Quartz Crystal Microbalance Data Research Articles

Robust Metal Oxide Adhesion Layers for Cellulose Nanofiber-Based QCM Sensors.

Here, we demonstrate the significant role of robust metal oxide adhesion layers on the cellulose nanofiber (CNF)-based quartz crystal microbalance (QCM) humidity sensor characteristics including sensitivity and stability. In this study, we deposited various metal oxide films (NiO, TiO2, ZnO, and WO3) onto QCM Au electrodes as adhesion layers before drop-casting CNF dispersion water. These metal oxide adhesion layers significantly enhanced the stability of CNF films on QCM sensors even in a high-humidity environment where a conventional adhesion layer (polyethylenimine) for CNF could not maintain stable adhesion. There was a significant difference between different metal oxide layers in the QCM data for humidity sensing. We found a negative correlation between the QCM sensitivity and the water wettability of metal oxide surfaces. Morphology analysis of the deposited CNF films revealed that the center-concentrated CNF microstructures on the metal oxide adhesion layers rigorously explained the observed negative correlation between the sensitivity and the wettability of metal oxide surfaces. This trend was further confirmed by gradually changing the hydrophobicity of the NiO adhesion surfaces. Thus, the proposed strategy using robust metal oxide adhesion layers will be a foundation for further development of various CNF-based QCM gas sensors.

Order-Order Transition in Statistical Copolymer Thin Film Induced by LCST-Type Behavior.

In this paper, we describe the formation of an ordered structure in a copolymer thin film through hydration, which subsequently transitions to a different ordered structure upon dehydration. A statistical copolymer of poly(N-octadecyl acrylamide-stat-hydroxymethyl acrylamide) with a comonomer content ratio of 1:1, denoted as p(ODA50/HEAm50), was synthesized via free radical copolymerization. We prepared a thin film of this copolymer on a solid substrate and annealed it at 60 °C under humid conditions. This treatment formed a side-chain segregated lamellar (SCSegL) structure, in which the ODA and HEAm units are oriented perpendicularly to the polymer backbone and opposite each other. Increasing the annealing temperature to 90 °C led to a transition to a side-chain mixed lamellar (SCMixL) structure, where the ODA and HEAm units are also oriented perpendicularly to the polymer backbone but in both directions. The quartz crystal microbalance (QCM) data indicate that p(ODA50/HEAm50) exhibits LCST-like behavior with a transition temperature of approximately 50 °C. We conclude that the formation of the SCSegL structure at 60 °C is due to pronounced segregation between the water-adsorbed HEAm groups and the hydrophobic ODA. Conversely, dehydration at 90 °C reduces the segregation forces, forming the SCMixL structure, which exhibits lower strain. These results demonstrate that the p(ODA50/HEAm50) film undergoes an order-to-order transition driven by the hydration-dehydration process. Additionally, we found that changes in the lamellar structure significantly alter the swelling properties of the film.

ALC_EQCM: Automated stoichiometric resolution in electrochemistry through Density Functional Theory aided, Electrochemical Quartz Crystal Microbalance

ALC_EQCM is a software for post-processing Electrochemical Quartz Crystal Microbalance (EQCM) data. The implemented functionalities allow qualitative and quantitative characterization of the EQCM response, which is used to derive information of stoichiometric changes during electrochemical reactions and automatically generate atomistic models compatible with EQCM data. Through extra user-defined directives, ALC_EQCM also provides input files to execute Density Functional Theory simulations of the generated models on high-performance computing facilities. The possibility of linking EQCM data with simulation capabilities offers a novel strategy to explore configurations only compatible with experiments and support the research of complex reactions in electro-active materials.

Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry Study.

