The effects of a water-soluble quaternary ammonium surfactant (called DA 50) on cyclopentane (CP) hydrate growth were studied at the water/CP interface. Microscopic observations were made without and with DA 50 at concentrations of 0.01, 0.1, and 1 wt % (in the aqueous phase). In addition, the effect of NaCl at different concentrations (0 to 4 wt %) was also investigated, in the presence and absence of the surfactant. Systems with 0, 0.1, or 1 wt % DA 50 and 0 or 2 wt % NaCl, as well as those with 0.01 wt % DA 50 and 2 or 3 wt % NaCl, all led to the formation of a hydrate layer, composed of an assembly of smooth and/or striated plates, at the water/CP interface. With 0.01 wt % DA 50 and without NaCl, hydrate needles formed at the interface before aggregating into a thick unconsolidated layer in the aqueous phase. For systems without DA 50 and with 3 or 4 wt % NaCl, and for the one with 0.01 wt % DA50 and 4 wt % NaCl, a few hexagonal, triangular, and needle-like crystals grew very slowly at the interface, and most of the interface remained free of hydrate crystals for several hours after the onset of crystallization. Spectacular changes in the hydrate growth pattern and morphology were observed for the systems with 3 or 4 wt % NaCl and 0.1 or 1 wt % DA 50, where small individual crystals, in the shape of step pyramids with their vertex pointing to the CP phase, formed at the interface. Results of interfacial tension measurements showed that the adsorption kinetics of the surfactant molecules and the amount of surfactant adsorbed on the water/CP interface increased significantly with NaCl concentration. A formation mechanism of the pyramidal hydrate crystals is proposed.

中文翻译：

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亲水性阳离子表面活性剂对水/环戊烷界面水合环戊烷水合物晶体生长的影响

在水/ CP界面处研究了水溶性季铵表面活性剂（称为DA 50）对环戊烷（CP）水合物生长的影响。在没有和有浓度为0.01、0.1和1重量％的DA 50下（在水相中）进行了显微镜观察。另外，在存在和不存在表面活性剂的情况下，还研究了不同浓度（0至4wt％）的NaCl的作用。含有0、0.1或1重量％DA 50和0或2重量％NaCl的体系，以及含有0.01重量％DA 50和2或3重量％NaCl的体系，都导致形成水合物层，由在水/ CP界面处的光滑和/或条纹板的组件。在具有0.01wt％的DA 50和没有NaCl的情况下，在聚集成水相中的厚的未固化层之前，在界面处形成水合物针。对于没有DA 50且具有3或4 wt％NaCl的系统，以及对于具有0.01 wt％DA50和4 wt％NaCl的系统，一些六角形，三角形和针状晶体在界面处生长非常缓慢，并且大多数结晶开始后数小时，界面仍保持无水合物晶体。在含有3或4 wt％的NaCl和0.1或1 wt％的DA 50的系统中，观察到水合物生长模式和形态的明显变化，其中小的单个晶体呈阶梯金字塔形状，其顶点指向CP相，在接口处形成。界面张力测量结果表明，表面活性剂分子的吸附动力学和在水/ CP界面上吸附的表面活性剂的数量随NaCl浓度的增加而显着增加。