Cationic polyacrylamide induced nanoparticles assembly in a cellulose nanofiber network.

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Polyacrylamides (PAs) are versatile polymers used to control nanoparticle (NP) behavior in composite materials.
• Understanding NP assembly is crucial for optimizing composite properties and functionality.

Purpose of the Study:

• To investigate the impact of high molecular weight cationic polyacrylamide (CPAM) charge and dosage on the assembly of silica nanoparticles (SiO2 NPs) within cellulose nanofiber composites.
• To elucidate the mechanisms governing NP assembly and retention in these engineered materials.

Main Methods:

• Engineered cellulose/SiO2 composites were fabricated and analyzed using Scanning Electron Microscopy (SEM) for local NP retention.
• Small-Angle X-ray Scattering (SAXS) was employed to determine average NP distribution and inter-particle distances.
• Dynamic Light Scattering (DLS) measured the hydrodynamic radius of CPAM adsorbed onto SiO2 NPs.

Main Results:

• SAXS revealed SiO2 NPs (74 nm diameter) forming structures with a 2.5 nm thick CPAM polyelectrolyte shell.
• CPAM induced SiO2 NP assembly with a consistent inter-particle distance, independent of polymer charge density.
• NP retention within the cellulose matrix significantly increased with higher CPAM dosage.

Conclusions:

• CPAM dictates SiO2 NP assembly through a balance of electrostatic and steric forces, forming a stable polyelectrolyte shell and inter-particle bridging.
• The observed constant inter-nanoparticle distance is maintained regardless of polymer charge density.
• CPAM dosage is a critical factor for enhancing NP retention in cellulose nanofiber composites, offering a pathway for material property optimization.