Xinli Jing

Preparation of a Stable Graphene Dispersion with High Concentration by Ultrasound

With unique structure and extraordinary electronic, thermal, and mechanical properties, graphene fascinates the scientific community. Due to its hydrophobic feature, preparation of a stable and highly concentrated graphene dispersion without the assistance of dispersing agents has generally been considered a challenge. Chemical reduction of graphene oxide (GO) is one of the most important methods for preparing a graphene dispersion. The aggregation of graphene sheets is a key reason to destabilize the resulting dispersion during conversion of aqueous GO dispersion to graphene. In this study, by replacing mechanical stirring with ultrasonic irradiation, the aggregation of various intermediates is effectively suppressed during the process of reduction of GO. Hence, a stable graphene dispersion with a high concentration of 1 mg.mL(-1) and relatively pure graphene sheets are achieved, and the as-prepared graphene paper exhibits a high electric conductivity of 712 S.m(-1). Ultraviolet-visible absorption spectroscopy and X-ray photoelectron spectroscopy show that ultrasound is the essence of enhancing chemical reaction rate. Fourier transformed infrared spectra and Raman spectra indicate that ultrasound has less damage to the chemical and crystal structures of graphene.

Formation of polyaniline nanofibers: a morphological study.

Polyaniline (PANI) powders were prepared by solution precipitation, rapid mixing polymerization, and interfacial polymerization to find the key factors that influence the formation and growth of PANI nanofibers. In chemical oxidative polymerization of aniline, the morphology of the product is mainly determined by aniline concentration. In the case of lower aniline concentration, PANI nanofibers were formed and can be preserved and collected as final product, while in the case of higher aniline concentration, larger sized PANI particles or agglomerates were obtained owing to the growth of the nanofibers. Without participation of the oxidizing step, solid PANI samples with compact structures and dissimilar morphologies were achieved by random accumulation of PANI molecules.

Facile preparation of a mechanically robust superhydrophobic acrylic polyurethane coating

A superhydrophobic (SH) surface is usually constituted by a combination of low surface energy substances and micro- and nanometer scale roughness structures. The latter, however, always have poor mechanical strength and require complicated fabrication procedures, seriously hindering the large-scale preparation and industrial application of SH surfaces. In this study, by introducing fluoroalkyl silane modified silica nanoparticles into hydroxyl acrylic resin using a simple spray-coating method, an SH acrylic polyurethane (SAPU) coating with good abrasion resistance and stable adhesion was obtained after cross-linking with polyisocyanate at room temperature. By virtue of the reaction between the silanol groups in silica NPs and the isocyanate groups in the curing agent, the hydrophobic silica NPs were stably anchored into the SAPU resin matrix while constructing hierarchical micro- and nanometer scale roughness structures on the coating surface. The dual characters ensure that the SAPU coating has a static water contact angle (CA) of >160°, a sliding angle of ∼10° and good mechanical properties, which exhibits CAs of >150° after wearing with sandpaper and maintains strong adhesion even after cross-cutting or impacting tests. Moreover, the SAPU coating retains an excellent water-repellent property after 12 h of immersion in hydrochloric acid with pH = 1, and can recover its water-repellent property after 12 h of immersion in sodium hydroxide solution with pH = 14 through hot air blowing. The facile spray-coating method as well as a mild room temperature curing process make this kind of SH coating especially suitable for non-wetting protection or modification of large-scale parts, providing a novel pathway for the development of a high performance SH surface.

Self-assembly of aniline oligomers in aqueous medium

By dissolving branched or linear aniline oligomers in polar solvent and introducing their stock solution into an aqueous acidic medium, sheet-like as well as wire-like supramolecular structures with well-defined morphology were obtained, respectively. These oligomeric supramolecular structures were constructed via a post-synthetic precipitation process, indicating that aniline oligomers are capable of self-assembling in an aqueous medium, which is similar to the reaction medium of aniline chemical polymerization. Possible formation mechanisms of these supramolecular structures were proposed, i.e., sheet-like products were probably constructed by collapsed molecular chains of aniline oligomers with branched units through π–π stacking and hydrogen bonding, whereas formation of the wire-like products was attributed to “oriented-attachment” of collapsed molecular chains of linear aniline oligomers. The findings obtained in this study are supposed to provide useful clues for uncovering the formation mechanism of polyaniline micro-/nanostructures.

Polyaniline micro-/nanostructures: morphology control and formation mechanism exploration

This article provides a brief overview of recent work by the authors’ group as well as related researches reported by others on controlling the morphology and exploring the formation mechanism of typical micro-/nanostructures of polyaniline (PANI) and aniline oligomers through template-free aniline chemical oxidation process. The contents are organised as follows: (i) tuning the morphology of aniline polymerisation products by employing ultrasonic irradiation, mass transfer, and pH profiles; (ii) exploring the formation mechanism of micro-/nanostructures during aniline chemical oxidation through examining the precipitation behaviours of aniline oligomers and polymers in a post-synthetic system; (iii) tailoring PANI micro-/nanostuctures into pre-designed morphology by introducing certain heterogeneous nucleation centres; (iv) application potential of PANI nanofibres in the areas of transparent conductive film, electromagnetic interference-shielding coating and graphene-based electrode materials. This short review concludes with our perspectives on the challenges faced in gaining the exact formation mechanism of PANI micro-/nanostructures and the future research possibility for morphologically precisely controlled PANI micro-/nanostructures.

