Two-Step Thermoresponsive Ultrafiltration Membranes from Polymerization of Lyotropic Liquid Crystals

Abstract

In this study, we present the fabrication of a two-step thermoresponsive ultrafiltration (UF) membrane through polymerization of a lyotropic liquid crystal (LLC). A mixture of commercially available Pluronic F127 block copolymer, water (containing ammonium persulfate as the initiator), and polymerizable oil (n-butyl acrylate/ethylene glycol dimethacrylate) is used to create an LLC with a lamellar structure, as characterized by cross-polarized light microscopy and atomic force microscopy. Differential scanning calorimetry is employed to evaluate the thermoresponsive behavior of the polymerized LLC (polyLLC). Two-step thermoresponsiveness (∼35 and ∼50 °C) of the polyLLC is observed due to the lower critical solution temperature (LCST) of F127 and melting of the crystalline structure of the polyethylene oxide (PEO) chains of the F127 surfactant. In the next step, the obtained mesophase is cast on a nonwoven polyester support sheet followed by thermal polymerization. The hydration capacity, water flux, water flux recovery after fouling, and molecular weight cutoff (MWCO) of the obtained membrane are evaluated at different temperatures to examine its thermoresponsiveness. The experimental results reveal that the UF membrane has a reversible thermoresponsive behavior at the LCST and PEO melting of polyLLC. Additionally, the cleaning efficiency of the fouled membrane can be enhanced by using its thermoresponsive behavior, resulting in an extended lifetime of the product. Furthermore, the MWCO of the membrane can be altered with temperature due to the pore size change with temperature stimulus.

Fibrous Structures: An Overview of Their Responsiveness to External Stimuli towards Intended Application

“…Leveraging the extensive surface area of clothing textiles, they can be transformed into smart interfaces, offering benefits in managing temperature and moisture for the wearer [47], providing active thermoregulation [48]. Other example are filtration membranes, where temperature-sensitive materials can optimize the filtration efficiency by adjusting pore size in response to temperature changes [49]. Furthermore, in biomedical applications, fibrous structures designed to respond to temperature fluctuation can be used in drug delivery systems [50].…”

“…This brought about a further increase in the molecular weight cutoff to 570 kDa (pore size ~50 nm). These temperature-induced alterations contributed to increased membrane porosity, leading to improved hydration capacity, enhanced permeability, and improved cleaning efficiency, particularly in dealing with fouled membranes [49].…”

“…Alongside the techniques outlined above, there are other methods used to make responsive structures. Saadat et al [49], for instance, prepared nonwoven thermo-responsive membranes by casting lyotropic liquid crystals (LLC) on nonwoven polyester sheets. The LLC were prepared with PEO-PPO-PEO, ammonium persulfate (APS), n-butyl acrylate (nBA) and EGDMA.…”

“…As mentioned above, multiple techniques have been applied in the construction of responsive fibrous structures. Many of them are based on the integration of responsive elements, like PCMs, SMPs and responsive polymers [30,32,49,105,160], while few make use of the properties of materials to endow the structures with the capacity to respond to stimuli [162,163]. Nevertheless, it is evident that the interest in SMPs and responsive polymers is increasing, while PCMs and chromic materials already appear to be more established.…”

Self-Assembled Nanofiltration Membranes with Thermo- and pH-Responsive Behavior

“…The incorporation of stimuli-responsiveness into membranes can offer new opportunities for applications by enabling dynamic selectivity and permeability, − and enhanced cleaning of a fouled membrane. ,, While there are some reports on the production of stimuli-responsive ultrafiltration (UF) membranes by using LLC templates, , there are only a few studies in the literature available on the synthesis of stimuli-responsive NF membranes from LLC templates. Zhu et al reported an LLC-based sodium selective isoporous membrane, which offered ion conductive channels lined with carboxylate groups.…”