Silica nanoparticles (NPs) have been synthesized by titration of potassium silicate with hydrochloric acid, characterized and the effects of process parameters on size and morphology have been investigated. The size of the NPs decreased with increasing temperature and potassium silicate concentration. Central composite design (CCD) was applied to systematically determine the most significant factors affecting the particle size and optimize the experimental conditions to achieve minimum particle size. The optimal experimental conditions were obtained at hydrochloric acid concentration of 0.6 M, potassium silicate concentration of 11.85 wt% and temperature of 63.3 °C. SEM images proved that the pH and temperature shifted the NPs to non-spherical morphologies. To identify the effect of NPs morphology on oil recovery, some micromodel tests were conducted using the synthesized NPs with different shapes (0.1 wt%). The results showed that spherical NPs with high uniformity were the most effective in interfacial tension (IFT) reduction (3.66 mN/m) and wettability alteration to more water wet state (47.1% reduction of contact angle) compared to other applied NPs, resulted in highest oil recovery (32%). This was attributed to more homogeneity and better dispersion of spherical NPs compared to others.

中文翻译：

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不同形态的二氧化硅纳米粒子的合成及其对提高采油率的影响

通过用盐酸滴定硅酸钾合成了二氧化硅纳米颗粒（NPs），并表征了工艺参数对尺寸和形貌的影响。NP的尺寸随温度和硅酸钾浓度的增加而减小。应用中央复合设计（CCD）来系统地确定影响粒径的最重要因素，并优化实验条件以实现最小粒径。在盐酸浓度为0.6 M，硅酸钾浓度为11.85 wt％，温度为63.3°C的条件下获得了最佳实验条件。SEM图像证明pH和温度使NPs转变为非球形形态。为了确定NP形态对采油率的影响，使用合成的具有不同形状（0.1 wt％）的NP进行了一些微模型测试。结果表明，与其他应用的NP相比，具有高均匀度的球形NP在降低界面张力（IFT）（3.66 mN / m）和将润湿性改变为更多水湿状态（接触角减少47.1％）方面最为有效，导致最高的石油采收率（32％）。这是由于与其他球形NP相比，球形NP具有更高的同质性和更好的分散性。