## 3 Results and Discussion
### Colloidal Stability of Various Late Dispersions
#### 3.3.3 Influence of Oligoglycidol Chain Length on Colloidal Stability  
Furthermore, we analysed the influence of the oligoglycidol chain length on the colloidal stability of polystyrene nanoparticles. Therefore, we used the particle dispersions (**4b**, **5**) with an average diameter of 273 and 405 nm and surface functionalised with surfmers **2b** and **2c** respectively (Figure 8, blue squares and yellow dots, respectively), in the above described experiment and compared the results to the stability test of **2a** functionalised particles with an average diameter of 243 nm and 369 nm respectively (Figure 8, orange diamonds and grey triangles, respectively). Both particle dispersions functionalised with **2b** and **2c** showed the same colloidal stability as particles functionalised with **2a** and similar particle size (Figure 8). The nanoparticles synthesized with **2b** and an average diameter of 243 nm were stable up to a NaCl concentration of 0.1 mol\(\cdot\)L\({}^{-1}\) and started to agglomerate at 0.25 mol\(\cdot\)L\({}^{-1}\). The nanoparticles synthesized with **2c** and an average diameter of 405 nm were colloidally stable up to an NaCl concentration of 0.5 mol\(\cdot\)L\({}^{-1}\) and only formed clusters of 2-3 particles for higher concentrations up to 5 mol\(\cdot\)L\({}^{-1}\). Ergo, no effect of oligoglycidol chain length on the colloidal stability was observed.  
Figure 8: Colloidal stability for nanoparticles with different surface functionality.  
Figure 7: **(a)** Average particle size and **(b)** PDI over time of nanoparticles with 195 nm average diameter and oligoglycidol\({}_{6}\) surface functionality at 0.05 mol\(\cdot\)L\({}^{-1}\) NaCl.  
The colloidal stability of all oligoglycidol functionalised polystyrene nanoparticles is based on a combination of surface charge due to the sulphate groups originating from the initiator, and the oligoglycidol surfrmer. The charge stabilisation is negated already when small amounts of ions are present in the solution, which we could show by investigating the colloidal stability of nanoparticles **6** at low NaCl concentrations. These particles, synthesized without the use of surfactant, already started to agglomerate at NaCl concentrations of 0.01 mol\(\cdot\)L\({}^{-1}\). Regarding the influence of different oligoglycidols on the colloidal stability, we initially expected an increase in the oligoglycidol chain length to lead to an increased hydrophilicity and therefore smaller, and colloidally more stable polystyrene particles. The results obtained however show that, contrary to our expectation, an increase in oligoglycidol chain length leads to increased hydrophobicity of the surfrmer and to larger particles when used in an emulsion polymerisation with styrene. A significant effect of oligoglycidol chain length on the colloidal stability of functionalized styrene particles, when subjected to NaCl solutions, could not be observed. For the same oligoglycidol chain length, our results show that an increase in surfrmer concentration leads to decreasing particle size. Furthermore the particles with the largest diameter, which are obtained with the least amount of surfactant, show the highest colloidal stability in the presence of NaCl.