Molecular Dynamics Study of Hydrophilic Sphalerite (110) Surface as Modified by Normal and Branched Butylthiols

Abstract

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) of the bare sphalerite (110) surface and the collector monolayer, respectively. Using the obtained γ 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). Both γ and γ exhibit a linear inverse dependence on surface coverage with a crossover point at 25% site coverage (about 50% surface coverage), above which γ falls below γ, 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%.

Arrangement of Monofunctional Silane Molecules on Silica Surfaces: Influence of Alkyl Chain Length, Head-Group Charge, and Surface Coverage, from Molecular Dynamics Simulations, X-ray Photoelectron Spectroscopy, and Fourier Transform Infrared Spectroscopy

“…It is proportional to the probability of finding the Si atom of a silane neighboring molecule for a given position on the plane, while the Si atom of the reference silane molecule is fixed at origin. 18,31 3. RESULTS AND DISCUSSION 3.1.…”

Effects of the Chemical and Structural Properties of Silane Monolayers on the Organization of Water Molecules and Ions at Interfaces, from Molecular Dynamics Simulations

“…Indeed, while amorphous poly(vinylidene fluoride) surfaces are less hydrophobic than the crystalline poly(vinylidene fluoride) surfaces, 1 random distribution of butylthiol molecules on the hydrophilic sphalerite surface results in a more hydrophobic surface than the one obtained with an ordered distribution. 2 While to the best of our knowledge, the interfaces between a liquid and a solid modified with an amorphous chemical functionalization have never been studied by MD simulations, several studies are focused on crystalline and idealized charged surfaces. 15,17 In particular, silica/water interfaces with discrete or homogeneously distributed charge density were studied.…”

“…Recent publications have demonstrated that the hydration layer and its organization at solid interfaces play a key role in several fundamental phenomena such as water wettability , or biomolecule , adsorption. For example, Hegemann et al have demonstrated that water molecules confined inside a plasma polymer film exhibit an amphiphilic subsurface gradient.…”

“…The structure of the underlying layers was also evidenced to participate in interfacial water molecule organization. Indeed, while amorphous poly­(vinylidene fluoride) surfaces are less hydrophobic than the crystalline poly­(vinylidene fluoride) surfaces, random distribution of butylthiol molecules on the hydrophilic sphalerite surface results in a more hydrophobic surface than the one obtained with an ordered distribution …”

Microscopic Diffusion Characteristics of Linear Alkylbenzene Sulfonates on the Surface of Anthracite: The Influence of Different Attachment Sites of Benzene Ring in the Backbone

“…The interaction energy of the surfactant and the anthracite after adsorption can be used to evaluate the adsorption strength. The more negative the interaction energy, the more energy is released, the more stable the structure after adsorption, and the higher the adsorption strength [37,38]. It should be pointed out that the interaction energy here only represents the strength of the interaction between the surfactant and the anthracite surface.…”