1 Preparation and Characterization of Oil-in-Water and Water-in-Oil Emulsions Prepared For Dr. Reza Foudazi, Ph.D. Chemical and Materials Engineering New Mexico State University By Muchu Zhou May 10, 2016
2 1 Introduction 1.1 Purpose of This Report The objective of this report is to clarify what I have done this semester for research course CHME 498. The research interest is Preparation and Characterization of Oil-in-Water and Water-in-Oil Emulsions. Thus, I would like to talk about what is emulsion, what are the main characteristics of emulsions, what are the existing methods for preparations of emulsions and how to make simple emulsions. 1.2 Background of This Report Emulsion is a kind of mixture comprised of two or more liquids, which usually are immiscible, and surfactant. The common types of emulsions are oil-in-water emulsion and water-in-oil emulsion. According to Aronson (1988), the emulsions have important industrial value in the wide range of field and it has been studied extensively recently. The emulsions play an important role in the industrial production and it has been applied to many fields including food industry, cosmetics industry and pharmaceutical industry. In the food industry, emulsifier can function as dough conditioners in order to improve tolerance to variations in flour and other ingredient quality. In the cosmetic industry, the majority of facial creams and lotions are emulsions. 1.3 Scope of This Report
3 This report is going to cover the following contents. Introduction of emulsions. Effect of surfactant. Common materials for preparation of emulsions. Main methods to make emulsions. How to make simple emulsions. Conclusions. 2 Emulsions 2.1 Introduction to emulsions What is emulsion? Emulsion is two or more different immiscible liquids with a surfactant. Thus, there is going to be two phases, one is continuous phase and another one dispersed phase. Generally speaking, the two phases are oil phase and water phase. Generally speaking, there are two common types of emulsions, one is oil-in-water emulsion, and another one is water-in-oil emulsion. The oil-in-water emulsion is usually common. Figure 2-1-1: Introduction to emulsion
4 Mason, T., Wilking, J., Meleson, K., Chang, C., & Graves, S. (2006). Nanoemulsions: Formation, structure, and physical propertites. Figure 2-1-2: The types of emulsion 2.2 Instability of Emulsions According to Aronson (1988), there are two main kinds of instabilities of emulsions, which are flocculation and coalescence. The flocculation is a reversible aggregation of droplets, which could result in phase separation in the field of gravity. Compare with flocculation, coalescence is caused by the rupturing of film of the continuous phase and it is a fusion of droplets into a larger droplets so that there will be separation of emulsion into discrete bulk phases.
5 Figure 2-2-1: Flocculation Figure 2-2-2: Instability of emulsions 2.3 Microemulsion and Nanoemulsion Moreover, there is existing microemulsion and nanoemulsion. Microemulsion is a kind of thermodynamically stable isotropic liquids including oil, water and surfactant. In the most microemulsion phases, the surfactant is highly soluble in both liquid phases. However, the nanoemulsion is a type of traditional emulsion and the droplets size is different.
6 According to Gupta (2010), the composition of the microemulsion and nanoemulsion are similar, are oil, water and surfactant. The droplets size is similar either. And the particle structure is similar, which is small spherical particles consisting of oil and surfactant molecular dispersed in the water phase. Yet they are absolutely different since the nanoemulsion is formed by mechanical shear and the micro emulsion is formed by self-assembly, that is why the microemulsion could be made without and external energy. 3 Effect of Surfactant The surfactant is so significant, because surfactant affects the emulsification in many ways. 3.1 Lowers interfacial tension If two immiscible liquids are in contact with each other, they will tend to maintain as small as interface as possible. Consequently, it is very difficult to mix them. When you shake them, they will become spherical droplets, but after a while, there will be phase separation since the liquids tend to maintain as small a surface area as possible and an interfacial tension will be maintained. However, when a surface active ingredient is added, its molecular will tend to be oriented between the two faces with the polar ends in the polar phase and non-polar ends in the non-polar phase, which will lower the cohesive force. 3.2 Allows an interfacial tension gradient dγ/dz to exist The presence of surfactant allows an interfacial tension gradient to exist which
7 implies that the tangential stress and velocity are no longer continuous across the droplet boundary, and the internal circulation in the droplet is impeded or even be prevented. It facilitates droplet deformation, hence breakup. 3.3 Coalescence is slowed down The instability coalescence is slowed down, it enhance the stability. 3.4 Interfacial instability can facilitate emulsification Interfacial instability may be occur, it facilitates the emulsification process. 4 Common materials for preparation of emulsions The common oil phases are the list as below. Density kg/m 3 Boiling Viscosity Structure Point C mpa s Silicone Oil 965-980(25C ) >140 100 Refined 920(20C ) 232 68 Sunflower Oil Paraffin Oil 800(25C ) 260 0.001 / Table 4-1: Common Oil Phases The common surfactants are the list as below.
