Physical Surface Modification Research Articles

Advances in surface modification and functionalization for tailoring the characteristics of thin films and membranes via chemical vapor deposition techniques

AbstractAdvanced materials are among the prime drivers for technological revolutions and transformation in quality of lives. Over time, several modification techniques have emerged enabling development of novel materials with extraordinary features. The present review aims to introduce various promising chemical and physical surface modification techniques instrumental for tailoring the characteristics of thin films and membranes. Meticulous discussions are provided over chemical vapor deposition (CVD) techniques evolved for addressing the demands for materials with desired functionalities. Also, essential criteria for the selection of substrates, modifying and precursor materials for an effective CVD modification are elaborated. Investigations are extended to unraveling the role of various process parameters on the quality and properties of deposition. Special attention is paid to the significance and performance of CVD‐based membranes and thin films for industrial applications ranging from desalination and water treatment to energy and environment, biomedical and life science as well as packaging. The goal has been to establish a scientific platform for a timely tracking of the prevailing trends in exploitation of CVD techniques and highlighting the unexplored opportunities. This also helps in identification of the scientific and technical gaps and setting directions for further progress in the fields of thin films and membranes.

Insights on the development of enhanced antifouling reverse osmosis membranes: Industrial applications and challenges

Reverse osmosis (RO) membranes are widely employed due to their inherent advantage of achieving excellent water permeation rates and high salt rejection. However, fouling is a main issue in RO applications that leads to increasing the operational cost, reducing the lifespan of the membrane, decreasing the permeate flux, and increasing the energy demand. Therefore, many techniques have been developed and used in the industry to minimize and control fouling in RO membranes, such as feed pretreatment and membrane cleaning. In the context of fouling mitigation and control, the development of antifouling and self-cleaning RO membranes has gained significant attention. This review aims to discuss membranes fouling, its types, and mechanisms. Moreover, factors affecting the fouling process in RO have been highlighted. The article provides an overview of the novel techniques, such as physical and chemical surface modification and thin-film nanocomposite membrane synthesis for imparting antifouling/self-cleaning properties to RO membranes. Finally, some related challenges are discussed, and future recommendations are presented.

Near-Surface Nanomechanics of Medical-Grade PEEK Measured by Atomic Force Microscopy.

Detecting subtle changes of surface stiffness at spatial scales and forces relevant to biological processes is crucial for the characterization of biopolymer systems in view of chemical and/or physical surface modification aimed at improving bioactivity and/or mechanical strength. Here, a standard atomic force microscopy setup is operated in nanoindentation mode to quantitatively mapping the near-surface elasticity of semicrystalline polyether ether ketone (PEEK) at room temperature. Remarkably, two localized distributions of moduli at about 0.6 and 0.9 GPa are observed below the plastic threshold of the polymer, at indentation loads in the range of 120-450 nN. This finding is ascribed to the localization of the amorphous and crystalline phases on the free surface of the polymer, detected at an unprecedented level of detail. Our study provides insights to quantitatively characterize complex biopolymer systems on the nanoscale and to guide the optimal design of micro- and nanostructures for advanced biomedical applications.

Probe the nanoparticle-nucleus interaction via coarse-grained molecular model.

The present study reports on a computational model that systematically evaluates the effect of physical factors, including size, surface modification, and rigidity, on the nuclear uptake of nanoparticles (NPs). The NP-nucleus interaction is a crucial factor in biomedical applications such as drug delivery and cellular imaging. While experimental studies have provided evidence for the influence of size, shape, and surface modification on nuclear uptake, theoretical investigations on how these physical factors affect the entrance of NPs through the nuclear pore are lacking. Our results demonstrate that larger NPs require a higher amount of energy to enter the nucleus compared to smaller NPs. This highlights the importance of size as a critical factor in NP design for nuclear uptake. Additionally, surface modification of NPs can impact the nuclear uptake pathway, indicating the potential for tailored NP design for specific applications. Notably, our findings also reveal that the rigidity of NPs has a significant effect on the transport process. The interplay between physicochemical properties and nuclear pore is found to determine nuclear uptake efficiency. Taken together, our study provides new insights into the design of NPs for precise and controllable NP-nucleus interaction, with potential implications for the development of efficient and targeted drug delivery systems and imaging agents.

