Irradiation shrinkage

Fig. 7. High-temperature neutron irradiation a-axis shrinkage behavior of pyrolytic graphite showing the effects of graphitization temperature on the magnitude of the dimensional changes [60].

The technique of graft copolymerization is used for the production of radiation-modified fabrics and fibers. The process consists of saturating the fabrics with vinyl monomers and then irradiating it in moist state with accelerated electrons. The fabrics thus produced have improved properties such as resistance to wrinkling and shrinkage, resistance to fire, color-fastness, good launderability, and dissipation of static charge. 

Fig. 7. High-tempemture neutron irradiation e-atis shrinkage behavior of pyrolytic graphite lLWges8[ r °f Sraphi,iza,i gni..dc of .

Block copolymer micelles containing PB cores were cross-linked either by UV or fast electron irradiation [79-81]. This was accompanied by a shrinkage of the micelles. 

Good thermo-mechanical, chemical and electrical properties rigidity gamma irradiation resistance UHF transparency good creep resistance and fatigue behaviour low moisture uptake low shrinkage heat behaviour fire resistance low coefficient of thermal expansion. 

Fig. 7.47 Plastic shrinkage of retarded and unretarded cement mortars of plastic consistency and OPC content of 550 kg m-3. Air temperature 30 C, wind velocity of 20 km h-i and IR irradiation (Soroka and Ravina [94]).

Figure 15.19 shows the relationship between the percentage of height decrease (A) calculated from surface profile measurements and the electron beam dose for both fluorinated and nonfluorinated polyimides. The surface profile between the irradiated and nonirradiated areas was measured. The film shrinks because of electron beam irradiation, and the maximum shrinkage reaches up to 0.4% at the film surface. 

A liquid preparation with solid polystyrene (0.6 g) dissolved in liquid styrene monomer (1.5 mL) was cast against a mold. Polymerization was accomplished with UV irradiation (21°C, 18 h). Solid PS was included to reduce the degree of shrinkage that occurred when monomeric styrene was photopolymerized [85]. In a similar manner, PMMA dissolved in MMA was cast against a Si master. Upon UV polymerization (with BME as the photoinitiator), a PMMA chip is formed. Nearly 100 PMMA chips can be replicated using a single Si master [223]. 

On the other hand, Tamada et al.44 have investigated stimulus-responsive gels utilizing the photochemical reaction of a polymeric azobenzene unit doped with IL (Fig. 23.5). Photoisomerization of the azobenzene group resulted in shrinkage of the irradiated site. It was also reported that ionic conductivity of the gel could be controlled by photoirradiation. The ionic conductivity of the gel decreased after UV light irradiation this effect was coupled with an increase in viscosity, in turn suppressing diffusion of the component ions within the gel. 

More recently, Sugiura et al.11 developed a fully functional microvalve based on this photoresponsive behavior, which was composed of poly(/V-isopropylacrylamide) functionalized with the chromophore spirobenzopyran (pSPNIPAAm). The microvalve was fabricated in a polydimethylsiloxane (PDMS) microchannel by in situ photopolymerization. Blue light irradiation (18 to 30 s) to the gel induced photoisomerization of the spirobenzopyran chromophore which resulted in shrinkage due to dehydration of the gel, thus causing the microvalves to open, as seen in Figure 23.7. In this example, localized irradiation enabled independent control of three photoresponsive polymer gel microvalves, which had been fabricated on a single microchip. 

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