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Fig. 3-6 Preparation of track pores Polymer films with cylindrical pores can be prepared by irradiation of thin polymer (CR-39, 50-100 micrometer) with U (11.6 MeV/n) or Kr (6.2 MeV/n) ions, followed by etching at 60 degrees cent. in the NaOH solution for 1 hr. Using films of various copolymers with CR-39, pore diameters in the range of 0.5 ~ 30 micrometer can be obtained.

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Fig. 3-7 Photos of atomic force microscopy: A polymer film (thickness: 50 micrometer) with pores (diameter: 1.3 micrometer) grafted with amino acid-containing gel layer (0.3 micrometer) The opening (b) and closing (a) of the pores depending on the temperature are demonstrated. Amino acid-containing gel made by radiation polymerization swells in water at temperatures below 14 degrees cent. (phase transition temperature) and shrinks at higher temperatures; the volume difference amounting to 425 times.

By chemical treatment of latent tracks formed when energetic heavy ions pass through a thin polymer film we can synthesize a film with pores of regulated shape, diameter, direction and number density. If we further graft specific molecules onto the film thus synthesized, we have a film for selective transportation of specific molecules or with an on-off function of the environment responsive character such that opens and closes dependent on temperature, pH and so on. Application to various fields is expected such as artificial organs, drug delivery system (system ensuring the effective distribution of drugs in the organ) and separation of blood components etc.

Reference M. Yoshida et al., Novel Thin Film with Cylindrical Nano-Pores that Open and Close Depending on Temperature: First Successful Synthesis, Macromolecules, 29(27), 8987 (1996).

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