Studying soft interfaces with shear waves: principles and applications of the quartz crystal microbalance (QCM)

The response of the quartz crystal microbalance (QCM) to loading with a diverse set of samples is reviewed in a consistent frame. After a brief introduction to the advanced QCMs, the governing equation (the small-load approximation) is derived. Planar films and adsorbates are modeled with the acoustic multilayer formalism. In liquid environments, viscoelastic spectros-copy and high-frequency rheology are possible, even on layers with a thickness in the monolayer range. For particulate samples, rheology is replaced by contact mechanics. The contact stiffness can be derived. Because the stress at the contact is large, nonlinear effects are seen. Partial slip, in particular, can be studied in detail. Advanced topics include structured samples and the extension of the small-load approximation to its tensorial version

Studying Soft Interfaces with Shear Waves: Principles and Applications of the Quartz Crystal Microbalance (QCM)

The response of the quartz crystal microbalance (QCM) to loading with a diverse set of samples is reviewed in a consistent frame. After a brief introduction to the advanced QCMs, the governing equation (the small-load approximation) is derived. Planar films and adsorbates are modeled with the acoustic multilayer formalism. In liquid environments, viscoelastic spectros-copy and high-frequency rheology are possible, even on layers with a thickness in the monolayer range. For particulate samples, rheology is replaced by contact mechanics. The contact stiffness can be derived. Because the stress at the contact is large, nonlinear effects are seen. Partial slip, in particular, can be studied in detail. Advanced topics include structured samples and the extension of the small-load approximation to its tensorial version

A modulation QCM applied to copper electrodeposition and stripping

A fast electrochemical quartz crystal microbalance with dissipation monitoring (EQCM−D) was applied to copper electrodeposition and subsequent stripping. Accumulation brings the frequency noise down to the mHz range, corresponding to 0.1 % of a monolayer. With this precision, the apparent mass transfer rate as determined from the time-derivative of the frequency shift can be directly compared to the current. Small but systematic deviations between the two can be attributed to nanoscale roughness. In the voltage range of underpotential deposition (UPD), the apparent mass transfer rate shows peaks and shoulders. The plating additive benzotriazole (BTA) leaves the magnitude of electrogravimetric signals unchanged, but shifts the UPD onset potential. The additive thiourea (TU) promotes UPD and strongly increases the bandwidth

Fouling pathways in emulsion polymerization differentiated with a quartz crystal microbalance (QCM) integrated into the reactor wall

Emulsion polymerization fouling at hot interfaces is studied in situ, making use of a quartz crystal microbalance with dissipation monitoring (QCM-D). The resonator crystal is heated with a ring-shaped thermal pad from the back, turning it into a plate with elevated temperature. Configured to be one of the walls of a small reactor for emulsion polymerization, this resonator is prone to heat-transfer fouling, similar to regular heated parts of process equipment. The fouling kinetics is readily quantified with this QCM. During polymerization at constant temperature (80 °C), some deposition is always observed. However, a film with a thickness of less than 1 μm (determined gravimetrically with the QCM) is sometimes found, which stabilizes the surface against the deposition of much thicker layers. When reaction fouling proceeds directly to thick deposits, a small increase in resonance bandwidth often occurs a few minutes prior to the main transition, presumably caused by coagulum formed in the bulk making first contact with the surface. Furthermore, particle fouling is studied with temperature ramps on nonreactive dispersions. Fouling, if present, is readily observed

A quartz crystal microbalance, which tracks four overtones in parallel with a time resolution of 10 milliseconds: application to inkjet printing

A quartz crystal microbalance (QCM) is described, which simultaneously determines resonance frequency and bandwidth on four different overtones. The time resolution is 10 milliseconds. This fast, multi-overtone QCM is based on multi-frequency lockin amplification. Synchronous interrogation of overtones is needed, when the sample changes quickly and when information on the sample is to be extracted from the comparison between overtones. The application example is thermal inkjet-printing. At impact, the resonance frequencies change over a time shorter than 10 milliseconds. There is a further increase in the contact area, evidenced by an increasing common prefactor to the shifts in frequency ,∆f, and half-bandwidth, ∆Γ. The ratio ∆Γ/(−∆f), which quantifies the energy dissipated per time and unit area, decreases with time. Often, there is a fast initial decrease, lasting for about 100 milliseconds, followed by a slower decrease, persisting over the entire drying time (a few seconds). Fitting the overtone dependence of ∆f(n) and ∆Γ(n) with power laws, one finds power-law exponents of about 1/2, characteristic of semi-infinite Newtonian liquids. The power-law exponents corresponding to ∆f(n) slightly increase with time. The decrease of ∆Γ/(−∆f) and the increase of the exponents are explained by evaporation and formation of a solid film at the resonator surface

Particle fouling at hot reactor walls monitored In situ with a QCM-D and modeled with the frequency-domain lattice Boltzmann method

Fouling at a hot reactor wall during emulsion polymerization was studied in-situ with a quartz crystal microbalance with dissipation monitoring (QCM-D). Transient maxima in resonance bandwidth were observed, which are typically interpreted as the signature of a coupled resonance. However, the most common type of coupled resonances, the film resonance, cannot explain these observations, because the film resonance should occur first on the high overtones (on the overtones with small wavelength). In experiment, the low overtones reach the maximum first. The maximum in dissipation can be explained with the particulate nature of the sample. As the particles flatten out and merge, the height of the layer decreases and the surface becomes smoother. The decreasing height lets the layer go through the film resonance in reversed order. Also, the decreasing roughness lets the bandwidth decrease, unrelated to the film resonance. The argument is substantiated with a simulation based on the frequency-domain lattice Boltzmann method (FD-LBM). Apart from explaining the features seen in QCM experiments on particle fowling, this case study demonstrates the capabilities of FD-LBM

Effect of Noise on Determining Ultrathin-Film Parameters from QCM-D Data with the Viscoelastic Model

Quartz crystal microbalance with dissipation monitoring (QCM-D) is a well-established technique for studying soft films. It can provide gravimetric as well as nongravimetric information about a film, such as its thickness and mechanical properties. The interpretation of sets of overtone-normalized frequency shifts, ∆f/n, and overtone-normalized shifts in half-bandwidth, ΔΓ/n, provided by QCM-D relies on a model that, in general, contains five independent parameters that are needed to describe film thickness and frequency-dependent viscoelastic properties. Here, we examine how noise inherent in experimental data affects the determination of these parameters. There are certain conditions where noise prevents the reliable determination of film thickness and the loss tangent. On the other hand, we show that there are conditions where it is possible to determine all five parameters. We relate these conditions to the mathematical properties of the model in terms of simple conceptual diagrams that can help users understand the model’s behavior. Finally, we present new open source software for QCM-D data analysis written in Python, PyQTM

Lessons Learned from Co-Evolution of Software Process and Model-Driven Engineering

Software companies need to cope with permanent changes in market. To stay competitive it is often inevitable to improve processes and adopt to new technologies. Indeed, it is well know that software processes and model-driven engineering (MDE) are subject to evolution. Simultaneously, it is known that MDE can affect process tailoring, which makes it possible that evolution in MDE triggers process evolution and vice versa. This can lead to undesired process changes and additional cost, when process adaptations constitute a need for further investments in MDE tooling. However, there is little knowledge so far whether this co-evolution exists and how it looks like. In this chapter, we present two industrial case studies onco-evolution of MDE and software process. Based on these case studies, we present an initial list of co-evolution drivers and observations made on co-evolution of softwareprocesses and MDE. Furthermore, we compile our lessons learned to directly help process managers dealing with co-evolution