Droplets, fluorocarbon

Other pharmaceutical applications have seen the SdFFF applied successfully to monitor droplet size distributions in emulsions, together with their physical state or stability. Some examples are fluorocarbon emulsions, safflower oil emulsions, soybean oil emulsions, octane-in-water emulsions, and fat emulsions. SdFFF is also able to monitor changes in emulsion caused by aging or by the addition of electrolytes. SdFFF has been used to sort liposomes, as unilamellar vesicles or much larger multilamellar vesicles, the cubosom, and polylactate nanoparticles used as drug delivery systems [41]. 

For cryogenic freezing, nitrogen is used in several forms—as a shower of liquid droplets, as a liquid bath for direct immersion, or as a cold gas. Carbon dioxide is used as a liquid or in solid snow" form. When used in a tunnel for 1QR applications, liquid carbon dioxide can freeze products at a temperature from -62 lo -78°C (-80 to 109°F). Fluorocarbons and halocarbons also have been used in conjunction with tunnel and spiral-type freezers thill are used in IQF methods. 

The rate of Ostwald ripening depends on the size, the polydispersity, and the solubility of the dispersed phase in the continuous phase. This means that a hydrophobic oil dispersed as small droplets with a low polydispersity already shows slow net mass exchange, but by adding an ultrahydrophobe , the stability can still be increased by additionally building up a counteracting osmotic pressure. This was shown for fluorocarbon emulsions, which were based on perfluo-rodecaline droplets stabilized by lecithin. By adding a still less soluble species, e.g., perfluorodimorphinopropane, the droplets stability was increased and could be introduced as stable blood substitutes [6,7]. 

An ideal solution to the problem of finding a universal method for making monodisperse imprinted beads would be a combination of the inertness of fluori-nated liquids with the quality of beads produced by the two-step swelling process. Unfortunately, to date it has not proved possible to make a microemulsion of the organic phase in a liquid fluorocarbon. It might be possible to get some control of particle size, however, by swelling a seed latex with the smallest droplet-size suspension which can be made. Work is in progress to evaluate this possibility. Other methods are available to achieve better particle size control in suspension polymerisation and these should also be evaluated [54]. 

Fluorinated surfactants (or fluorosurfactants, i.e., surfactants with hydrophobic tails comprising a fluorocarbon moiety) provide an alternative means of achieving extremely stable PFC emulsions, as they can provide very low PFC/water interfacial tensions [cr , another factor in Eq. (2)]. d s yet, this option has not been developed, in part because of the added cost involved in the evaluation for approval of a novel active excipient. A further means of effectively increasing the stability of EYP-based PFC emulsion consists of supplementing standard phospholipids with mixed fluorocarbon-hydrocarbon diblock compounds, such as 14 or 15. Such diblocks, which have fluorophilic-lipophilic amphiphilic properties, are expected to improve the adhesion of the phospholipid film onto the PFC droplet. 

Liquid Membrane Stability. While studies of other investigators have indicated that the blood has good compatibility with the liquid fluorocarbon surface, they also indicate that fluorocarbon droplets should not be introduced to the bloodstream of animals (6, 7, 8). Liquid membrane rupture in the oxygenator apparatus could produce droplets from the fluorocarbon which had formed the liquid membrane. These droplets would be entrained and returned to a test animal with the oxygenated blood. As a preliminary test for liquid membrane rupture and droplet formulation, the oxygen flow into apparatus was momentarily stopped, and blood samples were withdrawn for examination. 

The blood samples were centrifuged at 20,000 rpm at a distance of 4.5 inches for 20 minutes in a centrifuge maintained at 20°C. After centrifugation the blood separated into two layers, a top layer of plasma and a bottom layer of red cells. Since the liquid fluorocarbon is immiscible with the blood and is much heavier than the blood, entrainment of fluorocarbon in blood should result in the formation of a small, third layer of the fluorocarbon at the very tip of the pointed centrifuge tubes after such intensive centrifugation. However, no such layer was found in the tubes for all the four blood samples tested. The blood samples were also examined carefully under microscope. No tiny droplets of fluorocarbon were noticed. While it is possible that a few liquid membranes ruptured and escaped detection and more definitive testing would be required before application, instability of the liquid membranes does not seem to be a major problem. 

Based on the success of these fluoro-sulfosuccinates described above di-fluorocarbon phosphates have also been investigated. In terms of synthesis and raw materials costs these surfactants have significant advantages over the sulfosuccinates. Surfactants of this kind have also been studied by DeSimone et al (27 c), and the synthesis and purification are described elsewhere (27b, c). Detailed SANS experiments are described in these papers (27b, c), and it is clear that surfactants of diis kind stabilize aqueous nano-droplets. Hence, anionics other than sulfosuccinates may be employed in water-in-C(>2 microemulsions. Significantly, one of these conq>ounds (di-HCF6-P, see ref 27 b) stabilizes microemulsions in liquid CO2 at vapor pressure a potentially useftil result that may be of importance in facilitating applications. 

The results for water and blood drop absorption are presented in Table 7. The results showed that application of fluorocarbon on both polyester and polypropylene fabrics could produce a bric with acceptable water and blo< repellent properties as the time of water and blood absorption increases rapidly. The surflice tension of water is 72 dyn/cm and natural blood is around 52 dyn/cm. This means that these materials can spread rrq >idly on the polyester and polypropylene fabric surface. Application of fluorochranical reduces the surface energy of the fabric and do not permit the water or blood droplet to adsorb and spread on the fabric surface. With application of sufficient amount of fluorochonical on the fabric surfaces. It is possible to produce a fabric with water and blood repellent properties. This research showed that the amount of 2% fluorochemical was sufflcient to produce a febric with reasonable water repellent property. 

The design and synthesis of low-cost, green and low toxic effective CO2-S0I-uble surfactants represents a major challenge and draws attention from research groups around the world [25], So far, several fluorocarbon [26-29], sihcone [30,31], phosphate fluoro surfactants [32-34], and a series of fluorinated analogs of AOT [35-37], are shown to be effective surfactants for stabilizing water droplets in SCCO2 [38],... 

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