Crumpling and Unfolding of Montmorillonite Hybrid Nanocoatings as Stretchable Flame‐Retardant Skin

Abstract

Flame-retardant coatings are widely used in a variety of personnel or product protection, and many applications would benefit from film stretchability if suitable materials are available. It is challenging to develop flame-retardant coatings that are stretchable, eco-friendly, and capable of being integrated on mechanically dynamic devices. Here, a concept is reported that uses pretextured montmorillonite (MMT) hybrid nanocoatings that can undergo programed unfolding to mimic the stretchability of elastomeric materials. These textured MMT coatings can be transferred onto an elastomeric substrate to achieve an MMT/elastomer bilayer device with high stretchability (225% areal strain) and effective flame retardancy. The bilayer composite is utilized as flame-retardant skin for a soft robotic gripper, and it is demonstrated that the actuated response can manipulate and rescue irregularly shaped objects from a fire scene. Furthermore, by depositing the conformal MMT nanocoatings on nitrile gloves, the firefree gloves can endure direct flame contact without ignition.

Multifunctionality and Mechanical Actuation of 2D Materials for Skin‐Mimicking Capabilities

“…f) Evolution of surface morphology of MMT‐PVA/elastomer materials under 1D (to 80%) and 2D (to 225%) stretching. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…Our group also followed a similar approach to fabricate stretchable MMT/elastomer architectures as fire‐retardant skin, which can accommodate significant deformation and still preserve its intrinsic thermal resistance. An in situ tensile test of MMT/elastomer was carried out within a scanning electron microscope (SEM) to observe the evolution of surface topographical changes under different uniaxial and biaxial strains (Figure f) . When uniaxially stretching from 0 to 80%, the wrinkling angle increased from 84° to 140°; while stretching biaxially to 225% areal strain, the texture length scale increased from 9.2 to 19.2 µm.…”

“…f) The soft grippers and gloves with flame‐retardant skin can stay in contact with flame without immediate ignition. e,f) Reproduced with permission . Wiley‐VCH.…”

“…Textured MMT nanocoatings exhibited low oxygen permeability and high thermal stability, which can provide flame resistance and retard the thermal degradation. A combustibility testing assay was developed to: (i) examine flammability by cooking the bilayer composite above the flame of ethanol burner and (ii) investigate flammability under various uniaxial strain (Figure e) . In control experiment, unprotected Ecoflex were placed above the fire under three different strains, and the bare Ecoflex immediately got ignited (<5 s) and lost their material integrity.…”

Autonomous self-healing hydrogel with anti-drying properties and applications in soft robotics

“…Furthermore, the incorporation of carbon nanomaterials into polymer networks has led to intelligent materials that can respond to specific external stimuli [32] or provide the material with flame-retardant properties [34][35][36]. Such materials can serve, for instance, as a protective skin for soft robots in extreme situations such as fire scenes due to their high flame-resistance capabilities [37,38].…”