Universal attenuated total reflectance sampling accessory

NPs were characterized by Fourier transform infrared spectroscopy (FT-IR), using a Frontier FT-IR spectrometer with universal attenuated total reflectance sampling accessory (PerkinElmer, Waltham, MA, USA). For each NP spectrum, a 50-scan was collected with 4 cm⁻¹ resolution in the mid-infrared region (3,600–600 cm⁻¹). For these analyses, the NP dispersions were lyophilized using a VirTis AdVantage 2.0 BenchTop freeze dryer (SP Scientific, Gardiner, NY, USA). Samples were frozen at −60°C for 12 hours, and primary drying was performed at 20°C and 150 mTorr for 20 hours. Additionally, secondary drying was performed at 25°C and 100 mTorr for 20 hours, for complete sublimation. The condenser was maintained at −80°C and 150 mTorr.

The PCL–CIP–NP microspheres were characterized using a Fourier transform infrared spectrometer (Spectrum 400; PerkinElmer Inc., Waltham, MA, USA) equipped with a universal attenuated total reflectance sampling accessory (PerkinElmer Inc.). The samples were also measured by dynamic light scattering (DLS) measurements. The DLS measurements were performed on a Zetasizer Nano S (Malvern Instruments, Malvern, UK) equipped with an HeNe laser at 632.8 nm and a scattering detector at 173°C using water as a dispersant (refraction index =1.33 and viscosity =0.8872) at the room temperature with cumulants analysis. Raman spectra of the synthesized NPs were obtained using a Raman spectrometer (RamanStation 400; PerkinElmer Inc.) equipped with an excitation source of 350 mW near-infrared 785 nm laser. The spectra were obtained from 100 cm⁻¹ to 1,800 cm⁻¹ with a peak resolution of 4 cm⁻¹. The solutions of NPs and PCL–CIP–NPs were dropped and dried overnight on carbon-coated Formvar 200 mesh copper grids (Ted Pella, Inc., Redding, CA, USA). The grids were visualized using a Philips 400 120 keV transmission electron microscope (TEM; Philips, Hillsboro, OR, USA) with a high-tilt goniometer stage.