Supercooling phenomena in binary mixtures of acetamide and inorganic salts

Liquid—solid equilibrium temperatures are measured in binary mixtures of acetamide and inorganic salts [NaClO₄, LiCNS, LiNO₃, CH₃COOLi, Ca(NO₃)₂, (CH₃)₄ NCl, (C₂H ₅)₄ NBr]. In some ranges of concentration all these systems (with the exception of CH₃COOLi, R₄NX) exhibit supercooling phenomena and crystallization occurs only through vigorous agitation and in the presence of crystalline nuclei, or does not occur at all, according to the type of salt. A probable explanation is presented on the basis of the trend of ΔT/νmK vs. m.     

Molecular simulation of binary colloidal mixtures: Gelation and aging phenomena

We investigate the aging dynamics of colloidal depletion gel by computer simulation. In this study, we employ an alternative approach using the effective pair potential to avoid the slow convergence in binary mixtures due to cage effect, and the structural formation of colloidal depletion gels is then clarified. We study the mean square displacement (MSD) of each segment in depletion gels by stochastic molecular dynamic simulations. It is shown that the MSD obeys a power-law, indicating sub-diffusive behavior of depletion gels. We also observe aging phenomena of the colloidal depletion gels from intermediate scattering functions. Power-law behavior of a characteristic time in this system, as a function of a waiting time, is also clarified.     

Interaction in binary fluoride systems

A series of factors affecting the interaction between fluorides is considered. Fluorides are distributed by valence and are arranged in accordance with an increase in the polarizing effect of cations. For eutectic-type melting diagrams, deviations of the experimental liquidus from the ideal one calculated by the Schröder equation are analyzed. In many systems of this type, complex formation is noted in the melts. The most informative factors determining the type of melting diagrams of fluoride systems are refined. Interrelation of various types of melting diagrams is considered.     

Molecular recognition phenomena in polyelectrolyte systems

The term “molecular recognition” is commonly used to describe various specific interactions, sometimes being not well defined. Let's assume that some species A can separately interact with either species B₁, or B₂, (or B₃, B₄ etc.) forming A·B₁, or A·B₂, (or A·B₃, or A·B₄ etc.) complexes. Here we say “recognition” assuming selective complexation of A with B₁ in the mixture containing also B₂ (B₃, B₄… etc.). At the same time it means discrimination of all other B species except B₁.     

Relaxation phenomena in critical microemulsion systems

We discuss extensive sets of experimental data including static and dynamic light scattering, ultrasonic velocity measurements and high and low frequency dielectric relaxation, taken in the vicinity the critical point of a ternary microemulsion system. Upon approaching the critical point we observed a slowing down of the dielectric relaxation time and of the first cumulant of the time-dependent droplet density correlation function C²(t) which shows a non-exponential behavior at long time. These features can be well acccounted for by assuming that the microemulsion system is made of polydispersed transient fractal aggregates having a fractal dimension d_f=2.5 and a polydispersity index τ=2.2.     

Diffusion phenomena in ternary systems polymer-nonsolvent-solvent

Diffusion in a boundary between a polymer+solvent solution and non-solvent was treated by accounting for the presence of the four diffusion coefficients that describe the isothermal transport process in a three component system. Diffusion equations were integrated assuming a concentration dependence of diffusion coefficients that account for the thermodynamic conditions on the cross diffusion terms of Eq. (1). The presence of non-zero cross terms promotes an incongruent diffusion of polymer whose concentration increases at the boundary between the polymer+solvent solution and the non-solvent. Although our model describes diffusion in the range of homogeneous solution, this incongruent polymer diffusion is a process similar to that promoted by the solvent evaporation from the polymer+solvent film that some authors suggested as an intermediate step before the film immersion into the coagulation bath to obtain good asymmetric membranes.     

Reactions in binary iodide systems

Several factors that influence the interactions between iodides are considered based on the results of thermoanalytical experiments. The iodides are grouped according to the cation valence and are arranged in the increasing order of the cation polarizing powers (CPPs). The deviations of the liquidus in real eutectic iodide systems from an ideal liquidus are analyzed. Compound formation in melts, incomplete solid solubility, or immiscibility are observed in many systems. The structure of the melting-point diagram is found to correlate with the type of interaction in the system.     

