Growth mechanism of polymer membranes obtained by H-bonding across immiscible liquid interfaces

TL;DR

This study investigates the growth mechanism of H-bonded polymer membranes at liquid interfaces, revealing a diffusion-like process influenced by polymer molar mass and membrane microstructure, aiding rational membrane design.

Contribution

It provides a new model explaining membrane growth dynamics considering polymer diffusion and microstructure, advancing understanding of self-assembled polymer membranes.

Findings

Membrane thickness grows as t^(1/2), indicating diffusion-limited growth.

Higher PPO molar mass accelerates membrane formation, contrary to expectations.

Membrane structure is a gel-like porous network with small pores hindering chain diffusion.

Abstract

Complexation of polymers at liquid interfaces is an emerging technique to produce all-liquid printable and self-healing devices and membranes. It is crucial to control the assembly process but the mechanisms at play remain unclear. Using two different reflectometric methods, we investigate the spontaneous growth of H-bonded PPO-PMAA membranes at a flat liquid-liquid interface. We find that the membrane thickness h grows with time t as h~t^(1/2), which is reminiscent of a diffusion-limited process. However, counter-intuitively, we observe that this process is faster as the PPO molar mass increases. We are able to rationalize these results with a model which considers the diffusion of the PPO chains within the growing membrane. The architecture of the latter is described as a gel-like porous network, with a pore size much smaller than the radius of the diffusing PPO chains, thus inducing entropic barriers that hinder the diffusion process. From the comparison between the experimental data and the result of the model, we extract some key piece of information about the microscopic structure of the membrane. This study opens the route toward the rational design of self-assembled membranes and capsules with optimal properties.