Properties of Pickering Stabilized Associative Water-In-Water Emulsions Based on Ultra-High Molecular Weight Polyacrylamides

Completely water-based multicompartment systems have attracted a broad interest in recent years, mainly due to their versatile features such as permeability. Here, the associative formation of water-in-water (w/w) emulsions based on ultra-high molecular weight poly(N,N-dimethylacrylamide) (PDMA) and poly(4-acryloylmorpholine) (PAM) is studied. The system is investigated using a combination of fluorescence microscopy and spectroscopy techniques. The system phase-separates into aqueous droplets at very low polymer concentrations and exhibits intriguing physical properties. The formed emulsion droplets are extremely fluid (5–10 mPa.s), enable fast (5 µm² s⁻¹), nearly complete (mobile fraction ≈0.8) and unhindered diffusion within and across compartments, which is a hallmark of fluids. Furthermore, the very low interfacial tension (0.18–0.40 mN m⁻¹) enables droplet coalescence leading to equilibrium formation of various emulsion structures. These properties show similarities to cell cytoplasm and coacervates and hence this type of w/w emulsion formed via associative non-ionic interactions is a new direction in the field of synthetic cells and synthetic biology.