Biological tissues possess a unique deformation cascade of extreme softness followed by rapid stiffening to imbue the characteristic feeling of firmness. Unlike toughness enhancement, firm materials exhibit compliance on touch, yet resistance to large deformations through steady modulus increase. Although molecular design for matching tissue softness is well established, it is challenging to incorporate independent and programmable mechanisms for the sequential stiffening process. Herein we have designed physical polymer networks through self-assembly of linear-bottlebrush-linear ABA triblock copolymers resulting in hierarchically organized thermoplastic elastomers (plastomers). These materials display a telescoping sequence of deformation mechanisms including strand unfolding, backbone stretching, and crosslink yielding, which qualitatively mimics biological tissue. By tuning the degree polymerization of the linear block (na), bottlebrush backbone (nbb) and side chains (nsc), we developed an architectural code for independent control of Young’s modulus (E0) and strain-stiffening (β) to allow complete coverage of the softness-firmness map. Furthermore, we synthesized plastomers with systematically varied mixtures of short (nsc = 14) and long (nsc = 70) side chains, which drives these materials to previously unmatched softness (E0 = 103-105 Pa) and firmness (β &gt; 0.7) mimicking that of super-soft tissues such as brain and fat tissue. These accomplishments with this flexible platform are vital for emerging applications in soft robotics and biomedical devices where programming soft, yet firm materials are desired.

Architecturally tuning firmness of polymer networks

2019 Fall National Meeting

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