PANI‐PAN coaxial nanofibers have been prepared by electro‐spinning during polymerization. The surface of the resulting nanofibers is superhydrophobic with a water contact angle up to 164.5°. Conductivity of the PANI‐PAN nanofibers is about 4.3 × 10−2 S · cm−1. The superhydrophobic nanofibers show a chemical dual‐responsive surface wettability, which can be easily triggered by changing pH value or redox properties of the solution. A reversible conversion between superhydrophobicity and superhydrophilicity can be performed in a short time. The strategy used here may provide an easy method to control the wettability of smart surfaces by using properties of low‐cost functional polymers.
Superhydrophobic dandelion‐like 3D microstructures self‐assembled from 1D nanofibers of PANI were prepared by a self‐assembly process in the presence of perfluorosebacic acid (PFSEA) as a dopant. The dandelion‐like microspheres (about 5 µm) are composed of uniform Y‐shaped junction nanofibers of about 210 nm average diameter and several micrometers in length, as measured by SEM. The dandelion‐like microstructure is coreless with a hollow cavity, and the shell thickness is about one third of the sphere diameter, as measured by TEM. Since PFESA dopant has a low surface energy perfluorinated carbon chain and two hydrophilic COOH end groups, it has dopant, is a “soft‐template” and brings about superhydrophobic functions at the same time. Moreover, it is proposed that the self‐assembly of PANI 1D nanofibers, driven by a combined interaction of hydrogen bonding, π‐π stacking and hydrophobic interactions, leads to the formation of the 3D microstructures.
3‐D rose‐like microstructures of polyaniline (PANI), which are self‐assembled from 2‐D nanosheets consisted of 1‐D nanofibers, were synthesized by a template‐free method in the presence of ammonium peroxydisulfate (APS) as both oxidant and dopant under a high relative humidity of 80% for the first time. When the relative humidity increases from 25 to 80%, not only morphology of the micro/nanostructured PANI undergoes a change from 1‐D nanofibers to 2‐D nanosheets to 3‐D rose‐like microstructures, but also increase in crystallinity. It is proposed that a cooperation effect of the oriented water molecules at the vapor–water interface and difference in hydrogen bonding energies between the interface and the bulk induced by the relative high humidity results in the formation of the 3‐D rose‐like microstructures self‐assembled from 2‐D nanosheets. Moreover, the method reported may provide a simple approach for understanding self‐assembly of complex micro/nanostructures of PANI.
Polyaniline (PANI) microtubes with a hexagonal cross‐section are successfully synthesized by a self‐assembly process in the presence of 8‐hydroxyquinoline‐5‐sulfonic acid (HQS) as a dopant and FeCl3 as an oxidant. The wall thickness of the PANI/HQS microtubes can be adjusted by the content of the oxidant. It is proposed that the aniline/HQS salts serve as a hard template for the formation of the hexagonal‐cross‐section microtubes. Moreover, PANI/HQS microtubes combined with ZnSO4 show pH‐dependent fluorescence. PANI hexagonal‐cross‐section microtubes combined with a pH‐sensitive fluorescence may promise potential applications in fields such as chemical sensors and confined reaction vessels.
This feature article reviews the authors' work combined with highlighted specific aspects of polyaniline (PANI) macro/nanostructures, focusing on such issues as the following. 1) The new development of a hard‐template method. 2) Evaluation of a template‐free method in universality, controllability, and simplicity as well as the self‐assembly mechanism. 3) Multi‐functionality based on a template‐free method associated with other approaches. 4) Cooperation effect of a micelle soft‐template and molecular interactions as a new tool to complex 3D microstructures assembled from 2D or 1D nanostructures. 5) Electrical and transport properties of a single PANI nanotube, as measured by a four‐probe method. 6) Sensors guided by reversible switching wettability through a doping/de‐doping process. An outlook is also briefly given.
