Adsorption of functional molecules on the surface of hydrates is key in the understanding of hydrate inhibitors. We investigate the adsorption of a hydrocarbon chain, nonionic and ionic surfactants, and ions at the hydrate–aqueous interface. Our results suggest a strong connection between the water ordering around solutes in bulk and the affinity for the hydrates surface. We distinguish two types of water ordering around solutes: (i) hydrophobic hydration where water molecules form a hydrogen bond network similar to clathrate hydrates, and (ii) ionic hydration where water molecules align according to the polarity of an ionic group. The nonionic surfactant and the hydrocarbon chain induce hydrophobic hydration and are favorably adsorbed on the hydrate surface. Adsorption of ions and the ionic headgroups on the hydrate surface is not favorable because ionic hydration and the hydrogen bond structure of hydrates are incompatible. The nonionic surfactant is adsorbed by the headgroup and tail while adsorption of the ionic surfactants is not favorable through the head. Water ordering is analyzed using the hydrogen bond and tetrahedral density profiles as a function of the distance to the chemical groups. The adsorption of solutes is studied through the free energy profiles as a function of the distance to the hydrate surface. Salt lowers the melting temperature of hydrates, disrupts hydrophobic hydration, reduces the solubility of solutes in the aqueous solution, and increases the propensity of solutes to be adsorbed on hydrate surfaces. Our studies are performed by the unbiased and steered molecular dynamics simulations. The results are in line with experiments on the effect of salt and alkanes in hydrate antiagglomeration.

中文翻译：

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疏水水合以及NaCl盐对包合物水合物的碳氢化合物和表面活性剂吸附的影响

功能分子在水合物表面的吸附是理解水合物抑制剂的关键。我们研究了烃链，非离子和离子表面活性剂以及水合物-水界面处的离子的吸附。我们的结果表明，散装在溶质周围的水有序与水合物表面的亲和力之间有很强的联系。我们区分围绕溶质排列的两种类型的水：（i）疏水水合，其中水分子形成类似于笼形水合物的氢键网络，以及（ii）离子水合，其中水分子根据离子基团的极性排列。非离子表面活性剂和烃链诱导疏水水合，并有利地吸附在水合物表面上。由于离子水合和水合物的氢键结构不相容，因此在水合物表面上离子和离子头基的吸附是不利的。非离子型表面活性剂被头基和尾部吸附，而离子型表面活性剂的吸附则不利于头。使用氢键和四面体密度分布作为与化学基团距离的函数来分析水的有序性。通过自由能曲线研究了溶质的吸附，该自由能曲线是与水合物表面的距离的函数。盐降低了水合物的熔化温度，破坏了疏水水合，降低了溶质在水溶液中的溶解度，并增加了溶质在水合物表面上吸附的倾向。我们的研究是通过无偏的和受控的分子动力学模拟进行的。该结果与盐和烷烃在水合物抗附聚中的作用的实验吻合。