Mechanical oscillation accelerating nucleation and nuclei growth in hard-sphere colloidal glass

Nobutomo Nakamura,Hirotsugu Ogi,Shizuka Nakashima

doi:10.1038/s41598-019-49120-1

Abstract

Crystallization from amorphous solids is generally caused by activating phonons in a wide frequency range during heat treatment. In contrast, the activation of phonons in a narrow frequency range using ultrasonic treatment also causes crystallization below the glass transition temperature. These behaviors indicate that crystallization is related to the atomic motion in the glass state, and it is suggested that the activation of specific atomic motion can cause crystallization without increasing temperature. In this study, we observe nucleation and nuclei growth caused by mechanical oscillation in a hard-sphere colloidal glass and evaluate the effect of mechanical oscillation on the structural evolution in the early stage of the crystallization. Oscillation between 5 and 100 Hz is applied to the colloidal glass, and it is observed that the nucleation rate increases under the 70 Hz oscillation, resulting in formation of stable nuclei in a short amount of time. The nuclei growth is also accelerated by the 70 Hz oscillation, whereas increases in the nucleation rate and nuclei growth were not observed at other frequencies. Finally, activation of the diffusion-based rattling of particles by caging is considered as a possible mechanism of the observations.

Highlights

Controlled heat treatment is a common technique used to crystallize amorphous solids and produce nanocrystalline materials that possess characteristic mechanical and magnetic properties[1,2,3,4]
We used a colloidal suspension consisting of a mixture of water and dimethyl sulfoxide (DMSO) with fluorescein sodium salt (FSS) and silica particles of 1.5 μm diameter with polydispersity index less than 0.2
Mechanical oscillation was applied to the colloidal glass by moving an oscillator inserted into the colloidal suspension

Summary

Introduction

Controlled heat treatment is a common technique used to crystallize amorphous solids and produce nanocrystalline materials that possess characteristic mechanical and magnetic properties[1,2,3,4]. In Pd-based metallic glass, ultrasonic irradiation leads to crystallization below the glass transition temperature[5] This phenomenon is explained by specific atomic motion that is stochastically resonant with the ultrasonic vibrations; the activation leads to crystallization. In glass forming materials, characteristic atomic motion exists, e.g., α relaxation, β relaxation, and boson peak[6,7] Activating such atomic motion is considered to be a possible cause of accelerated crystallization. The crystallization frequency increased by increasing the inter-particle attractive force, and it implies that there are specific particle motions contributing to crystallization This phenomenon cannot be explained by the above described model, indicating different phenomenon was found.

Methods

Results

Conclusion