Precise Pore Size Tailoring and Surface Chemistry Modification of Polycarbonate Membranes Using Atomic Layer Deposition

Physical and chemical surface modifications are commonly used in many applications such as energy generation and storage, microelectronics, water purification, gas separation, and medical/plant biology. In recent several years, sequential infiltration synthesis (SIS), a variant of atomic layer deposition (ALD), has emerged as a promising technology that uses self-limiting reactions to create hybrid organic/inorganic materials within the polymer-free volume. Herein, we employed ALD/SIS of Al2O3, SnO2, Ga2O3, TiO2, and In2O3 to precisely tune the pore size and surface characteristics of track-etched polycarbonate membranes. We used in situ Fourier transform infrared spectroscopy to elucidate the chemistry for Al2O3 SIS in polycarbonate and in situ quartz crystal microbalance measurements to probe the extent of Al2O3 infiltration during SIS in polycarbonate thin films. Next, we used scanning electron microscopy, thermogravimetric analysis, and water permeance measurements to probe the pore size reduction and conformality of SIS Al2O3 in the track-etched polycarbonate membranes. We then used water permeance measurements to compare the water flux for a series of membranes with similar pore size but different pore wall chemistry and compared these results with water contact angle measurements. Interestingly, the hydrophilic metal oxide coatings yielded higher water flux values compared to hydrophobic coatings. Finally, we examined ion-selective transport in the modified track-etched polycarbonate membranes and rationalized the results using zeta potential measurements of the ALD metal oxides. Keywords: atomic layer deposition; sequential infiltration synthesis; metal oxides; hydrophilicity/hydrophobicity; permeability; surface charge; ion conductivity/selectivity.

Recent Advancements in Surface Modification, Characterization and Functionalization for Enhancing the Biocompatibility and Corrosion Resistance of Biomedical Implants

Metallic materials are among the most crucial engineering materials widely utilized as biomaterials owing to their significant thermal conductivity, mechanical characteristics, and biocompatibility. Although these metallic biomedical implants, such as stainless steel, gold, silver, dental amalgams, Co-Cr, and Ti alloys, are generally used for bone tissue regeneration and repairing bodily tissue, the need for innovative technologies is required owing to the sensitivity of medical applications and to avoid any potential harmful reactions, thereby improving the implant to bone integration and prohibiting infection lea by corrosion and excessive stress. Taking this into consideration, several research and developments in biomaterial surface modification are geared toward resolving these issues in bone-related medical therapies/implants offering a substantial influence on cell adherence, increasing the longevity of the implant and rejuvenation along with the expansion in cell and molecular biology expertise. The primary objective of this review is to reaffirm the significance of surface modification of biomedical implants by enlightening numerous significant physical surface modifications, including ultrasonic nanocrystal surface modification, thermal spraying, ion implantation, glow discharge plasma, electrophoretic deposition, and physical vapor deposition. Furthermore, we also focused on the characteristics of some commonly used biomedical alloys, such as stainless steel, Co-Cr, and Ti alloys.

Effects of Co-diluent on the pore structure, patterning fidelity, and properties of membranes fabricated by lithographically templated thermally induced phase separation

Surface patterning as a physical surface modification method is promising for improving performance of liquid-based membrane processes. Lithographically templated, thermally induced phase separation (lt-TIPS) process is recently demonstrated for fabricating surface patterned microporous polymer membranes. However, the mechanical properties of the poly(vinylidene fluoride) (PVDF) membranes casted from tributyl O-acetylcitrate (ATBC) were poor, due to the predominant spherulitic morphology. In this study, we investigate the influences of diphenyl carbonate (DPC) as co-diluent to ATBC on the pore structure and patterning fidelity of lt-TIPS fabricated PVDF membranes. With the increase of DPC content in the mixed diluents, the phase separation path of the PVDF solution transitions from solid-liquid (S-L) to liquid-liquid (L-L), and correspondingly, the membrane pore structures evolve from dispersed spherulitic to bi-continuous cellular. The interconnected cellular morphology resulted from ATBC/DPC ratio of 20/80 shows superior mechanical properties of membranes compared with all other membranes, improving the toughness by nine times compared with pure ATBC system. The patterning fidelity improves from 59% to 79% as DPC content increases. The presence of the surface patterns on the PVDF membranes improves both the water contact angle WCA (by 12–18%) and the liquid entry pressure LEP (by 5–20%) which are desirable for membrane distillation (MD) applications. Concomitantly, patterned membranes also showed improved pure water permeance and water vapor flux in MD measurement.

