Glassy dynamics within surface-bound molecular monolayers

Dynamics within a monolayer collection of surface-bound substituted-alkyl chains are studied with narrow-band dielectric spectroscopy. A transition from independent (intra-molecular) motion in low density systems to complex, glassy (inter-molecular) motion as the density is increased is observed. At high density, both the glassy mode [1,2] and the sub-Tg relaxation [3] have direct analogy to equivalent relaxations in polyethylene. Thus this experimental approach enables observation of the formation of a fragile glass as an explicit function of density; in addition by altering the molecular characteristics and surface arrangement, resultant changes in the nature of the glass transition (its glass transition temperature Tg and fragility m) can be determined. The effects of packing efficiency, chain length, and molecule-molecule interactions, as tuned by altering dipoles within the chain, will be discussed.\\[4pt] [1] M. C. Scott\textit{ etal.}, \textit{ACS Nano} \textbf{2}, 2392 (2008);\\[0pt] [2] M. Beiner, and H. Huth, \textit{Nature Materials} \textbf{2}, 595 (2003);\\[0pt] [3] Q. Zhang\textit{ et al.}, \textit{J. Phys. Chem. B} \textbf{110}, 4924 (2006).