Liping Heng

Advances in Fabrication Materials of Honeycomb Structure Films by the Breath-Figure Method

Creatures in nature possess almost perfect structures and properties, and exhibit harmonization and unification between structure and function. Biomimetics, mimicking nature for engineering solutions, provides a model for the development of functional surfaces with special properties. Recently, honeycomb structure materials have attracted wide attention for both fundamental research and practical applications and have become an increasingly hot research topic. Though progress in the field of breath-figure formation has been reviewed, the advance in the fabrication materials of bio-inspired honeycomb structure films has not been discussed. Here we review the recent progress of honeycomb structure fabrication materials which were prepared by the breath-figure method. The application of breath figures for the generation of all kinds of honeycomb is discussed.

Bioinspired design of honeycomb structure interfaces with controllable water adhesion.

Inspired by biological attachment systems, we fabricated the honeycomb structural films with different diameters by breath figure (BF) method, which were similar to the patterned octopus suckers. The experimental results showed, besides different van der Waals forces between the polystyrene (PS) surfaces and water, another important factor; that is, different negative pressures produced by different volumes of sealed air could be a crucial factor for the different adhesions. So the water adhesive forces of the as-prepared films can be effectively controlled from relative high to relative low adhesion by varying the pore diameters, which effectively adjusted the negative pressures produced by the pores. This unique adhesive phenomenon of honeycomb structure will be very useful for manipulating water droplet behaviors, as well as controlling liquid collection and transportation. These findings are interesting and helpful for us to further understand the biological attachment systems and to optimize the design of artificial analogues.

Solvent Fuming Dual-Responsive Switching of Both Wettability and Solid-State Luminescence in Silole Film

A multiresponsive switcher on both wettability and solid-state luminescence has great application potentials in novel smart devices. In this paper, a silole molecule of 1,2,3,4,5-hexaphenylsilole (HPS) was chosen to prepare thin films by spin-coating, and a solvent fuming dual-responsive switcher combining photoluminescent behavior and wettability was successfully achieved by changing the mode of solid-state molecular packing. This study suggests that HPS and other silole derivatives have a promising future for use in dual- and multifunctional switches in new technological applications.

Silole-Infiltrated Photonic Crystal Films as Effective Fluorescence Sensor for Fe3+ and Hg2+

We develop a highly effective silole-infiltrated photonic crystal (PC) film fluorescence sensor with high sensitivity, good selectivity and excellent reproducibility for Fe(3+) and Hg(2+) ions. Hexaphenylsilole (HPS) infiltrated PCs show amplified fluorescence due to the slow photon effect of PC because the emission wavelength of HPS is at the blue band edge of the selected PCs stopband. The fluorescence can be quenched significantly by Fe(3+)/Hg(2+) ions owing to electron transfer between HPS and metal ions. The amplified fluorescence enhances the sensitivity of detection, with a detection limit of 5 nM for Fe(3+)/Hg(2+) ions. The sensor is negligibly responsive to other metal ions and can easily be reproduced by rinsing with pure water due to the special surface wettability of PC. As a result, a highly effective Fe(3+)/Hg(2+) ions sensor based on HPS-infiltrated PC film has been achieved, which will be important for effective and practical detection of heavy metal ions.

Robust Underwater Oil‐Repellent Material Inspired by Columnar Nacre

Inspired by natural columnar nacre, artificial montmorillonite/hydroxyethyl cellulose columnar nacre-like materials with a site-specific layered structure in the interior and a hierarchical columnar structure on the surface are prepared. The materials exhibit improved tensile strength, good chemical stability in seawater, superior resistance to sand-grain impingement, and robust underwater low-adhesive superoleophobicity.

Optical waveguides based on single-crystalline organic micro-tiles.

Surface waveguides are an important topic because of their ability to transmit sub-wavelength information, [ 1 ] that is, details with dimensions less than the wavelength of visible light, which holds promise for utilization in faster and more compact optoelectronic communications and sensors. [ 2 ] Great effort has been put into optical waveguides based on onedimensional (1D) inorganic nanostructures. For example, Lieber’s group [ 3 , 4 ] and Yang and coworkers [ 5 , 6 ] have demonstrated that crystalline wireand ribbon-like nanomaterials of inorganic semiconductors can successfully serve as waveguides for light with wavelengths less than that of visible light. Then, Redmond and coworkers reported the waveguiding property of conjugated polymer nanowires. [ 7 ] Very recently, optical waveguides based on 1D structures of small organic molecules have been realized using nanowires, nanoribbons, and nanofi bers. [ 8–14 ] However, optical waveguides based on small organic molecules with 2D structures are still in their infancy. [ 15 ] They are expected to display waveguiding behavior different from that of 1D materials owing to their different microstructures. Furthermore, it should be of great scientifi c interest to extend the relevant research from solid 1D nanorods/wires/ tubes to 2D micro-tiles, because the 2D tile structures are more suitable for the application of controlling directional waveguides. Here, we report the preparation of 2D crystalline microstructures, that is, micro-tiles, from hexaphenylsiloles (HPSs), small organic compounds, by self-assembly. Characterization of single micro-tiles indicates that the 2D HPS microstructures can serve as active optical waveguides that allow locally excited photoluminescence to propagate along the abscissa of the 2D structures and out-couple at the ridge tips. The unique 2D optical waveguiding phenomenon of HPS micro-tiles might be useful

