Pearl chain formation

Table VI summarizes observed manifestations of field-generated forces- The field effects may manifest themselves as an orientation of particles in the direction of the field or perpendicular to it or, "pearl chain" formation, i.e., the alignment of particles in the field direction may occur. This has long been considered a mysterious demonstration of microwave induced biological effects. Deformation or destruction of cells can be achieved with fields. The movement of cells in inhomogeneous electrical fields can be affected.

The solute particles are held at the accumulation wall by a DEP force which depends on the dielectric properties of the particles and the surrounding medium, the frequency and magnitude of the electrical field, and the electrode geometry. DEP-FFF is an unconventional FFF technique in that the DEP force is inherently non-uniformly distributed over the channel, not only in the plane of the electrodes/channel wall, but also across the channel above the electrodes [282]. Since solute particles themselves are a source of local field non-uniformities, mutual attraction occurs due to DEP forces between the particles which in extreme cases can lead to what is called pearl-chain formation. As a consequence, DEP-FFF can be considerably disturbed by interparticular interactions [57]. 

When an AC field is applied, the cells introduced into the channel can be guided to the areas with the highest electric field with positive dielectrophoresis. This facilitates self-assembly of the cells at the micro orifice and results in cell contact and pearl-chain formation (Fig. 2b). When the diameter of the micro orifice is smaller than that of the cells, one-to-one cell contact is guaranteed as there is space for only one cell to fit in the orifice. 

Fig. 50. Diagrammatic representation of mutual dielectrophoresis 61K If the particles approach during dielectrophoresis they are attracted to each other due to their dipoles. This leads to the formation of pearl chains of cells...

Conformations of single polyelectrolyte chains can be probed by external forces [67, 68]. An interesting question which arises from the formation of the pearl necklace structure is the mechanical response of the chain to an external force. The simplest mean field result can be derived from the free energy proposed by [64], However, their free energy can by strongly modified to take the electrostatic interactions between the different structural ele-... 

The amidic bonds within amino acids can be also used to effect the organization of polymers into superstructures (Fig. 10). Thus, the formation of artificial helices on the basis of assembling polymers has been described by use of poly(acetylenes) bearing pendant L-valine side-chains. [71,72] Two effects are important for the association of these ladder-type polymers into double-stranded helices (a) the reduction of conformational freedom by the poly(acetylene) chain with respect to a conventional alkyl-chain and (b) the selective association of the L-valine residues by specific hydrogen bonding. An AFM image of the associates on a fiat surface demonstrates the presence of a string-pearl structure reminiscent of natural DNA. 

The results of experimental and theoretical research on water-soluble (nonstoichio-metric) IPECs based on nonlinear (branched) polyionic species (HPE) complexed with oppositely charged linear PEs (GPE) demonstrated that the main feature of such macromolecular co-assemblies is their pronounced compartmentalized structure, which results from a distinctly nonuniform distribution of the linear GPE chains within the intramolecular volume of the branched HPE. In the case of star-shaped PEs or star-like micelles of ionic amphiphilic block copolymers, this com-partmentalization leads to the formation of water-soluble IPECs with core-corona (complex coacervate core) or core-shell-corona (complex coacervate shell) structures, respectively. Water-soluble IPECs based on cylindrical PE brushes appear to exhibit longitudinally undulating structures (necklace) of complex coacervate pearls decorated by the cylindrical PE corona. 

We have studied the effects of mixture composition on droplet microstructure (5), and summarized these results in the form of a rich morphology diagram (Figure 3) in the parameter space of mass fraction and shear rate. Formation of strings of the suspended phase was observed over a broad composition window. At each composition, experiments were stopped when strings were formed. We also found a non-transient moiphology where we saw arrangement of the droplets in ordered pearl-necklace chain structures. 

FIGURE 14.5. In some polymer-surfactant interactions there is evidence for the formation of micelle-like or hemimicelle aggregates of surfactant molecules along the polymer chain—something like a string of pearls. ... 

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