Our results show that, for both NaCl and Na 2 SO 4 solutions, T 1 decreases upon increasing the salt concentration c s (Fig. ). In slits, T 1 decreases faster with c s than in bulk (compare full and open symbols in Fig. ), which suggests the presence of additional interfacial effects that are induced by the presence of the salt in the confined solutions. For a given salt concentration, T 1 is always lower for Na 2 SO 4 than for NaCl in the slit pores. For the highest salt concentrations considered here (6 mol/kg for NaCl, and 1.5 mol/kg for Na 2 SO 4 ), the values of T 1 are of similar magnitude for the two salts: T 1 ≈ 0.6 s for Na 2 SO 4 , and T 1 ≈ 0.4 s for NaCl, respectively, which is about a factor 5 smaller than pure water confined within a slit pore of same size.