Haijin Zhu

Temperature-Triggered Collection and Release of Water from Fogs by a Sponge-Like Cotton Fabric

A sponge-like cotton fabric autonomously collects and releases water from fogs triggered by typical day-and-night temperature variations. The reversible switching between absorbing-superhydrophilic/releasing-superhydrophobic states results from structural changes of a temperature-responsive polymer grafted on the very rough fabric-surface. This material and concept presents a breakthrough into simple and versatile solutions for collection, uni-directional flow, and purification of water captured from the atmosphere.

Phase change materials of n-alkane-containing microcapsules: observation of coexistence of ordered and rotator phases

In the present investigation, the crystallization and phase transition behaviours of normal alkane (n-docosane) in microcapsules with a mean diameter of 3.6 μm were studied by the combination of differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD) and variable-temperature solid-state nuclear magnetic resonance (VT solid-state (13)C NMR). The DSC and VT solid-state (13)C NMR results reveal that a surface freezing monolayer is formed prior to the bulk crystallization of the microencapsulated n-docosane. More interestingly, it is confirmed that after the bulk crystallization, the ordered triclinic phase coexists with the rotator phase I (RI) for the microencapsulated n-docosane. We argue that the reduction of the free energy difference between the two phases, resulting from the microencapsulation process, leads to the coexistence of the ordered triclinic and rotator phases of the normal alkanes.

Proton transport behaviour and molecular dynamics in the guanidinium triflate solid and its mixtures with triflic acid

Knowledge of the proton transport behaviour in electrolyte materials is crucial for designing and developing novel solid electrolytes for electrochemical device applications such as fuel cells or batteries. In the present work, high proton conductivity (approximately 10−3 S cm−1) was observed in the triflic acid (HTf) containing guanidinium triflate (GTf) composites. The proton transport mechanism in the composite was elucidated by comparing the diffusion coefficients obtained from NMR and conductivity measurements. Several orders of magnitude enhancement of conductivity is observed upon addition of HTf to the organic solid, and this appears to follow percolation behaviour with a percolation threshold of approximately 2% HTf. The data support a structural diffusion (or Grotthuss) mechanism of proton transport with a calculated Haven ratio significantly less than unity. 13C SUPER and 14N overtone NMR experiments were used to study the mobility and symmetry of the triflate anion and guanidinium cation respectively at a molecular level. The former experiment shows that the CF3 group in the anion displays fast and isotropic motion at room temperature. In contrast to the high mobility of the anion group, the 14N overtone experiments indicate that the guanidinium cation is static in both the pure and the acid-containing GTf samples at room temperature. It is anticipated that these solid-state NMR techniques may be also applied to other organic solid state electrolyte materials to achieve a better understanding of their transport mechanisms and molecular dynamics.

Functional Application of Noble Metal Nanoparticles In Situ Synthesized on Ramie Fibers

Different functions were imparted to ramie fibers through treatment with noble metal nanoparticles including silver and gold nanoparticles. The in situ synthesis of silver and gold nanoparticles was achieved by heating in the presence of ramie fibers in the corresponding solutions of precursors. The unique optical property of synthesized noble metal nanoparticles, i.e., localized surface plasmon resonance, endowed ramie fibers with bright colors. Color strength (K/S) of fibers increased with heating temperature. Silver nanoparticles were obtained in alkaline solution, while acidic condition was conducive to gold nanoparticles. The optical properties of treated ramie fibers were investigated using UV-vis absorption spectroscopy. Scanning electron microscopy (SEM) was employed to observe the morphologies of silver and gold nanoparticles in situ synthesized on fibers. The ramie fibers treated with noble metal nanoparticles showed remarkable catalytic activity for reduction of 4-nitrophenol (4-NP) by sodium borohydride. Moreover, the silver nanoparticle treatment showed significant antibacterial property on ramie fibers.

T2 distribution spectra obtained by continuum fitting method using a mixed Gaussian and exponential kernel function

Static (1)H NMR Free Induction Decay (FID) signals of polymer solids contain a lot of information about the molecular dynamics. A T2 analysis of the FID has generally been performed in terms of discrete two- or three-component models. However, this requires a priori assumption of the number of proton species before analysis. This paper presents a method of analyzing the FIDs of the polymer solid samples in terms of a continuous T2 distribution. A mixed Gaussian and Exponential kernel function was used to represent the true characteristic of FIDs of the polymer solids. A simple and realistic assumption has been made to reduce the number of degrees of freedom in the continuum fitting and to make the fitting stable. An experimental static (1)H NMR FID of a typical polymer solid sample was analyzed as an example in the end to demonstrate the application of this method.

Enhancement of ion dynamics in organic ionic plastic crystal/PVDF composite electrolytes prepared by co-electrospinning

Electrospun fibers are widely used in composite material design and fabrication due to their high aspect ratio, high surface area and favorable mechanical properties. In this report, novel organic ionic plastic crystal (OIPC) modified poly(vinylidene difluoride) (PVDF) composite fiber membranes were prepared by electrospinning. These composite materials are of interest for application as solid electrolytes in devices including lithium and sodium batteries. The influence of the OIPC, N-ethyl-N-methylpyrrolidinium tetrafluoroborate [C2mpyr][BF4], on the morphology and phase behavior of the composite fibers was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. Compared with pure electrospun PVDF fibers, which have an electroactive β phase and a small amount of non-polar α phase, the ion-dipole interaction between OIPC and the polymer in the co-electrospun composite system can reduce the non-polar α phase PVDF, resulting in almost entirely electroactive β phase PVDF. Differential scanning calorimetry shows that the ion-dipole interaction between the OIPC and PVDF can also interrupt the crystalline structure of the OIPC. Solid state NMR analysis also reveals different molecular dynamics of the [C2mpyr][BF4] in co-electrospun fibers compared with pure OIPC. Thus, electrospun [C2mpyr][BF4]/PVDF composite fibers that combine both increased ionic conductivity and almost pure β phase PVDF are demonstrated.

