Facile fabrication of a rigid and chemically resistant micromixer system from photocurable inorganic polymer by static liquid photolithography (SLP)

Highly effective mixing in microchannels is important for most chemical reactions conducted in microfluidic chips. To obtain a rigid and chemically resistant micromixer system at low cost, we fabricated a Y-shaped microchannel with built-in mixer structures by static liquid photolithography (SLP) from methacrylated polyvinylsilazane (MPVSZ) as an inorganic polymer photoresist which was then converted to a silicate phase by hydrolysis in vaporized ammonia atmosphere at 80 °C. The microchannel incorporating herringbone mixer structures was bonded with a matching polydimethylsiloxane (PDMS) open channel which was pre-coated by perhydropolysilazane (PHPS)-based mixture, and finally treated by additional hydrolysis at room temperature to convert the PHPS layer to a silica phase. Finally, the chemical resistance of the microfluidic system with embedded micromixer was confirmed with various solvents, and the excellent mixing performance in a short mixing length of 2.3 cm was demonstrated by injecting two different colored fluids into the microchannel.     

Chemical and physical processes for integrated temperature control in microfluidic devices

Microfluidic devices are a promising new tool for studying and optimizing (bio)chemical reactions and analyses. Many (bio)chemical reactions require accurate temperature control, such as for example thermocycling for PCR. Here, a new integrated temperature control system for microfluidic devices is presented, using chemical and physical processes to locally regulate temperature. In demonstration experiments, the evaporation of acetone was used as an endothermic process to cool a microchannel. Additionally, heating of a microchannel was achieved by dissolution of concentrated sulfuric acid in water as an exothermic process. Localization of the contact area of two flows in a microfluidic channel allows control of the position and the magnitude of the thermal effect.     

Hydrodynamic control of droplet division in bifurcating microchannel and its application to particle synthesis

We describe herein a microfluidic system for active and precise control of droplet division at a bifurcation point in a microchannel. Water-in-oil or oil-in-water droplets, which were initially formed at a T-junction, were introduced into the bifurcation point, and then divided into two daughter droplets. By continuously introducing 'tuning flow' into the downstream of one of the branch channels, and by controlling the flow rates distributed into the two branch channels, the sizes of the daughter droplets could be precisely tuned. The ratio of the volumetric flow rates into the branch channels was estimated by regarding the microchannel network as a resistive circuit. In addition, we performed synthesis of monodispersed polymer particles with controlled sizes utilizing the presented system. The ability to hydrodynamically control the droplet sizes will open new possibilities not only for producing useful emulsions, but also for conducting controlled chemical and biochemical reactions in a confined space.     

Solar heat storage using chemical reactions

As an alternative to storage of sensible heat in liquids or solids or as latent heat of fusion, heat storage by means of reversible chemical reactions is under investigation. By this method, a chemical is separated into two components by heating and heat absorption, following which the components are stored in separate vessels and are recombined to generate heat when it is needed. The attractiveness of this concept of heat storage is not only higher energy density, but the capability to store energy as long as desired at ambient temperature, the option of transporting the chemicals to generate heat at another location, and the high temperatures characteristic of some of the reactions which result in high efficiency when the stored heat is used to generate electricity. Many reactions have been proposed and analyzed. Experimental work is in progress on inorganic hydroxide/oxide reactions, the decomposition of ammoniated salts, sulfur trioxide decomposition, ammonium sulfate decomposition, and others. The problems to be solved and potential applications are illustrated by the results of work in progress on Mg(OH)₂ and Ca(OH)₂ decomposition.     

An actuated pump on-chip powered by cultured cardiomyocytes

Cellular functions are frequently exploited as processing components for integrated chemical systems such as biochemical reactors and bioassay systems. Here, we have created a new cell-based microsystem exploiting the intrinsic pulsatile mechanical functions of cardiomyocytes to build a cellular micropump on-chip using cardiomyocyte sheets as prototype bio-microactuators. We first demonstrate cell-based control of fluid motion in a model microchannel without check valves and evaluate the potential performance of the bio-actuation. For this purpose, a poly(dimethylsiloxane) (PDMS) microchip with a microchannel equipped with a diaphragm and a push-bar structure capable of harnessing collective cell fluid mechanical forces was coupled to a cultured pulsating cardiomyocyte sheet, activating cell-based fluid movement in the microchannel by actuating the diaphragm. Cell oscillation frequency and correlated fluid displacement in this system depended on temperature. When culture temperature was increased, collective cell contraction frequency remained cooperative and synchronous but increased, while displacement was slightly reduced. We then demonstrated directional fluid pumping within microchannels using cantilever-type micro-check valves made of polyimide. A directional flow rate of nL min(-1) was produced. This cell micropump system could be further developed as a self-actuated and efficient mechanochemical transducer requiring no external energy sources for various purposes in the future.     

