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Surfaces, Volume 8, Issue 3 (September 2025) – 10 articles

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33 pages, 6710 KiB  
Article
XPS Investigation of Sol–Gel Bioactive Glass Synthesized with Geothermal Water
by Helena Cristina Vasconcelos, Maria Meirelles and Reşit Özmenteş
Surfaces 2025, 8(3), 50; https://doi.org/10.3390/surfaces8030050 (registering DOI) - 14 Jul 2025
Abstract
Bioactive glasses are known for their surface reactivity and ability to bond with bone tissue through the formation of hydroxyapatite. This study investigates the effects of substituting ultrapure water with natural geothermal waters from the Azores in the sol–gel synthesis of 45S5 and [...] Read more.
Bioactive glasses are known for their surface reactivity and ability to bond with bone tissue through the formation of hydroxyapatite. This study investigates the effects of substituting ultrapure water with natural geothermal waters from the Azores in the sol–gel synthesis of 45S5 and MgO-modified bioglasses. Using high-resolution X-ray photoelectron spectroscopy (XPS), we examined how the mineral composition of the waters influenced the chemical environment and network connectivity of the glass surface. The presence of trace ions, such as Mg2+, Sr2+, Zn2+, and B3+, altered the silicate structure, as evidenced by binding energy shifts and peak deconvolution in O 1s, Si 2p, P 2p, Ca 2p, and Na 1s spectra. Thermal treatment further promoted polymerization and reduced hydroxylation. Our findings suggest that mineral-rich waters act as functional agents, modulating the reactivity and structure of bioactive glass surfaces in eco-sustainable synthesis routes. Full article
(This article belongs to the Special Issue Bio-Inspired Surfaces)
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22 pages, 795 KiB  
Review
Microbial Extracellular Polymeric Substances as Corrosion Inhibitors: A Review
by Naima Sayahi, Bouthaina Othmani, Wissem Mnif, Zaina Algarni, Moncef Khadhraoui and Faouzi Ben Rebah
Surfaces 2025, 8(3), 49; https://doi.org/10.3390/surfaces8030049 - 13 Jul 2025
Viewed by 174
Abstract
Microbial extracellular polymeric substances (EPSs) are emerging as sustainable alternatives to conventional corrosion inhibitors due to their eco-friendly nature, biodegradability, and functional versatility. Secreted by diverse microorganisms including bacteria, fungi, archaea, and algae, EPSs are composed mainly of polysaccharides, proteins, lipids, and nucleic [...] Read more.
Microbial extracellular polymeric substances (EPSs) are emerging as sustainable alternatives to conventional corrosion inhibitors due to their eco-friendly nature, biodegradability, and functional versatility. Secreted by diverse microorganisms including bacteria, fungi, archaea, and algae, EPSs are composed mainly of polysaccharides, proteins, lipids, and nucleic acids. These biopolymers, chiefly polysaccharides and proteins, are accountable for surface corrosion prevention through biofilm formation, allowing microbial survival and promoting their environmental adaptation. Usually, EPS-mediated corrosion inhibitions can take place via different mechanisms: protective film formation, metal ions chelation, electrochemical property alteration, and synergy with inorganic inhibitors. Even though efficacious EPS corrosion prevention has been demonstrated in several former studies, the application of such microbial inhibitors remains, so far, a controversial topic due to the variability in their composition and compatibility toward diverse metal surfaces. Thus, this review outlines the microbial origins, biochemical properties, and inhibition mechanisms of EPSs, emphasizing their advantages and challenges in industrial applications. Advances in synthetic biology, nanotechnology, and machine learning are also highlighted and could provide new opportunities to enhance EPS production and functionality. Therefore, the adoption of EPS-based corrosion inhibitors represents a promising strategy for environmentally sustainable corrosion control. Full article
(This article belongs to the Collection Featured Articles for Surfaces)
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13 pages, 3561 KiB  
Article
Preparing Surface-Functionalized Polymer Films with Hierarchically Ordered Structure by a Combination of Nanoimprinting and Controlled Graft Polymerization
by Masahiko Minoda, Daichi Shimizu, Tatsuya Nohara and Jin Motoyanagi
Surfaces 2025, 8(3), 48; https://doi.org/10.3390/surfaces8030048 - 11 Jul 2025
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Abstract
It is widely recognized that fine surface structures found in nature contribute to surface functionality, and studies on the design of functional materials based on biomimetics have been actively conducted. In this study, polymer thin films with hierarchically ordered surface structure were prepared [...] Read more.
