Emulsions hexadecane

Fig. XIV-4. Electrophoretic mobility of n-hexadecane drops versus the pH of the emulsion. (From Ref. 12.)...

The charge on a droplet surface produces a repulsive barrier to coalescence into the London-van der Waals primary attractive minimum (see Section VI-4). If the droplet size is appropriate, a secondary minimum exists outside the repulsive barrier as illustrated by DLVO calculations shown in Fig. XIV-6 (see also Refs. 36-38). Here the influence of pH on the repulsive barrier between n-hexadecane drops is shown in Fig. XIV-6a, while the secondary minimum is enlarged in Fig. XIV-6b [39]. The inset to the figures contains t,. the coalescence time. Emulsion particles may flocculate into the secondary minimum without further coalescence. 

Fig. XrV-6. (a) The total interaction energy determined from DLVO theory for n-hexadecane drops for a constant ionic strength - 5.0 nm) at various emulsion pH (b) enlargement of the secondary minimum region of (a). (From Ref. 39.)...

Mineral Oil Hydraulic Fluids. Absorption of a mineral oil in an emulsion was apparently very slow in female rats injected subcutaneously with 0.1 mL and in squirrel monkeys injected intramuscularly with 0.3 mL (Bollinger 1970). The emulsion contained 1 volume mannide monoleate, 9 volumes mineral oil, and 9 volumes water [14C]labeled hexadecane, a major component of the mineral oil, was added to the emulsion as a radiotracer. At 1 week and 10 months after treatment, radioactivity remaining at the sites of injection accounted for 85-99% and 25-33%, respectively, of the administered radioactivity. 

Experiments with monkeys given intramuscular injections of a mineral oil emulsion with [l-14C] -hexa-decane tracer provide data illustrating that absorbed C-16 hydrocarbon (a major component of liquid petrolatum) is slowly metabolized to various classes of lipids (Bollinger 1970). Two days after injection, substantial portions of the radioactivity recovered in liver (30%), fat (42%), kidney (74%), spleen (81%), and ovary (90%) were unmetabolized -hexadecane. The remainder of the radioactivity was found as phospholipids, free fatty acids, triglycerides, and sterol esters. Essentially no radioactivity was found in the water-soluble or residue fractions. One or three months after injection, radioactivity still was detected only in the fat-soluble fractions of the various organs, but 80-98% of the detected radioactivity was found in non-hydrocarbon lipids. 

Systems and materials. The reaction was carried out at several compositions in an ionic and in a nonionic system. The ionic system consisted of an emulsifier (49.6 wt % cetyltrimethyl ammonium bromide (CTAB)/50.4% n-butanol), hexadecane, and water. The nonionic emulsifier consisted of 65.7% polyoxyethylene (10) oleyl ether (Brij 96) and 34.4% n-butanol, again with hexadecane and water. In both systems, mlcroemulslon (pE) compositions used were obtained by diluting an initial 90 weight percent (%) emulsifler/10% oil mixture with varying amounts of water. Micro-emulsion samples thus obtained had final compositions of 30 to 80% water. Phase maps describing these systems have been published (10-11). 

Figure 2.20. (a) Disjoining pressure vs. thickness isotherm (dots, experimental data line, doublelayer fit) for an emulsion Him stabilized by 0.1% 8-casein, ionic strength of 10 mol/l NaCl, oil phase = hexadecane. (b) Comparison between the data obtained from TFB, MCT, and SFA. (Adapted from [87].)... 

Rgure 2.26. Six consecutive steps in shrinking of an emulsion film stabilized with 0.1 wt% BSA. Oil phase is hexadecane the ionic strength is 10 mol/1. The bar corresponds to 100 j,m. The local adhesion on aggregates is evident. Arrows indicate some of the points of adherence at the interfaces. (Adapted from [87].)... 

Because the size of the emulsion droplets dictates the diameter of the resulting capsules, it is possible to use miniemulsions to make nanocapsules. To cite a recent example, Carlos Co and his group developed relatively monodisperse 200-nm capsules by interfacial free-radical polymerization (Scott et al. 2005). Dibutyl maleate in hexadecane was dispersed in a miniemulsion of poly(ethylene glycol)-1000 (PEG-1000) divinyl ether in an aqueous phase. They generated the miniemulsion by sonication and used an interfacially active initiator, 2,2 -azobis(A-octyl-2-methyl-propionamidine) dihydrochloride, to initiate the reaction, coupled with UV irradiation. 

