Concentration, temperature, and pH dependence of sunset-yellow aggregates in aqueous solutions: An x-ray investigation

Journal Article · Tue Dec 01 04:00:00 EST 2009 · Phys. Rev. E

DOI:https://doi.org/10.1103/PhysRevE.80.041703· OSTI ID:1005946

Joshi, Leela; Kang, Shin-Woong; Agra-Kooijman, Dena Mae; Kumar, Satyendra

The dye sunset yellow (SY) forms columnar aggregates via {pi}-{pi} stacking in aqueous solutions. These aggregates develop orientational and translational order at elevated concentrations to exhibit the nematic (N) and columnar (C) mesophases. Positional-order correlation lengths of the aggregates in the directions parallel and perpendicular to the stacking direction were measured as functions of temperature, concentration, and ionic content of solutions with synchrotron x-ray scattering in magnetically aligned samples. Average length of aggregates (i.e., the number of SY molecules in an aggregate) grows monotonically with concentration while their effective transverse separation decreases. The scission energy, E, determined from the Arrhenius thermal evolution of the longitudinal correlation length, is found to be 4.3 {+-} 0.3 k{sub B}T and 3.5 {+-} 0.2 k{sub B}T, in the N and C phases, respectively. Temperature and concentration dependence of E suggests that chromonic aggregation is not an isodesmic process. The aggregate length decreases with decreasing pH when HCl is added to the solution.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE
• OSTI ID: 1005946
• Journal Information: Phys. Rev. E, Journal Name: Phys. Rev. E Journal Issue: (4) ; 2009 Vol. 80; ISSN 1539-3755
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

43 PARTICLE ACCELERATORS
AQUEOUS SOLUTIONS
DYES
SCATTERING
SYNCHROTRONS