Fig. 2: Secondary structure analysis of SPI self-assembly.

a, b ATR-FTIR spectra of SPI solution during cooling down from 90 to 20 °C (a) and their second derivatives (b). c Relative change in the secondary structure during cooling down from 90 to 20 °C. d, e ATR-FTIR spectra of original SPI powder and the dried self-assembled film (d) and their second derivatives (e). f Quantification of secondary structure content calculated from Amide I band of IR spectra for original SPI powder and the dried self-assembled film. The indicated error bars are the s.d. of the average of three different spectra, each one is co-average of 256 scans.