*2.4.1. Preperation of Poly(AAc-co-tBMA)*

316 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

by the SEM (scanning electron microscope, HITACHI S2500CX).

*2.3.3. Measurement of phase transition kinetics* 

0 vol % methanol.

*2.3.2. SEM Observation of the gels* 

After removing from their molds, the cylindrical gels were also cut in pieces 3.0 mm long and hydrated in a graded series of methanol-water mixtures for 1 day each in 75, 50, 25, and

The pH-responsive microphase-separated tubular gel was prepared as follows. The composition of monomers is same as the cylindrical microphase-separated gels, and they were dissolved in the water/acetone mixture solution (70/30 wt %). The mold was made by coupling different size of glass tubes (external/internal diameters are 2.6/2.0, 1.0/0.6 mm), and the monomer solution was flowed into the tube-shaped space (external/internal diameters are 2.0/1.0 mm). The tubular gel was cut in pieces 4.0 cm long and hydrated in a graded series of methanol-water mixtures for 1 day each in 75, 50, 25, and 0 vol % methanol.

Two samples were prepared in the following way. The microphase-separated gel cylinders were cut into pieces and soaked in acid (pH= 2) and base (pH = 11) solutions for 1 day until reaching the equilibrium. Then the gels were quickly frozen in liquid nitrogen and freezedried under vacuum for 1 day. The freeze-dried samples were fixed on the aluminum stubs and coated with the gold for 30 s under vacuum. The gel network structures were observed

In our measurement of the gels kinetics, two acid-base solutions with low and high pH (pH = 2 and pH = 11) were used. A piece of cylindrical gel under the equilibrium swelling in one solution was transferred quickly into the other. The changes of the cylindrical gel diameters were monitored by using a microscope equipped with a CCD camera controlled by a

*2.3.4. Experimental apparatus for causing the CT reaction in the pH-responsive tubular gel* 

The feeding solutions were stored in three separated reservoirs containing an alkaline sodium chlorite solution ([NaClO2] = 1.2 × 10<sup>−</sup>1 M, [NaOH] = 1.5 × 10<sup>−</sup>4 M), an alkaline potassium tetrathionate solution ([K2S4O6] = 3.0 × 10<sup>−</sup>2 M, [NaOH] = 1.5 × 10<sup>−</sup>4 M), and a sodium hydroxide solution ([NaOH] = 1.3 × 10<sup>−</sup>2 M). The solutions were pumped by peristaltic pumps (ATTO SJ-1211L) and premixed by a magnetic stirrer (AS-ONE CT-3A) before entering the tubular gel. The flows of chlorite and tetrathionate solutions were maintained at 30 mL/h, and the mixed solution flowed into the tubular gel by a peristaltic pump (ATTO SJ-1211H). The tubular gel was soaked in the mixed CT solution for 30 min in advance. After entering the flow of the mixed solution, an acid perturbation was applied by touching the gel at a particular spot with a paper soaked in a 1 M H2SO4 solution. The behavior of the tubular gel was observed by using a microscope equipped with a CCD camera controlled by a computer. Methyl red, a color indicator that changes from yellow

computer. The obtained images were analyzed by image processing software.

Using AAc (25.9 g), tert- butyl methacrylate (tBMA) (34.1 g), and 2,2'-azobisiso-butyronitrile (AIBN) (0.49 g) as an initiator, *poly(AAc-co-tBMA)* (Figure 4) was synthesized by the radical polymerization in ethanol (139.5 g) using a total monomer concentration of 30 wt%. The molar ratio of tBMA incorporated into the copolymer was 30 mol%. The polymerization was carried out at 60 °C under nitrogen flow for 24 h. The resulting reaction mixture was dialyzed against ethanol for seven days.

**Figure 4.** The chemical structure of poly(AAc-*co*-tBMA) polymer.
