(252f) Modelling of a Monodisperse Microparticle Production Process from the Controlled Hydrodynamic Instability of High Viscosity Polymer Jets

The importance of controlling the size of microparticles turns into a real engineering challenge for certain processes such as ink-jet printing or drug processing, becoming even more challenging when it deals with biomedical applications. For these, microparticles must possess strict biocompatible, biodegradable and mechanical features that allow them on the one hand integrating into biological tissues avoiding toxicity and removal difficulties and, on the other, withstanding physiological and administration conditions such as stresses at needle injection.

Biocompatibility and biodegradability concerns can be overcome with the use of natural polymers. They are well assimilated in human tissue environments and avoid surgical removal. However, relying on high viscosity polymers is a need to attain reliable microparticles in terms of mechanical resistance. This leads to difficulties in the microparticle production techniques, which generally involve constricted geometries, so that novel engineering solutions must be found in order to process such complex fluids.

We present the different modelling stages that have been conducted to analyze and optimize a novel technique that allows processing medium/high viscosity polymer solutions. The global aim lies in achieving a robust predictive modelling framework describing jet breakup and droplet formation.

The novel method easily controls microparticle size - ranging 300 to 600 μm - with zero-shear viscosities up to 3 Pa·s combining the use of a vibration-induced jet breakup technique and a pressurized system.

The analysis of the technique merges Hydrodynamics, Interfacial Dynamics and Material Sciencesconcepts performing experimental and rheological characterization and mathematical and computational modelling describing the sinusoidal instability induced in a free-surface polymer jet.

The experimental approach primarily embraces the obtaining of semiempirical relationships as a first predictive tool (function of viscosity and flow rate) and the performance of rheological analyses under different flow fields.

A linear mathematical approach addresses the physical multiphase phenomenon as a liquid jet injection into quiescent to obtain a dispersion relation describing the wave dynamics. A general viscoelastic model is used as constitutive equation in Navier-Stokes expressions to account for viscoelastic effects.

Dispersion curves and experimental verification make possible evaluating the influence of parameters (viscoelasticity, vibration, flow rate…) and determining the flow field that most affects the process. The model allows the prediction of the optimal conditions (in terms of vibration) to avoid nonlinear effects and obtain controlled size.

Finally Computational Fluid Dynamics (CFD) studies are performed to assess the numerical schemes and set up conditions that best deal with the interface tracking of the gas-liquid system of study. We find that Volume of Fluid method (VOF) is adequate to describe the profile patterns of main interest and allows a potential control of the process conditions.