Synthesis and optical levitation of ellipsoidal silica particles

In the present work, we present a sol-gel method to synthesize elliptic silica particles using a mixture of CTAB/L-tyrosine as structure-directing agents. Our results demonstrate that L-tyrosine is essential for the formation of ellipsoidal morphology, as reactions carried out under varying CTAB concentration only formed spherical to rod-like particles. With increased concentrations of L-tyrosine, the produced particles go from isotropic spherical particles to anisotropic prolate and oblate ellipsoidal particles with increased dimensions. A typical synthesis of ellipsoidal particles presents an average major axis of 137 nm and an average aspect ratio of 1.6. The small-angle X-ray scattering showed that the distance between centers of adjacent cylinders is on average ∼ 4.6 nm. Optical trapping of single particles was used to perfectly isolate individual ellipsoidal silica particle from their environment while measuring their geometric properties with great precision. We observed an average aspect ratio of 1.5 while measuring the particles in 3D space, which is consistent with the TEM analysis.本研究提出一种以十六烷基三甲基溴化铵（CTAB）/L-酪氨酸（L-tyrosine）混合物作为结构导向剂（structure-directing agents）的溶胶-凝胶法，用于合成椭圆形二氧化硅颗粒。实验结果表明，L-酪氨酸对于形成椭圆形形貌至关重要：仅改变CTAB浓度进行的反应仅能生成球形至棒状颗粒。随着L-酪氨酸浓度升高，所制备的颗粒从各向同性的球形颗粒，逐渐转变为尺寸增大的各向异性长椭球形与扁椭球形颗粒。典型的椭圆形颗粒合成体系中，颗粒的平均长轴长度为137 nm，平均长径比为1.6。小角X射线散射（small-angle X-ray scattering）测试显示，相邻圆柱颗粒的中心间距平均约为4.6 nm。采用单颗粒光镊（optical trapping）技术，可将单个椭圆形二氧化硅颗粒与周围环境完全分离，同时以极高精度测量其几何特性。在三维空间中对颗粒进行测量时，我们观测到的平均长径比为1.5，这与透射电子显微镜（TEM）分析结果一致。