Theory of electrostatics and electrokinetics of soft particles

Abstract

We investigate theoretically the electrostatics and electrokinetics of a soft particle, i.e. a hard particle covered with an ion-penetrable surface layer of polyelectrolytes. The electric properties of soft particles in an electrolyte solution, which differ from those of hard particles, are essentially determined by the Donnan potential in the surface layer. In particular, the Donnan potential plays an essential role in the electrostatics and electrokinetics of soft particles. Furthermore, the concept of zeta potential, which is important in the electrokinetics of hard particles, loses its physical meaning in the electrokinetics of soft particles. In this review, we discuss the potential distribution around a soft particle, the electrostatic interaction between two soft particles, and the motion of a soft particle in an electric field.     

Recent progress on magnetic iron oxide nanoparticles: synthesis,surface functional strategies and biomedical applications

Abstract

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.     

Oxide-based inorganic/organic and nanoporous spherical particles: synthesis and functional properties

Abstract

This paper reviews the recent progress in the preparation of oxide-based and heteroatom-doped particles. Surfactant-templated oxide particles, e.g. silica and titania, are possible candidates for various potential applications such as adsorbents, photocatalysts, and optoelectronic and biological materials. We highlight nanoporous oxides of one element, such as silicon or titanium, and those containing multiple elements, which exhibit properties that are not achieved with individual components. Although the multicomponent nanoporous oxides possess a number of attractive functions, the origin of their properties is hard to determine due to compositional/structural complexity. Particles with a well-defined size and shape are keys for a quantitative and detailed discussion on the unique complex properties of the particles. From this viewpoint, we review the synthesis techniques of the oxide particles, which are functionalized with organic molecules or doped with heteroatoms, the physicochemical properties of the particles and the possibilities for their photofunctional applications as complex systems.     

DISPLACEMENT OF PARTICLES DEPOSITED ON SOLID SURFACES BY A MOVING GAS-LIQUID-SOLID INTERFACE

ABSTRACT

Deposited small particles change their position and can build aggregates on surfaces when wetted/dewetted. The size and form of these aggregates depend on the amount of water condensed, the form of the particles and the contact angles. Experiments with glass spheres and quartz particles on three different surfaces with water as wetting liquid were carried out. Results of the wetting/dewetting experiments are shown and discussed. A model is presented to estimate the magnitude of involved forces and the displacement of the particles taking into account contact angles, amount of condensed water, and size of particles. The model explains, why particles, as observed, tend to gather near the edge of a droplet at small surface contact angles and near the droplet center at high surface contact angles.     

Fabrication of superhydrophobic surfaces for corrosion protection: a review

ABSTRACT

Steel, aluminium and magnesium are important engineering materials owing to their excellent mechanical properties. However, their applications are limited due to inadequate corrosion resistance. Various coatings and improvement technologies are used to enhance the corrosion resistance in industry and consumer products. Fabrication of hydrophobic surfaces is a very interesting approach to anticorrosion in that it is derived from the superhydrophobicity found in nature. This paper is a general review of the methods to construct a superhydrophobic surface, i.e. a thin coating layer, on various metallic materials surfaces to enhance their anticorrosion property, providing an introduction of the superhydrophobicity, including theory, properties and fabricating methods. Different methods including spray technique, laser ablation, electrochemical deposition, micro-arc oxidation and etching routes were discussed.     

Theory of electrostatics and electrokinetics of soft particles

We investigate theoretically the electrostatics and electrokinetics of a soft particle, i.e. a hard particle covered with an ion-penetrable surface layer of polyelectrolytes. The electric properties of soft particles in an electrolyte solution, which differ from those of hard particles, are essentially determined by the Donnan potential in the surface layer. In particular, the Donnan potential plays an essential role in the electrostatics and electrokinetics of soft particles. Furthermore, the concept of zeta potential, which is important in the electrokinetics of hard particles, loses its physical meaning in the electrokinetics of soft particles. In this review, we discuss the potential distribution around a soft particle, the electrostatic interaction between two soft particles, and the motion of a soft particle in an electric field.     

