Figure 6 showed PEG 2000 characteristic peaks at 3409 cm−1 indicating intermolecular hydrogen-bonded hydroxyl group (O–H) asymmetric stretching. Peaks at 2945 cm−1, 2884 cm−1, and 2860 cm−1 are assigned to C–H symmetrical stretching. C–H bending is observed at 2740 cm−1 (42). Peaks at 1240 cm−1, 1146 cm−1, 1099 cm−1, and 1059 cm−1 are assigned to C–O–C stretching (43,44). Chitosan’s broad peak at 3354 cm−1 and 3291 cm−1 are indexed to NH2 stretching vibration. Peaks at 1651 cm−1 and 1585 cm−1 are assigned to N–H bending of primary amine. Peaks 1199 cm−1 and 1150 cm−1 are attributed to C–O stretching of C–O–C. Two intense peaks at 1058 cm−1 and 1026 cm−1 indicate the presence of primary aliphatic amine stretching of C–N overlapping with secondary cyclic alcohol stretching of O–H 1 (42,43,45). A peak at 894 cm−1 is attributed to the pyranoid ring of chitosan (46).
Fig. 6 Stacked spectra of ATR-FTIR from 4000 to 600 cm−1 for PALNs, physical mixture, acyclovir, lecithin, chitosan, and PEG 2000