Polyaniline (PANI) micro/nanosheets are successfully synthesized by a template‐free method without using any conventional oxidants. Scanning electron microscopy, transmission electron microscopy, and FT‐IR spectroscopy are applied to characterize the products. By investigating the morphologies and chemical structures of the PANI micro/nanosheets, a possible formation mechanism is proposed. In addition, the influences of experimental parameters, such as the kind of dopant, concentration of aniline, and acidity of reaction system, on the morphologies of the PANI micro/nanosheets have been systematically investigated.
Camphor sulfonic acid (CSA) doped polyaniline (PANI) nanotubes (175 nm in outer diameter and 120 nm in inner diameter) were synthesized successfully by a self‐assembly method. It is found that the room‐temperature conductivity of an individual PANI nanotube is 30.5 S · cm−1; in particular, the intrinsic resistance of an individual nanotube (30 kΩ) is much smaller than the contact resistance of crossed nanotubes (500 kΩ).
A SEM image of two crossed PANI‐CSA nanotubes and the attached Pt electrodes. 相似文献
The preparation of self‐assembled polyaniline (PANi) microspheres via facile interfacial oxidation polymerization of aniline in the presence of DL ‐tartaric acid dopant is reported. Compared with PANis reported in the literature, the PANi prepared in this study exhibits a nanorod‐bundle morphology with exceptionally high crystallinity. These nanorods or nanorod bundles can self‐assemble into microspheres with unique alignment. The chemistry, morphology, and crystal structure of DL ‐tartaric acid doped microspheres were studied using SEM, TEM, SAED, XRD, and FTIR.
A facile one‐step method has been developed to prepare both superhydrophobic and superoleophilic surfaces of polystyrene (PS) without any chemical modification. A rough film consisting of micro‐bead and nano‐fiber mixed structures is formed by spraying a PS solution onto a large area and any type of substrate. The mixed structures with such unique wettability properties can be used in oil/water separation and as oil sorbents.
Summary: Three‐dimensional polyaniline (PANI) nanowire networks were synthesized in high yield using a “soft template” self‐assembled with hexadecyltrimethylammonium bromide and oxalic acid. The PANI nanowire networks had diameters from 35–100 nm depending on synthesis conditions and/or procedures. The networks and the “cross‐linking points” were clearly observed by field‐emission scanning electron microscopy and transmission electron microscopy. A possible mechanism for the formation of three‐dimensional PANI nanowire networks is discussed.
FESEM image of PANI with three‐dimensional nanowire networks. 相似文献
Summary: Under UV irradiation plus a photomask, a hydrophilic/hydrophobic hybrid polymer surface is created by sandwiching an ammonium persulfate solution between two polymer films. It is demonstrated that an effective conductive PANI micropattern can be fabricated on such a wettability patterned surface. For PET, a stable negative micropattern could be formed directly by the selective deposition of PANI onto the hydrophobic region. Alternatively, for PP or PI, direct deposition of PANI is non‐selective, however, the PANI layer remains preferentially on the hydrophilic region by peeling off the PANI layer on the hydrophobic region to form a positive micropattern.
Schematic illustration of the procedure used for the formation of a conducting polymer (PANI) micropattern on a wettability patterned polymer substrate. 相似文献
PANI nanofibers are prepared electrochemically by template‐free method on a stainless steel electrode. Both the hydrophilicity and the lipophilicity of the modified SS surface are enhanced by the nanostructured PANI, and a super‐amphiphilic surface is obtained in this way. The influence of polymerization conditions, such as polymerization potentials, polymerization time, the acidity, and the dopants on the super‐amphiphilic property, has been systematically investigated. In addition, the mechanisms of obtaining a super‐amphiphilic surface are briefly discussed.
Nanostructures with stimuli‐responsive properties are of great importance for the application of smart materials in nanotechnology. Unique hollow polypyrrole nanostructured arrays with a conical shape have been produced by a stepwise electropolymerization process. The polypyrrole conical nanocontainers exhibit a reversible switchable behavior between open and closed states, which is controlled by the movement of counter ions during electrically controlled reversible oxidation and reduction processes. The formation of conical nanocontainers is affected by the oleo‐wettability of the substrate. Conical nanocontainers can be formed on oleo‐phobic substrates in aqueous solution by using dopant‐stabilized pyrrole nanodroplets as the guiding template for the polymerization.
