Yielding behavior in colloidal glasses: comparison between "hard cage" and "soft cage"
writer：周治，Javoris Hollingsworth，洪崧，程賀，韓志超
keywords：colloidal glass, hard cage, soft cage
source：期刊
specific source：langmuir
Issue time：2014年
Rheological measurements are utilized to examine the yielding behavior of a
polystyrene (PS) core and poly (N-isopropyl acrylamide) (PNIPAM) shell microgel
system with varying shell/core ratio. For a shell/core ratio of 0.15 at high
concentrations, the suspensions show a typical hard sphere (HS) yielding response
where the loss modulus (G") exhibits a single peak due to cage breaking. As a result
of tighter cages and less cage distortion prior to yielding, the peak location of G"
decreases with volume fraction. For a shell/core ratio of 1.10, which behaves like a
soft jammed glass at high concentration, the suspensions exhibit a one-step yielding
behavior similar to that of HS glass. However, the location of the peak in G" increases
with volume fraction, demonstrating the important role of particle deformation in the
breakage of cages. For an intermediate shell/core ratio of 0.34, the system displays a
two-step yielding behavior, as observed in previous reports for attractive glasses. Byincreasing the volume fraction, the strain of the first peak increases while the second one decreases. In addition, as the effective volume fraction increases to 112%, the two peaks merge into one broad peak. It is demonstrated that the first peak of G'''''''' is due to deformation of the shell, and the second peak of G" is attributed to cage breaking as a result of the cores colliding with each other. Combining these results, a yielding state diagram from typical HS to soft jammed glass is demonstrated.