Millisecond treatment of cells using microfluidic devices via two-step carrier-medium exchange

We present herein a simple but versatile microfluidic system for the treatment of cells with millisecond chemical stimulus, by rapidly exchanging the carrier-medium of cells twice in a microchannel. A technique we refer to as 'hydrodynamic filtration' has been employed for the exchange of medium, in which the virtual width of flow in the microchannel determines the size of filtered cells/particles. The treatment time of cells could be rigidly adjusted by controlling the inlet flow rates and by changing the volume of the stimulating area in the microchannel. In the experiment, two types of microdevices were designed and fabricated, and at first, the ability for carrier-medium exchange was confirmed. As an application of the presented system, we examined the influence of the treatment time of HeLa cells with Triton X-100, a non-ionic surfactant used to solubilize the cellular membrane, on cell viability, varying the average treatment time from 17 to 210 ms. Both quantitative and qualitative analyses were performed to estimate the damage on cell membrane, demonstrating that the cell viability dramatically decreased when the treatment time was longer than approximately 40 ms. The obtained results demonstrated the ability of the presented system to conduct the rapid stimulation of cells, which would be useful for the analysis of biochemical reactions at the cell surface.     

High-temperature thermodynamics of chemical transport reactions in the tungsten-bromine system of halogen-incandescent lamps and its influence by hydrogen,oxygen and carbon

The simultaneous reaction equilibria in the heterogeneous system tungsten- bromine and its influence by hydrogen, oxygen and carbon can be evaluated on the basis of chemical thermodynamics. By an analysis of the temperature dependence of the mass-balance of tungsten the chemical transport reactions in these systems and the burning behaviour of halogen-incandescent lamps may be predicted.Using thermodynamic data as given in the JANAF Tables or evaluated by comparison with related systems computer-calculations have been made for temperatures 500–4000 K for the various reaction equilibria in the tungsten-bromine system including the influence of the additional constituents. Results for the chemical transport reactions are compared to lamp experiments. From the results of the thermodynamic analysis a scheme of the mechanism of the tungsten-bromine cycle in halogen-incandescent lamps is revealed.     

Autowave modes of polymerization and other reactions in solid frozen matrixes near of absolute zero and their role in mechanisms of fast chemical transformations of substance in universe

Almost two decades ago there were discovered new autowave selfpropagation phenomena in the cryo‐chemical reactions at investigating of chemical solid phase transformations near absolute zero of temperatures. Such an autowave regime is observed for different classes of chemical reactions (polymerisation, copolymerisation and also hydrocarbon halogenation, hydro‐halogenation etc). The chemical transformations studied at the such low temperatures 4–77 K proceeded with so great rates that they can be compared only with the fastest high‐temperature combustion reactions known in chemistry. It allows to advance a principally new autowave conception of the matter chemical activity in solid state. The essentially non‐Arrenius conception is based on the assumption that a mechanical energy accumulated in solid matrix can be transformated to the chemical forms.     

Polymer channel chips as versatile tools in microchemistry.

The paper describes the fabrication and chemical applications of polymer microchannel chips, with special reference to in situ observations of the chemical/physical processes occurring in polystyrene microchannel chips, including those in microchannel-microelectrode/microheater chips. On the basis of absorption/fluorescence microspectroscopy and microelectrochemistry techniques, we show some characteristic features of liquid/liquid extraction, electrochemical responses, and photochemical/electrochemical/thermal synthetic reactions in microchannel chips.     

Spectroscopy of Fluid Phases—The Study of Chemical Reactions and Equilibria up to High Pressures

The properties of fluid phases can be altered considerably by the external conditions. Phase equilibria and chemical equilibria can be greatly affected, and it is possible to carry out chemical reactions by exploiting the special properties of compressed fluid phases. The use of high pressure in chemical reactions is of considerable diagnostic and preparative value. Applied research is directed towards elucidating the details of existing technical high pressure processes and to the development of novel fluid phase reactions where the application of high pressure is able to induce selectivity. In order to pursue these lines of research, and to study structure and dynamics throughout the entire range from gaseous to liquidlike states, it is important to have spectroscopic methods for characterizing systems at high pressures and temperatures. This article is concerned with quantitative absorption spectroscopy in the infrared to the ultraviolet spectral region at pressures up to about 7 kbar and temperatures up to 900 K.     