Summary: Polyaniline nanofibers (from 93 to 220 nm) doped with β‐naphtalenesulfonic acid (PANI‐NSA) have been characterized. Nonhomogeneity in the thickness of fibers, as can be seen with scanning electron microscopy, is the reason for their instability under the HCl doping process. Resonance Raman spectral profiles of PANI‐NSA fibers suggest a lower protonation state than the emeraldine salt forms. Observation of Raman bands, which are a result of cross‐linking, confirms that one of the properties of the polymeric structure formed in micellar polymerization is the type of connection between chains.
Urchin‐like PANI microspheres with an average diameter of 5–10 µm have been successfully prepared. Their surfaces consist of highly oriented nanofibers of ≈30 nm diameter and 1 µm length. The solvent composition plays an important role in the formation process of urchin‐like PANI microspheres. The structure of the products has been characterized by FT‐IR, UV‐vis, and XRD. To investigate the self‐assembly of urchin‐like PANI microspheres, the effect of polymerization time on the morphology of the products has been studied. The morphological evolution process indicates that the urchin‐like microspheres originate from the self‐assembly of nanoplates, which then grow into urchin‐like microstructures with nanofibers on the surface.
Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π‐π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano‐sized crystals produced during the synthesis results in the formation of micrometer‐length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.
This work reports on thermally tunable surface wettability of electrospun fiber mats of: polystyrene (PS)/poly(N‐isopropylacrylamide) (PNIPA) blended (bl‐PS/PNIPA) and crosslinked poly[(N‐isopropylacrylamide)‐co‐[methacrylic acid)] (PNIPAMAA) (xl‐NIPAMAA). Both the bl‐PS/PNIPA and xl‐PNIPAMAA fiber mats demonstrate reversibly switchable surface wettability, with the bl‐PS/PNIPA fiber mats approaching superhydrophobic ≥150° and superhydrophilic contact angle (CA) values at extreme temperatures. Weight loss studies carried out at 10 °C indicate that the crosslinked PNIPAMAA fiber mats had better structural integrity than the bl‐PS/PNIPA fiber mats. PNIPA surface chemistry and the Cassie–Baxter model were used to explain the mechanism behind the observed extreme wettability.
Water dispersible nanofibrilar polyaniline (NF‐PANI) provides a novel and direct route towards carbon nanotube water dispersions of high concentration. Carrying out the chemical synthesis of NF‐PANI in the presence of carbon nanotubes (CNTs) results in an entirely nanostructured nanofibrilar polyaniline/carbon nanotube (NF‐PANI/CNT) composite material that contains well segregated CNTs partially coated by NF‐PANI. This new approach is simple, fast, and inexpensive, and enables the direct preparation of stable and homogeneous dispersions of the composites in water at concentrations up to 10 mg · mL−1, even for the highest CNT loadings of 50 wt.‐% without the participation of surfactants or stabilizers.
A green chemoenzymatic pathway for the synthesis of conducting polyaniline (PANI) composites is presented. Laccase‐catalyzed polymerization in combination with anionic polysaccharides is used to produce polysaccharide/PANI composites, which can be processed into flexible films or coated onto cellulose surfaces. Different polysaccharide templates are assessed, including κ‐carrageenan, native spruce O‐acetyl galactoglucomannan (GGM), and TEMPO‐oxidized cellulose and GGM. The resulted conducting biocomposites derived from natural materials provide a broad range of potential applications, such as in biosensors, electronic devices, and tissue engineering.
Summary: A superhydrophobic coating was facilely fabricated in one step by casting bisphenol A polycarbonate (PC) solution under moisture. Vapor‐induced phase separation occurred during the solidifying process and a rough surface with a micro‐nano‐binary structure (MNBS) similar to the microstructure shown on lotus leaf was formed.
