Corona Charged Research Articles

Investigation of polar organic solvents compatible with Corona Charged Aerosol Detection and their use for the determination of sugars by hydrophilic interaction liquid chromatography

A range of organic solvents (ethanol, isopropanol and acetone) has been investigated as alternatives to acetonitrile and methanol when used in conjunction with Corona Charged Aerosol Detection (Corona CAD). These solvents have been evaluated with regard to their effect on the response of the Corona CAD. Three dimensional response surfaces were constructed using raw data showing the relationship between detector response, analyte concentration and percentage of organic solvent in the mobile phase, using sucralose or quinine as the test analyte. The detector response was non-linear in terms of analyte concentration for all solvents tested. However, detector response varied in an approximately linear manner with percentage of organic solvent over the range 0–40% for ethanol or isopropanol and 0–80% for acetone and methanol. The chromatographic performance of the various solvents when used as aqueous–organic mobile phases was evaluated for isocratic and gradient separations of sugars and sugar alcohols by hydrophilic interaction liquid chromatography (HILIC) using an Asahipak NH2P-504E column coupled with Corona CAD detection. It was found that whilst acetonitrile provided the highest column efficiencies and lowest detection limits of the solvents studied, acetone also performed well and could be used to resolve the same number of analytes as was possible with acetonitrile. Typical efficiencies and detection limits of 5330platesm−1 and 1.25μgmL−1, respectively, were achieved when acetone was used as the organic modifier. Acetone was utilised successfully as an organic modifier in the HILIC separation of carbohydrates in a beer sample and also for a partially digested dextran sample.

Reactive ion etching of polymer materials for an energy harvesting device

In this paper, we have demonstrated deep reactive ion etching (RIE) of two MEMS compatible polymer materials CYTOP and TOPAS, which may be useful for energy harvesting devices. The CYTOP polymer was patterned and used as the electret for the following corona charging while the TOPAS polymer was used as the wafer bonding material. Three mask materials (Al, photoresist and Si) were investigated for the RIE process. Grass effect was observed for both polymers when Al was used as the etching mask. With an optimized RIE recipe, a [email protected] photoresist layer served well as an etching mask for [email protected] CYTOP and a high selectivity of 9 was achieved. The CYTOP polymer was corona charged with target surface potential after patterning. Wafer-level bonding between CYTOP and TOPAS polymers was successfully performed with a low temperature thermo-compression bonding technique.

The Corona Charged Aerosol Detector – A „Universal“ Detector for the Measurement of Non-volatile Components in Food, Natural Products and Supplements

The Corona® Charged Aerosol Detector® is a „universal“ mass-sensitive detector capable of measuring any non-volatile and many semi-volatile analytes. Its response is independent of chemical structure and does not require the analyte to possess a chromophore (a prerequisite for UV and fluorescence detection) or to be ionized (essential for MS detection). The Corona CAD is compatible with gradient elution, has a wide dynamic range (4+ orders of magnitude), high sensitivity (sub-nanogram), good reproducibility, and a predictable response independent of chemical structure. As discussed in this presentation, charged aerosol detection overcomes many of the limitations seen with other „universal“ detectors including evaporative light scattering, condensation nucleation light scattering, refractive index, and UV. Charged aerosol detection has great applicability to the measurement of foods, supplements, botanicals and natural products. Some of the topics I will discuss include the measurement of carbohydrates, profiling lipids, measurement of fat-soluble vitamins, analysis of antibiotics, examination of potential bioactives in foods and supplements, and the evaluation of the composition of supplements and botanicals.

Universal response model for a corona charged aerosol detector

The universality of the response of the Corona Charged Aerosol Detector (CoronaCAD) has been investigated under flow-injection and gradient HPLC elution conditions. A three-dimensional model was developed which relates the CoronaCAD response to analyte concentration and the mobile phase composition used. The model was developed using the response of four probe analytes which displayed non-volatile behavior in the CoronaCAD and were soluble over a broad range of mobile phase compositions. The analyte concentrations ranged from 1 μg/mL to 1 mg/mL, and injection volumes corresponded to on-column amounts of 25 ng to 25 μg. Mobile phases used in the model were composed of 0–80% acetonitrile, mixed with complementary proportions of aqueous formic acid (0.1%, pH 2.6). An analyte set of 23 compounds possessing a wide range of physicochemical properties was selected for the purpose of evaluating the model. The predicted response was compared to the actual analyte response displayed by the detector and the efficacy of the model under flow-injection and gradient HPLC elution conditions was determined. The average error of the four analytes used to develop the model was 9.2% ( n = 176), while the errors under flow-injection and gradient HPLC elution conditions for the evaluation set of analytes were found to be 12.5% and 12.8%, respectively. Some analytes were excluded from the evaluation set due to considerations of volatility (boiling point <400 °C), charge and excessive retention on the column leading to elution outside the eluent range covered by the model. The two-part response model can be used to describe the relationship between response and analyte concentration and also to offer a correction for the non-linear detector response obtained with gradient HPLC for analytes which conform to the model, to provide insight into the factors affecting the CoronaCAD response for different analytes, and also as a means for accurately determining the concentration of unknown compounds when individual standards are not available for calibration.

