报告摘要

Metamaterials have attracted considerable attentions for decades owing to their fantastic properties and a wide applications. The extraordinary properties of a metamaterial is based on its multistability, i.e., it can stay steadily in more than one stable or metastable states and switch among each other. I found a new mechanism to obtain a natural multi-stable material, i.e., confining a helical filament inside a tube. For the filament with isotropic bending rigidities, when c0R=0.5 and τ0R <0.15, where c0 is the intrinsic curvature of filament, τ0 is intrinsic twist rate and R is the radius of tube, the phase diagram for the stability of a helix contains three regimes. Regime I has a small τ0 and exhibits a bistable state which consists of two isoenergic helices. In regime II, the filament has a moderate τ0 and the bistable state consists of a metastable low-pitch helix and a stable nonhelix. In regime III, the helix is unstable, owing to a large τ0 . A similar phenomenon occurs when c0R∼0.5. Furthermore, our calculations reveal that the extension of filament can undergo a single-step abrupt transition under external force or torque. To make the filament jump from a low pitch helix up to a large pitch one it is more efficient to apply a stretching force; but to induce a collapse from a large pitch helix to a low pitch helix it is better to apply a positive torque.

On the other hand, we find that when c0R ∼0.5 and τ0R <0.11< c0R, confining a helical filament with anisotropic bending rigidities within a cylindrical tube can create a natural tristable status which is consisted of two low-pitch helices and one high-pitch helix. The relative heights of two low-pitch helices in a tristable status are close to zero. At some specific intrinsic parameters, the tristable status can include an isoenergic status with two helices of the same energy but distinct pitches.

主讲人简介

周子聪，台湾淡江大学物理系教授。曾任淡江大学物理系主任及淡江大学理学院院长。1985年在中国科学院物理研究所获得理学硕士学位。 1996年在加拿大渥太华大学获得哲学博士学位。在《Physical Review》A, B, E 等SCI期刊上发表60余篇研究论文。研究领域包括生物物理，计算物理，统计物理，凝态及软凝态物理。曾获中国科学院科技进步二等奖，台湾“国科会” 甲种研究奖励。