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Innovations in the chemistry and preparation of functionally gradient materials are sought for many high performance applications. Many natural materials particularly those functioning under conditions of asymmetric wear exhibit molecular gradients. These gradients are noteworthy because they appear highly correlated with graded mechanical properties. Two biomolecular materials have served as useful paradigms of gradients: mussel byssal threads and polychaete fangs. In byssal threads, the thread core consists of collagenous bent-core block copolymers in which the flanking blocks gradually change from stiff silk to soft elastic domains in a distal to proximal direction. In tension, byssal threads exhibit a graded stiffness that ranges from 50 to 500 MPa (figure). In the fangs, which function in bending and impact, the gradients involve a rather different chemistry. There is a proximal to distal gradient of imidazole groups (histidine) that is closely coupled to zinc ions and hardness (figure). We plan to prepare biomimetic films and fibers in which chemical gradients are exploited for useful mechanical, magnetic or electronic properties. 
Engineering Gate Dielectric and Self-Assembly of Conjugated Polymer for Ambipolar Light Emitting Semiconducting Polymer Field Effect Transistors (FETs) |
