  The contact of a hydrogel during the rotational shearing on glass surface in
concentrated polymer solution was observed in situ. Dynamic contact patterns
that rotate in-phase with the rotational shearing of the gel were observed for
the first time. The contact patterns with a periodicity in the circumferential
direction appeared and developed into fine characters with the shearing time.
The patterns appeared more quickly at elevated sliding velocity, polymer
concentration, and normal pressure. Furthermore, the softness of the gel also
substantially influenced the character of the patterns. The pattern formation
was discussed in terms of the non-linear rheology of the polymer solution at
the rotational soft interface.
