Acta Phys. -Chim. Sin. ›› 2019, Vol. 35 ›› Issue (4): 415-421.doi: 10.3866/PKU.WHXB201803141

• ARTICLE • Previous Articles     Next Articles

Method for Evaluating Stability of Highly Concentrated Emulsion and Its Application

Qun LEI1,Yurong ZHANG2,Jianhui LUO1,3,Rongcheng HAN2,Xiangfei GENG1,3,Xiaodong Lü2,Yan LIU2,Yuan WANG2,*()   

  1. 1 Research Institute of Petroleum Exploration and Development, Petrochina Company Limited, Beijing 100083, P. R. China.
    2 Beijing National Laboratory for Molecular Science, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China.
    3 Key Laboratory of Nano Chemistry, China National Petroleum Corporation, Beijing 100083, P. R. China
  • Received:2018-02-11 Published:2018-09-13
  • Contact: Yuan WANG E-mail:wangy@pku.edu.cn
  • Supported by:
    the PetroChina Scientific Research and Technology Development Project(2014A-1001);the National Key Research and Development Program of China(2016YFE0118700)

Abstract:

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 = {D22 +[(D12D22)/4δz + δz]2}1/2 or DC2–3 = {D32 + [(D22D32)/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|DC1–2DC2–3|/(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= D2D3 (or D3 = D2D1) 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.

Key words: Emulsion, Anti-coalescence stability, Salt-tolerance, Micro-imaging analysis, Double optical slice analysis

MSC2000: 

  • O648