The scattering of the low and high MW PII-2T in CB solution is fitted to the 2SFC model shown in Figure and B, respectively. The individual contributions are shown as well, shifted down slightly for visibility. We find that for low MW PII-2T in CB the mean fibril diameter 𝑅 𝑓 ̅̅̅ and polymer diameter 𝑅 𝑝 ̅̅̅̅ is 10.3 nm and 31.2 Å, respectively, which is in good agreement with the initial cross-sectional Guinier analysis and freeze-dried imaging results. Likewise, for high MW PII-2T in CB we find a mean fibril diameter of 78 nm and a polymer diameter of 30.6 Å, also in good agreement (the extracted fibril diameter can be treated as a lower bound). From the Voigt peak center 𝑞 𝑐 we can also determine the lamellar d-spacing to be ~28 Å for both low and high MW PII-2T in CB which is in agreement with the polymer diameters and the lamellar stacking distance in solid PII-2T. We also found that the Lorentzian fraction of the pseudo-Voigt peak 𝜇 nearly always converged to 1. Although peaks are convolutions of Gaussian and Lorentzian character, systems with large paracrystalline disorder will approach a purely Lorentzian shape , which is reasonable for pre-aggregates formed in solution. Fit parameters for the 2SFC model for low and high MW PII-2T in CB and Dec are shown in Table . In addition, since more of the polymer scattering is revealed in the high MW data we are able to fit the persistence length 𝑙 𝑝,𝑝 resulting in values of 7.9 and 6.5 nm in CB and Dec, respectively, close to our calculated value of 7.5 nm. For the low MW PII-2T we fix the persistence length to 7.5 nm since the model is rather insensitive to its value due to the overshadowing presence of fibril aggregate scattering at intermediate 𝑞. Alternatively, we also show that for the high MW PII-2T the larger SFC contribution can be replaced with a power law if one wishes to apply a more general approach. Fitting with the power law is summarized in Figure and Table , with the low 𝑞 power law slope being -3.77 and -3.9 for CB and Dec, respectively, which is close to the ideal Porod slope of -4 and confirms our previous conclusion that the scattering at low 𝑞 stems from interacial scattering of a separate population of large aggregates rather than due to a structural dimension. Additionally, we use the 2SFC model to fit the CB/Dec series shown in Figure . A summary of the fit parameters for the CB/Dec series can be found in the supplementary (Table ).