University Institute of Chemical Technology (Maharashtra, IN) scientists have developed a nanocavitation process for the preparation of nanoscale particles of elastic material. Nanosuspensions have emerged as a promising strategy for an efficient delivery of hydrophobic drugs because of their versatile features such as very small particle size.
Aniruddha B Pandit and Mohan Narayan Patil disclose a method for the manufacture of nanoscale particles of Styrene Butadiene Rubber (SBR) in U.S. Patent 7,671,113. Acoustic as well as hydrodynamic cavitation methods are used to create nanoparticles of Styrene Butadiene Rubber.
As SBR particles are elastic in nature, conventional methods of size reductions such as impacting, grinding are unable to achieve the final size. Pandit and Patil have successfully achieved size reduction of the elastic material to nano scale by carefully controlled hydrodynamic cavitation techniques.
The extreme transient conditions generated in the vicinity and within the collapsing cavitational bubbles have been used for the size reduction of the material to the nano scale. Nanoparticles synthesis techniques include sonochemical processing, cavitation processing, and high-energy ball milling. In sonochemistry, an acoustic cavitation process can generate a transient localized hot zone with extremely high temperature gradient and pressure.
The method for the preparation of nanosuspension/nanoemulsion of elastic materials comprises passing a cavitating liquid through a hydrodynamic cavitation device having a cavitation plate with one or more orifices. Passage of the liquid through the one or more orifices causing the pressure of the liquid to drop so as to generate multitude of cavities, simultaneously, feeding a suspension of particulate material to a hydrodynamic cavitation device and circulating the suspension through the cavities, allowing the pressure of the cavitating liquid to recover resulting in collapsing of the cavities. The collapsing of the cavities and associated high pressure pulse causes size reduction of the particulate material, characterized in that the particulate material is an elastic particulate material with an average particle size of 600 to 1000 microns. The hydrodynamic cavitation device is operated at a pressure of 3 to 20 atm. and at a constriction velocity of 10 to 40 m/s.
By means of passing the materials through the cavitation device the mean particle size can be reduced to nanoscale of 70 nanometers (nm), with 8-10% variation in the size distribution. The materials may be further reduced to a size of 20 nanometers with a 2% variation in size.
Acoustic cavitation is induced by passing high frequency (16 kHz-100 MHz) sound waves i.e., ultrasound through liquid media. When ultrasound passed through the liquid media, in the rarefaction region local pressure falls below the threshold pressure for the cavitation (usually the vapour pressure of the medium at the operating temperature), millions of the cavities are generated. In the compression region the pressure in the fluid rises and these cavities are collapsed. The collapse conditions are dependent on the intensity and frequency of the ultrasound as well as liquid physical properties, temperature of the liquid and the dissolves gases.
Hydrodynamic cavitation can simply be generated by the passage of the liquid through a specified geometry of constriction such as orifice plates, ventury etc. When the liquid passes through the constriction, the kinetic energy of the liquid increases at an expense of the pressure. If the throttling is sufficient to cause the pressure around the point of vena contracta to fall below the threshold pressure for the cavitation (usually the vapor pressure of the medium at the operating temperature) millions of the cavities are generated. Subsequently, as the liquid jet expands, the pressure recovers and this results in the collapse of the cavities releasing the energy in the form of a high magnitude pressure pulse. During the passage of the liquid through the constriction, the boundary layer separation occurs and substantial amount of the energy is lost in the form of turbulence and permanent pressure drop.