Interface droplet—matrix

The emulsifying effects of a small quantity of a block copolymer, A-B, added to immiscible blend of homopolymers A and B, were examined by Leibler (1988). The theory predicted the reduction of the interfacial tension coefficient, Vi2, caused by equilibrium adsorption of a copolymer at the interface. For well-chosen compositions and molecular weights of the copolymer, low values of Vj2 are to be expected. This suggests a possible existence of thermodynamically controlled stable droplet phase, in which the minor phase homopolymer drops are protected by an interfacial film of the copolymer, interfacing the matrix polymer. The size distribution of the droplets is expected to depend on the rigidity and spontaneous radius of curvature of the interfacial film that can be controlled by molecular structure of the copolymer. 

Here, A,okl1 is the total interfadal area in the material of volume V, n is the unit normal vector of the interface (cf. Figure 4), and is the dyadic of n averaged over the whole interfadal area. Equation [19] holds for blends having dther a discontinuous (droplet/matrix-typ>e) morphology or a co-continuous morphology. As dearly noted from eqn [19], Oint reflects anisotropy of the shape of the phase-separated domains. Thus, the relaxation of detects recovery of isotropic shape of the domains driven by the interfadal tension. (In this relaxed state, the interfacial tension works isotropically to balance the isotropic pressure.)... 

Often interfaces and colloids are discussed together. Colloids are disperse systems, in which one phase has dimensions in the order of 1 nm to 1 pm (see Fig. 1.1). The word colloid comes from the Greek word for glue and has been used the first time in 1861 by Graham1. He applied it to materials which seemed to dissolve but were not able to penetrate a membrane, such as albumin, starch, and dextrin. A dispersion is a two-phase system which is uniform on the macroscopic but not on the microscopic scale. It consists of grains or droplets of one phase in a matrix of the other phase. 

Figure 3. Interface with pulsed field droplet deposition. Principle of the electrically mediated liquid deposition (lower panel). Deposition of the eluents from 4 parallel LC separations (upper panel. A). Samples cociystallized with matrix on hydrophilic islands with 400 pm diameter (upper panel, B) and droplets just before application of electrical field (upper panel, C). Reprinted with permission from Ericson et al. 2003. Copyright 2003 American Chemical Society.

Solid Fat. The consistency and the emulsion stability of margarine and most other table spreads depends on crystallized fat. Freeze-fracture electron microscopy of deoiled margarine shows the crystalline nature of the water droplet interface as well as a continuous fat matrix that appears to be an interconnected network... 

Sundararaj and Macosko (1995) and Beck Tan et al. (1996) observed that the addition of a block copolymer to the droplet phase before mixing it with the matrix phase had little effect on the resulting droplet size at low droplet volume fraction. Although a block copolymer should reduce the interfacial tension between the two phases, and thereby lead to smaller droplets, the diffusion time of the block copolymer may be too long for it to saturate the new interfacial area that must form rapidly if a droplet is to fragment. However, block copolymers do seem to suppress coalescence, possibly by immobilizing the interface... 

The currently most frequently applied method for LC-MALDI-MS is automated post-column fractionation and on-plate collection in discrete spots of the LC colunm effluent. After the solvent is evaporated, the matrix solution can be added, and MALDI-MS analysis of the various spots can be performed. The procedure requires a liquid-handling robot, capable of disposition of effluent fractions at discrete spots on the MALDI target. A number of ways were proposed for deposition in discrete spots on the MALDI target, e.g., blotting via direct contact between droplet and target [139-140], piezoelectric flow-through microdispensing [141], pulsed electrical-mediated droplet deposition [142], and a heated droplet interface [143], Commercial LC-MALDI-MS devices were recently reviewed [144],... 

Polymers are quite special dielectrics in that they can be highly insulating and have extremely low dielectric constants. For example, polyethylene can exhibit a dielectric constant as low as 2.2 and conductivity as low as 10 19 S/cm. These two characteristics make polymers very susceptible to another source of polarization—accumulation of virtual charge at the interface between the polymer matrix and any more polar or conducting phase, for example, water droplets. This interfacial polarization can dominate the dielectric characteristics of the polymer at low to intermediate frequencies. As a result, the detection of this polarization becomes an effective means of demonstrating the presence of two phases in the polymer. Even phases in the nanometer range will show this effect. A schematic of such polarization is shown in Figure 7-4. 

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