Elastic light scattering from nonspherical and polydisperse particles in the size range from 100 to 2000 NM

In the case of monodisperse dilute systems it is possible to calculate the distance distribution function for homogeneous and inhomogeneous particles of arbitrary shape. The distance distribution function enables one to find a rough classification of the shape and to determine the size of the particle. This function can be deconvoluted to the radial polarization density profile for particles with spherical symmetry. A number, mass or intensity distribution can be calculated from the light scattering data from polydisperse systems if the distribution can be described by a single parameter and if it is possible to calculate the shape factor of the particles, as it is the case for spheres and spheroids. The range of applicability of the method depends on the experimental set-up, but is in most cases in the size range from 100 nm to several micrometers.     

Anisotropic colloidal particles interacting with polymers in a good solvent

We study the consequences of chain self-avoidance for the interaction between nonadsorbing polymers and colloidal particles of anisotropic shape, such as ellipsoids, lenses, and dumbbells. In the framework of a field theoretic operator expansion for small mesoscopic particles, we obtain exact results for self-avoiding polymers in d=2 spatial dimensions and we compare ideal and self-avoiding polymers in 2相似文献   

Electrokinetic sonic amplitude method as applied to studying adsorption of high-molecular-mass compounds at interfaces

It is shown that the regularities of the adsorption of high-molecular-mass compounds on particle surfaces in disperse systems can be studied by the electrokinetic sonic amplitude method. Procedures are developed for calculating parameters of polymer adsorption layers and the quantitative analysis of their structure. The parameters of the adsorption layers are calculated by the example of a hydrophilic polymer, ethyl-hydroxyethylcellulose, and hydrophilic particles of titanium dioxide and iron oxide dispersed in aqueous disperse systems subjected and nonsubjected to an intense mechanical treatment. The treatment of the disperse systems in the field of intense wave vibrations is found to enhance the adsorption interaction.     

Theory for hierarchical assembly with dielectrophoresis and the role of particle anisotropy

Nonuniform electric fields cause polarizable particles to move through an effect known as dielectrophoresis (DEP). Additionally, the particles themselves create nonuniform fields due to their induced dipoles. When the nonuniform field of one particle causes another to move, it represents a path to hierarchical assembly termed mutual DEP (mDEP). Anisotropic particles potentially provide further opportunities for assembly through intense and intricate local field profiles. Here, we construct a theoretical framework for describing anisotropic particles as templates for assembly through mDEP by considering the motion of small nanoparticles near larger anisotropic nanoparticles. Using finite element analysis, we study eight particle shapes and compute their field enhancement and polarizability in an orientation-specific manner. Strikingly, we find a more than tenfold enhancement in the field near certain particle shapes, potentially promoting mDEP. To more directly relate the field intensity to the anticipated assembly outcome, we compute the volume experiencing each field enhancement versus particle shape and orientation. Finally, we provide a framework for predicting how mixtures of two distinct particle species will begin to assemble in a manner that allows for the identification of conditions that kinetically bias assembly toward specific hierarchical outcomes.     

Effect of the preparation conditions of water-soluble akaganeite-chitosan hydrochloride adsorption complexes on the morphology of akaganeite particles

The phase and disperse compositions and particle shape of FeOOH in water-soluble iron-chitosan adsorption complexes have been studied by powder X-ray diffraction and transmission electron microscopy depending on their preparation conditions. It has been established that the heating of an iron-chitosan solution for 3–6 min prior to precipitation increases the content of Fe(III), as well as the sizes and polydispersity of akaganeite particles in iron-chitosan complexes. Adsorption complexes prepared without heating are characterized by a narrow size distribution of akaganeite spherulites (2–6 nm).     

Linearly polarized IR-spectroscopy of partially oriented solids as a colloid suspension in nematic host: a tool for spectroscopic and structural elucidation of the embedded chemicals

