The effect of nanoparticles on the surface hydrophobicity of polystyrene

The surface hydrophobicity of polystyrene-nanoparticle nanocomposites has been investigated as a function of the nanoparticle content. The addition of hydrophobically coated nanoparticles in polystyrene increased the contact angle θ of a water drop with respect to that on polystyrene surface due to change of surface composition and/or surface roughness. When the nanoparticles dispersed well in the polymer, cos θ decreased linearly with increasing amount of nanoparticles indicating a composite surface consisting of smooth polystyrene regions and rough nanoparticle regions. In case of formation of nanoparticle aggregates in polystyrene, cos θ decreased sharply at a critical concentration of nanoparticles. The observed behaviour was modeled in terms of a transition from Wenzel regime to Cassie-Baxter regime at a critical roughness length scale below which the Laplace pressure prevented the penetration of the water drop into the surface undulations. We argue that multiple length scales are needed below the critical roughness length scale to increase the contact angle further by decreasing the fraction of surface area of solid material (increasing the fraction of surface area of air) underlying the water drop.     

Measurement of filtration efficiency of Nuclepore filters challenged with polystyrene latex nanoparticles: experiments and modeling

Membrane filtration has been demonstrated to be effective for the removal of liquid-borne nanoparticles (NPs). Such technique can be applied to purify and disinfect drinking water as well as remove NPs in highly pure chemicals used in the industries. This study aims to study the filtration process of a model membrane filter, the Nuclepore filter. Experiments were carried out using standard filtration tools and the nanoparticle tracking analysis (NTA) technique was used to measure particle (50–500 nm) concentration upstream and downstream of the filter to determine the filtration efficiency. The NTA technique has been calibrated using 150-nm polystyrene latex particles to determine its accuracy of particle concentration measurement. Measurements were found reliable within a certain concentration limit (about 10⁸–10¹⁰ particles/cm³), which is dependent on the camera settings during the measurement. Experimental results are comparable with previously published data obtained using the aerosolization method, validating the capability of the NTA technique. The capillary tube model modified from that developed for aerosol filtration was found to be useful to represent the experimental results, when a sticking coefficient of 0.15 is incorporated. This suggests that only 15% of the particle collisions with the filter results in successful attachment. The small sticking coefficient found can be explained by the unfavorable surface interactions between the particles and the filter medium.     

Magnetic properties and heating effect in bacterial magnetic nanoparticles

A suspension of bacterial magnetosomes was investigated with respect to structural and magnetic properties and hyperthermic measurements. The mean particle diameter of about 35 nm was confirmed by transmission electron microscopy (TEM), X-ray and magnetic analysis. The X-ray powder diffraction peaks of magnetosomes fit very well with standard Fe₃O₄ reflections. The found value for specific absorption rate (SAR) of 171 W/g at 5 kA/m and 750 kHz means that magnetosomes may be considered as good materials for the biomedical applications in hyperthermia treatments. Moreover, they have biocompatible phospholipid membrane.     

