Fabrication of Ultrathin Membrane via Layer-by-Layer Self-assembly Driven by Hydrophobic Interaction Towards High Separation Performance

Abstract

A novel and facile layer-by-layer (LbL) selfassembly process driven by hydrophobic interaction and then reinforced by hydrogen bond was developed to prepare ultrathin membranes. Gelatin (GE) and tannic acid (TA) were alternately deposited on polyacrylonitrile (PAN) ultrafiltration membranes to obtain GE/TA membranes. The required number of deposition cycles for acceptable permselectivity of membrane was greatly reduced compared with that of the traditional LbL self-assembly process and could be ascribed to the rapid growth of membrane thickness and the integrity of the innermost gelatin layer. Higher surface hydrophilicity and more appropriate free volume characteristics were obtained for GE/TA multilayer membranes compared with pristine gelatin membrane. Moreover, the GE/TA multilayer membrane exhibited improved stability even at high water content of 30 wt %. The membrane separation experiments with pervaporation dehydration of ethanol aqueous solution as a model system demonstrated the GE/TA multilayer membrane achieved higher water permselectivity than the pristine gelatin membrane. High operation stability was acquired in the long-term membrane separation test. KEYWORDS: gelatin/tannic acid, layer-by-layer self-assembly, hydrophobic interaction, hydrogen bond, ultrathin membranes ■ INTRODUCTIONAs a facile method to prepare ultrathin films with tunable thickness, composition, structure, and permeability, layer-bylayer (LbL) self-assembly has received considerable research attention and exhibited prospective applications in realms such as membrane-based separation, 1,2 drug delivery, 3,4 biosensors, 5 and microreactors. 6,7 The most deeply studied driving force for LbL self-assembly is the electrostatic interaction between oppositely charged species (mainly polyelectrolytes). 8,9 In each assembly step, a polyelectrolyte layer is adsorbed on the charged substrate and reverses the surface charge so that in the next assembly step a polyelectrolyte layer with opposite charge can be adsorbed.10 With the development of LbL self-assembly technique, diverse functions and properties are often demanded for multilayer films, which require a broader range of components beyond charged species. As a result, constructing multilayer films on the basis of non-electrostatic interactions such as hydrophobic interaction, 11 hydrogen bond, 12,13 and metal−ligand coordination 6,9 has gained more and more attention. 8 Hydrophobic interaction refers to the interaction formed between hydrophobic groups in an aqueous environment under enthalpy effect and entropy effect, which makes the hydrophobic groups cluster to reduce their exposure to water molecules. Several researches have been carried out to investigate the functions of hydrophobic interaction in LbL self-assembly.14−17 Based on the experimental data and theoretical models, Kotov 15 confirmed that hydrophobic interaction was one of the decisive factors for forming polyelectrolyte multilayers. Furthermore, hydrophobic interaction can promote the assembly of weak polye...

Fabricating graphene oxide-based ultrathin hybrid membrane for pervaporation dehydration via layer-by-layer self-assembly driven by multiple interactions

“…The hybrid multilayer membranes were fabricated via LbL self-assembly employing a home-made single-side dip-coating device to avoid the deposition of GE and GO on the nonwoven fabric side of ultrafiltration membrane [19]. 2 mg/ml GE solution was prepared by dissolving GE in deionized water at 60 o C and stirring for 1h.…”

“…Manipulating the multiple interactions between GO and the pairing polymer, thus making the utmost use of the various groups on GO will be a facile approach to increase interaction sites between adjacent layers and create more stable interfaces [8]. Gelatin (GE) is a natural protein with both hydrophilic and hydrophobic amino acid side chains [19]. As a polyampholyte, GE is positively charged under acidic condition arising from protonated amino groups [19].…”

“…Gelatin (GE) is a natural protein with both hydrophilic and hydrophobic amino acid side chains [19]. As a polyampholyte, GE is positively charged under acidic condition arising from protonated amino groups [19]. Consequently, multiple interactions including electrostatic attraction, hydrogen bond and hydrophobic interaction can be formed between GE and GO.…”

“…Consequently, multiple interactions including electrostatic attraction, hydrogen bond and hydrophobic interaction can be formed between GE and GO. In addition, GE is a suitable membrane material utilized in water-related separation processes due to its high hydrophilicity and excellent film-forming ability [19,20].…”

Enhanced pervaporation performance of MIL-101 (Cr) filled polysiloxane hybrid membranes in desulfurization of model gasoline

“…Permeance and selectivity were calculated to reveal the intrinsic separation properties of the membranes. Permeance of liquid component i, (P/l) i (GPU, Baker et al, 2010;Zhao et al, 2013) is defined as…”