Papers by Keyword: Colloid

Abstract: Colloids composed of liquid-crystal hydrosols exhibit a rich set of interesting phenomena. The coupling between liquid-crystalline media and colloidal particles plays an essential role leading to an abundant source of new physics. In the last few years, peculiar behaviors of carbon-nanotube-doped calamitic liquid crystals have attracted considerable attention. This paper provides a brief introduction to this alluring subject for its on-going research development in this laboratory. First presented are our current understandings of the nematic colloidal system comprising carbon nanotubes and of their possible orientation and dynamics under the application of an external field. Various electro-optical and electrical properties of a liquid-crystal display rectified by the nanoscale carbonaceous guest are then addressed to a larger extent. Dielectric relaxation obtained from a nematic impregnated with carbon nanotubes is also discussed. With historical significance for the dawn of the liquid-crystal–carbon-nanotube research, several important findings of enhanced nonlinear optical properties in typical nematic mesomaterials consisting of suspended nanotubes are delineated. With the new colloidal systems of elongated nanoscale solids dispersed in anisotropic fluids in the mesophase, many new intriguing phenomena are awaiting theoretical and experimental explorations. Collaborations are called to draw attention of interested theoretical physicists, in particular.

Abstract: This study was triggered by our experience on electrophoretic deposition (EPD) with different suspension systems showing evidence of a particle concentration threshold, below which no deposit was formed. In this study, the role of particle concentration in the mechanism of EPD was investigated with a model system, consisting of isopropanol suspensions with TiO2 nanosized particles (d50 = 130 nm). The investigated concentration range was 0.01 - 0.4 vol% TiO2. Constant voltage EPD tests with variable particle concentration were performed for 1 min under different applied voltages (25 - 300 V corresponding to 62.5 - 750 V/cm). A longer deposition time (30 min) was tested for a lower concentration value (0.003 vol% TiO2). The deposition process was evaluated in situ by means of the current measured during EPD. The deposits obtained were characterized by weight and profile measurements and scanning electron microscope (SEM). The results confirmed the finding of a lower limit value of particle concentration, determining a threshold in the formation of an EPD coating. Above this threshold, proportionality between deposited mass and particle concentration was observed, in agreement with the equation of Hamaker. Below this threshold, the proportionality was lost with evidence of a lack of coating formation. A possible interpretation for this experimental finding was provided.

Abstract: For producing ultra smooth surface, a nanoparticle colloid jet machining system has been designed and manufactured in which a reversible polymerize and decompose reaction is utilized to remove surface atoms. The material removal characteristics of nanoparticle colloid jet machining were analyzed. A series of removal experiments were conducted to show the characteristics of the material removal in nanoparticle colloid jet machining. A K9 glass sample had been polished by using the nanoparticle colloid jet machining system, and an ultra smooth surface with micro roughness less than 1 nm RMS had been obtained. The experimental results prove that it is suitable to fabricate ultra smooth surface with nanoparticle colloid jet machining.

Abstract: Spherical submicrometer-sized silica particles were prepared from a reaction mixture containing tetraethoxysilane, ammonia and ethanol, and deposited onto silicon wafers. The properties of these SiO2 particles depend on their size, size distribution and shape. Even if some of these characteristics can be perfectly controlled by appropriate synthesis conditions, several alternative approaches must be explored in order to modify the shape of silica particles. The samples were then irradiated at room temperature with Si ions at different energies (4, 6 and 8 MeV) and fluences up to 5×1015 Si/cm2, at an angle of 45° with respect to the sample surface. After the Si irradiation the spherical silica particles turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and a decrease in the parallel direction. This effect increases with the ion fluence and depends on the electronic energy loss of the impinging ions. We observed that the particle deformation decreases with the beam energy, mainly because our samples were irradiated at room temperature. Thermal effects must be studied in detail in order to elucidate the complete deformation mechanism, as the existence of additional mechanisms related to the electronic energy loss effects can not be excluded.

Abstract: A nanoparticle colloid jet machining system has been developed for polishing ultra smooth surface of brittle materials. Interaction between nanoparticles and work surface in nanoparticle colloid jet machining has been given, and the theoretical dependence of the material removal rate with various important process parameters of the nanoparticle colloid jet machining have been investigated through material removal experiments. Some material removal results of nanoparticle colloid jet machining show that it is possible to obtain removal rates of one nanometer level per minute for glass surfaces with appropriate machining process parameters. A K9 glass surface was polished for obtaining ultra smooth surface. The surface roughness value of atomic force microscopy (AFM) observations is under 1nm Rms.

