Characterization of sodium chloride and water transport in crosslinked poly(ethylene oxide) hydrogels
Introduction
Numerous studies have highlighted the application of poly(ethylene oxide) (PEO)-based materials in biomaterials, tissue engineering, drug delivery devices, pharmacy, implanted sensors, etc. [1], [2], [3], [4], [5], [6], [7], and PEO-based materials are often biocompatible, highly hydrophilic, and resistant to protein adhesion. In the last decade, such materials have also gained significant attention for gas [8], [9], [10], [11] and liquid [12], [13], [14] separations. Because of their favorable interaction with acid gases, crosslinked PEO (XLPEO) polymers have interesting performance for separating acid gases (e.g. carbon dioxide and hydrogen sulfide) from light gases and hydrocarbons [8], [9], [10], [11], [15], [16]. In water purification, PEO-based materials have been explored to modify the surface of existing ultrafiltration (UF) membranes, resulting in improved fouling resistance of these UF membranes [12], [13], [17], [18], [19], [20]. For example, applying a coating layer of XLPEO to a polysulfone (PSF) UF membrane simultaneously increases water flux and organic rejection in oil/water emulsion tests, leading to significantly improved fouling resistance against emulsified oil droplets [21], [22]. Additionally, PEO-based coatings enhance fouling resistance of desalination membranes [23].
As we face a global water shortage in the 21st century, a flexible and viable long-term strategy that can efficiently supply clean water is needed [24], [25]. Polymeric membranes are rapidly becoming the technology of choice for water desalination because they are cost-effective, small, and simple to operate and maintain [26]. Commercial reverse osmosis (RO) membranes are capable of rejecting more than 99% of ions such as Na+ and other contaminants to produce water that meets requirements for human consumption and other beneficial uses. Commercial RO membranes (e.g. aromatic polyamides) typically have rough surfaces with high chemical affinities for proteins, oil droplets, and other organic foulants, making these membranes susceptible to surface fouling by organic components [27]. XLPEO polymers are interesting candidates as RO coatings, because they may reduce surface roughness and control surface chemistry, rendering the surface more hydrophilic and endowing it with enhanced fouling resistance towards organic foulants [27], [28]. However, the influence of XLPEO coatings on salt transport properties of RO membranes is not well-known, in part due to a lack of fundamental studies on salt transport in XLPEO.
This study reports salt (i.e. NaCl) solubility, diffusivity, and permeability in three series of XLPEO materials. These polymers were synthesized via UV-photopolymerization of aqueous prepolymerization mixtures containing: (1) PEGDA (n = 10) (XLPEGDA10), (2) PEGDA (n = 13) (XLPEGDA13), and (3) PEGDA (n = 13) and PEGA (n = 7) (XLPEGDA/PEGA), respectively. The prepolymerization water content was varied from 0 to 80 wt.%. For the XLPEGDA/PEGA series, the PEGA monomer has essentially the same ethylene oxide content (about 82 wt.%) as that of the crosslinker, PEGDA [9], [28], thereby maintaining polymer chemical composition essentially constant across this series of materials.
Salt diffusivity and permeability are interpreted using a free volume model, using the equilibrium water content as an estimate of free volume, as suggested in the literature [29], [30], [31]. In addition, free volume in hydrated XLPEO samples was also estimated from positron annihilation lifetime spectroscopy (PALS) measurements, and the PALS results are compared with the equilibrium water content in these materials.
Section snippets
Materials
The crosslinkers, poly(ethylene glycol) diacrylates (PEGDA: n = 10 and 13, where n is the average number of ethylene oxide units in the PEGDA molecule, based on the manufacturer's reported molecular weight), and the monomer, poly(ethylene glycol) acrylate (PEGA: n = 7) were purchased from Sigma–Aldrich (Milwaukee, WI). n-Heptane and 1-hydroxycyclohexyl phenyl ketone (HCPK, photoinitiator) were purchased from Sigma–Aldrich. All chemicals were used as received. All water used in this study was
Results and discussion
Polymer density was characterized in order to estimate the water volume fraction in the samples. The average density values of dry XLPEGDA10, XLPEGDA13, and XLPEGDA/PEGA polymers were 1.205, 1.186, and 1.185 g/cm3, respectively, with a standard deviation of 0.004 g/cm3. The measured density results are consistent with previously reported values [9], [28]. Films prepared at various prepolymerization water contents have essentially the same density, indicating that prepolymerization water content
Conclusions
Three series of XLPEO films were synthesized at various prepolymerization contents, and NaCl transport properties of these films were studied. Increasing prepolymerization water content systematically decreases effective crosslink density, resulting in increasing equilibrium water content in XLPEO films. XLPEO films with higher equilibrium water content generally exhibit higher NaCl and water permeability, but lower permeability selectivity for water over NaCl, indicating a distinct tradeoff
Acknowledgements
We gratefully acknowledge partial support of this research by the National Science Foundation (Grant IIP-0917971 and CBET-0932781/0931761). CSIRO's Water for a Healthy Country Flagship is acknowledged for their support of the internal membrane research program and this international collaboration.
