Actuating mechanisms for smart polymers

Such smart functions provided by smart materials are distinct from smart systems or facilities because they do not rely on the complicated sense-response structure of a feedback system. Instead, they can be intrinsically sensitive to changes in their ambient environment, such as temperature, optical wavelength, absorbed gas molecules and pH values. 

6 The rearrangement of spirolactone which leads to thermochromic effect between the colourless dye precursor and coloured dye. 

SMPs can be triggered by water or moisture due to the plasticizing effect of water molecules, which increases the flexibility of macromolecule chains . If a SMP has a hydrophilic or water soluble ingredient, the shape recovery can be accelerated. Pyridine unit, which is responsive to moisture, can be used to improve the moisture absorption in polyurethane. Hu and co-workers introduced pyridine unit into SMPU by N-bis(2-hydroxylethyl) isonicotinamine (BINA) and prepared moisture-responsive SMPU with high strain recovery and recovery speed. SMPs sensitive to their suitable solvents can be obtained which are similar to hydrophilic SMPs that are sensitive to water/moisture.  

Photochromic materials have been widely used in textiles. °°Typical organic photochromic compounds include azobenzenes, spiropyrans, sprroooxaztnes, viologens, fulgides, 1,4-dihydroxy anthraquinone and diarylethenes.They are based on different photochromisms, that is, isomerization of molecules, ionization of molecules and redox reaction of molecules. Azobenzenes, spiropyrans and viologens have been most widely used in textiles. 

In electrochromism, a reversible and visible colour change is observed in a material as a result of electrochemical oxidation or reduction. When 

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