Mutagenic effect of accelerated heavy ions on bacterial cells

The heavy ion accelerators of the Joint Institute for Nuclear Research were used to study the regularities and mechanisms of formation of different types of mutations in prokaryote cells. The induction of direct (lac⁻, ton B⁻, col B) mutations for Esherichia coli cells and reverse his⁻ → His⁺ mutations of Salmonella typhimurium, Bacillus subtilis cells under the action of radiation in a wide range of linear energy transfer (LET) was studied. The regularities of formation of gene and structural (tonB trp-) mutations for Esherichia coli bacteria under the action of accelerated heavy ions were studied. It was demonstrated that the rate of gene mutations as a function of the dose under the action of Γ rays and accelerated heavy ions is described by linear-quadratic functions. For structural mutations, linear “dose-effect” dependences are typical. The quadratic character of mutagenesis dose curves is determined by the “interaction” of two independent “hitting” events in the course of SOS repair of genetic structures. The conclusion made was that gene mutations under the action of accelerated heavy ions are induced by δ electron regions of charged particle tracks. The methods of SOS chromotest, SOS lux test, and λ prophage induction were used to study the regularities of SOS response of cells under the action of radiations in a wide LET range. The following proposition was substantiated: the molecular basis for formation of gene mutations are cluster single-strand DNA breaks, and that for structural mutations, double-strand DNA breaks. It was found out that the LET dependence of the relative biological efficiency of accelerated ions is described by curves with a local maximum. It was demonstrated that the biological efficiency of ionizing radiations with different physical characteristics on cells with different genotype, estimated by the lethal action, induction of gene and deletion mutations, precision excision of transposons, is determined by the specific features of energy transfer of the radiations that affect the character of induced DNA damage, and the efficiency inducible and constitutive cell repair systems. The growth of relative biological efficiency of heavy charged particles is determined by the growth of the damage yield of the DNA participating in the formation of radiation-induced effects, and higher efficiency of inducible repair systems. It was established that the LET value (L _max) for which the maximum (according to the applied irradiation criteria) coefficients of relative biological efficiency are observed varies depending on the character of the registered radiation induced effect. It was demonstrated that for gene mutations and induction of precision excision of mobile elements the values of L _max are realized in a LET range of ≈20 keV/μm. For lethal effects of irradiation and induction of deletion mutations the value of L _max is ≈ 100 and 50 keV/μm, respectively. The differences in the L _max for the studied radiation gene effectis are determined by the different type of DNA damage participating in the mutation process. A molecular model of the formation of gene mutations in Escherichia coli cells under the action of ionizing radiation was proposed. Basic DNA radiation damage and main repair ways were considered in the framework of this model. The basis is the idea of the decisive role of mutagenic, error-prone, branch of SOS repair in fixing premutation DNA damage into point mutations. It was demonstrated that the central mechanism in this process is the formation of an inducible multi-enzymatic complex including the DNA polymerase V (Umu C), RecA-protease, SSB proteins, subunits of DNA polymerase III, performing erroneous DNA synthesis on the damaged matrix. A mathematical model of induction of gene mutations under ultraviolet cell irradiation was developed based on the molecular model.     

Purification of transfection-grade plasmid DNA from bacterial cells with superparamagnetic nanoparticles

The functionalized magnetic nanobeads were used to develop a rapid protocol for extracting and purifying transfection-grade plasmid DNA from bacterial culture. Nanosized superparamagnetic nanoparticles (Fe₃O₄) were prepared by chemical coprecipitation method using Fe²⁺, Fe³⁺ salt, and ammonium hydroxide under a nitrogen atmosphere. The surface of Fe₃O₄ nanoparticles was modified by coating with the multivalent cationic agent, polyethylenimine (PEI). The PEI-modified magnetic nanobeads were employed to simplify the purification of plasmid DNA from bacterial cells. We demonstrated a useful plasmid, pRSETB-EGFP, encoding the green fluorescent protein with T7 promoter, was amplified in DE3 strain of Escherichia coli. The loaded nanobeads are recovered by magnetically driven separation and regenerated by exposure to the elution buffer with optimal ionic strength (1.25 M) and pH (9.0). Up to approximately 819 μg of high-purity (A₂₆₀/A₂₈₀ ratio=1.86) plasmid DNA was isolated from 100 ml of overnight bacterial culture. The eluted plasmid DNA was used directly for restriction enzyme digestion, bacterial cell transformation and animal cell transfection applications with success. The PEI-modified magnetic nanobead delivers significant time-savings, overall higher yields and better transfection efficiencies compared to anion-exchange and other methods. The results presented in this report show that PEI-modified magnetic nanobeads are suitable for isolation and purification of transfection-grade plasmid DNA.     

