Nonspherical particles have gained significant interest owing to their unique shapes and large specific surface areas, making them suitable for a wide range of applications, such as drug delivery, catalysis, and adsorption. However, conventional methods for preparing nonspherical particles face certain limitations. In this study, we propose a simple method for fabricating nonspherical cellulose acetate (CA) microparticles using a microfluidic device in which droplets undergo rapid diffusion in a continuous aqueous phase. The influence of variations in the flow rate ratio and continuous phase composition on the dimensionless Péclet number (Pe) within the droplet and shape of the resultant particles is investigated. Pe is critical, because it indicates the balance between polymer diffusion and droplet shrinkage dynamics. Our findings reveal that increasing the flow rate ratio and reducing the methyl acetate concentration in the continuous phase lead to faster droplet shrinkage and an increased Pe. A high Pe (>100) suggests that the reduction of the droplet interface predominates over polymer diffusion, resulting in the formation of a viscous layer near the droplet surface, which subsequently leads to nonspherical particle shapes (such as bowl-like or biconcave structures). In situ time-lapse observations of droplets from the top and side of a microchannel reveal that the formation of a viscous layer near the droplet surface and the deformation of the droplet, influenced by the z-axis location of the droplets during particle formation, ultimately determine the final particle shape. Based on these observations, a linear correlation between the initial conditions, i.e., the Pe and z-axis location at which the viscous layer formed, is established, enabling the prediction of the particle structure. In summary, the present study enhances the understanding of shape control in microfluidic particle formation and offers a novel guideline for the fabrication of spherical and nonspherical particles.

中文翻译：

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微流下非球形醋酸纤维素微粒的形成


非球形颗粒因其独特的形状和较大的比表面积而受到广泛关注，使其适用于广泛的应用，例如药物递送、催化和吸附。然而，制备非球形颗粒的常规方法面临一定的局限性。在这项研究中，我们提出了一种使用微流体装置制造非球形醋酸纤维素 （CA） 微粒的简单方法，其中液滴在连续水相中快速扩散。研究了流速比和连续相组成的变化对液滴内无量纲佩克莱特数 （Pe） 和所得颗粒形状的影响。PE 至关重要，因为它表示聚合物扩散和液滴收缩动力学之间的平衡。我们的研究结果表明，增加连续相中的流速比和降低乙酸甲酯浓度会导致更快的液滴收缩和 Pe 增加。高 Pe （>100） 表明液滴界面的减少比聚合物扩散占主导地位，导致在液滴表面附近形成粘性层，随后导致非球形颗粒形状（如碗状或双凹形结构）。从微通道顶部和侧面对液滴进行的原位延时观察表明，在颗粒形成过程中，受液滴 z 轴位置的影响，液滴表面附近粘性层的形成和液滴的变形最终决定了最终的颗粒形状。基于这些观察，初始条件之间的线性相关性，即，确定了形成粘性层的 Pe 和 z 轴位置，从而可以预测颗粒结构。总之，本研究增强了对微流体颗粒形成中形状控制的理解，并为球形和非球形颗粒的制造提供了新的指南。