skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Role of nanoparticle size and surface chemistry on ion transport and nanostructure of perfluorosulfonic acid ionomer nanocomposites
Title: Role of nanoparticle size and surface chemistry on ion transport and nanostructure of perfluorosulfonic acid ionomer nanocomposites
Herein, we present a systematic investigation of the impact of silica nanoparticle (SiNP) size and surface chemistry on the nanoparticle dispersion state and the resulting morphology and vanadium ion permeability of the composite ionomer membranes. Specifically, Nafion containing a mass fraction of 5% silica particles, ranging in nominal diameters from 10 nm to >1 μm and with both sulfonic acid- and amine-functionalized surfaces, was fabricated. Most notably, an 80% reduction in vanadium ion permeability was observed for ionomer membranes containing amine-functionalized SiNPs at a nominal diameter of 200 nm. Further, these membranes exhibited an almost 400% increase in proton selectivity when compared to pristine Nafion. Trends in vanadium ion permeability within a particular nominal diameter were seen to be a function of the surface chemistry, where, for example, vanadyl ion permeability was observed to increase with increasing particle size for membranes containing unfunctionalized SiNPs, while it was seen to remain relatively constant for membranes containing amine-functionalized SiNPs. In general, the silica particles tended to exhibit a higher extent of aggregation as the size of the particles was increased. From small-angle neutron scattering experiments, an increase in the spacing of the hydrophobic domains was observed for all composite membranes, though particle size and surface chemistry were seen to have varying impacts on the spacing of the ionic domains of the ionomer.  more » « less
Award ID(s):
1848347
PAR ID:
10337197
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Soft Matter
Volume:
18
Issue:
17
ISSN:
1744-683X
Page Range / eLocation ID:
3342 to 3357
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Journal of Materials Chemistry A)
    null (Ed.)
    Herein, a series of novel, lignin-based hydrogel composites was fabricated by incorporating ultraclean lignins (UCLs), of controlled molecular weight and low dispersity, into poly(vinyl alcohol) (PVA). The UCLs were obtained from a novel liquid–liquid fractionation of high dispersity crude bulk lignins (CBLs) obtained from Kraft black liquor. A complementary series of composite hydrogels was fabricated using these CBLs. Both the CBLs and UCLs were functionalized with vinyl-containing acrylate groups allowing the lignins to chemically crosslink with themselves, forming an interpenetrated network with the thermally-crosslinked network of PVA chains. Successful functionalization of the UCLs was demonstrated by proton and phosphorous nuclear magnetic resonance. PVA–lignin hydrogels containing 20 wt% UCL saw a reduction in methylene blue (MB) permeability by approximately two orders of magnitude when compared to neat PVA. Further, for composite hydrogels containing either 50 wt% UCL or CBL, no MB was detected in the receiving reservoir over the duration of the permeation experiment. In general, an increase in Young's moduli was observed in PVA–lignin hydrogels containing CBLs, where hydrogels composed of 50 wt% CBLs exhibited ∼40% increase when compared to neat PVA. In contrast, a ∼10% reduction in Young's moduli was observed for composite hydrogels containing 20 wt% UCLs or less, though these membranes exhibited the lowest MB permeabilities of all membranes investigated. However, the largest increase in membrane stiffness was observed for composite hydrogels containing 50 wt% UCLs, where a ∼70% increase in Young's modulus was observed. Finally, the concentration and functionalization of the lignins was seen to have a direct impact on the network structure of the soft composites, where in general, the molecular weight between crosslinks is seen to decrease with increasing lignin concentration. 
    more » « less
  2. ; ; ; ; (, Applied Spectroscopy)
    Infrared and Raman spectroscopy techniques were applied to investigate the drying and aggregation behavior of Nafion ionomer particles dispersed in aqueous solution. Gravimetric measurements aided the identification of gel-phase development within a series of time-resolved spectra that tracked transformations of a dispersion sample during solvent evaporation. A spectral band characteristic of ionomer sidechain end group vibration provided a quantitative probe of the dispersion-to-gel change. For sets of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra, adherence to Beer’s law was attributed to the relatively constant refractive index in the frequency region of hydrated -SO3 - group vibrations as fluorocarbon-rich ionomer regions aggregate in forming the structural framework of membranes and thin films. Although vibrational bands associated with ionomer backbone CF2 stretching vibrations were affected by distortion characteristic of wavelength-dependent refractive index change within a sample, the onset of band distortion signaled gel formation and coincided with ionomer mass % values just below the critical gelation point for Nafion aqueous dispersions. Similar temporal behavior was observed in confocal Raman microscopy experiments that monitored the formation of a thin ionomer film from an individual dispersion droplet. For the ATR FTIR spectroscopy and confocal Raman microscopy techniques, intensity in the water H-O-H bending vibrational band dropped sharply at the ionomer critical gelation point and displayed a time dependence consistent with changes in water content derived from gravimetric measurements. The reported studies lay groundwork for examining the impact of dispersing solvents and above-ambient temperatures on fluorinated ionomer transformations that influence structural properties of dispersion-cast membranes and thin films. 