Detection of algae and bacterial biofilms formed on titanium surfaces using micro-Raman analysis

Biofouling is one of the major impediments in the use of titanium in sea-water cooled condensers of power plants, which is otherwise an excellent material with respect to corrosion resistance. Raman microscopic experiments were carried out on biofilms grown on titanium surfaces to find out the chemical composition of complex extracellular polymeric substances (EPS) in the biofilm. Though the spectral resolution of normal Raman experiments on these systems was very poor, it was improved when micro-SERS experiments were carried out using mono and bimetallic Ag and Cu colloids. It was observed that spatial distribution of polysaccharides was higher than that of proteins in algae biofilms formed on titanium matrix. Similar experiments were performed on laboratory cultured bacterial films of Pseudomonas aeruginosa. It was evidenced that algal and bacterial biofilms on titanium can be clearly distinguished with the help of Raman mapping coupled with SERS technique using bimetallic Ag/Cu colloids.     

纳米α-Fe/PS复合材料的制备及其热力学性能研究

采用油包水(W/O)的微乳液体系制备了粒度为20~100 nm的α Fe。对纳米Fe进行表面有机改性后分散到苯乙烯（St）单体中,得到分散均匀的Fe/St分散体系,用本体聚合的方法制备了纳米Fe/PS复合材料。利用XRD,TEM,FTIR,SEM及TG DSC分别研究了所得纳米Fe的性能、复合材料的结构、纳米Fe在PS中的分散情况以及掺杂量对纳米Fe/PS复合材料的热力学行为的影响。研究结果表明：增加纳米α-Fe的掺杂量能提高PS的降解率,降低降解温度,增大热分解的焓变。     

纳米α-Fe/PS复合材料的制备及其热力学性能研究

 采用油包水(W/O)的微乳液体系制备了粒度为20~100 nm的α Fe。对纳米Fe进行表面有机改性后分散到苯乙烯（St）单体中,得到分散均匀的Fe/St分散体系,用本体聚合的方法制备了纳米Fe/PS复合材料。利用XRD,TEM,FTIR,SEM及TG DSC分别研究了所得纳米Fe的性能、复合材料的结构、纳米Fe在PS中的分散情况以及掺杂量对纳米Fe/PS复合材料的热力学行为的影响。研究结果表明：增加纳米α-Fe的掺杂量能提高PS的降解率,降低降解温度,增大热分解的焓变。     

Effect of substrate elasticity on evaporation kinetics and evaporative deposition of aqueous polystyrene nanoparticles droplets

Evaporation of aqueous polystyrene(PS) nanoparticles droplets on silicon and polydimethylsiloxane(PDMS) surfaces was studied. Experimental results showed that softer PDMS surfaces yielded a longer constant contact radius(CCR) stage, which could be ascribed to surface deformation of PDMS induced by the vertical component of liquid-vapor interfacial tension. Ringlike depositions of nanoparticles with different crack patterns were found on both silicon and PDMS surfaces. In-situ observation of crack formation showed that nanoparticle movement on the silicon surface was impeded, resulting in radial cracks with periodic distribution. In contrast, nanoparticles were shown to move easily on the PDMS surface. This observation indicated the difference in crack patterns on surfaces could be attributed to the friction force between nanoparticles and the substrate. A large friction force between nanoparticles and the substrate prevented cracks from moving, resulting in a radial crack pattern with periodic distribution, while a small friction force produced multiple large cracks.     

Investigation of β-Ga_2O_3 films and β-Ga_2O_3/GaN heterostructures grown by metal organic chemical vapor deposition

In this work,(-201) β-Ga_2O_3 films are grown on GaN substrate by metal organic chemical vapor deposition(MOCVD). It is revealed that the β-Ga_2O_3 film grown on GaN possesses superior crystal quality, material homogeneity and surface morphology than the results of common heteroepitaxial β-Ga_2O_3 film based on sapphire substrate. Further, the relevance between the crystal quality of epitaxial β-Ga_2O_3 film and the β-Ga_2O_3/GaN interface behavior is investigated. Transmission electron microscopy result indicates that the interface atom refactoring phenomenon is beneficial to relieve the mismatch strain and improve the crystal quality of subsequent β-Ga_2O_3 film. Moreover, the energy band structure of β-Ga_2O_3/GaN heterostructure grown by MOCVD is investigated by X-ray photoelectron spectroscopy and a large conduction band offset of 0.89 eV is obtained. The results in this work not only convincingly demonstrate the advantages of β-Ga_2O_3 films grown on GaN substrate, but also show the great application potential of MOCVD β-Ga_2O_3/GaN heterostructures in microelectronic applications.     

