Emulsions defined

Viscosity of Emulsions. The viscosity of an emulsion, defined as the ratio of shear stress to shear rate, depends upon several factors ... 

The stability of w/c emulsions, defined as the time required for the volume of the emulsion to settle from 100% to 90% based upon visual observation, has been measured for PFPE-COO"NH4" surfactants with molecular weights ranging from 667 to 7500 [17]. Figure 2.4-10 shows the stability of emulsions formed by the above microfluidizer for equal weights of water and CO2 and 1.3 wt% of 2500g/mol PFPE-COO NH4. For each experiment where non-flocculated emulsions were present during shear, the specific conductivity was less than O.lpS/cm, indicating water droplets in a CO2 continuous... 

ME - micro emulsion defined here as the phase containing the most surfactant. 

Squeegee moves ink across and through screen mesh Emulsion defines and gaskets printed pattern Mesh count, wire diameter, and emulsion affect deposit... 

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

The phase-inversion temperature (PIT) is defined as the temperature where, on heating, an oil—water—emulsifier mixture inverts from O/W to a W/O emulsion [23]. The PIT correlates very well with the HLB as illustrated in Fig. XIV-10 [72, 73]. The PIT can thus be used as a guide in emulsifier selection. 

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Butter. In the United States about 10 wt % of edible fats used are butter. Butter is defined as a product that contains 80% milk fat with not more than 16% moisture. It is made of cream with 25—40% milk fat. The process is primarily a mechanical one in which the cream, an emulsion of fat-in-semm, is changed to butter, an emulsion of semm-in-fat. The process is accompHshed by churning or by a continuous operation with automatic controls. Some physical properties are given in Table 16 (see Emulsions). 

Distribution of the monomer units in the polymer is dictated by the reactivity ratios of the two monomers. In emulsion polymerization, which is the only commercially significant process, reactivity ratios have been reported (4). IfMj = butadiene andM2 = acrylonitrile, then = 0.28, and r2 =0.02 at 5°C. At 50°C, Tj = 0.42 and = 0.04. As would be expected for a combination where = near zero, this monomer pair has a strong tendency toward alternation. The degree of alternation of the two monomers increases as the composition of the polymer approaches the 50/50 molar ratio that alternation dictates (5,6). Another complicating factor in defining chemical stmcture is the fact that butadiene can enter the polymer chains in the cis (1), trans (2), or vinyl(l,2) (3) configuration ... 

The concentration of monomers in the aqueous phase is usually very low. This means that there is a greater chance that the initiator-derived radicals (I ) will undergo side reactions. Processes such as radical-radical reaction involving the initiator-derived and oligomeric species, primary radical termination, and transfer to initiator can be much more significant than in bulk, solution, or suspension polymerization and initiator efficiencies in emulsion polymerization are often very low. Initiation kinetics in emulsion polymerization are defined in terms of the entry coefficient (p) - a pseudo-first order rate coefficient for particle entry. 

The preparation of microspheres can be accomplished by either of two methods thermal denaturation, in which the microspheres are heated to between 95 and 170°C, and chemical crosslinking with glutaraldehyde in a water-in-oil emulsion. Well-defined microspheres can be easily prepared using these methods in large batches which are usually physically and chemically stable. Newer preparation methods for the preparation of albumin microspheres have been described by several authors (84-88). 

Several of these morphological factors are illustrated in Figure 1. Figure lA is of the fat portion of bacon and has been stained for connective tissue. It is noted that fat tissue is not all lipid but has an extensive connective tissue component ranging from fairly thick layers to delicate layers defining each adipose cell. Figure IB is from a finely chopped emulsion. Connective tissue pieces are stained dark, the protein matrix is gray and the... 

A Malvern Mastersizer (Malvern Instruments Ltd, Malvern, UK) with optical parameters defined by the manufacturer s presentation code 0505 was used to determine the droplet size distribution. The measurement was made in triplicate at room temperature. Water was used to disperse the emulsion droplets. 

Biphasic media are macroheterogenous, with a well-defined liquid-liquid interface [25,63] [Fig. 1(g), (h)], or microheterogeneous consisting of an emulsion with a very important interface area [37,38] [Fig. 1-f]. The first medium is used for kinetic studies... 

Fig. 2.3.5 Profiles recorded from a drying alkyd left. The Peclet number is defined as HE/D emulsion layer are shown on the right. At low where H is the film height, the evaporation Peclet number (upper set of profiles), drying is rate and D the particle diffusivity. The upper set...

The defined size ranges and limits are somewhat arbitrary since there are no specific boundaries between the categories. The transition of size ranges, either from molecular dispersions to colloids or from colloids to coarse dispersions, is very gradual. For example, an emulsion may exhibit colloidal properties, and yet the average droplet size may be larger than 1 pm. This is due to the fact that most disperse systems are heterogeneous with respect to their particle size [1-2]. 

An interface is defined as a boundary between two phases. The solid/liquid and the liquid/liquid interfaces are of primary interest in suspensions and emulsion, respectively. Other types of interfaces such as liquid/gas (foams) or solid/gas interfaces also play a major role in certain pharmaceutical dosage forms, e.g., aerosols. 

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