Compositional asymmetry in a crystalline-amorphous block copolymer influences the phase and crystallization behaviors of its blend with an amorphous block copolymer.

This study determined the phase and crystallization behaviors of blends composed of asymmetric polystyrene-block-poly(ethylene oxide) (PS-PEO) and symmetric polystyrene-block-poly(methyl methacrylate) (PS-PMMA). The PS blocks in the various binary block copolymers exhibited nearly identical molecular weights, whereas the molecular weight ratios of PEO and PMMA varied. The compatibility of the PEO and PMMA chains aided the binary block copolymers in co-ordering in a lamellar microdomain morphology, with the PEO and PMMA blocks sharing a common microdomain. Adding short tethered PMMA chains to long tethered PEO chains led to a decrease in the common microdomain spacing and an increase in the grafting density. These behaviors increased PEO chain stretching, causing macrophase separation. The mismatch in PEO and PMMA block lengths divided the common PEO/PMMA microdomain into two sections: the coexisting PEO/PMMA section close to the microdomain interface and the neat PEO section far away from it. The high-glass-transition-temperature PMMA reduced PEO chain mobility, inhibiting PEO crystallization in the coexisting PEO/PMMA section but not in the neat PEO section. When the block length ratio of PEO to PMMA decreased, the neat PEO section narrowed. The increase in the extent of PEO confinement led to a reduction in PEO crystallizability.

In Situ Thermal Safety Aspect of the Electrospun Polyimide-Al2O3 Separator Reveals Less Exothermic Heat Energies Than Polypropylene at the Thermal Runaway Event of Lithium-Ion Batteries.

Polyimide-Al2O3 membranes are developed as a direct alternative to current polyolefin separators by the electrospinning technique and their chemical structures confirm the carbonyl group with the presence of asymmetric and symmetric stretching and bending vibrations at 1778, 1720, and 720 cm-1 and stretching vibration at 1373 cm-1 for the imide group. Porous nanofiber architecture morphology is realized with a nanofiber thickness of ∼200 nm and shows an ultrasmooth surface and >1 µm pore size in the architecture, built with the chemical constituents of carbon, nitrogen, aluminum, and oxygen elements. The galvanostatic cycling study of the Li/PI-Al2O3/LiFePO4 lithium cell delivers stable charge-discharge capacities of 144/143 mAh g-1 at 0.2 C and 110/100 mAh g-1 at 1 C for 1-100 cycles. The fabricated MCMB/PI-Al2O3/LiFePO4 lithium-ion full-cell reveals less charge transfer resistance of Rct ∼ 25 Ω and yields stable charge-discharge capacities of 125/119 mAh g-1. The thermogravimetric curve for the PI-Al2O3 separator discloses thermal stability up to 525 °C, and the differential scanning calorimetric curve shows a straight line until 300 °C and depicts high thermal stability than the PP separator. In situ multimode calorimetry analysis of the MCMB/PP/LiFePO4 full-cell showed a pronounced exothermic peak at 225 °C with a higher released heat energy of 211 J g-1 at the thermal runaway event, while the MCMB/PI-Al2O3/LiFePO4 full-cell revealed an almost 8-fold less exothermic released heat energy of 25 J g-1 than the Celgard polypropylene separator, which was because the MCMB anode and LiFePO4 cathode can be mechanically isolated without any additional separator's melting and burning reactions, as a fire-suppressant separator for lithium-ion batteries.

Carbon fibre-supported hierarchical NiCo layered double hydroxide nanosheets as non-enzymatic glucose sensors for sport drinks and serum.

We report a systematic study of carbon fibre (CF)-supported NiCo layered double hydroxide nanosheets (LDHNs) with and without heat treatment at 200 and 400 °C (CF-NiCo LDHN200 and CF-NiCo oxide nanoparticles (NPs), respectively) as catalysts and sensors for glucose oxidation reactions (GORs). Tafel measurements for the GORs showed that the exchange current density of CF-NiCo LDHN was 1.91 × 10-3 mA·cm-2 at an early rest potential of -0.422 V. This was markedly higher than those of CF-NiCo LDHN200 (1.22 × 10-3 mA·cm-2 at - 0.352 V) and CF-NiCo oxide NP (1.18 × 10-3 mA·cm-2 at -0.327 V). The electron transfer number and Tafel slopes suggested that the glucose dehydrogenation step and one-electron release occurred first in the GORs. Amperometric measurements revealed high recoveries (101.92% and 98.92%) and low relative standard deviations (1.98% and 2.34%) for the determination of glucose using the CF-NiCo LDHN in sports drink samples and human serum.

