PROBING HIDDEN POLYMERIC INTERFACES USINGIR-VISIBLE SUM-FREQUENCY GENERATION SPECTROSCOPY

Understanding the molecular-level processes underlying interfacial phenomena is important in the area of adhesion. We briefly introduce IR-visible sum-frequency generation spectroscopy (SFG) using a total-internal-reflection geometry for the study of polymer-air, polymer-solid, and polymer-polymer interfaces. The following examples, predominantly of work done in our lab, illustrating differences in molecular structure and dynamic properties at interfaces are presented: the air- and solid-interface structure of an amorphous polystyrene (PS) and a semicrystalline polymer with side-chain crystallinity, poly(octadecyl acrylate) (PA-18); structure of a polymer-polymer interface between thin films of a semicrystalline polymer with side-chain crystallinity, poly(vinyl-N-octadecylcarbamate- co-vinyl acetate), and an amorphous PS; thermal order-to-disorder transitions of the air and solid interface of PA-18, and the interface of this polymer with PS; and dynamic surface-relaxation studies of a rubbed PS film.     

Effect of doping ferrocene in the working fluid of electrohydrodynamic (EHD) micropumps

The effect of doping ferrocene in the working fluid of electrohydrodynamic micropumps was investigated under the application of DC electric fields. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100-micron-high, 5-mm-wide and 26-mm-long microchannel. The width of the emitter and collector electrodes was 20 and 40 µm, respectively, with inter-electrode spacing of 30 µm. A redox dopant, ferrocene, was diffused homogeneously into the working fluid HFE-7100 at 0.05, 0.1 and 0.2 % concentration by weight. The static pressure head generation and flow rate at different back pressure conditions were measured under different applied DC voltages. The current and pressure generated with the doped working fluid were significantly higher than with pure HFE-7100 under an applied DC field. A maximum static pressure of 6.7 kPa and flow rate of 0.47 mL/min at no back pressure were achieved at 700 V.     

Multiple responses analysis and modeling of Fenton process for treatment of high strength landfill leachate

Landfill leachate is one of the most recalcitrant wastes for biotreatment and can be considered a potential source of contamination to surface and groundwater ecosystems. In the present study, Fenton oxidation was employed for degradation of stabilized landfill leachate. Response surface methodology was applied to analyze, model and optimize the process parameters, i.e. pH and reaction time as well as the initial concentrations of hydrogen peroxide and ferrous ion. Analysis of variance showed that good coefficients of determination were obtained (R2 > 0.99), thus ensuring satisfactory agreement of the second-order regression model with the experimental data. The results indicated that, pH and its quadratic effects were the main factors influencing Fenton oxidation. Furthermore, antagonistic effects between pH and other variables were observed. The optimum H2O2 concentration, Fe(II) concentration, pH and reaction time were 0.033 mol/L, 0.011 mol/L, 3 and 145 min, respectively, with 58.3% COD, 79.0% color and 82.1% iron removals.     

Superconductivity and Fluctuation-Induced Conductivity (FIC) Analysis of (Cu0.5Tl0.5?x M x )Ba2Ca2Cu3O10?δ

Superconductivity has been improved by partial substitution of slightly higher electronegative (M=Bi, Hg) elements at Tl sites in (Cu_0.5Tl_0.5?x M _x )Ba₂O_4??? (x=0,0.25) charge reservoir layer of (Cu_0.5Tl_0.5?x M _x )Ba₂Ca₂Cu₃O_10??? superconductor. These samples were characterized by X-ray diffractometry, dc-resistivity, ac-susceptibility, FTIR absorption spectroscopy, and fluctuation-induced conductivity (FIC) analysis. The FIC analysis has been carried out in the light of Aslamasov?CLarkin (AL) theory on the resistivity versus temperature curves of (Cu_0.5Tl_0.5?x M _x )Ba₂Ca₂Cu₃O_10??? superconductor. The microscopic parameters such as cross-over temperature (T _o ), zero-temperature coherence length ?? _c (0), inter-layer coupling (J), and critical exponents (?? _2D and ?? _3D) have been determined from FIC analysis of these samples and tried to correlate them to the superconductivity order parameters. A?direct correlation between the cross-over temperatures (T _o ) and zero resistivity critical temperature {T _c (R=0)} and carrier concentration in these samples has been observed. The improvement in T _c (R=0) and the shift of 3D AL region to higher temperature values with the doping of Bi and Hg have also been observed.     

