Department of Chemistry, Materials Science, and Chemical Engineering (CMIC), Politecnico di Milano, Edificio 6, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
Phys Rev E. 2019 Oct;100(4-1):042607. doi: 10.1103/PhysRevE.100.042607.
Relaxation of internal stresses through a cascade of microscopic restructuring events is the hallmark of many materials, ranging from amorphous solids like glasses and gels to geological structures subjected to a persistent external load. By means of photon correlation imaging, a recently developed technique that blends the powers of scattering and imaging, we provide a spatially and temporally resolved survey of the restructuring and aging processes that spontaneously occur in physical gels originating from an arrested phase separation. We show that the temporal dynamics is characterized by an intermittent sequence of spatially localized "microquakes" that eventually lead to global rearrangements occurring at a rate that scales with the gel age. Notably, these dramatic upheavals of the gel structure are heralded by a progressive acceleration of the microscopic gel dynamics that originates from recognizable active spots and then spreads at a large but finite speed through the gel. Within the "slack" phase between two of these "macroquakes," the fluctuations of the degree of temporal correlation obey a non-Gaussian statistics described by a generalized logistic distribution. The evidence we obtained bear consistent analogies with the stress relaxation processes taking place in earthquake sequences and with the intermittent restructuring of plastic crystals at the microscale.
通过一系列微观重构事件来放松内应力是许多材料的特点，这些材料的范围从非晶态固体（如玻璃和凝胶）到受到持续外部载荷的地质结构。通过光子相关成像，一种新开发的技术，融合了散射和成像的功能，我们提供了对源自停滞相分离的物理凝胶中自发发生的重构和老化过程的空间和时间分辨的调查。我们表明，时间动力学的特征是空间局部化的“微震”的间歇性序列，这些微震最终导致以与凝胶年龄成正比的速率发生的全局重排。值得注意的是，这些凝胶结构的剧烈动荡是由微观凝胶动力学的逐渐加速引起的，这种加速源于可识别的活跃点，然后以较大但有限的速度通过凝胶传播。在这两个“巨震”之间的“松弛”阶段，时间相关度的波动服从广义逻辑分布描述的非高斯统计。我们获得的证据与地震序列中发生的应力松弛过程以及微尺度下塑料晶体的间歇性重构具有一致的类比。
