## 6 Variation of Droplet Radius with Surface Subcooling at Different Substrate Temperature  
The most significant advantage of synthesizing polymer nanodomes based on iCVD, in addition to being solvent-free, template-free, having an in situ characterization, and being rapid, is the distinct separation of monomer deposition from the initiator-initiated monomer polymerization process. This enables clear observation of the size variations in the polymer nanodomes, facilitating precise control over the size of the nanodomes (PNDs).  
During the first step of the two-stage control process, which involves the condensation phase of nanodomes, the filament within the chamber maintains the ambient temperature for monomer deposition throughout the chamber. However, as vapor-phase monomers come into contact with the bottom substrate, the nucleation, growth, and condensation of nanodomes are closely tied to the temperature of the substrate. The bottom substrate plays a crucial role in the gas-liquid interface phase transition.  
[PERSON] [37] focused his research on analyzing the impact of solid substrate temperature (T\({}_{\mathrm{s}}\)) during CDP on the growth of monomer droplets and the distribution of particle sizes. While keeping the monomer partial pressure constant, he examined how PNDs are influenced by variations in T\({}_{\mathrm{s}}\).  
Figure 6 depicts SEM images of the PNDs obtained on a pPFDA-coated substrate at temperatures of 21 \({}^{\circ}\)C, 24 \({}^{\circ}\)C, 27 \({}^{\circ}\)C, and 30 \({}^{\circ}\)C, with a scale bar of 200 nanometers [37]. From the comparison in the graph, it is evident that as the substrate temperature decreases, the final size of solidified nanodomes increases. This phenomenon is linked to the driving force behind particle nucleation. When a droplet reaches the minimum energy required for nucleation, it attains a critical radius to form a droplet nucleus. This concept draws parallels with the nucleation formula observed for water droplets under certain degrees of supercooling.  
In iCVD, a Temperature-Controlled Stage (TEC) device [38] is typically installed at the bottom to regulate the substrate temperature. When the substrate temperature is lower  
Figure 6: Size distributions of pHEMA PNDs obtained at substrate temperatures (Ts) of 21 \({}^{\circ}\)C, 24 \({}^{\circ}\)C, 27 \({}^{\circ}\)C, and 30 \({}^{\circ}\)C. Panels (**C–F**) show SEM images of the PNDs obtained at each Ts on a pPFDA-coated substrate, with a scale bar of 200 nm [38].  
than the ambient temperature, it provides supercooling for the nucleation and growth of nanodomes. Investigating the size variation patterns of nanodomes at different degrees of supercooling is of significant interest.  
The sub-cooling degree \(\Delta T=T_{sat}-T_{s}\) is the difference between the saturation temperature of the water vapor \(T_{sat}\) and the surface temperature \(T_{s}\), \(\sigma_{\rm i}\) is the surface tension of the liquid, and \(H_{\rm fg}\) and \(\rho_{\rm l}\) are the latent heat of the liquid and the liquid density, respectively. The critical nucleation radius [40; 41] is the minimum radius at which the nucleation droplet can keep thermodynamic stability, as shown in Figure 7. Once nucleation occurs on surfaces, continuous condensation on the droplet surface promotes the growth of droplets. Although this is a model for the mass transfer of water, it can be applied analogously to the nucleation of monomers in the liquid state. As the temperature, \(T_{s}\), decreases, the temperature difference, \(\Delta T\), also decreases, resulting in an inversely proportional increase in the radius of the nucleation droplet.