Microbubbles trigger oscillation of crystal size in solids

Abstract

An understanding of the nature and conditions of nonlinear processes in open systems is important for modulation of the microstructure of solids at a new level of complexity. We demonstrate that cavitation generated by high intensity ultrasound (HIUS) triggers nonlinear processes in microparticles and layers of titanium. We reveal a non-monotonic dependence of the size of grains in the treated solids on sonication time, and oscillation of titanium grain sizes vs. time of ultrasonic treatment, indicating the influence of two opposing forces: cavitation driven impact of shock heating and shear stress on surfaces. These nonlinear self-organization processes in solids promise new microstructured materials with applications among others in bio- and geosciences.

Spiral computed tomography evaluation of rabbit VX2 hepatic tumors treated with 20 kHz ultrasound and microbubbles

“…This smaller diameter improves the passage into the pulmonary capillary bed and allows the bubbles to reach the micro-circulation of rabbit hepatic tumors (39). MBs expand and contract in size in response to the oscillating pressure and energy accumulates when the MBs are constricted by sound pressure (40). Ultimately, the energy carried by cavitation bubbles is released when the MBs collapse and sonication cavitation occurs and during the cavitation, the MBs undergo volumetric oscillations, thereby changing the local mechanical condition of the tissue (40).…”

“…MBs expand and contract in size in response to the oscillating pressure and energy accumulates when the MBs are constricted by sound pressure (40). Ultimately, the energy carried by cavitation bubbles is released when the MBs collapse and sonication cavitation occurs and during the cavitation, the MBs undergo volumetric oscillations, thereby changing the local mechanical condition of the tissue (40). When MBs collapse, they can create shockwaves, increasing the local pressure by 100 atm and the local temperature by several thousands of degrees (41).…”

Using a chitosan nanolayer as an efficient pH buffer to protect pH-sensitive supramolecular assemblies

“…4A-D) confirm that the surface of chitosan increases in net positive charge under irradiation. For comparison, the effect of smoothing of the chitosan layer by decreasing the solution pH was observed previously by Lee et al 20 and was explained to result from a change of surface forces due to chitosan protonation. Here, irradiation triggers a local pH change on the semiconductor, and also may cause protonation of chitosan.…”

“…Morphological properties of the surface after sonochemical treatment were characterized in details in our previous work. 20 It is important here that the ultrasonically generated nanolayer of TiO 2 shows mild photoactivity under 405 nm illumination; which produces H + on the surface. A pH indicator shows an increase in fluorescence, seen in Fig.…”

“…The observed photosensitivity in the visible range could be attributed to the optical transitions involving electronic states in the forbidden zone which result from highly defective structure inherent in titania generated via intense ultrasonic treatment. 20 In addition to obtaining a classical I-V curve under chopped illumination we used conductive atomic force microscopy (C-AFM) to perform a local I-V study of the TiO 2 surface under illumination. Fig.…”