Self-assembly of aniline oligomers and their induced polyaniline supra-molecular structures

Aniline chemical oxidative polymerisation (COP), which produces various polyaniline (PANI) and oligoaniline supra-molecular structures, can be regarded as an in situ self-assembly process. This review provides a brief introduction to recent work on the structural characters and self-assembly behaviours of oligomeric aniline chemical oxidation products; it is focused on the relationships between the oligomeric species and morphology of the final products such as PANI nanoparticles, nanofibres/rods, nanotubes or oligoaniline nanosheets, micro/nanospheres in aniline COP systems. Several mechanisms proposed as explanations for the formation of typical supra-molecular structures are discussed in order to illustrate the roles of aniline oligomers. This article concludes with our perspectives on future work remaining to be done to uncover the formation mechanism of supra-molecular structures constructed by aniline chemical oxidation products and their controllable synthesis.

Polypyrrole composites with carbon materials for supercapacitors

Supercapacitors fill the gap between batteries and conventional solid state and electrolytic capacitors. Polypyrrole (PPy) is a very important electrode material for supercapacitors. However, the repeated volume changes usually damage PPy structure and result in PPy poor stability during a long-term charging/discharging process. PPy/carbon material composites were prepared to overcome the defects of pure PPy electrodes, and significant enhancement for the specific capacitance, charging/discharging rate and electrodes stability was demonstrated thereafter. The development of composite electrodes based on PPy and carbon materials is reviewed in this paper.

Easy preparation of an MRI contrast agent with high longitudinal relaxivity based on gadolinium ions-loaded graphene oxide

As far as the longitudinal relaxivity (r1) is concerned, gadolinium ions (Gd3+)-based MRI contrast agents modified by traditional carriers do not appear to be far superior to the clinically used Magnevist. In this study, a type of MRI contrast agent (Gd3+@CGO) possessing a significantly high r1 value was easily prepared using a carboxyl-functionalized graphene oxide (CGO) as a nanocarrier to directly interact with GdCl3·6H2O. With 2.8 wt% of Gd3+ loaded on CGO, the prepared Gd3+@CGO shows good dispersibility in water and possesses r1 of 63.8 mM−1 S−1, which is 14 times higher than that of Magnevist. It is exciting to note that Gd3+ anchored on CGO remains stable at least for one year, probably relying on the electrostatic adsorption and physical encapsulation effect of CGO towards Gd3+.

Thermal stability of phenolic resin: new insights based on bond dissociation energy and reactivity of functional groups

Density functional theory (DFT) was applied to model molecules of phenolic resin (PR) to interpret the relationship between the atomistic structure and thermal properties of the cured PR. The bond dissociation energy (BDE) of C–C (in methylene bridges) and C–O bonds (in hydroxyls), as well as the Fukui function of hydroxyl, benzene and methylene groups, were calculated. The isomers of bisphenol-F and the methyl substituents have a slight effect on the BDEs of C–C and C–O bonds, while the oxidized structures, such as p-benzoquinone and aldehyde groups, lead to a drastic decrease in the C–C bond BDEs. The high reactivity of the carbon atoms in the benzene groups and the oxidized structures results in an increased possibility of being attacked by free radicals and protects the methylenes from being attacked, but it will also lead to ring-opening reactions and weight loss. These results provide a great opportunity to understand the relationship between the atomistic structure and the thermal stability of the cured PR, which plays a pivotal role in the design and optimization of thermal stable polymers.

Polyaniline precipitation in aqueous medium: from bulk aggregates to nanoparticles

A postsynthetic self-assembly system was designed to investigate a construction process from suspended polyaniline (PANI) molecules to condensed aggregates. The conventionally synthesized PANI was dissolved in polar solvent and introduced into acidic medium with electrolytes similar to the aniline chemical oxidative polymerization (COP) medium. In this way, reaction interference that is usually encountered in the COP process could be avoided, and influences of medium conditions including organic electrolytes on the self-assembly behaviors of PANI were studied. It was discovered that, in a static aqueous medium with moderate pH and rich electrolytes, PANI molecules composed of bulk aggregates could self-assemble into well-dispersed nanoparticles with few structural changes. Electrostatic force is considered to dominate the self-assembly of PANI molecules as compared with other noncovalent interaction or the effect of soft templates such as ionic liquid and surfactant. The results are supposed to provide better understanding on the formation mechanism of micro/nanostructured PANI.