Surface modification of gold nanoparticles and their monolayer behavior at the air/water interface

Gold nanoparticles were prepared by two different methods. The first method was chemically grafting the particles with different lengths of alkylthiol (C₆SH, C₁₂SH and C₁₈SH). For the second method, the Au particles were surface modified first by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups which play a role to physically adsorb cationic surfactant in chloroform. This method was termed physical/chemical method. In the first method, the effects of alkyl chain length and dispersion solvent on the monolayer behavior of surface modified gold nanoparticles was evaluated. The gold nanoparticles prepared by 1-hexanthiol demonstrated the narrowest size distribution. Most of them showed narrower particle size distributions in chloroform than in hexane. For the physical/chemical method, the particles can spread more uniformly on the water surface which is attributed to the amphiphilic character of the particles at the air/water interface. However, the particles cannot pack closely due to the relatively weak particle-particle interaction. The effect of alkyl chain length was also assessed for the second method.     

Surface diffusion of k-mers in one-dimensional systems

The surface diffusion of interacting k-mers is studied both through analytical and Monte Carlo simulation methods in one-dimensional systems. Adsorption isotherms, jump diffusion coefficients and collective diffusion coefficients are obtained for attractive and repulsive k-mers, showing a variety of behaviors as a function of the size of particles, k. The following main results are found: (a) diffusion coefficients increase with k for non-interacting particles; (b) for fixed k, diffusion coefficients increase as the interaction energy increases from negative (attractive) to positive (repulsive) values; (c) for attractive interactions diffusion coefficients increase with k in the whole range of coverage; (d) for repulsive interactions diffusion coefficients decrease with k up to moderately high coverage and increase with k at high coverage. Results are rationalized in terms of the behavior of the vacancy probability distribution.     

Addition of surfactants in ozonated water cleaning for the suppression of functional group formation and particle adhesion on the SiO2 surface

Various kinds of surfactants were added to a cleaning solution and deionized (DI) water, and their effect on the suppression of organic function group formation and particle adhesion to a SiO₂ surface was analyzed using multi-internal reflection Fourier transform infrared spectroscopy. The results implied that attached organic functional groups are affected by the chemical structure of a surfactant in DI water. Furthermore, the addition of anionic glycolic acid ethoxylate 4-tert-butylphenyl ether (GAE4E) is the most effective in terms of preventing organic group attachment and particle adhesion to the SiO₂ surface, whether it was added to the cleaning solution or post-cleaning rinse water, with or without polystyrene latex particles. Moreover, it was possible to completely prevent particle adhesion to the SiO₂ surface with the proper addition of GAE4E in DIO₃ solution.     

Surface adhesion properties of graphene and graphene oxide studied by colloid-probe atomic force microscopy

Surface adhesion properties are important to various applications of graphene-based materials. Atomic force microscopy is powerful to study the adhesion properties of samples by measuring the forces on the colloidal sphere tip as it approaches and retracts from the surface. In this paper we have measured the adhesion force between the colloid probe and the surface of graphene (graphene oxide) nanosheet. The results revealed that the adhesion force on graphene and graphene oxide surface were 66.3 and 170.6 nN, respectively. It was found the adhesion force was mainly determined by the water meniscus, which was related to the surface contact angle of samples.     

Brownian dynamics simulations of a cubic haematite particle suspension with a more effective treatment of steric layer interactions

We have proposed a new repulsive layer model for describing the interaction between steric layers of coated cubic particles. This approach is an effective technique applicable to particle-based simulations such as a Brownian dynamics simulation of a suspension composed of cubic particles. 3D Brownian dynamics simulations employing this repulsive interaction model have been performed in order to investigate the equilibrium aggregate structures of a suspension composed of cubic haematite particles. It has been verified that Brownian dynamics employing the present steric interaction model are in good agreement with Monte Carlo results with respect to particle aggregate structures and particle orientational characteristics. From the viewpoint of developing a surface modification technology, we have also investigated a regime change in the aggregate structure of cubic particle in a quasi-2D system by means of Brownian dynamics simulations. If the magnetic particle–particle interaction strength is relatively strong, in zero applied magnetic field the particles aggregate in an offset face-to-face configuration. As the magnetic field strength is increased, the offset face-to-face structure is transformed into a more direct face-to-face contact configuration that extends throughout the whole simulation region.     

