Effect of ultrasounds on the aggregative behaviours of Methylene blue

The study of chemical effects of ultrasound is a rapidly growing research area. Some of the most important recent aspects of sonochemistry have been its applications in the synthesis and modification of both organic and inorganic materials. High-intensity ultrasound can induce a wide range of chemical and physical consequences. Physical effects of high-intensity ultrasound, which often have chemical consequences, include enhanced mass transport, emulsification, bulk thermal heating, and a variety of effects on solids. The chemical consequences of high-intensity ultrasound do not arise from an interaction of acoustic waves and matter at a molecular or atomic level. Instead, in liquids irradiated with highintensity ultrasound, acoustic cavitation (the formation, growth, and collapse of bubbles) provides the primary mechanism for sonochemical effects. During cavitation, bubble collapse produces intense local heating, high pressures, and very short lifetimes; these transient, localized hot spots drive high-energy chemical reactions. As described in detail elsewhere, these hot spots have temperaturesof »5000 oC, pressures of about 1000 atm, and heating and cooling rates above 1010 K/s. In addition, the interfacial region around cavitation bubbles has very large temperature, pressure, and (possibly) electric field gradients Liquid motion in this vicinity also generates very large shear and strain gradients; these are caused by the very rapid streaming of solvent molecules around the cavitation bubble, as well as the intense shockwaves emanated on collapse. These physical effects have special importance in many technologies such as petroleum industry in the extraction of crude oil. One of most important applications of ultrasounds is their special ability to break intermolecular bonds. Ionic dyes such as Methylene blue can easily form aggregation because of their planner structure. This aggregation cause decreasing the efficiency of quantum yield in the solution of these dyes. Many investigations have been done to decrease this aggregation. In the present work we could notably decrease this aggregation by ultrasound.