Colloid suspensions in nematic liquid crystal were employed for the first time in 2004 as a tool for the partial orientation of solids, to be examined by linearly polarized IR-(IR-LD) spectroscopy. It has been found is found that a partial orientation (15–20%) of suspended particles, is adequate for the recording of reasonable linearly polarized IR-spectra is achieved when: 5 ± 1% by weight of the given solid compound (organic, inorganic, transition metal complex or glass) with particle size within the limits 0.3–0.9 μm is mixed with a nematic liquid crystal substance (ZLI 1695, ZLI 1538 or MLC 6815) suitable for IR spectroscopy and the slightly viscous suspension obtained is phase pressed between two KBr-plates. These latter are roughened in one direction prior to use with fine sandpaper (C800) (size 5 μm). Then, the KBr-plattes and pressed suspension are moved repeatedly with 3 μm/s for 100 times. The optimal cell thickness is 100 μm. If mathematical procedures are used for polarized IR-spectra interpretation, then it is possible to perform structural elucidation of the embedded compounds, independently of their melting point, crystalline or amorphous state, and the quality of the monocrystals or polycrystalline of the e sample. The method permits the study of organic and inorganic compounds, transition metal complexes and glasses. Here we will discuss the fundamental questions concerning the above state such as the morphology of the suspended particles, the particle size, the influence of the physical chemistry properties of liquid crystal medium on the degree of orientation of suspended particles; the velocity of the shearing of the suspension, the degree of the roughening of the KBr-plates and their effects on the degree of orientation, the influence of the space group on the orientation parameter, the nature and balance of the forces acting on the suspended particles; their degree of orientation, the mathematical model used. Conventional and linearly polarized IR-spectroscopy and electron microscopy are used for elucidation of these points. Statistical approaches have also been applied in order to estimate the impact of the experimental parameters (size, velocity, thickness) on the IR-signal for each of the 13 systems studied. An experimental design of the type involving full factorial design on two levels of variation of the input factors is presented.     

Manipulating the optical properties of pyramidal nanoparticle arrays

This paper reports the orientation-dependent optical properties of two-dimensional arrays of anisotropic metallic nanoparticles. These studies were made possible by our simple procedure to encapsulate and manipulate aligned particles having complex three-dimensional (3D) shapes inside a uniform dielectric environment. Using dark field or scattering spectroscopy, we investigated the plasmon resonances of 250-nm Au pyramidal shells embedded in a poly(dimethylsiloxane) (PDMS) matrix. Interestingly, we discovered that the scattering spectra of these particle arrays depended sensitively on the direction and polarization of the incident white light relative to the orientation of the pyramidal shells. Theoretical calculations using the discrete dipole approximation support the experimentally observed dependence on particle orientation with respect to incident field. This work presents an approach to manipulate--by hand--ordered arrays of particles over cm(2) areas and provides new insight into the relationship between the shape of well-defined, 3D particles and their supported plasmon resonance modes.     

Magnetoanalysis of micro/nanoparticles: a review

Application of magnetic field on the separation and analysis of nano/microparticles is a growing subject in analytical separation chemistry. The migration phenomenon of a particle under inhomogeneous magnetic field is called magnetophoresis. The migration velocity depends on the magnetic susceptibility and the size of a particle. Therefore, magnetophoresis allows us to determine the magnetic susceptibility of particles, and to separate particles based on the magnetic properties. Magnetic separation of ferromagnetic particles in liquid has been utilized for a long time. For example, a high gradient magnetic separation under the non-uniform magnetic field generated by ferromagnetic mesh has been utilized in a wide region from chemical industry to bioscience. Recent progress on magnetic nanoparticles and microfluidic devices has made it possible to extend the range of application. Furthermore, it has been demonstrated that the very sensitive measurement of the magnetic susceptibility of microparticles can be performed by observing magnetophoretic velocity. In this review, we mainly introduce novel separation and detection methods based on magnetophoresis, which have been invented in this decade, and then new principles of particle migration under magnetic field are presented.     

Friction of rodlike particles adsorbed to a planar surface in shear flow

A planar hard surface covered with elongated stiff rodlike particles in shear flow is considered in the low-Reynolds-number regime assuming low particle surface coverage. The particles are modeled as straight chains of spherical beads. Multipole expansion of the Stokes equations (the accurate HYDROMULTIPOLE algorithm) is applied to evaluate the hydrodynamic force exerted by the fluid on the rodlike particles, depending on their shape, i.e., on the number of beads and their orientation with respect to the wall and to the ambient shear flow.     

An analytical solution to the problem of the orientation of rigid particles by planar obstacles. Application to membrane systems and to the calculation of dipolar couplings in protein NMR spectroscopy.

Nonspherical particles or molecules experience an ordering effect in the presence of obstacles due to the restrictions they place on the orientation of those molecules that are in their proximity. Obstacles may be the limits of a membrane in which the molecule is embedded, oriented mesoscopic systems such as bicelles, or membrane fragments used to induce weak protein alignment in a magnetic field. The overall shape of most proteins can be described to a good approximation by an ellipsoidal particle. Here we describe and solve analytically the problem of the orientation of ellipsoidal particles by planar obstacles. Simple expressions are derived for the orientational distribution function and the order parameter. These expressions allow the analytical calculation of the residual dipolar couplings for a protein of known three-dimensional structure oriented by steric effects. The results are in good agreement with experiment and with the results of previously described simulations. However, they are obtained analytically in a fraction of the time and therefore open the possibility to include the optimization of the overall shape in the determination of three-dimensional structures using residual dipolar coupling constraints. The equations derived are general and can also be applied to problems of a completely different nature. In particular, previous equations describing the orientation of particles embedded in membranes are verified and generalized here.     