Recent work has shown that ion-selective components may be transferred from nanoemulsions (NEs) to endow polymeric membranes with ion-selective sensing properties. This approach has also been used for nanopipette electrodes to achieve single-entity electrochemistry, thereby sensing the ion-selective response of single adhered nanospheres. To this date, however, the mechanism and rate of component transfer remain unclear. We study here the transfer of lipophilic ionic compounds from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS) films by chronoamperometry and quartz crystal microbalance. Thin-film cyclic coulovoltammetry measurements serve to quantify the uptake of lipophilic species into blank PVC-DOS membranes. Electrochemical quartz crystal microbalance data indicate that the transfer of the emulsion components is insignificant, ruling out simple coalescence with the membrane film. Ionophores and ion-exchangers are shown to transfer into the membrane at rates that correlate with their lipophilicity if mass transport is not rate-limiting, which is the case with more lipophilic compounds (calcium and sodium ionophores). On the other hand, with less lipophilic compounds (valinomycin and cation-exchanger salts), transfer rates are limited by mass transport. This is confirmed with rotating disk electrode experiments in which a linear relationship between the diffusion layer thickness and current is observed. The data suggests that once the nanoemulsion container approaches the membrane surface, transfer of components occur by a three-phase partition mechanism where the aqueous phase serves as a kinetic barrier. The results help better understand and quantify the interaction between nanoemulsions and ion-selective membranes and predict membrane doping rates for a range of components.

Erosion Rate Measurements for DART Spacecraft Ion Propulsion System

The Double Asteroid Redirection Test (DART) spacecraft was developed to provide the first measurement for orbital deflection of an asteroid upon intentional impact. The NEXT ion engine is part of the mission, on its maiden voyage. As part of the pre-launch risk reduction, erosion characteristics of the extraction grid system were evaluated using laser measurements of sputtered molybdenum atoms over the envelope of potential throttle conditions for the mission. Erosion rate dependence on propellant flow rate as well as relative density and directionality of molybdenum sputter from grid center to edge were measured. Sputtered atoms were found to have average radial velocity directed toward the engine perimeter and increasing with radial distance. The relative contribution of source and facility background gas and other sources of accelerator grid current was examined as well as the influence of several engine operating parameters. Facility background gas was found to influence engine operation more than a wall-mounted pressure gauge and typical assumptions about ingestion would indicate. Far-field flux was estimated over the full angular range based on the near-field relative density and velocity results and relying on quartz crystal microbalance data at one location to fix absolute numbers everywhere. The results substantially deepen knowledge and understanding of the complex grid erosion process of the engine and its lifetime, as grid failure via erosion is the normal life limiter. Study results are also relevant to thruster–spacecraft integration issues such as molybdenum deposition rate on solar cells and other spacecraft surfaces.

Role of Mass Transport in the Deposition, Growth, and Transformation of Calcium Carbonate on Surfaces at High Supersaturation.

We demonstrate how combined in-situ measurements and finite element method modeling can provide new insight into the relative contribution of mass transport to the growth of calcium carbonate on two model surfaces, glass and gold, under high-supersaturation conditions relevant to surface scaling. An impinging jet-radial flow system is used to create a high-supersaturated solution at the inlet of different cells: an optical microscope cell presenting a glass surface for deposition and quartz crystal microbalance (QCM) and in-situ IR spectroscopy cells, both presenting a gold surface. The approach described is quantitative due to the well-defined mass transport, and both time-lapse optical microscopy images and QCM data are analyzed to provide information on the growth kinetics of the calcite crystals. Initially, amorphous calcium carbonate (ACC), formed in solution, dominates the deposition process. At longer times, the growth of calcite is more significant and, on glass, is observed to consume ACC from the surface, leading to surface regions depleted of ACC developing around calcite microcrystals. On Au, the mass increase becomes linear with time in this region. Taken together, these microscopic and macroscopic measurements demonstrate that calcite growth has a significant component of mass transport control at high supersaturation. Finite element method (FEM) simulations of mass-transport-limited crystal growth support the strong mass transport contribution to the growth kinetics and further suggest that the observed growth must be sustained by more than just the Ca2+ and CO32– in solution, with dissolution/direct attachment of ACC and/or ion pairs also contributing to the growth process.

Vapor Sorption-Desorption Phenomena of HD and GB Simulants from Polyurethane Thin Films on Aluminum Oxide via a Quartz Crystal Microbalance.

