# Bi-Continuous Emulsions Stabilized by pH-Responsive Self-Assembled Aggregates of Amphiphilic Random Copolymer with One-Step Emulsification

## TL;DR

This paper introduces a simple method to create stable bi-continuous emulsions using a pH-sensitive polymer that self-assembles at the oil-water interface.

## Contribution

A one-step emulsification strategy using pH-responsive copolymer aggregates to form bi-continuous emulsions without complex modifications.

## Key findings

- Bi-continuous emulsions were formed using a 1.0% P(St-co-MAA) solution at pH 7.0–8.0 with a 6:4 oil-to-water ratio.
- The emulsions showed a three-dimensional elastic gel network confirmed by rheological analysis with G′ > G″.
- pH changes controlled the emulsion type from oil-in-water to bi-continuous to water-in-oil.

## Abstract

We reported a simplified one-step emulsification strategy to prepare bi-continuous emulsions with a gel-like property using the pH-responsive self-assembled aggregates of an amphiphilic random copolymer poly (styrene-co-methacrylic acid) (P(St-co-MAA)) as the interfacial stabilizers. Using caprylic/capric triglyceride (GTCC) as the oil phase, 1.0% P(St-co-MAA) aqueous solution with a pH between 7.0 and 8.0 as the water phase, and an oil/water phase ratio of 6:4, bi-continuous emulsions could be formed directly through one-step emulsification. Systematic characterization with a fluorescence microscope, scanning electron microscope, and confocal laser scanning microscope confirmed the formation of the bi-continuous emulsions. The three-phase contact angle measurements confirmed that the surface wettability of the self-assembled aggregates changed with pH, and the three-phase contact angles of the bi-continuous emulsions formed at a pH between 7.0 and 8.0 were close to 90°. Furthermore, rheological analysis of the bi-continuous emulsion showed the storage modulus (G′) dominating over the loss modulus (G″), which verified that the bi-continuous emulsion was attributed to the existence of a three-dimensional elastic gel network. The pH-dependent wettability of the self-assembled aggregates as the stabilizers enabled pH to control the emulsion type from O/W to bi-continuous to W/O. The work provides a simple, rapid, and robust approach to preparing bi-continuous emulsions without intricate particle modifications and cumbersome procedures.