Heterogeneous nucleation and growth of silver nanoparticles on unmodified polystyrene spheres by in situ reduction

The in situ reduction growth of Ag nanoparticles (NPs) on unmodified polystyrene (PS) spheres is investigated via controlling Ag nucleation and growth rates by continuous dripping addition of reductant solution in the absence of surfactants. The sub-micro PS spheres were coated by a uniform coverage of Ag NPs with several shapes like elongated islands, spherical particles, and particle aggregates. The reaction temperature and reductant concentration are demonstrated to influence the crystal structure, distribution, and stability of the Ag NPs on the PS substrates. The heterogeneous nucleation and growth of Ag NPs on PS spheres are found to depend on the inhibition of in-solution reduction and homogeneous nucleation.     

Metal contact effect on the persistent internal polarization in pure and doped polystyrene

Photo-electrets of pure and copperphthalocyanine doped polystrrene films (thickness 20 μm) were formed by UV- radiation in an electric field with Al, Cu, Ni, Zn, Cd and Pb as electrode materials. The depolarization current and the released charge show a strong dependence on the material of the electrode. Two distinct regions in the current decay characteristic indicate that the polarization consists of trapped holes and electrons. The amount of charge injected increases with decreasing work function of the contact metal. Doping increases the stability of the charge.     

Fatigue behavior of polystyrene and effect of mean stress

The behavior of polystyrene under cyclic loading has been investigated. Tests have been run under completely reversed axial stress and also at various superimposed mean stress values. In one series of tests, the alternating stress component was maintained at a value of 2500 psi, while the mean stress was varied, in steps of 500 psi, from 0 to 2500 psi. Over the stress range investigated, the logarithm of the fatigue lifetime was found to decrease linearly with increase of the mean stress component. In a second test series, the peak stress was maintained constant (2500 psi) while the mean stress component and the alternating stress component were both varied. For this set of tests, the specimen fatigue lifetimes increased steadily with increase of mean stress (to 1500 psi) and decrease of alternating stress (to 1000 psi). For higher mean stress values, and therefore lower alternating stress values, there was a rapid rise toward infinite lifetimes. The fracture surfaces of all specimens were examined by scanning electron microscopy. Introduction of tensile mean stress produced significant changes in some aspects of the fatigue fracture process and these changes are described and illustrated. Design implications of the data are discussed.     

Substrate effect on mechanical relaxation of polystyrene in ultrathin films

Mechanical relaxation behavior in ultrathin polystyrene (PS) films supported on silicon oxide (SiO_x) and gold (Au) substrates has been studied by dynamic viscoelastic measurement. Based on the method, effects of free surface and substrate interface on the segmental dynamics were discussed. In the case of thin PS films with a thickness of approximately 200 nm, α_a-relaxation process corresponding to the segmental motion did not show any deviation from the bulk behavior. In contrast, for the films thinner than about 50 nm, the relaxation time distribution for the α_a-process became broader, probably due to a mobility gradient in the surface and interfacial regions. When we sandwiched an ultrathin PS film between SiO_x layers, another relaxation process, in addition to the original α_a-process, appeared at a higher temperature side that we assigned to the interfacial α_a-relaxation process. However, this was never seen for an ultrathin PS film between Au layers, implying that restriction from the substrate interface might be weak in this case.     

Influence of fillers concentration on electrical properties of polystyrene matrix doped by gold nanoparticles and 8HQ

The analysis of the electrical properties of polystyrene films containing gold nanoparticles capped with 1-dodecanethiol and 8-hydroxyquinoline molecules is reported. The conductivity of the nanocomposite as a function of the doping level has been investigated both in planar and stacked configurations. While the former configuration evidenced low field tunneling between nanoparticles in the polymer matrix, stacked devices allowed us to investigate the main phenomena ruling the transport properties when switching effects are present close to critical electric fields. In particular, through the analysis of current-voltage characteristics we studied the charge transport at different fillers concentrations and sketched a physical picture of conductivity in such nanocomposite systems.     

