Pearl-necklace structure

In the presence of the polyelectrolyte polyallylamine hydrochloride (PAAN), the formation of a pearl-necklace structure between AOT-reversed micelles and PAAN was... 

The next subsections describe the properties of the pearl-necklace structure and the elongation of the pearl-necklace polymer chain by an external force. We will then present numerical simulations of single polyelectrolyte chains in a poor solvent. 

It decreases with the solvent quality and crosses over to the radius of a Gaussian polyelectrolyte for T (f-ls/b)1/3. In the pearl-necklace structure most of the polymer mass and charge belongs to the pearls but the size of the chain is dominated by the stretched strands. 

If the pearl-necklace structure contains only a few pearls, there are always pearls at the end of the chains and these pearls are slightly larger than the inner pearls. This can be proved by doing an explicit calculation of the local electrostatic potential along the necklace very similar to that done in the following section on annealed polyelectrolytes. 

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 Gibbs free energy provides also a useful investigation concerning the stability of the pearl necklace structure as it was mentioned in the preceding subsection. In Fig. 12 it is shown that the relatively flat minima can be easily disturbed by moderate forces. The shift of the minima is reached over a saddle point. 

The theory of Khokhlov [147] was revised by Dobrynin, Rubinstein and Obukhov [149], who demonstrated that a partially collapsed quenched PE chain acquires a pearl-necklace conformation, consisting of collapsed globular beads connected by stretched bridges. The pearl-necklace structure appears due to interplay of short-range monomer-monomer attraction with long range repulsion and is a manifestation of the Rayleigh instability constrained by the chain connectivity [ 158,159]. 

Using atomic force microscopy (AFM), Xu et al. [85] showed that similar macromolecular co-assemblies derived from the cylindrical PE brush based on quat-ernized poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMAQ) complexed with short poly(sodium styrene sulfonate) (PSSNa) have distinct longitudinal undulations (Fig. 8), thereby apparently providing experimental proof of a peculiar pearl-necklace structure of IPECs based on such branched PEs. 

The conclusions that we formulated in early 1990s are, in principle, in agreement with up-to-date knowledge. Water is a poor (but not too bad) solvent for non-ionized PMA and, hence, the conformational transition is expected to proceed not as a sharp transition, but via a cascade of pearl necklace structures. In Sect. 4.1, we will show that our recent MD simulations support the above description of the behavior. We included this almost-forgotten experimental study in the present feature article mainly because we returned to this problem and studied it theoretically within the POLYAMPHI network. 

PANI/multi-walled carbon nanotube (PANI/MWNT) composites have also been synthesized via an oxidative dispersion polymerization technique for ER fluid application [83], The morphology of PANI/MWNT composite particles seems to be pierced with MWNT like a pearl necklace structure as shown in Figure 14,6a, Under DC electric fields, the PANI/MWNT ER fluid shows a rapid and reversible change in shear viscosity with an applied electric field as shown in Figure 14,6b,... 

The composite r-PCC is found in clusters forming a pearl necklace structure with the fibrils, as shown in Fig. 5.6 right-hand side scanning electron microscopy (SEM) micrograph. Some fibrils are covered by a PCC particulate surface. 

Figure 6 Pearl-necklace structure In amphiphilic graft copolymer under poor solvent strength conditions for the main chain and good solvent strength conditions for the side chains m-4, n-40, and M-320). Molecular dynamics simulations snapshot kindly provided by P. Kosovan.

Figure 7 Molecular brushes with block copolymer side chain In selective solvent schematic presentation (a) and pearl-necklace structure In poly(acryllc acld)-Woc/(-poly(/7-butyl acrylate) molecular brushes In toluene (b), dip coated on mica (atomic force microscopy (AFM) phase Image). Adapted from Polotsky, A. V. Charlaganov, M. I. Xu, Y. etal. Macromolecules 200S, 41, 4020. ...

Uyaver S, Seidel C (2004) Pearl-necklace structures in annealed polyelectrolytes. J Phys ChemB 108(49) 18804-18814. doi 10.1021/jp0464270... 

The fact that the rotation correlation times of probes attached to PMAA chains with substantially different molar masses (starting at ca. 20 x lO g/mol) obey the same dependence on pH confirms the assumption that all the chains form different numbers of globules of the same size, each of them formed by parts of the chain roughly corresponding to 20 x 10" g/mol. The formation of the pearl necklace structure is further supported by high residual anisotropy at low pH the globules... 

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