Kazunori Kadota

Formation and morphology of asymmetric NaCl particles precipitated at the liquid-liquid interface

Abstract —Asymmetric particles of NaCl and KCl crystals have been obtained by using a crystallization method. The particles were produced by precipitation at the solution-1-butanol interface. The two solvents are essentially immiscible, but have slight mutual diffusion. When the aqueous solution contacts with 1-butanol, the interfacial area becomes supersaturated, resulting in nucleation and particle growth in the interfacial zone. The asymmetric particles featured a stepped surface on the side in contact with 1-butanol. The other surfaces in contact with the aqueous phase were a flat cubic structure. Precipitated NaCl particles showed very clear asymmetric structure. However, some of KCl particles had less well-defined structures. This is due to the high diffusion rate of hydrated K ions and the fast diffusion results in a supersaturated state around the interface. This situation can be explained by a model of crystal growth based on solute clusters in supersaturated solutions.

Inhibition of Photodegradation of Highly Dispersed Folic Acid Nanoparticles by the Antioxidant Effect of Transglycosylated Rutin

We developed highly dispersible and photostable nanoparticles of vitamin, folic acid (FA). FA was wet bead milled with milling and dispersing adjuvants and transglycosylated compounds such as α-glucosyl hesperidin (Hesperidin-G) and rutin (Rutin-G), which solubilized FA. The milled slurries of FA particles with transglycosylated compounds consisted of nanosized particles with a median diameter of <100 nm. The lyophilized formulations of these slurries retained their nanometer size after resuspension in water with no aggregation. The apparent solubility of FA in these formulations was 100-fold higher than that of untreated FA. The solubilizing effect of Rutin-G may affect the particle size reduction and dispersibility of FA. The photostability results showed that the strong antioxidant activity of Rutin-G substantially increased the photostability of FA solution. On the basis of these results, bead milling of FA with Rutin-G is a promising technique for developing highly dispersible, photostable nanoparticle FA formulations.

Diffusion behavior in a liquid-liquid interfacial crystallization by molecular dynamics simulations

Interfacial crystallization, such as surface crystallization in solution (solid-liquid) and liquid-liquid crystallization, gives us an asymmetric reaction field and is a technique for morphology control of crystals. In the liquid-liquid crystallization, the concentration distribution of solute ions and solvent molecules at the liquid-liquid interface directly relates to nucleation, crystal growth, and crystal morphology. Nonequilibrium molecular dynamics (MD) simulations have been performed at interfaces in NaCl solution/1-butanol and KCl solution/1-butanol system in order to clarify diffusion behavior of solute ions and solvent molecules. As simulation results, the hydrated solute ions were dehydrated with the diffusion of water from solution phase into 1-butanol phase. The different dehydration behaviors between NaCl and KCl solution can be also obtained from MD simulation results. Aggregated ions or clusters were formed by the dehydration near the solution/1-butanol interface. By comparison on the normalized number of total solute ions, the size and number of generated cluster in KCl solution/1-butanol interface are larger than those in the NaCl system. This originates in the difference hydration structures in the each solute ion.

Anomalous role change of tertiary amino and ester groups as hydrogen acceptors in eudragit E based solid dispersion depending on the concentration of naproxen.

