Slippery for scaling resistance in membrane distillation: a novel porous micropillared superhydrophobic surface

Scaling in membrane distillation (MD) is a key issue in desalination of concentrated saline water, where the interface property between the membrane and the feed become critical. In this paper, a slippery mechanism was explored as an innovative concept to understand the scaling behavior in membrane distillation for a soluble salt, NaCl. The investigation was based on a novel design of a superhydrophobic polyvinylidene fluoride (PVDF) membrane with micro-pillar arrays (MP-PVDF) using a micromolding phase separation (μPS) method. The membrane showed a contact angle of 166.0 ± 2.3° and the sliding angle of 15.8 ± 3.3°. After CF4 plasma treatment, the resultant membrane (CF4-MP-PVDF) showed a reduced sliding angle of 3.0o. In direct contact membrane distillation (DCMD), the CF4-MP-PVDF membrane illustrated excellent anti-scaling in concentrating saturated NaCl feed. Characterization of the used membranes showed that aggregation of NaCl crystals occurred on the control PVDF and MP-PVDF membranes, but not on the CF4-MP-PVDF membrane. To understand this phenomenon, a “slippery” theory was introduced and correlated the sliding angle to the slippery surface of CF4-MP-PVDF and its anti-scaling property. This work proposed a well-defined physical and theoretical platform for investigating scaling problems in membrane distillation and beyond

Unprecedented scaling/fouling resistance of omniphobic polyvinylidene fluoride membrane with silica nanoparticle coated micropillars in direct contact membrane distillation

Recent development of omniphobic membranes shows promise in scaling/fouling mitigation in membrane distillation (MD), however, the fundamental understanding is still under dispute. In this paper, we report a novel omniphobic micropillared membrane coated by silica nanoparticles (SiNPs) (SiNPs-MP-PVDF) with dual-scale roughness prepared by a micromolding phase separation (μPS) and electrostatic attraction. This membrane was used as a model for analysis of scaling behavior by calcium sulfate (CaSO4) scaling and fouling behavior by protein casein in comparison with commercial (C-PVDF) and micropillared (MP-PVDF) membranes. Unprecedented scaling/fouling resistance to CaSO4 and casein was observed in direct contact membrane distillation (DCMD) for SiNPs-MP-PVDF membrane. Similar scaling and fouling occurred for commercial PVDF and micropillared PVDF membranes. The observation corresponds well to the wetting state of all membranes as SiNPs-MP-PVDF shows suspended wetting, but MP-PVDF shows pinned wetting. From a hydrodynamic view, the suspended wetting attributes a slippery surface which reduces the direct contact of foulants to solid membrane part and leads to significantly reduced fouling and scaling. However, a pinned (or metastable) wetting state leads to a stagnant interfacial layer that is prone to severe fouling and scaling. This work highlights that both scaling and fouling resistance are indeed of suspended wetting state and slippage origin

Diffusion of hydrophobin proteins in solution and interactions with a graphite surface

<p>Abstract</p> <p>Background</p> <p>Hydrophobins are small proteins produced by filamentous fungi that have a variety of biological functions including coating of spores and surface adhesion. To accomplish these functions, they rely on unique interface-binding properties. Using atomic-detail implicit solvent rigid-body Brownian dynamics simulations, we studied the diffusion of HFBI, a class II hydrophobin from <it>Trichoderma reesei</it>, in aqueous solution in the presence and absence of a graphite surface.</p> <p>Results</p> <p>In the simulations, HFBI exists in solution as a mixture of monomers in equilibrium with different types of oligomers. The oligomerization state depends on the conformation of HFBI. When a Highly Ordered Pyrolytic Graphite (HOPG) layer is present in the simulated system, HFBI tends to interact with the HOPG layer through a hydrophobic patch on the protein.</p> <p>Conclusions</p> <p>From the simulations of HFBI solutions, we identify a tetrameric encounter complex stabilized by non-polar interactions between the aliphatic residues in the hydrophobic patch on HFBI. After the formation of the encounter complex, a local structural rearrangement at the protein interfaces is required to obtain the tetrameric arrangement seen in HFBI crystals. Simulations performed with the graphite surface show that, due to a combination of a geometric hindrance and the interaction of the aliphatic sidechains with the graphite layer, HFBI proteins tend to accumulate close to the hydrophobic surface.</p

