2.2 Sample Preparation
Dual crosslink gels and the corresponding chemical gels were prepared by radical
polymerization. For the chemical gel, an aqueous solution containing AAm (1.8 M),
VIm (0.2 M), MBA (2–10 mM, corresponding to 0.1–0.5 mol% of the total
monomer concentration, 2 M), and KPS (6 mM) was prepared under nitrogen flow
at low temperature (in an ice bath). The solution was then transferred in a glovebox,
and TEMED (20 mM) was added to initiate radical polymerization. After the
overnight reaction, the obtained P(AAm-co-VIm) chemical gels were used for
measurements as prepared. P(AAm-co-VIm)-M
2+ dual crosslink gels were prepared
in the same procedure, by adding further NiCl 2 or ZnCl 2 in the solution; the
concentration of MBA was fixed at 3 mM (0.15 mol%). After the overnight
crosslinking reaction, the obtained P(AAm-co-VIm)-M
2+ dual crosslink gels were
used for measurements as prepared.
2.3 Linear Viscoelastic Properties
The linear viscoelastic properties of the dual crosslink gels in small strain oscillatory
shear were characterized in a parallel plate geometry with roughened surfaces
(20 mm in diameter) with the ARES LS1 rheometer (TA instruments). The sample
thickness was 1.5 mm. Frequency sweep tests with a dynamic range varying from
0.1 to 100 rad/s were carried out at 25
C within the linear viscoelasticity regime
(0.2–0.8% strain).
2.4 Uniaxial Tensile Tests
The large deformation behavior of the gels was investigated by uniaxial tensile test
to fracture and step-cycle loading – unloading tests on an Instron 5565 tensile tester
with a 10 N load cell. Samples were rectangular in shape with 5 mm in width,
1.5 mm in thickness, and 15 mm in length L 0 (length between clamps). We kept the
samples in paraffin oil during all the tests to prevent them from drying following a
previously published procedure [18].
6
J. Zhao et al.
Dual crosslink gels and the corresponding chemical gels were prepared by radical
polymerization. For the chemical gel, an aqueous solution containing AAm (1.8 M),
VIm (0.2 M), MBA (2–10 mM, corresponding to 0.1–0.5 mol% of the total
monomer concentration, 2 M), and KPS (6 mM) was prepared under nitrogen flow
at low temperature (in an ice bath). The solution was then transferred in a glovebox,
and TEMED (20 mM) was added to initiate radical polymerization. After the
overnight reaction, the obtained P(AAm-co-VIm) chemical gels were used for
measurements as prepared. P(AAm-co-VIm)-M
2+ dual crosslink gels were prepared
in the same procedure, by adding further NiCl 2 or ZnCl 2 in the solution; the
concentration of MBA was fixed at 3 mM (0.15 mol%). After the overnight
crosslinking reaction, the obtained P(AAm-co-VIm)-M
2+ dual crosslink gels were
used for measurements as prepared.
2.3 Linear Viscoelastic Properties
The linear viscoelastic properties of the dual crosslink gels in small strain oscillatory
shear were characterized in a parallel plate geometry with roughened surfaces
(20 mm in diameter) with the ARES LS1 rheometer (TA instruments). The sample
thickness was 1.5 mm. Frequency sweep tests with a dynamic range varying from
0.1 to 100 rad/s were carried out at 25
C within the linear viscoelasticity regime
(0.2–0.8% strain).
2.4 Uniaxial Tensile Tests
The large deformation behavior of the gels was investigated by uniaxial tensile test
to fracture and step-cycle loading – unloading tests on an Instron 5565 tensile tester
with a 10 N load cell. Samples were rectangular in shape with 5 mm in width,
1.5 mm in thickness, and 15 mm in length L 0 (length between clamps). We kept the
samples in paraffin oil during all the tests to prevent them from drying following a
previously published procedure [18].
6
J. Zhao et al.