Control Of Surface Chemistry Research Articles

Oxidizing octadecylphosphonic acid molecules without disrupting their self-assembled monolayers

In examination of oxidation of octadecylphosphonic acid (OPA) self-assembled monolayers (SAMs) prepared on the native oxide of a Si wafer upon exposure to UV/ozone (UVO) for up to 5 min, atomic force microscopy studies of the surface elucidated that there were no changes in morphology of the SAMs. Surprisingly, investigations on the same samples of OPA SAMs using time-of-flight secondary ion mass spectrometry revealed that the intensity of the deprotonated molecular ion fragment decreased exponentially to approximately one fourth of that of the control. We clarify that UVO-induced oxidation of alkyl chains of the OPA molecules in their SAMs precedes the disruption of the monolayer structure, which is the basis for controlling surface chemistry of SAMs with brief UVO exposure.

Correlative light and electron microscopy using cathodoluminescence from nanoparticles with distinguishable colours

Correlative light and electron microscopy promises to combine molecular specificity with nanoscale imaging resolution. However, there are substantial technical challenges including reliable co-registration of optical and electron images, and rapid optical signal degradation under electron beam irradiation. Here, we introduce a new approach to solve these problems: imaging of stable optical cathodoluminescence emitted in a scanning electron microscope by nanoparticles with controllable surface chemistry. We demonstrate well-correlated cathodoluminescence and secondary electron images using three species of semiconductor nanoparticles that contain defects providing stable, spectrally-distinguishable cathodoluminescence. We also demonstrate reliable surface functionalization of the particles. The results pave the way for the use of such nanoparticles for targeted labeling of surfaces to provide nanoscale mapping of molecular composition, indicated by cathodoluminescence colour, simultaneously acquired with structural electron images in a single instrument.

Poly (hydroxyethyl methacrylate-glycidyl methacrylate) films modified with different functional groups: In vitro interactions with platelets and rat stem cells

Copolymerization of 2-hydroxyethylmethacrylate (HEMA) with glycidylmethacrylate (GMA) in the presence of α-α′-azoisobisbutyronitrile (AIBN) resulted in the formation of hydrogel films carrying reactive epoxy groups. Thirteen kinds of different molecules with pendant NH2 group were used for modifications of the p(HEMA-GMA) films. The NH2 group served as anchor binding site for immobilization of functional groups on the hydrogel film via direct epoxy ring opening reaction. The modified hydrogel films were characterized by FTIR, and contact angle studies. In addition, mechanical properties of the hydrogel films were studied, and modified hydrogel films showed improved mechanical properties compared with the non-modified film, but they are less elastic than the non-modified film. The biological activities of these films such as platelet adhesion, red blood cells hemolysis, and swelling behavior were studied. The effect of modified hydrogel films, including NH2, (using different aliphatic CH2 chain lengths) CH3, SO3H, aromatic groups with substituted OH and COOH groups, and amino acids were also investigated on the adhesion, morphology and survival of rat mesenchymal stem cells (MSCs). The MTT colorimetric assay reveals that the p(HEMA-GMA)-GA-AB, p(HEMA-GMA)-GA-Phe, p(HEMA-GMA)-GA-Trp, p(HEMA-GMA)-GA-Glu formulations have an excellent biocompatibility to promote the cell adhesion and growth. We anticipate that the fabricated p(HEMA-GMA) based hydrogel films with controllable surface chemistry and good stable swelling ratio may find extensive applications in future development of tissue engineering scaffold materials, and in various biotechnological areas.

Condensation on Superhydrophobic Surfaces: The Role of Local Energy Barriers and Structure Length Scale

Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range of industrial applications, including energy production, desalination, and environmental control. Nanotechnology has created opportunities to manipulate this process through the precise control of surface structure and chemistry, thus enabling the biomimicry of natural surfaces, such as the leaves of certain plant species, to realize superhydrophobic condensation. However, this "bottom-up" wetting process is inadequately described using typical global thermodynamic analyses and remains poorly understood. In this work, we elucidate, through imaging experiments on surfaces with structure length scales ranging from 100 nm to 10 μm and wetting physics, how local energy barriers are essential to understand non-equilibrium condensed droplet morphologies and demonstrate that overcoming these barriers via nucleation-mediated droplet-droplet interactions leads to the emergence of wetting states not predicted by scale-invariant global thermodynamic analysis. This mechanistic understanding offers insight into the role of surface-structure length scale, provides a quantitative basis for designing surfaces optimized for condensation in engineered systems, and promises insight into ice formation on surfaces that initiates with the condensation of subcooled water.

