Figure 4:

The second virial coefficients (B₂) derived from SAXS experiments at multiple [NA] quantify interchain interactions in solutions containing different concentrations of a) Na⁺ and b) Mg²⁺. B₂ > 0 signifies molecular repulsion, B₂<0 signifies molecular attraction. Uncertainties are derived from the error in fit parameters required to obtain B₂, as shown and detailed in the Supplementary Information. Filled data points for poly rA at high values of NaCl and MgCl₂ denote B₂ values extracted from only two sample concentrations (see SI), and thus have undefined uncertainties.