A new approach to nucleation of cavitation bubbles at chemically modified surfaces

Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.     

Monoclinic Cu3(SeO3)2Cl2: an oxo­halide with an unusual CuO4Cl trigonal–bipyramidal coordination

In single crystals of a new monoclinic (C2/m) form of tricopper(II) diselenium(IV) dichloride hexa­oxide, Cu₃(SeO₃)₂Cl₂, the Se atom is in the 4i position, while the two Cu atoms are in 2a and 4i positions. The structure is based on layers of CuO₄Cl trigonal bipyramids, CuO₄ square planes and SeO₃E tetra­hedra. The Cu polyhedra are connected by edge‐ and corner‐sharing to form [010] chains and these chains are bridged by the Se atoms to form (001) layers. The compound is isostructural with Cu₃(TeO₃)₂Br₂.     

Soft X-ray microscopy to characterize polyelectrolyte assemblies

Transmission microscopy with soft X-rays (TXM) is applied to image in-situ polyelectrolyte assemblies in aqueous environment. The method is element specific and at this stage exhibits a lateral resolution of 20 nm. With the specific examples of hollow capsules and full spheres made of PAH/PSS polyelectrolyte multilayers, it is shown quantitatively that heat treatment irreversibly reduces the water content in the membrane. These experiments complement those reported recently on the polyion system PDADMAC/PSS, which shows a different glass-transition behavior. Finally, the potential and present limitations of TXM are discussed.     

Self-assemblies of luminescent rare earth compounds in capsules and multilayers

This review addresses luminescent rare earth compounds assembled in microcapsules as well as in planar films fabricated by the layer-by-layer (LbL) technique, the Langmuir–Blodgett (LB) method and in self-assembled monolayers. Chemical precipitation, electrostatic, van der Waals interactions and covalent bonds are involved in the assembly of these compounds. Self-organized ring patterns of rare earth complexes in Langmuir monolayers and on planar surfaces with stripe patterns, as well as fluorescence enhancement due to donor–acceptor pairs, microcavities, enrichment of rare earth compounds, and shell protection against water are described. Recent information on the tuning of luminescence intensity and multicolors by the excitation wavelength and the ratio of rare earth ions, respectively, are also reviewed. Potential applications of luminescent rare earth complex assemblies serving as biological probes, temperature and gas sensors are pointed out.     

Preparation of protein microcapsules with narrow size distribution by sonochemical method

Protein microcapsules with narrow size distribution have been prepared by sonochemical method which is a simple, fast, environmental friendly and cost-effective method. The prepared microcapsules are composed of a water-insoluble core and an outer protein shell. The hydrophobic drugs could be encapsulated into protein microcapsules directly via sonochemical method by dissolving drugs in the nontoxic and edible vegetable oil before ultrasonication, which is a potential solution for drug resistance by hiding cytotoxic drugs in the carrier and allows for the delivery of high doses in relatively small volume. The size and size distribution of protein microcapsules are very important for their practical application. In this paper, the factors affecting the size and size distribution of protein microcapsules are investigated in detail. Moreover, confocal laser scanning microscopy and transmission electron microscopy confirmed that the protein microcapsules with narrow size distribution were obtained.