高浓度乳液稳定性评价方法及其应用

Method for Evaluating Stability of Highly Concentrated Emulsion and Its Application

分散相液滴的粒径及其分布是影响乳液性质的重要因素,其随时间及环境的变化可用于评价乳液的稳定性。动态光散射等方法难以用于准确测量高浓度乳液液滴粒径。本文报道了一种可用于准确、高效测量乳液液滴粒径的成像表征方法。该方法采用荧光染料标记乳液液滴,利用激光扫描共聚焦荧光显微成像技术获取三张焦平面间距确定的乳液光学切片,由光学切片给出的乳液液滴表观直径计算进而确定所测量乳液液滴的粒径。我们将上述方法用于表征高浓度原油模拟物-水乳液的稳定性,结果表明本文提出的方法可以准确、高效地测量乳液液滴的抗凝聚稳定性,而目前广泛采用的"瓶试法"则难以反映乳液液滴的抗凝聚稳定性。

The average diameter and size distribution of dispersed-phase droplets are important factors affecting the properties of emulsions, and the changes in these parameters with time and environment can be used to evaluate the emulsion stability. Traditional size characterization methods such as dynamic light scattering (DLS) are not applicable to highly concentrated emulsions. Herein, we report an imaging-based method to measure the droplet size in highly concentrated emulsions. This method comprises three steps: 1) emulsions are labeled with a fluorescent dye, 2) three optical slices with a certain distance between two adjacent focal plans are measured sequentially via confocal laser scanning microscopy, 3) the sizes of dispersed-phase droplets are determined from the apparent diameters of droplets in the optical slices. When the apparent diameter of a droplet in the three optical slices increases or decreases monotonically, droplet diameter is calculated according to the following equations: DC1–2 ={D2^2 +[(D1^2 - D2^2)/4δz +δz]^2}^1/2 or DC2–3 ={D3^2 +[(D2^2 – D3^2)/4δz +δz]2}^1/2, where D1, D2, D3 is the apparent diameter of the droplet measured from the consecutively-obtained optical slices 1-3, respectively;DC1–2 represents the calculated diameter of the droplet from the slices 1 and 2, and DC2–3 is that from the slices 2 and 3, and δz is the distance between two focal planes of the adjacent optical slices. To avoid an obvious interference from the droplet movement, we use the equation 2|DC1–2 - DC2–3|/(DC1–2 + DC2–3)= X, where a smaller X value indicates a less extent of movement during measurement, and that the calculated average diameter (DC1–2 + DC2–3)/2 is closer to the measured size of the droplet. The experimental results showed that when X was 15%, the difference between the calculated and measured diameters was about 10%. When X was less than 15%, the calculated average droplet diameter was adopted as an effective diameter. However,when the condition D1 = D2 ≥ D3 (or D3 = D2 ≥ D1) was met, D2 was used as the effective droplet diameter. The present method combines the advantages of fluorescent labeling, double optical slices analysis, and a strategy for eliminating the error caused by droplet movement. The stability of highly concentrated emulsions (oil volume percentage: 60%-80%), prepared by mixing a crude oil model mixture containing n-decane, naphthaline, decalin, and tetraphenylporphyrin (92.3%, 4.1%, 3.6%, and 0.1‰ by mass, respectively) with aqueous solutions containing surfactants, was studied with the proposed method. The experimental results indicated that the present method allowed for the effective and accurate measurement of the anti-coalescence stability of emulsion dispersed-phase droplets. In contrast, the widely adopted “bottle test” method could not provide accurate information on the anti-coalescence stability of the dispersed phase droplets.