Molecular dynamics simulation was used to study the wettability of the hydrophilic sphalerite (110) surface chemically modified by butylthiols made up of normal and branched alkyl tails, referred to as n-butylthiol and i-butylthiol hereafter, at different adsorption site coverages. Butylthiol molecules were grafted onto the adsorption sites of the surface in two different distributions—ordered and random. The results showed that for a given butylthiol at a given site coverage, random surface distribution yielded a slightly larger contact angle. This observation was attributed to the fact that average distances between the first and second nearest neighbors of butylthiol molecules are shorter in the case of random surface distribution, resulting in smaller patches of bare surface exposed to water molecules compared to those of the ordered surface distribution. Regardless of the tail structure, the random surface distribution exhibited hydrophobic character (i.e., contact angle ≥ 90°) at a relatively low site coverage of about 25%. The test area method and the Kirkwood and Buff approach were adopted to estimate surface energies (γ_SV) of the bare sphalerite (110) surface and the collector monolayer, respectively. Using the obtained γ_SV values of these two pure states, the apparent surface energy as a function of surface coverage was determined based on Cassie’s law. This allowed us to estimate the corresponding values of solid–liquid apparent interfacial tension (γ_SL). Both γ_SV and γ_SL exhibit a linear inverse dependence on surface coverage with a crossover point at 25% site coverage (about 50% surface coverage), above which γ_SV falls below γ_SL, leading to contact angles greater than 90°. The results also revealed that contact angles of the two butylthiols are comparable at site coverages below ∼85%, but above that, they are significantly lower for the branched thiols compared to their normal counterparts. Considering the Lennard-Jones interaction energies between the water cluster and the butylthiols, stronger attractive interactions were present in the case of i-butylthiol due to the presence of two methyl groups in its alkyl chain. This difference was the most intense at site coverages above ∼85%.

中文翻译：

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正丁醇和支链丁硫醇修饰的亲水闪锌矿（110）表面的分子动力学研究

使用分子动力学模拟研究了由正硫醇和支链烷基尾巴组成的丁硫醇化学改性的亲水闪锌矿（110）表面的润湿性，分别称为正丁硫醇和i此后，丁硫醇在不同的吸附位点覆盖。丁硫醇分子以两种不同的分布（有序和无规）接枝到表面的吸附位上。结果表明，对于给定的丁硫醇，在给定的位点覆盖范围内，随机的表面分布会产生稍大的接触角。该观察结果归因于以下事实：在随机表面分布的情况下，丁硫醇分子的第一和第二最近邻之间的平均距离较短，与有序表面分布的裸露表面相比，暴露于水分子的裸露斑块较小。无论尾部结构如何，在约25％的相对较低的位点覆盖率下，随机表面分布都表现出疏水特性（即接触角≥90°）。裸闪锌矿（110）表面的_SV）和捕集剂单层。使用获得的这两个纯态的_γSV值，根据卡西定律确定视在表面能随表面覆盖率的变化。这使我们能够估计固液表观界面张力（_γSL）的相应值。既γ _SV和γ _SL展览上表面覆盖的线性逆依赖性用交叉点以25％上盖面积（约50％表面覆盖率），高于该γ _SV低于γ _SL，导致接触角大于90°。结果还表明，两种丁硫醇的接触角在低于〜85％的位点覆盖率下是可比的，但高于该值时，支链硫醇的接触角明显低于其正常对应物。考虑到水簇和butylthiols之间的伦纳德-琼斯相互作用能量，更强的吸引力相互作用存在于箱子我-butylthiol由于两个甲基的在其烷基链的存在。当站点覆盖率达到〜85％时，这种差异最为明显。