Indenter geometries used in the experiments.
Photographs and schematic illustrations of the gel structure for pNIPAM above and below the critical temperature.
The probe tack apparatus.
Load and displacement histories for a typical experiment.
Load-displacement relationship illustrating the onset of nonlinear response for large using a radius circular punch and a pNIPAM gel: (a) , ; and (b) , . The boxes on the graph indicate the regimes in which the oscillatory experiments were conducted (Fig. 4). The dashed lines represent the linear response given by Eqs. (1) and (2).
Idealized relaxation behavior of an elastic gel under compression.
Oscillatory load-displacement behavior at for a pNIPAM gel, using a circular punch with : (a) 22, and (b) .
Values of the shear modulus obtained from application of Eq. (13) to data obtained from the oscillatory experiments.
Phase angles obtained from application of Eq. (12) to the oscillatory data. The solid line is a representation of the inverse square root dependence given by Eq. (33), with parameters chosen to give a phase angle of 3° at the lowest experimental frequency, as explained in the text.
Calculated phase angles as a function of the normalized angular frequency from Eq. (31), for different values of relaxed Poisson’s ratio .
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