Multimorphic Materials: Spatially Tailoring Mechanical Properties via Selective Initiation of Interpenetrating Polymer Networks

Abstract

Access to multimaterial polymers with spatially localized properties and robust interfaces is anticipated to enable new capabilities in soft robotics, such as smooth actuation for advanced medical and manufacturing technologies. Here, orthogonal initiation is used to create interpenetrating polymer networks (IPNs) with spatial control over morphology and mechanical properties. Base catalyzes the formation of a stiff and strong polyurethane, while blue LEDs initiate the formation of a soft and elastic polyacrylate. IPN morphology is controlled by when the LED is turned “on”, with large phase separation occurring for short time delays (≈1–2 min) and a mixed morphology for longer time delays (>5 min), which is supported by dynamic mechanical analysis, small angle X‐ray scattering, and atomic force microscopy. Through tailoring morphology, tensile moduli and fracture toughness can be tuned across ≈1–2 orders of magnitude. Moreover, a simple spring model is used to explain the observed mechanical behavior. Photopatterning produces “multimorphic” materials, where morphology is spatially localized with fine precision (<100 µm), while maintaining a uniform chemical composition throughout to mitigate interfacial failure. As a final demonstration, the fabrication of hinges represents a possible use case for multimorphic materials in soft robotics.

Correlating Nanomechanical Mapping and Single-Molecule Localization Microscopy for Local Properties in Interpenetrating Network Elastomers

“…Using an in-house MATLAB program, we selected all domains with a maximum Feret diameter greater than 170 nm to ensure that we are analyzing images significantly larger than the smallest 150 nm features visualized in the previously discussed silica nanospheres experiment (Figure S7a). We note that smaller domains are almost certainly present, but we do not analyze them as they are below the resolution limit of our technique. , For each selected domain, the modulus was determined from the NM image by fitting the domain shape to an ellipse and averaging modulus values over the inner 75% of the ellipse. The average PMMA concentration in each domain was determined from the SMLM image using a similar method and the same sized ellipse, with slight position adjustments to account for the mismatch in the domain size between NM and SMLM images.…”

“…We note that smaller domains are almost certainly present, but we do not analyze them as they are below the resolution limit of our technique. 59,60 For each selected domain, the modulus was determined from the NM image by fitting the domain shape to an ellipse and averaging modulus values over the inner 75% of the ellipse. The average PMMA concentration in each domain was determined from the SMLM image using a similar method and the same sized ellipse, with slight position adjustments to account for the mismatch in the domain size between NM and SMLM images.…”

CuAAC–methacrylate interpenetrating polymer network (IPN) properties modulated by visible-light photoinitiation

“…Previous work has shown that if a methacrylate or acrylate network is polymerized further into the conversion of a polyurethane network, a step growth network analogous to the CuAAC network, then a higher degree of interpenetration and a lower degree of phase separation occurs. 13,43…”

“…By manipulating IPN formation, the degree of phase separation between the networks and therefore the final properties of the material can be controlled. 13,14 Click chemistry provides a facile route for sequential IPN formation. Click reactions are characterized by high selectivity and high yields, ensuring orthogonal network formation in presence of other functional chemistries.…”

“…By manipulating IPN formation, the degree of phase separation between the networks and therefore the final properties of the material can be controlled. 13,14…”