Surface modifications of cellulose nanocrystals: Processes, properties, and applications

The interest in nanocellulose has recently increased in many fields due to its natural abundance, exceptional mechanical/optical properties, and better biocompatibility. During the production of cellulose nanocrystals (CNCs) via sulfuric acid hydrolysis, sulfate groups are introduced, which decrease the thermal stability of CNCs and, thus, have a profound negative effect on the potential application of CNCs in nanocomposites. Also, mechanical methods exhibit poor morphological properties in CNCs with a reduced degree of crystallinity. Therefore, to improve the processability and performance of CNCs and extend their industrial applications and quality, nano-cellulose undergoes surface modifications by physical and chemical means. Surface modifications of CNCs lower the surface energy, increase hydrophobicity, improve interfacial adhesion, enhance their compatibility between nanocomposite components, and improve their dispersion and interaction. Surface-modified CNCs have wide applications in medicine, catalysis, optics, remediation processes, electronics, textiles, pulp, paper, etc. Other applications of CNCs are: supporting catalysts and sensors, as diaphragms in earphones; for tissue engineering, scaffolds, for toughened paper, as polymer nanocomposites for developing membranes, in flexible panels for flat panel displays, in the optical application and biomimetic foams, and as rheology modifiers. This review provides the latest advances in surface modification of CNCs and the relevant processes, properties, and applications. • Acid hydrolysis of cellulose introduces sulfate groups on cellulose nanocrystals (CNCs) surface, limiting their applications. • Surface modification is an effective method to mitigate the shortcomings of CNCs. • Recent advancements in physical and chemical surface modifications are summarized. • The applications of CNCs, including polymer nanocomposites, are intensively studied.

Enzymatic modification and adsorption of hydrophobic zein proteins on lactic acid bacteria stabilize Pickering emulsions

The effect of enzymatic and physical modifications of the surface of two different strains from lactic acid bacteria, Lactobacillus rhamnosus (LGG) and Lactobacillus delbruekii subs. lactis ATCC 4797 (LBD), to stabilize medium-chain triglyceride (MCT) oil based Pickering emulsions were investigated. A section of cell wall degrading enzymes, lysozyme from chicken egg white and human, lysostaphin, mutanolysin from Streptomyces globisporus and proteinase k and the hydrophobic protein zein were used for enzymatic and physical surface modifications. Cell surface modifications were characterized by optical microscopy, scanning electron cryo-microscopy (Cryo-SEM), transmission electron microscopy (TEM), microbial adhesion to hexadecane (MATH) test and zeta potential measurements. The modified cell hydrophobicity in terms of MATH values were increased (around four times) by the enzymatic and physical modifications for LBD and LGG compared to the control. Emulsions stabilized by modified bacterial cells showed higher stability in comparison with unmodified samples, especially for the samples modified with chicken egg lysozyme. Confocal microscopy revealed that the modified bacterial cells were absorbed at the interface between oil and water and preventing the oil particles from coalescence. Thus, modified bacterial cells can be used to formulate food-grade stable Pickering emulsions. Such Pickering emulsions can potentially be clean label alternatives to replace the conventional emulsion preparations.

