Operating limits and parametric sensitivity of laboratory device for continuous production of liquid marbles

Abstract

Encapsulation of active compounds into liquid marbles (LMs) represents an emerging technology with potential applications in several fields including food, cosmetics and pharmaceutics. However, existing methods for the preparation of LMs are either based on manual one-by-one fabrication or on batch processes such as high-shear granulation, which lack the required precision in LM size distribution. We present a device capable of continuous LM production with high reproducibility, control over the LM properties and production rate flexibility. The device utilizes droplet impact onto a continuously moving powder bed on a belt conveyor with subsequent product separation by sieving. The device has been applied for fabricating LMs from various combinations of coating powders and core liquids including water- and oil-based systems as well as melts. Monodisperse populations of all three LM types were obtained in the range of 2.0–3.5 mm depending on the nozzle setting, and the maximum productivity of the device was up to 50 LMs per second. The effect of process parameters was investigated and guidelines for defect-free production were obtained. We 0.5 Re 0.25 above a critical value was found to indicate the onset of undesirable satellite droplet generation or interface jamming upon the droplet impact; the critical value was also found to depend on the thickness of the moving powder bed. Surprisingly, the minimum safe interval between consecutive LMs that was necessary to avoid coalescence was found to be invariable with respect to both LM type and diameter. The device was capable of laboratory-scale LM production for a range of product testing and prototyping purposes and provided useful data for subsequent process scale-up. • New device for continuous fabrication of liquid marbles was construced • Aqueous, oil- and melt-based liquid marbles were successfully produced • Feasible regions of opearing parameters for defect-free operation were determined • Criteria for trouble-shooting and scale-up were established