The different self-assembled way of n- and t-dodecyl mercaptan on the surface of copper

The self-assembled monolayers (SAMs) of n- and t-dodecyl mercaptan on the surface of copper have been obtained. As evidenced by electrochemical impedance spectroscopy (EIS), two kinds of the alkanethiols can self-assemble on the copper surface. But the results of the quartz crystal microbalance (QCM) show that the self-assembled way of the two alkanethiols are different. The SAMs of n-dodecyl mercaptan can increase the weight of the QCM electrode and the SAMs of t-dodecyl mercaptan, on the contrary, make the weight of the QCM electrode decrease. Inspected with the SEM, it is found that a lot of pits spread all over the copper surface after having been modified with t-dodecyl mercaptan. All the results suggest that the self-assemble of t-dodecyl mercaptan on the copper surface can erode and dissolve copper surface sharply.     

A contact angle and ToF-SIMS study of SAM-thiol interactions on polycrystalline gold

A process of chemical differentiation of neighboring Au features on a substrate (for biosensing applications) involves a step, where after electrochemical removal of a self-assembled monolayer (SAM) from one feature, another SAM is deposited onto it by incubation with a different thiol. During this incubation step, other undesorbed features are also exposed to this thiol which may lead to a partial SAM-thiol exhange, the extent of which is a function of time. Here, such surface reactions were followed on polystalline Au in both directions using contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The thiols involved were dodecanethiol (DDT) which forms SAM promoting adsorption of proteins and 11-mercaptoundecyl)tri(ethylene glycol) (TPEG) whose SAM prevents such adsorption. The surface reactions in both directions cannot be described by a simple pseudo-first-order kinetics. It was found that while the DDT SAM interaction with a TPEG solution leads eventually to a total replacement, the reverse process, TPEG SAM interaction with DDT, leads to no noticeable exchange over the first 3 h and then asymptotically approaches ∼50% replacement.     

Fabrication of hydrophobic surface of titanium dioxide films by successive ionic layer adsorption and reaction (SILAR) method

Titanium dioxide (TiO₂) films were fabricated on fluorine doped tin oxide (FTO) coated glass substrate using successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction, scanning electron microscopy, transmission electron microscopy, optical absorption and contact angle measurement were applied to study the structural, surface morphological, optical and surface wettability properties of the as-deposited and annealed TiO₂ films. The X-ray diffraction studies revealed both as-deposited and annealed TiO₂ films are amorphous. Irregular shaped spherical grains of random size and well covered to the fluorine doped tin oxide coated glass substrates were observed from SEM studies with some cracks after annealing. The optical band gap values of virgin TiO_2, annealed, methyl violet and rose bengal sensitized TiO₂ were found to be 3.6, 3.5, 2.87 and 2.95 eV, respectively. Surface wettability studied in contact with liquid interface, showed hydrophobic nature as water contact angles were greater than 90°. The adsorption of dyes, as confirmed by the photographs, is one of the prime requirements for dye sensitized solar cells (DSSC).     

XPS study of protein adsorption onto nanocrystalline aluminosilicate microparticles

X-ray photoelectron spectroscopy (XPS) was used to study the interaction of two different sized proteins, bovine serum albumin (BSA) and fibrinogen, with an aluminosilicate system containing yttrium and iron that is a potential biomaterial. Serum albumin and fibrinogen are two major plasma proteins and the most relevant proteins adsorbed on the surface of biomaterials in blood contact.The aluminosilicate samples were incubated for several exposure times, up to 24 h, in simulated body fluid enriched with BSA, and in buffered fibrinogen solution. Time dependence of proteins adsorption onto surface of the investigated samples is reflected by the evolution of the new N 1s photoelectron peak and by the modification of C 1s core-level spectra recorded from the samples immersed in protein solution.     

Estimating critical surface tension from droplet spreading area

Critical surface tension (CST) is a measure of solid surface tension and is mainly determined by measuring the contact angle of a droplet on a target solid surface. The concept of CST makes it possible to determine solid surface tension without any unprovable assumptions such as the Fowkes hypothesis. However, it requires somewhat special devices and skills for measuring the contact angle. In this work, we propose a simple method to determine the CST of a solid by measuring the droplet spreading area. This method is developed by combining the conventional CST with a simple analytical droplet model. The difference in estimated CSTs between our method and the conventional one is within 3.0%. Our method enables a quick and simple evaluation of the solid surface tension without special devices for measuring the contact angle.     

Annealing effect on surface segregation behavior of hydroxypropylcellulose/polyethylenimine blend films

The surface properties of hydroxypropylcellulose (HPC) and polyethylenimine (PEI) blend films prepared by solution casting method before and after annealing were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and contact angle measurements. SEM and AFM analysis of the blends revealed that the PEI component segregated on the surface of the air-surface side of the blend films with increasing annealing temperature. The band intensity of PEI component at 1630 cm⁻¹ also increased depending on annealing temperature. The water contact angle decreased abruptly with increasing annealing temperature and reached almost 31° on the surface of the air-surface side of the blends at 150 °C. The results of these studies showed that the PEI chains with low surface energy segregated or enriched mainly on the surface of the air-surface side, and that, on the other hand, HPC chains with high surface energy oriented to the surface of the glass-surface side and inside of the films with increasing annealing temperature.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.     

