For more than a century, density gradient theory (DGT) has been developed and applied for interfacial property calculations of pure and mixed fluid systems. However, due to the local density approximation, DGT has not been applicable to amphiphilic molecules. By developing a modified DGT model with the chain contribution to the free energy, this paper extends the application of the DGT model to heteronuclear chain molecules, such as surfactants. The chain contribution term is derived based on the work from the iSAFT model. With the help of the Stabilized Density Gradient Theory (SDGT) algorithm developed in our previous work and the PC-SAFT equation of state (EoS), the modified DGT model is tested in water/oil/surfactant mixture systems, the results of which have been qualitatively verified with other theories and experimental data.

中文翻译：

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用于油/水界面的表面活性剂分子的改进密度梯度理论

一个多世纪以来，密度梯度理论（DGT）得到了发展，并应用于纯流体系统和混合流体系统的界面特性计算。但是，由于局部密度近似，DGT不适用于两亲性分子。通过开发具有对自由能的链贡献的改进的DGT模型，本文将DGT模型的应用扩展到异核链分子，例如表面活性剂。链贡献项是基于iSAFT模型的工作得出的。借助我们先前工作中开发的稳定密度梯度理论（SDGT）算法和PC-SAFT状态方程（EoS），在水/油/表面活性剂混合系统中对改进的DGT模型进行了测试，其结果具有已被其他理论和实验数据定性验证。