Micro, Volume 1, Issue 1 (September 2021) – 12 articles

The antifouling properties of self-assembled monolayers (SAMs) on gold generated from custom-designed bidentate unsymmetrical spiroalkanedithiols containing both oligo(ethylene glycol) and hydrocarbon tailgroups (EG3C7-C7 and EG3C7-C18) were evaluated and compared to SAMs derived from analogous monodentate octadecanethiol (C18SH) and the tri(ethylene glycol)-terminated alkanethiol EG3C7SH. Complementary techniques, including in situ surface plasmon resonance spectroscopy (SPR), ex situ electrochemical quartz crystal microbalance (QCM) measurements, and ex situ ellipsometric thickness measurements, were employed to assess the protein resistance of the SAMs using proteins having a wide range of sizes, structures, and properties: protamine, lysozyme, bovine serum albumin (BSA), and fibrinogen. The studies found that SAMs generated from the bidentate adsorbates EG3C7-C7 and EG3C7-C18, which contain a 1:1 mixture of OEG and hydrocarbon tailgroups, exhibited a diminished capacity to resist protein adsorption compared to the EG3C7SH SAMs, which possess only OEG tailgroups. The data highlight the critical role of hydration of the OEG matrix for generating antifouling OEG-based surface coatings. Full article

Functionalisation of single-walled carbon nanotubes (SWNTs) with atoms and molecules has the potential to prepare charge–transfer complexes for numerous applications. Here, we used density functional theory with dispersion correction (DFT + D) to examine the encapsulation and adsorption efficacy of single-walled carbon nanotubes to trap halogens. Our calculations show that encapsulation is exoergic with respect to gas-phase atoms. The stability of atoms inside SWNTs is revealed by the charge transfer between nanotubes and halogens. Encapsulation of halogens in the form of diatomic molecules is favourable with respect to both atoms and diatomic molecules as reference states. The adsorption of halogens on the outer surfaces of SWNTs is also exothermic. In all cases, the degree of encapsulation, adsorption, and charge transfer is reflected by the electronegativity of halogens. Full article

Implant-associated infections are an increasingly severe burden on healthcare systems worldwide and many research activities currently focus on inhibiting microbial colonization of biomedically relevant surfaces. To obtain molecular-level understanding of the involved processes and interactions, we investigate the adsorption of synthetic adhesin-like peptide sequences derived from the type IV pili of the Pseudomonas aeruginosa strains PAK and PAO at abiotic model surfaces, i.e., Au, SiO₂, and oxidized Ti. These peptides correspond to the sequences of the receptor-binding domain 128–144 of the major pilin protein, which is known to facilitate P. aeruginosa adhesion at biotic and abiotic surfaces. Using quartz crystal microbalance with dissipation monitoring (QCM-D), we find that peptide adsorption is material- as well as strain-dependent. At the Au surface, PAO(128–144) shows drastically stronger adsorption than PAK(128–144), whereas adsorption of both peptides is markedly reduced at the oxide surfaces with less drastic differences between the two sequences. These observations suggest that peptide adsorption is influenced by not only the peptide sequence, but also peptide conformation. Our results furthermore highlight the importance of molecular-level investigations to understand and ultimately control microbial colonization of surfaces. Full article

Sinapic acid (SA), belonging to the phenylpropanoid family, and its derivatives are secondary metabolites found in the plant kingdom. In recent years, they have drawn attention because of their various biological activities, including neuroprotective effects. In this study, SA was incorporated into two different nanoparticle systems, solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC). The influence of different concentrations of SA on the nanoparticle systems was evaluated. It was studied the efficacy of the nanoparticle systems to release the active ingredient at cell level through the use of models of biological membranes represented by multilamellar vesicles (MLV) of dimyristoylphosphatidylcholine (DMPC) and conducting kinetic studies by placing in contact SLN and NLC, both unloaded and loaded with two different amounts of SA, with the same biological membrane model. Differential scanning calorimetry (DSC) was used for these studies. The results indicated a different distribution of SA within the two nanoparticle systems and that NLC are able to incorporate and release SA inside the structure of the biological membrane model. Full article

Formulations based on mineral fillers and polymeric matrices of different nature were studied to obtain halogen-free flame retardant compounds (HFFR) for cable applications. The work was carried out by comparing fire-retardant mineral fillers of natural origin with synthetic mineral ones available on the market. As a reference, a formulation based on micronized natural magnesium hydroxide (n-MDH, obtained from brucite) and an ethylene-vinyl acetate copolymer with 28% by weight (11% by moles) of vinyl acetate were selected, and the mechanical and flame retardant properties compared with formulations based on secondary polymers combined with EVA, metal hydroxides, and carbonates. Notably, we found a synergistic effect in the mechanical, rheological and flame retardant properties for the composite containing a mixture of n-MDH and boehmite in a 3:1 weight ratio. Overall, the present work provided a complete and optimized recipe for the formulation of polymer composites characterized by the required flame retardant and mechanical features in electric cables applications. Full article

The paper investigates the mechanisms of microwave absorption in microcellular foamed conductive composites dedicated to protection against electromagnetic interferences (EMI). A multi-layered electromagnetic one-dimensional (1D) model mimicking the microcellular foam structure is built and validated using previous measurements carried out on various fabricated composite foams. Our model enables us to perform a parametric analysis of the absorption behaviour in a foamed composite, using as parameters the size of the hollow cell, the thickness of the cell’s walls and its conductivity, as well as the overall thickness of the composite and the frequency. Our investigations demonstrate that multiple reflections of the microwave signal between the cellular walls are not the main mechanism responsible for absorption, although they are often reported as a cause of enhanced absorption in the literature. On the contrary, our work demonstrates that the enhancement of the absorption observed in foamed conductive composite compared to unfoamed composite is mainly due to the presence of air in the microcells of the composite. Full article