Fabrication of fluoropolymer piezoelectrets by using rigid template: Structure and thermal stability

Fluorocarbon films with regular void structure, made of compact fluoroethylenepropylene (FEP), or skived polytetrafluoroethylene (PTFE), and patterned porous PTFE layers, are successfully fabricated by using a rigid template and fusion bonding process. A corona charging technique is used to make the films piezoelectric, i.e., to be piezoelectrets. The results show that the typical Young’s moduli of the films are in the range of 0.45–0.80 MPa. A maximum quasistatic piezoelectric d33 coefficient up to 500 pC/N is achieved. Compared to the laminated FEP/porous PTFE piezoelectrets without regular void structure, the presently fabricated films show significantly improved thermal stability. Furthermore, when the films are designed, fabricated, and corona charged such that positive charges are deposited in the porous PTFE layers, the thermal stability of d33 coefficients can be further improved. For example, after annealing at 90 °C for 4500 min, these samples have a remaining d33 value of 86% compared with 77% for samples where positive charges are deposited in both, the porous PTFE and the compact FEP layers.

Influence of gamma irradiation on surface potential decay of corona charged polyethylene

In the present paper the surface potential decay after dc corona charging of gamma-irradiated low-density polyethylene (LDPE) has been studied. The irradiation was carried out in air, nitrogen gas and vacuum to investigate the effect of irradiation environment on the surface potential of LDPE. Samples with different absorbed doses were obtained by exposing samples to 60Co for various times at room temperature. It has been found that there is a significant change in the surface potential decay characteristics after different irradiation dose and the surface potential decay pattern depends also on irradiation environment. The possible surface potential decay mechanisms responsible for the above were discussed. The results are useful in the context of long-term performance of electrets.

Decay of electric charge on corona charged polyethylene

In this paper, the surface potential decay of corona-charged low density polyethylene (LDPE) films has been investigated. It has been found that for the same sample thickness the faster decay occurs in the sample with a higher charging voltage. For the same charging voltage, the surface potential in the thinner sample shows rapid decay. Our new evidence from both the surface potential measurement on multilayer samples and space charge measurement suggests the surface potential decay is a bulk limited process. More importantly, space charge measurement indicates double injection has taken place during corona charging process.

Decay of electric charge on corona charged polyethylene

This paper describes a study on the surface potential decay of corona charged low density polyethylene (LDPE) films. A conventional corona charging process is used to deposit charge on the surface of film and surface potential is measured by a compact JCI 140 static monitor. The results from corona charged multilayer sample reveal that the bulk process dominates charge decay. In addition, the pulsed-electro-acoustic (PEA) technique has been employed to monitor charge profiles in corona charged LDPE films. By using the PEA technique, we are able to monitor charge migration through the bulk. Charge profiles in corona charged multilayer sample are consistent with surface potential results. Of further significance, the charge profiles clearly demonstrate that double injection has taken place in corona charged LDPE films.

Study of thermally poled and corona charged poly(vinylidene fluoride) films

AbstractThe effect of thermal poling and corona charging on the structure and characteristics of poly(vinylidene fluoride) films (PVDF) was investigated. The structure and chemical change of PVDF films with different polarizing treatments was examined using Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy, respectively. The characteristics including piezoelectric coefficients, ferroelectric hysteresis, and leakage current were measured. It was found that both polarized methods contribute to dramatic improvement on the piezoelectricity and ferroelectricity of PVDF films, while thermal poling leads to structure change with the generation of new carbon composition. The reason to cause leakage current was also analyzed. POLYM. ENG. SCI., 47:1344–1350, 2007. © 2007 Society of Plastics Engineers