Dye adsorption behavior of anatase- and rutile-type TiO2 nanoparticles modified by various heat-treatments

TiO₂ colloidal particles with a fixed crystalline phase of anatase or rutile were heat-treated under different conditions (air-heating and hydrothermal-heating) to modify their surface characters which essentially affected the adsorption behavior of a Ru-complex dye on the surfaces. Changes in the number of surface OH group (N _(OH)), apparent crystallite size, pore structure were evaluated as a function of heat-treatment conditions for various TiO₂ nanoparticles. The amount of a Ru-complex dye adsorbed (N _(dye)) was correlated to those surface properties of TiO₂ samples. N _(dye) values tended to increase with increasing crystallinity for only the anatase-type TiO₂ particles. However, there was no simple, common relationship between N _(dye) and N _(OH) for all the TiO₂ nanoparticles examined. Considerable difference in N _(dye) values obtained in different nanoparticles might be explained on the basis of the surface pore structures of those particles.     

<Emphasis Type="Italic">Streptococcus sanguinis</Emphasis> adhesion on titanium rough surfaces: effect of shot-blasting particles

Dental implant failure is commonly associated to dental plaque formation. This problem starts with bacterial colonization on implant surface upon implantation. Early colonizers (such as Streptococcus sanguinis) play a key role on that process, because they attach directly to the surface and facilitate adhesion of later colonizers. Surface treatments have been focused to improve osseointegration, where shot-blasting is one of the most used. However the effects on bacterial adhesion on that sort of surfaces have not been elucidated at all. A methodological procedure to test bacterial adherence to titanium shot-blasted surfaces (alumina and silicon carbide) by quantifying bacterial detached cells per area unit, was performed. In parallel, the surface properties of samples (i.e., roughness and surface energy), were analyzed in order to assess the relationship between surface treatment and bacterial adhesion. Rather than roughness, surface energy correlated to physicochemical properties of shot-blasted particles appears as critical factors for S. sanguinis adherence to titanium surfaces.     

Evaluation of Surface and Bulk Characteristics of Cellulose I Powders in Relation to Compaction Behavior and Tablet Properties

Abstract

The particle properties and solid-state characteristics of two celluloses, Avicel PH101 and cellulose obtained from the alga Cladophora sp., were evaluated and related to the compaction behavior and the properties of the tablets made from them. The surface area of the celluloses was measured at different levels of penetration capacity, ranging from external surface area of particles to molecular texture with Blaine permeametry, Kr-gasadsorption, and solid-state NMR. The important cellulose fibril surface area was best reflected by solid-state NMR, although for the Cladophora cellulose, Kr-gas adsorption also resulted in a surface area of the order of what has been suggested earlier on the basis of the cellulose fibril dimensions. The difference in fibril dimension and, thereby, the fibril surface area of the two celluloses was shown to be the primary factor in determining their properties and behavior. Properties such as the crystallinity and the tablet disintegration could be related to the fibril dimensions. The Cladophora cellulose resulted in rather strong compacts that still disintegrated rapidly. The irregular surface morphology of the particles and the fragmenting behavior of Cladophora probably contributed to the strength of the tablets.     

The biological seal of the implant–soft tissue interface evaluated in a tissue-engineered oral mucosal model

For dental implants, it is vital that an initial soft tissue seal is achieved as this helps to stabilize and preserve the peri-implant tissues during the restorative stages following placement. The study of the implant–soft tissue interface is usually undertaken in animal models. We have developed an in vitro three-dimensional tissue-engineered oral mucosal model (3D OMM), which lends itself to the study of the implant–soft tissue interface as it has been shown that cells from the three-dimensional OMM attach onto titanium (Ti) surfaces forming a biological seal (BS). This study compares the quality of the BS achieved using the three-dimensional OMM for four types of Ti surfaces: polished, machined, sandblasted and anodized (TiUnite). The BS was evaluated quantitatively by permeability and cell attachment tests. Tritiated water (HTO) was used as the tracing agent for the permeability test. At the end of the permeability test, the Ti discs were removed from the three-dimensional OMM and an Alamar Blue assay was used for the measurement of residual cells attached to the Ti discs. The penetration of the HTO through the BS for the four types of Ti surfaces was not significantly different, and there was no significant difference in the viability of residual cells that attached to the Ti surfaces. The BS of the tissue-engineered oral mucosa around the four types of Ti surface topographies was not significantly different.     

