Journal of Colloid and Interface Science 286 (2005) 378–386 www.elsevier.com/locate/jcis Drop deformation dynamics and gel kinetics in a co-flowing water-in-oil system Bernhard Walther a , Carsten Cramer b , Armin Tiemeyer b , Lars Hamberg a , Peter Fischer b , Erich J. Windhab b , Anne-Marie Hermansson a,∗ a SIK, The Swedish Institute for Food and Biotechnology, P.O. Box 5401, SE-402 29 Göteborg, Sweden b Swiss Federal Institute of Technology (ETH Zurich), Institute of Food Science and Nutrition, Laboratory of Food Process Engineering, Schmelzbergstrasse 9, CH-8092 Zurich, Switzerland Received 27 August 2004; accepted 19 January 2005 Available online 21 February 2005 Abstract Drop deformation and superimposed gel kinetics were studied in a fast continuous-flow process for a water-in-oil system. Highly monodis- perse drops were generated in a double capillary and then deformed passing through a narrowing rectangular channel geometry. Nongelling deformation experiments were used to establish the process and compare it with existing theories. Thereafter, temperature induced drop gelation was included to study its effect on deformation and gel kinetics on short timescales and at high temperature gradients. The disperse phase was a κ -carrageenan solution with additional sodium and potassium ions for gelation experiments. Sunflower oil was used for the continuous phases. Nongelling experiments showed that shear forces are able to deform drops into ellipsoids. A comparison with the small deformation theory by Taylor was surprisingly good even when drop deformation and flow conditions were not in steady state. Superimposed gelation on the deformation process showed clearly the impact of the altered rheological properties of the dispersed and continuous phase. Deformation first increased on cooling the continuous phase until the onset of gel formation, where a pronounced decrease in deformation due to increasing droplet viscosity/viscoelasticity was observed. Drop deformation analyses were then used to detect differences in gelation kinetics at high cooling rate within process times as short as 1.8 s.  2005 Elsevier Inc. All rights reserved. Keywords: Drop deformation; Shear flow; Gelation; Viscoelasticity; Viscosity; Carrageenan 1. Introduction Simultaneous drop deformation and gel formation are rel- evant to the formation of special emulsion and suspension properties. Flow processes and techniques are available to deform liquid emulsion droplets on their way to suspended gelled particles and thus imprint liquid–liquid deformation onto solid particles. This modifies the rheological properties of the emulsion or suspension [1,2]. To further develop such processes, drop deformation and gel kinetics have to be in- vestigated under relevant flow conditions. * Corresponding author. Fax: +46-31-83-37-82. E-mail address: amh@sik.se (A.-M. Hermansson). In this investigation, drop generation, drop deformation, and gel kinetics are combined to study drop deformation in a fast continuous flow process with and without simultaneous gel formation under high temperature gradients. Particular attention is paid to the impact of gel formation, i.e., gel ki- netics and the viscoelastic parameters of the disperse phase. Drops are generated in a double capillary. Deformation and gel formation occur downstream along a narrowing rectan- gular deformation channel, which deforms drops into ellip- soids. The process demands two continuous liquid phases, one for drop generation, the continuous generation phase, and one for drop deformation, the continuous deformation phase. In contrast to previous studies of drop deformation and simultaneous gel formation in a 4 roll-mill apparatus with silicon oil as the continuous phase [3–5], it is now pos- 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.01.054