No abstract

Polymeric fibres that have a unique capability to change their structure in response to small environmental changes such as pH, electrolyte and electric field are an attractive alternative for artificial muscles. Stimuli sensitive fibres were prepared by the modification of commercial polyacrylonitrile (PAN) fibres. The modification was carried out in two steps: thermo-oxidation and hydrolysis. During the thermo-oxidation step, the crosslinks imparted through the pendant nitrile groups provided a stable structure. While in the subsequent saponification step, the uncrosslinked nitrile groups were converted to responsive carboxylic acid groups. The effect of stabilization parameters and saponification conditions on the structure, properties and swelling behaviour of these fibres was investigated. The fibres showed muscle like expanding and contracting behaviour stimulated by changes in pH of the environment.

A new microfeature embossing method utilizing a slowly crystallizing mechanism was investigated to eliminate thermal cycling, as needed in standard hot embossing. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by melt casting onto a chilled roll. The resulting amorphous film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than the polymer's half-time of crystallization. During constant-temperature embossing, the film is softened first, caused by rubber softening of the amorphous phase, and is then hardened, resulting from the crystallization of the amorphous phase at the same embossing temperature. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio microribs, were consistently patterned using a total cycle time about 40s. The embossed films were characterized using DSC and rotational rheometry to elucidate the physical mechanism for softening and hardening the polymer during constant-temperature embossing.

In the standard hot embossing process for thermoplastic polymers, thermal cycling is needed in order to soften and subsequently cool and solidify the polymer. This thermal cycling, however, not only results in long cycle times but also deteriorates the quality of embossed features. A new embossing method based on slowly crystallizing polymers was investigated to eliminate thermal cycling. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by casting a PET melt onto a chill roll. The amorphous PET film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than PET’s half-time of crystallization. During constant-temperature embossing, the film first liquefies, caused by rubber softening of the amorphous phase, and then solidifies, resulting from the crystallization of the amorphous phase. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio rectangular microchannels, were successfully embossed using a total cycle time about 40 s.