The reactive states of ions: Antiaromatic seven-membered N-substituted-1H-azepines and isomeric aromatic substrates

Comparison of the electron impact and chemical ionization mass spectra of N-substituted-1H-azepines and isomeric aromatic substrates reveals significant differences. The data indicate that the substituted azepincs examined are stable to electron impact at low temperatures and retain their antiaromatic 8π electron seven-membered cyclic system prior to their fragmentation. The electron impact data are supported by low electron-volt and metastable scan techniques. Electron impact or chemical ionization induced transformation of azepines to aromatic substrates similar to the thermal transformation of neutral analogues is not observed at low temperatures. Chemical ionization mass spectra of N-ethoxycarbonyl-1H-azepines and N-phenylcarbamates were complicated owing to thermal decomposition reactions at high temperatures.     

Microchip-based enzyme-linked immunosorbent assay (microELISA) system with thermal lens detection

A microchip-based enzyme-linked immunosorbent assay (microELISA) system was developed and interferon-gamma was successfully determined. The system was composed of a microchip with a Y-shaped microchannel and a dam structure, polystyrene microbeads, and a thermal lens microscope (TLM). All reactions required for the immunoassay were done in the microchannel by successive introduction of a sample and regents. The enzyme reaction product, in a liquid phase, was detected downstream in the channel using the TLM as substrate solution was injected. The antigen-antibody reaction time was shortened by the microchip integration. The limit of the determination was improved by adopting the enzyme label. Moreover, detection procedures were greatly simplified and required time for the detection was significantly cut. The system has good potential to be developed as a small and automated high throughput analyzer.     

Stability of chemical sequence in a periodic polymeric nematogen

The stability of a polymeric nematogen's chemical sequence was studied by differential scanning calorimetry, optical microscopy, and ¹³C-NMR; the nematogen studied was a thermotropic polyester and had a periodic chemical structure. Model compounds were used to investigate transesterfication in the melt at different temperatures with the addition of phenol or benzoic acid as analogues of polymer end groups. Ester interchange reactions at high temperature were found to be partly suppressed when acidic end groups of the periodic nematogen were capped. However, sequence reorganization was completely suppressed in capped nematogens when temperatures remained below the isotropization transition of the nematogen investigated. Rapid disordering of the periodic nematogen was observed above the nematic-isotropic transition, suggesting that both chemical and physical factors play a role in sequence redistribution of periodic nematogens. © 1994 John Wiley & Sons, Inc.     

RP-3航空煤油高温骨架机理构建及验证

依据RP-3航空煤油的成分,考虑平均分子量及碳氢摩尔比等性质,本文提出其三组分替代燃料模型,其中正癸烷74.24%、1,3,5-三甲基环己烷14.11%和正丙基苯11.65%(质量分数)。采用机理生成程序ReaxGen得到详细化学反应机理;采用机理简化程序ReaxRed,运用直接关系图法与主成分分析法获得高温骨架机理(79物种,311反应)。该机理针对多个工况进行了点火延迟时间与层流火焰速度的验证,能较好地预测实验结果。路径分析结果表明高温下替代燃料通过氢提取反应、单分子裂解反应及β-断键反应消耗。敏感性分析表明高温点火过程由多种小分子自由基(H、CHO、C2H3等)的氧化及分解反应和大分子燃料的氢提取反应控制;影响火焰传播过程的关键反应来源于C0-C3的小分子核心机理。本文所提出的这个尺寸较小但精度较高的骨架机理可用于发动机燃烧过程的高保真数值模拟。     