Influence of surface affinity of planar walls on effective interaction between the wall and colloids

Using density functional theory, we investigate the effective interaction between a big colloid immersed in a sea of small colloids and a wall which has different affinity to the small colloids. Steele 10-4-3 potential is introduced to mimic both short-range repulsive and long-range attractive interactions between the wall and the small colloids. It is found that the surface affinity of the wall has a significant influence on the effective interaction. In the short-range repulsive case, the repulsion greatly enhances the big colloid-wall effective attraction, which sensitively depends on the concentration of small colloids, and is not sensitive to the repulsive strength. In the long-range attractive case, both the concentration of small colloids and the attractive strength have great effect on the effective interaction, and with an increase of the attractive strength, a strong repulsion may be induced when the big colloid is close to the wall. In low density limit of small colloids, the present results agree well with those of the Asakura and Oosawa(AO) approximation.     

Rare gas coadsorption with Cs or K on Ag(111)

Rare gas (RG) coadsorption with submonolayer amounts of Cs or K on Ag(111) was studied using low-energy electron diffraction (LEED). A crossover in the alkali-RG interaction from repulsive to attractive was observed as a function of alkali species and of alkali coverage. The K---RG interaction was observed to be repulsive at all coverages, while the Cs---RG interaction was observed to be attractive at low Cs coverages and apparently repulsive at high Cs coverages. For the K + RG adsorption system, desorption data were analyzed to determine the spreading pressure in the alkali layer, thus showing that RG can be used as a 2D manometer in some coadsorption systems. From the spreading pressure it is possible to obtain some information about the properties of the adsorbed alkali such as the energy differences between commensurate and incommensurate phases. We also demonstrate that work function measurements from such coadsorption systems do not necessarily have a simple interpretation.     

The water-silicas interfacial interaction energies

The water-silicas interfacial interaction energies were calculated for samples of quartz, silicas and silicas outgassed at high temperatures using own and published data of the spreading pressure of water, its surface tension, its contact angle and using formulas obtained by the combination of the Young equation with a general equation of pair interaction. The values obtained for 18 different samples were in the range 7.80-6.92 kJ mol⁻¹. Lower values of energies are for samples that contain relatively less amounts of water at P/P₀ = 0.25 and are characterized also by relatively low values of surface pressures.     

Adsorption and co-adsorption of CH<Subscript>3</Subscript> and H on flat and defective nickel (111) surfaces

We use a periodic density functional theory (DFT) code to study the adsorption of CH₃ and H, as well as their co-adsorption on a Ni(111) surface with and without Ni ad-atom, at a surface coverage of 0.25 monolayer (ML). We systematically investigate the site preference for CH₃ and H. Then we combine CH₃ and H in many co-adsorbed configurations on both surfaces. Methyl and hydrogen adsorption on a flat Ni(111) surface favours the hollow site over the top site. The presence of a Ni ad-atom stabilizes the adsorption of CH₃ better than a flat surface, while hydrogen is more stable on a flat Ni(111) surface. When H and CH₃ are co-adsorbed at nearest Ni neighbours on the (111) surface, their interaction is always repulsive. However, the dissociative adsorption of CH₄ is stabilised when the fragments are infinitely separated. For the co-adsorbed fragments CH₃ and H, in the presence of an ad-atom, the repulsive interaction is lowered, so that the dissociative form of CH₄ is locally stable.     

