Measurements of homogeneous nucleation in normal-alkanes

The homogeneous nucleation of normal-alkanes with carbon numbers 15 less than or equal to n less than or equal to 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 Delta T of up to 2 degrees 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, Delta T/T(m)approximate to 0.04, for 17 less than or equal to n less than or equal to 30, and a gradually increasing one for 32 less than or equal to n less than or equal to 60. A value of Delta T/T(m)approximate to 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. (C) 2000 American Institute of Physics. [S0021-9606(00)51015-0].