Electrochemical degradation of petroleum hydrocarbons (PAHS) from synthetic aqueous solutions

Water separated from crude oil and wastewater discharge from petroleum oil refineries contains significant quantity of dissolved hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs) are major toxicants in wastewater of refineries. It is difficult to treat wastewater containing PAHs due to their recalcitrant property and low solubility. Conventional techniques for the treatment of wastewater are still a concern of toxicity. Electrochemical oxidation process has been found to be a favorable for treating wastewater. Electrodes with high stability and electrocatalytic activity are important factors for a successful electrochemical oxidation of toxic organics in wastewater. In this study titanium anodes were coated with tin, antimony and iridium oxide mixture from their respective salts by thermal decomposition method. FESEM and XRD used for surface characterization of Ti/SnO₂–Sb₂O₅–IrO₂ anode. Quantification of PAHs was done using GC–MS. Results confirm the presence of respective oxides on anode surface. Their electrocatalytic capability was tested for degradation of 16 priority PAHs in aqueous solution. Results reveal the complete degradation of naphthalene, acenaphthylene, acenaphthene and fluorene without using NaCl electrolyte. While in the presence of NaCl naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene were completely removed. About 98% of total PAHs removal was found at all initial pH values 3, 6, and 9 in the presence of electrolyte. Current study will be helpful in improving quality of petroleum industry wastewater containing PAHs.     

Synthetic,spectroscopic, magnetic,thermal, and antimicrobial approach towards new biocidal coordination polymers

O‐aminophenol was reacted with glutraldehyde to obtain Schiff base, which was then reacted with formaldehyde in slight acidic medium to generate phenolic groups. Now the substituted Schiff base was reacted with the transition metal acetates of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) to get polymeric metal complexes. Their structures have been elucidated on the basis of elemental analyses, ¹H NMR spectra, ¹³C NMR spectra, magnetic measurements, thermogravimetric analyses, electronic spectra, and infrared spectra. The results are in accordance with an octahedral environment around the central metal ion. The polychelates of Mn(II), Co(II), Ni(II), and Cu(II) are paramagnetic while Zn(II) polychelate was found to be diamagnetic. The synthesized Schiff base acted as a uninegative bidentate ligand and bonding occurs through the hydroxyl oxygen and nitrogen atoms. The thermal behavior of these coordinating polymers was studied by TGA in nitrogen atmosphere up to the temperature range of 800°C. All the synthesized polychelates were also screened for their biocidal activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis (bacteria), Candida albicans, and Muller species (yeast) by using agar well diffusion method. All the metal polychelates show promising antimicrobial activities. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124:3971–3979, 2012     

Threshold current reduction in InGaN MQW laser diode withλ/4 air/semiconductor Bragg reflectors

A 13% reduction in the threshold current density of InGaN laser diodes is demonstrated upon the introduction of two 5λ/4 air/nitride Bragg reflectors. These are defined at one end of the laser cavity by means of focused ion beam etching     

Himalayan glaciers as a sustainable water resource

The Himalayan glaciers, which number around 15 000, cover an area of 33 000 km² and are nursed in the steepest and highest valleys in the world. Runoff from the seasonal melting of snow and ice contributes to the streamflows of the Indus, Ganga and Brahamputra river systems of the Indian subcontinent. The annual contribution from snowmelt and runoff from non‐glacierized areas during the early part of summer (April to June) amounts to 20%. As summer proceeds (July to September) the contributions from melting glacier ice and water stored within the glaciers reach 50%. In this paper the pattern of water release by melting and its chemical characteristics are described for a glacier in the Lahul‐Spiti valley of Himachal Pradesh, India.     

Systematic design of wideband ΔΣ modulators for WiFi/WiMAX receivers

Modern multi-standard receivers in deep-submicron technologies pose significant design challenges on the analog baseband. Moving this analog filtering to the digital domain simplifies the design, yielding a process-scalable implementation. However, analog-to-digital converter (ADC) specifications now become more stringent and must be obtained by comprehending the standard and the system. Assuming a receiver NF of 5.96 dB and SNR degradation of 0.36 dB by the ADC, the proposed dual-mode WiFi/WiMAX receiver attains an input sensitivity of −74 dBm (20 MHz channel bandwidth). To accommodate the high dynamic range and the anti-alias rejection needed for the system, a Delta-Sigma (ΔΣ) ADC is proposed. Single-loop and Multi-Stage Noise-Shaping (MASH) architectures that achieve a SNR of 69 dB at a low oversampling ratio (OSR) of 8 for a conversion bandwidth of 40 MHz (108 Mbps, OFDM) are investigated at system level. Based on thermal noise, harmonic distortion, and power tradeoffs, a ΔΣ ADC design that meets the design specifications is presented.