References (64)
- et al.
Release of protein from highly cross-linked hydrogels of poly(ethylene glycol) diacrylate fabricated by UV polymerization
Biomaterials
(2001) - et al.
Characterization of permeability and network structure of interfacially photopolymerized poly(ethylene glycol) diacrylate hydrogels
Biomaterials
(1998) - et al.
Mass transfer in rapidly photopolymerized poly(ethylene glycol) hydrogels used for chemical sensing
Polymer
(2001) - et al.
Diffusion of small molecular weight drugs in radiation-crosslinked poly(ethylene oxide) hydrogels
Journal of Controlled Release
(1996) - et al.
Gas solubility, diffusivity and permeability in poly(ethylene oxide)
Journal of Membrane Science
(2004) - et al.
Transport and structural characteristics of crosslinked poly(ethylene oxide) rubbers
Journal of Membrane Science
(2006) - et al.
Materials selection guidelines for membranes that remove CO2 from gas mixtures
Journal of Molecular Structure
(2005) - et al.
Dense hydrophilic composite membranes for ultrafiltration
Journal of Membrane Science
(1995) - et al.
Photo-induced graft polymerization surface modifications for the preparation of hydrophilic and low-protein-adsorbing ultrafiltration membranes
Journal of Membrane Science
(1996) - et al.
Modification of polysulfone ultrafiltration membranes with UV irradiation and hydrophilicity increasing agents
Journal of Membrane Science
(1991)
Increasing membrane permeability of UV-modified poly(ether sulfone) ultrafiltration membranes
Journal of Membrane Science
Low fouling synthetic membranes by UV-assisted graft polymerization: monomer selection to mitigate fouling by natural organic matter
Journal of Membrane Science
Surface modification of ultrafiltration membranes by low temperature plasma. II. Graft polymerization onto polyacrylonitrile and polysulfone
Journal of Membrane Science
Crosslinked poly(ethylene oxide) fouling resistant coating materials for oil/water separation
Journal of Membrane Science
Effects of polyether–polyamide block copolymer coating on performance and fouling of reverse osmosis membranes
Journal of Membrane Science
PEG-based hydrogel membrane coatings
Polymer
Preparation and characterization of crosslinked poly(ethylene glycol) diacrylate hydrogels as fouling-resistant membrane coating materials
Journal of Membrane Science
The solution-diffusion model: a review
Journal of Membrane Science
Reformulation of the solution-diffusion theory of reverse osmosis
Journal of Membrane Science
Partitioning and diffusion of solutes in hydrogels of poly(ethylene oxide)
Biomaterials
Positron annihilation—a probe for nanoscale voids and free volume?
Progress in Polymer Science
Macroporous copolymer networks
Progress in Polymer Science
Positron annihilation spectroscopy for chemical analysis: a novel probe for microstructural analysis of polymers
Microchemical Journal
Structure and mobility in water plasticized poly(ethylene oxide)
Polymer
Poly(ethylene glycol): Chemistry and Biological Applications
Biomedical membranes from hydrogels and interpolymer complexes
Advances in Polymer Science
Plasticization-enhanced hydrogen purification using polymeric membranes
Science
Gas and liquid separations using membranes: an overview
ACS Symposium Series
Gas and vapor solubility in cross-linked poly(ethylene glycol diacrylate)
Macromolecules
The effect of cross-linking on gas permeability in cross-linked poly(ethylene glycol diacrylate)
Macromolecules
Synthesis and characterization of surface coated ultrafiltration membranes to enhance oil/water fouling resistance
PMSE Preprints
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