Izumi Ichinose

A careful examination of the adsorption step in the alternate layer-by-layer assembly of linear polyanion and polycation

Abstract In order to elaborate alternate layer-by-layer assembly as a means to prepare ultrathin films, details of conventional polyion assemblies have been quantitatively analyzed by quartz crystal microbalance (QCM) technique with the aid of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The alternate adsorption of poly(styrenesulfonate) (PSS) and poly(allylamine) (PAM) onto oppositely-charged surfaces displayed the pseudo first-order kinetics and was saturated within 10–20 min at pH 3 and 22°C. It was revealed that drying at every step increased the thickness of adsorbed films due to enhanced surface roughness of the films. Therefore, frequent drying is not profitable for preparing films in a good quality. Non-contact AFM observation revealed that drying of the film with nitrogen stream, forced polymer chains to align to one direction with increasing surface roughness. In contrast, water washing between the consecutive adsorptions was effective for successful alternate adsorption. About 10% of an adsorbed polyion layer was removed by 5-min water washing probably due to removal of the loosely-attached materials.

Molecular film assembly via layer-by-layer adsorption of oppositely charged macromolecules (linear polymer, protein and clay) and concanavalin A and glycogen

Abstract Protein multilayer assemblies were prepared by two different methods: (1) alternate adsorption of oppositely charged polyions; (2) alternate adsorption with specific enzyme/substrate interaction. The formation of alternate outermost layers (opposite charge or opposite specificity) at each adsorption cycle is the key point of the procedure. Three modes of polyion film assembly were demonstrated: (a) alternation of linear polyanions and polycations; (b) insertion of charged particles in the multilayer at every other step (twelve different globular proteins were assembled alternating with Na (poly (styrenesulfonate), poly(ethyleneimine)) or Cl (poly(diallyldimethylammonium))); (c) alternation of polyions and preformed charged plates: delaminated montmorillonite clay. Specific interaction was obtained between consecutive layers of glycogen and concanavalin A. Concanavalin A possesses four binding sites for its ligand D-glucose and allows the binding of glycogen (branched poly (glucose)) layers on both sides of the protein.

Ultrathin films of inorganic materials (SiO2 nanoparticle, montmorillonite microplate, and molybdenum oxide) prepared by alternate layer-by-layer assembly with organic polyions

Abstract We have been investigating alternate assembling of inorganic materials, SiO 2 nanoparticles, clay microplate, and polyoxometalates with oppositely-charged polyions. In this paper, previously reported results are summarized and compared in order to establish a unified interpretation. Reproducible film growth is observed in assembly of anionic SiO 2 particles and cationic poly(diallyldimethylammonium chloride) (PDDA). The adsorption time required for successful assembly of SiO 2 nanoparticles is only 2 s. Scanning electron microscopic (SEM) observation shows that the obtained film has a surprisingly flat surface. Similarly montmorillonite clay microplate is successfully assembled with cationic PDDA and poly(ethyleneimine) (PEI), but its adsorption required 5–6 min. These adsorption kinetics are interpreted based on the nature of the adsorbent. Adsorption of rigid and spherical SiO 2 particles is diffusion-limited and very fast, probably because the relaxation process is not conceivable during the adsorption. In contrast, relaxation processes may play an important role in the adsorption of planar clay plates, as suggested previously for adsorption of organic polyions. Multilayer films of molybdenum oxide are prepared by alternate adsorption of ammonium octamolybdate ((NH 4 ) 4 [Mo 8 O 26 ]) and poly(allylamine) hydrochloride (PAH). Adsorption of molybdenum oxide does not show saturation. Protonation and condensation of the molybdenum oxide are probably accelerated on the pre-adsorbed molybdenum surface, resulting in film growth without saturation.

Fabrication of porphyrin–titanium oxide–fullerene assemblies on an ITO electrode and their photocurrent responses

Abstract A porphyrin–fullerene assembly via titanium oxide coordinative bonding was constructed on an ITO electrode, by using the techniques of self-assembly and the surface sol–gel process. In the presence of triethanolamine, clear photocurrent responses from the modified electrode were observed in the anodic direction, and they were much larger than the electrodes modified with the porphyrin or the fullerene alone. It is suggested that the photocurrent is ascribed to photoinduced charge separation between the porphyrin and the fullerene moieties.

Spectral characteristics of low-dimensional PbBr4 clusters prepared by the use of multibilayer cast films

Anionic lead halide clusters of the composition PbBr42- were synthesized at the interlayer space of cationic multibilayer cast films. Absorption spectra of the interbilayer PbBr42- species displayed marked blue shifts compared to those of the two-dimensional layered perovskite-type compounds, which was interpreted by the exciton confinement effect in dimension diminished clusters. Amphiphilic structures as well as thermal treatment of the composite cast film exert profound influences on these spectral characteristics.