Facile fabrication of recyclable robust noncovalent porous crystals from low-symmetry helicene derivative

Abstract Porous frameworks constructed via noncovalent interactions show wide potential in molecular separation and gas adsorption. However, it remains a major challenge to prepare these materials from low-symmetry molecular building blocks. Herein, we report a facile strategy to fabricate noncovalent porous crystals through modular self-assembly of a low-symmetry helicene racemate. The P and M enantiomers in the racemate first stack into right- and left-handed triangular prisms, respectively, and subsequently the two types of prisms alternatively stack together into a hexagonal network with one-dimensional channels with a diameter of 14.5 Å. Remarkably, the framework reveals high stability upon heating to 275 °C, majorly due to the abundant π-interactions between the complementarily engaged helicene building blocks. Such porous framework can be readily prepared by fast rotary evaporation, and is easy to recycle and repeatedly reform. The refined porous structure and enriched π-conjugation also favor the selective adsorption of a series of small molecules

Synthesis of pyridinium N-chloramines for antibacterial applications

To develop more efficacious antibacterial agents, a new type of cationic N-chloramines that contain a pyridinium moiety and a N-chloramine moiety covalently linked via an alkyl chain were prepared and characterized. Preliminary assays indicated that 1) the compound with a propylidene linker exhibited higher antibacterial activity than the quaternary ammonium counterpart; 2) the chain length of the alkyl linker had major effects on their biocidal properties. Our results may inspire exploration of more pyridinium N-chloramines for antibacterial applications. (C) 2016 Elsevier Ltd. All rights reserved

Synthesis of quaternary phosphonium N-chloramine biocides for antimicrobial applications

The recently developed quaternary ammonium (QA) N-chloramine has been proved to be a promising "composite" biocide with drastically boosted antibacterial efficacy afforded by the QA moiety. In this work, a series of quaternary phosphonium (QP) N-chloramine biocides, covalently combining an N-chloramine moiety and a QP moiety via varied aliphatic methylene units, were synthesized by means of multi-step chemical reactions. Preliminary antibacterial tests against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) showed that the synthetic QP N-chloramine exhibited distinctively higher biocidal efficacy than the QA counterpart. Furthermore, bactericidal tests also indicated that QP N-chloramine with a linker of -(CH2)(12)-showed the highest biocidal efficacy, suggesting synergistic action between the N-chloramine moiety and QP moiety

The <i>syn/anti</i> patterns of the intermediates.

<p>The bases that have formed native hydrogen bonds in between are plotted side-by-side and in the same plane. The red squares denote the nucleotides with configurations, the blue the ; and the gradient color indicates a fluctuating configuration between and . The nucleotides indicated by arrows correspond to either fluctuating (with gradient color) or wrong <i>syn/anti</i> configurations. Here by wrong we mean that they retain a <i>syn/anti</i> configuration different from the native one. The details of the trajectories are given in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003562#pcbi.1003562.s011" target="_blank">Figure S11</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003562#pcbi.1003562.s012" target="_blank">S12</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003562#pcbi.1003562.s013" target="_blank">S13</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003562#pcbi.1003562.s014" target="_blank">S14</a>.</p

The ion binding probabilities for the four intermediates.

<p>(A)–(D) are for the intermediate-II, III, IV, and V, respectively. The color code is the same as in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003562#pcbi-1003562-g001" target="_blank">Figure 1</a>, i.e., the red, green, and purple histograms correspond to the three G-tetrads, respectively. The black histograms indicate the binding probabilities on the non-native sites.</p