Origin of surface ordered phase in poly(n-alkyl acrylates) above the bulk melting temperature (Tm)

We present the first surface tension ($\gamma )$ measurements as a function of temperature above T$_{m}$ for poly(n-alkyl acrylates) to explain the presence of surface ordered phase. The surface tension increases with increase in temperature indicating that the surface molecules have lower entropy than in the bulk. There is an abrupt change in slope of $\gamma $ \textit{vs} T at T$_{s2}$ ($>$T$_{m})$ indicating a first order surface transition. The temperature range of the ordered phase is much larger than that observed for small molecule alkanes and alcohols. We determine that this is primarily due to partial crystallinity within the side chains. The consequences of these results have important implications in similar systems containing chemically attached hydrophobic side chains such as surfactants, dendrimers and biomolecules.