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

In this work, the yield stress of wax-decane gels at 20 °C was correlated with both the amount and the composition of the precipitated n-alkanes (Cn) in six wax-decane gels at 20 °C, which were obtained using the techniques of centrifugation, HTGC and XRD. Because the carbon number distribution of the precipitated Cn can be adequately regressed as “normal distribution”, the standard deviation (σ) was used to express the degree of n-alkane polydispersity in precipitated Cn. 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 Cn. The wax-decane gel with the higher amount of precipitated Cn and higher degree of n-alkane polydispersity provided lower yield stress than that of lower amount of precipitated Cn and lower degree of n-alkane polydispersity. The degree of n-alkane polydispersity reflected by σ was found directly related with the conformation disorder of Cn molecules in wax crystal. Using the differences (Δn) between the two average carbon numbers separately obtained from HTGC (μ) and XRD (nc) for the precipitated Cn to describe the conformation disorder, a linear relationship between Δn and σ was obtained. When the precipitated Cn 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.