A new combined approach to metal-ceramic implants with controllable surface topography, chemistry, blind porosity, and wettability

The present work focuses on the surface modification of Ti alloys using a combination of various techniques such as cold spray (CS), selective laser sintering (SLS), pulsed electro-erosion treatment (PEET), and magnetron sputtering to control surface topography (roughness and blind porosity), surface chemistry, and wettability, i.e. the characteristics which affect osseointegration. The sample structure, elemental composition, surface topography, and wettability were studied using X-ray diffraction, optical and scanning electron microscopy, glow discharge optical emission spectroscopy, energy dispersive spectroscopy, and water contact angle measurements. The obtained results show that Ti coatings deposited by CS can be divided into three groups with a characteristic value of average roughness Ra: (i) 4μm (single particles and agglomerates on the surface), (ii) 22μm (thin coatings), and (iii) 80μm (thick coatings). PEET with pulse discharge energies of 0.025 and 0.38J resulted in the average values of surface roughness of 3 and 8μm, respectively. During SLS, Ti powder paths were sintered by a laser beam in mutually perpendicular directions to form surface network structures. By varying the distance between the tracks, samples with blind porosity 1.0–5.1×10−3mm3 were obtained. In order to modify the surface chemistry, multifunctional bioactive nanostructured TiCaPCON films, 1–2μm thick, were deposited atop the CS, PEET, and SLS samples by sputtering a composite TiC0.5+Ca3(PO4)2 target. The wettability measurements showed that the CS and PEET modified surfaces exhibit high values of water contact angle. Ion etching in vacuum and TiCaPCON film deposition made the samples highly hydrophilic. The influence of the surface chemistry and surface topography on adhesion, proliferation, and early stages of osteoblasts differentiation was studied. The combination of high surface roughness and blind porosity with hydrophilicity and biocompatibility makes the fabricated metal-ceramic materials promising candidates for applications involving tissue regeneration.

Early and Intermediate Stages of Guided Dewetting in Polystyrene Thin Films

We investigated the early and intermediate stages of the guided dewetting of polystyrene (PS) thin films on chemically patterned silicon, achieved by micro-contact printing of non-wettable self-assembling monolayers of an alkylsilane. Two different types of ordered patterns could be achieved depending on the annealing temperature and time. Study of the dynamics of hole growth revealed a deviation of the growth profile from the trend on homogeneous substrates, attributed to the pinning of the PS rims on the borders of the hydrophobic regions. The ordered patterns produced could be useful in applications that require spatially localized features of controlled surface chemistry, such as studies in proteomics, single cell studies, and biosensors.

Role of Oxygen Functional Groups in Carbon Nanotube/Graphene Freestanding Electrodes for High Performance Lithium Batteries

AbstractHierarchical functionalized multiwalled carbon nanotube (MWNT)/graphene structures with thicknesses up to tens of micrometers and relatively high density (>1 g cm−3) are synthesized using vacuum filtration for the positive electrode of lithium batteries. These electrodes, which are self‐standing and free of binder and current collectors, utilize oxygen functional groups for Faradaic reactions in addition to double‐layer charging, which can impart high gravimetric (230 Wh kg−1 at 2.6 kW kg−1) and volumetric (450 Wh L−1 at 5 kW L−1) performance. It is demonstrated that the gravimetric and volumetric capacity, capacitance, and energy density can be tuned by selective removal of oxygen species from as‐prepared functionalized MWNT/graphene structures with heat treatments in H2/Ar, potentially opening new pathways for the design of electrodes with controlled surface chemistry.

Use of Surface Chemistry Control and Low Temperature Growth Methods for Overcoming Perceived Limitations in III-Nitride Epitaxy

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Designing Quantum Rods for Optimized Energy Transfer with Firefly Luciferase Enzymes

The bioluminescence resonance energy transfer (BRET) between firefly luciferase from Photinus pyralis (Ppy) with core/shell semiconductive quantum rods (QRs) has been studied as a function of QR aspect ratio and internal microstructure. The QRs were found to be ideal energy acceptors, and Ppy-to-core distances were optimized using rod-in-rod microstructures that were achieved by the synthetic control of rod morphology, surface chemistry, and Ppy:QR loading. The BRET ratios of >44 measured are the highest efficiencies to date.

Surface and Interfacial Chemistry

Based on a molecular approach combining controlled surface chemistry, advanced spectroscopic methods, in particular solid-state NMR, and computational chemistry, it is possible to develop single-site species and to control the growth of nanoparticles on supports. This allows the generation of highly efficient catalysts combining the advantages of both homogeneous and heterogeneous catalysts and function materials with defined properties.