Hydrogen Bonding-Induced Assembled Structures and Photoresponsive Behavior of Azobenzene Molecule/Polyethylene Glycol Complexes.

We investigated the self-assembled structures and photoresponsive and crystallization behaviors of supramolecules composed of 4-methoxy-4'-hydroxyazobenzene (Azo) molecules and polyethylene glycol (PEG) that were formed through hydrogen-bonding interactions. The Azo/PEG complexes exhibited the characteristics of photoresponse and crystallization, which originated from Azo and PEG, respectively. When Azo/PEG complexes were dissolved in solvents, hydrogen-bonding interaction hindered the rotation and inversion of mesogens, causing a reduction in the photoisomerization rate compared with the photoisomerization rate of the neat Azo. The confinement of Azo/PEG complexes in thin films further resulted in a substantial decrease in the photoisomerization rate but an increase in the amounts of H-aggregated and J-aggregated mesogens. Regarding PEG crystallization, ultraviolet irradiation of Azo/PEG complexes increased the quantity of high-polarity cis isomers, which improved the compatibility between mesogens and PEG, subsequently increasing the crystallization temperature of PEG. Moreover, the complexation of Azo and PEG induced microphase separation, forming a lamellar morphology. Within the Azo-rich microphases, mesogens aggregated to form tilted monosmectic layers. By contrast, PEG crystallization within the PEG-rich microphases was hard confined, indicating that the domain size of the lamellar morphology was unchanged during PEG crystallization.

Hydrothermal and plasma nitrided electrospun carbon nanofibers for amperometric sensing of hydrogen peroxide.

Nitrogen-doped carbon nanofibers (CNFs) were prepared by an electrospinning method, this followed by a hydrothermal reaction or nitrogen plasma treatment to obtain electrode for non-enzymatic amperometric sensing of H2O2. The hydrothermally treated electrode performs better. Its electrochemical surface is 3.7 × 10-3 mA cm-2, which is larger than that of a nitrogen plasma treated electrode (8.9 × 10-4) or a non-doped CNF (2.45 × 10-4 mA cm-2). The hydrothermally treated CNF with rough surface and a complex profile with doped N has a higher sensitivity (357 µA∙mM-1∙cm-2), a lower detection limit (0.62 µM), and a wider linear range (0.01-0.71 mM) than N-CNFP at a working potential of -0.4 V (vs. Ag/AgCl). The electrode gave high recoveries when applied to the analysis of milk samples spiked with H2O2. Graphical abstract Nitrogen-doped carbon nanofibers prepared by an electrospinning method followed by a hydrothermal reaction (N-CNFht) or nitrogen plasma treatment (N-CNFP) are directly used as non-enzymatic amperometric H2O2 sensors.

Morphology-Mediated Photoresponsive and Fluorescence Behaviors of Azobenzene-Containing Block Copolymers.

We investigated the relationship between the self-assembled morphology of poly( tert-butyl acrylate)- block-poly(6-[4-(4'-methoxyphenylazo)phenoxy]hexyl methacrylate) (P tBA- b-PAzoMA) block copolymers and their photoresponsive and fluorescence behaviors. The morphology of P tBA- b-PAzoMA copolymers was manipulated by dissolving them in mixed dimethylformamide (DMF)/hexanol solvents. When P tBA- b-PAzoMA was dissolved in DMF-rich (neutral) solvents, a favorable interaction between the DMF molecules and both blocks resulted in a random-coiled conformation. The unconfined morphology facilitated the formation of both nonassociated and head-to-head organized azobenzene mesogens, which promoted fluorescence emission. When hexanol, a P tBA-selective solvent, was added to DMF, the solvency of P tBA- b-PAzoMA worsened, leading to its assembly into micelles, with PAzoMA in the micelle core. The confinement of azobenzene moieties in the micelle core hindered their trans-to- cis photoisomerization, thereby considerably decreasing the kinetics of photoisomerization and the population of cis isomers. Additionally, a nanoconfined geometry resulted in compactly packed chromophores, causing fluorescence loss. When P tBA- b-PAzoMA was exposed to UV light, the increased number of cis isomers hampered the closely packed mesogens, resulting in a substantial enhancement of fluorescence emission. When the mole fraction of the PAzoMA block was increased, P tBA- b-PAzoMA formed clusters, causing the slow kinetics of photoisomerization and fluorescence quenching.

