On the application of electric fields, the suspensions consisting of polarizable particles dispersed in insulating oils undergo a rapid transition from Newtonian liquids to rigid solids, and this effect is referred to as electrorheology (ER). In electrified suspensions, the dipole-dipole interactions cause chains of particles in the direction parallel to the field vector. The fibrous structures are responsible for the solidlike responses of suspensions. When the dielectric constants of the particles and the oils are substantially different, each particle acquires an induced dipole in electric fields. Basically, the intrinsic mechanism of ER is a dielectric mismatch. However, in actual suspensions, the ER effect is strongly affected by the substances at the particle surface, rather than the particle material itself. The effects of surface conditions on the ER are discussed in relation to the method of formulating excellent ER fluids.
In the field of cosmetics, it is very important to investigate catalytic activities of powders, which may degrade the quality of products, such as foundations, lipsticks, and blushers. Inactivation of the powders is indispensable in the preparation of high quality cosmetics. We have developed a novel method for producing functional powders in a two-step method; (1) chemical vapor deposition (CVD) of tetramethylcyclotetrasiloxane (H-4), and (2) hydrosilylation. After the H-4/CVD process, it was found that the H-4 molecules deposited on powders formed a network structure of polymethylsiloxane (PMS), which seems to have been caused by catalytic activities of the powders, as shown by the following reaction; 2 >Si-H + H2O → >Si-O-Si< + H2 The thickness of PMS film on the powder surface was estimated to be less than 1 nm, which corresponds to a mono- or bimolecular layer. In spite of their small thickness, the catalytic activity of PMS-powders was totally eliminated. In the second step, various functional groups could be added to the PMS film by the following reaction; >Si-H + CH2=CHR → >SiCH2CH2R (R: functional group) Introduction of several different functional groups, for example, alkyl, hydroxyl, and quaternary ammonium groups was attempted, and applied to novel powders for cosmetics and novel columns for high performance liquid chromatography.
Assembly of particles draw much attention because of their potential applications in electronics, photo-optics and biochemical technology fields. Three- and two-dimensionally assembled particles have been studied in wide research fields, and many review papers and books are available. Recently one- and zero dimensionally assembled particles and new patterning methods are reported. However there are few review papers on this assembled particles and the methods. This paper will focus on the process of particles patterning on substrates in the scale range from micron to nano meter. The following five techniques for the patterning processes are reviewed: aerosol gas depositing, ink jet printing, particles assembling on a self-assembled monolayer, particles assembling on an electrified pattern and solidification of particle suspension using a micro-molding. The methods using the aerosol gas depositing and the ink jet printing will be used in industrial fields in near future.
Particle electrification is an inevitable phenomenon in various powder handling processes. Here the contact electrification of particles is discussed and it is revealed that the physical properties as well as the contact potential difference between a particle and the wall have an important role in the particle electrification. In actual processes, particle concentration and equipment size can also affect the electrification. Additional important factors are time constants of charge generation and charge relaxation relating to the contact frequency between particle and wall. Further, a contact potential measuring system developed in our laboratory is discussed showing the effectiveness in the evaluation of functional composite particles.
Surface-modified silica gel was produced to improve the surface affinity to an oily medicine, phytonadione (VK 1). The effect of the degree of surface modification of the silica gel on the drug release behavior from the silica porous matrix was investigated. The silica gel was surface modified using the silan coupling agent, 3-methacryloxypropyl-trimethoxysilane (C 7), octadecyltriethoxysilane (C 18), or 3,3,3-trifluoropropyltrimethoxysilane (F 3). A mixture of VK 1 solution and surface-modified silica gel was evaporated under reduced pressures at room temperature, then the resulting powder was dried in vacuo. The degree of surface modification was evaluated from elementary analysis. The dissolution profiles of the samples were investigated in Japanese Pharmacopoeia XII, 1st fluid buffer (pH 1.2, 37+0.5oC) containing 1.5% sodium lauryl sulfate. The FT-IR spectra of VK 1-loaded surface modified-silica gels suggested that the amount of hydrogen-bonded VK 1 with the silanol group on the gel surface decreased with increasing hydrophobicity of the silica gel. Since the modified group was rotating on the silica gel surface and inhibited the adsorption of VK 1 to the surface, the attractive molecular interaction between VK 1 and the silica gel surface might decrease with increasing length of the modified functional group. However, the characteristics of the affinity of VK 1 to the functional groups significantly differed among the groups. The VK 1 release from the modified silica gels was initially rapid, slowed markedly after 1 h, and continued for more than 24 h. The amount of VK 1 released from the modified surface silica gels by C 7, C 18, or F 3 increased with increasing density of the surface modification group. The mean drug release moment (MDT) decreased with an increase in surface modified group density.
Powders are frequently used in material processings such as synthesis of ceramics. For the control of dispersibility and cohesion it is indispensable to understand the adhesion force between particles. The adhesion force is influenced by the environmental factor to which the powder is exposed and the properties of the particles. In handling powder the surface changes caused by humidity is especially important. In this paper, the influences of humidity and the physico-chemical properties of particle surfaces on the adhesion between particles were reviewed.
This paper is concerned with the mechanisms of various surface-related phenomena on glass and the analytical techniques suitable for the study. As a phenomenon with respect to optical properties of glass surface, the mechanisms of optically dimming phenomenon caused by interaction with the environment, namely weathering resistance of the glass, are explained on the basis of changes in the surface layer composition. Furthermore, as a phenomenon with respect to chemical reactivity of glass surface, factors governing the adsorption property of float glass as the majority of flat glass have been discussed extensively in terms of the surface OH group as an adsorptive site, including the SnOH group originated from tin penetration into the glass during a float process. Additionally, a typical contamination substance on glass surface and a newly developed technique for the removal of them are introduced. In these practical examples, the applications of advanced surface analytical techniques such as SIMS have been mentioned to characterize successfully the glass surface, and it may contribute to the development of highly efficient glass applications.
This paper reviews the factors governing the properties of thin films coated on glass surface, in order to provide newly optical and/or mechanical properties for a normal flat glass. The durability mechanisms of sputtering ZrO2-B2O3 film, that provide mechanical and chemical durabilites for glass, are discussed in terms of surface roughness caused by the presence of crystalline grain and changes in the borate structure. Furthermore, in the case of the ultraviolet (UV) rays shielding glass, performed by the deposition of sol-gel film containing cerium oxide as a UV absorption substance, the factors governing the UV absorption properties are described on the basis of both oxidation and coordination states of the cerium element. Additionally, as an example of the phenomenon related to the sputter deposition process, differences in the structures of the films between reactive and oxide target sputtering methods as a typical deposition technique of metal oxide film are explained by the effects of O− ion implantation into substrate during the deposition. In these practical examples, the applications of advanced surface analytical techniques including XPS have been mentioned to characterize successfully the thin films coated on glass substrates, and this may contribute to the development of highly efficient glass applications.
Nilsson et al. have recently proposed new interpretations of interactions between carbon monoxide and metal surfaces, based on their experimental results with X-ray Emission Spectroscopy (XES) and theoretical ones. The purpose of this article is to introduce the interpretations and to criticize them from our different viewpoint.