Intermolecular interactions in chemistry and biology are governed by complex potential energy surfaces. Despite recent advances in nanoscale interaction force measurements, determination of the potential energy barriers remains difficult. We present a simple force microscopy technique that can extract tip-sample interaction potential depth and width from the pull-off force measurements. We show that determination of the thermodynamic parameters for the interaction requires measuring the pull-off force as a function of the loading rate and temperature. We apply this variable-temperature dynamic force spectroscopy technique to determine thermodynamic parameters for the interactions between a silicon nitride tip and a mica surface and for the interactions of tip and surface terminated with carboxylic acid functionalities in ethanol. For both cases, we observed that pull-off force increases logarithmically as a function of loading speed, with the rate of the increase determined by the width of the interaction potential. Analysis of the temperature dependence of the interaction forces provides estimates for the enthalpy and entropy of the interactions and reveals an important role of solvation effects in these systems.
ASJC Scopus subject areas
- Colloid and Surface Chemistry
- Physical and Theoretical Chemistry