When isotropic solids are unequally stretched in two orthogonal directions, the true stress (force per actual cross-sectional area) in the larger strain direction is typically higher than that in the smaller one. We show that thiol-acrylate liquid crystal elastomers with polydomain texture exhibit an unusual tendency: The true stresses in the two directions are always identical and governed only by the area change in the loading plane, independently of the combination of imposed strains in the two directions. This feature proves a previously unidentified state of matter that can vary its shape freely with no extra mechanical energy like liquids when deformed in the plane. The theory and simulation that explain the unique behavior are also provided. The in-plane liquid-like behavior opens doors for manifold applications, including wrinkle-free membranes and adaptable materials.

当各向同性固体在两个正交方向上不均匀拉伸时，较大应变方向上的真实应力（单位实际横截面积的力）通常高于较小应变方向上的真实应力。我们表明，具有多域结构的硫醇丙烯酸酯液晶弹性体表现出一种不寻常的趋势：两个方向上的真实应力始终相同，并且仅受加载平面中的面积变化控制，与两个方向上施加的应变的组合无关。这一特征证明了一种以前未被识别的物质状态，当在平面上变形时，它可以自由地改变其形状，而不需要像液体那样额外的机械能。还提供了解释独特行为的理论和模拟。面内类似液体的行为为多种应用打开了大门，包括无皱膜和适应性材料。