Figure D3.4.7 showstypical results obtained from a storage stability test (see Basic Protocol 1) of an oil-in-water emulsion that consists of a 20% (v/v) hexadecane-in-water emulsion stabilized by 2% (w/v) polyoxyethylene-20-sor-...

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

Hindle, S., Povey, M.J.W., Smith, K.W. 2000. Kinetics of crystallization in n-hexadecane and cocoa butter oil-in-water emulsions accounting for droplet collision mediated nucleation.. / Coll. Interface Sci. 232, 370-380. 

In Fig. 8 the calorimetric curve of a typical miniemulsion polymerization for 100-nm droplets consisting of styrene as monomer and hexadecane as hydrophobe with initiation from the water phase is shown. Three distinguished intervals can be identified throughout the course of miniemulsion polymerization. According to Harkins definition for emulsion polymerization [59-61], only intervals I and III are found in the miniemulsion process. Additionally, interval IV describes a pronounced gel effect, the occurrence of which depends on the particle size. Similarly to microemulsions and some emulsion polymerization recipes [62], there is no interval II of constant reaction rate. This points to the fact that diffusion of monomer is in no phase of the reaction the rate-determining step. 

For the moderately hydrophilic hydroxyethyl methacrylate, cyclohexane and hexadecane were chosen as the continuous phase. As initiators, PEGA200 which is soluble in the monomer phase, but not in cyclohexane, turned out to be applicable. AIBN which is mainly soluble in the cyclohexane phase could also be successfully used. KPS cannot be employed as initiator due to solubility problems. Small amounts of water act as lipophobe, and it could be shown by turbidity measurements that the addition of water increases the emulsion stability. 

Span surfactant niosomes have been dispersed in oil-in-water emulsions to yield a vesicle in a water-in-oil system, v/w/o, using the same surfactant that was used to make niosomes [152]. The release of CF from these systems followed the trend v/w/odifference between the v/w/o and w/o formulations was minimal. The release of CF encapsulated within these niosomes was influenced by the emulsion oil following the trend, isopropyl myristate>octane>hexadecane and by the nature of the surfactant, following the trend span 20>span 40>span 60. Span 80 v/w/o systems had a rather faster release rate due to the unsaturation in the oleyl alkyl chain, which leads to the formation of a more leaky membrane. 

We have developed new reaction systems based on colloidal dispersions [23, 24], namely highly concentrated water-in-oil (gel) emulsions, which could overcome most of the disadvantages of the aqueoussolvent mixtures such as inactivation of the aldolase and incomplete aldehyde solubilization in the medium. These emulsions are characterized by volume fractions of dispersed phase higher than 0.73 [25] therefore, the droplets are deformed and/or polydisperse, separated by a thin film of continuous phase. Water-in-oil gel emulsions of water/Ci4E4/oil 90/4/6 wt%, where C14E4 is a technical grade poly(oxyethylene) tetradecyl ether surfactant, with an average of four moles of ethylene oxide per surfactant molecule and oil can be octane, decane, dodecane, tetradecane, hexadecane, or squalane, were typically chosen as reaction media [23, 26]. 

Gel emulsions were applied successfully for the first time in aldol additions of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde as model aldehydes catalyzed by RAMA [24]. The first interesting observation was that the stability of RAMA in water-in-oil gel emulsions improved by 25-fold compared to that in dimethylformamide/water l/4v/v co-solvent mixture. The reported experimental data concluded that both the highest enzymatic activities and equilibrium yields were observed in water-in-oil gel emulsion systems with the lowest water-oil interfacial tension attained with the most hydrophobic oil component (i.e. tetradecane, hexadecane, and squalane). 

Effect of hexadecane as additive In a series of papers Hallworth and Carless (7,8,9,TO) have investigated the effect of the nature oT the internal phase on the stability of oil in water emulsions as well as the effect of addition of long chain fatty alcohols with sodium dodecyl sulphate or sodium hexadecyl sulphate as the ionic emulsifier. They found that light petroleum and chlorobenzene emulsions prepared only with sodium hexadecyl sulphate were much less stable than those produced using the longer chain paraffins, white spirit and light liquid paraffins. 

In Fig. 12 are given some of hexadecane is compared with the stability of the emulsions homogenizer and with the cationic OPB emulsifier. The figure also includes a result of an experiment with OPB without any additive, which as expected led to a very unstable emulsion. 

