Saline-Responsive and Hydrogen Bond Gating Effects in Self-Healing Polyaniline

Abstract

Stimuli-responsive microcapsules that can release encapsulated small molecules under external environmental stimuli have been extensively employed in delivering small molecules to targeted sites. Here, salt-activated hydrogen bonding chemistry was exploited to develop responsive release systems for self-healing (guest) molecules from capsular polyaniline (PANI) particles. Payloads were physically entrapped within PANI nanoparticles constructed by interface-templated polymerization, where responsive payload release was achieved by using saltdependent (sodium chloride) gradients. We propose a coactivation mechanism for release of guest molecules attributed to hydrogen bonding and polymer osmotic expansion. The release mechanism relies on a salt activator with cleavage of saline-responsive noncovalent interactions within the mesoporous particles. The responsiveness and guest release are coactivated by changes in polymer shell permeability, expansion, and polymer shell hydrophobicity. Anion hydration and its concentration (degree of doping) play a pivotal role for the ion responsiveness. NaCl stimuli offer a versatile and simple method for triggering sustained release of self-healing materials which hold enormous potential for applications in enhanced anticorrosion protection in harsh salt-attacking environments.

Capsules with responsive polymeric shells for applications beyond drug delivery

“…Ionic strength (e.g., salt concentration) has also been used as a stimulus for polymeric responsive capsules and generally employs free ions (e.g., ions from NaCl) to induce molecular level rearrangements of the shells (e.g., hydrogen bonding rearrangements) or to tune the electrostatic interactions between the capsule shell components. [44][45][46] Of note, ionic strength-responsive polymeric capsules are mostly prepared from multilayer-deposited polyelectrolytes (e.g., prepared by LbL) due to the relatively weak interactions between the multilayers. As shown in Fig.…”

“…Alternatively, Dolatkhah and colleagues constructed salineresponsive capsules possessing polyaniline (PANI) shells with anti-corrosion agents (e.g., benzotriazole) encapsulated. 46 Intramolecular hydrogen bonding between the PANI backbones and intermolecular hydrogen bonding between PANI and the encapsulated nitrogenous molecules drives the salineresponsivity. Upon addition of salt solution (e.g., NaCl), the PANI backbone experiences cation-doping, which induces the emeraldine base form changing to emeraldine salt form.…”

Smart protective coatings with self‐sensing and active corrosion protection dual functionality from pH-sensitive calcium carbonate microcontainers

“…Active corrosion protection coatings can repair the corrosion damages and/or inhibit corrosion deterioration with minimal or no external intervention [20]. The active protection process of these smart coatings could be achieved by the release of healing agents such as polymerizable materials [21,22] or corrosion inhibitors [23,24] which through various encapsulation technologies could be conveniently released when triggered by different conditions (light [25,26], pH [27,28], humidity [29], temperature [30] or ions [31]). Among the encapsulation technologies for healing agents that have been applied to the active corrosion protection coatings, the layer-by-layer (LbL) self-assembly approach is a prominent one [32][33][34].…”

A Virtual Special Issue on Self-Healing Materials

“…Light-induced healing systems can be realized by introducing photoreversible bonds (ditelluride or hexaarylbiimidazole) for direct chemical healing or introducing TiO 2 -coated polymeric microcapsules where light-triggered healing is indirect through photodegradation of the microcapsules to release agents for crack healing . Environmental factors can also be used to promote release of healing agents from microcapsules with salt-responsive microcapsules demonstrated for corrosion protection . The Schiff base reaction produces dynamic covalent imine bonds, which provides a facile self-healing mechanism that can be included with natural polymers .…”

“…6 Environmental factors can also be used to promote release of healing agents from microcapsules with saltresponsive microcapsules demonstrated for corrosion protection. 7 The Schiff base reaction produces dynamic covalent imine bonds, which provides a facile self-healing mechanism that can be included with natural polymers. 8 The combination of supramolecular catechol-Fe 3+ bonds and dynamic covalent imine bonds form an interlocked polymer network.…”