Eudragit E (EGE) is a basic polymer incorporating tertiary amino and ester groups. The role of the functional groups of EGE in the formation of solid dispersion (SD) with Naproxen (NAP) was investigated. The glass transition temperature (Tg) of EGE decreased with the plasticizing effect of NAP up to 20% weight ratio. Addition of NAP at over 30% induced a rise in Tg, with the maximum value being reached at 60% NAP. Further addition of NAP led to a rapid drop of the Tg. A dramatic difference of physical stability between the SDs including 60 and 70% NAP was confirmed. The SD including 70% NAP rapidly crystallized at 40 °C with 75% relative humidity, while the amorphous state could be maintained over 6 months in the SD with 60% NAP. The infrared and (13)C solid state-NMR spectra of the SDs suggested a formation of ionic interaction between the carboxylic acid of NAP and the amino group of EGE. The SD with 20% NAP raised the (13)C spin-lattice relaxation (T1) of the amino group, but it decreased with over 30% NAP. The change in the (13)C-T1 disappeared with 70% NAP. The (13)C-T1 of the ester group rose depending on the amount of NAP. From these findings, we concluded that the role as hydrogen acceptor shifted from the amine to the ester group with an increase in amount of NAP. Furthermore, the amino group of EGE did not contribute to the interaction at over 70% NAP. These phenomena could be strongly correlated with Tg and stability.

Effect of surface properties of calcium carbonate on aggregation process investigated by molecular dynamics simulation

The control of the morphology and polymorphs of CaCO3 has been required, since their capabilities are dependent on particle characteristics of CaCO3. It is difficult to clarify the formation mechanism only by the experimental approaches because the nucleation and crystal growth of CaCO3 occurred at nanoscale. The objective of the present work is to investigate the effect of surface properties including in the charge density and the dielectric constant of water on the aggregation process of primary particles by means of molecular dynamics simulations. The grain boundary energy was also calculated by molecular dynamics simulation to investigate the change of energy in the aggregation process of primary particles. From the results of molecular dynamics simulation, we found that the interface of (001)Ca and (001)CO3 contacted with water charged positively and negatively and the interface of (100) and (104) contacted with water charged neutrally. When the distance of interfaces between CaCO3 particles came close to colliding, the dielectric constant of water became small except the interface of (001)CO3. The boundary energy of interface between (001)Ca and (001)CO3 was the lowest among five types of interfaces. It indicates that the aggregation of (001)Ca and (001)CO surface is the easiest among all types of interfaces.

Structural dependence of ionic motion at interfaces between NaCl crystal surfaces and supersaturated solutions in crystallization process

The effects of surface structure and solution concentration on crystal morphology have been investigated through molecular dynamics (MD) simulation in the NaCl crystallization process. Four types of crystal surface structures were prepared for simulation. The probability of ion existence suggests that the solute ions were hardly taken into flat surfaces, while they were easily taken into roughs with some kinks and steps. This is because solute ions are more stable at a kink than at a terrace. The present simulated results suggest that the mechanism of crystal growth is dependent on the solution concentration. It was demonstrated that some ions are slotted on the crystal surface at low supersaturation after moving to the crystal surface. Under high supersaturation, the clusters are formed and adsorbed on the crystal surface. When comparing the crystal growth rates of Na+ and Cl−, the attractive force of Na+ from the crystal surface was found to be larger than that of Cl−. Moreover, the repulsive force of Na+ from the crystal surface was smaller than that of Cl− in approaching the crystal surface. The adsorption of Na+ was also found to occur before that of Cl−.

Effect of interfacial structures on ionic conductivity in particle-dispersed composite electrolytes

Abstract Enhancement of ionic conduction in NaCl-Al 2 O 3 and NaCl-TiO 2 composites has been investigated by non-equilibrium molecular dynamics (NEMD) simulations. For quantitative discussion of ionic diffusion in NaCl matrices, activation energy of sodium vacancy V Na in an imperfect NaCl crystal was initially evaluated from results of NEMD simulations under some electric fields. The activation energy agrees well with experimental data. Simulations with NaCl(100)-Al 2 O 3 (110) and NaCl(100)-TiO 2 (001) hetero-interfaces have been performed for clarifying vacancy motion near interfaces. Structural disorder appeared around the hetero-interface. The simulation cells were constituted of ordered and disordered structure even if in equilibrium state without applying an electric field. The vacancies near the hetero-interface show large diffusion constants on the ionic conductivity in the present NEMD simulations. It seems that the vacancy motion near the interface contributes to the enhancement of the conduction in the composites.