Nicolet 460

FTIR experiments were performed using an FTIR spectrophotometer (Nicolet-460, Thermo Fisher Scientific, Waltham, MA, USA). The complexes obtained after freeze-drying were milled and pressed with potassium bromide and polymer in a ratio of 200:1. Transmittance values between 4000 cm⁻¹ and 400 cm⁻¹ were measured to determine the functional relationship between the different compounds.
XRD analyses of the samples were performed using a smart X-ray diffractometer (SmartLab 3KW, Rigaku Corporation, Tokyo, Japan), according to Dong et al. [20 (link)], with slight modifications. The prepared powder was flattened on a glass plate for X-ray diffraction analysis, and the scanning range was 2θ from 5o to 50°, with a step size of 5 °/min/scan rate.
Scanning electron microscopy (SEM) of the samples was conducted using a SU1510 SEM (Hitachi, Tokyo, Japan). The freeze-dried powder was adhered to a double-sided adhesive tape, coated with gold, and observed using a scanning electron microscope at a magnification of 500×.
An FEI Tecnai 12 (FEI Company, Hillsboro, NH, USA) was used for transmission electron microscopy (TEM). A drop of the complex coacervate solution was placed on a 400-mesh copper grid. The grids were then dried overnight at 40 °C, and the morphology of the samples was observed using an electron microscope with a single-tilt sample rack at an accelerating voltage of 100 kV.

¹H NMR were recorded with a 500 MHz Bruker Avance instrument and FTIR were recorded with Nicolet-460 (Thermo Fisher, Waltham, MA, USA). The diameters and zeta potentials of PILs were determined by DLS at 25 °C and electrophoretic light scattering (ELS) using a zeta Sizer Nano ZS (Malvern Instruments, Westborough, MA, USA).
The gelation time and the rheological properties of the hydrogels were evaluated at a constant frequency f = 1 Hz (25 °C) by a Malvern Kinexus pro rheometer. Following hydrogel formation, the frequency sweep experiment was performed at γ = 0.5%, and f = 0.1–100 Hz, and the amplitude sweep experiment was performed f = 1 Hz and γ = 0.1–100%.
The surface morphology of the freeze-dried hydrogels was observed using FE-SEM (Zeiss Sigma 500, Oberkochen, Germany). All samples were coated with gold before characterization.
Compressive stress–strain measurements of the freeze-dried hydrogels (d = 2 mm, h = 5 mm) were obtained using compression test machine (Bose ELF3200, Framingham, MA, USA). The load cell was 10 N, and the compression velocity was 1 mm/min. The stress and strain values were taken at the rupture point when the freeze-dried hydrogels brake.