Abstract: This paper presents on a new damping element called the colloidal damper which is used a principle of surface extension force in nano pore. The direction acting of the surface extension force of water in hydrophobic nano pore is different in pressurization and decompressurization processes [1,2]. This principle is applied to a damping element. The nano pore is constructed by silica gel. A silica gel ball of 100-200 micrometer dia. has many nano pores of 5-20 nanometer dia. in it [3,4]. The coated spherical silica gel and water are inserted in a piston - cylinder unit in order to work as a damper. If compression and decompression forces are added to the piston - cylinder unit (damper), water flows into and moves out the nano pore under balance of pressure. A contact angle of compression formed by the hydrophobic nano pore and water is larger than that of decompression. This difference of the contact angle produces a damping energy. In this paper, behavior of water in the pore of silica gel is investigated using the molecular dynamics. Dissipation energy of the colloidal damper is concerned with the contact angles of water in the pore. So the contact angles are calculated for changing parameters, i.e. size of the pore, length of the hydrophobic material, velocity (pressure) of water flows into the pore. Then these results are compared with the experimental ones.

Abstract: The synthesis of fluorescent nanocrystals is receiving a lot of attention for potential application in biological labeling as well as phosphors for field emission devices. Zinc sulphide doped with manganese (ZnS:Mn2+) is one of the most efficient electroluminescent phosphor displaying a wide emission band centred around 590 nm resulting from the intra-ionic transition in Mn2+ ions. We report a unique synthesis of zinc sulphide nanoparticles doped with manganese using a biocompatible passivating agent ‘chitosan’, with bright luminescence peaking at 590 nm. This high luminescence efficiency of the synthesized nanocrystals are ideal for quantum dot based bio-labeling applications. Synthesis of the nanoparticles was carried out by precipitation reaction in aqueous media of zinc acetate and sodium sulphide where manganese acetate was added as the dopant. The obtained nanoparticles were around 4 to 6 nm in size and were found to be stable for months of shelf life. The photoluminescence intensity did not degrade when the colloid was heated up to 65 oC for prolonged periods.

Abstract: We developed a nanoparticle colloid jet machining to fulfill the requirement for ultrasmooth surface in terms of the studying on micro structure of work surface, the high surface energy and intense adsorption of SiO2 nanoparticle. In this paper, three types impact in nanoparticle colloid jet machining have been analysed and the atom removing model has been founded based on the physical chemistry theory of solid surface and interface. The factors which may influence the nanoparticle colloid jet machining quality (such as the diameter of nanoparticle, colloid jet velocity and dynamical viscidity) have been studied to provide theoretical support for further studying in nanoparticle colloid jet machining.

Abstract: We address the problem of measuring the refractive index of biological materials. We limit our analysis to the case of colloids and consider the use of common automatic critical-angle refractometers to measure their effective refractive index. We provide rough guidelines to when these refractometers will incur in large errors and alternative techniques should be used.

Abstract: Nano-scale BN-C-silicone oil composite colloid was prepared in a planetary ball mill by using wet grinding techniques. Frictional experiments with GCr15 and 35CrMo as frictional pairs were then conducted under a wide range of temperature (from ambient temperature to 300°C) on a pin-plate friction and wear tester. Results show that lubricating properties of the colloid were improved significantly. In particular, the frictional coefficient of the colloid is lower than that of the pure silicone oil at both ambient temperature and high temperature. For example, at ambient temperature, the frictional coefficients ( f ) of the BN-C-silicone oil composite colloid and pure silicone oil are about 0.05 and 0.18, respectively; while at 300°C, the f value of the BN-C-silicone oil composite colloid and pure silicone oil are about 0.13 and 0.36, respectively. The characteristic of the worn surface film was also investigated by using SEM. SEM images show that on the worn surface, the concave zone is filled with some nano BN-C particles; while the rest of the particles are dispersed in the surface film. Therefore, BN-C particles may repair the worn surface, which tend to improve the boundary lubricity of the silicone oil. Finally, based on the model proposed by T.A.Stolarski, the rupture ratio of the lubricating film was discussed to address why BN-C-silicone oil composite colloid has relatively lower frictional coefficient even at high temperature.