Molecular relaxation dynamics of self-assembled monolayers

Area of Science:

• Materials Science
• Physical Chemistry
• Surface Science

Background:

• Alkylsilane self-assembled monolayers (SAMs) are crucial for modifying surfaces.
• Understanding molecular motion within these thin films is key to controlling material properties.
• Disorder in monolayers can significantly impact molecular dynamics.

Purpose of the Study:

• To quantify molecular motion in alkylsilane SAMs on porous glass using dielectric relaxation spectroscopy.
• To investigate the effect of monolayer disorder on molecular mobility.
• To isolate and study relaxation processes in different parts of the monolayer.

Main Methods:

• Dielectric relaxation spectroscopy over a wide temperature range (-150 to -30 °C).
• Systematic variation of coating densities of alkylsilane SAMs.
• Introduction of polar cyano (CN) end groups to probe canopy dynamics.

Main Results:

• A dominant relaxation process with an activation energy of ~25 kJ/mol was identified for SAM-chain segments near the substrate.
• Varying coating density allowed for the assessment of disorder's impact on mobility.
• Polar end groups enabled the isolation and study of relaxation in the monolayer canopy.

Conclusions:

• Monolayer disorder plays a significant role in the molecular mobility of thin films.
• Localized relaxation dynamics can be probed by functionalizing the monolayer canopy.
• The methodology is adaptable for studying various substituent polar groups in surface-grafted films.