Chemical stabilization of porous silicon for enhanced biofunctionalization with immunoglobulin

Abstract

Porous silicon (PSi) is widely used in biological experiments, owing to its biocompatibility and well-established fabrication methods that allow tailoring its surface. Nevertheless, there are some unresolved issues such as deciding whether the stabilization of PSi is necessary for its biological applications and evaluating the effects of PSi stabilization on the surface biofunctionalization with proteins. In this work we demonstrate that non-stabilized PSi is prone to detachment owing to the stress induced upon biomolecular adsorption. Biofunctionalized non-stabilized PSi loses the interference properties characteristic of a thin film, and groove-like structures resulting from a final layer collapse were observed by scanning electron microscopy. Likewise, direct PSi derivatization with 3-aminopropyl-triethoxysilane (APTS) does not stabilize PSi against immunoglobulin biofunctionalization. To overcome this problem, we developed a simple chemical process of stabilizing PSi (CoxPSi) for biological applications, which has several advantages over thermal stabilization (ToxPSi). The process consists of chemical oxidation in H₂O₂, surface derivatization with APTS and a curing step at 120 °C. This process offers integral homogeneous PSi morphology, hydrophilic surface termination (contact angle θ = 26°) and highly efficient derivatized and biofunctionalized PSi surfaces (six times more efficient than ToxPSi). All these features are highly desirable for biological applications, such as biosensing, where our results can be used for the design and optimization of the biomolecular immobilization cascade on PSi surfaces.     

Modelling optical properties of soft tissue by fractal distribution of scatterers

Abstract

A knowledge of the local refractive index variations and size distribution of scatterers in biological tissue is required to understand the physical processes involved in light-tissue interaction. This paper describes a method for modelling the complicated soft tissue, based on the fractal approach, permitting numerical evaluation of the phase functions and four optical properties of tissue—scattering coefficient, reduced scattering coefficient, backscatter-ing coefficient, and anisotropy factor—by the use of the Mie scattering theory. A key assumption of the model is that refractive index variations caused by microscopic tissue elements can be treated as particles with size distribution according to the power law. The model parameters, such as refractive index, incident wavelength, and fractal dimension, that are likely to affect the predictions of optical properties are investigated. The results suggest that the fractal dimension used to describe how biological tissue can be approximated by particle distribution is highly dependent on how the continuous distribution is discretized. The optical properties of the tissue significantly depend on the refractive index of tissue, implying that the refractive index of the particles should be carefully chosen in the model in order accurately to predict the optical properties of the tissue concerned.     

Appropriate selection of an aggregation inhibitor of fine particles used for inhalation prepared by emulsion solvent diffusion

Abstract

Context: Dry powder inhaler (DPI) formulations have been developed to deliver large amounts of drugs to the lungs.

Objective: Fine particles of a poorly water-soluble drug, the model drug ONO-2921, were prepared by the emulsion solvent diffusion (ESD) method for use in a DPI.

Methods: The effects of additives on the fine particle formation of ONO-2921 were estimated when droplets of an ethanolic drug solution were dispersed into aqueous media containing various additives. Subsequently, the suspensions were freeze-dried to create powdered samples to estimate the inhalation properties using a twin impinger and an Andersen cascade impactor.

