Designing Cellulose Nanofibrils for Stabilization of Fluid Interfaces

Area of Science:

• Materials Science
• Colloid and Surface Chemistry

Background:

• Particles of biological origin are increasingly used for Pickering stabilization of foams and emulsions.
• Cellulose nanofibrils (CNFs) are promising biocompatible and eco-friendly stabilizers, but their interfacial behavior is not fully understood.
• The reason for CNFs' inability to stabilize foams while effectively stabilizing emulsions remains unclear.

Purpose of the Study:

• To investigate the behavior of cellulose nanofibrils (CNFs) at the air-water interface.
• To understand the mechanisms behind CNFs' interfacial stabilization properties.
• To explore how CNF contour length and charge density affect foam and emulsion stabilization.

Main Methods:

• Production of CNFs with varying contour lengths and charge densities.
• Adsorption studies at the air-water interface.
• Measurement of surface tension and surface pressure.
• Neutron reflectometry to determine interfacial layer properties and wetting behavior.

Main Results:

• CNFs reduce surface tension and form viscoelastic interfacial layers, contributing to colloid stability.
• Lower CNF charge density accelerates adsorption and increases surface pressure.
• CNFs form monolayers with approximately 40% surface coverage.
• Neutron reflectometry revealed a contact angle <90°, indicating primary wetting by the aqueous phase.

Conclusions:

• CNF surface charges limit adsorption and surface coverage at the air-water interface.
• The observed low contact angle (<90°) suggests an energetically unfavorable state for CNFs at the air-water interface.
• This unfavorable wetting is proposed as a key reason for the poor foaming capacity of CNFs.