Solvation forces in branched molecular liquids

Area of Science:

• Surface science
• Physical chemistry
• Nanotechnology

Background:

• Understanding molecular behavior under confinement is crucial for nanotechnology and materials science.
• Squalane, a highly branched hydrocarbon, presents unique challenges for studying confined molecular dynamics.
• Atomic force microscopy (AFM) is a key technique for probing forces at the nanoscale.

Purpose of the Study:

• To measure the solvation force of squalane confined between a silicon tip and a graphite surface.
• To investigate the molecular ordering and interactions of squalane under nanoscale confinement.
• To compare experimental findings with existing computational simulations and macroscopic force balance experiments.

Main Methods:

• Atomic force microscopy (AFM) was employed to precisely measure forces.
• Controlled confinement was achieved between a sharp silicon tip and a flat graphite surface.
• Force-distance curves were analyzed to reveal oscillatory solvation forces.

Main Results:

• Squalane exhibited oscillatory force profiles, characteristic of confined molecular layers.
• The innermost squalane molecules showed tight binding to the graphite surface.
• Evidence of molecular interdigitation was observed, suggesting complex packing arrangements.
• Experimental results aligned with computer simulations for branched molecules but diverged from macroscopic force balance data.

Conclusions:

• Confinement effects significantly influence the solvation forces and molecular packing of squalane.
• The smaller confinement area and differing surface chemistries explain discrepancies with macroscopic experiments.
• AFM provides valuable insights into the nanoscale behavior of branched molecules, complementing simulation studies.