It is widely recognized that fine surface structures found in nature contribute to surface functionality, and studies on the design of functional materials based on biomimetics have been actively conducted. In this study, polymer thin films with hierarchically ordered surface structure were prepared by combining both nanoimprinting using anodically oxidized porous alumina (AAO) as a template and surface-initiated atom transfer radical polymerization (SI-ATRP). To prepare such polymer films, we designed a new copolymer (poly{[2-(4-methyl-2-oxo-2H-chromen-7-yloxy)ethyl methacrylate]-co-[2-(2-bromo-2-methylpropionyloxy)ethyl methacrylate]}; poly(MCMA-co-HEMABr)) with coumarin moieties and α-haloester moieties in the pendants. The MCMA repeating units function to fix the pillar structure by photodimerization, and the HEMABr ones act as the polymerization initiation sites for SI-ATRP on the pillar surfaces. Surface structures consisting of vertically oriented multiple pillars were fabricated on the spin-coated poly(MCMA-co-HEMABr) thin films by nanoimprinting using an AAO template. Then, the coumarin moieties inside each pillar were crosslinked by UV light irradiation to fix the pillar structure. SEM observation confirmed that the internally crosslinked pillar structures were maintained even when immersed in organic solvents such as 1,2-dichloroethane and anisole, which are employed as solvents under SI-ATRP conditions. Finally, poly(2,2,2-trifluoroethyl methacrylate) and poly(N-isopropylacrylamide) chains were grafted onto the thin film by SI-ATRP, respectively, to prepare the hierarchically ordered surface structure. Furthermore, in this study, the surface properties as well as the thermoresponsive hydrophilic/hydrophobic switching of the obtained polymer films were investigated. The surface morphology and chemistry of the films with and without pillar structures were compared, especially the interfacial properties expressed as wettability. Grafting poly(TFEMA) increased the static contact angle for both flat and pillar films, and the con-tact angle of the pillar film surface increased from 104° for the flat film sample to 112°, suggesting the contribution of the pillar structure. Meanwhile, the pillar film surface grafted with poly(NIPAM) brought about a significant change in wettability when changing the temperature between 22 °C and 38 °C. Full article
(This article belongs to the Special Issue Surface Science: Polymer Thin Films, Coatings and Adhesives)
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13 pages, 3840 KiB  
Article
Second Harmonic Generation Imaging of Strain-Induced Domain Evolution Across Grain Boundaries in SrTiO3 Bicrystals
by Yuhang Ren and Piyali Maity
Surfaces 2025, 8(3), 47; https://doi.org/10.3390/surfaces8030047 - 1 Jul 2025
Viewed by 251
Abstract
Understanding strain behavior near grain boundaries is critical for controlling structural distortions and oxygen vacancy migration in perovskite oxides. However, conventional techniques often lack the spatial resolution needed to analyze phase and domain evolution at the nanoscale. In this paper, polarization-dependent second-harmonic generation [...] Read more.
