Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy.
J Chem Phys. 2011 Sep 14;135(10):104502. doi: 10.1063/1.3626869.
We investigate the vibrational density of states (vDOS) in harmonic approximation of a binary mixture of colloidal patchy particles with two and three patches for different relative compositions x(2). At low temperature, this system forms a thermo-reversible gel, i.e., a fully bonded network of chains of two-patches particles, in which the branching points are provided by three-patches particles. For all the compositions, we find in the vDOS a pronounced peak at low frequency whose height grows on increasing the fraction of two-functional particles or equivalently with the average length of the chains. To identify the various spectral features, we compare the vDOS of the whole system with the one of small representative structures of the network and with the vDOS of a long linear chain of two-patches particles and we find that these structures are indeed able to rationalize the various peaks in the vDOS of the full system. At large x(2) the vDOSs of the gel and of the long chain show remarkable similarities. Analyzing the dispersion relations and the spectrum of the linear chain we show that the excess of low frequency modes, the analog of the boson peak in glassy disordered systems, arises from the strong coupling between rotations and translations.
我们研究了胶体斑粒子二元混合物在简谐近似下的振动态密度（vDOS），这些斑粒子有两个和三个斑，相对组成 x(2) 不同。在低温下，该系统形成了一个热可逆凝胶，即由两斑粒子的链组成的完全键合的网络，其中三斑粒子提供了分支点。对于所有组成，我们在 vDOS 中发现了一个在低频处明显的峰值，其高度随着两官能团粒子的分数或等效地随着链的平均长度的增加而增加。为了识别各种光谱特征，我们将整个系统的 vDOS 与网络的小代表性结构的 vDOS 以及两斑粒子的长线性链的 vDOS 进行比较，我们发现这些结构确实能够合理地解释全系统 vDOS 中的各种峰。在大 x(2) 时，凝胶和长链的 vDOS 非常相似。分析线性链的色散关系和谱，我们表明，低频模式的过剩，即玻璃无序系统中玻色峰的类似物，来自于旋转和平移之间的强耦合。