Physical shish-kebab modification vs. chemical surface coating on expanded polytetrafluoroethylene vascular grafts for enhanced endothelial cell adhesion

Promoting rapid adhesion of endothelial cells is of significance for the viability of vascular grafts for small-diameter blood vessels (SDBVs) made of expanded polytetrafluoroethylene (ePTFE). Many physical and chemical surface modification methods have been developed to overcome the inertness of ePTFE and to promote cell adhesion. In this study, a biomimetic poly(ε-caprolactone) (PCL) shish-kebab microstructure was formed on the fibrillated domains of ePTFE through induced crystallization. The surface morphology and chemistry, mechanical property, cytocompatibility, and endothelial cell adhesion of PCL shish-kebab modified ePTFE were investigated. The effectiveness of and synergy between this physical topology modification and the traditional chemical RGD dig-coating in terms of cell adhesion were also evaluated. The positive effect of the shish-kebab structure on cell adhesion was found to be more significant than that of RGD coating, and there is a strong synergy between ePTFE surface modification and RGD coating. The biomimetic shish-kebab structure could be a promising material platform for further grafting and/or surface functionalization of ePTFE for other tissue engineering applications.

Surface reformed anisotropic polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene‐graft‐maleic anhydride layer via ion‐beam irradiation for liquid crystals

AbstractThe surface modifications and liquid crystal (LC) alignment properties of polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene‐graft‐maleic anhydride (SEBS‐g‐MA) films induced by ion‐beam (IB) irradiation are reported herein. Changes to the surfaces of the SEBS‐g‐MA films from IB irradiation at various incidence angles and changes in the LC orientations upon LC cell fabrication were analyzed. The physical surface modifications due to IB irradiation were observed via atomic force microscopy. Additionally, changes in the molecular composition of the surface were observed through X‐ray photoelectron spectroscopy analysis. Polarized optical microscopy analysis shows that excellent LC alignment properties could be obtained after IB irradiation at angles exceeding 45°. Further, the anisotropy caused by IB irradiation was more responsible for uniform LC alignment than the corrugated pattern.

Biofouling and Mitigation Methods: A Review

Biofouling accumulates living organisms on surfaces in contact with the water and causes significant economic, structural, and microbial problems on ship hulls, piers, oil rigs, power plants, pipework, water treatment facilities as well as medical devices. In order to mitigate problems associated with biofouling, many toxic and non-toxic antifouling methods have been developed. Unfortunately, most of the methods used to control biofouling are either harmful to the environment or, in some cases, considered effective. Thus, antifouling research's main objective is to develop green, sustainable, viable, widely applicable, and environmentally friendly antifouling technology. In this review, chemical, physical, and biological mitigation methods to prevent biofilm formation employed in the past and present have been discussed along with the current literature. Chemical antifouling methods generally contain antifouling (AF) paints with biocides including copper, silver, thiocyanate, Copper powder, Irgarol 1051, Zinc pyrithione, and Tributyltin (TBT). The physical antifouling control methods employ physical force or surface modifications such as low drag, low adhesion, wettability (super hydrophobicity or super hydrophilicity), as well as microtextured structures that minimize microorganism adhesion and/or accumulation on contact surfaces, hindering the formation of biofouling. The use of nature-inspired antibiological and biomimetic surfaces like shark skin, whale skin, dolphin skin, and lotus leaves are promising for the effective control of biofouling and present opportunities for developing non-polluting technologies.

Fabrication of Noncytotoxic Functional Siloxane-Coated Bacterial Cellulose Nanocrystals

Bacterial cellulose nanocrystals (BCNC) stand out as versatile biocolloidal building blocks for materials that are high-performance, owing to their inherently high crystallinity and specific modulus and surface area, and sustainable, as BCNC are both biobased and biodegradable. BCNC materials are also promising for their multifunctionality because of their huge potential to undergo physical and/or chemical surface modification. This is particularly appealing for biomedical applications thanks to the biocompatibility, high purity, and low toxicity of BCNC. We report on films based on surface-modified BCNC with varying contents of 3-glycidyloxypropyltrimethoxysilane (GPTMS) or 3-aminopropyltriethoxysilane (APTS). Importantly, these highly pure and crystalline needle-shaped BCNC were isolated from scraps generated at industrial operations when shaping bacterial cellulose membranes into wound dressings. The films were extensively characterized as far as their structural characteristics, with emphasis on the major features targeting at biological applications. Compared with pristine BCNC, the films performed better from the thermal stability standpoint and maintained the noncytotoxicity against nontransforming fibroblasts. The latter claim was independent of GPTMS content, but dose-dependent for APTS and valid for films containing up to 30% of this coupling agent. Altogether, this contribution expands the wingspan of nanocellulose-based materials in biomedical applications while mitigating the waste of natural resources by upcycling an industrial byproduct, falling within the circular bioeconomy framework.