Surface tailoring of SiO2 nanoparticles by mechanochemical method based on simple milling

An appropriate modifying agent is obviously important with regard to the surface treatment of nanoparticles. Moreover, a right physical mixer that can provide enough energy to break up the secondary structure (aggregate and agglomerate) of nanoparticles is absolutely critical to the modification as well. However, it is not easy to give consideration to both of them during the process of modification. As is often the case, we tend to take care of the modifying agent but lose sight of the physical mixer. In this paper, hybrid particles of SiO₂/2,4-Diisocyanatotoluene (SiO₂/TDI) and SiO₂/2,4-Diisocyanatotoluene/hydroxyl silicone oil (SiO₂/TDI/(PDMS-OH)) were fabricated by mechanochemical method based on simple milling. The prepared hybrid particles (SiO₂/TDI and SiO₂/TDI/(PDMS-OH)) were characterized by infrared spectroscopy (FT-IR), static contact angle (CA), water sorption measurement, thermal analysis (TGA and DSC) and transmission electron microscopy (TEM). FT-IR spectra and thermal analysis (DSC) results demonstrate that TDI together with PDMS-OH is chemically anchored to the surface of nano-SiO₂. TGA results show that the grafting density of TDI is as high as 2.62 TDI/nm², while the grafting density of PDMS-OH is 0.0156 PDMS-OH/nm². Deduced from static contact angle (CA) and water sorption measurement, both hybrid particles exhibit strong hydrophobic (140^o for SiO₂/TDI and 144^o for SiO₂/TDI/(PDMS-OH)) after modification. TEM images reveal that hybrid particles (SiO₂/TDI and SiO₂/TDI/(PDMS-OH)) prepared by ball milling method exhibit much better miscibility and dispersibility in PDMS matrix when compared with those particles prepared by a common mixing device.     

Particles movement and surface quality in PLD/PR systems

A three-dimensional model based on Monte-Carlo and Finite Elements techniques has been used for simulating plume behavior, ‘micron-sized particles’ movement and interaction with obstacles in a Pulsed Laser Deposition with Plasma Reflection (PLD/PR) system. Have been investigated the influences of mass, surface size and emission time on trajectory and film surface quality as well. Droplet and ‘big-size particles’ deposition statistics are presented and a comparison between theoretical and experimental results upon thin film surface quality as well. One can observe that particles mass and surface size have a strong influence on the particles trajectory by affecting the collisions parameters during the entire propagation process. The emission time should influence the particles trajectory by affecting the probability of interaction with other particles. By making a 10,000 particles statistic for a normal distribution of these investigated parameters, we obtain reasonable good results in modeling ‘big-size particles’ tendency to be deposited at lower reflection angles. These results sustain assumption of ‘big particles’ deflection by plume fine particles during the propagation process.     

Effective interactions of colloids on nematic films

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations d. The elastic interaction is repulsive and of quadrupolar type, varying as d^-5. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to d^-5 as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern formation of colloidal droplets on nematic films.     

A study on the distribution of adsorbed nanoparticles

We use Monte Carlo simulation to calculate the distributions of particles under adsorption force near planar and cylindrical surfaces,respectively.Both hard sphere interaction and repulsive Yukawa (screened coulomb) interaction are employed in our simulations.We study the influence of the inter-particle potentials.The difference between the MC simulation results and the analytical results of ideal gas model shows that the interaction between particles plays an important role in the density distribution under external fields.Moreover,the 2-dimensional constructions of particles close to the surface are studied and show relations of the interaction between particles.These results may indicate us how to improve the methods of building nanoparticle coatings and nano-scale patterns.     

A study on the distribution of adsorbed nanoparticles

We use Monte Carlo simulation to calculate the distributions of particles under adsorption force near planar and cylindrical surfaces, respectively. Both hard sphere interaction and repulsive Yukawa (screened coulomb) interaction are employed in our simulations. We study the influence of the inter-particle potentials. The difference between the MC simulation results and the analytical results of ideal gas model shows that the interaction between particles plays an important role in the density distribution under external fields. Moreover, the 2-dimensional constructions of particles close to the surface are studied and show relations of the interaction between particles. These results may indicate us how to improve the methods of building nanoparticle coatings and nano-scale patterns.     

