Lixia Rong

High-flux thin-film nanofibrous composite ultrafiltration membranes containing cellulose barrier layer

A novel class of thin-film nanofibrous composite (TFNC) membrane consisting of a cellulose barrier layer, a nanofibrous mid-layer scaffold, and a melt-blown non-woven substrate was successfully fabricated and tested as an ultrafiltration (UF) filter to separate an emulsified oil and water mixture, a model bilge water for on-board ship bilge water purification. Two ionic liquids: 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate, were chosen as the solvent to dissolve cellulose under mild conditions. The regenerated cellulose barrier layer exhibited less crystallinity (determined by wide-angle X-ray diffraction, WAXD) than the original cotton linter pulps, but good thermal stability (determined by thermal gravimetric analysis, TGA). The morphology, water permeation, and mechanical stability of the chosen TFNC membranes were thoroughly investigated. The results indicated that the polyacrylonitrile (PAN) nanofibrous scaffold was partially imbedded in the cellulose barrier layer, which enhanced the mechanical strength of the top barrier layer. The permeation flux of the cellulose-based TFNC membrane was significantly higher (e.g. 10×) than comparable commercial UF membranes (PAN10 and PAN400, Sepro) with similar rejection ratios for separation of oil/water emulsions. The molecular weight cut-off (MWCO) of TFNC membranes with cellulose barrier layer was evaluated using dextran feed solutions. The rejection was found to be higher than 90% with a dextran molecular weight of 2000 KDa, implying that the nominal pore size of the membrane was less than ∼50 nm. High permeation flux was also observed in the filtration of an emulsified oil/water mixture as well as of a sodium alginate aqueous solution, while high rejection ratio (above 99.5%) was maintained after prolonged operation. A variation of the barrier layer thickness could dramatically affect the permeation flux and the rejection ratio of the TFNC membranes, while different sources of cellulose, ionic liquids, and non-woven supports did not. As ionic liquids can be recycled and reused without obvious decomposition, the chosen method also demonstrates a benign pathway to fabricate the cellulose barrier layer for other types of membranes.

Competition between liquid crystallinity and block copolymer self-assembly in core–shell rod–coil block copolymers

Core-shell type of architecture revealed the subtle competition between liquid-crystalline ordering and block copolymer (BCP) self-assembly in a rod-coil BCP system.

Complexation of DNA with cationic surfactants as studied by small-angle X-ray scattering

The phase behaviors of the complex formed by didodecyldimethylammonium bromide (DDAB) and cetyltrimethylammonium bromide (CTAB) interacting with three different types of DNAs, salmon testes DNA (∼2000 bp), 21-bp double-stranded oligonucleotides (oligo-dsDNA), and 21-nt single-stranded oligonucleotides (oligo-ssDNA) were studied by synchrotron small-angle X-ray scattering. It was found that the DNA length and flexibility, together with the positive/negative charge ratio, determined the final structure. At higher charge ratios, the DNA length exhibited negligible effect. Both oligo-dsDNA and salmon DNA formed inverted hexagonal packing of cylinders with CTAB, as well as bilayered lamella with DDAB. However, at lower charge ratios, oligo-dsDNA formed a distorted hexagonal phase with CTAB and a new structure with DDAB, which was different from the behaviors of salmon DNA. The flexible oligo-ssDNA formed rich structures that were subject to environmental disturbance. Kinetic study also indicated that the structures of the complex formed by oligo-ssDNA took much longer to mature than the structures formed by oligo-dsDNA. We attributed this result to the conformational adjustment of oligo-ssDNA in the complex.