Jian-Jun Yuan

Synthesis of poly(ethyleneimine)s?silica hybrid particles with complex shapes and hierarchical structures

Shaped silica constructed by silica fiber with axial poly(ethyleneimine)s (PEIs) filaments was available simply from rapid hydrolytic condensation of tetramethoxysilane (TMOS) upon aggregates of PEIs with different architecture.

Fabrication of silver porous frameworks using poly(ethyleneimine) hydrogel as a soft sacrificial template

This paper describes a new approach to the controllable fabrication of macroporous silver frameworks with various structures and shapes by calcination of Ag nanoparticle–polymer pastes which were mediated by the differently organized linear poly(ethyleneimine) (PEI) hydrogels and silver ions without extra reductant. The porous silver frameworks could be a dome-like shape with inner chambers and can be changed into stair-like crystalline silver film depending on calcination temperature. In addition, macroporous silver monoliths with different porous sizes were easily controllable with changing the preparation conditions of the pastes via routine modulation of the PEI hydrogel and silver ion concentrations. Such changeable features of the silver framework with shape and porous size depending on PEI hydrogels is very unique and would have potential in applications.

Direct Generation of Silica Nanowire-Based Thin Film on Various Substrates with Tunable Surface Nanostructure and Extreme Repellency toward Complex Liquids

We report our new achievement on the direct generation of linear polyethylenimine@silica hybrid and silica thin films on various substrates, which is composed of 10 nm nanowire silica structure with tunable micro/nano hierarchical surface morphology. We found that a process for the rapid and controlled self-assembly of crystalline template layer of linear polyethylenimine on substrate surface is critical for the formation of ultrathin silica nanowire structure and micro/nano hierarchical morphology, since the template linear polyethylenimine layer directly promotes the hydrolytic condensation of alkoxysilanes. Templated silica mineralization on the self-assembled linear polyethylenimine layer was confirmed by the studies of X-ray photoelectron spectroscopy (XPS) and thin film X-ray diffraction (XRD). The surface of silica nanostructure and hierarchy could be well controlled by simply adjusting the conditions for LPEI assembly, such as the polymer concentrations and substrate surface property. After a simple fluorocarbon modification, the hierarchical silica nanowire thin film demonstrated robust and reliable super-repelling property toward a series of aqueous liquids (such as commercial inkjet (IJ) ink, soy source, milk). Comparative studies clearly confirmed the critical importance of surface hierarchy for enhancing super-repelling property. Moreover, we found that the forcibly formed dirty sports (both wet and dry) from the complexly composed liquids on the super-antiwetting surface could be easily and completely cleaned by simple water drop flow. We expect these tailored nanosurfaces would have the potentials for practical technological applications, such as liquid transferring, self-cleaning, microfluid, and biomedical-related devices.

Water motion and movement without sticking, weight loss and cross-contaminant in superhydrophobic glass tube.

We report that a simple fabrication of a superhydrophobic nanosurface consisted of a grass-like silica thin film on the inner wall of a glass tube and its feature in water motion and water movement. The glass tube with a superhydrophobic inner wall can make the water flow with friction-drag reduction and completely preventing water sticking. Transferring water by this tube did not cause weight loss at all. Therefore, aqueous solutions containing high content metal ions were cross-moved without washing the tube used and no cross-contamination occurred after cross-movement. Furthermore, in an inside diameter of 6.0 mm glass tube where the half-length of the inner surface is covered by superhydrophobic nanograss and the other half is an unmodified hydrophilic surface, the water droplets flowing down from the hydrophilic side can be stopped spontaneously at the hydrophilic-superhydrophobic boundary as if there is an invisible flow-stopping fence built inside the glass tube.

Temporally and spatially controlled silicification for self-generating polymer@silica hybrid nanotube on substrates with tunable film nanostructure

This paper describes a novel approach to templated silicification that could directly generate a tubular structure with a polymer@silica hybrid wall. We developed a new process for the crystallization-driven self-assembled formation of a linear polyethyleneimine (LPEI) template on a substrate surface, which involves the key step of alkali-quenching of the complete deprotonation reaction of the adsorbed, protonated LPEI fraction on the substrate at room temperature. This alkali-induced LPEI template allowed the temporally and spatially controlled silicification reaction, leading to the self-generation of a tubular structure with a 3 nm LPEI@silica hybrid wall. The elemental nanotubes were organized hierarchically into two-dimensional mats and the mats were further vertically arrayed into a thin film. Such nanotube-based hybrid films could be formed reproducibly either on glass or on plastic. The surface morphology and nanostructure of the film could be tunable by simply adjusting solution conditions for LPEI self-assembly or by using substrates with controlled surface chemistry. After introducing hydrophobic residues on the film, the hierarchical nanotube surface showed the best repellency toward inkjet ink compared to the nanoribbon- and nanowire-based superhydrophobic surface. We also expanded this templated silicification to synthesize hybrid nanotube powders in solution. Both Brunauer–Emmett–Teller (BET) and transmission electron microscopy (TEM) studies supported direct formation of an approximately 3 nm hollow structure. Thin film X-ray diffraction measurements (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetry analysis (TGA) characterizations indicated the hybrid nature of the LPEI@silica wall. This new approach advanced on the conventional methods of using an organic template to direct inorganic materials, and is expected to be generally applicable to directly generate other organic–inorganic hybrid nanostructures.