Results: This simple ESD method produced submicron-sized ONO-2921 particles (approximately 600?nm) in combination with suitable additives. In addition, the freeze-dried powder produced using additives exhibited superior in vitro inhalation properties. Among these methods, the freeze-dried powder produced with 0.50% weight/volume one type of polyvinyl alcohol (PVA-205) displayed the most efficient features in the fine particle fraction (FPF). These results could be explained by the stabilization of the ONO-2921 suspension by PVA-205, indicating that PVA-205 acts as an aggregation inhibitor of fine particles.

Conclusions: The ESD method, in combination with appropriate types and amounts of additives, may be useful for preparing a DPI suitable for delivering drugs directly to the lungs without the assistance of carrier particles.     

Effect of Surface Modification on Flow Properties and Pressure Filtration of Alumina Slurries

ABSTRACT

The purpose of this research is to evaluate the effectiveness of various dispersants in fine particle processing. The surface of alumina in aqueous solution was modified by using both non-ionic and ionic surfactants. The rheological properties of highly loaded alumina suspensions were studied as a function of surfactant concentration. Pressure filtration experiments were also carried out in order to evaluate the dispersion properties and consolidation behavior. The pressure filtration results could be used to distinguish between well-dispersed and flocculated slurries. The results of rheology measurements and pressure filtration experiments are interpreted using suitable models. To assist the analysis, electrokinetic sonic amplitude (ESA) technique was used for characterization of electrical double layer.     

Preparation of superhydrophobic surfaces on cotton textiles

Abstract

Superhydrophobic surfaces were fabricated by the complex coating of silica nanoparticles with functional groups onto cotton textiles to generate a dual-size surface roughness, followed by hydrophobization with stearic acid, 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane or their combination. The wettability and morphology of the as-fabricated surfaces were investigated by contact angle measurement and scanning electron microscopy. Characterizations by transmission electron microscopy, Fourier transformation infrared spectroscopy, and thermal gravimetric analysis were also conducted.     

Correlated K-distributed Clutter Models

In this paper we examine the way in which a correlated K-distributed clutter model may be applied in the study of coherent-imaging systems. The theoretical background behind the model is discussed and various different correlated gamma-distributed surface models are analysed. The K-distributed clutter properties consequent on coherent imaging of such surfaces are next derived and their dependence on the imaging response function demonstrated. The theoretical results for a double coherence length surface model are then compared with overland images obtained with the RSRE X -band synthetic-aperture radar (SAR) processor. It is demonstrated that the model provides a reasonable representation of the dependence of the real image on the system resolution. The significance of such correlated K-distribution models on the understanding and prediction of clutter statistics is discussed and the direction for future research indicated.     

Contact properties determination of macroscopic fine disperse glass particles via compression tests in normal direction

The paper describes the deformation behavior of spherical, dry and non-porous particles during a single particle compression test in normal direction. Therefore a compression tester was built. Industrial used soda lime glass particles with two macroscopic fine disperse sizes (d_1,50,3 = 284.30 μm and d_2,50,3 = 513.20 μm) were applied as model material to investigate the micromechanical contact behavior. In order to influence the elastic-plastic contact properties of particles, the surfaces were altered with chemical modification by means of silanization.The determination of various micromechanical contact properties (e.g. adhesion force, modulus of elasticity and contact stiffness) was carried out model-based with the contact model ‘stiff particles with soft contacts’ by means of a back-calculation.It could be shown that the model-based determination of material properties was a good alternative compared to the comprehensive tensile tests and pull-off force measurements.In addition to the gained normal force-displacement data in normal direction, the friction limits for tangential loading and rolling with the load-dependent adhesion force were model-based determined.     