8 Melt Density kg/m 3 Structure Point C PGPR 90 / / SDS 204-207 1010 F 68 52 / Table 4-2: Common Surfactants 5 Main methods to make emulsions There are many ways to produce emulsions. What I used is injection and stirring. Injection method is that the disperse phase (oil phase) is injected into the continuous phase and then it could be broken into large droplets. And stirring method is that using some equipments to make emulsion mixed homogenously and broke the large droplets into smaller one. 6 How to make simple emulsions What I have done is made some emulsion samples. The main method is combination of injection with stirring. The procedure is the following steps: Weight the surfactant.
9 Add water. Stir the liquid. Add silicone oil slowly using syringe pump. Stir the mixture for mixing homogeneously. Reduce the droplet size by the shear stress. The following figures are the samples. Figure 6-1: Sample with Ф = 0.4 silicone oil and wt% 1.0 SDS
10 Figure 6-2: Sample with Ф = 0.4 silicone oil and wt% 5.0 SDS Figure 6-3: Sample with Ф = 0.4 silicone oil and wt% 10.0 SDS
11 Figure 6-4: Sample with Ф = 0.3 silicone oil and wt% 5.0 Pluronic F68 Figure 6-5: Sample with Ф = 0.4 silicone oil and wt% 5.0 Pluronic F68
12 Figure 6-6: Sample with Ф = 0.3 silicone oil and wt% 5.0 SDS Figure 6-7: Sample with Ф = 0.4 silicone oil and wt% 5.0 SDS
13 7 Conclusions Figure 7-1: Observation through Microscope The figure as above is oil-in-water emulsion I made through microscope. The black line is from ruler which is 1mm length. The sample composition is wt% 5.0 SDS and Ф0.4 silicone oil. According to measurement, the max diameter is about 44 μm, and the min diameter is about 11μm. Thus, we can conclude that the droplet size is larger than we expected. The new question I need to think about is how to make the droplet size become much smaller. Increase the agitation energy means higher rotating speed when mixing two phases. If there is higher mixing speed, more shear stress could be obtained and the shear stress is significant in the disruption of droplets. The objective is to generate smaller stable droplets. We want to have rapid adsorption, lower the interfacial tension and form protective membrane. And we want to control the droplet size, so the disruption of droplet size is significant.
14 8 Appendix Method Related to method Drop formation Drops manly disrupted by a Energy density b Mode of operation c Restrictions d 1.Shaking 4a + (T) L B N 2.Pipe flow a.laminar 5 (+) V L - M C V 4a + T L - M C N b.turbulent 3.Injection 10a + - L C 4.Stirring a.simple 1, 2b + T, V L B, C stirrrer b.rotor- (5) + T, V M - H B, C stator c.scraper 5 + V L - M B, C V 8a +? L B, C N d.viberator 5.Colloid 2a, 4c, 6 (+) V M - H C V mill 6.Ball and 5 + V M B (C) V roller mills 7.High-press. (2b) - T, C, V H C N homogenizer 8.Ultrasonic a.vibrating 4d + C, T M - H C W knife + C M - H B, C W b.magnetostriction a V = viscous forces in laminar flow, T = turbulence, C = cavitation. b L = low, M = moderate, and H = high. c B = batch and C = continuous d The continuous phase should be V = viscous, N = not too viscous, W = aqueous. (This table is from Encyclopedia of Emulsion Technology, Volume 1 ) 9 References Aronson, M. P. (1989). The role of free surfactant in destabilizing oil-in-water
15 emulsions. Langmuir, 5(2), 494-501. Elbers, N. A., Jose, J., Imhof, A., & van Blaaderen, A. (2015). Bulk Scale Synthesis of Monodisperse PDMS Droplets above 3 μm and Their Encapsulation by Elastic Shells. Chemistry of Materials, 27(5), 1709-1719. Fryd, M. M., & Mason, T. G. (2012). Advanced nanoemulsions. Annual review of physical chemistry, 63, 493-518. Gupta, A., Eral, H. B., Hatton, T. A., & Doyle, P. S. (2016). Nanoemulsions: formation, properties and applications. Soft matter, 12(11), 2826-2841. Márquez, A. L., Medrano, A., Panizzolo, L. A., & Wagner, J. R. (2010). Effect of calcium salts and surfactant concentration on the stability of water-in-oil (w/o) emulsions prepared with polyglycerol polyricinoleate. Journal of colloid and interface science, 341(1), 101-108. Mason, T. G., Wilking, J. N., Meleson, K., Chang, C. B., & Graves, S. M. (2006). Nanoemulsions: formation, structure, and physical properties. Journal of Physics: Condensed Matter, 18(41), R635.