Cleaning of Oil Fouling with Water Enabled by Zwitterionic Polyelectrolyte Coatings: Overcoming the Imperative Challenge of Oil–Water Separation Membranes

Abstract

Herein we report a self-cleaning coating derived from zwitterionic poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC) brushes grafted on a solid substrate. The PMPC surface not only exhibits complete oil repellency in a water-wetted state (i.e., underwater superoleophobicity), but also allows effective cleaning of oil fouled on dry surfaces by water alone. The PMPC surface was compared with typical underwater superoleophobic surfaces realized with the aid of surface roughening by applying hydrophilic nanostructures and those realized by applying smooth hydrophilic polyelectrolyte multilayers. We show that underwater superoleophobicity of a surface is not sufficient to enable water to clean up oil fouling on a dry surface, because the latter circumstance demands the surface to be able to strongly bond water not only in its pristine state but also in an oil-wetted state. The PMPC surface is unique with its described self-cleaning performance because the zwitterionic phosphorylcholine groups exhibit exceptional binding affinity to water even when they are already wetted by oil. Further, we show that applying this PMPC coating onto steel meshes produces oil-water separation membranes that are resilient to oil contamination with simply water rinsing. Consequently, we provide an effective solution to the oil contamination issue on the oil-water separation membranes, which is an imperative challenge in this field. Thanks to the self-cleaning effect of the PMPC surface, PMPC-coated steel meshes can not only separate oil from oil-water mixtures in a water-wetted state, but also can lift oil out from oil-water mixtures even in a dry state, which is a very promising technology for practical oil-spill remediation. In contrast, we show that oil contamination on conventional hydrophilic oil-water separation membranes would permanently induce the loss of oil-water separation function, and thus they have to be always used in a completely water-wetted state, which significantly restricts their application in practice.

Adaptable bioinspired special wetting surface for multifunctional oil/water separation

“…Most of the materials fabricated using existing technologies can separate only one of the two fluids, and separating the other one requires a different technology151617181920212223242526272829303132333435363738. The possibility to selectively separate both fluids using the same material offers flexibility for different oil/water separation applications.…”

“…As a result, multiple fabrication techniques and materials are used to realize seemingly similar oil/water separation tasks. For example, aerogels, powders, graphene oxide films, sponges modified with graphene, carbon nanotubes (CNT), nanoparticles or low-surface energy chemicals are used for oil absorption from water415161718192021222324; superhydrophobic CNT membranes, metal meshes or textiles chemically modified or coated with metal oxide nanoparticles and nanorods are utilized for oil filtration from oil/water mixtures25262728293031; and underwater superoleophobic porous nanotube membranes, meshes and textiles modified with palygorskite powders, zeolites, TiO 2 nanostructures, nanoparticles, zwitterionic polymers or cellulose aerogels are used for filtrating water from oil/water mixtures3233343536373839. To ensure a better control over the oil/water separation process, materials which switch their wetting properties in response to external stimuli such as changing electric or magnetic field, pH, temperature or light illumination, and pre-wetted materials were developed64041424344.…”

Superdurable Coating Fabricated from a Double‐Sided Tape with Long Term “Zero” Bacterial Adhesion

“…This implied the surface of the DURA-Z coating had superior antifouling property as good as a zwitterionic hydrogel. [8] Water contact angle (Figure 2b) indicated that the DURA-Z coating was superhydrophilic with great wettability (the water drop spread out quickly as demonstrated by Movie S1 in the Supporting Information), similar to pure PCBAA hydrogel surface.…”

“…Superhydrophilic zwitterionic polymer materials are known for their superior antifouling properties. [8] But they, like common hydrophilic coatings, drastically tend to dissolve in the aqueous environment resulting in poor coating durability. [9,10] The vulnerability to mechanical damages further prevents these hydrophilic coatings from being practically applied.…”

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane

“…In general, water is used to clean the fouled membrane surface. However, it is difficult to fully remove the organic materials of AEMs25. A current strategy for controlling membrane fouling is to cross-link an antifouling layer on the surface of the AEMs26272829.…”