Inducing healing-like human primary macrophage phenotypes by 3D hydrogel coated nanofibres

Immune cells are present in the blood and in resident tissues, and the nature of their reaction towards biomaterials is decisive for materials success or failure. Macrophages may for example be classically activated to trigger inflammation (M1), or alternatively activated which supports healing and vascularisation (M2). Here, we have generated 3D nanofibrous meshes in different porosities and precisely controlled surface chemistries comprising PLGA, hydrogel-coated protein repellant and protein repellant endowed with the bioactive peptide sequences GRGDS or GLF. We also prepared 2D substrates with corresponding surface chemistry for a systematic evaluation of primary human macrophage adhesion, migration, transcriptome expression, cytokine release and surface marker expression. Our data show that material morphology is a powerful means in biomaterial design to influence immune cell response. Flat substrates lead to an increased number of M2 classified CD163+ macrophages. However, these M2 cells released large amounts of pro-inflammatory cytokines. In contrast, 3D nanofibres with corresponding surface chemistry yielded M1 classified 27E10+ macrophages with a significantly increased release of pro-angiogenic chemokines and angiogenesis related molecules and a strong decrease of pro-inflammatory cytokines. We thus suggest that, for macrophages in contact with biomaterials, cytokine release is taken as main criterion instead of surface-markers for macrophage classifications.

Dynamics of Ice Nucleation on Water Repellent Surfaces

Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

Synthesis and characterization of ratiometric nanosensors for pH quantification: a mixed micelle approach

Optical nanoparticle pH sensors designed for ratiometric measurements have previously been synthesized using post-functionalization approaches to introduce sensor molecules and to modify nanoparticle surface chemistry. This strategy often results in low control of the nanoparticle surface chemistry and is prone to batch-to-batch variations, which is undesirable for succeeding sensor calibrations and cellular measurements. Here we provide a new synthetic approach for preparing nanoparticle pH sensors based on self-organization principles, which in comparison to earlier strategies offers a much higher design flexibility and high control of particle size, morphology and surface chemistry.

Temporally and spatially controlled silicification for self-generating polymer@silica hybrid nanotube on substrates with tunable film nanostructure

This paper describes a novel approach to templated silicification that could directly generate a tubular structure with a polymer@silica hybrid wall. We developed a new process for the crystallization-driven self-assembled formation of a linear polyethyleneimine (LPEI) template on a substrate surface, which involves the key step of alkali-quenching of the complete deprotonation reaction of the adsorbed, protonated LPEI fraction on the substrate at room temperature. This alkali-induced LPEI template allowed the temporally and spatially controlled silicification reaction, leading to the self-generation of a tubular structure with a 3 nm LPEI@silica hybrid wall. The elemental nanotubes were organized hierarchically into two-dimensional mats and the mats were further vertically arrayed into a thin film. Such nanotube-based hybrid films could be formed reproducibly either on glass or on plastic. The surface morphology and nanostructure of the film could be tunable by simply adjusting solution conditions for LPEI self-assembly or by using substrates with controlled surface chemistry. After introducing hydrophobic residues on the film, the hierarchical nanotube surface showed the best repellency toward inkjet ink compared to the nanoribbon- and nanowire-based superhydrophobic surface. We also expanded this templated silicification to synthesize hybrid nanotube powders in solution. Both Brunauer–Emmett–Teller (BET) and transmission electron microscopy (TEM) studies supported direct formation of an approximately 3 nm hollow structure. Thin film X-ray diffraction measurements (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetry analysis (TGA) characterizations indicated the hybrid nature of the LPEI@silica wall. This new approach advanced on the conventional methods of using an organic template to direct inorganic materials, and is expected to be generally applicable to directly generate other organic–inorganic hybrid nanostructures.

Carbon-based ionogels: tuning the properties of the ionic liquid via carbon–ionic liquid interaction

The behavior of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium dicyanamide [Emim][DCA] and 1-ethyl-3-methylimidazolium triflate [Emim][TfO], in (meso)porous carbonaceous hosts was investigated. Prior to IL incorporation into the host, the carbon matrix was thermally annealed between 180 and 900 °C to control carbon condensation and surface chemistry. The resulting materials have an increasing "graphitic" carbon character with increasing treatment temperature, reflected in a modified behavior of the ILs when impregnated into the carbon host. The two ILs show significant changes in the thermal behavior as measured from differential scanning calorimetry; these changes can be assigned to anion-π interaction between the IL anions and the pore wall surfaces of these flexible carbonaceous support materials.

