Surfaces, Volume 3, Issue 4 (December 2020) – 9 articles

The lack of scalable synthesis of transition metal dichalcogenides, such as molybdenum disulfide (MoS₂), has proved to be a significant bottleneck in realization of fundamental devices and has hindered the commercialization of these materials in technologically relevant applications. In this study, a cost-efficient and versatile thin-film fabrication technique based on ionized jet deposition (IJD), i.e., a technique potentially providing high processing efficiency and scalability, is used to grow MoS₂ thin films on silicon substrates. The operating conditions of IJD were found to influence mainly the ablation efficiency of the target and only slightly the quality of the deposited MoS₂ thin film. All as-deposited films show chemical properties typical of MoS₂ with an excess of free, elemental sulfur that can be removed by post-deposition annealing at 300–400 °C, which also promotes MoS₂ crystallization. The formation of an interface comprised of several silicon oxide species was observed between MoS₂ and the silicon substrate, which is suggested to originate from etching and oxidizing processes of dissociated water molecules in the vacuum chamber during growth. The present study paves the way to further design and improve the IJD approach for TMDC-based devices and other relevant technological applications. Full article

The surface functionalization of inorganic nanoparticles is an important tool for the production of homogeneous nanocomposites. The chemical adaptation of the nano-filler surface can lead to effective weak to strong interactions between the fillers and the organic matrix. Here we present a detailed systematic study of different surface-functionalized particles in combination with a SAXS method for the systematic investigation of the interface interaction in the development of epoxy nanocomposites. We investigated the effect of surface modification of spherical SiO₂ nanoparticles with 9 nm and 72 nm diameter and crystalline ZrO₂ nanoparticles with 22 nm diameter on the homogeneous distribution of the fillers in diethylenetriamine (DETA) cured bisphenol-F-diglycidylether epoxy resin nanocomposites. Unmodified nanoparticles were compared with surface-modified oxides having diethylene glycol monomethyl ethers (DEG), 1,2-diols, or epoxy groups attached to the surface. The influence of surface modification on dispersion quality was investigated by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) for inorganic filler contents of 3, 5 and 10 wt%. It was shown that the dispersion quality can be optimized by varying the coupling agent end group to obtain homogeneous and transparent nanomaterials. UV/VIS measurements confirmed the transparency/translucency of the obtained materials. The relationship between particle–matrix interaction and particle–particle interaction plays a decisive role in homogeneity and is controlled by the surface groups as well as by the type, size, and morphology of the nanoparticles themselves. Full article

This research investigates deformation behavior of polystyrene (PS) as a thermoplastic resist material for the thermal nanoimprint lithography (T-NIL) process. Molecular dynamics modeling was conducted on a PS substrate with dimensions 58 × 65 × 61 Å that was imprinted with a rigid, spherical indenter. The effect of indenter size, force, and imprinting duration were evaluated in terms of indentation depth, penetration depth, recovery depth, and recovery percentage of the polymer. The results show that the largest indenter, regardless of force, has the most significant impact on deformation behavior. The 40 Å indenter with a 1 µN of force caused the surface molecules to descend to the lowest point compared to the other indenters. An increase in indenter size resulted in higher penetration depth, recovery depth, and recovery percentage. Higher durations of imprint cycle (400 fs) resulted in plastic deformation of the PS material with minimal recovery (4 Å). The results of this research lay the foundation for explaining the effect of several T-NIL process parameters on virgin PS thermoplastic resist material. Full article

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas. Full article

MoS₂ supported on oxides like TiO₂ has a broad range of applications. The atomic structure of this system is therefore very useful to study. Previous research work in this area has made use of high-temperature synthesis methods, while the preparation of an MoS₂/TiO₂ in very important applications, such as catalysis, makes use of a low-temperature synthesis method. In this work, we investigate a low-temperature synthesis strategy for MoS₂ slabs supported on rutile TiO₂(110). Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, we demonstrate that not only flat MoS₂ slabs with irregular shapes but also MoS_x stripes with a large number of coordinatively unsaturated Mo atoms are formed. In particular, it becomes evident that, for atomic structural characterization of MoS₂/TiO₂ and similar oxide-supported systems grown by low-temperature synthesis methods, the surface structure of the support becomes highly relevant. Full article