Understanding strain behavior near grain boundaries is critical for controlling structural distortions and oxygen vacancy migration in perovskite oxides. However, conventional techniques often lack the spatial resolution needed to analyze phase and domain evolution at the nanoscale. In this paper, polarization-dependent second-harmonic generation (SHG) imaging is employed as a tool to probe local symmetry breaking and complex domain structures in the vicinity of a low-angle grain boundary of SrTiO3 (STO) bicrystals. We show that the anisotropic strain introduced by a tilted grain boundary produces strong local distortions, leading to the coexistence of tetragonal and rhombohedral domains. By analyzing SHG intensity and variations in the second-order nonlinear optical susceptibility, we map the distribution of strain fields and domain configurations near the boundary. In pristine samples, the grain boundary acts as a localized source of strain accumulation and symmetry breaking, while in samples subjected to intentional electrical stressing, the SHG response becomes broader and more uniform, suggesting strain relaxation. This work highlights SHG imaging as a powerful technique for visualizing grain-boundary-driven structural changes, with broad implications for the design of strain-engineered functional oxide devices. Full article
(This article belongs to the Collection Featured Articles for Surfaces)
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17 pages, 2685 KiB  
Article
Co-Effect of pH Control Agent and pH Value on the Physical Properties of ZnO Thin Films Obtained by Chemical Bath Deposition for Potential Application in Dye-Sensitized Solar Cells
by Alphonse Déssoudji Gboglo, Mazabalo Baneto, Komlan Segbéya Gadedjisso-Tossou, Ognanmi Ako, Ayayi Claude Ahyi, Muthiah Haris, Muthusamy Senthilkumar, Kekeli N’konou, Bruno Grandidier, Katawoura Beltako, Komi Apélété Amou and Milohum Mikesokpo Dzagli
Surfaces 2025, 8(3), 46; https://doi.org/10.3390/surfaces8030046 - 1 Jul 2025
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Abstract
This study presents the influence of pH control agents and pH value on the physical properties of ZnO thin films obtained by chemical bath deposition. ZnO thin films were synthesized on glass substrates using precursor solutions of different pHs prepared from two bases: [...] Read more.
This study presents the influence of pH control agents and pH value on the physical properties of ZnO thin films obtained by chemical bath deposition. ZnO thin films were synthesized on glass substrates using precursor solutions of different pHs prepared from two bases: sodium hydroxide (NaOH) and ammonia (NH3). The effect of pH values on the morphological, structural, and optical properties of ZnO thin films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible spectroscopy. XRD results showed that all the synthesized ZnO thin films are polycrystalline and crystallize in a hexagonal wurtzite structure. The crystallite size, calculated using the Debye–Scherrer formula, varied from 10.50 nm to 11.69 nm for ZnO thin films obtained with NH3 and from 20.79 nm to 27.76 nm for those obtained with NaOH. FTIR analysis confirmed the presence of functional groups. SEM images indicated that not only the base but also the pH affects the morphology of the films, giving rise to different granular shapes. Overall, the ZnO thin films obtained with NaOH looked more mesoporous compared to those obtained with NH3. Optical characterization results showed that whatever the base used, the pH of the precursor solution affected the ZnO thin film transmittance. Films synthesized with NH3 exhibited the best transmittance (80%) at pH 8.5, while the best transmittance (81%) of films synthesized with NaOH was obtained at pH 8 in the visible region. Based on optical and morphological properties, ZnO films obtained from NH3 at pH 8.5 are found to be more suitable as photoanodes in dye-sensitized solar cells. Full article
(This article belongs to the Special Issue Surface Engineering of Thin Films)
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13 pages, 6820 KiB  
Article
An Exploration of SPS Fabrication and the Sliding Wear Properties of γ-TiAl-Ag Self-Lubrication Materials
by Na Xiao, Chenglong Yang, Shengfei Zhou, Yuliang Yin, Dian Zhao, Yulong Shi and Kang Yang
Surfaces 2025, 8(3), 45; https://doi.org/10.3390/surfaces8030045 - 30 Jun 2025
Viewed by 233
Abstract
To promote the optimization of the anti-friction and anti-wear behavior of lightweight TiAl alloys, γ-TiAl-10 wt.% Ag self-lubricating composites were fabricated, and their mechanical and tribological properties were tested. The results showed that the silver in TiAl-10 wt.% Ag slightly reduced its mechanical [...] Read more.
