Xrdynamic500

The freezing point of water
placed on the gradient polymers was determined by in situ X-ray diffraction
during freezing. A low-temperature chamber allowed us to measure the
exact temperature of the crystallographic transition of water when
the drop froze. The cooling rate was 1 °C/min from 10 to −25
°C. The experiments were done in an air atmosphere and repeated
under a N₂ atmosphere. An Anton Paar’s XRDynamic
500 equipped with a TTK 600 low-temperature chamber with liquid nitrogen
cooling was used. It was equipped with a Primux 3000 sealed-tube X-ray
source with the Cu anode and a Pixos 2000 detection unit featuring
a solid-state pixel detector was used. A divergent beam Kα1,2
monochromator was placed in the primary beam path to work in an optimized
Bragg–Brentano geometry.

X-ray diffraction (XRD) analysis was performed under ambient conditions in open air, using Anton Paar XRDynamic 500. SEM images were obtained from an FEI Quanta FEG 250 SEM. Lyophilized samples frozen in liquid nitrogen and dried at −80 °C for 3 d (Labconco FreeZone) were prepared and coated with iridium for 8 s for SEM imaging. FTIR spectra data were obtained using the attenuated total reflectance (ATR) mode of a Thermo Scientific™ Nicolet™ iS50 FTIR spectrometer with a diamond ATR attachment. Conductivity was measured using a 2-probe Ohmmeter mode of Keithley 2450 multimeter. Tensile mechanical tests were performed using the Instron 5982 universal testing machine with a 100 N load cell. Filament-shaped specimens of ~1 mm diameter and rectangle-shaped specimens of ~8 mm width and ~1.5 mm thickness were prepared and tested at 5 mm min⁻¹ load speed. Digital optical microscope (Keyence VHX) was used to capture images of the folding actuator. Gel permeation chromatography analysis was performed using 4.0 mg/mL PNIPAM and 7.1 mg/mL PAM aqueous solutions through Shimadsu™ LC-2050 having UV detector, with Wyatt Instruments™ MALS light scattering (LS) and OptiLab differential refractive index (RI) detectors. The molecular weight of polymers was almost similar regardless of the detectors, and the molecular weight stated above was calculated based on the UV detector.