Structural changes of the molecular complexes and consolute phenomena in binary liquid mixtures

Consolute phenomena in the aqueous solutions of the polymers are considered In view of the temperature induced structural changes of the hydrogen bonds between water and functional groups of polymer. The lower and upper critical consolute points are attributed to the appearance of the “critical” concentration of the complexes with one hydrogen bond between single water molecule and functional group of polymer. Namely such kind of the hydrogen bonds are responsible for the formation of the strongly associated water clusters, that may be followed by phase separation. Experimentally observed dependences of the critical consolute temperatures for the aqueous solutions of polyethylene glycol on the molecular weight of polymer and adding of salts are well reproduced in the framework of the proposed model.     

On the rate of nucleation in binary systems

The technique used by many authors for finding a saddle point on the free energy surface in a binary system has been criticized recently. It is shown that the new approach proposed in two recent articles does not lead to any better agreement between theory and experiment than the previous method, especially for mixtures presenting strong surface enrichment effects.     

Co-precipitation in some binary sulphate systems

Studies have been made of the distribution behaviour of tracers with alkaline earth sulphates, using the technique of precipitation from homogeneous solution. The co-precipitation of strontium with barium sulphate and of lead, lanthanum, and yttrium, separately, with barium sulphate, and with strontium sulphate, were investigated. Although there was qualitative correlation between the observed values of the distribution coefficient and the theoretical solubility product ratios for each of the binary systems studied, the divergence between theory and observation was so great that it seems unlikely that there is any quantitative correlation.     

Percolation phenomena in diffusion-controlled polymer matrix systems

The controlled release of two kinds of drugs,5-fluorouracil (5-FU) and hydrocortisonum (Hydro.) loaded in poly(ethylene-vinylalcohol) (EVAL) was dealt with,of which 5-FU/EVAL and Hydro /EVAL matrix systems are composed.The results were analyzed using the pseudo-steady-diffusion models coupled with the fundamental concepts of percolation theory.The percolation thresholds for the two systems were calculated,which could indicate the contributions of pore diffusion and matrix diffusion.     

Supercooling behavior in aqueous solutions

Using the emulsion method, we measured the homogeneous nucleation temperature depression, DeltaT(f,hom), and equilibrium melting points depression, DeltaT(m), of various aqueous solutions and then calculated lambda for each solute using the linear relationship DeltaT(f,hom) = lambdaDeltaT(m). We defined lambda as the solute-specific supercooling capacity and examined its correlation with some known hydration characteristics. The results showed that lambda is correlated with D0, the self-diffusion coefficient of solute molecules in infinite dilution.     

Molecular dynamics and thermodynamic simulations of segregation phenomena in binary metal nanoparticles

Journal of Thermal Analysis and Calorimetry - An approach combining atomistic molecular dynamics (MD) and thermodynamic simulations has been applied to predict the distribution of components in...     

Studies on interfacial electrochemical phenomena in pigment-vehicle systems

Sedimentation potentials under a centrifugal field are studied with the disperse system titanium dioxide, alkyd resin and xylene. The relationships between the sedimentation potential and the rotation speed, the distance apart of the electrodes in the cell and the total weight of particles in the disperse system are examined. From the theoretical evaluation of the initial sedimentation potential, the zeta potential of the pigment in the disperse system is calculated. The calculated value was almost coincident with that obtained by the electrophoretic method. As the sedimentation potential is proportional to the total weight of pigment in the space between the electrodes in the cell, the particle-size distribution of pigment can be obtained from the sedimentation potential-time curve. The particle-size distribution in the above-mentioned disperse system was examined with respect to the effect of rotation speed and the pigment content. The modal diameter for the particle-size distribution obtained by this method had almost the same value as that obtained by the electron microscope method. By use of this method for particle-size analysis, the particle-size distribution for particles of diameter < 1 mum can be obtained in a short time (ca, 10-30 min) and the zeta potential of the particles in the disperse system can be calculated.     

Adsorption of gas-water binary systems in carbon micropores: Computer simulation

The adsorption of gas-water mixture in micropores of carbon materials at 298 K has been studied using computer simulation. Methane, nitrogen, ammonia, carbon dioxide, and hydrogen sulfide were considered as gas components. In the grand canonical ensemble Monte-Carlo simulation of adsorption, the displacement of a gas component from a pore as a result of the formation of water microclusters was observed for all systems studied. Cluster growth conditions on graphite-like and activated surfaces differ significantly. The comparative stability of adsorbed gas-water mixtures has been determined for all gases.