Mayer C, Zaccarelli E, Stiakakis E, Likos C N, Sciortino F, Munam A, Gauthier M, Hadjichristidis N, Iatrou H, Tartaglia P, Löwen H, Vlassopoulos D
Dipartimento di Fisica and CNR-INFM-SOFT, Università di Roma La Sapienza, I-00185 Rome, Italy.
Nat Mater. 2008 Oct;7(10):780-4. doi: 10.1038/nmat2286. Epub 2008 Sep 14.
The long-standing observations that different amorphous materials exhibit a pronounced enhancement of viscosity and eventually vitrify on compression or cooling continue to fascinate and challenge scientists, on the ground of their physical origin and practical implications. Glass formation is a generic phenomenon, observed in physically quite distinct systems that encompass hard and soft particles. It is believed that a common underlying scenario, namely cage formation, drives dynamical arrest, especially at high concentrations. Here, we identify a novel, asymmetric glassy state in soft colloidal mixtures, which is characterized by strongly anisotropically distorted cages, bearing similarities to those of hard-sphere glasses under shear. The anisotropy is induced by the presence of soft additives. This phenomenon seems to be generic to soft colloids and its origins lie in the penetrability of the constituent particles. The resulting phase diagram for mixtures of soft particles is clearly distinct from that of hard-sphere mixtures and brings forward a rich variety of vitrified states that delineate an ergodic lake in the parameter space spanned by the size ratio between the two components and by the concentration of the additives. Thus, a new route opens for the rational design of soft particles with desired tunable rheological properties.
长期以来的观察结果表明，不同的非晶态材料在压缩或冷却时会表现出明显的粘度增强，并最终玻璃化，这一现象因其物理起源和实际应用，一直吸引并挑战着科学家们。玻璃形成是一种普遍现象，在包括硬颗粒和软颗粒的物理性质截然不同的系统中都能观察到。人们认为，一个共同的潜在情形，即笼状结构的形成，会导致动力学停滞，尤其是在高浓度时。在这里，我们在软胶体混合物中发现了一种新型的非对称玻璃态，其特征是笼状结构强烈各向异性扭曲，与剪切作用下硬球玻璃的笼状结构相似。这种各向异性是由软添加剂的存在引起的。这种现象似乎在软胶体中很普遍，其起源在于组成颗粒的可穿透性。由此产生的软颗粒混合物的相图与硬球混合物的相图明显不同，并呈现出丰富多样的玻璃化状态，这些状态在由两种组分的尺寸比和添加剂浓度所跨越的参数空间中勾勒出一个遍历性的区域。因此，为合理设计具有所需可调流变特性的软颗粒开辟了一条新途径。
