Interfacial Thermal Active Modes and Dispersion Forces

Thermal active modes, i.e., molecular and submolecular mobilities, inherent to the relaxation behavior of solid condensed organic matter, such as polymers and molecular self-assemblies, and, interfacial and surface free energies, are of great importance for many practical applications. For instance, in organic second-order nonlinear optical materials (NLO), pursued for photonic device applications, the molecular mobility plays a pivotal role in producing stable NLO materials of high poling efficiency [1]. Other applications such as frictional sliding systems or nanocomposites, both involving nanoconstrained materials, depend on the surface/interfacial energies. Common to thermal modes and interfacial forces are that they are difficult to quantify, in particular, in systems that either possess an amorphous complex entropic structure, or are of small size.

From scanning force microscopy (SFM) an approach has been devised over the years, providing direct and local insight into thermal modes and interfacial forces via an energetic analysis that is based on the time-temperature superposition principle [2]. Dubbed “intrinsic friction analysis” (IFA), it utilizes the mechanical scattering process between a sliding SFM tip in contact with the thermal active modes of the scanned sample. In the past, in particular, rotational and translational modes have been investigated involving complex organic systems, such as polymers and organic molecular glasses [2-5]. Recently, also molecular binding interactions [1] and surface dispersion interactions [6-7] could be energetically analyzed with IFA. In this paper, we will focus on both aspects, namely the molecular mobility in self-assembled systems depending on the molecular interaction strength, and the quantum electro-dynamic binding fluctuations between Van der Waals interacting surfaces.

[1] D. B. Knorr, S. J. Benight, B. Krajina, C. Zhang, L. R. Dalton, R.M. Overney, J. Phys. Chem. B, 116, (2012) 13793.

[2] D.B. Knorr, R.M. Overney, J. Chem. Phys., 129, (2008) 074504.

[3] S.E. Sills, T. Gray, R.M. Overney, J. Chem. Phys., 123, (2005) 134902.

[4] T. Gray et al., NanoLetters, 8, (2008) 754.

[5] D.B. Knorr, Jr., L. S. Kocherlakota, J. P. Killgore, and R. M. Overney, J. Membrane Sci., 346, ( 2010) 302.

[6] B.A. Krajina, L.S. Kocherlakota, R.M. Overney, J. Chem. Phys., 141, (2014) 164707

[7] L. S. Kocherlakota, Brad A. Krajina, R. M. Overney, Local Energetic Analysis of the Surface Energies of Graphene from the Single Layer to Graphite, J. Chem. Phys., 143, 241105 (2015)