Liqin Ge

Hydrogel improved the response in the titania/graphene oxide one-dimensional photonic crystals.

Recently, one-dimensional photonic crystals (1DPCs) have attracted considerable interest because they exhibit a material-specific response profile to external stimuli. In our previous work, TiO2/GO 1DPCs, the stopbands of which can be made to span the whole visible range, were fabricated by spin-coating technique. The prepared 1DPCs have a double response to both dimethyl sulfoxide and alkali solution. However, the response is slow, insensitive, and irreversible. To improve the responsiveness of the 1DPCs, poly(ethylene glycol) (PEG)-cross-linked poly((methyl vinyl ether)-co-maleic acid) (PMVE-co-MA) hydrogels were embedded in those crystals. The results demonstrated that modified 1DPCs with different stopbands could be obtained by controlling the speed of the spin-coating technique. The prepared 1DPCs have better responsiveness to external solution pH.

Patterned one-dimensional photonic crystals with acidic/alkali vapor responsivity

A series of patterning responsive one-dimensional photonic crystals (1DPCs) were developed by using a photolithography technique to etch the template for acidic/alkali vapor sensing by the naked eye through a change in color.

Fabrication of Multilayered Hollow Nanofibers and Estimation of Its Young's Modulus

Hollow multilayered polyelectrolyte (PE) fibers were fabricated by the combination of the electrostatic layer-by-layer (LBL) and electrospinning methods. The influence of the deposition conditions on the structure of the obtained hollow multilayered PE fibers was studied systemically. The results showed that the formation of multilayered PE films on polystyrene (PS) fiber surface was strongly influenced by the number of repetitions of deposition and the pH value. The spaces among the adjacent fibers in fibrous mats were blocked by 15 poly(allylamine hydrochloride) (PAH)/poly(styrenesulfonate) (PSS) bilayers. The film growth speed was the highest in a strongly acidic solution. The theoretical Young’s modulus of such a hollow multilayered PE nanofiber was also obtained to be around 21.6 GPa, which is much larger than that of normal synthetic organic fibers but is similar to that of human bone fibers. [DOI: 10.1143/JJAP.46.6790]

A Smart Colorful Supercapacitor with One Dimensional Photonic Crystals

To meet the pressing demands for portable and flexible equipment in contemporary society, developing flexible, lightweight, and sustainable supercapacitor systems with large power densities, long cycle life, and ease of strongly required. However, estimating the state-of-charge of existing supercapacitors is difficult, and thus their service life is limited. In this study, we fabricate a flexible color indicative supercapacitor device with mesoporous polyaniline (mPANI)/Poly(N-Isopropyl acrylamide-Graphene Oxide-Acrylic Acid) (P(NiPPAm-GO-AA)) one dimensional photonic crystals (1DPCs) as the electrode material through a low-cost, eco-friendly, and scalable fabrication process. We found that the state-of-charge could be monitored by the structural color oscillation due to the change in the photonic band gap position of the 1DPCs. The flexible 1DPCs supercapacitor is thin at 3 mm and exhibits good specific capacitance of 22.6 F g−1 with retention of 91.1% after 3,000 cycles. This study shows the application of the 1DPCs supercapacitor as a visual ultrathin power source. The technology may find many applications in future wearable electronics.

Highly transparent and self-healing films based on the dynamic Schiff base linkage

Self-healing optically transparent coatings have attracted significant attention due to their high transparency and ability to heal damages at the same time. In this study, we report an optically transparent and self-healing film via a layer by layer assembly. This film is based on chitosan (CS) and poly(ethylene glycol) functionalized by dialdehyde groups (DF-PEG). The dynamic equilibrium of Schiff base linkage between the aldehyde groups on DF-PEG and amino groups on CS resulted in the self-healing property of the film. The CS/DF-PEG film can heal damages several times at the same location. Moreover, the Schiff base-bonded CS/DF-PEG films are highly transparent with a transmittance of up to 99.47%, and the transmittance of the film can remain at 99% after ten damage/healing processes. The combination of self-healing property and high transparency provides a new method for fabricating the optically transparent devices.

Self-healing polyelectrolyte multilayer composite film with microcapsules

Self-healing materials are gradually being developed because they can restore structural properties and maintain their function after being damaged. Here, branched poly(ethyleneimine) (bPEI), poly(acrylic acid) (PAA), and microcapsules were used to fabricate a functional (bPEI/PAA)*30-microcapsule composite PEM film based on a layer-by-layer (LbL) self-assembly technique. As a proof of concept, the model molecules hydrophilic rhodamine B (RB) and hydrophobic roxithromycin (ROX) were loaded in (bPEI/PAA)*30-microcapsule composite PEM films, and tests with these self-healing films showed them to be endowed with the desired functional properties and hence showed the microcapsules to constitute a promising functional carrier candidate. The results indicated that the microcapsules can be assembled successfully on polyelectrolyte multilayer (PEM) films, and the as-prepared (bPEI/PAA)*30-microcapsule composite PEM film can not only be tailored with desired properties but also show an excellent self-healing ability. Based on our study, we expect more functional molecules to be grafted onto self-healing PEM films using microcapsules and expect functional self-healing PEM composite films to have great potential applications in the future.

