Droplets orientation

Fig. 26. Previously synthesized homogeneous material of the quaternary X-Y-phase solid solution series (composition CuFeMo6S9), heated up to 1800 °C, and the melt regulus cooled to room temperature in less than 15 min. The figure shows relics of a darker Cu-Fe-rich sulfidic phase (approx, bornite composition) which separated from the Mo-rich sulfide. Thus, a large region of liquid immiscibility must exist throughout the quaternary system (cf. Figs. 15 and 20). Owing to some vapor loss molybdenum (white) has exsolved and remains in small droplets oriented in the sulfidic groundmass. Oil immersion, x 2500...

Figure 2 Aqueous droplets dispersed in crade oil and sub-jected to an electric field (a) no field (b) 5 s, 1 kV/cm -droplet orientation in chains along the direction of the field. The droplets become small net dipoles in the dielectric oil continuum and are attracted to each other, forming chains in the direction of the field. High field strengths will cause interdroplet membrane rupture and coalescence. The principle has been utilized for measuring emulsion stability (i.e., resistance to electrically forced breakdown) in the high voltage-time domain spectroscopy (HiV-TDS) (71,72) and conductivity techniques (73).

Fig. 7.6 Droplet orientation of NOA65/E7 DPDLC composite films doped with 0.015 wt% of dichroic azo red dye (a) without electric field and (b) 2.2 V/p...

Bridging flocculation is the easier to visualise. This occurs when the surfaces of the droplets are attractive to the added polymer and polymer adsorption occurs at the droplet surface. When insufficient polymer is added to coat completely the droplets surfaces, encounters may occur between droplets orientated such that an area with adsorbed polymer on one drop meets an area free from polymer on a second drop. Under these circumstances the polymer molecule(s) already adsorbed to one drop may frirther adsorb to the second drop, creating a polymer bridge. The resilience of this bridge then maintains the droplets at a elose droplet-droplet separation (i.e. flocculated). 

In the case of bipolar structure (Fig. 4.1), a new low frequency mode appears in the spherical droplets, in which reorientation of the average droplet direction occurs. As there is no restoring torque for this type of motion, this mode represents free diffusion of the droplet orientation. This can, however, be strongly influenced by external electric fields. 

In the gas/liquid spray form of nebulizer, a stream of gas interacts with a stream of liquid. Depending on the relative velocity of the two streams and their relative orientation, the liquid flow is broken down into a spray of droplets, as in the common hair sprays. 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

Oriented strandboard (OSB) resins are quite similar to plywood resins, though they tend to be lower in alkalinity and higher in solids. Sinee OSB resins are sprayed onto dry wood in small discrete droplets rather than applied in glue lines, the problems associated with holding the glue on the wood surfaee are not usually issues of coneem. Adhesive dry-out and loss of flow displace over-penetration as major difficulties. 

The formation of a fibrillar structure in TLCP blends makes the mechanical properties of this kind of composites similar to those of conventional fiber reinforced thermoplastics [11,26]. However, because the molecular orientation and fibrillation of TLCPs are generally flow-induced, the formation, distribution, and alignment of these droplets and fibers are considerably more processing-dependent. We do not know ... 

In all cases of the processing conditions, TLCP domains were well dispersed and deformed to droplets in the core layer, but there was only a narrow distribution of their aspect ratio (about Hd 6) and less orientation. In both transition and skin layers, the domains were also well dispersed, but more oriented and fibrillated in the flow direction. From this reason, we give the distribution of aspect ratio Ud) and fiber number (N) versus fiber length class in Fig. 22, only for skin and transition layers, respectively. 

According to the composite theory, tensile modulus of fiber reinforced composites can be calculated by knowing the mechanical constants of the components, their volume fraction, the fiber aspect ratio, and orientation. But in the case of in situ composites injection molded, the TLCP fibrils are developed during the processing and are still embedded in the matrix. Their modulus cannot be directly measured. To overcome this problem, a calculation procedure was developed to estimate the tensile modulus of the dispersed fibers and droplets as following. 

GA is well recognized as emulsifier used in essential oil and flavor industries. Randall et al., 1998, reported that the AGP complex is the main component responsible for GA ability to stabilize emulsions, by the association of the AGP amphiphilic protein component with the surface of oil droplets, while the hydrophilic carbohydrate fraction is oriented toward the aqueous phase, preventing aggregation of the droplets by electrostatic repulsion. However, only 1-2% of the gum is absorbed into the oil-water interface and participates in the emulsification thus, over 12% of GA content is required to stabilize emulsions with 20%... 

Other noncontact AFM methods have also been used to study the structure of water films and droplets [27,28]. Each has its own merits and will not be discussed in detail here. Often, however, many noncontact methods involve an oscillation of the lever in or out of mechanical resonance, which brings the tip too close to the liquid surface to ensure a truly nonperturbative imaging, at least for low-viscosity liquids. A simple technique developed in 1994 in the authors laboratory not only solves most of these problems but in addition provides new information on surface properties. It has been named scanning polarization force microscopy (SPFM) [29-31]. SPFM not only provides the topographic stracture, but allows also the study of local dielectric properties and even molecular orientation of the liquid. The remainder of this paper is devoted to reviewing the use of SPFM for wetting studies. 

Of special interest in liquid dispersions are the surface-active agents that tend to accumulate at air/ liquid, liquid/liquid, and/or solid/liquid interfaces. Surfactants can arrange themselves to form a coherent film surrounding the dispersed droplets (in emulsions) or suspended particles (in suspensions). This process is an oriented physical adsorption. Adsorption at the interface tends to increase with increasing thermodynamic activity of the surfactant in solution until a complete monolayer is formed at the interface or until the active sites are saturated with surfactant molecules. Also, a multilayer of adsorbed surfactant molecules may occur, resulting in more complex adsorption isotherms. 

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