Surface-assisted laser desorption–ionization mass spectrometry on titanium dioxide (TiO2) nanotube layers

The paper reports on the use of a titanium oxide (TiO(2)) nanotube layer as a sensitive substrate for surface-assisted laser desorption-ionization mass spectrometry (SALDI-MS) of peptides and small molecules. The nanotube layers were prepared by electrochemical anodization of titanium foil. The optimized TiO(2) nanotubes morphology coupled to a controlled surface chemistry allowed desorption-ionization (D/I) of a peptide mixture (Mix1) with a detection limit of 10 femtomoles for the neurotensin peptide. The performance of the TiO(2) nanotubes for the D/I of small molecules was also tested for the detection of sutent, a small tyrosine kinase inhibitor, and verapamil. A detection limit of 50 fmol was obtained for these molecules, as compared to 500 fmol using classical matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS). Both amorphous and anatase TiO(2) layers displayed a comparable performance for D/I of analyte molecules. In a control experiment, we have performed D/I of analyte molecules on a flat TiO(2) layer. The absence of signal emphasizes the role of the nanostructured substrate in the D/I process.

Evaporative assembly of ordered microporous films and their hierarchical structures from amphiphilic random copolymers

Ordered microporous films were obtained via evaporative assembly from amphiphilic random copolymers of poly(acryloyl chloride) with self-crosslinked components. The quality and morphology of the porous structures were found to be highly dependent on the ratio of good solvent for the polymer (e.g. acetone) and nonsolvent (e.g. toluene), choice of nonsolvent, and surface chemistry of the supporting substrate. When increasing the polymer concentration in acetone–toluene solution, a morphological evolution from vesicles to microporous films with decreased pore size was observed. Using SU-8 micropillar arrays with spatially controlled surface chemistry to direct the evaporative assembly, we constructed hierarchical microporous structures with tunable pore size and symmetry (e.g. square arrays vs. hexagonal arrays). Finally, we selectively assembled TOPO-stabilized CdSe nanocrystals into the hydrophobic core of the random copolymers dispersed in acetone–toluene, and created fluorescent microporous structures after solvent evaporation.

Gyroid Nanoporous Membranes with Tunable Permeability

Understanding the relevant permeability properties of ultrafiltration membranes is facilitated by using materials and procedures that allow a high degree of control on morphology and chemical composition. Here we present the first study on diffusion permeability through gyroid nanoporous cross-linked 1,2-polybutadiene (1,2-PB) membranes with uniform pores that, if needed, can be rendered hydrophilic. The gyroid porosity has the advantage of isotropic percolation with no need for structure prealignment. Closed (skin) or opened (nonskin) outer surface can be simply realized by altering the interface energy in the process of membrane fabrication. The morphology of the membranes' outer surface was investigated by scanning electron microscopy, contact angle, and X-ray photoelectron spectroscopy. The effective diffusion coefficient of glucose decreases from nonskin, to one-sided skin to two-sided skin membranes, much faster than expected by a naive resistance-in-series model; the flux through the two-sided skin membranes even increases with the membrane thickness. We propose a model that captures the physics behind the observed phenomena, as confirmed by flow visualization experiments. The chemistry of 1,2-PB nanoporous membranes can be controlled, for example, by hydrophilic patterning of the originally hydrophobic membranes, which allows for different active porosity toward aqueous solutions and, therefore, different permeability. The membrane selectivity is evaluated by comparing the effective diffusion coefficients of a series of antibiotics, proteins, and other biomolecules; solute permeation is discussed in terms of hindered diffusion. The combination of uniform bulk morphology, isotropically percolating porosity, controlled surface chemistry, and tunable permeability is distinctive for the presented gyroid nanoporous membranes.

Supported Pt-particles on multi-walled carbon nanotubes with controlled surface chemistry

Multi-walled carbon nanotubes (MWCNTs) were functionalized by HNO 3 hydrothermal oxidation at 200 °C. The degree of surface functionalization was described by an exponential function in terms of HNO 3 concentration. Very small Pt particles, with mean particle size of 1.7 ± 0.3 nm, could be supported on the surface of pristine MWCNTs and also on MWCNTs treated with HNO 3 concentrations up to 0.20 mol L − 1 , while a broader range of particle sizes, and larger Pt particles (3.4 ± 1.3 nm) were obtained on the MWCNTs treated with a higher HNO 3 concentration (0.30 mol L − 1 ). Therefore, the amounts of surface groups and Pt particle sizes can be selected by tuning the HNO 3 concentration used in the hydrothermal treatment.

ChemInform Abstract: Nanostructured Materials for Hydrogen Storage

AbstractReview: 79 refs.