To promote the optimization of the anti-friction and anti-wear behavior of lightweight TiAl alloys, γ-TiAl-10 wt.% Ag self-lubricating composites were fabricated, and their mechanical and tribological properties were tested. The results showed that the silver in TiAl-10 wt.% Ag slightly reduced its mechanical properties compared with those of pure TiAl alloys. A silver-enriched lubrication film formed on a wear scar, which was helpful in improving the friction and wear behavior. It was found that a large amount of silver gathered at a wear scar, gradually spread out under the action of the sliding friction force, and then increased the silver distribution areas on the wear scar, leading to the good formation of a silver-rich film. Furthermore, an identification model was established to calculate the specific area η of the silver film. A quantitative relationship indicated that an increase in the Ag distribution area improved the tribological behavior of γ-TiAl-10 wt.% Ag. When the specific area η of a silver-rich film was maintained at 44–51%, the small friction coefficient (almost 0.28) and wear rate (about 2.25 × 10−4 mm3·N−1·m−1) were well stabilized. This provides a new research method to improve the tribological performance of TiAl-Ag samples. Full article
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10 pages, 1777 KiB  
Communication
Glucose-Mediated Microstructure Refinement of Electroless Silver Coatings on Atomized Fe Particles
by Dehou Song, Tiebao Wang, Lichen Zhao, Pan Gong and Xin Wang
Surfaces 2025, 8(3), 44; https://doi.org/10.3390/surfaces8030044 - 25 Jun 2025
Viewed by 270
Abstract
Electroless silver (Ag) plating has emerged as a simple yet effective surface modification technique, garnering significant attention in consumer electronics and composite materials. This study systematically investigates the influence of glucose dosage on the microstructural refinement of Ag coatings deposited from silver–ammonia solutions [...] Read more.
Electroless silver (Ag) plating has emerged as a simple yet effective surface modification technique, garnering significant attention in consumer electronics and composite materials. This study systematically investigates the influence of glucose dosage on the microstructural refinement of Ag coatings deposited from silver–ammonia solutions onto iron (Fe) particles while also evaluating the oxidation resistance of Ag-plated particles through thermogravimetric analysis. Optimal results were achieved at a silver nitrate concentration of 0.02 mol/L and a glucose concentration of 0.05 mol/L, producing Fe particles with a uniform and dense silver coating featuring an average Ag grain size of 76 nm. The moderate excess glucose played a dual role: facilitating Ag+ ion reduction while simultaneously inhibiting the growth of Ag atomic clusters, thereby ensuring microstructural refinement of the silver layer. Notably, the Ag-plated particles demonstrated superior oxidation resistance compared to their uncoated counterparts. These findings highlight the significance of fine-grained electroless Ag plating in developing high-temperature conductive metal particles and optimizing interfacial structures in composite materials. Full article
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15 pages, 11303 KiB  
Article
Hierarchical Manganese-Doped Nickel–Cobalt Oxide Electrodes with Graphene for Use as High-Energy-Density Supercapacitors
by Kuan-Ching Lee, Guan-Ting Pan, Thomas Chung-Kuang Yang, Po-Cheng Shen, Kuan Lun Pan, Timm Joyce Tiong, Aleksandar N. Nikoloski and Chao-Ming Huang
Surfaces 2025, 8(3), 43; https://doi.org/10.3390/surfaces8030043 - 25 Jun 2025
Viewed by 271
Abstract
Thin films of manganese–nickel–cobalt oxide with graphene (G@MNCO) were deposited on copper foam using electrochemical deposition. NiCo2O4 is the main phase in these films. As the proportion of graphene in the precursor solution increases, the oxygen vacancies in the samples [...] Read more.
