## 3 Results
### Particle Size Measurements by Dynamic Light Scattering (DLS)  
The evaluation of the PNIPAM/magnetic nanoparticle size distribution profile in solution was important to establish the main dimensional differences between the nanoparticles according to the preparation conditions. Poly(N-isopropylacrylamide) is a stimuli-responsive polymer that exhibits a reversible phase transition in aqueous solution (sol-gel) at 32-34 \({}^{\circ}\)C [46; 47], called lower critical solution temperature (LCST). The three nanoprecipitation temperatures were chosen to act below the LCST (30 \({}^{\circ}\)C), near the LCST (34 \({}^{\circ}\)C), and above the LCST (38 \({}^{\circ}\)C). This approach could reveal the conformational behavior of PNIPAM chains within dual LCST and nanoprecipitation. The PNIPAM chains' spatial arrangement is of great importance to the nanoparticle size. At 30 \({}^{\circ}\)C nanoprecipitation temperature (Table 2), DLS results revealed PNIPAM/magnetic nanoparticles with dimensions between 106 and 260 nm, depending on the polymer concentration. The increase in the polymer concentration led to an increase in the nanoparticle size. This behavior was previously observed in some research studies with other nanoparticles [48; 49; 50]. The results followed the same trend for 34 \({}^{\circ}\)C and 38 \({}^{\circ}\)C nanoprecipitation temperatures depending on the polymer concentration (Table 2). At the same polymer concentration and different nanoprecipitation temperatures, the nanoparticle size changes. Therefore, the smaller nanoparticle sizes were achieved at 34 \({}^{\circ}\)C for most polymer concentrations. This behavior was previously presented in the literature for PNIPAM/inorganic particle systems. The obtained results are in good agreement with the appropriate studies [51; 52]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Precipitation Temperature (\({}^{\circ}\)C)** & **Sample Name** & **Diameter, nm** \\ \hline \multirow{4}{*}{30} & PNIPAM 0.25\% & 106 \(\pm\) 5 \\  & PNIPAM 0.5\% & 112 \(\pm\) 7 \\  & PNIPAM 1\% & 141 \(\pm\) 7 \\  & PNIPAM 2\% & 190 \(\pm\) 20 \\  & PNIPAM 4\% & 260 \(\pm\) 16 \\ \hline \multirow{4}{*}{34} & PNIPAM 0.25\% & 91 \(\pm\) 3 \\  & PNIPAM 0.5\% & 105 \(\pm\) 5 \\  & PNIPAM 1\% & 122 \(\pm\) 15 \\  & PNIPAM 2\% & 160 \(\pm\) 15 \\  & PNIPAM 4\% & 192 \(\pm\) 18 \\  & PNIPAM 0.25\% & 102 \(\pm\) 4 \\  & PNIPAM 0.5\% & 114 \(\pm\) 6 \\
38 & PNIPAM 1\% & 124 \(\pm\) 10 \\  & PNIPAM 2\% & 155 \(\pm\) 15 \\  & PNIPAM 4\% & 172 \(\pm\) 16 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Particle size of PNIPAM/magnetic nanoparticles by DLS. Figure 3: Histogram of size distributions of PNIPAM/magnetic NPs at various temperatures (0.25% PNIPAM solution). PNIPAM chains are water-soluble below the LCST due to the numerous hydrogen bonds between the polymer and water molecules. The nanoprecipitation involves the addition of polymer solution into acetone as a non-solvent. The water (solvent) and acetone (non-solvent) are miscible and allow the entrapment of water molecules within nanoparticles during preparation. Around the LCST, PNIPAM chains collapse towards a hydrophobic-like nature. This approach may be the main reason for the smaller size, as the water molecules are pulled out of the nanoparticles, resulting in a major volume shrinkage (Table 2). At temperatures above the LCST, the interaction between the polymer chains and water molecules leads to the breakage of the hydrogen bonds; therefore, the hydrophobic interaction between the hydrophobic moieties is strengthened while hydrogen bonding is simultaneously weakened. The thermodynamic size of the PNIPAM nanoparticles decreased gradually when the precipitation temperature was 34 and 38 \({}^{\circ}\)C since the polymer molecules became hydrophobic. Nanoprecipitation above the LCST occurs when the polymer chains probably start to relax and rearrange after collapsing. However, this process will not further allow the water molecules to penetrate the nanoparticle volume.