Self-propagating metathesis routes to metastable group 4 phosphides

Group 4 phosphides, which are typically prepared at high temperatures (> 800 degrees C) over several days, are synthesized in self-propagating metathesis (exchange) reactions in seconds. These reactions produce cubic forms of zirconium phosphide (ZrP) and hafnium phosphide (HfP) which are normally made at temperatures greater than 1425 degrees C and 1600 degrees C, respectively. To test whether the high temperatures reached in the metathesis reactions are responsible for the formation of the cubic phases, inert salts are added to lower the maximum reaction temperatures. The lower temperature reactions still result in cubic phosphides, although smaller crystallites form. Further experiments with phosphorus addition indicate that the phosphorus content is not responsible for cubic phase formation. Templating is ruled out using lattice mismatched KCl and hexagonal ZnS as additives. Therefore, the direct synthesis of the high-temperature cubic phase in metathesis reactions appears to be caused by nucleation of the metastable cubic form that is then trapped by rapid cooling. Heating the cubic phase of either ZrP or HfP to 1000 degrees C for 18 h, or carrying out metathesis reactions in sealed ampules at 1000 degrees C, results only in the hexagonal phase.     

Hydrogenation reactions using scCO2 as a solvent in microchannel reactors

We have developed an effective microfluidic system for hydrogenation reactions in scCO(2); the reactions proceeded very rapidly (within 1 second), by making the best use of scCO(2) and utilizing the large specific interfacial area of the microchannel reactor, and high reaction productivity was attained in each channel.     

Compact fluorescence detection using in-fiber microchannels-its potential for lab-on-a-chip applications

This paper reports a compact and practical fluorescence sensor using an in-fiber microchannel. A blue LED, a multimode PMMA or silica fiber and a mini-PMT were used as an excitation source, a light guide and a fluorescence detector, respectively. Microfluidic channels of 100 microm width and 210 microm depth were fabricated in the optical fibers using a direct-write CO(2) laser system. The experimental results show that the sensor has high sensitivity, able to detect 0.005 microg L(-1) of fluorescein in the PBS solution, and the results are reproducible. The results also show that the silica fiber sensor has better sensitivity than that of the PMMA fiber sensor. This could be due to the fouling effect of the frosty layer formed at the microchannel made within the PMMA fiber. It is believed that this fiber sensor has the potential to be integrated into microfluidic chips for lab-on-a-chip applications.     

Side reactions in controlling the quality, yield, and stability of high quality colloidal nanocrystals

Effects of side reactions during the formation of high quality colloidal nanocrystals were studied using ZnO as a model system. In this case, an irreversible side reaction, formation of esters, was identified to accompany formation of ZnO nanocrystals through the chemical reaction between zinc stearate and an excess amount of alcohols in hydrocarbon solvents at elevated temperatures. This irreversible side reaction made the resulting nanocrystals stable and with nearly unity yield regardless of their size, shape, and size/shape distribution. Ostwald ripening and intraparticle ripening were stopped due to the extremely low solubility/stability of the possible monomers because all free ligands in the solution were consumed by the side reaction. However, focusing on size distribution and 1D growth that are needed for the growth of high quality nanocrystals could still occur for high yield reactions. Upon the addition of a small amount of stearic acid or phosphonic acid, immediate partial dissolution of ZnO nanocrystals took place. Although the excess alcohol could not react with the resulting zinc phosphonic acid salt, it could force the newly formed zinc stearate gradually but completely back onto the existing nanocrystals. The results in this report indicate that side reactions are extremely important for the formation of high quality nanocrystals by affecting their quality, yield, and stability under growth conditions. Due to their lack of information in the literature and obvious practical advantages, studies of side reactions accompanying formation of nanocrystals are important for both fundamental science related to crystallization and industrial production of high quality nanocrystals.     

Quantum theory of chemical reactions in the presence of electromagnetic fields

We present a theory for rigorous quantum scattering calculations of probabilities for chemical reactions of atoms with diatomic molecules in the presence of an external electric field. The approach is based on the fully uncoupled basis set representation of the total wave function in the space-fixed coordinate frame, the Fock-Delves hyperspherical coordinates, and the adiabatic partitioning of the total Hamiltonian of the reactive system. The adiabatic channel wave functions are expanded in basis sets of hyperangular functions corresponding to different reaction arrangements, and the interactions with external fields are included in each chemical arrangement separately. We apply the theory to examine the effects of electric fields on the chemical reactions of LiF molecules with H atoms and HF molecules with Li atoms at low temperatures and show that electric fields may enhance the probability of chemical reactions and modify reactive scattering resonances by coupling the rotational states of the reactants. Our preliminary results suggest that chemical reactions of polar molecules at temperatures below 1 K can be selectively manipulated with dc electric fields and microwave laser radiation.