Measurements of homogeneous nucleation in normal-alkanes

The homogeneous nucleation of normal-alkanes with carbon numbers 15≤n≤60 is studied by scanning calorimetry, using the droplet technique. Pure, nonemulsified samples show near-zero undercoolings below the melting point, T_m, except for both ends of the n-range, where undercoolings ΔT of up to 2°C are observed. The emulsions have much larger undercoolings. The relative undercoolings show three regimes: A fast decreasing one, up to n = 17, an anomalously low constant one, ΔT/T_m = 0.04, for 17≤n≤30, and a gradually increasing one for 32≤n≤60. A value of ΔT/T_m≈0.086 is reached at n = 60. The connections of these results with the bulk rotator phases and the recently discovered surface freezing effect are discussed. Strong intrinsic interrelations among these are indicated.