Tuning thermal properties of latent heat storage material through confinement in porous media: The case of (1-CnH2n+1NH3)2ZnCl4 (n=10 and 12)

• Nanocomposites of alkylammonium tetrachlorozincates (CnZn, n=10, 12) in porous glass (11.5-300 nm) are prepared.• Transition temperature of the nanocomposite can be tuned to ~10 degrees below the bulk.• Latent heat of the pore CnZn varies in the range of 30~80 % of the bulk value.• Adjusting thermal property of the PCMs through nanoconfinement provides a promising way of further using those ideal heat storage materials.

In practical use, latent heat storage system always faces a lack of phase change materials (PCMs) that have ideal performance at desirable temperature and high efficiency to treat thermal effects from various outer heat sources. To solve this problem, some new latent heat storage composites were prepared by incorporating those well-performed PCMs in porous materials. In doing this, the layered perovskite-type compounds, (1-C10H21NH3)2ZnCl4 (C10Zn) and (1-C12H25NH3)2ZnCl4 (C12Zn), were embedded in controlled porous glass (CPG), which can acquire size-dependent thermal properties. Heat storage nature, morphology and crystalline structures of the materials were characterized using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and powder X-ray diffractions (XRD). Under confinement of the porous glass with nominal pore sizes of d=12–300 nm, the porous CnZn compound gains a regulation window of around 10 °C in relation to the bulk by its solid–solid phase transition. The transition temperature (Td), depression of the transition temperature (∆Ttrs), and enthalpy change of the transition (∆trsHd) of the confined compound show a linear relation to the reverse pore size. A same stable thermal cycling property is observed in the pore compound as the bulk, which is consistent with similar diffraction patterns among them. The supercooling of the pore form becomes larger than the bulk. The retention of the layered structure and complete crystallization in the pore CnZn is responsible for its reversible heat storage property.