Protection and decontamination of surfaces after exposure to chemical warfare agents (CWAs) are of considerable interest to the homeland defense and battlespace operation communities. In this work, polyurethane was spin-coated onto aluminum oxide quartz crystal microbalance (QCM) sensors. Polyurethane film thickness was varied by altering the concentration of the polymer/chloroform solution used for spin-coating. Atomic force microscopy confirmed the formation of smooth, homogeneous films on the QCM sensor surface. Aluminum oxide QCM sensors coated with polyurethane were exposed to saturated vapors of dichloropentane (DCP), a mustard gas (HD) simulant, and dimethyl methylphosphonate (DMMP), a sarin gas (GB) simulant, and the mass uptake, diffusion coefficient, volume fraction, and partition coefficient of the simulant in the film were determined from QCM data. Results showed that both DCP and DMMP readily sorbed into the films although the mass uptake of DCP was greater than that of DMMP owing to DCP’s higher vapor pressure. Additionally, the CWA simulant uptake increased with polyurethane film thickness. Sorption diffusion coefficients were 1 × 10–13 cm2/s and 1 × 10–12 cm2/s for DCP and DMMP vapor, respectively. Simulant desorption was also measured and showed that some DMMP remained in the film/substrate system, while DCP sorption was fully reversible. Reversible desorption for both CWA simulants was relatively quick and independent over the range of film thicknesses studied, with average desorption diffusion coefficients of 2 × 10–9 cm2/s and 1 × 10–11 cm2/s for DCP and DMMP, respectively. Collectively, this study is expected to inform protection and decontamination strategies of equipment and structures upon exposure to CWAs.

Analysis of dissolution kinetics of narrow polydispersity poly(4-hydroxystyrene) in alkaline aqueous solution using machine learning

Understanding the dissolution kinetics of resist materials is essential for their efficient development. In this study, we investigated the dissolution kinetics of poly(4-hydroxystyrene) (PHS) with a weight-average molecular weight (M w) of 8000–30 000 and a polydispersity index (M w /M n) of 1.07–1.20. The dissolution kinetics of PHS films was observed in tetramethylammonium hydroxide (TMAH) aqueous developers by a quartz crystal microbalance (QCM) method. The TMAH concentration was changed from 0 to 2.38 wt%. The formation of a thick transient swelling layer at these M w /M n values was suppressed compared with that at M w /M n > 2. QCM data were analyzed using the polynomial regression to clarify the effects of M w and M w /M n on the dissolution kinetics in a narrow polydispersity region. Both dissolving and swelling kinetics largely depended on M w/M n. M w had little effect in 2.38 wt% TMAH developer; however, it had a large effect on the swelling when 2.38 wt% TMAH developer was diluted.

The Misconception of Mg2+ Insertion into Prussian Blue Analogue Structures from Aqueous Solution

Prussian blue analogues (PBAs) are commonly believed to reversibly insert divalent ions, such as calcium and magnesium, rendering them as perspective cathode materials for aqueous magnesium-ion batteries. In this study, the occurrence of Mg2+ insertion into nanosized PBA materials is shown to be a misconception and conclusive evidence is provided for the unfeasibility of this process for both cation-rich and cation-poor nickel, iron, and copper hexacyanoferrates. Based on structural, electrochemical, IR spectroscopy, and quartz crystal microbalance data, the charge compensation of PBA redox can be attributed to protons rather than to divalent ions in aqueous Mg2+ solution. The reversible insertion of protons involves complex lattice water rearrangements, whereas the presence of Mg2+ ion and Mg salt anion stabilizes the proton (de)insertion reaction through local pH effects and anion adsorption at the PBA surface. The obtained results draw attention to the design of proton-based batteries operating in environmentally benign aqueous solutions with low acidity.

Highly Efficient Defluoridation of Water through Reusable poly(aniline-co-o-aminophenol) Copolymer Modified Electrode Using Electrochemical Quartz Crystal Microbalance

