Quartz Crystal Microbalance Technique Research Articles

Thermal stability and gas absorption characteristics of ionic liquid-based solid polymer electrolytes.

Ionic liquid (IL)-based solid polymer electrolytes (SPE) with stable thermal properties and low electrical resistivity have been evaluated. Two candidates for the polymer component of the SPE, poly(ethylene glycol) diacrylate (PEGDA) and Nafion, were considered. Differential scanning calorimetry analysis and electrical resistivity tests revealed that PEGDA, in comparison to Nafion, enables the formation of uniform SPEs with lower electrical resistivity and better thermal stability within a range of 25 °C-170 °C. Therefore, PEDGA was selected for further evaluation of the IL component effect on the resulting SPE. Six IL candidates, including 1-butyl-3-methylimidazolium methanesulfonate ± methanesulfonic acid (BMIM.MS ± MSA), diethylmethylammonium triflate ±bis(trifluoromethanesulfonyl)imine (Dema.OTF±HTFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ± bis(trifluoromethanesulfonyl)imine (BMIM.TFSI ± HTFSI), were selected to test the effect of hydrophobicity/hydrophilicity of the IL on the resulting SPE. Fourier transformation infrared spectrometer analysis revealed that the BMIM.MSA-based electrolytes have the highest tendency to absorb from the environment and keep the moisture, while Dema.OTF has the fastest curing time. The SPE candidates were further evaluated for absorption characteristics of different gasses and vapors, such as N2, O2, ethanol vapor, and diluted CO/N2, that were tested with the in situ quartz crystal microbalance (QCM) technique. Among all six candidates, BMIM.MS showed the largest N2 and O2 absorption capacity from the environment. Dema.OTF + HTFSI, meanwhile, demonstrated a higher level of interactions with the ethanol vapor. In the case of CO/N2, QCM analysis revealed that BMIM.MS+MSA has the largest, ∼13 µg/cm2, absorption capacity that is reached within 400 s of being exposed to the gas mixture.

Aromatik hidrokarbonların dedekte edilmesi için kaliksaren bazlı diamid kimyasal sensor çiplerinin geliştirilmesi

In the present work, a new macrocycle materials (SB77) was selected and Langmuir-Blodgett thin films of this macrocycle compounds were examined for its vapor sensing capabilities against vapor of aromatic BTX hydrocarbons (benzene, toluene, xylene) through Quartz Crystal Microbalance (QCM) technique. In accordance with this aim, the calix[4]arene LB thin films were prepared onto quartz crystal substrates. The characterization of SB77 LB thin film was performed for nine LB layers fabricated onto the quartz crystal. The frequency shifts and the mass changes for monolayer of these LB thin films were obtained as 32.35 Hz / per layer and 2206.65 ng (8.32 ng mm-2), respectively. All QCM results indicated that SB77 LB thin film chemical sensors exhibits high response, a good sensitivity and selectivity for benzene vapor at saturated or different concentrations than other aromatic hydrocarbon vapors. These LB thin film sensors with SB77 calix [4]arene macrocycle materials have been potential candidates for organic vapor sensing applications with simple and low cost preparation at room temperature.

Electrospun zinc oxide nanofibers for UV sensing with quartz crystal microbalance technique

An ultraviolet (UV) sensor consisting of a zinc oxide (ZnO) nanofiber sensing membrane and a quartz crystal microbalance (QCM) was fabricated. ZnO nanofibers were prepared by electrospinning and calcination. The morphology and structure of the nanofiber sensing membrane were characterized by scanning electron microscopy and X-ray diffraction. The QCM sensor based on ZnO nanofibers was found to be sensitive to 254-nm UV light in nitrogen, oxygen and air atmospheres. When the QCM sensor was placed under UV irradiation, the resonant frequency difference rapidly decreased. When the light was removed, the frequency difference recovered until reaching 0 Hz. The stability and repeatability of the proposed ZnO nanofiber-based QCM sensor were demonstrated, and the sensing mechanism was briefly discussed.

Deposition behavior of lignin on solid surfaces assessed by stagnation point adsorption reflectometry.