Binder-Free N- and O-Rich Carbon Nanofiber Anodes for Long Cycle Life K-Ion Batteries.

Carbon nanofibers produced by electrospinning of polyacrylonitrile polymer and subsequent carbonization were tested as freestanding potassium-ion anodes. The effect of oxygen functionalization on K-ion carbon anode performance was tested for the first time via plasma oxidation of prepared carbon nanofibers. The produced materials exhibited exceptional cycling stability through the amorphous carbon structuring and one-dimensional architecture accommodating significant material expansion upon K+ intercalation, resulting in a stable capacity of 170 mAh g-1 after 1900 cycles at 1C rate for N-rich carbon nanofibers. Excellent rate performance of 110 mAh g-1 at 10C rate, as compared to 230 mAh g-1 at C/10 rate, resulted from the K-ion surface storage mechanism and the increased K+ solid diffusion coefficient in carbon nanofibers as compared to graphite. Plasma oxidation treatment augmented surface storage of K+ by oxygen functionalities but increased material charge transfer resistance as compared to N-rich carbon fibers. Ex situ characterization revealed that the one-dimensional structure was maintained throughout cycling, despite the increase in graphitic interlattice spacing from 0.37 to 0.46 nm. The carbon nanofibers demonstrate great potential as an anode material for potassium-ion batteries with superior cycling stability and rate capability over previously reported carbon materials.

The dispersion state of magnetic nanorods in homopolymers and block copolymers.

We investigated the dispersion state of pyridine-modified magnetic nanorods in poly(2 vinylpyridine) (P2VP) homopolymers and poly(styrene-b-2 vinylpyridine) (PS-P2VP) diblock copolymers. In the P2VP/nanorod mixtures, the dispersion of nanorods was enhanced in systems in which the molecular weight of P2VP was increased because the long P2VP chains provided steric hindrance and thus screened the attractive interparticle interactions, inhibiting the rod aggregation. When nanorods were mixed with PS-P2VP, the phase stability of the mixtures varied considerably according to changes in the lamellar period of PS-P2VP (D). When D was large, nanorods were sequestered into the P2VP domains through enthalpically driven self-assembly, and the nanorods became spatially organized. By contrast, when D was small, the introduction of nanorods caused substantial distortion of chain conformations. This entropically unfavorable condition can be offset by excluding nanorods from the ordered phases, causing particle aggregation. At a high particle loading, the attractive interparticle interactions outweighed the particle-polymer interaction and entropic contribution of polymers. Consequently, nanorods underwent extensive aggregation.

Effect of molecular properties of random copolymers on the stability and domain dimension of block copolymer/random copolymer blends.

The morphological behavior of binary mixtures containing poly(styrene-b-2-vinylpyridine) (PS-b-PVP) diblock copolymer and poly(styrene-r-2-vinylpyridine) (PS-r-PVP) random copolymer was investigated as a function of the molecular weight ratio of PS-b-PVP and PS-r-PVP (R), the PS fraction in PS-r-PVP, and the concentration of PS-r-PVP in the blends (ϕr). When R was high, the addition of symmetric PS-r-PVP caused lateral expansion of microdomains and reduced the interdomain distance of the blend, indicating localization of PS-r-PVP at the PS-b-PVP interface. At high ϕr, packing constraints prevented all PS-r-PVP from assembling at the PS-b-PVP interface, which induced macrophase separation and formed a coexisting morphology composed of ordered polymer phase and random copolymer-rich regimes. Reducing the R value reduced the amount of PS-r-PVP that could be assembled at the PS-b-PVP interface, and macrophase separation occurred at a low PS-r-PVP content. When asymmetric PS-r-PVP was introduced into PS-b-PVP, PS-r-PVP was located in the preferred domain of PS-b-PVP because of the favorable interaction of PS-r-PVP with the particular domain. The enthalpically driven self-assembly rendered to swell the preferred domain and increased the interfacial curvature that, in turn, induced an order-order transition.

Effect of rod length on the morphology of block copolymer/magnetic nanorod composites.

