Novel Flow Field with Superhydrophobic Gas Channels Prepared by One-step Solvent-induced Crystallization for Micro Direct Methanol Fuel Cell

The CO2-induced capillary blocking in anode flow field is one of the key adverse factors to reduce the performance of a micro-direct methanol fuel cell(l DMFC). In order to solve this problem, new polycarbonate(PC) flow field plates with nested arrangement of hydrophilic fuel channels and superhydrophobic gas channels were designed,fabricated, and tested in this work. The gas channels were treated with solvent-induced crystallization using acetone solution. The superhydrophobicity with 160° water contact angle and 2° tilting angle was obtained on the PC substrates. A dummy cell using hydrogen peroxide decomposition reaction and a test loop were separately set up to evaluate the flow fields' performance. It was found that a 37 % pressure drop decrease can be obtained in the new serpentine flow field compared with that of the conventional one. The benefit of the new flow field to remove gas bubbles was also confirmed by an in situ visualization study on the dummy cell. Results show that the auxiliary superhydrophobic gas channels can speed up the discharge of the gas bubbles from the flow field, which will in turn improve the l DMFC performance.

Taking into Account Density Fluctuations in a Solvent in a Model of Dissolution

Earlier it was shown by different authors that there are cavities (vacancies, holes) in any liquid. The cavities should play a prominent role in dissolution processes. Nevertheless this fact was ignored in previous model of dissolution. The sizes of the cavities in different solvents containing benzene molecules were determined using solvent induced spectral shift method. The measurements of S1←S0 benzene transition spectral shifts permit to conclude that 1) macroscopic excess volumes play an almost negligible role in processes of benzene dissolution in very different solvents and 2) the minimal size of the cavity in water able to accommodate benzene molecule coincides with the solute size. Generalization of this conclusion to other nonpolar aromatics leads to evaluation contraction of the solutes under aqueous solvent influence permits to predict the solubility values of other aromatics in water and to evaluate effect of enhancement hydrate cell around these molecules on solubility.

Solvent Effects on the UV Absorption Spectrum of Carmofur

In this article, we reported that carmofur could be induced by some solvent to produce conformational alteration. Ultraviolet (UV) spectra were used to study the conformation alteration of carmofur. Upon the addition of acid in the some solvent, UV spectroscopy of carmofur could change gradually. When base was added to this system, UV spectroscopy of carmofur could return to the original state, and the change process was reversible. The variable temperature 1H and 13C-NMR spectrum were used to testify that temperature did not have any effect on the conformation alteration of carmofur in Acetonitrile: Trifluoroacetic-acid (9:1). These two conformers of carmofur were structurally stable in Acetonitrile: Trifluoroacetic-acid (9:1).

Investigating the Absorption and Desorption Behavior of Methylene Chloride in the Poly(aryl ether ketone) Film with Different Crystallinities

Poly(aryl ether keton e)(PAEK) films with different crystallinities were obtained by controlling the cooling rate,which were subjected to the absorption and desorption of methylene chloride(CH_(2)Cl_(2)).We employed attenuated total reflection Fourier transform infrared(ATR-FTIR)spectroscopy analyses to investigate the diffusion behavior of CH_(2)Cl_(2) in PAEK films with different crystallinities.According to the Fickian diffusion model,the calculated diffu sion coefficients of CH_(2)Cl_(2) in PAEK films were observed to decrease with increasing crystallinity.The effect of CH_(2)Cl_(2)absorption and desorption on the mechanical properties of PAEK films with different crystallinity was further analyzed using tensile tests.The tensile tests exhibited that CH_(2)Cl_(2) has two concurrent effects:plasticization and solvent-induced crystallization.Differential scanning calorimetry(DSC) and wide-angle X-ray diffraction(WXRD) techniques further confirmed solvent-induced crystallization behavior.The results would be beneficial to understand the solvent resistance of PAEK materials and consequently provide the practical application conditions of PAEK with a theoretical basis.

Flexible Dry Hydrogel with Lamella-Like Structure Engineered via Dehydration in Poor Solvent

Hydrogels are among the most promising biologic materials in recent technology with numerous desired applications,including serving as biosensors,drug delivery vehicles,and tissue-engineered products for cell matrices.However,they often dehydrate,and become stiff and brittle in air,causing loss of flexibility and functions.Several layered structures have been proven to increase the strength,toughness,and even flexibility of these materials,which might provide a new clue for the sustenance of the flexibility of drying gels.Herein,we report a novel solvent-dehydrated hydrogel engineering approach,aimed to change the inner structure and keep the flexibility of a dehydrated hydrogel in the air via solvent-induced dehydration,for example,acetonedehydrated polyacrylic acid hydrogel.This flexible dry gel could be folded,twisted,and stretched without any damage due to the assumed lamella-like structures,contrary to dry gels without these microstructures or those with porous structures,which retain brittle consistency.The flexible dry gel also exhibited excellent self-healing capability with the assistance of solvents.Fascinatingly,this flexible gel film displayed strain-visualizing paper writing/erasing performance properties,with water acting as invisible ink.Thus,this fabricated flexible hydrogel film might function as confidential information storage material.Our current approach is versatile,hence applicable to other hydrogels,and provides insight into the engineering of other functional gels for extended future applications.

Solvent-molecule interaction induced gating of charge transport through single-molecule junctions

To explore solvent gating of single-molecule electrical conductance due to solvent-molecule interactions, charge transport through single-molecule junctions with different anchoring groups in various solvent environments was measured by using the mechanically controllable break junction technique. We found that the conductance of single-molecule junctions can be tuned by nearly an order of magnitude by varying the polarity of solvent. Furthermore, gating efficiency due to solvent–molecule interactions was found to be dependent on the choice of the anchor group. Theoretical calculations revealed that the polar solvent shifted the molecular-orbital energies, based on the coupling strength of the anchor groups. For weakly coupled molecular junctions, the polar solvent–molecule interaction was observed to reduce the energy gap between the molecular orbital and the Fermi level of the electrode and shifted the molecular orbitals. This resulted in a more significant gating effect than that of the strongly coupled molecules. This study suggested that solvent–molecule interaction can significantly affect the charge transport through single-molecule junctions.