Polymerization behavior and polymer properties of eosin-mediated surface modification reactions

Surface modification by surface-mediated polymerization necessitates control of the grafted polymer film thicknesses to achieve the desired property changes. Here, a microarray format is used to assess a range of reaction conditions and formulations rapidly in regards to the film thicknesses achieved and the polymerization behavior. Monomer formulations initiated by eosin conjugates with varying concentrations of poly(ethylene glycol) diacrylate (PEGDA), N-methyldiethanolamine (MDEA), and 1-vinyl-2-pyrrolidone (VP) were evaluated. Acrylamide with MDEA or ascorbic acid as a coinitiator was also investigated. The best formulation was found to be 40 wt% acrylamide with MDEA which yielded four to eightfold thicker films (maximum polymer thickness increased from 180 nm to 1420 nm) and generated visible films from fivefold lower eosin surface densities (2.8 versus 14 eosins/μm²) compared to a corresponding PEGDA formulation. Using a microarray format to assess multiple initiator surface densities enabled facile identification of a monomer formulation that yields the desired polymer properties and polymerization behavior across the requisite range of initiator surface densities.     

Manganese oxide electrochemical capacitor with potassium poly(acrylate) hydrogel electrolyte

An aqueous gel electrolyte has for the first time been successfully applied to the MnO₂·nH₂O-based pseudocapacitive electrochemical capacitors (ECs). The gel electrolyte is made of potassium poly(acrylate) (PAAK) polymer and aqueous solution of KCl. With the selected composition, PAAK:KCl:H₂O = 9.0%:6.7%:84.3% by weight, the gel shows no fluidity, possessing an ionic conductivity in the order of 10⁻¹ S cm⁻¹. The gel electrolyte has been found to give substantially higher specific capacitances than those in the liquid electrolyte with the same salt (KCl) composition (1 M) and high power capability (>10 kW/kg).     

On length-separating test tube systems

In this article we introduce a new variant of test tube systems based on splicing where the communication of the words among the test tubes is based on filtering by their lengths. The model, called length-separating test tube systems, is motivated by the gel electrophoresis laboratory technique. We prove that these constructs, even with restricted size parameters, simulate the Turing machines. We also discuss some natural restrictions and generalizations of the model, which may be used to find efficient ways to realize DNA transformations in the laboratory.     

Propane hydrate nucleation: Experimental investigation and correlation

In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally using a stirred batch reactor. The experiments have been performed isothermally recording the pressure as a function of time. Experiments were conducted at different stirring rates, but in the same supersaturation region. The experiments showed that the gas dissolution rate rather than the induction time of propane hydrate is influenced by a change in agitation. This was especially valid at high stirring rates when the water surface was severely disturbed.Addition of polyvinylpyrrolidone (PVP) to the aqueous phase was found to reduce the gas dissolution rate slightly. However the induction times were prolonged quite substantially upon addition of PVP.The induction time data were correlated using a newly developed induction time model based on crystallization theory also capable of taking into account the presence of additives. In most cases reasonable agreement between the data and the model could be obtained. The results revealed that especially the effective surface energy between propane hydrate and water is likely to change when the stirring rate varies from very high to low. The prolongation of induction times according to the model is likely to be due to a change in the nuclei-substrate contact angle.     

Preserving Shipboard AFFF Fire Protection System Performance While Preventing Hydrogen Sulfide Formation

There is a very serious problem aboard US Navy ships from generation of toxic hydrogen sulfide (H₂S) in Aqueous Film-Forming Foam (AFFF) solutions used for shipboard fire protection. This is the result of the action of sulfate reducing bacteria (SRB) in mixtures of seawater and AFFF, which remain stagnant for significant time periods in shipboard fire protection system piping. Similar to microbial generation of H₂S in sewage, over time microbes present in seawater consume organic materials in the AFFF mixture and can deplete the dissolved oxygen. If the reduction-oxidation potential falls low enough, anaerobic action of the SRB on the sulfate present in seawater can then result in H₂S generation, reaching dangerous levels. The recommended ceiling for exposure to H₂S is only 10 ppm. If the microbes causing oxygen depletion and/or the SRB can be eliminated (or sufficiently minimized), the dangerous generation of H₂S would not occur. The Navy Technology Center for Safety and Survivability is participating in a research project for the Naval Sea Systems Command (NAVSEA) to evaluate several treatment modalities for their ability to inhibit H₂S formation in AFFF/seawater mixtures and for possible deleterious effects on AFFF performance. Various approaches have been considered employing laboratory evaluations (dynamic surface tension and Ross-Miles foamability), and 28 ft² (2.6 m²) pool fire extinguishment and burnback protection field tests (Military Standard MIL-F-24385F). The protocol selected for NAVSEA shipboard H₂S generation mitigation testing is a combination of a commercial broad-spectrum biocide with a molybdenum compound which is a specific inhibitor of SRB.     

Multilayer film preparation of poly(4-vinylphenol) from aqueous media

The use of weak polyelectrolytes in multilayer polymer systems provides a means of altering the physico-chemical properties of these thin films. This paper examines the limits of the polyanions by incorporating the extremely weak polyelectrolyte, poly(4-vinylphenol) (PVPh), into a multilayer system with poly(allylamine hydrochloride) (PAH) from a dilute aqueous media. Film growth was monitored using absorption spectroscopy and revealed a clear linear trend in film thickness. The surface morphology, thickness, and swelling of the multilayer films systems were examined using atomic force microscopy (AFM). Film thickness greatly depended upon the pH of the polymer precursor solutions; 50-layer systems created at pH 12.5 and 11.0 were 8.2 and 246.6 nm thick, respectively, a difference of over 2900%. This is the first report on the incorporation of PVPh into a multilayer system from an aqueous media.     

