Conformational changes in single carboxymethylcellulose chains on a highly oriented pyrolytic graphite surface under...

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Carboxymethylcellulose (CMC) is a water-soluble, hydrophilic polyelectrolyte.
• Understanding CMC's behavior on different surfaces is crucial for its applications.
• Atomic Force Microscopy (AFM) is a key technique for visualizing molecular structures.

Purpose of the Study:

• To investigate conformational changes of individual CMC chains on highly oriented pyrolytic graphite (HOPG).
• To compare CMC adsorption on HOPG versus hydrophilic mica surfaces.
• To explore the influence of salt concentration on CMC conformation on HOPG.

Main Methods:

• Deposition of CMC solutions with varying salt concentrations onto HOPG and mica surfaces.
• High-resolution imaging using tapping-mode Atomic Force Microscopy (AFM) under ambient conditions.
• Analysis of molecular chain alignment and conformational changes based on AFM images and vertical profiles.

Main Results:

• CMC chains were clearly visualized and distinguishable at the molecular level on HOPG, often aligning with the graphite lattice.
• Higher NaCl concentrations induced significant conformational changes, from single chains to globular aggregates, on HOPG.
• Unique molecular attachment on HOPG was observed, potentially due to CH-pi bonding between CMC and graphite.

Conclusions:

• HOPG serves as a unique substrate for observing CMC conformational dynamics.
• The observed phenomena suggest potential for nano-scale morphological control of cellulosic polymers using HOPG.
• This study highlights the interplay between surface properties, salt concentration, and polymer conformation.