Learning from Biosilica: Nanostructured Silicas and Their Coatings on Substrates by Programmable Approaches

Silica-based materials are important for a wide range of technological applications, such as catalysts, polymeric fillers, coatings, chemical and biological separations, sensors, photonic and electronic devices, bio-encapsulation, enzyme immobilization, bioimaging, drug delivery, and so on (Davis, 2002). Recently, silica synthesis with the control of nanostructures and surface chemistry has been demonstrated to be important to improve the performance for various applications. For example, self-assembled surfactants have been used as templates for the controlled synthesis of mesoporous silicas (Kresge et al., 1992). Fibrous or tubular silicas could be synthesized by templating organogelators (van Bommel et al., 2003). However, these silica productions often involve hash and environmentally unfriendly conditions, such as high or low pH, high temperature and/or pressure, long reaction time, use of toxic and/or expensive organic solvents, as well as multiple steps and complex protocols. Moreover, precise control over the silica nanostructure and morphology still remains a major technical challenge, despite recent advances (Yang et al., 1997). In contrast, silica biomineralization occurs in water under ambient conditions for various biological systems such as diatoms and sponges, producing exquisite hierarchical structures and multiple morphologies with precise nanoscale control (Schroder et al., 2008; Hildebrand, 2008). Marine organisms produce more than 6 gigatonnes of silicon each year to build their silica skeletons (Treguer et al., 1995). As a typical example, diatom is eukaryotic single-celled algae with cell walls of being intricately and ornately shaped on the nanometer scale. Such cell wall structure is species-specific, indicating the molecular control of intracellular processes by which organics direct mineral formation (Kroger & Poulsen, 2008). The architecture and organic-silica composite nature of diatom wall exhibit remarkable mechanic strength and serve as protector armor against phytoplankton predators (Smetacek, 1999). The diatom is important for the biological cycling of both silicon and carbon, with about 20% of total photosynthetic CO2 fixation. This is equivalent to the photosynthetic activity of all rainforests combined (Field et al., 1998). The recent studies on diatom wall also indicate that (i) the cell wall of Thalassiosira weisflogii acts as a proton buffer for improving the CO2 acquisition via an extracellular carbonic anhydrase (Milligan & Morel, 2002), and (ii) the square lattice of hole pattern in the girdle band region of the cell wall of Coscinodiscus

Polyamine@silica hybrid nanograss: biomimetic fabrication, structure characterization and surface functionalization

This is a report on the controlled generation of a polyamine@silica hybrid nanograss surface on arbitrary substrates. A very simple biomimetic silica mineralization reaction (i.e., ambient temperature and neutral aqueous medium conditioned hydrolytic polycondensation of alkoxy silane) performed on a self-assembled, nanostructured linear polyethyleneimine (LPEI) matrix allowed the production of nanostructured silica films with specific surface morphologies. It was found that the well-defined and densely arrayed nanograss surface of hybrid LPEI@silica could be achieved by adjusting the crystallization time of LPEI on the substrates, silica deposition time and LPEI concentrations. Comparative studies indicated that the LPEI with a linear backbone is important for nanograss formation due to its specific crystalline nature. By using a polystyrene substrate with tunable surface chemistry, we have confirmed that an efficient molecular-level interaction of LPEI with substrates is important for creation of a high-quality and continuous silica nanograss film. The combined studies from XRD, XPS and ζ potential supported that the crystalline, self-assembled and nanostructured LPEI layer on the substrate serves as catalyst-active and biomimetic template for site-selective silica mineralization to give the polyamine@silica nanograss. Moreover, by modifying the nanograss surface with a fluorocarbon compound, we are able to create a super-liquid-repellent surface, which shows the contact angle of >179°, 149.6° and 147.3° for water, 1 : 1 water–ethanol in volume (γ = 24.7 mN M−1) and inkjet ink (γ = 24.0 mN M−1), respectively. Our nanograss surface has potential applications for liquid transferring, self-cleaning, microfluid devices, sensing and cell engineering.

Approaches to nanostructure control and functionalizations of polymer@silica hybrid nanograss generated by biomimetic silica mineralization on a self-assembled polyamine layer

Summary We report the rational control of the nanostructure and surface morphology of a polyamine@silica nanoribbon-based hybrid nanograss film, which was generated by performing a biomimetic silica mineralization reaction on a nanostructured linear polyethyleneimine (LPEI) layer preorganized on the inner wall of a glass tube. We found that the film thickness, size and density of the nanoribbons and the aggregation/orientation of the nanoribbons in the film were facile to tune by simple adjustment of the biomimetic silicification conditions and LPEI self-assembly on the substrate. Our LPEI-mediated nanograss process allows the facile and programmable generation of a wide range of nanostructures and surface morphologies without the need for complex molecular design or tedious techniques. This ribbon-based nanograss has characteristics of a LPEI@silica hybrid structure, suggesting that LPEI, as a polymeric secondary amine, is available for subsequent chemical reaction. This feature was exploited to functionalize the nanograss film with three representative species, namely porphyrin, Au nanoparticles and titania. Of particular note, the novel silica@titania composite nanograss surface demonstrated the ability to convert its wetting behavior between the extreme states (superhydrophobic–superhydrophilic) by surface hydrophobic treatment and UV irradiation. The anatase titania component in the nanograss film acts as a highly efficient photocatalyst for the decomposition of the low-surface-energy organic components attached to the nanosurface. The ease with which the nanostructure can be controlled and facilely functionalized makes our nanograss potentially important for device-based application in microfluidic, microreactor and biomedical fields.