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. 2015 Oct 13:5:15124.
doi: 10.1038/srep15124.

Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles

Eunsu Lee  1 , Dowan Kim  1 , Haneul Kim  1 , Jinhwan Yoon  1
Affiliations

Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles

Eunsu Lee et al. Sci Rep. .

Abstract

To overcome the slow kinetics of the volume phase transition of stimuli-responsive hydrogels as platforms for soft actuators, thermally responsive comb-type hydrogels were prepared using synthesized poly(N-isopropylacrylamide) macromonomers bearing graft chains. Fast responding light-responsive hydrogels were fabricated by combining a comb-type hydrogel matrix with photothermal magnetite nanoparticles (MNP). The MNPs dispersed in the matrix provide heat to stimulate the volume change of the hydrogel matrix by converting absorbed visible light to thermal energy. In this process, the comb-type hydrogel matrix exhibited a rapid response due to the free, mobile grafted chains. The comb-type hydrogel exhibited significantly enhanced light-induced volume shrinkage and rapid recovery. The comb-type hydrogels containing MNP were successfully used to fabricate a bilayer-type photo-actuator with fast bending motion.

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Figures

Figure 1
Figure 1. Synthesis of PNIPAm macromonomer through free-radical polymerization.
Figure 2
Figure 2
(a) Temperature-dependent linear swelling ratio (λf) during heating run for normal PNIPAm (n-PNIPAm) and grafted PNIPAm hydrogels (g-PNIPAm) with various degrees of polymerization (DP) of PNIPAm macromonomers. (b) Schematic illustration for the volume shrinking of the grafted hydrogels containing MNPs under irradiation of light. (c) Normalized linear swelling ratio <λf> for n-PNIPAm and g-PNIPAm containing magnetite nanoparticles (MNPs) exposed to visible light (41.8 mW/cm2) for 1 min at 25 °C. The red line is the fitting result from equation (1).
Figure 3
Figure 3. Normalized linear swelling ratios <λf> for n-PNIPAm and g-PNIPAm(209) containing MNP exposed to visible light (41.8 mW/cm2) at 25 °C.
Dotted lines are drawn at <λf> = 1.0 and 0.9.
Figure 4
Figure 4. Bending motion of the bilayer-type actuator comprising poly(acrylamide) (PAAm) and g-PNIPAm(209)/MNP under visible light irradiation.
(a) schematic illustration of the bilayer-type actuator; (b) micrographs for the bilayer actuator before (left) and after (right) irradiation with 41.8 mW/cm2 of visible light for 1 min at 30 °C; (c) curvature (κ) changes of the actuators; (d) empirically determined κ for the bilayer actuator comprising PAAm and g-PNIPAm(209)/MNP recorded for 30 cycles under visible light irradiation with various intensities (1 cycle: irradiation with visible light for 60 s followed by removal from light source for a further 60 s).
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