## 3 Results and Discussions
### Thermo- and pH-Responsive Behavior in Aqueous Solution
#### 3.2.3 Thermo- and pH-Responsive Behavior of SiO\({}_{2}\)-g-P(OEGMA-_stat_-AA)  
The hydrodynamic diameter and the zeta potential of the prepared SiO\({}_{2}\)-g-P(OEGMA-_stat_-AA) nanoparticles were determined over the pH range from 8 to 12 (Figure 7a,b). For all of the three nanoparticles, the hydrodynamic diameter increases and the zeta potential decreases with increasing pH, which can be attributed to an increase of electrostatic repulsive force between polymer chains at higher pH. The zeta potential of the three nanoparticles decreases with increasing pH, owning to the -COOH groups in the polymer chains are mostly dissociated at a higher pH. The hydrodynamic diameter of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-IBA\({}_{70}\)) and SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) is similar at the investigated pH (Figure 7a). The hydrodynamic diameter of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) is smaller than that of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-IBA\({}_{70}\)) and SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) over the pH range of 8-10 while it is larger at pH 11 and 12. We suggest that this is due to AA becoming more negatively charged as pH increases, resulting in a higher swelling ratio of the polymers. At the investigated pH, the zeta potential of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) and SiO\({}_{2}\)-_g-_P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) nanoparticles is similar (Figure 7b). The zeta potential of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)) nanoparticle is slightly more negative than that of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) and SiO\({}_{2}\)-_g-_P(OEGMA\({}_{70}\)-_stat_-IBA\({}_{30}\)), which can be attributed to a higher AA content in SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)). Considering the stability of the polymer-grafted SiO\({}_{2}\) nanoparticles, we determined the hydrodynamic diameter of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)), SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)), and SiO\({}_{2}\)-_g-_P(OEGMA\({}_{70}\)-_stat_-BA\({}_{30}\)) nanoparticles by DLS under different temperatures at a pH value of 11 (Figure 8). The LCST of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)), SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)), SiO\({}_{2}\)-_g-_P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) was found to be 57 \({}^{\circ}\)C, 66 \({}^{\circ}\)C, 70 \({}^{\circ}\)C, respectively. This result indicates that the LCST of the nanoparticles can be tunable by changing the ratio of the monomers and that the LCST of the SiO\({}_{2}\)-_g-_P(OEGMA-_stat_-AA) nanoparticles increased with increasing OGEMA content. Our result shows that compared to SiO\({}_{2}\)-_g-_P_-POEGMA, the LCST of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)) is lower than that of SiO\({}_{2}\)-_g-_P_-POEGMA, while the LCST of SiO\({}_{2}\)-_g-_P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) and SiO\({}_{2}\)-_g-_P_(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) is slightly higher than that of SiO\({}_{2}\)-_g-_P_-OEGMA. It has been reported that the LCST of P(MA-_co_-OEGMA) polymers is lower than that of OEGMA and the LCST increases with increasing OGEMA content at pH below 7, owing to the intramolecular hydrogen bonding interactions between the acid groups and the ethyleneglycol chains that can expel the water from the hydration shell [39; 40].