stability.Pickering emulsion alternately adds oxidant and reducing agent at normal temperature.On the one hand,the hydrophobicity of SiO₂ nanoparticles changes due to the adsorption of oxidation state Fc A and the desorption of Fc A on the surface of SiO₂.The stability of the emulsion can be converted between stable and unstable by redox triggering at room temperature,and the regulation process can be repeated at least three times.On the other hand,the fluorescence intensity and amphiphilicity of Fc A molecules can be adjusted by redox stimulation,so changes in the fluorescence behavior of the emulsion droplets can be observed in the redox cycle.This work will help to better understand the regulation mechanism of redox-stimulated Pickering emulsions,and at the same time open up new ways for fluorescent labeling of Pickering emulsions without introducing additional fluorescent molecules.3. The stability of the oil-in-water Pickering emulsion prepared by non-covalent surface-modified inorganic nano-SiO₂particles was studied by electrical impedance spectroscopy（EIS）.Observe that the emulsion is characterized by a semicircle in the Nyquist diagram,and the average particle size of the emulsion droplets decreases with the increase of the emulsification rate,indicating that the stability of the emulsion is higher.Through simulation analysis of the frequency response data of the emulsion obtained by EIS,it was found that the fitted impedance R_O/Wvalue of the emulsion prepared at different emulsification speeds decreased with decreasing particle size.In addition,with the increase of the storage time of the emulsion,the average particle size of the emulsion increases and the stability is poor.The fitted impedance R_O/W value of the emulsion is consistent with the particle size trend.It shows that EIS is a suitable technique for characterizing the stability of O/W Pickering emulsions prepared by modified SiO₂ particles,and it is of great significance for the storage and use of emulsions.更多还原