A visual film sensor based on silole-infiltrated SiO2 inverse opal photonic crystal for detecting organic vapors

The reversible color change of the silole-infiltrated SiO2 inverse opal photonic crystal (IOPC) film can be obtained by alternating its exposure to different vapor environments. When the film was put in diethyl ether or petroleum ether vapor, a stopband red shift of more than 100 nm could be clearly observed, while the color changed from green to red. When exposed to air, the stopband underwent a blue shift and the color changed back to green. The result is attributed to the silole molecules, hexaphenylsilole (HPS), which can be transformed reversibly between the crystal and amorphous state when alternately exposed to air and vapors of diethyl ether/petroleum ether. When crystal HPS changed to amorphous HPS in an atmosphere of organic vapors, both the specific surface area and refractive index of HPS increased. The higher specific surface area of HPS improved the adsorption behavior of organic vapors. Both the improved adsorption and higher refractive index of HPS increased the effective refractive index of HPS-infiltrated SiO2 IOPC, which resulted in the red shift of the stopband and the color change, according to the Bragg Law. Based on the reversible aggregation state transfer and the adsorption–desorption of organic vapors, the effective refractive index of the film varied repeatedly, which caused the reversible stopband shift and color change. The visual detection of organic vapors can be realized because of the remarkable color change of the IOPC film, which provides a simple route for monitoring volatile organic compounds, and is important for chemical and biological sensors.

Multiscale bio-inspired honeycomb structure material with high mechanical strength and low density

We report a kind of polymer ordered porous honeycomb structure film with enhanced mechanical strength and low density. The film is fabricated with polyimide as a basic structure and nano-clay as the enhanced layer in the honeycomb walls, which mimics the multi-scale structure of natural honeycombs. After examining the mechanical properties of the bio-inspired honeycomb structures with different contents of clay, we find that the hardness of the honeycomb films increases with increasing clay content, and reaches a maximum value of 0.037GPa on average, which is about 5 times that for the honeycomb film without clay. Because of the existence of the porous structure, the bulk density of the multiscale bio-inspired honeycomb structure films fabricated with the solution containing 0.9 wt% clay content is 35.7% of the honeycomb structure films fabricated with the solution without clay, and the apparent density of the honeycomb structure films fabricated with the solution containing 0.9 wt% clay content is 67.5% of the honeycomb structure films fabricated with the solution without clay, and the porosity increases by 45.6%. In addition, the study of the thermal properties indicates that the porous structure does not decrease the thermal stability of the original materials. Meanwhile, the introduction of the clay into the film can increase the thermal stability of the materials slightly. So this kind of multiscale bio-inspired honeycomb structure, with high mechanical strength, low density and excellent thermal stability, is considered to have wide applications in the areas of tissue engineering, aeronautical materials, separation films in lithium-ion batteries, and so on.

Fabrication of small organic luminogens honeycomb-structured films with aggregation-induced emission features

We report the successful fabrication of honeycomb structure by breath figure (BF) process from the small molecule tetraphenylethene (TPE) derivatives, showing an extraordinary phenomenon of aggregation-induced emission (AIE). In this process, TPE derivatives with the twist and non-planar substituted groups are chosen; TPE units are easier to become amorphous than crystalline. This is critical for gaining the viscosity and stabilizing the water droplets during evaporation. Characteristics of the confocal fluorescence and the fluorescent spectrum indicate that these honeycomb structures are highly emissive due to the AIE feature of TPE derivatives. These structures lead to a small red-shift of the photoluminescence compared to the smooth film. The success of fabricating TPE derivatives honeycomb structure may, for certain applications, represent an advance with respect to the more commonly used polymers, due to the inherent drawbacks of polymers such as phase separation, non-reproducibility of molecular weight distribution from batch to batch. These findings should open a way for the development of the honeycomb structure material with small organic molecules. Such a structure will be useful in many areas, such as sensors, microelectronics, optoelectronics and even biomaterials.

Ordered honeycomb structural interfaces for anticancer cells growth.

The patterned honeycomb structure film with the aggregation-induced emission property was prepared successfully by the breath figure method and photopolymerization method. Characterization of the HeLa and HepG2 cell culture on this surface indicates the porous honeycomb structures show anticancer cells growth function. So this kind of honeycomb structure will be promising for the control of cancer cell growth behaviors and achieving the application of anticancer.