1 research outputs found
Long Time Response of Soft Magnetorheological Gels
Swollen physical magnetorheological (MR) gels were obtained
by
self-assembling of triblock copolymers containing dispersed soft magnetic
particles. The transient rheological responses of these systems were
investigated experimentally. Upon sudden application of a homogeneous
magnetic field step change, the storage modulus of MR gels continued
to increase with time. Such increase trend of the storage modulus
could be expressed by a double-exponential function with two distinct
modes, a fast and a slow one. The result was compared with the transient
rheological response of equivalent MR fluids (paraffin oil without
copolymer) and a MR elastomer (PDMS) and interpreted as the consequence
of strong rearrangement of the original particle network under magnetic
field. Similar to the structure evolution of MR fluids, the ensemble
of results suggests that “chaining” and “clustering”
processes are also happening inside the gel and are responsible for
the rheological behavior, provided they are happening on a smaller
length scale (long chains and clusters are hindered). We show that
response times of several minutes are typical for the slow response
of MR gels. The characteristic time <i>t</i><sub>2</sub> for the slow process is significantly dependent on the magnetic
flux density, the matrix viscoelastic property, particle volume fraction,
and sample’s initial particle distribution. In order to validate
our results, the role of dynamic strain history was clarified. We
show that, in the linear viscoelastic region, the particle rearrangement
of MR gels was not hindered or accelerated by the dynamic strain history