# Geometric Confinement of 3D Smectic Liquid Crystal Foams
## 3 Results
We first noticed that the regularity of both LC and SDS systems is similar at low airflow rates. Secondly, we found that the overall size of SDS cells increases linearly with the airflow rate, like LC cells. However, SDS cells are always bigger than LC cells (Figure 2e). The slope of the linear fit for the cell sizes versus the airflow rates is more significant for the SDS than the LC (larger by five times). Additionally, we found that it is possible to fabricate SDS foams with highly regular patterns beyond the smectic threshold airflow rate of 38 mL/min. The possibility to fabricate SDS foams beyond the airflow rate of 38 mL/min is due to SDS's absence of LC elasticity that prevents smectic bubbles from forming at higher rates. Square confinement: When the LC foam was fabricated in square containers, we found that it was possible to increase the airflow rate from 2 mL/min to 62 mL/min, as shown in Figure 3, unlike the previous case of rectangular confinement. Within the low airflow region (2 mL/min, 14 mL/min, and 26 mL/min), smectic cells present polygonal structures with no significant difference in size and organization (Figure 3a-c, respectively). They are stable for about one hour at room temperature. When the airflow was increased to 38 mL/min, we observed the formation of large bubbles with some defects in their assembly, as shown in Figure 3d. The large bubble formation is due to the fact that some cells collapse after we create the foam. Despite this irregularity, we still have organized packaging compared to LC foams confined in rectangular containers. When the airflow rate is increased to 38 mL/min, 50 mL/min, and 62 mL/min (Figure 3d-f), the smectic foams start to create more polygonal structures, indicating that the volume fraction of the foam is decreasing (thinner 8 CB films between the cells). The overall size of the foam continues to grow with the airflow rate, as shown in Figure 3g. We also found that the system's durability weakens because the foams are less stable and collapse quickly after five to ten minutes. We note here that all samples prepared in the square containers present better regularity than those fabricated in rectangular ones, thus confirming the foam's sensitivity to the geometry of their boundaries. For SDS foams fabricated in the same conditions, we found that they have highly ordered structures under different airflow rates (from 2 mL/min to 62 mL/min), as shown in Supplementary Figure S2. Additionally, they have better regularity than the smectic foams, particularly at higher airflow rates. The SDS cells show fewer deformations than the ones in LC, but their durability is much shorter (around 20 min). Cylindrical confinement: Our results show that the most optimal structures among all three confinements in terms of regularity and stability are obtained using the cylindrical containers for both the SDS and LC foams, as shown in Figure 4 and Supplementary Figure S3. At 2 mL/min (Figure 4a), the cells show a perfect polygonal arrangement near the glass wall. They are stable for more than 2 h for the LC and an hour and a half for the SDS. When the airflow rate is increased to 14 mL/min (Figure 4b), we observe a significant growth in the size of the smectic cells from 2.187 \(\pm\) 0.03 mm\({}^{2}\) to 5.04 \(\pm\) 0.03 mm\({}^{2}\), as shown in Figure 4b. At higher flow rates, 26 mL/min and 38 mL/min (Figure 4c,d), the bubble size expands, causing cells' distortions, which affect their structure and organization. If we continue to increase the airflow rate, we obtain less stable foams with distorted structures, as shown in Figure 4e,f (lifetime is about 15 min). Unlike the smectic, SDS foams created in cylindrical containers show higher regularity at all airflow rates, ranging from 2 mL/min to 62 mL/min (Supplementary Figure S3). However, their growth rate is much slower than the smectic ones (Figure 4g). This is different from the cases of rectangular and square containers. Additionally, they are less stable than the LC foams.