Phase behavior of a blend of polymer-tethered nanoparticles with diblock copolymers

Using the self-consistent field theory (SCFT), we investigate the phase behavior of a mixture of diblock copolymers and nanoparticles with monodisperse polymer chains tethered to their surfaces. We assume the size of the nanoparticles to be much smaller than that of the attached polymer chains and therefore model the particles with their grafted polymer "shell" as star polymers. The polymer chains attached to the particles are of the same species as one of the blocks of the symmetric diblock copolymer. Of primary interest is how to tune the shell of the particle by changing both the length and number of tethered polymers in order to achieve higher loading of nanoparticles within an ordered structure without macrophase separation occurring. We find that the phase behavior of the system is very sensitive to the size of the particle including its tethered shell. The region of microphase separation is increased upon decreasing the star polymer size, which may be achieved by shortening and/or removing tethered polymer chains. To explore the possible structures in these systems we employ SCFT simulations that provide insight into the arrangement of the different species in these complex composites.     

Morphology-dependent nanocatalysis: metal particles

The rapid development of materials science now enables tailoring of metal and metal oxide particles with tunable size and shape at the nanometre level. As a result, nanocatalysis is undergoing an explosive growth, and it has been seen that the size and shape of a catalyst particle tremendously affects the reaction performance. The size effect of metal nanoparticles has been interpreted in terms of the variation in geometric and electronic properties that governs the adsorption and activation of the reactants as well as the desorption of the products. At the same time, it has been verified that the morphology of a catalyst particle, determined by the exposed crystal planes, also considerably affects the catalytic behavior. This is termed as morphology-dependent nanocatalysis: a catalyst particle with an anisotropic shape alters the reaction performance by selectively exposing specific crystal facets. This perspective article initially surveys the recent progress on morphology-dependent nanocatalysis of precious metal particles to emphasise the chemical nature of the morphology effect. Then, the fabrication of transition metal particles with controllable size/morphology is examined, and their shape is correlated with their catalytic properties, with the aim to clarify the structure-reactivity relationship. Finally, the future outlook presents our personal perspectives on the concept of morphology-dependent nanocatalysis of metal particles, which is a rapidly growing topic in heterogeneous catalysis.     

The baculovirus expression system as a tool for generating diversity by viral surface display

It has become a major goal of molecular biologists, biochemists, and immunologists to be able to modulate the structure of proteins, in order to increase their antigenicity, alter their biological properties and/or explore their function. Based on the concept of bacterial phage display, by which proteins are being selected and analyzed in conjunction with their genetic information, eukaryotic systems have been investigated for their use in generating biomolecular diversity. The advantage of posttranslational modification and the possible harbouring of structural complex proteins has lead scientists to include eukaryotic systems in the wide field of molecular design. The ideal expression vectors for surface display are eukaryotic viruses, that allow large gene insertions, efficiently present foreign proteins on the particle surface, are easy to propagate and, if possible, not pathogenic to humans. By inserting peptides into a native virus coat protein or by expressing foreign proteins as coat protein fusion proteins or linked to specific anchor domains it becomes possible to display polypeptides of interest on the surface of replicating particles. A variety of different strategies are currently under investigation in order to utilize the baculovirus insect cell expression system for efficient display on the surface of virus particles as well as on the surface of virally infected insect cells. Increasing the transfection efficiency, optimizing cloning procedures, and establishing applicable selection methods have lead to the development of a powerful tool for drug screening and ligand screening.     

Monte Carlo simulations of a coarse grained model for an athermal all-polystyrene nanocomposite system

The structure of a polystyrene matrix filled with tightly cross-linked polystyrene nanoparticles, forming an athermal nanocomposite system, is investigated by means of a Monte Carlo sampling formalism. The polymer chains are represented as random walks and the system is described through a coarse grained Hamiltonian. This approach is related to self-consistent-field theory but does not invoke a saddle point approximation and is suitable for treating large three-dimensional systems. The local structure of the polymer matrix in the vicinity of the nanoparticles is found to be different in many ways from that of the corresponding bulk, both at the segment and the chain level. The local polymer density profile near to the particle displays a maximum and the bonds develop considerable orientation parallel to the nanoparticle surface. The depletion layer thickness is also analyzed. The chains orient with their longest dimension parallel to the surface of the particles. Their intrinsic shape, as characterized by spans and principal moments of inertia, is found to be a strong function of position relative to the interface. The dispersion of many nanoparticles in the polymeric matrix leads to extension of the chains when their size is similar to the radius of the dispersed particles.     

