Stefan Chisca

Hydroxyl Functionalized Polytriazole-co-polyoxadiazole as Substrates for Forward Osmosis Membranes

Hydroxyl functionalized polytriazole-co-polyoxadiazole (PTA-POD) copolymers have been synthesized and cast as promising highly thermally stable, chemically resistant, and antiorganic/biological fouling porous substrates for the fabrication of thin-film composite (TFC) forward osmosis (FO) membranes. The roles of PTA/POD ratios in the membrane substrates, TFC layers, and FO membrane performance have been investigated. This study demonstrates that the substrate fabricated from the copolymer containing 40 mol % PTA is optimal for the TFC membranes. Compared to the POD-TFC membrane, the 40 mol % PTA-TFC membrane exhibits a remarkable decrease in structural parameter (S) of more than 3.3 times. In addition, the 40 mol % PTA-TFC membrane is characterized by high water fluxes of 24.9 LMH and 47.2 LMH using 1 M NaCl as the draw solution and DI water as the feed under FO and pressure retarded osmosis (PRO) modes, respectively. Compared to a polysulfone (PSU) supported TFC-FO membrane under similar fabrication conditions, the 40% mol PTA-TFC membrane shows better FO performance and enhanced antifouling properties on the support (lower protein binding propensity and improved bacterial inhibition). Moreover, the performance of the 40 mol % PTA supported TFC-FO membrane can be improved to 37.5 LMH (FO mode)/78.4 LMH (PRO mode) and potentially higher by optimizing the support morphology, the TFC formation, and the post-treatment process. Hence, the use of newly developed hydroxyl functionalized polytriazole-co-polyoxadiazole copolymers may open up a new class of material for FO processes.

Crosslinked copolyazoles with a zwitterionic structure for organic solvent resistant membranes

The preparation of crosslinked membranes with a zwitterionic structure based on a facile reaction between a newly synthesized copolyazole with free OH groups and (3-glycidyloxypropyl)trimethoxysilane (GPTMS) is reported. The new OH-functionalized copolyazole is soluble in common organic solvents, such as tetrahydrofuran (THF), dimethylsulfoxide (DMSO), N,N′-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) and can be easily processed by phase inversion. After crosslinking with GPTMS, the membranes acquire high solvent resistance. We show the membrane performance and the influence of the crosslinking reaction conditions on the thermal stability, surface polarity, pore morphology, and solvent resistance. By using UV-spectroscopy we monitored the solvent resistance of the membranes in four aggressive solvents (THF, DMSO, DMF and NMP) for 30 days. After this time, only minor changes (less than 2%) were detected for membranes subjected to a crosslinking reaction for 6 hours or longer. Our data suggest that the novel crosslinked membranes can be used for industrial applications in wide harsh environments in the presence of organic solvents.

Dielectric and conduction properties of polyimide films

Dielectric and conduction properties of polyimides were evaluated on the basis of dielectric constant, dielectric loss, electric modulus and AC conductivity, and their variation with frequency and temperature. Polyimide films exhibited good insulating properties with dielectric constants values in the range of 2.78–3.48 and dielectric loss comprised between 0.01 and 0.03 at 1Hz at room temperature.

A Microfiltration Polymer-Based Hollow-Fiber Cathode as a Promising Advanced Material for Simultaneous Recovery of Energy and Water.

A novel electrocatalytic and microfiltration polymeric hollow fiber is fabricated for simultaneous recovery of energy (H2 ) and clean fresh water from wastewater, hence addressing two grand challenges facing society in the current century (i.e., providing adequate supplies of clean fresh water and energy as the worlds population increases).

In situ growth of biocidal AgCl crystals in the top layer of asymmetric polytriazole membranes

Scalable fabrication strategies to concentrate biocidal materials in only the surface of membranes are highly desirable. In this letter, tight-UF polytriazole membranes with a high concentration of biocide silver chloride (AgCl) crystals dispersed in only their top layer are presented. They were made following a simple dual-bath process that is compatible with current commercial membrane casting facilities. These membranes can achieve a 150-fold increase in their antimicrobial character compared to their silver-free counterpart. Moreover, fine-tuning of their properties is straightforward. A change in the silver concentration in one of the baths is sufficient to tune the permeance, molecular weight cut-off (MWCO) and silver loading of the final membrane.

A new sensitizer containing dihexyloxy-substituted triphenylamine as donor and a binary conjugated spacer for dye-sensitized solar cells

The synthesis and application to dye-sensitized solar cells (DSSC) of a new dihexyloxy-substituted triphenylamine-based organic dye is reported. The dye design, based on the push–pull concept, consists of dihexyloxy-substituted triphenylamine as an electron donor and a cyanoacrylic acid as an anchoring group and electron acceptor connected through a π-conjugated bridge. The electron spacer containing furan and thiophene moieties was employed in the dye sensitizer for expansion of the π-conjugated fragment to adjust the absorption spectra and HOMO–LUMO levels of the dye. The relationship between the dye chemical structure and the photophysical, electrochemical, and photovoltaic properties determined by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations was thoroughly investigated. The photovoltaic performance of the dye as sensitizer was assessed in DSSC cells realized using electrolytes containing the iodide/triiodide redox couple. The cells obtained with the new dye show a power conversion efficiency of 5.14%, without using any coadsorbant and optimization.

Artificial 3D hierarchical and isotropic porous polymeric materials

We report a simple method for rapid replication of hierarchical, isotropic porous materials that mimic complex living structures. Hierarchical porous materials that replicate complex living structures are attractive for a wide variety of applications, ranging from storage and catalysis to biological and artificial systems. However, the preparation of structures with a high level of complexity and long-range order at the mesoscale and microscale is challenging. We report a simple, nonextractive, and nonreactive method used to prepare three-dimensional porous materials that mimic biological systems such as marine skeletons and honeycombs. This method exploits the concurrent occurrence of the self-assembly of block copolymers in solution and macrophase separation by nucleation and growth. We obtained a long-range order of micrometer-sized compartments. These compartments are interconnected by ordered cylindrical nanochannels. The new approach is demonstrated using polystyrene-b-poly(t-butyl acrylate), which can be further explored for a broad range of applications, such as air purification filters for viruses and pollution particle removal or growth of bioinspired materials for bone regeneration.

Study of dielectric behavior of aromatic polyimide films

Aromatic polyimide films were prepared and their dielectric constant and relaxation behavior were studied. Polyimide films have good insulating properties with dielectric constant values in the range of 2.88 – 3.48 at 1Hz and room temperature. Three relaxation processes (γ, β<inf>1</inf> and β<inf>2</inf>) at sub-glass temperatures were observed and investigated. The cooperativity of the molecular motions associated with the relaxation processes was discussed.