Walther Bernhard, Hamberg Lars, Walkenström Pernilla, Hermansson Anne-Marie
SIK, The Swedish Institute for Food and Biotechnology, P.O. Box 5401, SE-402 29 Göteborg, Sweden.
J Colloid Interface Sci. 2004 Feb 1;270(1):195-204. doi: 10.1016/j.jcis.2003.09.017.
Drop shaping, i.e., flow-induced deformation and fixation by gel formation, was studied under dynamic conditions in a fast continuous process for a water-in-oil system. The system consisted of sunflower oil with different surfactant concentrations (0.1-2% Admul Wol) and a 1.5% kappa-carrageenan solution with different Na(+) and K(+) concentrations. The continuous phase flowed in a 10-mm-wide straight channel into which the dispersed phase was injected via a thin needle. A subsequent shaping channel with a width of 1 or 2 mm deformed the drops. Gel formation was induced by a temperature gradient between the continuous and dispersed phase. Drop sizes in the range 220-roughly 1000 microm were produced at the needle tip by varying the ratio between the oil and carrageenan flow rate. A diffusion zone before the narrow channel allowed the surfactant to adsorb at the interface. In the elongation flow at the entrance of the shaping geometry, drops underwent initial elongation. In the narrow channel, the drops developed a parabolic shape within a residence time of 0.03-0.15 s. Choosing the correct parameter combinations made it possible to fix the deformation by gel formation within this time period. Shaped drops were shown to be functional. At a concentration of 25% in an emulsion, they increased the viscosity by about 15-20% compared to spherical drops even though 45% of the shaped drops had an aspect ratio of less than 1.2.
在快速连续过程中，在动态条件下对油包水体系的液滴成型（即流动诱导变形和通过凝胶形成进行固定）进行了研究。该体系由具有不同表面活性剂浓度（0.1 - 2% Admul Wol）的向日葵油和具有不同Na(+)和K(+)浓度的1.5% κ-卡拉胶溶液组成。连续相在一个10毫米宽的直通道中流动，分散相通过细针注入该通道。随后一个宽度为1或2毫米的成型通道使液滴变形。连续相和分散相之间的温度梯度诱导凝胶形成。通过改变油和卡拉胶流速之间的比例，在针尖处产生了尺寸范围为220 - 约1000微米的液滴。狭窄通道之前的扩散区使表面活性剂能够在界面处吸附。在成型几何结构入口处的拉伸流动中，液滴经历初始伸长。在狭窄通道中，液滴在0.03 - 0.15秒的停留时间内形成抛物线形状。选择正确的参数组合使得在这段时间内通过凝胶形成固定变形成为可能。已证明成型液滴具有功能性。在乳液中浓度为25%时，与球形液滴相比，它们使粘度增加了约15 - 20%，尽管45%的成型液滴的纵横比小于1.2。