Bioinspired Topographic Surface Modification of Biomaterials.

Physical surface modification is an approach that has been investigated over the last decade to reduce bacterial adhesion and improve cell attachment to biomaterials. Many techniques have been reported to modify surfaces, including the use of natural sources as inspiration to fabricate topographies on artificial surfaces. Biomimetics is a tool to take advantage of nature to solve human problems. Physical surface modification using animal and vegetal topographies as inspiration to reduce bacterial adhesion and improve cell attachment has been investigated in the last years, and the results have been very promising. However, just a few animal and plant surfaces have been used to modify the surface of biomaterials with these objectives, and only a small number of bacterial species and cell types have been tested. The purpose of this review is to present the most current results on topographic surface modification using animal and plant surfaces as inspiration to modify the surface of biomedical materials with the objective of reducing bacterial adhesion and improving cell behavior.

Advanced Surface Modification for 3D-Printed Titanium Alloy Implant Interface Functionalization.

With the development of three-dimensional (3D) printed technology, 3D printed alloy implants, especially titanium alloy, play a critical role in biomedical fields such as orthopedics and dentistry. However, untreated titanium alloy implants always possess a bioinert surface that prevents the interface osseointegration, which is necessary to perform surface modification to enhance its biological functions. In this article, we discuss the principles and processes of chemical, physical, and biological surface modification technologies on 3D printed titanium alloy implants in detail. Furthermore, the challenges on antibacterial, osteogenesis, and mechanical properties of 3D-printed titanium alloy implants by surface modification are summarized. Future research studies, including the combination of multiple modification technologies or the coordination of the structure and composition of the composite coating are also present. This review provides leading-edge functionalization strategies of the 3D printed titanium alloy implants.

Recent Advancements in Polyphenylsulfone Membrane Modification Methods for Separation Applications.

Polyphenylsulfone (PPSU) membranes are of fundamental importance for many applications such as water treatment, gas separation, energy, electronics, and biomedicine, due to their low cost, controlled crystallinity, chemical, thermal, and mechanical stability. Numerous research studies have shown that modifying surface properties of PPSU membranes influences their stability and functionality. Therefore, the modification of the PPSU membrane surface is a pressing issue for both research and industrial communities. In this review, various surface modification methods and processes along with their mechanisms and performance are considered starting from 2002. There are three main approaches to the modification of PPSU membranes. The first one is bulk modifications, and it includes functional groups inclusion via sulfonation, amination, and chloromethylation. The second is blending with polymer (for instance, blending nanomaterials and biopolymers). Finally, the third one deals with physical and chemical surface modifications. Obviously, each method has its own limitations and advantages that are outlined below. Generally speaking, modified PPSU membranes demonstrate improved physical and chemical properties and enhanced performance. The advancements in PPSU modification have opened the door for the advance of membrane technology and multiple prospective applications.

Fluorescent carbon dots for sensing metal ions and small molecules

As one kind of new carbon nanomaterials, carbon dots (CDs) have excellent optoelectric properties and indicate widespread applications in sensing, display, energy storage and catalysis. Although the precise structure of CDs needs to be further analyzed and investigated, it is generally accepted that there are large amounts of electron-rich groups and substituents on the surface of CDs, such as amino, hydroxyl, carboxyl, thiol, and heterocycles, depending on the precursors used and preparation route. Therefore, the inherent advantages of electron-rich CDs make them very suitable for sensing specific substances including metal ions and electron-deficient small molecules. The sensing performance of CDs can be further improved through physical or chemical surface modification. The recent progress in CDs application for sensing metal ions and small functional molecules in recent years is specifically summarized and the sensing mechanism behind that was elaborated. Finally, the research prospective and performance improvement for CDs are addressed.

