Phase-resolved emission spectroscopy of a hydrogen rf discharge for the determination of quenching coefficients

Collisional effects can have strong influences on the population densities of excited states in gas discharges at elevated pressure. The knowledge of the pertinent collisional coefficient describing the depopulation of a specific level (quenching coefficient) is, therefore, important for plasma diagnostics and simulations. Phase resolved optical emission spectroscopy (PROES) applied to a capacitively coupled rf discharge excited with a frequency of 13.56 MHz in hydrogen allows the measurement of quenching coefficients for emitting states of various species, particularly of noble gases, with molecular hydrogen as a collision partner. Quenching coefficients can be determined subsequent to electron-impact excitation during the short field reversal phase within the sheath region from the time behavior of the fluorescence. The PROES technique based on electron-impact excitation is not limited â?? in contrast to laser techniques â?? by optical selection rules and the energy gap between the ground state and the upper level of the observed transition. Measurements of quenching coefficients and natural fluorescence lifetimes are presented for several helium (3 1S,4 1S,3 3S,3 3P,4 3S), neon (2p1 ,2p2 ,2p4 ,2p6), argon (3d2 ,3d4 ,3d18 and 3d3), and krypton (2p1 ,2p5) states as well as for some states of the triplet system of molecular hydrogen.

Electrochemical synthesis and characterization of conducting polymers using room temperature melt as an electrolyte

Aromatic monomers can be polymerised using the chloroaluminate room temperature melt obtained by mixing 1:2 ratio of cetyl pyridinium chloride and anhydrous aluminium chloride miscible in all proportions with organic solvents as an electrolyte. The chloroaluminate (AlCl4-) anion generated in this melt having a tetrahedral symmetry with equal bond lengths and bond angles is the dopant to stabilize macrocation generated near the vicinity of anode to yield better conducting and better ordered electronically conducting free standing polymer film. In this communication, we discuss the polymers derived from benzene and pyrrole and their characterization by various techniques.

Determination of quenching coefficients in a hydrogen RF discharge by time-resolved optical emission spectroscopy

In gas discharges at elevated pressure, radiation-less collisional de-excitation (quenching) has a strong influence on the population of excited states. The knowledge of quenching coefficients is therefore important for plasma diagnostics and simulations. A novel time-resolved optical emission spectroscopic (OES) technique allows the measurement of quenching coefficients for emission lines of various species, particularly of noble gases, with molecular hydrogen as collision partner. The technique exploits the short electron impact excitation during the field reversal phase within the sheath region of a hydrogen capacitively coupled RF discharge at 13.56 MHz. Quenching coefficients can be determined subsequent to this excitation from the effective lifetime of the fluorescence decay at various hydrogen pressures. The measured quenching coefficients agree very well with results obtained by means of laser excitation. The time-resolved OES technique based on electron impact excitation is not limited - in contrast to laser techniques - by optical selection rules and the energy gap between the ground state and the observed excited level.

Nucleation and growth in fluidised hot melt granulation

Fluidised hot melt granulation (FHMG) is a novel technology for granulation process in pharmaceutical industry, which has distinct advantages over other commercial techniques. The aim of this research was to investigate granulation and the effect of process parameters that may affect FHMG process. In this work, ballotini beads were used as the model particles and Lutrol (R) F 68 Poloxamer 188 was used as meltable solid binder. In order to determine the granulation and nucleation mechanism in this co-melt FHMG system, several parameters were investigated, such as binder content, particle size of binder and particle size and hydrophobicity of ballotini. These parameters were correlated to granule size distribution, mean granule size and granule shape. Furthermore, these experimental investigations were designed so that the coalescence model could be applied to the co-melt FHMG system. The analysis indicated that the non-inertial regime extends over a relatively short time period of

On the self-aggregation and fluorescence quenching aptitude of surfactant ionic liquids

The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and H-1 NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [C(n)mpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n = 4, 10, 12, 14, 16, or 18), [C(12)mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C(12)mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C(12)mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established.

Investigation of the temperature homogeneity of die melt flows in polymer extrusion

Polymer extrusion is fundamental to the processing of polymeric materials and melt flow temperature homogeneity is a major factor which influences product quality. Undesirable thermal conditions can cause problems such as melt degradation, dimensional instability, weaknesses in mechanical/optical/geometrical properties, and so forth. It has been revealed that melt temperature varies with time and with radial position across the die. However, the majority of polymer processes use only single-point techniques whose thermal measurements are limited to the single point at which they are fixed. Therefore, it is impossible for such techniques to determine thermal homogeneity across the melt flow. In this work, an extensive investigation was carried out into melt flow thermal behavior of the output of a single extruder with different polymers and screw geometries over a wide range of processing conditions. Melt temperature profiles of the process output were observed using a thermocouple mesh placed in the flow and results confirmed that the melt flow thermal behavior is different at different radial positions. The uniformity of temperature across the melt flow deteriorated considerably with increase in screw rotational speed while it was also shown to be dependent on process settings, screw geometry, and material properties. Moreover, it appears that the effects of the material, machine, and process settings on the quantity and quality of the process output are heavily coupled with each other and this may cause the process to be difficult to predict and variable in nature

Shape stabilised phase change materials based on a high melt viscosity HDPE and paraffin waxes

Shape stabilised phase change materials (SSPCMs) based on a high density poly(ethylene)(hv-HDPE) with high (H-PW, Tm = 56–58 °C) and low (L-PW, Tm = 18–23 °C) melting point paraffin waxes were readily prepared using twin-screw extrusion. The thermo-physical properties of these materials were assessed using a combination of techniques and their suitability for latent heat thermal energy storage (LHTES) assessed. The melt processing temperature (160 °C) of the HDPE used was well below the onset of thermal decomposition of H-PW (220 °C), but above that for L-PW (130 °C), although the decomposition process extended over a range of 120 °C and the residence time of L-PW in the extruder was <30 s. The SSPCMs prepared had latent heats up to 89 J/g and the enthalpy values for H-PW in the respective blends decreased with increasing H-PW loading, as a consequence of co-crystallisation of H-PW and hv-HDPE. Static and dynamic mechanical analysis confirmed both waxes have a plasticisation effect on this HDPE. Irrespective of the mode of deformation (tension, flexural, compression) modulus and stress decreased with increased wax loading in the blend, but the H-PW blends were mechanically superior to those with L-PW.