Although the World Health Organization (WHO) recommends a limit of 1.5 mg l−1 fluoride ions in drinking water, this is not satisfied in many parts of the world. When this limit is exceeded, the electrochemically switched ion-exchange (ESIX) technique (mainly based on conductive polymers) has been identified as a promising method for removing the excess fluoride ions. The present study aimed to develop an efficient method based on the ESIX technique by using poly(aniline-co-o-aminophenol) copolymer to extract fluoride ions. Electrochemical quartz crystal microbalance (EQCM) and acoustic admittance data were utilized to assay the synthetic efficiency of copolymer deposition, and to evaluate the dependence of the defluoridation process on the proportions of the monomers in the copolymer matrix and on film thickness. The resulting films were characterised by Fourier transform infrared spectroscopy (FTIR) and scanning electrochemical microscopy (SEM) techniques. For optimized co-monomer ratio in the feedstock, poly(aniline-co-o-aminophenol) at an applied potential of 0.30 V showed excellent performance for fluoride removal from water at pH 6.6, to the extent of 20 (mg F−) (g polymer)−1. Comparison of the performance of ESIX using poly(aniline-co-o-aminophenol) with that of other techniques and materials reveal that it has significant potential for water defluoridation.

Lipid Membrane Interaction of Peptide/DNA Complexes Designed for Gene Delivery.

Among gene delivery systems, peptide-based gene carriers have received significant attention because of their selectivity, biocompatibility, and biodegradability. Since cellular membranes function as a barrier toward exogenous molecules, cell-penetrating peptides (CPPs), which are usually cationic and/or amphiphilic, can serve as efficient carriers to deliver cargo into the cytosol. Here, we examined the interactions of carrier peptides and their DNA complexes with lipid membranes using a quartz crystal microbalance (QCM) and high-speed atomic force microscopy (HS-AFM). The carrier peptides are a 12-residue partial presequence of yeast cytochrome c oxidase subunit IV (Cytcox) and BP100, which are a mitochondria-targeting signal peptide and a CPP, respectively. QCM data showed that BP100 has a higher binding affinity than Cytcox to both plasma membrane- and mitochondrial membrane-mimicking lipid bilayers. The DNA complexes with either Cytcox or BP100 exhibited the same tendency. Furthermore, HS-AFM data demonstrated that the DNA complexes of either peptide can disrupt the lipid membranes, forming larger pores in the case of Cytcox. Our results suggest that the binding affinity of the peptide/DNA complex to the plasma membrane is more critical than its membrane disruption ability in enhancing the cellular uptake of DNA.

Nanoparticle and Bioparticle Deposition Kinetics: Quartz Microbalance Measurements.

Controlled deposition of nanoparticles and bioparticles is necessary for their separation and purification by chromatography, filtration, food emulsion and foam stabilization, etc. Compared to numerous experimental techniques used to quantify bioparticle deposition kinetics, the quartz crystal microbalance (QCM) method is advantageous because it enables real time measurements under different transport conditions with high precision. Because of its versatility and the deceptive simplicity of measurements, this technique is used in a plethora of investigations involving nanoparticles, macroions, proteins, viruses, bacteria and cells. However, in contrast to the robustness of the measurements, theoretical interpretations of QCM measurements for a particle-like load is complicated because the primary signals (the oscillation frequency and the band width shifts) depend on the force exerted on the sensor rather than on the particle mass. Therefore, it is postulated that a proper interpretation of the QCM data requires a reliable theoretical framework furnishing reference results for well-defined systems. Providing such results is a primary motivation of this work where the kinetics of particle deposition under diffusion and flow conditions is discussed. Expressions for calculating the deposition rates and the maximum coverage are presented. Theoretical results describing the QCM response to a heterogeneous load are discussed, which enables a quantitative interpretation of experimental data obtained for nanoparticles and bioparticles comprising viruses and protein molecules.

Interaction of Proteins with a Planar Poly(acrylic acid) Brush: Analysis by Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D)

We describe the preparation of a poly(acrylic acid) (PAA) brush, polymerized by atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and subsequent acid hydrolysis, on the flat gold surfaces of quartz-crystal microbalance (QCM) crystals. The PAA brushes were characterized by Fourier transform infrared (FT-IR) spectroscopy, ellipsometry and water contact angle analysis. The interaction of the PAA brushes with human serum albumin (HSA) was studied for a range of ionic strengths and pH conditions by quartz-crystal microbalance with dissipation monitoring (QCM-D). The quantitative analysis showed a strong adsorption of protein molecules onto the PAA brush. By increasing the ionic strength, we were able to release a fraction of the initially bound HSA molecules. This finding highlights the importance of counterions in the polyelectrolyte-mediated protein adsorption/desorption. A comparison with recent calorimetric studies related to the binding of HSA to polyelectrolytes allowed us to fully analyze the QCM data based on the results of the thermodynamic analysis of the binding process.

