Interior Of Liquid Research Articles

Bubble-induced fast crystal growth of indomethacin polymorphs in a supercooled liquid

Physical stability is one of the main challenges when developing robust amorphous pharmaceutical formulations. This article reports fast crystal growth behaviors of the γ and α forms of indomethacin (IMC) initiated by bubbles in the interior of a supercooled liquid. Bubble-induced crystal growth of γ-IMC exhibits approximately the same kinetics as its surface crystal growth, supporting the view that bubble-induced crystal growth is a surface-facilitated process. In contrast, the rates of bubble-induced crystal growth of α-IMC are much faster than those of its surface crystal growth. These results indicate that the bubble-induced crystal growth not only depends on the interface created by the bubble but also strongly correlates with the true cavitation of the bubble. Moreover, bubble-induced fast crystal growth of γ- and α-IMC can be terminated at different temperatures by cooling. These outcomes are meaningful for the in-depth understanding of physical stability and pre-formulation study of amorphous pharmaceutical solids showing surface-facilitated crystal growth.

Transport of oil in a compound vortex

The oil redistribution pattern in a compound vortex created by a uniformly rotating disk located on the bottom of a cylindrical tank is investigated. At the initial instant, a round spot of a lightweight oil is deposited on the free surface of the liquid at the center of the tank. In the course of the formation of the compound vortex, the oil is partially entrained into the interior of the liquid and forms a body of revolution. On the free surface, the spot loses the round shape, spiral branches stretch out from the appeared protrusions and cusps. The orientation of these branches is opposite to the direction of fluid rotation in the tank. Geometrical parameters of the structures for different flow regimes are studied.

Consistency of Ion Adsorption and Excess Surface Tension in Molecular Dynamics Simulations of Aqueous Salt Solutions

Molecular dynamics simulations of the liquid−vapor interface of aqueous solutions of sodium fluoride and of sodium iodide have been carried out using nonpolarizable force fields for ions and water molecules. Despite the absence of explicit polarizability, the tendency of iodide ions to show an enhanced concentration at the surface that was reported for polarizable force fields (Jungwirth, P.; Tobias, D. J. J. Phys. Chem. B 2001, 105, 10468) is reproduced, while sodium and fluoride ions prefer the interior of the bulk liquid. These observations are confirmed by the contributions of the different species to the surface potential. The systems we study here are much larger than the ones investigated in previous simulations by other authors, which enables us to calculate the adsorption of ions at the interface from the density profiles and subsequently—via Gibbs’ adsorption isotherm—the corresponding excess surface tension over that of pure water. The so-obtained values for the surface tension are compared with the results calculated directly from the normal and lateral components of the pressure tensor in the simulation. Consistency is found among the data, but the directly obtained values have significantly larger error bars and are intrinsically more scattered. The Gibbs adsorption isotherm thus not only is a thermodynamic requirement to be met but also offers a reliable and less error-prone way of calculating the surface tension increment from density profiles.

Measurement of flow velocity distribution by multiple-exposure speckle photography

Measurement of flow velocity distribution in the interior of transparent liquid is made by use of speckle photography. In order to increase effective energy of scattered light, a multiple-exposure method is used. Some of the features of multiple-exposure speckle photography are discussed and an advantage of the speckle technique over the holographic technique is suggested.