Effect of the amount and the composition of precipitated n-alkanes on the yield stress of wax-decane gels

摘要

In this work, the yield stress of wax-decane gels at 20 degrees C was correlated with both the amount and the composition of the precipitated n-alkanes (C) in six wax-decane gels at 20 degrees C, which were obtained using the techniques of centrifugation, HTGC and XRD. Because the carbon number distribution of the precipitated C-n can be adequately regressed as "normal distribution", the standard deviation (sigma) was used to express the degree of n-alkane polydispersity in precipitated C-n The competing effect on yield stress of wax-decane gel was quantitatively identified between the degree of n-alkane polydispersity and the amount of precipitated C-n The wax-decane gel with the higher amount of precipitated C-n and higher degree of n-alkane polydispersity provided lower yield stress than that of lower amount of precipitated C-n and lower degree of n-alkane polydispersity. The degree of n-alkane polydispersity reflected by sigma was found directly related with the conformation disorder of C molecules in wax crystal. Using the differences (Delta n) between the two average carbon numbers separately obtained from HTGC (mu) and XRD (n(c)) for the precipitated C-n to describe the conformation disorder, a linear relationship between Delta n and sigma was obtained. When the precipitated C-n has a higher n-alkane polydispersity, a significant conformation disorder of n-alkane molecules occurs in wax crystal. Therefore, the n-alkane molecule stacking layers are more loosely packed and the crystal structure becomes weak, resulting that the wax-decane gel shows a lower yield stress. (C) 2016 Elsevier B.V. All rights reserved.