Separating oil-water mixtures is critical in a variety of practical applications, including the treatment of industrial wastewater, oil spill cleanups, as well as the purification of petroleum products. Among various methodologies that have been utilized, membranes are the most attractive technology for separating oil-water emulsions. In recent years, selective wettability membranes have attracted particular attention for oil-water separations. The membrane surfaces with hydrophilic and in-air oleophobic wettability have demonstrated enhanced effectiveness for oil-water separations in comparison with underwater oleophobic membranes. However, developing a hydrophilic and in-air oleophobic surface for a membrane is not a trivial task. The coating delamination process is a critical challenge when applying these membranes for separations. Inspired by the above, in this study we utilize poly(ethylene glycol)diacrylate (PEGDA) and 1H,1H,2H,2H-heptadecafluorodecyl acrylate (F-acrylate) to fabricate a hydrophilic and in-air oleophobic coating on a filter. We utilize methacryloxypropyl trimethoxysilane (MEMO) as an adhesion promoter to enhance the adhesion of the coating to the filter. The filter demonstrates robust oil repellency preventing oil adhesion and oil fouling. Utilizing the filter, gravity-driven and continuous separations of surfactant-stabilized oil-water emulsions are demonstrated. Finally, we demonstrate that the filter can be reused multiple times upon rinsing for further oil-water separations.
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Reduced Biofilm Formation at the Air–Liquid–Solid Interface via Introduction of Surfactants
Reduced biofilm formation is highly desirable in
applications ranging from transportation to separations and
healthcare. Biofilms often form at the three-phase interface
where air, liquid, and solid coexist due to the close proximity to
nutrients and oxygen. Reducing biofilm formation at the triple
interface presents challenges because of the conflicting requirements
for hydrophobicity at the air−solid interface (for selfcleaning
properties) and for hydrophilicity at the liquid−solid
interface (for reduced foulant adhesion). Meeting those needs
simultaneously likely entails a dynamic surface, capable of shifting
the surface energy landscape in response to wetting conditions and
thus enabling hydrophobicity in air and hydrophilicity in water.
Here, we designed a facile approach to render existing surfaces
resistant to biofilm formation at the triple interface. By adding trace amounts (∼0.1 mM) of surfactants, biofilm formation of
Pseudomonas aeruginosa (known to form biofilm at the triple interface) was reduced on all surfaces tested, ranging from hydrophilic
to hydrophobic, polar to nonpolar. That reduced fouling was not a result of the known antimicrobial effects. Instead, it was attributed
to the surface-adsorbed surfactants that dynamically control surface energy at the triple interface. To further understand the effect of
surfactant−surface interactions on biofilm reduction, we systematically varied the surfactant charge type and surface properties
(surface energy and charge). Electrostatic interactions between surfactants and surfaces were identified as an influential factor when
predicting the relative fouling reduction upon introduction of surfactants. Nevertheless, biofilm formation was reduced even on the
charge-neutral, fluorinated surface made of poly(1H, 1H, 2H, 2H-perfluorodecyl acrylate) by more than 2-fold simply via adding 0.2
mM dodecyl trimethylammonium chloride or 0.3 mM sodium dodecyl sulfate. Given its robustness, this strategy is broadly
applicable for reducing fouling on existing surfaces, which in turn improves the cost-effectiveness of membrane separations and
mitigates contaminations and nosocomial infections in healthcare.
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- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10227956
- Date Published:
- Journal Name:
- ACS Biomaterials Science & Engineering
- ISSN:
- 2373-9878
- Page Range / eLocation ID:
- 1-12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Biofouling at the solid–liquid–air interface poses a serious threat to public health and environmental sustainability. Despite the variety of antifouling materials developed, few have proven to resist fouling at the three‐phase contact line. In fact, antifouling at the liquid–solid interface and the air–solid interface call for opposite surface properties—hydrophilic for the former and hydrophobic for the latter. By devising a new design strategy, one that maximizes the mismatch of surface energies of comonomers for dynamic chain reorientation at the three‐phase contact line, an antifouling amphiphilic copolymer is obtained. The novel amphiphilic copolymer reduces the formation of biofilms by
Pseudomonas aeruginosa and outperforms a zwitterionic polymer, the current leading antifouling chemistry. The copolymer is synthesized using initiated chemical vapor deposition (iCVD), which leads to molecular‐level heterogeneities composed of zwitterionic and fluorinated moieties by avoiding undesirable surface tension effects. Atomic force microscopy, x‐ray diffractometry, and Fourier transform infrared spectroscopy confirm the copolymer's amphiphilicity and lack of microphase separation. Scanning electron microscopy provides visual confirmation of the diminished biofilm growth. The versatile iCVD technique is amenable to a range of substrates and enables the application of this new material to food processing, healthcare, and underwater performance. -
Bicontinuous interfacially jammed emulsion gels (bijels) formed via solvent transfer induced phase separation (STrIPS) are new soft materials with potential applications in separations, healthcare, or catalysis. To facilitate their applications, means to fabricate STrIPS bijels with nanoparticles of various surface chemistries are needed. Here, we investigate the formation of STrIPS bijels with nanoparticles of different wettabilities, ranging from partially hydrophobic to extremely hydrophilic. To this end, the surface wettability of silica nanoparticles is tailored by functionalization with ligands bearing either hydrophobic or hydrophilic terminal groups. We show that partially hydrophobic particles with acrylate groups can impart short-term stability to STrIPS bijels on their own. However, to enable long-term stability, the use of cationic surfactants is needed. Partially hydrophobic particles require short chain surfactants for morphological stability while glycerol-functionalized hydrophilic particles require double chain cationic surfactants. Variation of the surfactant concentration results in various STrIPS bijel morphologies with controllable domain sizes. Last, we show that functional groups on the nanoparticles facilitate interfacial cross-linking for the purposes of reinforcing STrIPS bijels. Our research lays the foundation for the use of a wide variety of solid particles, irrespective of their surface wettabilities, to fabricate bijels with potential applications in Pickering interfacial catalysis and as cross-flow microreactors.more » « less
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The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO100PO65EO100) and Pluronic P123 (EO19PO69EO19), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.more » « less
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Achieving reversible and tunable assembly of silica nanoparticles at liquid–liquid interfaces is vital for a wide range of scientific and technological applications including sustainable subsurface energy applications, catalysis, drug delivery and material synthesis. In this study, we report the mechanisms controlling the assembly of silica nanoparticles (dia. 50 nm and 100 nm) at water–heptane and water–toluene interfaces using sodium dodecyl sulfate (SDS) surfactant with concentrations ranging from 0.001–0.1 wt% using operando ultrasmall/small-angle X-ray scattering, cryogenic scanning electron microscopy imaging and classical molecular dynamics simulations. The results show that the assembly of silica nanoparticles at water–hydrocarbon interfaces can be tuned by controlling the concentrations of SDS. Silica nanoparticles are found to: (a) dominate the interfaces in the absence of interfacial SDS molecules, (b) coexist with SDS at the interfaces at low surfactant concentration of 0.001 wt% and (c) migrate toward the aqueous phase at a high SDS concentration of 0.1 wt%. Energetic analyses suggest that the van der Waals and electrostatic interactions between silica nanoparticles and SDS surfactants increase with SDS concentration. However, the favorable van der Waals and electrostatic interactions between the silica nanoparticles and toluene or heptane decrease with increasing SDS concentration. As a result, the silica nanoparticles migrate away from the water–hydrocarbon interface and towards bulk water at higher SDS concentrations. These calibrated investigations reveal the mechanistic basis for tuning silica nanoparticle assembly at complex interfaces.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsbiomaterials.0c01691