Charge Distribution of Corona Charged Toner Particles

Toner charge distributions in corona charged toner layers on a grounded metal plate were investigated. The charge distributions were measured through image analysis of the toner particles displaced onto a filter, depending on their charge to diameter ratio, after being blown off from the toner inlet into an electric field and dispersed. It has been confirmed that the toner charge distributions became broader by corona charging. In order to clarify the cause, dual toner layers have been formed by using different color toners, and the charge distributions at the upper and lower layers have been measured separately. The results show that the lower toner layer has a wider charge distribution than that of the upper layer. This result is attributable to the fact that the lower parts of the toner layer are covered with the upper toner layer and difficult to corona charge. The toner particles in the lower layer located at the opening of the overlapped upper layer tend to be highly corona charged, while the toner particles around the opening in the upper layer receive only a small amount of the corona charge. It has thus been shown that difference in charge distribution between the upper and lower parts of the toner layer is caused by the following mechanisms: 1) The toner particles at the lower part of the layer are shielded from corona charging ions by the upper layer; 2) The toner particles in the lower layer, which are located at the opening of the charged particles in the upper layer, receive more charging ions by concentration of the electric field; 3) The toner particles at the upper layer receive fewer charging ions because of higher electric potential owing to a longer distance from the grounded plate.

Kelvin probe force microscopy on corona charged oxidized semiconductor surfaces

We present results demonstrating that Kelvin probe force microscopy (KPFM) can be used with high accuracy for corona charge aided oxide thickness mapping. In our experiments, corona charge layers of varying density were deposited onto the surface of thermally oxidized silicon wafers with different oxide thicknesses. After deposition, the surface potentials of the samples were characterized using both the standard Kelvin probe method and KPFM. Comparison of the surface potentials measured by both techniques showed that the values are in excellent agreement, and that only insignificant discharging of the corona charge layer occurred during the topography scan necessary in KPFM measurements.

451 Irradiation-driven tumor selectivity of liposome-based gene therapy targeting Akt activation

The presented work describes the development and validation of a rapid UHPLC-UV/CAD method using a core–shell particle column for the separation and quantitative analysis of seven plant sterols and stanols. The phytosterols (ergosterol, brassicasterol, campesterol, fucosterol, stigmasterol, and β-sitosterol) and the phytostanol stigmastanol were separated and analyzed in 8.5 min. The sample pre-treatment procedure was optimized to be less time-consuming than any other published method, especially due to no need of derivatization, evaporation and even reconstitution step. The chromatographic separation was performed on the Kinetex 1.7 μ Phenyl-hexyl column (100 × 2.1 mm) with a mobile phase acetonitrile/water according to the gradient program at a flow rate of 0.9 mL min−1 and a temperature of 60 °C. A tandem connection of PDA and CAD (Corona Charged Aerosol Detector) was used and both detection techniques were compared. The method was validated using saponification as a first step in sample pre-treatment and an universal CAD as the detector. Recoveries for all analyzed compounds were between 95.4% and 103.4% and relative standard deviation ranged from 1.0% to 5.8% for within-day and from 1.4% to 6.7% for between-day repeatability. The limits of detection were in the range of 0.4–0.6 μg mL−1 for standard solutions and 0.3–1.2 μg mL−1 for phytosterols in real samples. Although several gradient programs and different stationary phases were tested, two compounds, campesterol and campestanol, were not separated. Their peak was quantified as a sum of both analytes.

Negative corona charge stability in plasma treated polytetrafluoroethylene teflon films

In recent work, we found that the stability of the negative corona charge in radio frequency plasma treated polytetrafluoroethylene (PTFE) films (18 µm thickness) strongly depends on the plasma sources, the exposure time and the condition of the film in the plasma, i.e. the film orientation on the holder and whether the film is one-sided metallized or non-metallized, as well as the film side for corona charged. Using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, we conclude that two factors affect the negative charge stability: oxide formed on the surface and positive charges trapped in the film. The oxides serve to retain the negative corona charges and the plasma-generated positive charges recombine with the negative corona charges and cause the corona charge discharge after heating.

Corona charging and pyroelectric behavior in acrylonitrile-co-methylacrylate films

Annealed and stretched films of P(AN-MA) were charged with negatively constant-voltage corona at different temperatures. Electric field induces phase transition, which is determined by the wide angle X-ray diffraction. Using the thermally stimulated depolarization technique, pyroelectric currents have been investigated in unpolarized and corona charged P(AN-MA) films over the temperature range 25-140C. Stretching films produces an enhancement in pyroelectricity. The increase in crystallinity and the presence of space charge build-up during corona charging are believed to be the chief contributors to the higher pyroelectric activity in the stretched films.

Corona charging and pyroelectric behaviour in acrylonitrile-co-methylacrylate films

Annealed and stretched films of P(AN-MA) were charged with negatively constant voltage corona at different temperatures. Electric fields induce a phase transition which is determined by wide angle X-ray diffraction. Using the thermally stimulated depolarisation technique, pyroelectric currents have been investigated in unpolarised and corona charged P(AN-MA) films over the temperature range 25–140°C. Stretching films produces an enhancement in pyroelectricity. The increase in crystallinity and the presence of space charge build-up during corona charging are believed to be the chief contributors to the higher pyroelectric activity in the stretched films.

