The present invention provides methods and devices for producing particles with an average diameter less than about 15 .mu.m using the precipitation with compressed fluid-antisolvent (PCA) process and the carbon-dioxide assisted nebulization with a bubble dryer (CAN-BD) process. In the methods and nozzles of the invention, at least one jet of supercritical or near-supercritical fluid and at least one jet of solution interact to mix the supercritical or near-supercritical fluid and the solution within a chamber. The solution contains at least one solvent and at least one solute. At least one of the jets is a swirling jet. To form particles, the solvent and supercritical or near-supercritical fluid are then injected into a PCA or a CAN-BD process chamber. The degree of mixing depends in part on the power input into the mixing chamber. Power inputs of about 6.5.times.10.sup.9 W/m.sup.3 enhance the degree of mixing and allow production of nanoscale particles with the PCA process. The nanoscale particles have a size distribution so that polydispersity is less than about 1.75.