Growth Mechanism of Polymer Membranes Obtained by H-Bonding Across Immiscible Liquid Interfaces

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.

Ionic Strength-Dependent Assembly of Polyelectrolyte-Nanoparticle Membranes via Interfacial Complexation at a Water–Water Interface

“…The macroscopic membrane thickness h ( t ) evolves as h false( t false) ∼ t 1 / 2 (Figure b(iv)). This scaling highlights the importance of diffusion in the membrane growth process; similar trends have been reported for interfacially grown membranes at oil–water interfaces. , The apparent diffusion coefficient estimated from this data is roughly 10 –12 m 2 /s. While this coefficient does not reflect the self-diffusivity of the complexing species in the membrane, it does reflect a growth process that relies on the incorporation of the two species.…”

One‐Step Synthesis of Hydrogen‐Bonded Microcapsules for pH‐Triggered Protein Release

“…This suggests that the dewetting time scale is related to the diffusion of the PMAA to the interface, which decreases with the molecular weight [ 20 ] as well as the diffusion flux of PPO that is proportional to the concentration gradient. [ 21 ] To also verify the origin of the dewetting phenomena, we conduct a separate experiment in which we prepare analogous PPO/PMAA microcapsules dispersed in IPM utilizing water‐in‐oil‐in‐oil (W 1 /O 1 /O 2 ) double‐emulsion droplets as templates. Collection of the resulting emulsion droplets in a vial containing 10 wt% PVA aqueous solution shows that the microcapsules formed within the IPM phase spontaneously partition to the underlying aqueous phase after interfacial complexation due to the preferential interaction of the PPO/PMAA shell membrane with the aqueous phase than IPM (Figure S3, Supporting Information).…”

“…As a result, PMAA with smaller molecular weight forms a denser network, which leads to smaller pore size and thus lower permeability, as observed similarly by others. [ 21 ] Of note is that the permeability of the PPO/PMAA microcapsule also affects the reswelling behavior of the capsule in PVA solution after shrinkage. As reswelling is due to diffusion of PVA, the time scale of capsule reswelling not only depends on the molecular weight of the PVA but also on the pore size of the microcapsule shell, which is a function of PMAA molecular weight, as evidenced by the longer reswelling time for PPO/PMAA microcapsules consisting of lower‐molecular‐weight PMAA (Figure S5, Supporting Information).…”

Mechanical characterization of core-shell microcapsules

“…There are various well developed methods for assembling the shell of microcapsules [2]. However, if we limit ourselves to the microcapsules with fluid cores wrapped by elastic shells, the assembly process can, in general, be classified into two categories: polymerization/crosslinking [38] and interaction bonding [39,40]. Two steps are generally involved: the formation of droplets by emulsification, and the shell assembly at the droplets interfaces.…”

“…Typical examples are nylon capsules [41], polysiloxane microcapsules [42], and albumin microcapsules [17]. If oppositely charged polyelectrolytes exist in the immiscible phases, the shell can be formed by interaction bonding such as electrostatic adsorption [6,7] and H-bonding [5,40]. The layer-by-layer (LbL) technique is introduced to precisely tailor the structure and mechanical properties of the shell of the microcapsules.…”