This study investigates the role of polyvinylpyrrolidone (PVP) as a capping and stabilizing agent for the synthesis of gold nanoparticles (AuNPs) in a nonaqueous choline chloride–urea deep eutectic solvent (DES).

The specific features of the phase diagrams of aqueous Pluronic systems, and particularly those of reverse Pluronics, are critically important for their broad range of applications, notably as nanocarriers for anticancer molecules. This work aims to investigate the effect of increasing hydrophobicity, achieved by varying the PPO/PEO ratio and the molecular weight, on the phase behavior of three reverse Pluronics: 10R5 [(PPO)₈–(PEO)₂₂–(PPO)₈], 17R4 [(PPO)₁₄–(PEO)₂₄–(PPO)₁₄] and 31R1 [(PPO)₂₆–(PEO)₇–(PPO)₂₆]. A broad set of physical measurements, including density, sound velocity, viscosity, and surface tension, was used to characterize the physical properties of the solutions. These data were complemented by additional techniques such as direct observation, dynamic light scattering, and rheological measurements. Based on the primary measurements, molar volume, apparent adiabatic compressibility, and hydration profiles were subsequently derived. Phase diagrams were constructed for each system over concentration ranges of 0.1–90 wt.% and temperatures between 6 and 70 °C, identifying distinct regions corresponding to random networks, flower-like micelles, and micellar networks. Notably, the 31R1/water system does not form flower-like micelles, whereas both the 17R4/water and 10R5/water systems display such structures, albeit in a narrow interval, that shift toward higher concentrations and temperatures with increasing PPO/PEO ratio. Altogether, the present study provides new insights into the physicochemical behavior of reverse Pluronic systems, offering a foundation for their rational design as hydrophobic nanocarriers, either as standalone entities or in conjunction with other copolymers.

Systems 10R5 [(PPO)₈ – (PEO)₂₂ – (PPO)₈], 17R4 [(PPO)₁₄ – (PEO)₂₄ – (PPO)₁₄] and 31R1 [(PPO)₂₆ – (PEO)₇ – (PPO)₂₆], selected based on their different molecular weights and PPO/PEO ratios, were studied in aqueous solution in order to investigate the effect of the variation of the copolymer hydrophobicity on the phase behavior of the system. Measurements and analysis of density, sound velocity, viscosity, and surface tension of the solutions were carried out, as well as confirmatory methods such as direct observation, dynamic light scattering and dynamic and shear rheological properties of the systems. From the density and sound velocity results, molar volume, apparent adiabatic compressibility, and hydration profiles were calculated. The zones of random networks, flower-like micelles and micellar networks were delineated for the three systems and plotted within phase diagrams in the concentration ranges of 0.1 - 90 wt.% and temperatures from 6 to 70°C. The results also show that the 31R1/water system does not form flower-like micelles. In contrast, the 17R4/water and 10R5/water systems form them in a small interval each, which moves at higher concentration and temperature values with the PPO/PEO ratio, as well as the zones where the micellar networks and their transition are located. The study of the physicochemical behavior of the three systems is reported, providing important information for future research to evaluate their use as hydrophobic nanocarriers, either individually or in combination with another copolymer.