Foams stabilized with solid particles carrying stimuli-responsive polymer hairs.

Area of Science:

• Materials Science
• Colloid and Surface Science
• Polymer Chemistry

Background:

• Particulate stabilizers are crucial for creating stable foams.
• Stimuli-responsive polymers offer tunable properties for interfacial applications.
• Polystyrene (PS) particles with poly[2-(diethylamino)ethyl methacrylate] (PDEA) hairs present a novel approach to foam stabilization.

Purpose of the Study:

• To synthesize and characterize submicrometer PS particles with stimuli-responsive PDEA hairs.
• To investigate the efficacy of these hairy particles as stabilizers for aqueous foams.
• To explore the influence of PDEA hair length, particle concentration, and pH on foamability and foam stability.

Main Methods:

• Dispersion polymerization was used to synthesize PS particles with varying PDEA hair lengths (degrees of polymerization 30, 60, 90).
• Foamability, foam stability, and foam microstructure were evaluated under different pH conditions and particle concentrations.
• Foam destabilization was induced using HCl vapor to study the stimuli-responsive behavior.

Main Results:

• The PDEA-PS particles effectively stabilized aqueous foams in basic media (pH > 7) where PDEA hairs are uncharged.
• Foamability and stability significantly increased with longer PDEA hairs, with foams persisting over a month.
• Foams were unstable in acidic media (pH < 7) due to protonation and water solubility of PDEA hairs.
• Optimal particle concentration for foam stabilization was found to be up to 10 wt% using a touch mixer, while a homogenizer allowed stable foams at 40 wt% concentration.
• Foam defoamation was successfully induced by exposure to HCl vapor, leading to hair protonation and particle desorption.

Conclusions:

• Stimuli-responsive PDEA-PS particles are effective foam stabilizers in aqueous systems, particularly in basic conditions.
• The length of the PDEA hairs plays a critical role in enhancing foamability and long-term foam stability.
• The pH-dependent behavior of PDEA hairs allows for controlled foam formation and destabilization, offering tunable interfacial properties.