Optical density (OD) variation of PNIPA/AA nanohydrogels as a function of pH and temperature.

<p>PNIPA(5) (A) and PNIPA-20AA(5) (C) nanohydrogels were previously swelled in distilled water (12.5 mg mL⁻¹) at 25°C. The surface represents the fitting of the experimental data with the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087190#pone.0087190.e058" target="_blank">Equation 19</a>. Figures B (PNIPA(5)) and D (PNIPA-20AA(5)) show pH-T phase diagrams, in which the critical line marks the temperature and pH conditions at which the nanohydrogel begins to undergo the volume phase transition.