81 research outputs found
Effects of the Polymer Amount and pH on Proton Transport in Mesopores
Proton exchange membranes (PEMs) have various applications, such as in electrolysis technology for hydrogen generation, vanadium flow batteries for energy storage, and fuel cells for energy conversion. To increase PEM performance and expand the range of PEM applications, the underlying transport mechanisms of PEMs need to be understood. Mesoporous silica thin films are versatile model materials for proton transport investigation and are prepared with a pore size of â12 nm and film thickness of â565 nm by evaporationâinduced selfâassembly, providing an ordered, mesoporous, rigid matrix that allows us to deduce the structureâproperty relationship with respect to proton conductivity. Different amounts of sulfonic acidâbearing groups are introduced into the mesopores using the graftingâthrough polymerization of sulfopropylmethacrylate. The relationship between proton transport and the pH of the surrounding solution in polyâsulfopropylmethacrylateâfunctionalized mesopores is investigated using electrochemical impedance spectroscopy. The proton conductivity is found to depend on both the proton concentration in solution and the number of proton transporting groups inside the pore, indicating the major role of charge regulation and the confinement effect on proton transport
Recommended from our members
Mesoporous Coatings with Simultaneous LightâTriggered Transition of Water Imbibition and Droplet Coalescence
A systematic study of gating water infiltration and condensation into ceramic nanopores by carefully adjusting the wetting properties of mesoporous films using photoactive spiropyran is presented. Contact angle measurements from the side reveal significant changes in wettability after irradiation due to spiropyran/merocyanine-isomerization, which induce a wetting transition from dry to wet pores. The change in wettability allows the control of water imbibition in the nanopores and is reflected by the formation of an imbibition ring around a droplet. Furthermore, the photoresponsive wettability is able to overcome pinning effects and cause a movement of a droplet contact line, facilitating droplet coalescence, as recorded by high-speed imaging. The absorbed light not only effectuates droplet merging but also causes flows inside the drop due to heat absorption by the spiropyran, which results in gradients in the surface tension. IR imaging and particle tracking is used to investigate the heat absorption and temperature-induced flows, respectively. These flows can be used to manipulate, for example, molecular movement inside water and deposition inside solid mesoporous materials and are therefore of great importance for nanofluidic devices as well as for future water management concepts, which include filtering by imbibition and collection by droplet coalescence. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH Gmb
Mechanistic Understanding and ThreeâDimensional Tuning of Fluid Imbibition in SilicaâCoated Cotton Linter Paper Sheets
Paperâbased microfluidic devices are used in point of care diagnostic, sensor technology or labâonâaâchip devices. Although a number of studies has been reported, only relatively few paperâbased diagnostic tools are available on the market. A remaining challenge is the mechanistic understanding and precise design of capillary flow in paper. Here, silica coatings are applied to control paper wettability, fiber swelling, and thus fluid transport in all three dimensions of a paper sheet via a simple dipâcoating and postâtreatment process. By adjusting the threeâdimensional silica coating distribution, a threeâdimensional asymmetric wettability gradient within the paper sheet is obtained which controls the fluid distribution and imbibition. The correlation between silica coating amount and silica distribution with the resulting fluid behavior is systematically elaborated by analyzing the interaction between fiber and fluid as well as the fiber swelling by applying confocal microscopy. Three different silicaâamount dependent fluid distribution states are demonstrated. These new insights into the mechanism of fluid imbibition using simple silica coatings enable the specific design of different imbibition mechanisms and thus the adjustment of the microfluidic properties in paperâbased microfluidic devices with control over all three spatial dimensions of a paper sheet in one fabrication step
Fluid Flow Programming in Paper-Derived SilicaâPolymer Hybrids
In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control
Effects of the Polymer Amount and pH on Proton Transport in Mesopores