Corona charging and charge decay of Teflon-PFA

The outstanding features and the charge stability achieved by negative and positive charging tetrafluoroethylene-perfluoromethoxyethylene copolymer (PFA) at elevated temperature have been investigated by means of corona charging and thermally stimulated current (TSC) experiments. Optimal charging temperatures for negative and positive charging have been determined. Activation energies, which are obtained from the initial rise of the TSC peaks, and by the peak cleaning technique, are 0.7, 1.0, 1.3, and 1.1 eV at room temperature (RT), 1.4 eV at 200 degrees C for negative charging. Mean charge depths and charge distributions were measured at various stages of open-circuit TSC measurements on corona charged PFA by means of the laser-induced pressure pulse (LIPP) method. The spatial charge distribution of the different energy levels along the thickness direction of the sample has been determined by means of electron beam charging in combination with TSC measurements. The charged state of some virgin PFA films is discussed. Some electrical and mechanical properties of PFA are compared with those of fluorinated ethylene propylene (FEP). >

Surface potential homogeneity of corona charged FEP and PVDF electrets

Polymeric electrets on the basis of FEP and PVDF have found a wide-spread application up till now. For electret charging corona discharge is a powerful method. For a simple point-to-plane corona we investigated the homogeneity of charging especially when the electrect voltage exceeds the dielectric strength of the polymeric material. Therefore a combined device for corona charging and spatial surface potential measurement was developed. For electret voltages lower than the critical value for local breakdown of the foil a good surface potential homogeneity was found.

TSDC spectra in negatively corona charged ABS electrets

Corona charging technique has been used during polymer electret formation. Investigations of the thermally stimulated depolarization current (TSDC) in the electrets formed from Acrylonitrile-Butadiene-Styrene (ABS) terpolymer films were carried out. The optimum conditions for negatively corona-charged ABS films were determined. With the aid of partial heating technique, a single peak was obtained at T=381±2 K. This peak is associated with the temperature which was attributed to the motion of the bulk detrapping electrons arising from the thermal agitation as well as from erosion of the traps by the molecular motion. The activation energy of the process has been calculated. The electret property can be described in terms of dipolar relaxation process.

Stability of a ferroelectric copolymer-induced inversion layer in silicon

A copolymer of vinylidene fluoride and tetrafluoroethylene is solution cast on a p-type silicon wafer. A strong inversion is produced at the silicon surface when the copolymer film is corona charged or when a subsequently evaporated aluminum gate is biased. Although the dipole alignment in the copolymer is stable, the inversion decays. The decay of the inversion layer is monitored by measuring the decay of the surface channel currents between a source and a drain. For the case of corona charging, an initial rapid decay not observed in the gated device is explained by the motion of excess positive charges (dielectric relaxation). The slow decay subsequently observed is explained in terms of the thermionic injection of inversion electrons across an interface barrier and also using a space-charge-limited injection model. Both models fit the results and their validity is discussed.

Effective surface charge densities on two surfaces and thermally stimulated depolarization currents of polyvinyl chloride films charged by friction and corona discharge

Effective surface charge density (σ ∗) on charged (S1) and back (S2) surfaces of polyvinyl chloride films charged by friction with polystyrene films and negative corona discharge and thermally stimulated depolarization current (TSDC) of these films were investigated. In the films charged by friction, the polarity of σ ∗ on S1 and S2 was negative. The absolute value of σ ∗ on S1 was larger than that on S2. After rinsing the charged films with ethyl alcohol, S1 carried negative charge but S2 positive charge. In temperature dependence of σ ∗ of the charged and alcohol-treated films, a peak was observed at about 63°C. This shows that charges generated by friction entered into the surface layer of the films. In corona electrification, the polarity of σ ∗ on S2 changed depending on the distance, d, between the film and an earthed metal plate. Charge density on S1 and S2 of the film charged at d = 0 mm decayed in negative and positive quadrants, respectively, but unsymmetrically. The polarity of σ ∗ on S2 of the film charged at d = 6 mm was negative but changed to positive after a certain period of decay. The same tendency was observed in the film charged by friction. The decay data were analyzed using a three-exponential sum equation. Three relaxation times and corresponding three charge mobilities were estimated. In TSDC of corona charged films, three peaks were found which decreased with an increase in the period in which the charged films were left in air after the electrification. The polarity of the peak caused by the motion of CCl polar groups changed from negative to positive in the decay process. Poling temperature dependence of TSDC showed that orientation of polar groups occurred in frictional and corona charging process.