Microfluidic formation of ionically cross-linked polyamine gels

Area of Science:

• Polymer Chemistry
• Materials Science
• Fluid Dynamics

Background:

• Microfluidic systems enable precise control over chemical reactions.
• Electrostatic interactions are crucial for polymer gelation.
• Shear flow can significantly influence polymer behavior and network formation.

Purpose of the Study:

• To investigate in situ polymer gelation in microfluidic channels.
• To understand the role of electrostatic interactions and shear flow in gel formation.
• To characterize the resulting viscoelastic gel phases.

Main Methods:

• Reactant streams of poly(allylamine hydrochloride) (PAH) and sodium citrate were introduced into microfluidic channels.
• The influence of shear flow on gelation was studied.
• Factors such as pH, charge ratio, and ion diffusivity were analyzed.

Main Results:

• PAH exhibited shear-thickening behavior, forming stable viscoelastic gels at room temperature.
• Gelation occurred in the PAH stream due to higher citrate ion diffusivity and laminar flow.
• Gel formation was dependent on pH (below PAH pKa of 8.38) and citrate state (disodium or trisodium).
• Charge ratio and flow conditions influenced the formation of aggregates, gels, and droplets.

Conclusions:

• In situ polymer gelation is achievable in microfluidics via electrostatically mediated interactions under shear flow.
• The study elucidates the mechanism of PAH-citrate gelation, involving aggregate formation and subsequent network assembly.
• Controlled gelation and potential for droplet formation within gels were demonstrated, highlighting tunable material properties.