Ultrasonic atomization of titanium isopropoxide at room temperature for TiO2 atomic layer deposition

Room temperature evaporation of titanium isopropoxide [Ti[OCH(CH3)2]4, TTIP] precursor was performed using ultrasonic atomization for TiO2 atomic layer deposition (ALD). Quartz crystal microbalance data show comparable results between room temperature TTIP ultrasonic atomization and conventional thermal evaporation. The TiO2 ALD saturation window is established for room temperature atomized TTIP exposure time and reactor temperatures. Room temperature atomized TTIP grown TiO2 films show smooth surface morphology before/after the annealing treatment. Two-dimensional TiO2 film thickness mappings on a 150 mm diameter Si(100) wafer were performed by spectroscopic ellipsometry. The thickness variation of TiO2 films by the room temperature atomized TTIP is less uniform than that of TiO2 films by thermally evaporated TTIP, probably due to the incomplete evaporation of the TTIP liquid droplets, which is more difficult to transport than its vapor.

Electrodeposition of a mirror zinc coating from a choline chloride-ethylene glycol-based deep eutectic solvent modified with methyl nicotinate

Abstract A number of studies have reported the effects of additives on metal coatings electrochemically deposited from deep eutectic solvents (DESs). However, no previous study has investigated the influences of methyl nicotinate (MN) as an additive on the electrodeposition of zinc on a copper substrate from a DES. The results of this investigation show that MN significantly develops the Zn deposition in this system compared to the corresponding system in its absence. This is the first study to date to show that a mirror zinc coating can be obtained on a copper substrate using such a mechanism. Various electrochemical methods such as cyclic voltammetry, chronocoulometry, and chronoamperometry have been used to understand the electrochemical properties of Zn electrolytes in the absence and presence of MN. These experiments found that the redox reaction currents decline when the additive was included in the Zn electrolyte, and that Zn deposition followed an instantaneous nucleation mechanism in the absence of the additive while in its presence the mechanism was closer to that of progressive growth. Further, the current efficiency decreased from 98.99% in the absence of additive to approximately 82% as a result of including the additive in the Zn plating bath, according to electrochemical quartz crystal microbalance (EQCM) data. The resultant roughness, thickness and surface morphology of the deposited zinc were characterised using atomic force microscopy, scanning electron microscopy, and X-ray diffraction, indicating that methyl nicotinate, as an additive, functions as a highly influential brightener that allows the formation of highly homogeneous and flat zinc deposits.

Interactions of Surface-Functionalized Starch Nanoparticles with Pepsin and Trypsin in Simulated Gastrointestinal Fluids.

Nanoparticles (NPs) can form a protein corona (PC) with proteins in biological fluids. We examined whether starch nanoparticles (SNPs) form a PC and interact with digestive enzymes in simulated gastric and intestinal fluids. We investigated the adsorption of pepsin and trypsin on unmodified, carboxyl-, and amino-modified SNPs (SNPs, COOH-SNPs, and NH2-SNPs, respectively). Quartz crystal microbalance data showed that a tight and irreversible pepsin corona formed on the NH2-SNPs, pepsin had little or no binding to the SNPs and COOH-SNPs, and trypsin had weak binding to all three kinds of NPs. Dynamic light scattering data showed that pepsin significantly increased the size of the NH2-SNPs from 120 ± 2.6 to 203 ± 12.2 nm and decreased their surface potential from 23.2 ± 1.0 to 12.7 ± 0.2 mV. NH2-SNPs could induce the fluorescence quenching of pepsin and change its secondary structures without affecting its activity.

