silicon and octane

In this work, a highly reproducible standard gas generating vial is proposed. The vial is comprised of a silicon diffusion pump oil spiked with an appropriate calibration compound, such as modified McReynolds probes (benzene, 2-pentanone, pyridine, 1-nitropropane, 1-pentanol, and n-octane), and then mixed with polystyrene/divinylbenzene (PS/DVB) particles. The concentrations of these compounds in gaseous headspace were found to substantially decrease in comparison to previously developed hydrocarbon pump oil based vials; hence, the amount of standard loaded onto SPME fibers was at most, half that of the previous vial design. Depletion for all compounds after 208 successive extractions was shown to be less than 3.5%. Smaller quantities of standards being used resulted in a vial that depleted slower while remaining statistically repeatable over a wider number of runs. Indeed, it was found that depletion could be largely predicted by using a mass balance theoretical model. This behavior allowed a further increase in the number of loadings that could be performed repeatedly. At a 95% level of confidence, the ANOVA test demonstrated that the prepared vials were statistically identical, with no significant intra- or inter-batch differences. In addition, it was found that vials stored under different conditions (e.g. under light exposure, room temperature, and within a refrigerator) were stable over 10 weeks. Silicon based vials proved to be ideal for performing instrument quality control and loading of internal standards onto fibers, both of which are of great importance when performing on-site analysis using portable GC-MS instrumentation and high throughput determinations in laboratory.

Topics: Benzene; Calibration; Gas Chromatography-Mass Spectrometry; Gases; Nitroparaffins; Octanes; Pentanols; Pentanones; Polystyrenes; Propane; Silicon; Solid Phase Microextraction

A general approach for selective, differential functionalization of the interior and exterior surfaces of mesoporous Si is reported. The method employs two immiscible liquids, one inert and the other chemically reactive with the porous Si nanostructure. First, a porous Si sample is prepared by electrochemical etch and then it is mildly oxidized, which places a thin layer of silicon oxide at the surface. The inner pore walls of the partially oxidized porous Si film are then infiltrated with an inert liquid (octane). The sample is then immersed in aqueous solution containing hydrogen fluoride (HF), which serves as the reactive liquid. The hydrophobic phase is retained in the interior of the porous nanostructure, and HF(aq) attacks only the exposed surfaces of the oxidized porous Si sample, generating a hydrophobic, hydrogen-terminated (Si-H) outer layer. The reaction is self-limiting due to the immiscibility of octane and water, and the extent of penetration of the Si-H surface into the porous layer is dependent on the time of exposure to HF(aq). The Si-H surface can then be modified by thermal hydrosilylation (1-dodecene or 10-bromo-1-decene) in a subsequent step, resulting in a bifunctional porous Si film containing hydrophobic pore entrances to hydrophilic inner pores. The hydrophobic dodecyl species at the mouths of the pores is found to form a barrier for molecular transport; it decreases the rate of leaching (into water) of a rhodamine test molecule that is preloaded into the sample by >8 fold.

Topics: Crystallization; Hydrogen; Macromolecular Substances; Materials Testing; Molecular Conformation; Nanostructures; Octanes; Particle Size; Porosity; Silicon; Surface Properties; Water

Nanometer-size menisci of organic liquids such as octane and 1-octene have been formed and used to confine chemical reactions. The application of a bias voltage between a conductive scanning probe tip separated a few nanometers from a silicon surface allows the field-induced formation of nanometer-size liquid menisci that can subsequently be used to fabricate nanometer-size structures. We report the fabrication of sub-10-nm nanostructures in 0.1 ms. Growth kinetics studies reveal that the nanostructure composition and its formation mechanism are organic-solvent-dependent. Both voltage polarities can be used to grow nanostructures, although the growth rate is significantly higher for positively biased samples. These experiments allow us to produce in the same sample two chemically different nanostructures that are easily addressed and positioned and have sub-10-nm features.

Topics: Alkenes; Kinetics; Macromolecular Substances; Microscopy, Atomic Force; Models, Molecular; Nanostructures; Nanotechnology; Octanes; Oscillometry; Oxygen; Silicon; Time Factors; Water