## 3 Results
### Morphological Characterization of LiCl-PDMS Foam during Hydration Reaction  
An environmental SEM analysis was conducted on the LiCl-PDMS foam simulating the hydration/dehydration reaction conditions. This approach allowed for visually evaluating the morphological modification while hydrating and dehydrating the LiCl salt embedded in the porous silicon matrix. The dehydration and hydration conditions were obtained with varying temperature and water vapor pressure in the ranges of 5-40 \({}^{\circ}\)C and 10-800 Pa, respectively, in order to vary the chamber RH at which the material was exposed.  
Initially, the material was fully dehydrated and the RH during the analysis was increased from 0.1% to 91.3% in order to favor the hydration reaction. Afterwards, the RH was decreased to 0.1% to favor the LiCl salt dehydration reaction. Hence, the experiment reproduced the operating conditions of a whole hydration/dehydration cycle. In Figure 6, we report the micrographs at the selected pressure and temperature conditions in the climatic chamber of the microscope. The area selected for the analysis is an inner part of the foam and is indicative of the overall morphology.  
At an RH of 0.1%, according to the DVS analysis, the LiCl salt in the PDMS foam should be in its anhydrous phase, and from SEM micrographs on the foam surface, some asperities (1) and bubbles (2) are visible (Figure 6a). It is likely that the asperities consist of loose salt agglomerates, while the bubbles, with a smooth surface and different sizes, might embed the salt in the foam matrix, thus functioning as a covering layer.  
By increasing the RH to 5.4%, no visible morphological modifications could be detected (Figure 6b). Nevertheless, at such an RH value, the beginning of the hydration was expected from the hydration profile, with a water mass uptake of \(\sim\)17 wt.%. As the RH increased to 10.9%, the hydration reaction was more promoted and the bubbles began to swell (Figure 6c), and their volume increased as the RH increased clearly due to the progressive acquisition of more water molecules (Figure 6d,e), in agreement with the DVS analysis.  
At an RH of 25.1%, the conversion of LiCl into its monohydrate phase was complete (Figure 5), and above this RH value, the deliquescence phenomenon was expected to occur. The bubbles doubled and tripled their volume at an RH of 91.3% (as indicated by point 3 in Figure 6e). The asperities (red circles in Figure 6e) increased their volume as well as the RH increased, assuming a roundish shape typical of a drop, thus likely indicative of the deliquescence phenomenon. No detachment of the salt from the foam was observable because of the volume expansion. Nevertheless, the loose salt (asperities) appeared to be slightly agglomerated. Additionally, no damages were evident on the PDMS foam where the salt was embedded (bubbles), thus indicating the ability of the material to easily expand and contract as a consequence of the hydration/dehydration cycles and to both effectively protect and retain the embedded salt hydrate.  
As final step of the ESEM analysis, the environmental chamber conditions were restored to the initial ones, that is, an RH of 0.1%. Under these conditions, the dehydration reaction was induced and the hydration/dehydration cycle was completed. It could be clearly observed that the material morphology was almost unmodified, that is, no damages due to the retained water and volume expansion/contraction were present, thus preserving the reusability of the foam. The presence of incomplete dehydrated salts cannot be excluded. Remarkably, no defects or cracks were detected, confirming the effectiveness of this approach for obtaining a durable, flexible, and porous-sorbents composite.  
Figure 6: Environmental SEM analysis on LiC-PDMS foam under varying temperature and water vapor pressure in the ranges of 5-40 \({}^{\circ}\)C and 10-800 Pa, respectively.