An Aminopyridine Bearing Pillar[5]arene-Based QCM Sensor for Chemical Sensing Applications: Design, Experimental Characterization, Data Modeling, and Prediction

This study presented that deca pyridin-2-amine bearing Pillar[5]arene (P5-PA) was designed in an appropriate cavity, which acts a part significant role in host–guest interactions of the macrocyclic molecules. P5-PA monolayer was deposited onto suitable substrates as an active layer by using Langmuir-Blodgett (LB) coating technique to examine its vapor sensing capabilities against vapor of some aliphatic hydrocarbons through Quartz Crystal Microbalance (QCM) technique. The kinetic vapor studies were occurred by exposing the P5-PA/LB thin film to different percentage of organic VOCs vapors such as dichloromethane, chloroform and carbon tetrachloride in air-VOCs mixture. The early-time Fick’s diffusion law was handled to extract the diffusion coefficients by utilizing QCM data depending real time. It is observed that there were two different regions with two slopes indicating that one belongs to slow surface diffusion and another fast for bulk diffusion into LB thin film. The collected experimental data with 1 Hz sampling frequency was modelled with deep learning models (NARNET and LSTM) which could get satisfactory results on small datasets. The models were trained with 83% samples of data; the remaining 17% data is used to evaluate the developed models prediction performance. The predicted values of models were compared with the original (measured) data in the results section. It is observed from the results; the developed deep learning models have higher than 0.98 correlation coefficient for each vapor, which is satisfactory for prediction applications.

Monitoring and Modeling of Living Cell Responses in the Attachment Process and Reaction to the Antitumor Reagent Cisplatin Studied by a Quartz Crystal Microbalance Combined with a Microscope

The attachment process and response to an antitumor reagent for cultured cells were monitored with a quartz crystal microbalance (QCM) combined with a microscope. To fit the experimentally obtained curves of the resonant frequency, model equations of resonant frequency curves were built, and parameters of time constants and scale coefficients were determined. For the cell attachment process, a first-order lag response curve well fit the experimental curves. For the response to cisplatin, two response steps were observed in both QCM data and microscopic images, where the cells loosened in the first step and shrank in the second step. Resonant frequency responses for both processes were well fit by two logarithmic normal distribution functions. In addition, the dependence of the resonant frequency change on the cell number was also studied, and a cell-cell interaction model for attached cells was proposed to explain the saturation of the resonant frequency change in high density cell seeding.

Adsorption, permeation, and DFT studies of PVC/PVIm blends for separation of CO2/CH4

In this study, in order to improve the performance of polyvinyl chloride membrane, polyvinyl chloride was blended with poly(1–vinylimidazole) in different compositions for separation of carbon dioxide and methane gases. The blend polymers were characterized using differential scanning calorimetry (DSC) analyses. The morphology of prepared membrane was studied using Scanning Electron Microscope (SEM). The kinetics and thermodynamics of CO2 adsorption were studied at different pressures and temperatures using quartz crystal microbalance (QCM) and experimental data were fitted using the dual-mode model. The evaluated kinetics and thermodynamic parameters of CO2 adsorption revealed that CO2 adsorption has physisorption and exothermic nature. The obtained results indicated that permeation selectivity of polyvinyl chloride membrane with poly(1–vinylimidazole) is higher than those of polyvinylchloride membrane for CO2/CH4 gases. Also, DFT calculation was performed to evaluate interactions between polymer and CO2 or CH4 gases. DFT calculations verified that the interaction of the polymer with CO2 is stronger than those of CH4.

Study of CO2 adsorption onto poly(1–vinylimidazole) using quartz crystal microbalance and density functional theory methods

Polymers were used widely for the CO2 separation from natural gas. Therefore, poly (1–vinylimidazole) (PVIm) was synthesized by free-radical polymerization in solution. PVIm was characterized using proton nuclear magnetic resonance (1HNMR) and Fourier transform infrared (FT-IR) spectroscopy. The kinetics and thermodynamics of CO2 adsorption were studied at different pressures and temperatures using quartz crystal microbalance (QCM) and experimental data were fitted using the dual-mode model. The evaluated kinetics and thermodynamics parameters of CO2 adsorption reveal that CO2 adsorption has physisorption and exothermic nature. Density functional theory (DFT) studies were performed to evaluate the relative affinity of the n-VIm from 1 to 4 monomers for the interacting molecules of CO2. Adsorption energies were computed and larger energy of adsorption in tetra-VIm–CO2 complex was seen compared to other n-VIm–CO2 complexes.