Uses of novel technologies for improving the durability and lifespan of the construction materials have emerged as viable solutions toward the sustainable future wherein the coating industry plays a significant role in economy growth and better livelihoods. Thus, the continual innovation of various technologies to introduce diverse market products has become indispensable. Properties of materials like color stability under UV, elevated temperatures and aggressive environments, and skid and abrasion resistance are the main challenges faced by commercial coating materials, leading to more demand of natural materials as sustainable agents. Lately, nanostructured core–shell pigments with unique compositions have widely been utilized in composite materials to enhance their properties. Core–shell particles exhibit smart properties and have immense benefits when combined with building materials. Based on these facts, we comprehensively overviewed the state-of-the-art research of core–shell nanomaterials in terms of their preparation and performance evaluation methods, as well as feasible applications. The first part of this article discusses effective shell materials, including most common silica and titanium oxides. In addition, nanotechnology enabling the production and patterning of low-dimensional materials for widespread applications is emphasized. The second part deals with various potential core materials used to achieve core–shell nanostructures. The third part of this paper highlights some interesting mechanisms of core–shell structures in the modified systems that display high stability, durability, efficiency, and eco-friendliness. Finally, different applications of these core–shell nanostructures are underscored together with their test methods to evaluate their performances. Full article

Ultrathin films of Ni₀.₉Co₀.₁ were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni₀.₉Co₀.₁/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy. Mild thermal annealing at 250 °C enhanced a tendency for perpendicular magnetic anisotropy, mainly due to an increase of the uniaxial volume anisotropy term. Spin reorientation transition, exchange bias larger than 700 Oe, and strong coercivity enhancement were observed via a superconducting quantum interference device at low temperatures after field cooling. Full article

Niobium-doped nanocrystalline Li₄Ti₅O₁₂ (LTO) is synthesized by the solid-state reaction method, and the influence of dopant concentration (x = 2–10 mol%) on microstructural and electrochemical properties is studied. The X-ray diffraction and Raman patterns assessed the cubic spinel structure of Li₄Ti_5−xNb_xO₁₂ phase in all samples. Marginal changes in the lattice parameters, unit cell volume and dislocation density of LTO are observed with Nb substitution. The higher ionic radius of Nb induces a lattice expansion, which may be favorable for more ion intercalation/deintercalation. The SEM and TEM images display uniformly distributed nano-sized cubical particles. The represented (hkl) orientations of the SAED pattern and d-spacing (0.46 nm) between bright fringes confirm the well-crystallized LTO phase. The EDS and elemental mapping results demonstrate that Nb elements are uniformly doped in LTO with a proper stoichiometric ratio. The optimized 8%Nb-doped LTO electrode exhibits pseudocapacitive behavior and delivers a high specific capacitance of 497 F g⁻¹ at a current density of 1 A g⁻¹ with 92.3% of specific capacitance retention even after 5000 cycles. Full article

A hypergolic system is a combination of organic fuel and oxidizer that ignites spontaneously upon contact without any external ignition source. Although their main usage pertains to rocket bipropellants, it is only recently that hypergolics have been established from our group as a revolutionary preparative method for the synthesis of different types of carbon nanostructures depending on the organic fuel-oxidizer pair. In an effort to further enrich this concept, the present work describes new hypergolic pairs based on 1,3-cyclohexadiene and 1,3-cyclooctadiene as the organic fuels and fuming nitric acid as the strong oxidizer. Both carbon-rich compounds (ca. 90% C) share a similar chemical structure with unsaturated cyclopentadiene that is also known to react hypergolically with fuming nitric acid. The particular pairs ignite spontaneously upon contact of the reagents at ambient conditions to produce carbon nanosheets in suitable yields and useful energy in the process. The nanosheets appear amorphous with an average thickness of ca. 2 nm and containing O and N heteroatoms in the carbon matrix. Worth noting, the carbon yield reaches the value of 25% for 1,3-cyclooctadiene, i.e., the highest reported so far from our group in this context. As far as the production of useful energy is concerned, the hot flame produced from ignition can be used for the direct thermal decomposition of ammonium dichromate into Cr₂O₃ (pigment and catalyst) or the expansion of expandable graphite into foam (absorbent and insulator), thus demonstrating a mini flame-pyrolysis burner at the spot. Full article

Polystyrene (PS)/silicate composites were prepared with the addition of two organoclays (orgMMT and orgZenith) and two mesoporous silicas (SBA-15 and MCF) via (i) solution casting and (ii) melt compounding methods. X-ray diffraction (XRD) analysis evidenced an intercalated structure for PS/organoclay nanocomposites. Thermogravimetric analysis indicated improvement in the thermal stability of PS-nanocomposites compared to the pristine polymer. This enhancement was more prevalent for the nanocomposites prepared with a lab-made organoclay (orgZenith). Tensile measurement results indicated that elastic modulus increment was more prevalent (up to 50%) for microcomposites prepared using mesoporous silicas as filler. Organoclay addition led to a decrease in oxygen transmission rate (OTR) values. This decrement reached up to 50% for high organoclay content films in comparison to pristine PS film. Decrement above 80% was measured for microcomposites with mesoporous silicas and 5 wt% filler content obtained via melt compounding. Full article