Measurements of homogeneous nucleation in normal-alkanes

The homogeneous nucleation of normal-alkanes with carbon numbers $\text{15⩽n⩽60}$ 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 $\mathrm{\Delta T}$ 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 $\text{n=17,}$ an anomalously low constant one, ${\mathrm{\Delta T/T}}_m\text{≈0.04,}$ for $\text{17⩽n⩽30,}$ and a gradually increasing one for $\text{32⩽n⩽60.}$ A value of ${\mathrm{\Delta T/T}}_m\text{≈0.086}$ is reached at $\text{n=60.}$ 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.