A small-angle neutron scattering investigation of rigid polyelectrolytes under shear

Abstract

Solutions of a rigid polyelectrolyte molecule, sulfo-poly(phenyleneterephthalamide) (SPTTA), in deuterated water have been investigated using small-angle neutron scattering. At low concentrations (1 wt%) the scattering spectrum presents a soft maximum similar to that of the interaction of rod-like objects. Two counterions are used, H + and Li + , and it is shown that aggregation is favoured as the proportion of Li + counterions increases. When kept at rest at room temperature, the solutions exhibit spontaneous birefringence. A 1 wt% solution was investigated under shear and it is shown that a very small shear rate is needed to produce a very strong alignment of rod-like objects. Such alignment saturates at high shear rates. Upon cessation of shear, a very long relaxation time is observed. The set of results strongly suggest aggregation of rigid polyelectrolyte molecules into long needles exhibiting very small cross sections.

A supramolecular nematic phase in sulfonated polyaramides

“…Further structural studies provide strong evidence for the presence of supramolecular aggregates in these gels. 3,4 Similar behaviour was recently reported for poly(p-benzamide) in DMAc/LiCl. 5 We have found that by displacing the sulfonic acid group along the polymer backbone -from the diamine to the acid ring -it is possible to avoid gel formation in water and instead a free flowing nematic phase is obtained.…”

“…Fig 4. Band-texture formed after cessation of simple shear flow on a 6wt% "sulfo-invert-PPTA" solution in water.…”

Formation of aqueous molecular nematic liquid crystal phase in poly(p-sulfophenylene sulfoterephthalamide)

“…Further structural studies provide strong evidence that the gel formation is due to the presence of needlelike supramolecular aggregates in solution. 5,6 In a recent publication, we reported the synthesis and the formation of a supramolecular nematic phase in a poly(p-phenylene sulfoterephthalamide) namely ''Sulfo Invert PPTA'' obtained from sulfonated terephthalic acid and para-phenylene diamine. 7 Surprisingly, the displacement of the sulfonic acid group, from the diamine to the acid ring, tremendously improves the solubility of the polymer resulting in a free flowing nematic solution.…”

Observation of transition cascades in sheared liquid crystalline polymers

“…Similarly, Picken and coworkers employed the Onsager relation to estimate of the dimensions of similar rodlike supramolecular assemblies of sulfonated derivatives of the well-known aramid, poly(para-phenylene terephthalamide) (PPTA). 49,50 Assuming a density of PBDT of 1.4 g mL −1 , * = 0.0085 and = 467. The diameter of PBDT rods is ~0.8 nm; thus, the estimated is 373 nm.…”