The organization of magnetic nanorods in microphase-separated diblock copolymers composed of poly(styrene-b-2-vinylpyridine) (PS-PVP) as a function of rod length and rod concentration was investigated using both transmission electron microscopy and small-angle X-ray scattering. Our results reveal that the nanorods were sequestered into the PVP domains, which is attributed to the preferential interaction between pyridine-tethered nanorods and PVP. Meanwhile, the addition of nanorods in PS-PVP caused chain stretching. To minimize the energy penalty, nanorods tended to align parallel to the interface between PS and PVP to increase the conformational entropy. As the length of nanorods increased, the increasing van der Waals interaction and magnetic interaction caused extensive rod aggregation, which suppressed the domain size of PVP and amplified the local compositional fluctuations. This creates conditions to induce disorder in the polymer morphology and nanorods undergo macrophase separation.

Effect of particles on the structure of solvent-annealed block copolymer/nanoparticle composite thin film.

The structure of nanocomposite thin films composed of polystyrene-b-poly(2 vinylpyridine)/Au nanoparticles (PS-PVP/Au) during chloroform vapor annealing was investigated. Our results revealed that the morphology of these composites depends on particle size and volume fraction. During solvent annealing, particles segregate to both polymer/substrate and air/polymer interfaces. The segregation of particles to the polymer/substrate interface balances the preferential interaction of two domains to the substrate, resulting in the transition of ordered domains from parallel to normal to the substrate. The introduction of large particles facilitates the segregation of particles to the top of the film. When the volume fraction of segregated particles is high, particles are repelled from the preferred domains to form particle-rich regimes. The wetting behavior of a thin film could be improved by the presence of nanoparticles. Our results showed that small particles provide the better ability to prevent thin film from dewetting.

Synthesis and characterization of magnetic nanoparticle/block copolymer composites.

A simple strategy to improve the particle dispersion and structural ordering of magnetic nanoparticle/block copolymer composites is demonstrated. This method consists of manipulating both the block copolymer structure in a solvent and the relative interactions of particle/solvent and polymer/solvent to facilitate the self-assembly of particles in the preferred domain of the block copolymer. In a neutral solvent, the freely expanded structure of the polymer and the slightly weaker affinity between particle and solvent than between particle and polymer promotes the selection of particles in the preferred domain of the block copolymer. Furthermore, more particles are allowed to be incorporated into the polymer matrix while still obtaining the nicely ordered structure when these particles exhibit smaller magnetization.

pH- and temperature-dependent phase behavior of a PEO-PPO-PEO-based pentablock copolymer in aqueous media.

We investigated the structural features of micelles formed by the self-association of the pentablock copolymer poly[ N,N -(diethyl amino)ethyl methacrylate]-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethyleneoxide)-block-poly[ N,N -(diethylamino)ethyl methacrylate] (PDEAEM-PEO-PPO-PEO-PDEAEM) in aqueous solutions by using small-angle neutron scattering SANS. The pentablock copolymer solutions exhibit micellar and gel phases in response to changes in both the temperature and pH by virtue of (1) the lower critical solution temperature of the PPO blocks and (2) the polyelectrolyte character of the pendant PDEAEM blocks. Two modeling schemes were employed to describe the SANS data of semidilute copolymer solutions at higher temperature as they contain interacting charged micelles at pH<7.5 and interacting neutral micelles at higher pH. We have elucidated the structures of the micelles in terms of size, shape, polydispersity, association number, number density, and surface charge. At low pH the charged spherical micelles are less packed with the copolymers presumably due to the electrostatic repulsion between the charged pendant groups. On the other hand, at higher pH the hydrophobic character of the neutral pendant groups enable them to sequester within the micelle core along with the PPO, thus increasing the number density and the core size of the spherical micelles. At higher copolymer concentration reversible thermoresponsive sol-gel transitions were observed at all pH conditions and the rheological behavior of the gels nicely correlates with different organization of micelles with different shapes.

Effect of interfacial interaction on the cross-sectional morphology of tobacco mosaic virus using GISAXS.

We have investigated the effect of the interfacial interaction on the cross-sectional morphology of the tobacco mosaic virus (TMV) in solution and on two types of solid substrates, SiOx (polar) on Si(100) and polystyrene film (nonpolar) on Si(100), using small-angle X-ray scattering (SAXS) and grazing incidence small-angle X-ray scattering (GISAXS), respectively. Results reveal that the flexible chains at the outer surface of TMV either expand or contract depending on the nature of the substrate. Although the unfavorable interaction between the TMV and the PS causes a minimal effect, the stronger attractive interaction between the outer protein surface of TMV and the SiOx substrate induces pronounced deformation of its cross-sectional morphology.