Du 800 uv vis spectrometer

The polymeric micelles were prepared by the solvent evaporation method. The amphiphilic triblock copolymer (total mass 0.015 g) was dissolved in 5 mL of acetone/THF mixture (1:1), and the solution was added dropwise to 15 mL of deionized water at room temperature under stirring (800 min⁻¹). The resulting dispersion was stirred for 30 min and the organic solvent was evaporated using a rotary vacuum evaporator to afford stable aqueous micellar solution with a concentration of 1 gL⁻¹.
The critical micelle concentration (CMC) was determined spectrophotometrically by a method employing the hydrophobic dye 1,6-diphenyl-1,3,5-hexatriene (DPH). Aqueous copolymer solutions (2 mL) with different concentrations (between 0.005 and 1 gL⁻¹) were prepared and methanol solution of DPH (20 μL, 0.4 mM) was added to each sample. The samples were incubated in a dark place for 16 h at room temperature before recording the UV–vis absorption spectra of DPH in the wavelength range 250–600 nm at 25 °C (Beckman Coulter DU 800 UV–vis spectrometer). The CMC values were determined as the inflection points of the absorbance intensity (at 356 nm) vs. polymer concentration curve.
The resistance of micelles against degradation in an acidic medium was assessed by adding DPH-loaded micelles in a buffer with pH = 1.2. After storage for 3 h, the UV–vis absorption spectrum of DPH was recorded.

Measurements were carried out using a DU800 UV-Vis spectrometer (Beckman Coulter, Fullerton, CA). Samples (1- 2 μM) were heated gradually from 6 to 80°C, and absorbance at 260 nm was continuously recorded. The measured melting curves were analyzed as described [23 (link)] to obtain the standard state enthalpy (ΔH⁰) and entropy (ΔS⁰) of the transition, from which the standard state free energy of transition at 37°C (ΔG⁰_37°C) was computed.