Vibration spectroscopy of weakly interacting mesoscopic colloids
Vibration spectroscopy of weakly interacting mesoscopic colloids
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DOI：
10.1039/c2sm07034k
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发表时间：
2012-01-01
期刊：
影响因子：
3.4
通讯作者：
Fytas, George
中科院分区：
文献类型：
--
作者：
Mattarelli, Maurizio;Montagna, Maurizio;Fytas, George
用布里渊光谱法研究了不同尺寸球形聚苯乙烯（PS）颗粒团簇的振动动力学。在第一近似中，谱可以用兰姆理论的连续统近似内的单粒子模型来描述。该模型对直径大于或接近500nm的颗粒得到了很好的结果，但由于受限振动线的拓宽和移位，该模型无法解释较小颗粒振动谱中观察到的最低频率信号的线形。在小颗粒（小于或接近400nm）的情况下，该模型也无法预测额外的极低频宽带。这一波段归因于声子在粒子间相互作用控制的多粒子簇中的传播。这些相互作用还产生与单球兰姆模密切相关的扩展模态。一个简单的粒子相互作用模型可以表示新的光谱特征，并估计相互作用的强度和胶体团中的长波纵向速度。它们在PS玻璃化转变附近的热退火增强了相互作用，这种相互作用表现在与单个球体振动相关的低频粒子振动谱和声子带。新兴的粒子振动光谱成为研究胶体热力学性质及其相互作用的灵敏工具。
Brillouin spectroscopy has been used to study the vibrational dynamics of clusters of spherical polystyrene (PS) particles with different size. In a first approximation, the spectra can be described by a single particle model within the continuum approximation of the Lamb theory. The model yields excellent results for particles with diameter d greater than or similar to 500 nm, but fails in accounting for the lineshapes of the observed lowest frequency signals in the vibration spectrum of smaller particles due to a broadening and shift of the lines of confined vibrations. The model also fails to predict an additional very low frequency broad band in the case of small particles (d less than or similar to 400nm). This band is attributed to phonon propagation in multiple-particle clusters governed by the interactions among particles. These interactions also produce extended modes in close relation to the Lamb modes of the single sphere. A simple model for the particle interaction allows to represent the new spectral features and estimate the strength of the interactions and the long wavelength longitudinal velocity in the colloidal clusters. Their thermal annealing near the glass transition of PS enhances the interactions which are manifested in the low frequency particle vibration spectrum and the phonon bands associated with the vibrations of the individual spheres. The emerging particle vibration spectroscopy becomes a sensitive tool of the colloids' thermo-mechanical properties as well their interactions.