Insight into Local Structure and Molecular Dynamics in Organic Solid‐State Ionic Conductors

Elucidating the rate and geometry of molecular dynamics is particularly important for unravelling ion-conduction mechanisms in electrochemical materials. The local molecular motions in the plastic crystal 1-ethyl-1-methylpyrrolidinium tetrafluoroborate ([C2 mpyr][BF4 ]) are studied by a combination of quantum chemical calculations and advanced solid-state nuclear magnetic resonance spectroscopy. For the first time, a restricted puckering motion with a small fluctuation angle of 25° in the pyrrolidinium ring has been observed, even in the low-temperature phase (-45 °C). This local molecular motion is deemed to be particularly important for the material to maintain its plasticity, and hence, its ion mobility at low temperatures.

Amino-functionalized mesoporous silica based polyethersulfone–polyvinylpyrrolidone composite membranes for elevated temperature proton exchange membrane fuel cells

It is important to find alternative membranes to the state-of-the-art polybenzimidazole based high temperature proton exchange membranes with high proton conductivity at elevated temperature but with simple synthesis procedures. In this work, inorganic–organic nanostructured hybrid membranes are developed based on a polyethersulfone–polyvinylpyrrolidone (PES–PVP) polymeric matrix with hollow mesoporous silica (HMS), amino-functionalized hollow mesoporous silica (NH2-HMS) and amino-functionalized mesoporous silica (NH2-meso-silica). The composite membranes show a significant increase in proton conductivity and a decrease in the activation energy for proton diffusion in comparison with the phosphoric acid (H3PO4, PA) doped PES–PVP membrane. And the composite membrane with NH2-HMS shows the best performance under the conditions in this study, achieving the highest proton conductivity of 1.52 × 10−1 S cm−1 and highest peak power density of 480 mW cm−2 at 180 °C under anhydrous conditions, which is 92.7% higher than that of the PA doped PES–PVP membrane at identical conditions. Such enhancement results from the facilitated proton transportation in the ordered mesoporous channels via the hydrogen bond between the –NH2 groups and H3PO4. The high water retention capability of silica materials with a hollow structure also contributes to the decrease of the activation of proton diffusion. Consequently, the results show promising potential of the NH2-HMS based PES–PVP composite membrane for the elevated temperature proton exchange membrane fuel cells.

Preparation and characterization of gel polymer electrolytes using poly(ionic liquids) and high lithium salt concentration ionic liquids

Polymerized ionic liquids or poly(ionic liquids) (polyILs) have been considered as promising hosts for fabrication of gel polymer electrolytes (GPEs) containing ionic liquids. In this work, a novel GPE based on a polyIL, poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA TFSI), and a high lithium-concentration phosphonium ionic liquid, trimethyl(isobutyl)phosphonium bis(fluorosulfonyl)imide (P111i4FSI), is prepared. The composition-dependent behaviour of the GPEs is investigated by differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS) and solid-state nuclear magnetic resonance (solid-state NMR). The effects of Al2O3 nano-particles on the polymer electrolyte properties are also discussed. It is shown that the introduction of high lithium-concentration ionic liquids into the polyIL can effectively decrease the glass transition temperature (Tg) of the resulting GPE, leading to improved ion dynamics and higher ionic conductivity. The Al2O3 nano-particles effectively enhanced the mechanical stability of the GPEs. Most importantly, although adding PDADMA TFSI to the ionic liquids decreases the diffusion coefficient of both Li+ and anions, a greater decrease in the anion diffusion is observed, resulting in a higher Li+ transport number (as evaluated by NMR) than that seen in the original ILs. Finally, a highly conductive free-standing GPE membrane is fabricated, and extremely stable lithium symmetrical cell performance is demonstrated.

Modelling Ion‐Pair Geometries and Dynamics in a 1‐Ethyl‐1‐methylpyrrolidinium‐Based Ion‐Conductive Crystal

Full conformational and energy explorations are conducted on an organic ionic plastic crystal, 1-ethyl-1-methylpyrrolidium tetrafluoroborate [C2mpyr][BF4]. The onsets of various stages of dynamic behaviour, which appear to account for low-temperature solid-solid phase transitions, are investigated by using quantum-chemical simulations. It is suggested that pseudorotation of the pyrrolidine ring occurs in the first instance; the partial rotation of the entire cation subsequently occurs and may be accompanied by reorientation of the ethyl chain as the temperature increases further. A cation-anion configuration, whereby BF4(-) interacts with the C2 mpy cation from the side of the ring, is the most likely structure in the low-temperature phase IV region. These interpretations are supported by (13)C nuclear magnetic resonance chemical-shift analysis.