Aptamer-functionalized P(NIPAM-AA) hydrogel fabricated one-dimensional photonic crystals (1DPCs) for colorimetric sensing

As heavy metals cannot be biodegraded and are easily accumulated in food chain organisms and so enter the human body, a simple detection method becomes particularly important for human health. A robust means for the visual detection of highly toxic mercury ion (Hg2+) is developed with aptamer-functionalized one-dimensional photonic crystals (1DPCs). 1DPCs consisting of TiO2 and poly(N-isopropylacrylamide-acrylic acid), P(NIPAM-AA), were successfully fabricated by a spin-coating technique, whose stopbands span the total visible range. When the 1DPCs were exposed to mercury ion solution, the specific binding of cross-linked single-stranded aptamers and heavy metal ions in the hydrogel network caused the hydrogel to shrink. At the same time, there was a homologous blue shift in the Bragg diffraction peak position of the TiO2/P(NIPAM-AA) 1DPCs. The shift value could be used to estimate the number of target ions quantitatively. It was found that the 1DPCs apta-sensor could screen a wide concentration range of heavy metal ions with selectivity and sensitivity. It is expected that the technology may also be widely used in screening a wide range of metal ions in drugs, food, and the environment.

Elasticity of polymer vesicles by osmotic pressure: An intermediate theory between fluid membranes and solid shells

The entropy of a polymer confined in a curved surface and the elastic free energy of a membrane consisting of polymers are obtained by scaling analysis. It is found that the elastic free energy of the membrane has the form of the in-plane strain energy plus Helfrichs curvature energy [Z. Naturforsch. C 28, 693 (1973)]. The elastic constants in the free energy are obtained by discussing two simplified models: one is the polymer membrane without in-plane strains and asymmetry between its two sides, which is the counterpart of quantum mechanics in a curved surface [H. Jensen and H. Koppe, Ann. Phys. (N.Y) 63, 586 (1971)]; the other is the planar rubber membrane with homogeneous in-plane strains. The equations to describe equilibrium shape and in-plane strains of the polymer vesicles by osmotic pressure are derived by taking the first-order variation of the total free energy containing the elastic free energy, the surface tension energy, and the term induced by osmotic pressure. The critical pressure above which a spherical polymer vesicle will lose its stability is obtained by taking the second-order variation of the total free energy. It is found that the in-plane mode also plays an important role in the critical pressure because it couples with the out-of-plane mode. Theoretical results reveal that polymer vesicles possess mechanical properties intermediate between those of fluid membranes and solid shells.

Highly Active TiO2/Polyelectrolytes Hybrid Multilayered Hollow Nanofibrous Photocatalyst Prepared from Electrouspun Fibers Using Electrostatic Layer-by-Layer Technique

Compared to conventional film photocatalysts, fiber photocatalyst has a greater surface-to-volume ratio and a 3-D open structure that allows its surface active sites to be accessible for reactants more easily and effectively. However, TiO 2 powder (Degussa P25), by itself, cannot be prepared in the form of fibers, but with the help of a polymer nanofiber, TiO 2 particles can be immobilized in a fibrous network of polyelectrolyte. Here, hybrid multilayered hollow nanofibers (HMHNFs) composed of TiO 2 /polyelectrolyte (PE) have been prepared by a combination of a electrospinning method and layer-by-layer (LBL) technology. The results show that both the average diameter and the wall thickness of the HMHNFs can be well controlled by the template, as well as the number of coating layers. The dried morphology of the obtained HMHNFs is dependent on the inner deposited numbers of the polyelectrolyte layers. When compared with other nanostructured TiO 2 materials, such as commercial TiO 2 nanoparticles (P25, Degussa) and TiO 2 films, the hollow TiO 2 /PE hybrid nanofibers exhibited higher photocatalytic activities.

Self-healing polyelectrolyte multilayered coating for anticorrosion on carbon paper

Ideally, if the corrosion resistance coating on carbon paper (CP) can be endowed with the self-healing property, the service life and the reliability of the carbon paper will be greatly increased as the gas diffusion layer. In this paper, different cycles of s branched poly (ethyleneimine) (bPEI) and poly (acrylic acid) (PAA) were modified on the surface of the carbon paper via layer-by-layer (LbL) self-assembly technology. The prepared polyelectrolyte multilayered coatings can not only protect the carbon fiber from corrosion, but also take advantages of the surrounding water to quickly repair themselves after damaged. The effects of the assembly cycles on morphology, resistance, air permeability and the contact angle of carbon papers were investigated, then the differences of the carbon papers in electrolysis process were explored. The results reveal that all the prepared coatings can protect carbon papers from corrosion, while when the assembly cycles was 10, the coatings are most efficient.