Temperature effect on microchannel oil-in-water emulsification

Abstract

Microchannel (MC) emulsification is a promising technique to produce monodisperse emulsions by spontaneous interfacial-tension-driven droplet generation. The purpose of this study was to systematically characterize the effect of temperature on droplet generation by MC emulsification, which is a major uncharted area. The temperature of an MC emulsification module was controlled between 10 and 70°C. Refined soybean oil was used as the dispersed phase and a Milli-Q water solution containing sodium dodecyl sulfate (1 wt%) as the continuous phase. Monodisperse oil-in-water (O/W) emulsions with a coefficient of variation below 4% were produced, and at all the operating temperatures, their average droplet diameter ranged from 32 to 38 lm. We also investigated the effect of flow velocity of the dispersed phase on droplet generation characteristics. The maximum droplet generation rate (frequency) from a channel at 70°C exceeded that at 10°C by 8.1 times, due to the remarkable decrease in viscosity of the two phases. Analysis using dimensionless numbers indicated that the flow of the dispersed phase during droplet generation could be explained using an adapted capillary number that includes the effect of the contact angle of the dispersed phase to the chip surface. Keywords Microchannel emulsification Á Temperature Á Uniform droplets Á Droplet productivity Á Capillary number List of symbols Variables A disk Initial disk area of a dispersed phase (m 2 ) A drop Droplet surface area (m 2 ) A MC Channel cross-sectional area (m 2 ) Ca d Capillary number of a dispersed phase (-) Ca h d Adapted capillary number of a dispersed phase (-) CV Coefficient of variation (-) d drop Droplet diameter (m) " d Dimensionless droplet diameter (-) d n,drop Number-weighted mean droplet diameter (m) d MC Channel hydraulic diameter (m) f MC Frequency per channel (s -1 ) f MC,max Maximum frequency per channel (s -1 ) g Acceleration due to gravity (m/s 2 ) Dh d Height of a dispersed phase chamber (m) h terrace Terrace height (m) DP d Pressure applied to a dispersed phase (Pa) DP d,bt Breakthrough pressure of a dispersed phase (Pa) T C Celsius temperature (8C) t det Detachment time (s) t gen Droplet generation time (s) U d,MC Flow velocity of a dispersed phase inside a channel (m)Greek symbols c Dynamic interfacial tension (N/m) c 0 Interfacial tension between the two phases in the absence of surfactant (N/m) jRelative rate of surfactant creation (s) s d Diffusion of surfactant molecules (s) c eq Equilibrium interfacial tension (N/m) g c Viscosity of a continuous phase (Pa s)

Effect of Temperature on Production of Soybean Oil-in-Water Emulsions by Microchannel Emulsification Using Different Emulsifiers

“…Figure 3 illustrates the relationship of the equilibrium interfacial tension (γ eq ) between the two phases at each temperature from 10℃ to 70℃. γ eq for the sodium oleate-containing system increased exponentially as T C increased, similar to the results for the sodium dodecyl sulfate-containing system (Butron Fujiu et al, 2010). In contrast, γ eq for the systems containing Tween 20 and PGM decreased exponentially as T C increased.…”

“…The equilibrium interfacial tension across the two phases was measured by the pendant drop method using a Full Automatic Interfacial Tensiometer (PD-W, Kyowa Interface Sciences Co., Ltd., Saitama, Japan). The contact angle of the dispersed phase to the channel wall was measured using a new MC array method proposed by Butron Fujiu et al (2010). Prior to each contact-angle measurement, the dispersed phase was introduced into hydrophilic channels (20-μm wide, 5-μm deep, and 2000-μm long) filled with the continuous phase.…”

“…Although temperature is also a parameter affecting the physical and physicochemical properties of two-phase systems containing an emulsifier, most of the MC emulsification research was performed at a control temperature of 20℃ or 25℃. As far as the authors know, only a paper by Butron Fujiu et al (2010) reported the effect of temperature on MC emulsification using a model oil/water/surfactant system. The aim of this study was to investigate the effect of temperature on MC emulsification using different food-grade emulsifiers.…”

Long-Term Continuous Production of Soybean Oil-in-Water Emulsions by Microchannel Emulsification

“…2b(i), the interfacial shape was kept symmetric to the center line of the MC. These results are typical behaviors for successful, stable droplet generation by MC emulsification (Butron Fujiu et al, 2011a). Figure 3a illustrates the variation of the d av and CV of the resultant O/W emulsion droplets stabilized by SDS during the continuous MC emulsification.…”

“…Butron Fujiu et al (2011a;2011b) reported that the maximum generation rate of uniformly sized soybean oil droplets stabilized by nonionic Tween 20 is lower than those stabilized by anionic SDS when using a hydrophilic silicon MC array plate. Kobayashi et al (2012) also reported some affinity between the dispersed phase covered by Tween 20 molecules and the plate surface, as the absolute ζ-potentials of soybean oil droplets stabilized by Tween 20 and the chip surface are markedly lower than those for the SDS-containing system.…”