Emulsion initiation

Fig. 9.16 Schematic illustration of drying process for SWNT-filled polymer emulsion. Initially the nanotubes and polymer particles are uniformly suspended in water (left). Once most of water has evaporated, the polymer particles assume a close-packed configuration with the nanotubes occupying interstitial space(center). Finally, the polymer particles will interdiffuse (i.e., coalesce) to forma coherent film, locking the SWNTs within a segregated network (right) (Keren et al, 2003. With permission from Wiley-VCH)...

Taking into account that the initial size of this second regime, do, is either the emulsion initial size or the size after the first regime, that is, da, the expression of d t) can be derived ... 

Figure 5.1. Microscopic image of an emulsion initially composed of monodisperse droplets having a diameter of about 1.5 xm, which has been submitted to an osmotic stress of 0.6 atm for 15 days at room temperature. (Reproduced from [8], with permission.)...

Several investigations have shown that iodine transfer polymerisation can occur by emulsion or radical initiation. When emulsion initiation is chosen, a per-fluoroalkyl iodide is involved and limits the molecular weights [378,379]. This is not described here but several articles and patents from Tatemoto are sug-... 

Fig. 7. Diagram of the Couette mixer. The premixed emulsion, initially located in the syringe, is forced by a piston into the gap between the rotor and the stator. The sheared emulsion is collected at the top of the mixer...

Several investigations have shown that iodine transfer polymerization can be processable by emulsion or radical initiations. When emulsion initiation is... 

Of a large number of possible fluorinated acrylates, the homopolymers and copolymers of fluoroalkyl acrylates and methacrylates are the most suitable for practical applications. They are used in the manufacture of plastic lightguides (optical fibers) resists water-, oil-, and dirt-repellent coatings and other advanced applications [14]. Several rather complex methods to prepare the a-fluoroalkyl monomers (e.g., a-phenyl fluoroacrylates, a-(trifluoromethyl) acrylic and its esters, esters of perfluoromethacrylic acid) exist and are discussed in some detail in [14]. Generally, a-fluoroacrylates polymerize more readily than corresponding nonfluorinated acrylates and methacrylates, mostly by free radical mechanism [15], Copolymerization of fluoroacrylates has been carried out in bulk, solution, or emulsion initiated with peroxides, azobisisobutyronitrile, or y-irradiation [16]. Fluoroalkyl methacrylates and acrylates also polymerize by anionic mechanism, but the polymerization rates are considerably slower than those of radical polymerization [17]. 

The effects of commercial grades of polyvinyl alcohol obtained from several manufacturers on the rate of polymerisation of vinyl acetate aqueous solutions and emulsions initiated by potassium persulphate at 60°C have been investigated. Increasing concentrations of polyvinyl alcohol in the same range tend to reduce the rate of polymerisation of the solutions but Increase the rate of polymerisation of emulsions. Considerable differences were noted between the effects of nominally simileir grades from different sources. Attempts to correlate the effect on the rate of polymerisation of vinyl acetate solutions with the acetyl content and molecular weight of the polyvinyl alcohol appear to have been confounded by an uncontrolled variable. A subsequent publication from the U.S.S.R. indicates that this may be the concentration of a by-product formed during the hydrolysis of the polyvinyl acetate. Other factors which may account for the effects are also discussed. 

Since the early 1980 s, Princen s work was continued by several other authors, e.g., by Reinelt [1993]. The latter author considered theoretical aspects of shearing three-dimensional, highly concentrated foams and emulsions. Initially, the structure is an assembly of interlocked tetrakaid-ecahedra (which have six square surfaces and eight hexagonal ones). An explicit relation for stress tensor up to the elastic limit was derived. When the elastic limit is exceeded, the stress-strain dependence is discontinuous, made of a series of increasing parts of the dependence, displaced with a period of y = 2. ... 

Princen s work was followed by (Reinelt 1993), who considered theoretical aspects of shearing three-dimensional, highly concentrated foams and emulsions. Initially, the structure is an assembly of interlocked tetrakaidecahedra (which have... 

Reactors for the emnlsion poljunerization of methacrylic esters are made of stainless steel and are jacketed for temperature control these reactors are bnilt to withstand pressnres of 446 kPa (65 psi) and contain emergency stacks with rupture disks in case of excess pressure buildup within the reactor. Agitation is a critical issne for emnlsion polymerization. Variable-speed drive shafts are used along with stainless steel agitators to mix the batch. Baffles on the reactor walls are also common featnres of indnstrial emulsion polymerization reactors. Temperature control is maintained through the use of steam and cold water circulation with the jacket of the reactor. Feed lines for the monomer emulsion, initiators, and... 

Effect of Surfactant Concentration. Raising the surfactant concentration increases the stability of adsorption layer which enhances resistance of the emulsion to coalescence. The radius of the aqueous internal phase droplets in the emulsion initially diminishes with the increase in surfactant concentration and then remains constant. This results from the tendency of the dispersed phase to minimize the interfacial area for a given amount of surfactant. Despite a high degree of dispersion of the internal phase, the droplets coalesce until they attain a surfactant content at the interface which is close to the limiting value of adsorption. When the surfactant is present in an amount sufficient for stabilization of all of the drops of internal phase formed as a result of the dispersion, a maximum stability of the emulsion (Figure 1) and a minimum coalescence rate constant (Figure 2, curve 1) are attained. 

Figure 8.18 The degradation of an emulsion initially composed of a mixture of 0.5 fim and 1 /im radius droplets of equal number concentration, showing the droplet diameters...

McNulty and Karel define a dimensionless parameter [F J/[F J which is always greater than 1.0 in their model and is a measure of the potential extent of release, defined as the potential extent of increase in aqueous concentration. The release potential is determined by the difference between [F ] and [F ]. Fig. 8.42 shows the influence of partition coefficient P and < j on the aqueous concentration of flavour immediately after emulsion dilution [F, ] and at equilibrium [F ] when /c = 2, and [F J = lOOppm. Uptake curves [Fwe]/[Fwd] < are obtained for the model when an emulsion initially containing no flavour is diluted with an aqueous phase containing an initial... 

First trials of FTP of styrene with CgFis-I were unsuccessful due to mass transfer limitations of the hydrophobic transfer agent through the aqueous phase. A less hydrophobic transfer agent, methyl-2-iodopropionate, was successfully used in FTP of styrene in emulsion, initiated by 2,2 -azobis(N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate... 

In addition to styrene, the other monomers that have been particularly well studied in TEMPO-mediated radical polymerization are 4-vinylpyridine (4-VP), " 2-vinylpyridine (2-VP), and to a lesser extent 3-vinylp yridine (3-VP). The NMP led to a good control over the polymer characteristics and well-defined architectures could be easily produced, such as amphiphilic block or graft copolymers. " Not only TEMPO was used as a stable radical mediator but also SGI, which led to well-controlled polymerization systems either in solution or in emulsion initiated by a water-soluble poly (acrylic acid) (PAA) macroinitiator. 

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