Microbial synthesis of iron-based nanomaterials—A review

Nanoparticles are the materials having dimensions of the order of 100 nm or less. They exhibit a high surface/volume ratio leading to different properties far different from those of the bulk materials. The development of uniform nanoparticles has been intensively pursued because of their technological and fundamental scientific importance. A number of chemical methods are available and are extensively used, but these are often energy intensive and employ toxic chemicals. An alternative approach for the synthesis of uniform nanoparticles is the biological route that occurs at ambient temperature, pressure and at neutral pH. The main aim of this review is to enlist and compare various methods of synthesis of iron-based nanoparticles with emphasis on the biological method. Biologically induced and controlled mineralization mechanisms are the two modes through which the micro-organisms synthesize iron oxide nanoparticles. In biologically induced mineralization (BIM) mode, the environmental factors like pH, pO₂, pCO₂, redox potential, temperature etc govern the synthesis of iron oxide nanoparticles. In contrast, biologically controlled mineralization (BCM) process initiates the micro-organism itself to control the synthesis. BIM can be observed in the Fe(III) reducing bacterial species of Shewanella, Geobacter, Thermoanaerobacter, and sulphate reducing bacterial species of Archaeoglobus fulgidus, Desulfuromonas acetoxidans, whereas BCM mode can be observed in the magnetotactic bacteria (MTB) like Magnetospirillum magnetotacticum, M. gryphiswaldense and sulphate-reducing magnetic bacteria (Desulfovibrio magneticus). Magnetite crystals formed by Fe(III)-reducing bacteria are epicellular, poorly crystalline, irregular in shapes, having a size range of 10–50 nm super-paramagnetic particles, with a saturation magnetization value ranging from 75–77 emu/g and are not aligned in chains. Magnetite crystals produced by MTB have uniform species-specific morphologies and sizes, which are mostly unknown from inorganic systems. The unusual characteristics of magnetosome particles have attracted a great interdisciplinary interest and inspired numerous ideas for their biotechnological applications. The nanoparticles synthesized through biological method are uniform with size ranging from 5 to 100 nm, which can potentially be used for various applications.     

Fabrication of a thermoresponsive cell culture dish: a key technology for cell sheet tissue engineering

Abstract

This article reviews the properties and characterization of an intelligent thermoresponsive surface, which is a key technology for cell sheet-based tissue engineering. Intelligent thermoresponsive surfaces grafted with poly(N-isopropylacrylamide) exhibit hydrophilic/hydrophobic alteration in response to temperature change. Cultured cells are harvested on thermoresponsive cell culture dishes by decreasing the temperature without the use of digestive enzymes or chelating agents. Our group has developed cell sheet-based tissue engineering for therapeutic uses with single layer or multilayered cell sheets, which were recovered from the thermoresponsive cell culture dish. Using surface derivation techniques, we developed a new generation of thermoresponsive cell culture dishes to improve culture conditions. We also designed a new methodology for constructing well-defined organs using microfabrication techniques.     

Microstructural alterations through heat treatment and its influence on wear response of a silicon containing zinc based alloy under different test conditions

Abstract

Observations pertaining to the influence of microstructural alterations brought about through heat treatment on the sliding wear behaviour of a zinc based alloy comprising of silicon have been analysed in this study. The effects of sliding conditions such as pressure and speed on the wear response of the alloy in as cast and heat treated conditions have also been investigated. The as cast alloy revealed dendritic structure consisting of primary α, eutectoid α + η, and ? phase. Silicon was present in the alloy microstructure as discrete particles. Heat treatment caused breaking of the dendritic structure and more homogeneous distribution of various microconstituents without affecting the morphology and mode of distribution of the silicon particles. The heat treated alloy attained superior wear response as compared with the as cast one especially under more severe wear conditions. Wear rate versus pressure plots revealed two slopes wherein the slope was low at low pressures and increased considerably beyond a critical pressure. The critical pressure decreased with speed while it was more for the heat treated alloy. The wear behaviour of the specimens deteriorated with pressure and speed. High wear rates were supplemented with severe surface/subsurface damage and coarse debris formation and vice versa. Changing microstructural features of the regions at different depths below the wear surface were attributed to the changing degree of deformation they experienced during wear. The wear behaviour of the specimens has been explained in terms of specific characteristics of various phases such as lubricating and load carrying capability, thermal stability and cracking tendency. Typical characteristics of worn surfaces/subsurface regions and debris further supplemented the specific wear behaviour of the alloy in different test/material conditions.