True Chemical Structure of Double Network Hydrogels

Nakajima, Tasuku; Furukawa, Hidemitsu; Takai, Yoshimi; Kurokawa, Takayuki; Osada, Yoshihito; Gong, Jian Ping

doi:10.1021/ma802148p

Cited by 270 publications

(283 citation statements)

References 20 publications

(44 reference statements)

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“…Especially, the double network gels (DN gels), though with a high water content (>90 wt%), have extremely high fracture energy of ~10 3 J/m 2 . This value is much higher than that of classic gels, and even 45 comparable with that of some industrial rubbers [6][7][8] . The tough DN gels have a contrast structure that the second polymer network, flexible and loosely cross-linked, is densely packed and interpenetrated in the cage of first polymer network that is a rigid skeleton, highly cross-linked and in dilute concentration.…”

Section: Introductionmentioning

confidence: 58%

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Characterization of internal fracture process of double network hydrogels under uniaxial elongation

et al. 2013

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5Previously we revealed that the high toughness of double network hydrogels (DN gels) derives from the internal fracture of the brittle network during deformation, which dissipates energy as sacrificial bonds. In this study, we intend to elucidate the detailed internal fracture process of DN gels. We quantitatively analysed the tensile hysteresis and re-swelling behaviour of a DN gel that shows a well-defined necking and strain hardening, and obtained the following new findings: 1) Fracture of the 1 st network PAMPS 10 starts far below the yielding strain, and 90% of the initially load-bearing PAMPS chains already breaks at the necking point.2) The dominant internal fracture process occurs in the necking and hardening region although the softening mainly occurs before necking.3) The internal fracture efficiency is very high, 85% of the work is used for the internal fracture and 9% of all PAMPS chains break at sample failure. 4) The internal fracture is anisotropic, fracture occurs preferentially perpendicular to the tensile direction than 15 other two directions, but the fracture anisotropy decreases in the hardening region. Result 1) and 2) is in agreement with a hierarchical structural model of PAMPS network. Based on these findings, we present a revised description of the fracture process of DN gels.

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Section: Introductionmentioning

confidence: 58%

“…Truly-independent DN gels, or simply t-DN gels, are special types of DN gels that do not contain any covalent bonds between the two networks 7 . As t-DN gels have a simpler structure than 85 conventional DN gels, t-DN gels were useful for analysing the fracture process of DN gels.…”

Section: Synthesis Of T-dn Gelsmentioning

confidence: 99%

Characterization of internal fracture process of double network hydrogels under uniaxial elongation

et al. 2013

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“…The resulting hydrogels achieve stiffness and toughness significantly beyond those of existing hydrogels ( Figure 1). work are compared with other soft materials, including hybrid gels with long-chain alginate only, 13 double network hydrogels, 18,35 polyvinyl alcohol hydrogels (PVA), 36 17 along with data for polyacrylamide hydrogels (PAAm) and alginate hydrogels. 13 An alginate-polyacrylamide hydrogel consists of two interpenetrating polymer networks.…”

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confidence: 99%

Hybrid Hydrogels with Extremely High Stiffness and Toughness

et al. 2014

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The development of hydrogels for cartilage replacement and soft robotics has highlighted a challenge: load-bearing hydrogels need to be both stiff and tough. Several approaches have been reported to improve the toughness of hydrogels, but simultaneously achieving high stiffness and toughness remains difficult. Here we report that alginate-polyacrylamide hydrogels can simultaneously achieve high stiffness and toughness. We combine short-and long-chain alginates to reduce the viscosity of pregel solutions and synthesize homogeneous hydrogels of high ionic cross-link density. The resulting hydrogels can have elastic moduli of ∼1 MPa and fracture energies of ∼4 kJ m −2 . Furthermore, this approach breaks the inverse relation between stiffness and toughness: while maintaining constant elastic moduli, these hydrogels can achieve fracture energies up to ∼16 kJ m −2 . These stiff and tough hydrogels hold promise for further development as load-bearing materials.

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“…Given that the first network is highly swollen in the second monomer solution, the second network is effectively entangled with the first network to form a very strong DN gel. [62][63][64][65][66][67] The first network contributes to an increase in elastic stress, whereas the second network contributes to an increase in strain. Numerous polymer pairs have been used to optimize the characteristic behaviors of DN gels, and the methyl-propane sulfonate polymer/acrylamide polymer pair has been found to be the most promising.…”

Section: Double Network Gelsmentioning

confidence: 99%

“…(Reproduced with permission from Haraguchi et al 53 ) Figure 13 Structural model of a methyl-propane sulfonate polymer/ acrylamide polymer double network gel. (Reproduced with permission from Nakajima et al 66 )…”

Section: Double Network Gelsmentioning

confidence: 99%

Recent advances in hydrogels in terms of fast stimuli responsiveness and superior mechanical performance

Imran

Seki

Takeoka

2010

Polym J

137

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This review addresses the potential development of polymer hydrogels in terms of fast stimuli responsiveness and superior mechanical properties. The slow response and mechanical weakness of stimuli-sensitive hydrogels have been considered as the main barriers for their further development and practical application. It has been a dream of scientists to have fast stimuliresponsive hydrogels with superior mechanical performance. In this review, the principal reasons behind the poor stimulus sensitivity and mechanical strength of polymer gels are highlighted, and we present some pioneering physical and chemical efforts aimed at fabricating hydrogels with high stimuli sensitivities and/or superior mechanical properties. Polymer Journal ( Keywords: butterfly pattern; fast stimuli sensitivity; hydrogel; LCST; mechanical property INTRODUCTION Polymer hydrogels (hereafter called 'hydrogels') are three-dimensional polymer networks in which the voids are filled with water. These hydrogels are widely used in a variety of industrial and consumer products such as oil dewatering systems, mechanical absorbers, diapers and contact lenses. One of the most remarkable areas of research on hydrogels in the past few decades has been their stimulus sensitivity. Hydrogels composed of stimuli-responsive polymers reversibly alter their shape and volume in response to small variations in the environment, such as pH, temperature, light and electric and magnetic fields, thereby changing their physico-chemical characteristics. 1 Among all of the available environmentally responsive hydrogels, temperature-responsive hydrogels have attracted the most attention because of the facile tuning of their properties. In particular, poly(Nisopropylacrylamide) (poly(NIPA)) hydrogels have been widely investigated as thermosensitive hydrogels. Poly(NIPA) has a low critical solution temperature (LCST) at around 32 1C in water. The flexible coil of poly(NIPA) (soluble) converts into a compact globular state (insoluble) at the LCST, and this conformational change is reversible. 2 Thus, hydrogels composed of poly(NIPA) undergo a reversible volume change at a similar transition temperature in water. Poly(NIPA) hydrogels have potential applications in drug delivery systems, therapeutic agents, diagnostic devices, biomaterials, cell cultivation, biocatalysts, sensors, microfluidic devices, actuators, optical devices and size-selective separation among others. [3][4][5] A recent subject that has attracted much attention in the field of gel science is the fabrication of hydrogels with the rapid stimuli responsiveness and superior mechanical properties required for many applications of stimuli-responsive hydrogels. The creation of durable

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True Chemical Structure of Double Network Hydrogels

Cited by 270 publications

References 20 publications

Characterization of internal fracture process of double network hydrogels under uniaxial elongation

Characterization of internal fracture process of double network hydrogels under uniaxial elongation

Hybrid Hydrogels with Extremely High Stiffness and Toughness

Recent advances in hydrogels in terms of fast stimuli responsiveness and superior mechanical performance

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