Amphiphilic Heterografted Molecular Bottlebrushes with Tertiary Amine-Containing Side Chains as Efficient and Robust pH-Responsive Emulsifiers

By combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli-responsive polymers, we show that MBBs with randomly grafted poly(n-butyl acrylate) and pH-responsive poly(2-(N,N-diethylamino)ethyl methacrylate) (PDEAEMA) side chains are efficient and robust pH-responsive emulsifiers. Water-in-toluene emulsions were formed at pH 4.0 and disrupted by increasing the pH to 10.0. The emulsion generation and disruption was reversible over the ten cycles investigated, and the bottlebrushes remained intact. The exceptional emulsion stability stemmed from the high interfacial binding energy of MBBs, imparted by their large molecular size and Janus architecture at the interface, as evidenced by the interfacial jamming and wrinkling of the assemblies upon reducing the interfacial area. At pH 10.0, PDEAEMA became water-insoluble, and the MBBs desorbed from the interface, causing de-emulsification. Consequently, we have shown that the judicious design of MBBs can generate properties of particle emulsifiers from their large size, while the responsiveness of the MBBs enables more potential applications. Molecular bottlebrushes with randomly grafted hydrophobic and pH-responsive polymer side chains are efficient and robust responsive emulsifiers for generation of water-in-oil emulsions, which exhibit both high stability, derived from large molecular sizes and interfacial Janus structures, and stimuli-responsive behavior. The formation and disruption of emulsions were repeated 10 times, and the bottlebrushes remained intact.image

Automated summary

By combining the characteristics of molecular bottlebrushes and stimuli-responsive polymers, researchers have developed efficient and robust pH-responsive emulsifiers. The emulsions formed at pH 4.0 and disrupted at pH 10.0, with reversible behavior over multiple cycles. The high stability of the emulsions is attributed to the large size and Janus architecture of the molecular bottlebrushes at the interface.