Synthesis, characterization and catalytic properties of a LEV type silicoaluminophosphate molecular sieve, SAPO-35 from aqueous media using aluminium isopropoxide and hexamethyleneimine template

A small-pore silicoaluminophosphate molecular sieve, SAPO-35 was synthesized using hexamethyleneimine template and aluminium isopropoxide as aluminium source in aqueous media is reported for the first time. Pure, highly crystalline samples were obtained in short period (96 h). The samples crystallize at narrow silicon content (0.3 M SiO₂). Fourier transform Infrared spectroscopic studies reveal the presence of three different silanol groups. A comparison with multinuclear solid-state Magic angle spinning nuclear magnetic resonance spectroscopic studies with FT-IR studies shows that these groups are located at Double six member ring, near to D6R and near to single six member ring. Other characterizations and methanol to olefin reaction studies shows that the molecular sieves synthesized by aqueous and non-aqueous media are having comparable properties. It reveals a possible application of this catalyst for industrial process.     

Microwave-hydrothermal synthesis and characterization of Co-VSB-5 microporous framework

The crystallization of cobalt metal incorporated microporous nickel phosphate framework, Co-VSB-5, with initial Ni/P gel ratio of about 1.0, 1.5 and 2.5, respectively, has been investigated under microwave-hydrothermal conditions. Attempts are made to incorporate metal ion in the range of 2.5–10 atomic % in the VSB-5 framework having varied Ni/P ratio by varying gel pH. The prepared samples were characterized by means of X-ray diffraction, scanning electron microscopy, UV-visible diffuse reflectance spectroscopy (UV-visible DRS), and nitrogen adsorption–desorption measurements at 77 K. The prepared samples are found to be crystalline in nature. The initial gel pH is found to be critical for crystallization of nickel phosphate framework with varied Ni/P ratio. Like wise, isomorphic substitution is favored with an increase in Ni/P gel ratio. The results for UVDRS demonstrated the incorporation of transition metal ions in the octahedral position for nickel sites in VSB-5 framework. The textural properties, such as surface area and micropore volume, of the Co-VSB-5 samples crystallized from initial Ni/P gel ratio of 2.5, were found to lower than those crystallized from initial Ni/P gel ratio of 1.5 at equivalent metal content level. Interestingly, crystallization of framework having micro-mesoporosity is favored with an increase in Ni/P gel ratio. Furthermore, scanning electron microscopy revealed the crystallization of samples with rod shaped morphology irrespective of the nature of metal ion and its concentration from gel comprising of Ni/P of 1.5 and 2.5. The results of UV-Vis DRS demonstrated the incorporation of transition metal ions in the octahedral position for nickel sites in VSB-5 framework.     

A pilot-plant study of the adsorptive micellar flocculation process: Optimum design and operation

A pilot-plant scale study of the adsorptive micellar flocculation (AMF) process is presented for the first time, and builds on the solid foundation provided by previous fundamental laboratory studies. A number of experimental tests were conducted to validate the feasibility of using an AMF pilot rig to remove phenol from aqueous effluent streams. Several key factors, including flocculation time, floc settling time, optimum air flow-rate for agitation, and flocculant dosage, were determined. Residual concentrations in treated water indicated a surfactant removal efficiency of 95–98%, and pollutant removal reached 78% in two stages of process operation. A strategy for the separate recycling of surfactant, flocculant and pollutant has already been developed. The present study has thus made further progress in developing, testing, validating and optimising the operating conditions of a pilot-scale process. As such, it has demonstrated the feasibility of scaling up from the bench-scale to a commercial, continuously operated unit.     

Highly conductive alumina/NCN composites electrodes fabricated by gelcasting and reduction-sintering—An electrochemical behavior study in aggressive environments

A novel highly conductive alumina/nano-carbon network composites (alumina/NCN composites) was fabricated by gelcasting and reduction-sintering method under argon atmosphere. The electrochemical behaviors of the alumina/NCN composites were studied systematically in some aggressive solutions (HCl, H₂SO₄, HNO₃, NaOH, and KOH), using potentiodynamic polarization and chronoamperometry and X-ray diffraction and SEM observations. The results showed that the electrochemical stability and reproducibility of the composite electrodes in these diluted acids and alkalis were very good and had, in some extent, an electro-catalytic activity toward formation of hydrogen evolution and reduction of dissolved oxygen in aqueous solutions in comparison with a commercial graphite electrode. In addition, the pyrolyzed nano-carbon contents, size, and shape in the alumina matrix, have greatly effects on the electrochemical performances and electrode reactions in these solutions. It is found that the minimal residual carbon content of 0.62 wt.% in the matrix is enough to improve electrochemical performances and avoid to loss the ceramics physical properties at the same time. When the additional potential in all the tested electrolytes was at +1700 mV (vs. SCE), alumina particles at the electrode surface were not observed to dissolve into solution in this case, indicating the material being suitable for electrodes in aggressive solutions.