Smart Polymeric Nanoparticles: Influence of Functional Groups on Their Structural Behavior Under Specific Physical and Chemical Stimuli

Smart materials at the nanoscale level have seen significant advancements, leading to innovative applications in materials science and engineering. These materials are able to respond to physical, chemical, and/or biological stimuli. In particular, the behavior of sensitive polymer particles and their unique properties are strongly influenced by functional groups (GFs) attached to the main chain. For this reason, they can be used in several knowledge areas. The aim of this research is to synthesize Ph-thermo-responsive polymeric nanoparticles functionalized with carboxylic and amide groups by emulsion polymerization to be used as drug delivery systems. According to the methodology, series 1 (core–shell) and series 2 (core with concentration gradient) were prepared using a two-stage semicontinuous process and a power feed process, respectively. Polymers were characterized using dynamic light scattering (DLS), electrophoresis (zeta potential, ζ), and scanning electron microscopy (SEM), and viscosity (η) values, storage (G’) and loss (G’’) moduli were determined via rheological analysis. Measurements were performed in a temperature range of 25 ºC to 70 ºC. DLS analysis showed changes in the particle diameter (250≤Dz/nm≤1000) over the entire temperature range attributed to the phase transition temperatures. Negative zeta potential values (-45 ≤ ζ/mv ≤ -22) were observed, indicating high stability. As temperature rose, ζ approached zero, suggesting a loss of stability. Rheological tests revealed shear-thinning behavior for all polymers. Their elastic and viscous moduli provided insights into the linear viscoelastic regions and how yield points change with temperature variations. After a titration process, SEM images revealed distinct surface morphologies, including popcorn-like, cauliflower-like, and semi-spherical structures. In conclusion, the materials exhibit high sensitivity to temperature and pH changes, which induce conformational and morphological alterations influenced by the location and concentration of GFs within the particles. Therefore, they are suitable for use as nanocarries.