Phase transitions of water solutions in mesoconfined systems

LONGINOTTI M.P; I. ANGARITA; FUENTES-LANDETE, VIOLETA; LOERTING, THOMAS; CORTI, HORACIO R

Buenos Aires

Workshop; Workshop on Structure and Dynamics of Glassy, Supercooled and Nanoconfined Fluids; 2019

The effect of confinement at the nanoscale on mixtures is a problem with many questions still unsolved. In the last years, several studies were published in the literature considering the nanoscale confinement effect on the dynamics and phase behavior of different mixtures. Among those mixtures aqueous solutions are of great interest.In this talk, I will discuss the effect of confinement at the nano scale on the phase behavior of glycerol and LiCl aqueous solutions. In the former case, we studied the glass transition temperature (Tg) of aqueous glycerol solutions over the concentration range between 70 and 100 wt% polyol. In the latter, we analyzed the glass transition of LiCl aqueous solutions with salt concentrations with eutectic (R = 7, with R = moles of water/moles of LiCl) and subeutectic compositions (7 < R ≤ 15). All aqueous solutions were confined in mesoporous silica matrixes with pore diameters between 2 and 58 nm.The results show that for glycerol-aqueous solutions Tg decreases with decreasing pore size, being this effect more pronounced with increasing polyol content. This effect will be discussed in terms of the cooperative rearranging regions length scale.In the case of LiCl aqueous solutions, we observed that the glass transition temperature increases by about 2-5 K for the smallest pore diameters, which is equivalent to the effect of applying a pressure of up to 100 MPa on the bulk samples. This behavior is opposite to that observed in aqueous subeutectic NaCl solutions confined within similar silica matrixes.