Supramolecular assemblies

Fibrous self-assembly incorporated polymer film

Chirally-oriented lipid aggregates were doped into a solid polymer film, which was readily prepared by casting and removing a solvent from anionic L-glutamide-derived organogels and polystyrene. When a cationic achiral dye was mixed into this system, the resultant polymer film showed tunable circular dichroism (CD) due to chiral complex formation with the achiral dye on the highly-ordered structures based on the L-glutamide lipid.

Hybrid hydrogels (webgel)

Nanoparticles-webbed hybrid gels

Recently hybrid hydrogels containing nanoparticles have been attracting considerable attention because of their wide range applicability in various fields. Hybridization of nanoparticles with the polymer hydrogel network improves the mechanical properties of the hydrogels. Furthermore, this method can be used to manipulate the optical, thermal, magnetic, and electric properties of the hydrogels.

We have also reported novel hybrid polymer hydrogels in which the polymer network was formed by webbing with silica nanoparticles as multi-crosslinking points (Webbing GEL). This hybrid hydrogels were prepared in a facile manner involved simple mixing of an aqueous solution of a water-soluble copolymer having reactive side chains with an aqueous suspension of silica nanoparticles. This facile method provided an important breakthrough for hydrogel preparation through a new cross-linking system with inorganic nanoparticles as multiple crosslinking points.

Self-assembly-crosslinked hybrid gels

Hetero-network hydrogels composed of hydrophilic polymers with terminal alkyl chains and nanofibrous self-assemblies were successfully fabricated. The gel formation was not observed in both cases of the self-assemblies in aqueous solution and hydrophilic polymer in aqueous solution. Furthermore the gel-to-liquid crystalline phase transition temperatures of nanofibrous self-assemblies were lowered by addition of hydrophilic polymers with terminal alkyl chains. From these observations, it was considered that the alkyl chains at polymer termini intercalated into the bilayer membrane-based nanofibrous self-assemblies to form cross-linking points. As far as we know, the hybrid hydrogel introduced in this communication is the first example of a hetero-network structure composed of supramolecular assemblies. When the hetero-network hydrogel was crushed by mechanical shearing, these hydrogels recovered by heating at temperatures above their gel-to-liquid crystalline transition temperatures.

Core-shell hybrid particles

Microspheres with layered-shell of nanoparticles

The hybrid microspheres with layered shell of inorganic nanoparticles were prepared by modified suspension polymerization of polymerizable monomers containing surface-modified (modifier: 3-methacryloyl propyl trimethoxy silane) inorganic nanoparticles. Typical SEM images of hybrid particles with silica nanoparticle shell were shown in Fig. 1d. It is expected that the silica nanoparticles were self-assembled at the interface between monomer droplet and aqueous phase in the O/W suspension, and finally immobilized on the surface of polymer microsphere through crosslinking reaction (covalent bond). The packing density of silica nanoparticles could be facilely controlled by the concentration of the silica nanoparticles. Similar hybrid microspheres were successfully obtained with other inorganic nanoparticles such as titania, ceria and diamond nanoparticles.

The surface layering of inorganic nanoparticles was also demonstrated by the hybridization with supercritical carbon dioxide (scCO2). Typical micrographs for the layered shell of nano-diamond and graphite were depicted in Figure 1a and 1b respectively. The surface of polymer core was softened by lowering the glass transition temperature in scCO2 and the nanoparticles were physically attached on the surface of the polymer core.

Polymer-grafted particles

Polymer-grafted magnetic nanoparticles

Cationic polymer-grafted magnetic nanoparticles were prepared by grafting of a polymer with terminal reactive group onto the surface of magnetic nanoparticles. The ligand-branched polymer-grafted magentic nanoparticles were used for the magnetically-collectable selective adsorbent of metal ions. The Mag- Im18 showed a selective binding of divalent metal ions with a binding strength in the order of Cu2+ . Ni2+ > Co2+. At pH 5.3, the limiting adsorption capacity for Cu2+ ion was 0.11 mmol g-1. Selective separation/recovery of Cu2+ ions from a Cu2+/Co2+ aqueous solution was demonstrated over a pH range of 3-7.

Pyridinium-based cationic polymer-grafted magnetic nanoparticles were useful for the gene delivery system. In vitro transfection experiments were assayed in human embryonic kidney 293 cells (HEK293 cells) using pmaxGFP plasmid as a reporter gene. Gene expression was found to be strongly influenced by the length of the side alkyl chains. Higher transfection efficiencies were observed with longer alkyl chains (C6 > C4 > C2 ≥ C1), indicating that hydrophobic side chains were effective in increasing transfection efficiency.

Polymer-grafted porous silica for separation science

Polymer-grafting is a useful technique to modify the surface of substrates. The terminally-grafted polymer exhibits different behavior from monomer-grafting. In last two decades, we have applied polymer-grafting method to functionalize the surface of porous silica microspheres for HPLC packing materials. The surface polymer recognized molecular shapes in reversed phase (RP) mode, in which the polymer chains worked effectively. Recently, we demonstrate to integrate pyridinium-based functional ionic groups-branched polymer onto the surface of porous silica microspheres for separation materials. Figure 1 showed chemical structures of poly(vinyl pyridinium)-grafted porous silica microspheres, to which various side chains could be introduced to pyridyl groups through quaternization reaction of alkyl halide. In this paper, we introduce the preparation of zwitter ionic polymer-grafted porous silica and their recognition behaviors in hydrophilic interaction liquid chromatography (HILIC) mode separations. A HILIC is recently developed for effective separations of polar compounds using polar stationary phases with polar mobile phases and the HILIC technology is known as a practical tool in separations of hydrophilic and/or charged bio-molecules such as peptides, proteins, oligosaccharides, drugs, metabolites and various natural compounds.