Fig. 8
From: Bonding dissimilar polymer networks in various manufacturing processes
Mechanical manipulation during bonding. a A silane-modified polyacrylic acid (PAAc) hydrogel, with or without prestretch, is bonded to a silane-modified PDMS. Upon immersing the bilayer in a 0.1 M NaHCO3 solution, the PAAc hydrogel swells to ~9 times the original thickness. The swelling causes the hydrogel with prestretch to form a one-dimensional pattern, and causes the hydrogel without prestretch to form a two-dimensional pattern. The scale bar is 2 mm. b Co-drawing of an elastomer-coated hydrogel fiber. A fiber of oxygen-tolerant resin is extruded from a syringe (Supplementary Movie 4). The fiber is then dip-coated in a PDMS precursor. We keep both polymers uncrosslinked, and co-draw them into a thinner fiber. Subsequently, the coupling agents condensate to crosslink the networks and bond them. Subject to a uniaxial stretch λ, the hydrogel fiber length increases by a factor of λ while the diameter reduces by a factor of 1/λ1/2. c Digital images (up) and microscopic images (down) of an elastomer-coated hydrogel fiber. The fiber has an initial diameter ~1.4 mm, and is drawn to a fiber of diameter 154 µm. The scale bar is 500 μm. d SEM images showing the cross-sections of a PDMS-coated PAAm fiber. The scale bars are 20 μm (up) and 1 μm (down). e Dip-coat two layers of PAAm resins with PDMS coatings, stack them together, keep both polymers uncrosslinked, and press them into a thinner laminate. After curing, PDMS forms an insulating layer between two PAAm hydrogels, as well as a coating layer covering the surface. f Images of the cross-section of multilayered PAAm-PDMS structure. The scale bars are 2.5 mm (left) and 250 μm (right)