Ethanol adsorption on MgO surface with and without defects from a theoretical point of view

In this work, the ethanol adsorption on a perfect MgO(1 0 0) surface, and also on topologic surface defects of MgO, is studied. Terrace, edge and corner sites were analyzed, whose O and Mg ions are five, four and three fold coordinated, respectively. All the calculations were performed using a cluster approach and the DFT based method. The ethanol molecule chemisorbs non-dissociatively on terrace sites of MgO by means of a two fold interaction while strong dissociative chemisorptions are produced on edge and corner sites. The weakened alcohol OH group is always oriented so that its oxygen (O_a) atom is linked to a Mg cation and the H atom to a surface O anion. The MgO_a distance for edge and corner sites is smaller than that for the terrace site. This indicates that lowering the coordination number of ions in the adsorption site yields an increase of molecule-surface bond strength in agreement with a greater basicity of low coordinate sites. The behavior of the adsorption energy and the charge transfers are in accord with the idea of a strong basic character for the MgO substrate, which is more pronounced as the coordination number of ions decrease.     

分子取向对CO在Pd(111)面吸附的影响

用基于密度泛函理论广义梯度近似下的平面波赝势方法计算了在Pd(111)晶面两种不同CO分子取向的吸附结构。计算结果表明,CO分子碳端和氧端靠近Pd(111)面的吸附能分别为-1.75,-0.28 eV,碳端吸附的结构比氧端吸附能力强。因此,分子取向影响CO在Pd(111)面上的吸附,通过控制CO的取向可能减小Pd(111)的吸附进而减弱Pd(111)面CO分子的中毒。     

第一性原理研究氧在Ni(111)表面上的吸附能及功函数

采用基于密度泛函理论（DFT）广义梯度近似（GGA）下的第一性原理方法系统地研究了不同覆盖度下O在Ni（111）表面的吸附特性.计算结果表明,O在Ni（111）表面的稳定吸附位为三重面心立方（fcc）洞位,吸附能随着覆盖度的增加而减小,O诱导Ni（111）表面功函数的变化量与覆盖度成近线性关系,并随着覆盖度的增加而增大.同时,通过对电子密度和分波态密度的分析发现：O在Ni（111）表面的吸附使得Ni表面电子向O原子转移,形成表面偶极矩,导致功函数增加;表面Ni原子的3d轨道和O的2p轨道通过耦合、杂化作用形成成键态和反键态,而反键态几乎不被占据,因而O—Ni键相互作用比较强,吸附能较大. 关键词： 表面吸附 密度泛函理论 吸附能 功函数     

Reactive sputtering TiO2 films for surface coating of poly(dimethylsiloxane)

Titanium dioxide (TiO₂) films were prepared on poly(dimethylsiloxane) (PDMS) substrate by direct current (DC) reactive sputtering to change surface physical properties of PDMS. The effects of the changes were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analysis, water contact angle measurements and protein adsorption tests. Improved wettability and reduced adsorption properties were observed on PDMS surface coated TiO₂ films.     

Dependence of surface distribution of self-assembled InSb nanodots on surface morphology and spacer layer thickness

Self-assembled InSb nanodots (NDs) were grown on a GaSb (1 0 0) substrate using metal-organic vapour phase epitaxy (MOVPE). The effects of etching depth of the substrate and thickness of the GaSb buffer layer on the density and size distribution of single and double layer dots were studied for detector applications. The etch depth of the substrate was varied up to 30 μm. In this particular study, the dots were grown at 450 °C and the GaSb spacer thickness was varied between 50 nm and 200 nm. The optimum substrate etch depth was found to be 30 μm while the best spacer thickness was found to be 200 nm.     

A new approach to immobilize poly(vinyl alcohol) on poly(dimethylsiloxane) resulting in low protein adsorption

The hydrophobic characteristics of PDMS and non-specific protein adsorption are major drawbacks for its application in biosensing. Here we have combined surface oxidation by plasma and chemical binding of polyvinyl alcohol (PVA) to obtain long-term stability of hydrophilic PDMS surfaces. Mercaptopropyltrimethoxisilane and aminopropyltrimethoxisilane were used as adhesives between the plasma-oxidized PDMS surface and the PVA, immobilized at room temperature. This approach has allowed for fast, uniform, and very stable modification of the PDMS surface, which maintained a hydrophilic character for as long as 30 days. In addition, the modified hydrophilic surface presented minimized protein adsorption when compared to pristine PDMS. The results obtained in this work are important contributions to the growing field of integrated microfluidic biosensors.     

Water adsorption on the Be(0001) surface: from monomer to trimer adsorption

In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be(0001) surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of ～437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a₁-like molecular orbital with the (s, p_z) orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the 1b₁-like orbital of the H₂O molecule plays a dominant role.     