As shown, the application of the homogenizer for preparing the emulsions did not lead to any increase in the stability of the emulsion with hexadecanol as additive as determined by measuring the amount of adsorbed OPB as a function of time with stirring at 60 °C. Addition of hexadecane leads to an extremely stable emulsion even at the relatively stirring at 60 °C. In fact, the decane as additive is even more obtained with n-eicosanol. 

With hexadecane the electron micrographs of the emulsion immediately after preparation (Fig. 15) show approximately the same size and size distribution as obtained with hexadecanol. With hexadecane, however, the electron micrograph taken after 23 h stirring at 60 °C (Fig. 16), reveals that the small droplets to a large extent are still present and that only a relatively small number of larger droplets in the range of 1 urn have been formed. 

Figure 15. Electron micrograph of monomer emulsion of Figure 12 with OPB + hexadecane immediately after homogenization...

Figure 17. Electron micrograph of final latex from an emulsion prepared as the one in Figure 15 with AIBN added to the styrene before homogenization, homogenized, and polymerized. Styrene = 250 g, H,0 = 750 g, OPB = 2.0 g/dm H,0. AIBN = 6.0 g in 250 g styrene. Molar ratio hexadecane OPB — 4 1. Temp. = 60°C.

Davies and Smith suggest that the effect of addition of small amounts of hexadecane on stability may be due to a prevention of emulsion degradation by molecular diffusion. This approach to emulsion instability was first presented by Higuchi and Misra (12), and was based on the fact that small droplets will demonstrate deviations in physical properties as compared to larger droplets or plane surfaces. 

Figure 9.10 Emulsion switching for a hexadecane-water 2 1 (v/v) mixture containing switchable surfactant, after carbon dioxide treatment and 10 min shaking and (A) 5 min wait period, (B) 30 min wait period and (C) 24 h wait period. (D) After subsequent treatment with argon to turn off emulsification. [Reprinted with permission from Science 2006, 313, 958-960. Copyright 2006 American Association for the Advancement of Science.]...

Fig. 11. Conversion versus time curves for seeded emulsion polymerizations of styrene with hexadecane present in the monomer phase. T — 333 K.

Machi et at. (1974) first reported an investigation of the radiation-induced emulsion polymerization of tetrafluorocthylene, with ammonium perfluorooctanoate as the emulsifier. A 200-ml stainless steel autoclave, equipped with a magnetically driven propeller-type stirrer, was used. The standard recipe used was 28gm of monomer in 150 ml of water with 1% emulsifier (based on tbe water). n-Hexadecane (2.0 ml) was added to inhibit any gas-phase polymerization. The polymerizations were conducted at... 

Platinum salts were incorporated into water in an oil emulsion, e.g. penta-ethylene glycol dodecyl ether in hexadecane/water (= inverted micelle) with well-defined cavities. The platinum colloids which are then produced by hydrazine hydrate are uniform. No measurable particles fell outside the limit of... 

The same apparatus was used to measure the kinetics of emulsion crystallization under shear. McClements and co-workers (20) showed that supercooled liquid n-hexadecane droplets crystallize more rapidly when a population of solid n-hexa-decane droplets are present. They hypothesized that a collision between a solid and liquid droplet could be sufficient to act as a nucleation event in the liquid. The frequency of collisions increases with the intensity of applied shear field, and hence shearing should increase the crystallization rate. A 50 50 mixture of solid and liquid n-hexadecane emulsion droplets was stored at 6 -0.01 °C in a water bath (i.e., between the melting points and freezing points of emulsified n-hexadecane). A constant shear rate (0-200 s ) was applied to the emulsion in the shear cell, and ultrasonic velocities were determined as a function of time. The change in speed of sound was used to calculate the percentage solids in the system (Fig. 7). Surprisingly, there was no clear effect of increased shear rate. This could either be because increase in collision rate was relatively modest for the small particles used (in the order of 30% at the fastest rate) or because the time the interacting droplets remain in proximity is not affected by the applied shear. 

Fig. 7. Crystallization kinetics of mixtures 10 wt% liquid n-hexadecane emulsion droplets in the presence of 10 wt% solid n-hexadecane emulsion droplets at 6°C. Measurements were conducted at a shear rate of 100 s .

Kaneko, N., T. Horie, S. Ueno, J. Yano, T. Katsuragi, and K. Sato, Impurity Effects on Crystallization Rates of n-Hexadecane in Oil-in-Water Emulsions, J. Crystal Growth 197 263-270 (1999). 

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