The effect of oxidation on the structure of nickel nanoparticles

The structural properties of nickel nanoparticles which are prepared by means of DC sputtering in argon and subsequently oxidized in ambient air are reported. Ex situ structural and chemical investigations utilizing (high resolution) transmission electron microscopy and electron energy loss spectroscopy reveal that the particles consist of a metallic core surrounded by an oxide shell. The lattice constant of the nickel core is found to increase significantly with decreasing particle size. This widening of the nickel lattice is attributed to an interfacial stress that originates from the lattice mismatch between nickel and nickel oxide. Received 21 December 2000     

Comparing the interparticle coupling effect on sensitivities of silver and gold nanoparticles

The wavelength shift of surface plasmon resonance peak resulting from the electromagnetic coupling noble metal nanoparticle increases with the increase in the dielectric constant of the medium and the decrease in the interparticle separation distance. In this work, the discrete dipole approximation method was used to calculate the extinction efficiency spectra of the silver–silver and gold–gold nanoparticle pairs. This work shows that the silver coupled-particle system has higher plasmon resonance sensitivity as compared to the gold coupled-particle system. However, the silver coupled-particle system has lower and a faster near-exponential decay of sensitivity enhancement factor than the gold coupled-particle system. Thus, the silver coupled-particle may be more suited for sensing applications as compared to the gold coupled-particle, but the interparticle coupling effect displays more pronounced effect on the gold coupled-particle system as compared to the silver coupled-particle system.     

非晶化与量子限域效应

当材料尺度减小到几个纳米时，材料内部电子结构会表现为分立能级，这就是所谓的量子限域效应。通过晶态和非晶Pd纳米颗粒的单电子隧穿实验发现，在晶态Pd颗粒中能观察到量子限域效应，而在同样大小的非晶Pd颗粒中却没有观察到。考虑到有序／无序结构的静态效应并结合电子散射等动态效应，解释了非晶Pd颗粒实验中没有观察到量子限域效应的原因。这一结果表明，尺寸减小并不足以使纳米体系表现量子行为，原子结构有序度对于决定纳米体系表现经典行为或量子行为具有同等重要作用。     

Au nanoparticles in PMMA matrix: In situ synthesis and the effect of Au nanoparticles on PMMA conductivity

Thin PMMA films with and without gold nanoparticles were subjected to ±10 V d.c. and a.c. (square wave) excitations in various frequencies while recording their XPS spectra, and the resulting differences due to charging were examined. Both pure PMMA films and films containing gold nanoparticles showed charging shifts, but those of pure PMMA were more extensive than of PMMA containing gold nanoparticles, suggesting enhanced conductivity, induced by the incorporated gold nanoparticles. Non-charging behavior for these films was also observed with the increase of gold nanoparticle concentration. Gold nanoparticles were in situ synthesized and photo-patterned within the polymer films by UV irradiation.     

Luminescence studies and effect of etching on cerium-doped CaS nanoparticles

Cerium-doped calcium sulphide nanoparticles were synthesized using the solid state diffusion method. The formed nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The XRD pattern confirmed a cubic CaS phase with an average grain size of 53 nm of the formed samples. The TEM image showed non-agglomerated particles with an average size of 60 nm, which is in close agreement with the XRD result. The PL-emission spectrum showed peaks at 506 and 565 nm due to the transition from the excited state to the ground state of Ce³⁺. The effect of etching has been studied on the luminescent properties of CaS:Ce phosphors. With an increase in the etching time there is decrease in the size of the particles, as a result of which the PL spectrum showed a slight blue shift. The UV-visible absorption spectrum also showed a blue shift with an increase in etching time, which is in agreement with the nanosize effect.