Electrooxidation of alcohols in an N-oxyl-immobilized rigid network polymer particles/water disperse system

The electrooxidation of alcohols in an aqueous disperse system with N-oxyl-immobilized poly(p-phenylene benzobisthiazole) network polymer particles (PBZT_NT-N-Oxyl) as a disperse phase was performed successfully in a simple beaker-type undivided cell under a constant current condition to afford the corresponding ketones, aldehydes, and/or carboxylic acid in moderate to good yields. Recycle use of both the PBZT_NT-N-Oxyl particles and the aqueous media could be achieved successfully by immobilization of additional N-oxyl moiety on the polymer particles in an appropriate interval. Notably, the shape and the particle size of PBZT_NT-N-Oxyl were not appreciably changed even after 60 times recycle use.     

AC electrohydrodynamic propulsion and rotation of active particles of engineered shape and asymmetry

This review presents the recent progress in the development of active particles driven by alternating-current (AC) electrokinetic effects. These particles propel by asymmetrically dissipating the external energy provided by the fields. An AC field can trigger several electrohydrodynamic mechanisms depending on the field frequency and amplitude, which can also control particle–particle interactions and collective behavior. Recently there has been a strong focus on powering and controlling the motion of self-propelling particles with engineered shape, size, and composition. We introduce a tiered classification of AC field-driven active particles and discuss the fundamental electrohydrodynamic effects acting in individual and multi-particle systems. Finally, we address the limitations and challenges in the current state of AC-field driven engineered particles.     

Analyzing adhesion in microstructured systems through a robust computational approach

Analyzing surface forces for myriad geometric structures facilitates the design of properties in interacting interfacial systems. Along these lines, we demonstrate a generalized technique that can be utilized to evaluate the orientation dependence of a particle interacting with multiple finite or semi‐infinite objects. Specifically, the surface element integration technique is modified to account for surface elements of a particle not directly adjacent to the object with which it is interacting; this facilitates the analysis of objects with finite shape and with arbitrary orientations. Furthermore, as a technology‐relevant proof‐of‐concept demonstration, the influence of van der Waals (vdW) forces on the performance and reliability of microstructured systems used for the collection of trace particles is reported. The importance of the location of the particle contact with the microstructure and the independence of vdW forces generated by each microstructure is demonstrated using the developed computational approach. Thus, the methodology presented here can ultimately be utilized for a variety of interfacial forces generated by nontrivial systems with heterogeneous properties in order to provide design motifs in a low‐cost, high‐throughput manner.     

SAXS and TEM Investigations on Thermoplastic Nanocomposites Containing Functionalized Silica Nanoparticles

Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) were used to characterize the morphology of thermoplastic nanocomposites. These materials were based on a thermoplastic matrix of a copolymer of methylmethacrylate (MMA) and 2-hydroxyethylmethacrylate (HEMA) with spherical 10 nm silica particles as a filler (filler content 2, 5 and 10 vol%, respectively). Depending on the surface modification of the particles, it was possible to control the aggregation tendency of the primary filler particles. With uncoated particles large aggregates about 100 nm in size could be observed by TEM. For nanocomposites containing particles coated with methacryloxypropyltrimethoxysilane (MPTS), TEM showed that the particles were better dispersed in the polymer matrix only forming aggregates comprised of two or three primary particles. In comparison to the TEM results, the volume weighted particle size distribution calculated from SAXS for the systems with uncoated particles is monomodal and shows particle sizes in the range of primary particles whereas the systems with MPTS coated particles revealed a bimodal size distribution with particle sizes comparable to those measured with TEM. To obtain complete information about the morphology of the nanocomposites above the critical upper limit of detectable scattering vectors (particle sizes >50 nm) SAXS has to be supported by TEM, whereas in the nanosize range below the critical limit both methods exhibit an excellent correspondence.     

Design,properties, and applications of protein micro- and nanoparticles

The design of protein particles with tailored properties has received an increased attention recently. Several approaches, from simple heat treatment in dilute systems to the combination of heat and mechanical treatments in concentrated protein solutions, have been used to obtain protein particles with varying functional properties. Control of particle size, morphology, surface- and internal properties is crucial for obtaining protein particles with the necessary properties for emerging applications. The latter include not only the use of protein particles in foods, where they can improve the stability of foods at high protein content, but also as food-grade particles for the delivery of bio-actives. By tuning the morphology and size of protein particles, protection or controlled release of various bio-active components may be obtained. We review the various methods that have been used to prepare protein particles and discuss the behavior of the particles in dispersed systems and their possible applications.     

Geometry dependent features of optically induced forces between silver nanoparticles

A recently devised, discrete-dipole approximation (DDA) based method for computing optical forces is used to explore geometry dependent aspects of the light induced interactions between pairs of silver nanoparticles, including the influence of particle shape, relative positioning of the particles, and incident field orientation. The interactions are observed to have a large degree of generic character, independent of the details of the particle shape. The size of the optical forces is also compared to estimates for the van der Waals forces, and the results are used to assess the potential importance of radiation forces on recent experiments demonstrating photoinduced self-assembly of triangular silver nanoprisms.