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Mean radical lifetimes and fluctuations in lifetime are shown to decrease with conversion and polydispersity index for atom transfer radical polymerization (ATRP) of both methyl methacrylate and st...

A composite film made of a stable gold nanoparticle (NP) array with well-controlled separation and size atop a TiO2 nanorod film was fabricated via the oblique angle deposition (OAD) technique. The fabrication of the NP array is based on controlled, Rayleigh-instability-induced, solid-state dewetting of as-deposited gold aggregates on the TiO2 nanorods. It was found that the initial spacing between as-deposited gold aggregates along the vapor flux direction should be greater than the TiO2 interrod spacing created by 80° OAD to control dewetting and produce NP arrays. A numerical investigation of the process was conducted using a phase-field modeling approach. Simulation results showed that coalescence between neighboring gold aggregates is likely to have caused the uncontrolled dewetting in the 80° deposition, and this could be circumvented if the initial spacing between gold aggregates is larger than a critical value smin. We also found that TiO2 nanorod tips affect dewetting dynamics differently than pl...

The Constrained Vapor Bubble (CVB) is a wickless, grooved heat pipe and is the first, full-scale fluids experiment flown on the U.S. module of the International Space Station. The CVB promises to provide new insight into the operation of a heat pipe in space. It is a relatively simple device constructed from a spectrophotometer cuvette and uses pentane as the working fluid. The pentane flows within the corners of the cuvette due to a curvature gradient in the liquid menisci associated with the cuvette corners. The curvature of the liquid interface can be determined by viewing the meniscus through the transparent quartz walls. Extremely accurate temperature and pressure measurements were obtained in addition to the images. In the article, the results from the first two CVB modules—a dry calibration module and a wet heat pipe module—are presented. We show that the axial temperature profiles are significantly different in space. The heat pipes were seen to operate at a higher pressure and higher temperature ...

A new type of draft tube spout-fluid bed (DTSFB) is described in which the draft tube physically separates the particle feeder section from the particle separator section as seen in Figure 2, creating an extremely versatile fluid/solids processing apparatus. This arrangement, denoted a type 2 DTSFB, allows the fluid mass flow rate in the draft tube and the dynamic pressure drop across it to be independently specified. As a result, the solids mass flow rate in the draft tube can be set and/or varied by changing the solids fraction, the particle velocity, or both. An additional property of this new DTSFB is that the effluents from the draft tube and annulus do not mix. Either stream can be collected or recycled as needed. In addition, the unit is easily controlled and scaled, and fluid—particle processing can be conducted in the draft tube, annulus, fluid—particle separator, or a combination of all of these. Equations are presented and sample calculations made to show how this new DTSFB works and how the solids fraction and particle velocity in the draft tube are set and varied. The data of Grbavcic et al. (Can. J. Chem. Eng. 1992, 71, 895-905) form the basis for the sample design calculations presented for a water-driven type 2 DTSFB. It is also shown that three independent variables capable of specifying the total mass fluid flow rate entering the inlet section, the split in that flow between the draft tube and annulus surrounding the draft tube and the dynamic pressure drop across the draft tube completely specifies the fluid and particle flows. Basic control schemes are outlined. A general equation is derived for calculating the maximum superficial fluid velocity allowable in the annulus (U a.max ). That velocity must be less than (U mF - ∈ a υ a ). Calculations demonstrate the effects of varying the total fluid mass flow rate supplied to the inlet section, the split of that fluid flow rate between the draft tube and the annulus, and the effect of the solids fraction and the dynamic pressure drop across the draft tube. Other calculations showing the effect of feeding all the inlet fluid flow to the draft tube provides a means for calculating the bounding limits that the annulus flow has on the operation of a type 2 DTSFB. Finally, we show the maximum particle circulation rate in the draft tube for a given fluid velocity in the annulus that will result in incipient fluidization of the annulus solids.

The ability to pattern different polymers in microfluidic channels is indispensable for the development of multifunctional, "lab-on-a-chip" devices. A simple method, based on the concept of selective filling, is described for introducing different polymers at defined locations in microfluidic channels. Selective filling is based on the difference in the free energy of filling between an open and a covered part of the channel. It is implemented by covering part of the channel, along its length, with a temporary poly(dimethylsiloxane) (PDMS) slab. Preferential filling is related to the contact angle of the liquid solution on the chip surface. An expression for the critical contact angle is derived, and its dependence on the geometry of the channel is established. It is further shown that a trapezoidal geometry of the cross-section of the channel is optimal for selective filling. Experimental verification of the applicability of the critical contact angle in predicting selective filling is demonstrated by introducing liquid prepolymer solutions of different contact angles in the glass channel that was etched using photolithography and wet etching. Finally, patterning of two different polymers along the axial direction of the microfluidic channel is demonstrated using this selective filling technique.

Water adsorption is undesirable in microelectronics processing because it increases the dielectric constant of the insulator, may lead to the corrosion of metal lines, and can act as a source for the generation of copper ions that can lead to copper drift in a dielectric. We have shown by chemical modification of the surface that the degree of hydrophobicity is a function of the chemical nature of porous low-k dielectric films. Chemical surface modification of nanoporous silica films markedly reduces the moisture uptake and reveals the importance of chemically bound or adsorbed water species in the dielectric and how it triggers metal diffusion. That is, when the organic groups left by the surface modifier are removed by high-temperature sintering, the hydrophobicity of the dielectric film is markedly reduced, more copper ions are generated, and copper drift in the dielectric is increased significantly. We propose that water-related traps in the dielectric films have two effects on metal diffusion: (a) they ionize the metal to form a nonstoichiometric oxide, which acts as the source of metal ions for diffusion; and (b) water-related traps in the dielectric are generated by the action of the external electric field and once generated they create space-charged regions where the local electric field exceeds the external applied field by a substantial amount; this enhances metal charge injection. The relationship between moisture uptake and porosity in nanoporous dielectrics is presented and correlated to metal charge injection. A quantitative analysis by capacitance-voltage measurements is presented of Cu drift in dense and nanoporous low-k dielectric films that reveals the role of Cu ions in the degradation and breakdown of a dielectric. The mechanism for metal diffusion and charge injection, and its dependence on porosity, pore size, surface area, and surface chemistry of the dielectric, are discussed. A physically based mathematical model of diffusion through dense and nanoporous solids has been developed considering bulk and surface diffusion and different concentrations of water-related traps. This model is used to interpret some of the experimental results obtained and confirms that diffusion barriers markedly reduce the injection of copper into dielectrics.

The slow growth characteristics of a condensing ethanol sessile drop on a quartz substrate were studied experimentally. Using interference microscopy measurements of the transient liquid film profile (curvature) to obtain the pressure field and a Kelvin−Clapeyron model of interfacial mass flux to obtain the interfacial temperature difference, changes in the apparent contact angle were related to interfacial subcooling and, therefore, adsorption. We found that while the radius of curvature of the growing drop increased linearly with time, the apparent contact angle remained the same during slow growth at a constant condensation heat flux. The radii of curvature and the apparent contact angles at different axial locations were measured and compared. The results demonstrated that the curvature, the contact angle, the interfacial subcooling, the interfacial mass flux, the spreading velocity, and adsorption are coupled at the moving contact line. Motion and the apparent contact angle are governed by the conden...