Abstract
Smart hydrogels, or stimuli-responsive hydrogels, are three-dimensional networks composed of crosslinked hydrophilic polymer chains that are able to dramatically change their volume and other properties in response to environmental stimuli such as temperature, pH and certain chemicals. Rapid and significant response to environmental stimuli and high elasticity are critical for the versatility of such smart hydrogels. Here we report the synthesis of smart hydrogels which are rapidly responsive, highly swellable and stretchable, by constructing a nano-structured architecture with activated nanogels as nano-crosslinkers. The nano-structured smart hydrogels show very significant and rapid stimuli-responsive characteristics, as well as highly elastic properties to sustain high compressions, resist slicing and withstand high level of deformation, such as bending, twisting and extensive stretching. Because of the concurrent rapid and significant stimuli-response and high elasticity, these nano-structured smart hydrogels may expand the scope of hydrogel applications, and provide enhanced performance in their applications.
Highlights
Smart hydrogels, or stimuli-responsive hydrogels, are three-dimensional networks composed of crosslinked hydrophilic polymer chains that are able to dramatically change their volume and other properties in response to environmental stimuli such as temperature, pH and certain chemicals
The thermo-responsive swelling ratio of our nano-structured hydrogels (NSG) in responding to temperature changing from 45 °C to 15 °C is as high as 8,000%, and the characteristic time of gel shrinking from fully swollen state to fully collapsed state upon heating from 25 °C to 55 °C for a NSG hydrogel with characteristic dimension of 422 mm is only B6 min
Controllable activated nanogels (ANGs) bearing unsaturated double bonds are fabricated by precipitation polymerization of NIPAM and MBA at 60 °C, which is initiated by potassium persulfate (KPS) in the presence of SDS (Fig. 1a,b)
Summary
Stimuli-responsive hydrogels, are three-dimensional networks composed of crosslinked hydrophilic polymer chains that are able to dramatically change their volume and other properties in response to environmental stimuli such as temperature, pH and certain chemicals. As a kind of typical thermo-responsive smart hydrogels that can undergo a reversible volume phase transition near the lower critical solution temperature (LCST, B32 °C), normal poly(N-isopropylacrylamide) (PNIPAM) hydrogels crosslinked by chemical crosslinkers such as N,N-methylenebisacrylamide (MBA) are always elastically poor and shrink/swell slowly upon heating/cooling across the LCST. To overcome these limitations, intense efforts have been devoted to synthesizing hydrogels with either improved response properties[12,13,14,15,16,17] or improved elastic properties[18,19,20,21,22]. The large responsive swelling ratio, rapid response rate and high elasticity of our NSG hydrogels can be obtained simultaneously without any conflict
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