Relative apparent molar enthalpies of dilution of some polyoxyethylene glycol monodecyl ethers (C10En), of decanol in cyclohexane and heptane, and of C10E6 aqueous mixtures in decane at 298.15 K

The relative apparent molar enthalpies, Lφ, of polyoxyethylene glycol monodecyl ether, C10En for n=1–8 and decanol were measured in cyclohexane and heptane at 298.15 K by using a flow calorimeter. Also, the measurements for C10E6 in decane were carried out with addition of small amounts of water. The aggregation of C10En proceeds gradually with increasing molality of solutes due to van der Waal’s force acting among hydrophilic groups, the OH groups being blocked from forming intramolecular hydrogen bonding. However, by adding a small amount of water the aggregation is strongly enhanced due to the intermolecular hydrogen bonds formed by a bridge of water across the hydrophilic groups. Those results are consistent with the results obtained by heat capacity measurements reported previously.