Nanotechnologies / Materials

Fig. 2 Average number ofparticle

Rheology, Amorphous materials

Universality in the physics of jamming

１2. ご自身の顔写真のご提供※ 印刷可能な解像度のものを電子

Cybermedia Center
Associate Professor Hajime Yoshino
Researchmap https://researchmap.jp/read0076565

Nanotechnologies / Materials

Abstract

図１ ジャミング密度近傍にある高密度の剛体球ガラス
in our daily life and industrial products.

We performed computer simulations to compress and shear
glassy states of hard-spheres, which is the simplest glass. As theresult we succeeded to generate a large number of jammed stateswith various densities and degree of anisotropy (Fig 1). We foundthe diverse jammed states are all marginally stable in the mechanical sense and exhibit universal criticalities. For instance, the number of surrounding particles at a distance r from a given particle
shows a universal behavior independent of the jamming density φj.
From the left panel, we find that the average contact number is 6
meaning that the jammed states are just marginally stable. From
the right panel we find the number of particles almost in contact
obeys a power law with a universal exponent meaning that the system is in a critical state. The results of this work will promote basic
understanding of the physics of glasses, which is far less well understood compared with that of crystals.

▍ Background & Results

Fig. 1 Hard-sphere glass at a high density close to jamming density

Historically it has been discussed for a long time howFig.
one can
1 Hard-sphere glass at a high density
pack spheres most densely in a box. In 17 century J. Keppler
prejamming
densitydicted that the close packing or densest packing in 3 dimensions
is the face-centered cubic (FCC) lattice. Only 400 years later thisconjecture was proved to be true by Thomas Hale in 1998. The
volume fraction of the close packing is 0.74048... Quite a different
packing, called random close packing, was studied by J. Bernard
and J. Mason experimentally in 1960 who found spheres randomly
packed typically have volume fraction around 0.64. Later it was
discovered that jammed states created by random packing canhave various volume fractions depending for instance on the ways
to prepare the initial configurations before compression. Jamming
is an important phenomenon that controls the mechanical properties of various soft matters used in our daily like mayonnaise, toothpastes, e.t.c.
Fig. 2 Average number of particles at distance r from a particle
図 2not粒子の中心から距離 r にある他の粒子の平均的な数
We found various jammed configurations can be generated
only by compression but also by putting shear on the container
performing extensive numerical simulations of hard-sphere glasses
Fig. 2 Average number of particles at distance r from aby supercomputers. Shear-jamming has been known for the caseparticleof spheres with frictions but we showed the friction is not necessary. Moreover, we found the jammed states created by various
different combinations of compression and shear all exhibit universal features as shown in Fig. 2: the average contact number is 6(left), physical quantities exhibit universal critical phenomena (right). １2. ご自身の顔写真のご提供
These features are very different from those of close packing: the ※ 印刷可能な解像度のものを電子ファイルにてご提供ください。
contact number is 12, the configuration is unique and mechanicallyvery stable.

close to▍ Significance of the research and Future perspective
Our achievement will promote progress on the physics of glasses which is far less well understood compared with that of crystals.
Our result will be useful to control soft-matters commonly found以上P a t e n t
T r e a t i s e Jin, Yuliang; Yoshino, Hajime. A jamming plane of sphere packings. PNAS. 2021; 118 (14): e2021794118. doi: 10.1073/pnas.2021794118
UR
L http://www.cp.cmc.osaka-u.ac.jp/~yoshino/
K e y w o r d statistical physics, soft-matter physics, glass transitions, jamming