Self-assembly of polymers at the interface between two poor solvents

Interfacially inactive materials do not assemble a liquid surface/interface unless they interact with interfacially active species, e.g., hydrophilic silica nanoparticles assembling at the water-oil interface with the help of surfactant molecules. Here, we show that polymers can spontaneously assemble at an interface between two poor solvents with the help of a good solvent. Polyacrylonitrile (PAN) is not soluble in toluene or water. Dimethyl sulfoxide (DMSO) is a good solvent for PAN and is miscible with toluene and water. We found that by adding a mixture of PAN and DMSO in toluene, PDMS spontaneously diffused across the liquid interface and dissolved in water. During this process, the interfacially inactive material, PAN, is trapped at the interface between toluene and water, therefore forming a solid interfacial film. By conducting various in situ measurements, such as in situ liquid-liquid atomic force microscopy measurements, interfacial tension measurements, etc., we systematically studied the formation and structure of this self-assembled interfacial layer and further explored their use in 3-dimensional all liquid print and thin film fabrication.