Narrow Results

Depending on the pH-value and salt concentration of Al₂O₃ suspensions different microstructures can form. Especially the clustered one is of major interest for industrial purposes as found in the production of ceramics. In this paper we investigate the clustered microstructure by means of a coupled Stochastic Rotation Dynamics (SRD) and Molecular Dynamics (MD) simulation. In order to gain statistics within a system containing numerous clusters, large simulation volumes are needed. We present our parallel implementation of the simulation algorithm as well as a newly developed cluster detection and tracking algorithm. We then show first results of measured growth rates and cluster size distributions to validate the applicability of our method.

Computer simulations of bi-continuous two-phase fluids with interspersed dumbbells show that, unlike rigid colloids, soft dumbbells do not lead to arrested coarsening. However, they significantly alter the curvature dynamics of the fluid–fluid interface, whose probability density distributions are shown to exhibit (i) a universal spontaneous transition (observed even in the absence of colloids) from an initial broad-shape distribution towards a highly localized one and (ii) super-diffusive dynamics with long-range effects. Both features may prove useful for the design of novel families of soft porous materials.

Colloidal suspensions are ubiquitous in nature. They also occur in many processes of industrial and technological interest. However, an understanding of the basic microscopic interactions and the rich phase behavior exhibited by colloidal suspensions is still lacking. In the present paper we give a short overview of the different statistical-mechanical approaches that have been proposed to account for the phase behavior and phase transitions occurring in systems made up of spherical colloidal particles immersed in a fluid matrix of structureless solvent particles. Effective interactions in these systems are seen to be invariably of a very short-ranged nature, and particular emphasis is put on different models that very accurately approximate these interactions. A central theme of this review is the effect of correctly incorporating the correlation structure of the colloidal system into the statistical-mechanical treatment, and how this feature very decisively affects the quality of the theoretical predictions for the colloid thermodynamics and phase behavior. Based on the importance of the correlation structure, theories relying on perturbative expressions are seen to fail to a higher or lesser extent when applied to systems of particles interacting via short-ranged potentials, and a critical discussion is provided on different proposals to overcome these difficulties. In particular, a recently proposed self-consistent nonperturbative theory is reviewed, and some of its more recent applications are shown.

We have proposed and investigated a model of drying colloidal suspension drop placed onto a horizontal substrate in which the sol to gel phase transition occurs. The temporal evolution of volume fraction of the solute and the gel phase dynamics were obtained from numerical simulations. Our model takes into account the fact that some physical quantities are dependent on volume fraction of the colloidal particles.

The second-order nonlinear optical properties of polystyrene particles coated with two well-characterized nonlinear optical chromophores with different molecular symmetry have been studied. From the markedly different depolarization ratio for the hyper-Rayleigh scattering from the molecular scatterers and from the largely different second-harmonic intensity from particles coated with these chromophores, we conjecture that contributions from antisymmetric molecular electronic states are necessary to observe second-order nonlinear effects from centrosymmetrical particles in isotropic solution.

Amorphous silicon nanocolumns, square nanospirals, and multilayer spiral/column rods are fabricated on bare Si substrates and monolayer colloid substrates by glancing angle deposition. The grown films are studied by scanning electron microscopy and transmission electron microscopy. The size of the deposited Si columns and spirals increases with the size of colloid particles for fixed incident angle of deposition flux. The feasibility of fabricating separated, well-ordered square spirals provides a cost effective and simple way to fabricate photonic crystals.

The engineering of multifunctional nanoparticles carrying photosensitizer drugs (PS) and exposing binding groups for cellular receptors is of increasing interest in therapeutics and diagnostics applications. Natural and modified cyclodextrins (CDs) offer useful scaffolds to bind PS guests by supramolecular interactions. In particular, amphiphilic β-CDs, which form nanoaggregates of diverse shape and size according to the polarity of substituent groups on the rims, include in their different compartments as CD cavity, hydrophilic and hydrophobic portion, PS with different physicochemical properties. PS embedded in cationic amphiphilic CD nanoassemblies are effective in inducing photodynamic damage in cancer cells. For a carrier/PS system to be used in photodynamic therapy (PDT) or photodynamic diagnosis (PDD), the appropriate combination of the delivery characteristics with the preservation of the photodynamic activity of the PS is strictly required. Homogeneous multilayer films based on cationic amphiphilic β-CD entrapping anionic porphyrins can be constructed to exploit interfacial electrostatic interactions between the two components. The capability of CDs to generate restricted microenvironments for PS which can facilitate photoinduced energy transfer with suitable donor molecules was investigated for potential application in fluorescence diagnosis. Besides, recent findings suggest that PDT could represent a useful tool for properly addressing an alternative approach for killing pathogens and combating infections at a clinical level. Finally, modified CDs can bind gold nanoparticles, yielding hybrid organic/inorganic nanoparticles which were studied in water solution and after casting on solid substrates. These binary assemblies could further encapsulate PS or other conventional drugs, opening new intriguing routes on multimodal therapy.