Abstract Proton exchange membranes (PEMs) have various applications, such as in electrolysis technology for hydrogen generation, vanadium flow batteries for energy storage, and fuel cells for energy conversion. To increase PEM performance and expand the range of PEM applications, the underlying transport mechanisms of PEMs need to be understood. Mesoporous silica thin films are versatile model materials for proton transport investigation and are prepared with a pore size of â12Â nm and film thickness of â565Â nm by evaporationâinduced selfâassembly, providing an ordered, mesoporous, rigid matrix that allows us to deduce the structureâproperty relationship with respect to proton conductivity. Different amounts of sulfonic acidâbearing groups are introduced into the mesopores using the graftingâthrough polymerization of sulfopropylmethacrylate. The relationship between proton transport and the pH of the surrounding solution in polyâsulfopropylmethacrylateâfunctionalized mesopores is investigated using electrochemical impedance spectroscopy. The proton conductivity is found to depend on both the proton concentration in solution and the number of proton transporting groups inside the pore, indicating the major role of charge regulation and the confinement effect on proton transport
Ultrashort Peptide Grafting on Mesoporous Films and Its Impact on Ionic Mesopore Accessibility
An approach for direct in-pore solid-phase ultrashort peptide synthesis on mesoporous films using the amino acids arginine, leucine, and glycine is presented. Although the number of grafted amino acids remains low, the ionic mesopore accessibility can be gradually adjusted. The addition of arginine in up to five reaction cycles leads to a progressive increase in positive mesopore charge density, which gradually increases the anionic mesopore accessibility at acidic pH. At basic pH, the remaining silanol groups at the pore wall still dominate counter-charged cation mesopore accessibility. Thus, specific peptide sequence design is demonstrated to be a sensitive tool for molecular transport control in nanoscale pores. Overall, the direct in-pore solid-phase ultrashort peptide synthesis on mesoporous films using the sequences of different amino acids opens up exciting opportunities for the development of innovative materials with precisely tailored properties and functions based on specific peptide sequence design
Programming Ionic Pore Accessibility in Zwitterionic Polymer Modified Nanopores
Creating switchable and gradually tunable pores or channels that display transport control similar to biological pores remains a major challenge in nanotechnology. It requires the generation and manipulation of complex charge situations at the nanoscale and the understanding of how confinement influences chemistry and transport. Here, two different pore sizes, âŒ100 nm and less than 10 nm, functionalized with varying amounts of responsive zwitterionic polycarboxybetaine methyl acrylate (PCBMA) give fascinating insight into the confinement controlled ionic transport of pores functionalized with pH-dependent zwitterionic polymers. Under basic conditions, the zwitterionic state offers complex, strongly pore-size-dependent ionic permselectivity characteristics. For mesoporous films with pore sizes smaller than 10 nm, complete ion exclusion is observed after reaching a critical zwitterionic polymer amount, clearly indicating an electrostatic behavior of âbipolar chargedâ pores. This ion exclusion is not observed for pore diameters of âŒ100 nm. In addition, the solution pH of equal pore accessibility for oppositely charged ions and pore sizes smaller than 10 nm shifts with increasing polymer amount from a pH of 2.5 to 8.2, and the quantity of ions accessing the pores depends on the pore size. These observations clearly show the potential of controlling pore accessibility based on controlled functional composition at the nanoscale without changing the components themselves as well as the influence of spatial confinement on pore accessibility in the presence of complex (zwitterionic) charged states
Gradually controlled wetting properties and its influence on ionic transport in mesoporous silica thin films
Pushing the limits of nanopore transport performance by polymer functionalization
Inspired by the design and performance of biological pores, polymer functionalization of nanopores has emerged as an evolving field to advance transport performance within the last few years. This feature article outlines developments in nanopore functionalization and the resulting transport performance including gating based on electrostatic interaction, wettability and ligand binding, gradual transport controlled by polymerization as well as functionalization-based asymmetric nanopore and nanoporous material design going towards the transport direction. Pushing the limits of nanopore transport performance and thus reducing the performance gap between biological and technological pores is strongly related to advances in polymerization chemistry and their translation into nanopore functionalization. Thereby, the effect of the spatial confinement has to be considered for polymer functionalization as well as for transport regulation, and mechanistic understanding is strongly increased by combining experiment and theory. A full mechanistic understanding together with highly precise nanopore structure design and polymer functionalization is not only expected to improve existing application of nanoporous materials but also opens the door to new technologies. The latter might include out of equilibrium devices, ionic circuits, or machine learning based sensors
Influence of Chain Architecture on Nanopore Accessibility in Polyelectrolyte BlockâCoâOligomer Functionalized Mesopores
- âŠ