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We describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities

Spraying asymmetry into functional membranes layer-by-layer

NATURE MATERIALS, no. 6 (2009): 512.0-518

被引用295|浏览8
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摘要

As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membr...更多

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简介
  • As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation.
  • Similar to the way in which many naturally occurring membranes simultaneously regulate mass transfer and undergo chemical reactions with solute molecules, this technique enables portions of the textile to act as an inert barrier while the bulk material acts as a high-surface-area scaffold capable of a wide variety of functionalities.
重点内容
  • As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation
  • By drawing a pressure gradient across porous substrates during the spray-assisted layer-by-layer process, we have found that highly conformal coatings can be developed on individual fibres, wires or pores throughout the thickness of the bulk porous substrate
  • ES nylon treated with vac(PDAC/TiO2)[25] shows high surface area for catalytic reaction, degrading 15% of the chloroethyl ethyl sulphide (CEES) dosage when exposed to ultraviolet light, but the reaction remains rate limited by the rate of adsorption of CEES onto the fibre surfaces, enabling significant amounts of CEES contaminant to move diffusively through the highly porous mat. (Note: to confirm that TiO2 is necessary for CEES degradation a negative control test using untreated nylon under ultraviolet light was conducted
  • The dramatic increase in surface area observed when as-spun nylon fibres are conformally treated with (PDAC/TiO2)[25] coatings does not translate to increased photocatalytic ability until a barrier layer is added to mitigate vapour-phase diffusion through the membrane and increase the residence time for reaction to occur
  • Selecting materials that fit this criterion, we demonstrate the creation of asymmetrically functionalized ES membranes using the weak-polyelectrolyte systems (LPEI/poly(acrylic acid) (PAA))n at pH 5 and (PAMAM/PAA)n at pH 4, as well as the strong polyelectrolyte system (PDAC/PAA)n, as bridging agents
  • Mats were flipped and sprayed with either PAMAM and PAA titrated to pH 4 or such as poly(sodium 4-styrenesulfonate) (SPS) and poly(dimethyldiallylammonium chloride) (PDAC) titrated to pH 10 to develop 50-bilayer coatings, or linear poly(ethyleneimine) (LPEI) and PAA titrated to pH 5 to develop 100-bilayer coatings
结果
  • An ES nylon sample that has been treated with (PDAC/TiO2)[25] in the presence of a pressure gradient to create a high-surface-area photocatalytic region, followed by (PAMAM/PAA)[50] treatment in the absence of a gradient to create a CEES transport barrier, can be seen in its entirety.
  • ES nylon treated with vac(PDAC/TiO2)[25] shows high surface area for catalytic reaction, degrading 15% of the CEES dosage when exposed to ultraviolet light, but the reaction remains rate limited by the rate of adsorption of CEES onto the fibre surfaces, enabling significant amounts of CEES contaminant to move diffusively through the highly porous mat.
  • The dramatic increase in surface area observed when as-spun nylon fibres are conformally treated with (PDAC/TiO2)[25] coatings does not translate to increased photocatalytic ability until a barrier layer is added to mitigate vapour-phase diffusion through the membrane and increase the residence time for reaction to occur.
  • The remaining 90% of the mat contains conformal vac(PDAC/TiO2) functionality, and is capable of degrading contaminant molecules, with the aid of ultraviolet light, during their prolonged residence time in this portion of the membrane.
  • When compared with ES vac(PDAC/TiO2) material with no bridged layer, ES vac(PDAC/TiO2) + (PAMAM/PAA)[50] samples demonstrate an increase in photocatalytic capability from 15 to 74%, while maintaining a water-vapour flux of 14.2 kg m−2-d−1.
  • Measured photocatalytic capabilities as well as water-vapour flux rates for ES vac(PDAC/TiO2) + (PDAC/SPS)[50] and ES vac(PDAC/TiO2) + (LPEI/PAA)[100] are tabulated in Table 1 along with BET surface areas for the two best-performing films.
结论
  • The ability to control chemical identity, thickness and degree of bridging in the flux-limiting portion of the membrane enables enhancement of the reactive properties while maintaining membrane breathability, producing an engineered textile that shows the reactive capability of non-porous barrier materials and water-vapour flux similar to that of highly porous untreated ES mats.
  • ES vac(PDAC/TiO2) + (PAMAM/PAA)[50] shows a significant decrease in membrane surface area due to the pore-bridging ability of the dendritic PAMAM molecules, as well as high water-vapour flux due to their hydrophilic nature.
总结
  • As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation.
  • Similar to the way in which many naturally occurring membranes simultaneously regulate mass transfer and undergo chemical reactions with solute molecules, this technique enables portions of the textile to act as an inert barrier while the bulk material acts as a high-surface-area scaffold capable of a wide variety of functionalities.
  • An ES nylon sample that has been treated with (PDAC/TiO2)[25] in the presence of a pressure gradient to create a high-surface-area photocatalytic region, followed by (PAMAM/PAA)[50] treatment in the absence of a gradient to create a CEES transport barrier, can be seen in its entirety.
  • ES nylon treated with vac(PDAC/TiO2)[25] shows high surface area for catalytic reaction, degrading 15% of the CEES dosage when exposed to ultraviolet light, but the reaction remains rate limited by the rate of adsorption of CEES onto the fibre surfaces, enabling significant amounts of CEES contaminant to move diffusively through the highly porous mat.
  • The dramatic increase in surface area observed when as-spun nylon fibres are conformally treated with (PDAC/TiO2)[25] coatings does not translate to increased photocatalytic ability until a barrier layer is added to mitigate vapour-phase diffusion through the membrane and increase the residence time for reaction to occur.
  • The remaining 90% of the mat contains conformal vac(PDAC/TiO2) functionality, and is capable of degrading contaminant molecules, with the aid of ultraviolet light, during their prolonged residence time in this portion of the membrane.
  • When compared with ES vac(PDAC/TiO2) material with no bridged layer, ES vac(PDAC/TiO2) + (PAMAM/PAA)[50] samples demonstrate an increase in photocatalytic capability from 15 to 74%, while maintaining a water-vapour flux of 14.2 kg m−2-d−1.
  • Measured photocatalytic capabilities as well as water-vapour flux rates for ES vac(PDAC/TiO2) + (PDAC/SPS)[50] and ES vac(PDAC/TiO2) + (LPEI/PAA)[100] are tabulated in Table 1 along with BET surface areas for the two best-performing films.
  • The ability to control chemical identity, thickness and degree of bridging in the flux-limiting portion of the membrane enables enhancement of the reactive properties while maintaining membrane breathability, producing an engineered textile that shows the reactive capability of non-porous barrier materials and water-vapour flux similar to that of highly porous untreated ES mats.
  • ES vac(PDAC/TiO2) + (PAMAM/PAA)[50] shows a significant decrease in membrane surface area due to the pore-bridging ability of the dendritic PAMAM molecules, as well as high water-vapour flux due to their hydrophilic nature.
表格
  • Table1: Permeability to CEES and water vapour shown by multifunctionalized samples
Download tables as Excel
基金
  • This research was supported in part by the US Army through the Institute for Soldier Nanotechnologies under contract DAAD-19-02-0002 with the US Army Research Office, and by the G
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