In this study, the surfaces of the stainless-steel fibers of the kind primarily utilized in fiber-reinforced composite materials were modified by an acid treatment to increase the interfacial adhesion between the fibers and epoxy resins in composite materials. The interfacial shear strength between the resins and acid-treated fibers was determined by a single fiber microdroplet test, where the resin droplet was located at the center of the fiber. The etching effect at the surface of the fibers increased with the increase in the acid-treatment time. The interfacial shear strength between the stainless-steel fiber and epoxy resin increased with the increase in the specific surface area of contact between the fiber and resin. Furthermore, there was no significant deterioration in the mechanical properties of the stainless-steel fibers with the increase in the surface etching effect. The modification of the surfaces of the stainless-steel fibers by the acid treatment resulted in an increase in the interfacial shear strength between the fibers and resins. Thus, this study demonstrated the possibility of widening the scope of the applications of stainless-steel fiber/epoxy resin composites. Full article

In this work, three Ibuprofen tin complexes were synthesized and characterized by Fourier Transform Infrared spectroscopy (FTIR), ¹H and ¹¹⁹Sn-Nuclear Magnetic Resonance (NMR), and Energy Dispersive X-ray (EDX) spectroscopies to identify the structures. The complexes were mixed separately with poly(vinyl chloride) (PVC) to improve its photo-stability properties. Their activity was demonstrated by several approaches of the FTIR to exhibit the formation of new groups within the polymer structure due to the exposure to UV light. Moreover, the polymer’s weight loss during irradiation and the average molecular weight estimation using its viscosity before and after irradiation were investigated. Furthermore, different techniques were used to study the surface morphology of the PVC before and after irradiation. Field-emission scanning electron microscopy (FESEM) and optical microscope demonstrated that applying Ibuprofen tin complexes keeps the surface of PVC smoother, with fewer cracks and spots after irradiation comparing to the blank PVC. Finally, It seems possible that such synthesized Ibuprofen tin complexes can work as excellent photo-stabilizers of PVC. In particular, complex 1 showed the best results among other stabilizers due to the large conjugation system of the stabilizer. Full article

Multilayered doped BaTiO₃ thin films have been fabricated by physical vapor deposition (PVD) on low-cost polycrystalline substrates with the aim to improve dielectric properties by controlling point charge defects at the interfaces. We show that carefully designed interfaces lead to increasing the relative permittivity of the BaTiO₃ thin films, in contradiction with the common belief that interfaces behave as dead layers. High relative permittivity up to 1030 and tanδ = 4% at 100 kHz and room temperature were obtained on BaTiO₃ multilayered films deposited on Si/Pt substrates by PVD. The large permittivity is suspected to be an extrinsic contribution due to band bending at the interfaces, as inferred by in-situ X-ray photoelectron spectroscopy. A 20-nm depletion layer was found to be associated with an interdiffusion of dopants, as measured by depth profiling with time-of-flight secondary ion mass spectrometry. The films exhibit high permittivity and low dielectric losses stable between 200 and 400 K, which meet the requirement of electronic applications. Full article

Fluorinated surfactants, which fall under the class of per- and polyfluoroalkyl substances (PFAS), are amphiphilic molecules that comprise hydrophobic fluorocarbon chains and hydrophilic head-groups. Fluorinated surfactants have been utilized in many applications, e.g., fire-fighting foams, paints, household/kitchenware items, product packaging, and fabrics. These compounds then made their way into the environment, and have been detected in soil, fresh water, and seawater. From there, they can enter human bodies. Fluorinated surfactants are persistent in water and soil environments, and their adsorption onto mineral surfaces contributes to this persistence. This review examines how fluorinated surfactants adsorb onto mineral surfaces, by analyzing the thermodynamics and kinetics of adsorption, and the underlying mechanisms. Adsorption of fluorinated surfactants onto mineral surfaces can be explained by electrostatic interactions, hydrophobic interactions, hydrogen bonding, and ligand and ion exchange. The aqueous pH, varying salt or humic acid concentrations, and the surfactant chemistry can influence the adsorption of fluorinated surfactants onto mineral surfaces. Further research is needed on fluorinated surfactant adsorbent materials to treat drinking water, and on strategies that can modulate the fate of these compounds in specific environmental locations. Full article