Thin films of manganese–nickel–cobalt oxide with graphene (G@MNCO) were deposited on copper foam using electrochemical deposition. NiCo2O4 is the main phase in these films. As the proportion of graphene in the precursor solution increases, the oxygen vacancies in the samples also increase. The microstructure of these samples evolves into hierarchical vertical flake structures. Cyclic voltammetry measurements conducted within the potential range of 0–1.2 V reveal that the electrode with the highest graphene content achieves the highest specific capacitance, approximately 475 F/g. Furthermore, it exhibits excellent cycling durability, maintaining 95.0% of its initial capacitance after 10,000 cycles. The superior electrochemical performance of the graphene-enhanced, manganese-doped nickel–cobalt oxide electrode is attributed to the synergistic contributions of the hierarchical G@MNCO structure, the three-dimensional Cu foam current collector, and the binder-free fabrication process. These features promote quicker electrolyte ion diffusion into the electrode material and ensure robust adhesion of the active materials to the current collector. Full article
(This article belongs to the Special Issue Surface Science in Electrochemical Energy Storage)
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12 pages, 2254 KiB  
Article
Hydrophobic Boron Nitride Nanoflower Coatings on Mild Steel Surfaces
by Aamir Nadeem, Muhammad Faheem Maqsood, Mohsin Ali Raza, Syed Muhammad Zain Mehdi and Shahbaz Ahmad
Surfaces 2025, 8(3), 42; https://doi.org/10.3390/surfaces8030042 - 25 Jun 2025
Viewed by 373
Abstract
Growing demand for chemically resistant, thermally stable, and anti-icing coatings has intensified interest in boron nitride (BN)-based materials and surface coatings. In this study, BN coatings were developed on mild steel (MS) via chemical vapour deposition (CVD) at 1200 °C for 15, 30, [...] Read more.
Growing demand for chemically resistant, thermally stable, and anti-icing coatings has intensified interest in boron nitride (BN)-based materials and surface coatings. In this study, BN coatings were developed on mild steel (MS) via chemical vapour deposition (CVD) at 1200 °C for 15, 30, and 60 min, and their structural, surface, and water-repellent characteristics were evaluated. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy confirmed the successful formation of BN, while water contact angle measurements indicated high hydrophobicity, demonstrating excellent barrier properties. Scanning electron microscopy (SEM) revealed morphological evolution from flower- and needle-like BN structures in the sample placed in the CVD furnace for 15 min to dense, coral-like, and tubular networks in the samples placed for 30 and 60 min. These findings highlight that BN coatings, particularly the one obtained after 30 min of deposition, have a high hydrophobic character following the Cassie–Baxter model and can be used for corrosion resistance and anti-icing on MS, making them ideal for industrial applications requiring long-lasting protection. Full article
(This article belongs to the Special Issue Surface Engineering of Thin Films)
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18 pages, 10483 KiB  
Article
The Effect of Low-Temperature Plasma Treatment on the Adhesive Bonding Performance of CF/PEKK Surfaces
by Liwei Wen, Zhentao Dong and Ruozhou Wang
Surfaces 2025, 8(3), 41; https://doi.org/10.3390/surfaces8030041 - 20 Jun 2025
Viewed by 264
Abstract
Polyaryletherketone (PAEK) polymers inherently exhibit low surface activity, leading to poor adhesive bonding performance when using epoxy-based adhesives. In this study, low-temperature plasma surface modification was conducted on carbon fiber-reinforced polyetherketone ketone (CF/PEKK) composites to investigate the influence of plasma treatment parameters on [...] Read more.
Polyaryletherketone (PAEK) polymers inherently exhibit low surface activity, leading to poor adhesive bonding performance when using epoxy-based adhesives. In this study, low-temperature plasma surface modification was conducted on carbon fiber-reinforced polyetherketone ketone (CF/PEKK) composites to investigate the influence of plasma treatment parameters on their lap shear strength. Surface characterization was systematically performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis to evaluate morphological, chemical, and wettability changes induced via plasma treatment. The results demonstrated a significant enhancement in lap shear strength after plasma treatment. Optimal bonding performance was achieved at a treatment speed of 10 mm/s and a nozzle-to-substrate distance of 5 mm, yielding a maximum shear strength of 28.28 MPa, a 238% improvement compared to the untreated control. Notably, the failure mode transitioned from interfacial fracture in the untreated sample to a mixed-mode failure dominated by cohesive failure of the adhesive and substrate. Plasma treatment substantially reduced the contact angle of CF/PEKK, indicating improved surface wettability. SEM micrographs revealed an increased micro-porous texture on the treated surface, which enhanced mechanical interlocking between the composite and adhesive. XPS analysis confirmed compositional alterations, specifically elevated oxygen-containing functional groups on the plasma-treated surface. These modifications facilitated stronger chemical bonding between CF/PEKK and the epoxy resin, thereby validating the efficacy of plasma treatment in optimizing surface chemical activity and adhesion performance. Full article
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