Physical and chemical surface modification of carbon nanotubes for adsorptive desulfurization of aromatic impurities in diesel fuel.

Due to some environmental problems of sulfur compounds, it is necessary to eliminate these impurities from hydrocarbon fuels. To achieve effective removal of aromatic sulfur compounds such as benzothiophene and dibenzothiophene, different surface modification of carbon nanostructures, physical and chemical surface modifications, were utilized to reach the adsorptive desulfurization and oxidative desulfurization processes. The acid treatment by H2SO4/HNO3 and polymer-wrapping technique by polyethylene glycol were used for chemical and physical surface modification, respectively. Additionally, we tried to control the intensity and types of functional groups on the surface of carbon nanotubes. Besides, the efficiency of sulfur removal was measured. Both single-walled and multi-walled carbon nanotubes were utilized, and prepared samples have been investigated by FTIR, UV-Visible, TEM, Raman, and TGA techniques. The adsorption capacity values of each sample were evaluated by the temperature, time, and concentration parameters. The result shows that this surface modification can significantly improve the impurity removal of hydrocarbon fuel. Polymer-coated complexes showed higher removal values due to better dispersion than surface-oxidized carbon nanotubes. It was demonstrated that 90% of sulfur impurities with aromatic structure could be removed using an insignificant amount of the synthesized complex at moderate conditions. Besides, a comparison of laboratory data by conventional adsorption isotherms was investigated, and finally, the best operating conditions for maximum adsorbent performance were evaluated.

Magnetospheric Ion Bombardment of Europa’s Surface

Abstract Jupiter’s moon Europa is exposed to constant bombardment by magnetospheric charged particles, which are expected to be a major source of physical and chemical surface modification. Here we have investigated the flux of magnetospheric ions at Europa’s surface by carrying out single particle tracing within realistic electromagnetic fields from multifluid magnetohydrodynamic simulations of the moon’s interaction with Jupiter’s magnetosphere. We find that magnetic field line draping and pileup leads to shielding and drastically reduced flux at low latitudes across Europa’s trailing (upstream) hemisphere. Furthermore, we find that magnetic induction within Europa’s subsurface ocean leads to additional shielding when the moon is located at high magnetic latitudes in Jupiter’s magnetosphere. Overall, we find that the high-latitude and polar regions on Europa receive the largest flux of magnetospheric ions. Both spacecraft and ground-based observations have previously identified a non–water ice surface species concentrated at Europa’s trailing (upstream) hemisphere, possibly hydrated sulfuric acid formed from radiolysis of water ice with implanted S ions. Our results demonstrate that the S ion flux across Europa’s equatorial trailing (upstream) hemisphere is strongly reduced, possibly indicating that the formation of the observed non–water ice species is controlled primarily by energy input from magnetospheric electrons, rather than the flux of S ions. We find that that O and S ions at >1 MeV energies have nearly uniform access to the surface, while energetic protons in this energy range are constrained to a “bull’s-eye” centered on the trailing (upstream) hemisphere.

Biomedical Alloys and Physical Surface Modifications: A Mini-Review.

Biomedical alloys are essential parts of modern biomedical applications. However, they cannot satisfy the increasing requirements for large-scale production owing to the degradation of metals. Physical surface modification could be an effective way to enhance their biofunctionality. The main goal of this review is to emphasize the importance of the physical surface modification of biomedical alloys. In this review, we compare the properties of several common biomedical alloys, including stainless steel, Co–Cr, and Ti alloys. Then, we introduce the principle and applications of some popular physical surface modifications, such as thermal spraying, glow discharge plasma, ion implantation, ultrasonic nanocrystal surface modification, and physical vapor deposition. The importance of physical surface modifications in improving the biofunctionality of biomedical alloys is revealed. Future studies could focus on the development of novel coating materials and the integration of various approaches.