Behavior of Ru surfaces after ozonated water treatment

In order for the development of cleaning technology of extreme ultra violet lithography photomask, the behavior of Ru surfaces after treatment with ozonated deionized water (DIO₃) solution was studied using Ru and ruthenium oxide particles and 2 nm-thick Ru capping layers. No significant changes in crystalline structures or chemical states of the Ru surfaces, nor any similarities with the structures or states of ruthenium oxide, were observed after DIO₃ treatment. Oxidation of ruthenium to form RuO₂ or RuO₃ was not observed. Adsorption of H₂O molecules on the Ru layer increased the surface roughness, but the desorption of H₂O molecules recovered it. Local chemisorption of H₂O molecules on the Ru surface may be the reason why rougher Ru surfaces were observed after DIO₃ cleaning.     

对利用动态光散射法测量颗粒粒径和液体黏度的改进

光散射技术通过测量悬浮液中布朗运动颗粒的平移扩散系数,得到颗粒流体力学直径或液体黏度.本文由单参数模型入手,建立了低颗粒浓度下,单颗粒平移扩散系数与颗粒集体平移扩散系数和颗粒浓度之间的线性依存关系并将其引入光散射法中,从而对现有的测量方法进行了改进.改进后的测量方法可实现纳米尺度球型颗粒标称直径的测量和液体黏度的绝对法测量.以聚苯乙烯颗粒+水和二氧化硅颗粒+乙醇两个分散系为参考样本,通过实验,验证了改进后方法的可行性.此外,还针对上述两个分散系,实验探讨了温度和颗粒浓度对颗粒集体平移扩散系数的影响规律,发现聚苯乙烯颗粒+水分散系中,颗粒间相互作用表现为引力;二氧化硅颗粒+乙醇分散系中,颗粒间相互作用表现为斥力.讨论了颗粒集体平移扩散系数随颗粒浓度变化规律与第二渗透维里系数的关系.     

Dynamic corrections to the image force

The electrical interaction of a non-relativistic point particle (charge, dipole) with a flat metal surface has been studied in the case of lateral particle motion in vacuum with a constant velocity. A new representation of attractive and friction forces has been obtained in the in the continuous medium model for metals. For fast particles moving close enough to the surface, the repulsive interaction has been detected in the Drude model.     

Bacterial adhesion on ion-implanted stainless steel surfaces

Stainless steel disks were implanted with N⁺, O⁺ and SiF₃⁺, respectively at the Surrey Ion Beam Centre. The surface properties of the implanted surfaces were analyzed, including surface chemical composition, surface topography, surface roughness and surface free energy. Bacterial adhesion of Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus, which frequently cause medical device-associated infections was evaluated under static condition and laminar flow condition. The effect of contact time, growth media and surface properties of the ion-implanted steels on bacterial adhesion was investigated. The experimental results showed that SiF₃⁺-implanted stainless steel performed much better than N⁺-implanted steel, O⁺-implanted steel and untreated stainless steel control on reducing bacterial attachment under identical experimental conditions.     

An ab initio study of SiH2 fragments on the Si(001) surface

Density functional theory calculations have been performed to find the minimum energy adsorption configuration for SiH₂ on the Si(001) surface. Of the four sites considered, the two most stable are found to differ in adsorption energy by less than 0.01 eV. The energy of a second adsorption event on an adjacent site has been evaluated for the two favourable structures; in one case a strong repulsive interaction is found between the adsorbates, effectively preventing this structure from contributing to the growth mechanism. Recent experimental studies are assessed in the light of these results.     

Dispersion of Nano TiO2 in Ethylene Glycol and Poly(ethylene terephthalate)

Nano TiO₂ was dispersed in ethylene glycol (EG) by the replacement of dispersion medium from water sol. EG/TiO₂ suspension was well stabilized by the electrostatic repulsive force when pH value of suspension was less than 4.3. In situ polymerization starting from bis(2-hydroxyethyl) terephthalate (BHET) and EG/TiO₂ suspension was carried out to prepare a series of poly(ethylene terephthalate) (PET)/TiO₂ nanocomposites. Under highly acidic conditions, 97% particles dispersed in PET matrix had the size less than 100 nm. With the increase of pH value, aggregation occurred and larger size particles appeared. A tensile test showed that Young's modulus of PET was increased by the addition of nano TiO₂