    more » « less
  3. ; ; ; ; ; (, Journal of Applied Polymer Science)
    Abstract A carbon nanotubes (CNTs) reinforced Nafion membrane (CNT/N) with reduced interfacial resistance was prepared and served as a promising ion exchange membrane for vanadium redox flow batteries (VRFBs). The reinforcement of CNT effectively enhanced the tensile properties of Nafion membranes. The electrochemical properties of CNT/N membrane were analyzed by electrochemical impedance spectroscopy (EIS) and fitted with an analytical model to investigate the ionic and interfacial resistances. The EIS measurement reveals that the exposed CNT on the composite membrane surface significantly reduced the interfacial resistance of the membrane. The VRFB single cell performance of the CNT/N shows higher voltage efficiency (93% vs 89%) and energy efficiency (86% vs 83%) than recast Nafion at a current density of 40 mA cm−2. The cycling stability measurement showed that the discharge capacity retention of the VRFB cell equipped with CNT/N was greatly enhanced. The results suggest that the incorporation of CNT in ion exchange membrane is an effective approach for achieving lower membrane bulky and interfacial resistance, and thus, improving capacity retention, voltage, and energy efficiency. 
    more » « less
  4. ; ; ; ; ; (, Nanoscale)
    Silica nanomaterials have been studied based on their potential applications in a variety of fields, including biomedicine and agriculture. A number of different molecules have been condensed onto silica nanoparticles’ surfaces to present the surface chemistry needed for a given application. Among those molecules, (3-aminopropyl)triethoxysilane (APS) is one of the most commonly applied silanes used for nanoparticle surface functionalization to achieve charge reversal as well as to enable cargo loading. However, the colloidal stability of APS-functionalized silica nanoparticles has not been thoroughly studied, which can be problematic when the high reactivity of amine groups is considered. In this study, four different types of silica nanoparticles with varied location of added APS have been prepared via a reverse micro emulsion process, and their colloidal stability and dissolution behavior have been investigated. Systematic characterization has been accomplished using transmission electron microscopy (TEM), silicomolybdic acid (SMA) spectrophotometric assay, nitrogen adsorption–desorption surface area measurement, and aerosol ion mobility-mass spectrometry to track the nanoparticles’ physical and chemical changes during dissolution. We find that when APS is on the interior of the silica nanoparticle, it facilitates dissolution, but when APS is condensed both on the interior and exterior, only the exterior siloxane bonds experience catalytic hydrolysis, and the interior dissolution is dramatically suppressed. The observation and analyses that silica nanoparticles show different hydrolysis behaviors dependent on the location of the functional group will be important in future design of silica nanoparticles for specific biomedical and agricultural applications. 
    more » « less
  5. ; ; ; ; ; ; ; (, Advanced Materials Interfaces)
    Abstract Proton‐exchange membrane fuel cell vehicles offer a low‐carbon alternative to traditional oil fuel vehicles, but their performances still need improvement to be competitive. Raising their operating temperature to 120 °C will enhance their efficiency but is currently unfeasible due to the poor mechanical properties at high temperatures of the state‐of‐the‐art proton‐exchange membranes consisting of perfluorosulfonic acid (PFSA) ionomers. To address this issue, xx designed composite membranes made of two networks: a mat of hybrid fibers to maintain the mechanical properties filled with a matrix of PFSA‐based ionomer to ensure the proton conductivity. The hybrid fibers obtained by electrospinning are composed of intermixed domains of sulfonated silica and a fluorinated polymer. The inter‐fiber porosity is then filled with a PFSA ionomer to obtain dense composite membranes with a controlled fibers‐to‐ionomer ratio. At 80 °C, these obtained composite membranes show comparable performances to a pure PFSA commercial membrane. At 120 °C however, the tensile strength of the PFSA membrane drastically drop down to 0.2 MPa, while it is maintained at 7.0 MPa for the composite membrane. In addition, the composite membrane shows a good conductivity of up to 0.1 S cm −1 at 120 °C/90% RH, which increases with the ionomer content. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email