forming an interdigitated side chain structure [110, 133, 134]. Hybrid semicrystalline hydrogels undergo up to 120-fold reversible change in their modulus by
changing the temperature between below and above the crystalline melting
temperature [129].
Later on, semicrystalline hybrid hydrogels of Osada et al. were synthesized via
micellar polymerization in aqueous solutions of WLMs instead of the solution
polymerization in ethanol [91]. The block-like structure of poly(AAc-co-C18A)
copolymer chains formed in a micellar solution enhances the hydrophobic interactions leading to two to three orders of magnitude change in the storage modulus in
response to a change in the temperature. Figure 17a shows temperature-dependent
variations of G
0 , G
00 , and tan δ during a thermal cycle between 80 and 5
C for PAAc
hydrogels formed via micellar polymerization with 1 mol% BAAm and varying
amounts of C18A between 20 and 50 mol%. The dotted vertical lines in the upper
panel indicate the melting T m and recrystallization temperatures T cry . The hydrogels
at 5
C exhibit a storage modulus G
0 in the MPa level, i.e., 3.6, 8, and 17.6 MPa for
20, 35, and 50 mol% C18A, respectively. During heating, G
0 drastically decreases at
around T m , 48 Æ 2
C, and attains a value between 16 and 27 kPa at 80
C, which is
130- to 700-fold smaller than the initial modulus at 5
C [91]. The temperatureinduced modulus change is totally reversible as such upon cooling, G
0 rapidly
increases at around T cry , 43 Æ 2
C, to attain the initial MPa level modulus
(Fig. 17b) [91].
(A)
Temperature / °C
15 30 45
G'' / MPa
10 -2
10 -1
10 0
15 30 45 60
tan
δ δ
0.0
0.2
0.4
G'' / MPa
10 -2
10 -1
10 0
G' / MPa
10 -1
10 0
10 1
Temperature / °C
20
40
60
80
Temperature / °C
20 40 60 80
G' / MPa
10 -2
10 -1
10 0
10 1
50 %
35 %
80 °C
5 °C
80 °C
T cry
T m
(B)
Fig. 17 (a) Temperature-dependent variations of the dynamic moduli G
0 and G
00 and tan δ of
semicrystalline hybrid PAAc hydrogels with varying amount of C18A during a thermal cycle
between 80 and 5
C. C18A ¼ 20 (), 35 (), and 50 mol% (). BAAm ¼ 1 mol%. (b) G
0 and G
00
of PAAc hydrogels with 35 (left panel) and 50 mol% C18A (right panel) during the thermal cycle.
Down and up arrows indicate increasing and decreasing temperatures, respectively. ω ¼ 6.28 rad s
À1
.
γ o ¼ 0.1%. From [91] with permission from the American Chemical Society
48
O. Okay
changing the temperature between below and above the crystalline melting
temperature [129].
Later on, semicrystalline hybrid hydrogels of Osada et al. were synthesized via
micellar polymerization in aqueous solutions of WLMs instead of the solution
polymerization in ethanol [91]. The block-like structure of poly(AAc-co-C18A)
copolymer chains formed in a micellar solution enhances the hydrophobic interactions leading to two to three orders of magnitude change in the storage modulus in
response to a change in the temperature. Figure 17a shows temperature-dependent
variations of G
0 , G
00 , and tan δ during a thermal cycle between 80 and 5
C for PAAc
hydrogels formed via micellar polymerization with 1 mol% BAAm and varying
amounts of C18A between 20 and 50 mol%. The dotted vertical lines in the upper
panel indicate the melting T m and recrystallization temperatures T cry . The hydrogels
at 5
C exhibit a storage modulus G
0 in the MPa level, i.e., 3.6, 8, and 17.6 MPa for
20, 35, and 50 mol% C18A, respectively. During heating, G
0 drastically decreases at
around T m , 48 Æ 2
C, and attains a value between 16 and 27 kPa at 80
C, which is
130- to 700-fold smaller than the initial modulus at 5
C [91]. The temperatureinduced modulus change is totally reversible as such upon cooling, G
0 rapidly
increases at around T cry , 43 Æ 2
C, to attain the initial MPa level modulus
(Fig. 17b) [91].
(A)
Temperature / °C
15 30 45
G'' / MPa
10 -2
10 -1
10 0
15 30 45 60
tan
δ δ
0.0
0.2
0.4
G'' / MPa
10 -2
10 -1
10 0
G' / MPa
10 -1
10 0
10 1
Temperature / °C
20
40
60
80
Temperature / °C
20 40 60 80
G' / MPa
10 -2
10 -1
10 0
10 1
50 %
35 %
80 °C
5 °C
80 °C
T cry
T m
(B)
Fig. 17 (a) Temperature-dependent variations of the dynamic moduli G
0 and G
00 and tan δ of
semicrystalline hybrid PAAc hydrogels with varying amount of C18A during a thermal cycle
between 80 and 5
C. C18A ¼ 20 (), 35 (), and 50 mol% (). BAAm ¼ 1 mol%. (b) G
0 and G
00
of PAAc hydrogels with 35 (left panel) and 50 mol% C18A (right panel) during the thermal cycle.
Down and up arrows indicate increasing and decreasing temperatures, respectively. ω ¼ 6.28 rad s
À1
.
γ o ¼ 0.1%. From [91] with permission from the American Chemical Society
48
O. Okay