# Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms
## 3 Results and Discussion  
For studying snow adhesion strength to various surfaces, liquid water content (LWC) in snow plays an important role. Figure 4a shows snow shear adhesion strength to aluminum (AI 6061) and photovoltaic (PV) glass as a function of the LWC in snow. At low liquid water content values, the snow has a powdery structure and its adhesion strength is low due to the lack of free water to form capillary actions at the interface. Many air gaps can occur at the surface because the snow is dry and this can result in lower contact area between the snow and the substrate, leading to lower snow adhesion strength. As the LWC increases, the capillary forces increase, forming a strong adhesive bond between the snow and the substrate. Once the LWC in snow surpasses \(\sim\)20% the snow becomes slushy, and the excessive water forms a liquid layer to allow gliding of the snow grains on the substrate, leading to decrease in adhesion strength between the snow and the substrate. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Substrate**} & **RMS** & **Polar Surface** & **Dispersive** & **Total Surface** & **Average Shear Adhesion** \\  & **(\(\mu\)m)** & **Energy** & **Surface Energy** & **Energy** & **Strength of Snow** \\ \hline \multirow{8}{*}{AL 6061} & 7.17 \(\pm\) 0.13 & 3.16 \(\pm\) 0.04 & 27.13 \(\pm\) 0.26 & 30.29 \(\pm\) 1.18 & 29.9 \\ \cline{2-6}  & 15.34 \(\pm\) 0.22 & 0.38 \(\pm\) 0.21 & 27.71 \(\pm\) 5.06 & 28.09 \(\pm\) 4.85 & 187.7 \\ \cline{2-6}  & 134.4 \(\pm\) 0.16 & 0.56 \(\pm\) 1.80 & 26.59 \(\pm\) 0.12 & 27.16 \(\pm\) 1.92 & 151.1 \\ \cline{2-6}  & 169.42 \(\pm\) 1.94 & 2.86 \(\pm\) 1.72 & 28.46 \(\pm\) 3.12 & 31.31 \(\pm\) 4.84 & 137.3 \\ \cline{2-6}  & 238.29 \(\pm\) 1.47 & 15.01 \(\pm\) 1.31 & 13.77 \(\pm\) 2.91 & 28.78 \(\pm\) 2.12 & 51.5 \\ \cline{2-6}  & 273.31 \(\pm\) 2.88 & 19.17 \(\pm\) 7.47 & 9.44 \(\pm\) 6.44 & 28.61 \(\pm\) 1.42 & 50.8 \\ \cline{2-6}  & 308.33 \(\pm\) 2.43 & 9.37 \(\pm\) 4.56 & 21.58 \(\pm\)6.01 & 30.95 \(\pm\) 1.56 & 32.4 \\ \cline{2-6}  & 36.4 \(\pm\) 1.96 & 9.86 \(\pm\) 0.98 & 16.34 \(\pm\) 2.74 & 26.20 \(\pm\) 1.76 & 331.4 \\ \hline HDPE & 36.4 \(\pm\) 4.36 & 6.15 \(\pm\) 2.62 & 31.03 \(\pm\) 1.37 & 37.18 \(\pm\) 1.25 & 29.6 \\ \hline Stainless Steel & 36.4 \(\pm\) 2.31 & 7.41 \(\pm\) 1.85 & 29.64 \(\pm\) 3.09 & 37.05 \(\pm\) 4.32 & 66.4 \\ \hline Copper & 36.4 \(\pm\) 1.34 & 1.15 \(\pm\) 2.69 & 34.26 \(\pm\) 0.92 & 35.40 \(\pm\) 1.77 & 73.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Surface energy measurements taken from the Kruss Mobile Surface Analyzer as well as the surface roughness measurements taken from the Keyence VHX 6000 are shown for the substrates that were tested during snow adhesion measurements. Figure 4: Impact of LWC and surface roughness on snow adhesion strength. (**a**) Results of snow shear adhesion strength on aluminum (AI) 6061 and photovoltaic (PV) glass. Maximum snow adhesion strength values are observed on both substrates, when the LWC of snow is around 20%. **(b)** Results are shown for shear adhesion strength (at LWC of \(\sim\)22%) of snow on aluminum 6061 substrates as a function of surface roughness (RMS = 7 to 308 \(\mu\)m). We hypothesize that the higher snow adhesion strength of Al 6061, when compared to the PV glass substrate, is due to differences in their roughness and surface energy. To study the impact of each parameter separately, first we treated the Al 6061 substrates with aluminum oxide paper to obtain surfaces with various roughness. The surface roughness was measured using the Keyence VHX 6000 tool; the roughness values of the substrates are listed in Table 1. Next, we measured snow adhesion strength on these substrates, similar to the method reported earlier where the LWC in snow and substrate temperature were kept at -22% and 0 \({}^{\circ}\)C respectively. As mentioned earlier, the diameter of the snow particles (at LWC of -22%) was \(43.53\pm 24.99\) um.