Multilayer Reactors for Metallic and Semiconducting Particles Microporous Films

This process was recently introduced by Joly et al. [75]. First, polyelectrolyte multilayers with controlled content of free nonionized carboxylic acid groups were fabricated with weak polyions (e.g., poly(acrylic acid) via suitable pH-adjustments of the processing solutions). These groups were then used to bind various inorganic ions that were subsequently converted into 2-nm diameter particles (e.g., Ag, Pb, or PbS). The spatial control over the growth of the nanoparticles was achieved by the use of multilayer heterostructures which also contain bilayer blocks that are not able to bind inorganic ions. These nonbonding bilayers were fabricated from strong polyions, such as poly(styrenesulfonate). A density modulation with a few nanometer-resolution across the polymeric films is possible by selective synthesis of heavy atom nanoparticles.

A simple process to convert multilayers of weak polyelec-trolytes (e.g., poly(acrylic acid) and poly(allylamine)) into uniform microporous films has been developed by Mendelsohn et al. [76]. These multilayers were immersed briefly into acidic solution (pH 2.4) to effect an irreversible transformation of the film morphology. The resulting microporous structure thickness is 2-3 times less than the thickness of the original films, and possesses reduced relative density of 1/2 to 1/3. The interconnected pores ranging in size from 100 to 500 nm. A refractive index of the porous PAA/PAH film was n = 1.18 ± 0.01. It is much less than the origin n = 1.54 for the untreated polyion multilayer. Correspondingly, a dielectric constant of the porous PAA/PAH film dropped to e' = 2 from the initial e' = 5-7.

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