Mechanism And Process Of Uniform-Sized Droplets Prepared By The Jet Vibration

With the application and development of the synthetic chemistry and chromatog-raphy separation technology of biological and medical macromolecules, it has become an advanced research hotspot to develop a universal process for producing uni-form-sized polymer bead, along with the increasing demand for ones with a specific diameter range of 0.4-0.6 mm. Bulk polymerization is usually adopted to prepare large uniform-sized polymer beads and the prerequisite that assures polymer bead uniformity is to form controllable uniform-sized monomer droplets, which directly determine the size of polymer beads. Therefore, how to disperse monomer phase into uniform-sized polymerization unit, is the key issue of process development.In this thesis, needle-type jet dispersion technology was employed, combined with pulse disturbance technology to promote liquid column’s collapse, in order to prepare uniform-sized monomer droplets. Meanwhile, the requirement for adjustability of monomer droplet diameter was implemented, through investigating the factors includ-ing monomer property, jet velocity, pinhole diameter and frequency of imposed dis-turbance, which simultaneously provided basis research results and feasible technology method for the polymerization process development of large uniform-sized polymer bead. The specific research work was as follows:Primarily, a novel electrostrictive droplet generation device has been design inde-pendently, which adopted the function signal generator and power amplifier as oscilla-tion source and the double piezoelectric ceramic membrane as vibration component, to provide and impose perturbation with specific frequency on jet liquid column directly, thus contributed to the column’s collapse. The monomer droplet diameter was con-trolled by adjusting the velocity, pinhole diameter and disturbance frequency.On the basis of the droplet generation device, a series of experiments were carried out to investigate the effects of different fluids (pure water,50% ethanol aqueous solu-tion and pure ethanol, their surface tension was 72.53,58.18,21.87 mN·m-1, respec-tively), pinhole diameter (0.10-0.52 mm), monomer jet velocity (0-40 mL·min-1) and disturbance frequency (0～300Hz) on the jet vibration fracture process, diameter and uniformity of monomer droplet. The experimental results showed that monomer jet velocity and disturbance frequency were the key factors that affected droplet diameter and uniformity, the quicker velocity and frequency provided favorable conditions for reducing the droplet diameter; meantime, it could significantly enhance the droplet uniformity when imposing external disturbance. Within experimental conditions of natural jet, the maximum deviation of droplet mean diameter (1.03 mm) was 0.18 mm and monomer droplets within the mean diameter ±0.05 mm accounted for 89% of total in condition (water, surface tension 72.53 mN·m-1, pinhole diameter 0.42 mm, velocity 3.469 m·s-1), when exerting perturbation with frequencies ranging from 100 to 200 Hz, the maximum deviation reduced to 0.10 mm and proportion was up to above 95% in the same condition, which fully satisfied the industry requirements.Aimed at process development and industrial amplification, according to Ray-leigh-Sakai Jet Fracture Theory, two physical quantities, property coefficient k and inherent vibration representation index f0, were proposed to develop the mathemati-cal model of droplet diameter with jet velocity, disturbance frequency and pinhole di-ameter. k corrected the effect of monomer viscosity and surface tension, and subse-quently, the empirical formula of property coefficient was obtained by fitting the ex-perimental and literature data. The f0 combined inherent oscillation with imposed disturbance, which reflected the natural vibration energy resulting from the interaction between fluid and surrounding that arise from surface energy and kinetic energy. Eventually, the model calculation desirably matched with the results of consequent verification experiments, and the number average relative error of droplet diameter was 1.12%, which demonstrated the reliability of the droplet diameter expanding mathe-matical model and confirmed the feasibility and validity of needle-type jet dispersion technology for process development of large uniform-sized polymer bead.