The effect of working pressure on the chemical bond structure and hydrophobic properties of PET surface treated by N ion beams bombardment

Polyethylene terephthalate (PET) surface was bombarded by N ion beams at room temperature. Varying the working pressure of the ion beams, PET surfaces with different composition and properties were obtained. Characterization by X-ray photoelectron spectrometry showed that only on film surface, ester bonds, especially C-O bonds, were broken and N element chemical bonded with C. The influence depth was less than 5 nm because of the lower ion energy (about 10³ eV). Contact angle results revealed that with increasing the working pressure of ion beams, the contact angle of PET surface to pure water increased from 51° to 130°. With these results, one conclusion could be deduced that the hydrophilic and hydrophobic properties of PET surface could be influenced by N atom chemical bond with C, which in turn is controlled by the working pressure of N ion beams.     

Deformation and motion by gravity and magnetic field of a droplet of water-based magnetic fluid on a hydrophobic surface

Motion and deformation of a water-based magnetic fluid on a hydrophobic surface were investigated under gravity and a magnetic field. Surface energy and the resultant contact angle of the magnetic fluid depend on the surfactant concentration. The fluid viscosity is governed mainly by magnetite concentration. The front edge of the droplet moved under a weak external field. The rear edge required a higher external field for movement. The forces of gravity and the magnetic field for moving of the front edge are almost equal. However, those of the rear edge are different. The motion of magnetic fluids by an external field depends on concentrations of surfactants and magnetic particles, the external field, and experimental assembly.     

Competitive adsorption of multiple proteins to nanoparticles: the Vroman effect revisited

ABSTRACT

Proteins adsorbed from the blood plasma change nanoparticles interactions with the surrounding biological environment. In general, the adsorption of multiple proteins has a non-monotonic time dependence, that is, proteins adsorbed at first may slowly be replaced by others. This ‘Vroman effect’ leads to a highly dynamic protein corona on nanoparticles that profoundly influences the immune response of the body. Thus, the temporal evolution of the corona must be taken into account when considering applications of nanocarriers in, e.g., nanomedicine or drug delivery. Up to now, the Vroman effect is explained solely in terms of diffusion: Smaller proteins which diffuse faster are adsorbed first, while larger ones, having a stronger interaction with the surface, are preferred at equilibrium. Here we use dynamic density functional theory (DDFT) including steric and electrostatic interactions to provide a full model for the temporal evolution of the protein corona. In particular, we demonstrate that proper consideration of all interactions leads to Vroman-like adsorption signatures in widely different scenarios. Moreover, consideration of energetic terms predicts both competitive as well as cooperative adsorption. In this way, DDFT provides a reacher picture of the evolution of the dynamic protein corona.     

Wettability and surface energy of parylene F deposited on PDMS

For the first time, the wettability and surface energy of parylene F were investigated. The results showed that parylene F had a hydrophobic surface with an eigen water contact angle of 104.7 ± 0.6°. We found that 3.5 μl probe liquid was an optimal value for the contact angle measurement of parylene F. Moreover, we found that the Lifshitz–van der Waals/acid–base approach was unsuitable for determining the surface energy of parylene F, whereas the Owens–Wendt–Kaelble approach and the limitless liquid–solid interface wetting system were compatible. The surface energy of parylene F was estimated to be 27.06 mJ/m² (Owens–Wendt–Kaelble) and 40.41 mJ/m² (Limitless liquid-solid interface wetting system). Furthermore, this investigation also provided a reference for the applications of empirical and physics-based semi-empirical approaches for the estimation of surface energy.     

Albumin adsorption on oxide thin films studied by spectroscopic ellipsometry

Thin films of tantalum, niobium, zirconium and titanium oxides were deposited by reactive magnetron sputtering and their wettability and surface energy, optical properties, roughness, chemical composition and microstructure were characterized using contact angle measurements, spectroscopic ellipsometry, profilometry, X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The purpose of the work was to correlate the surface properties of the films to the Bovine Serum Albumin (BSA) adsorption, as a first step into the development of an initial in vitro test of the films biocompatibility, based on standardized protein adsorption essays. The films were immersed into BSA solutions with different protein concentrations and protein adsorption was monitored in situ by dynamic ellipsometry; the adsorption-rate was dependent on the solution concentration and the immersion time. The overall BSA adsorption was studied in situ using spectroscopic ellipsometry and it was found to be influenced by the wettability of the films; larger BSA adsorption occurred on the more hydrophobic surface, the ZrO₂ film. On the Ta₂O₅, Nb₂O₅ and TiO₂ films, hydrophilic surfaces, the overall BSA adsorption increased with the surface roughness or the polar component of the surface energy.     

NO_x在Pt及其合金表面吸附的第一性原理模拟研究

本研究通过密度泛函理论(DFT)模拟氮氧化物(NO_X)在Pt及Pt/(Au,Rh)合金slab模型(111)表面的吸附行为,计算其吸附能与结合能.对比NO和NO_2的实验结果,表明合金元素的添加,可能使Pt(111)对NO_X的吸附能力和选择性发生变化,其中Au元素表面置换使得总吸附能力下降,但更容易吸附NO_2; Rh元素表面置换则使得总吸附能力提高,且更容易吸附NO.