Emulsion Preparation with Microstructured

Emulsion Preparation with Microstructured Systems, Fig. 1 Outline of some microfluidic emulsification geometries, (a) Cross section of a microchannel with a depth difference at the junction. The dispersed phase is pushed onto the terrace (indicated by the arrow) and an emulsion droplet is formed when the dispersed phase falls from the terrace into the deeper well (see also Fig. 2). (b) Top view of a T-Junction with a uniform... 

Emulsion Preparation with Microstructured Systems, Fig. 2 Impression of spontaneous droplet formation in terrace-based systems the entire system is covered with a top plate that is not shown for clarity reasons. In image (a), the to-be-dispersed phase is pushed through the channel on the left onto the terrace where it forms a disk. As soon as the disk reaches the end of the terrace (image (b)), the liquid can flow in a deeper part and assume... 

Emulsion Preparation with Microstructured Systems, Fig. 4 Snapshots of experiments left) and simulations (right) of droplet detachment at a T-junction. The flow rate of the continuous phase is 2 mL h and that of the to-be-dispersed phase is 0.2 mL h [5] (Reprinted with permission from Graaf, S. van der Nisisako, T. ... 

Emulsion Preparation with Microstructured Systems, Table 1 General comparison of shear-driven emulsification techniques ... 

Emulsion Preparation with Microstructured Systems, Table 2 Estimation of the device volume Vdevice and required area Adevice needed to handle oil at 1 m x h in various emulsification devices. The droplet size is between 5 and 10 pm ... 

Emulsion Preparation with Microstructured Systems, Fig. 6 Outlines of mass-parallelized microfluidic systems. Left, Y-junctions, top circular layout in the insert a single Y-junction with continuous-phase flow indicated by the light gray arrow and the dispersed-phase flow by the dark gray double-headed arrow. Bottom, linear layout, C and D represent the continuous-phase and dispersed-phase supply, respectively, and E the emulsion collecting area. Dimensions are not according to scale. Right top. 

Emulsion Preparation with Microstructured Systems, Fig. 7 Interfacial tension gas function of hexadecane flow rate for a. 3.0 wt% SDS solution ( ) at a constant continuous-phase flow rate of 0.23 mLh and for b. 0.15 (D), 0.25 (0), and 3.0 wt% SDS solution ( ) at continuous-phase flow rates varying... 

Emulsion Preparation with Microstructured Systems, Fig. 8 Left, overview of the coalescence chamber, with an image of coalescing droplets. Right, so-called film drainage profile the distance between the central points of the droplets is shown as function of time. Remarkably, the droplets stay in close proximity for 15 milliseconds prior... 

Roesch, R.R. and Corredig, M. (2002) Texture and microstructure of emulsions prepared with soy protein concentrate by high-pressure homogenization. Food Sci. Technol, 36,113. 

Commercial random SBR polymers (solution SBR) prepared by alkyllithium-initiated polymerization typically have 32% cis-, A-, 41% trans-, A-, and 27% vinyl-microstructure compared to 8% cw-1,4-, 74% trans-, A-, and 18% vinyl-microstructure for emulsion SBR with the same comonomer composition [3, 221]. Solution SBRs typically have branched architectures to eliminate cold flow [17, 49]. Compared to emulsion SBR, solution random SBRs require less accelerator and give higher compounded Mooney, lower heat buildup, increased resilience, and better retread abrasion index [3]. Terpolymers of styrene, isoprene, and butadiene (SIBR) have been prepared using a chain of single-stirred reactors whereby the steady-state concentration of each monomer and Lewis base modifier at any degree of conversion could be controlled along the reactor chain [3, 222-224]. 

Macierzanka, A., Szelag, H., Moschakis, T., Mrtrray, B. S. Phase transitions and microstructure of emulsion systems prepared with acylglycerols/zinc stearate emulsifier. Langmuir. 2006 22(6) 2487-2497. Fitzhugh, O. G, Bourke, A. R., Nelson, A. A., Frawley, J. P. Chronic oral toxicities of four stearic acid emulsifiers. Toxicol. Appl. Pharm. 1959 1(3) 315-331. 

Polymer materials can easily be prepared from HIPEs if one or the other (or both) phases of the emulsion contain monomeric species. This process yields a range of products with widely differing properties. Additionally, as the concentrated emulsion acts as a scaffold or template, the microstructure of the resultant material is determined by the emulsion structure immediately prior to polymerisation. 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

Figure 7.22 Microstructure of acidified mixed emulsions (20 vol% oil, 0.5 wt% sodium caseinate) containing different concentrations of dextran sulfate (DS). Samples were prepared at pH = 6 in 20 mM imidazole buffer and acidified to pH = 2 by addition of HCl. Emulsions were diluted 1 10 in 20 mM imidazole buffer before visualization by differential interference contrast microscopy (A) no added DS (B) 0.1 wt% DS (C) 0.5 wt% DS (D) 1 wt% DS. Particle-size distributions of the diluted emulsions determined by light-scattering (Mastersizer) are superimposed on the micrographs, with horizontal axial labels indicating the particle diameter (in pm). Reproduced with permission from Jourdain et al. (2008).

Cetostearyl alcohol is used in cosmetics and topical pharmaceutical preparations. In topical pharmaceutical formulations, cetostearyl alcohol will increase the viscosity and impart body in both water-in-oil and oil-in-water emulsions. Cetostearyl alcohol will stablize an emulsion and also act as a co-emulsifier, thus decreasing the amount of surfactant required to form a stable emulsion. Cetostearyl alcohol is also used in the preparation of nonaqueous creams and sticks. Research articles have been published in which cetostearyl alcohol has been used to slow the dissolution of water-soluble drugs.In combination with surfactants, cetostearyl alcohol forms emulsions with very complex microstructures. These microstructures can include liquid crystals, lamellar structures, and gel phases. ... 

Three different techniques, namely FFEM [20, 22], Cryo-Direct Imaging (Cryo-DI) [104] and freeze-fracture direct imaging (FFDI) [105], can be used to visualise the structure of micro emulsions. In FFEM the samples are prepared in a protected fashion in a sandwich. They are then rapidly frozen, fractured, shadowed with metal, and replicated with a thin carbon film. The replica of the fractured surface, the morphology of which is controlled by the sample s microstructure, is then studied by a TEM. In contrast to FFEM, in Cryo-DI thin films of the sample are rapidly frozen but immediately, without replication, trans-... 

In the previous sections the diaractnization of the molecular structure of polymers prepared by emulsion polymerization has been discussed. The eventual aim of making emulsion polymers is invariably the preparation of polymeric materials with desired properties. The present section deals briefly with exanqrles of the thermal and mechanical properties of emulsion polymers. Also special attention will be givoi K> flie important relation between molecular microstructure and properties. 

---