The dynamical properties of interacting colloids spatially restricted to move in one-dimensional channels [J. Chem. Phys. 133, 114902 (2010)] and subjected to external periodic energy landscapes [Phys. Rev. E 86, 081123 (2012)] have been recently reported in terms of the long-time self-diffusion behavior. However, the full description of the mean-square displacement, ranging from short times to long times, is still missing. Thus, by means of Brownian dynamics computer simulations, we revisit the process known as single-file diffusion in driven interacting colloidal systems at all time scales. In particular, we review three different pair potentials, namely, Weeks–Chandler–Andersen, Yukawa and superparamagnetic potentials. We mainly focus on the importance of the correlation between particles via the coupling among hydrodynamic interactions and the external periodic field, resulting in nontrivial particle dynamics along the file in systems composed of repulsively interacting particles.

 Special Issue Comments: This article reviews results on the dynamical properties of interacting colloids in a single file when they are subjected to external periodic energy landscapes presented before in [J. Chem. Phys. 33, 114902 (2010)] and [ Phys. Rev. E 86, 081123 (2012)]. We analyze different interactions that cover from short to long ranges of the interparticle potentials. We mainly focus on the importance of the correlation between particles via the coupling among the hydrodynamic interactions and the external periodic field.

Note from Publisher: In the captions of Figs. 1 through 4, "??" has appeared where the number 9 should appear.

In table 1, in the WCA section, the variable "φ" shows the values: 0.2,0.3,0.3,0.3,0.3,0.3.

The correct values are: 0.2, 0.3, 0.4, 0.5 , 0.6 , 0.7.

Specific features of the dielectric response of colloid systems with electrically interacting components (polar liquid matrix and solid spherical inclusions) have been revealed. A theory was developed to describe dielectric dispersion and anisotropy of the liquid phase caused by the electric field of surface charges on the solid particles. It was found that the local dielectric permittivity in different directions can vary over a wide range and strongly depends on the strength of the inner field. The existence of the interphase interaction leads to the formation of thin structured liquid layers in the contact area of two phases and, therefore, to a decrease in the average dielectric permittivity of the considered system. Nonuniform structure of the polar liquid was taken into account while the derivation of a mixing formula which clearly demonstrates the contribution of the interphase interaction to the dielectric response of the investigated colloid system.

Properties of materials determined by their size are indeed fascinating and form the basis of the emerging area of nanoscience. In this article, we examine the size dependent electronic structure and properties of nanocrystals of semiconductors and metals to illustrate this aspect. We then discuss the chemical reactivity of metal nanocrystals which is strongly dependent on the size not only because of the large surface area but also a result of the significantly different electronic structure of the small nanocrystals. Nanoscale catalysis of gold exemplifies this feature. Size also plays a role in the assembly of nanocrystals into crystalline arrays. While we owe the beginnings of size-dependent chemistry to the early studies of colloids, recent findings have added a new dimension to the subject.

Properties of materials determined by their size are indeed fascinating and form the basis of the emerging area of nanoscience. In this article, we examine the size dependent electronic structure and properties of nanocrystals of semiconductors and metals to illustrate this aspect. We then discuss the chemical reactivity of metal nanocrystals which is strongly dependent on the size not only because of the large surface area but also a result of the significantly different electronic structure of the small nanocrystals. Nanoscale catalysis of gold exemplifies this feature. Size also plays a role in the assembly of nanocrystals into crystalline arrays. While we owe the beginnings of size-dependent chemistry to the early studies of colloids, recent findings have added a new dimension to the subject.

Hard and soft disks in external periodic (light-) fields show rich phase diagrams including freezing and melting transitions when the density of the system is varied. Monte Carlo simulations for detailed finite-size scaling analysis of various thermodynamic quantities like the order parameter, its cumulants, etc. have been used in order to map the phase diagram of the system for various values of the density and the amplitude of the external potential.

Interpreting hard disks as the simplest model of an atomic fluid, quantum effects on the phase diagram are investigated by path integral Monte Carlo simulations.

This contribution provides a brief overview of recent advances in the theoretical and experimental study of the critical Casimir effect originating from the confinement of the enhanced thermal fluctuations which occur close to a critical point. The resulting effect turns out to be highly tunable, it influences the behavior of soft matter, from wetting films of fluids to colloidal dispersions, and therefore might find applications for the manipulation of matter at the micrometer and sub-micrometer scale.