The deposition behavior of lignin on a solid surface was studied using stagnation point adsorption reflectometry (SPAR) comprehensively. In this study, the light absorption coefficient of lignin (τ = 20 476 m−1) at 633 nm wavelength was considered to define a new imaginary refractive index (k) used in the SPAR technique for adsorption analysis. The inclusion of k in the adsorption model yielded an adsorbed amount (Γ) of 1.11 mg m−2, leading to the quality factor (Qf) of 31.71 mg m−2. At a lower concentration, the deposition of lignin on the surface was increased, and it generated a maximum sticking coefficient of β = 0.71 at 25 mg L−1 on the surface. At the concentration range of 35 and 45 mg L−1, lignin formed clusters and its deposition dropped. The use of Quartz crystal microbalance (QCM) and SPAR techniques also confirmed that the proportion of water in the deposited lignin adlayer was greater when a lower concentration (5–25 mg L−1) of lignin solution was used for adsorption. The findings of this study revealed the potential use of the SPAR technique for evaluating the deposition performance of lignin-based materials on varied surfaces, which would facilitate the development of coating and composite applications for lignin.

High adhesion ability of anammox granular microbes directly revealed by QCM-D technique

Anammox bacteria are widely found to grow in bioaggregates form, but the reason for their high aggregation ability remains elusive. In this study, four kinds of sludge, i.e., anammox granules, anaerobic granules, aerobic granules, and partial nitrification flocs, were studied and compared to investigate their differences in adherence properties. We directly explored the adherence properties of sludge samples before and after extracellular polymeric substances (EPS) extraction, using quartz-crystal microbalance technique with dissipation monitoring technique. Results showed that EPS indeed stimulated the adherence properties of all sludge samples. The most striking feature here is that anammox consortia had the highest adhesion rate and mass, and formed the most compact layer on the gold-coated sensor surfaces both before and after EPS extraction among the four sludge samples, indicating their inherent high adhesion ability. The composition and spectral characteristics of EPS samples were also investigated, and it reveals that the relatively high extracellular proteins/polysaccharides ratio of anammox granules (3.2 ± 0.4) rather than total EPS concentration had contributed to their high adhesion ability. The findings are helpful for understanding the adherence properties of anammox bacteria, and will serve as a guide for further researches to exploring the aggregation process of anammox bacteria.

Homosistein tayini amaçlı QCM-temelli biyosensör

High plasma homocysteine levels can cause an increased risk of cardiovascular, cerebrovascular, and peripheral arterial diseases. Besides this, Alzheimer’s disease and other dementias, osteoporosis, diabetes and renal disease due to folate and B-vitamin deficiency, various drugs or pre-existing atherosclerotic diseases may be the result of high homocysteine levels. The presented research work aimedto perform the detection of Homocysteine (Hcy) by using Quartz Crystal Microbalance (QCM) biosensor. The temperature controlled QCM system was a home-made designed and constructed equipment which can use silver electrod quartz crystal. The modification of silver electrod quartz crystals surfaces was achieved by the surface cleaning process with sodium hydroxide, acetone and methanol in a consecutive manner. Then self-assembled monolayer of cysteamine and chemical coupling of glutaraldehyde (GA) to free end of monolayer was achieved to create the new functional surface in order to complete the formation of spacer arm/ligand. Homocysteine specific recognizing ligand, anti-Homocysteine antibody was immobilized to glutaraldehyde coupled surfaces. The change in resonance frequency values were measured for each modification step. The optimization of dilution ratio of the antibody solution was performed to modified surfaces. The least dilution ratio of antibody, 1/10000 v/v, was determined as optimum antibody ratio. The detection of homocystein was analysed at a detection limit of 0.1 µM and the linear ranges of calibration curves were estimated as 0.1-2.0 µM and 10-50 µM. Homocysteine values indicated good linearities (R2=0.9813 and 0.9875, respectively). The relative standart deviation (RSD %) for precision was calculated as less than 10%. In conclusion, it was found that the detection of homocysteine can be done both in nano- and micro-molar concentration levels. Additionally, designed biosensor showed desired stability and reproducibility. Finally, a new method different from the present methods for the use in the analysis of Hcy was proposed and developed which detects homocysteine by designed QCM technique with a rapid, cheeper and less pretreatment processes. Additionally, homocysteine detection was performed in nano- and micro- molar concentration values.

A high temperature dual-mode quartz crystal microbalance technique for erosion and thermal desorption spectroscopy measurements.

An improved quartz crystal microbalance measurement method is described, which allows us to determine erosion, implantation, and release rates of thin films, during changing temperatures and up to 700 K. A quasi-simultaneous excitation of two eigenmodes of the quartz resonator is able to compensate for frequency drifts due to temperature changes. The necessary electronics, the controlling behavior, and the dual-mode temperature compensation are described. With this improved technique, quantitative in situ temperature-programmed desorption measurements are possible and the quartz crystal microbalance can be used for quantification of thermal desorption spectroscopy measurements with a quadrupole mass spectrometer. This is demonstrated by a study of the retention and release behavior of hydrogen isotopes in fusion-relevant materials. We find that more than 90% of the deuterium implanted into a thin film of beryllium is released during a subsequent temperature ramp up to 500 K.

Characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on gold electrodes

The modification of surfaces by polyethylene glycol (EGn) is an approach used to reduce the antifouling effects of these materials in a biological medium. It has been found that the packing density and conformational order of these molecules in the films are crucial for the inhibition of unspecific protein adsorption. In this work, we present a study of the formation and characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on either poly-oriented or Au(111) single crystal surfaces. The final properties of the formed EG7-SAMs are studied by examining the reductive desorption process as well as the electronic and ionic blocking behaviour of these layers, under different experimental conditions, by using cyclic voltammetry and electrochemical impedance spectroscopy. Additional information of the structure, composition and organization is obtained by absorption-reflection infrared and X ray photoelectron spectroscopies and contact angle measurements. In contrast to the behaviour observed with alkanethiols, the EG7-SAM shows the best final organization at a modification time of 1 h. The antifouling properties of this EG7-SAM against the adsorption of the bovine serum albumin protein in a phosphate saline medium, has been evidenced by using the electrochemical quartz crystal microbalance technique.

In situ analysis of pore size effect of ionic solvation during the formation of double electric layers

Electrochemical quartz crystal microbalance (EQCM) technique was used to characterize the influence of pore size and ion size and, solvation effect on the formation of electric double-layer capacitors (EDLCs). Based on quantitative calculation and analysis, the apparent molecular mass ( M sx ) was calculated from the slope of the electrode mass change ( Δm ) vs. the charge ( ΔQ ) passed in the electrode during charging/discharge. Comparing M sx with the molar mass of bare ion, the value of specific solvation number( x )was deduced. Findings indicate that the formation of double layers at electrode interface by ionic absorption was accompanied by solvation effect. The solvation effect was weakened as the pore size of the electrode decreased, concluding that the pore size effect exist concurrently with solvation effect during ionic adsorption. The pore size effect was influenced by the size of the counter-ions, polarity of solvent molecules and ionic concentrations.

Grafen Kaplı Kimyasal Sensörlerin Şişme Davranışları ve Matematiksel Modelleme

Bu çalışmada, grafen kaplı Langmuir-Blodgett (LB) ince filmlerin şişme davranışları Kuartz Kristal Mikrobalans (KKM) tekniği kullanılarak incelenmiştir. Bu filmler, bazı organik buharların (aseton, etanol ve metanol) difüzyon katsayı değerlerinin hesaplanması (Fick’in erken-zaman difüzyon kanunu kullanılarak) için oda sıcaklığında etkileşmeye bırakılmıştır. Difüzyon katsayı değerleri sırası ile aseton, etanol ve metanol için 20.43 x 10−16, 1.30 x 10−16 ve 0.91 x 10−16 cm2 s−1 olarak hesaplanmıştır. Benzer sıralama grafen kaplı KKM sensörünün tepkisi (frekans değişimi, Δf) için de aseton (342 Hz) > etanol (76 Hz) > metanol (51 Hz) olarak elde edilmiştir.

In-situ and real-time probing cellulase biosensor formation and its interaction with lignosulfonate in varied media

It is a challenge to interpret the signals obtained by Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) accompanied with in the significant changes of the density and/or refractivity of media. The work presented herein focuses on demonstrating a universal in-situ and real-time monitoring methodology for ultrathin film formation on gold chips in varied media. Biomimetic model cellulase/enzyme film was immobilized in-situ on gold surface of sensors, followed by revealing its interaction with lignosulphonate in the media changed from ethanol-based to aqueous ones. Combining the techniques of Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and Multi-parametric Surface Plasmon Resonance (MP-SPR) along with respective software and models enabled us to precisely characterize the thickness, viscous and shear elastic moduli, and the coupled solvent for individual layer formed over the entire process, which are unachievable with conventional methods. The methodology provides real-time monitoring of filming process and offers us an in-situ qualify control approach to the biomimetic model films formed on different substrates including gold chip.

Tetraphenyl porphyrin films as selective detectors for amino acid molecules

The interaction of different amino acids and vacuum evaporated tetraphenyl porphyrin films was investigated by using kinetic isotherms, UV-vis spectroscopy, quartz crystal microbalance and density functional theory techniques. The adsorption process was analyzed by using pseudo-first-order and pseudo-second-order models. From these results, the adsorption order changed depending on the chemical characteristics of the porphyrin film, although most of the interactions were classified as pseudo-second-order at the films interface. From absorbance measurements, red shifts on the Soret peak positions were observed for all amino acids interacting with the metal free and the ZnTPP systems, while the position of the Soret peak barely change for the CuTPP surface, except for a slight bathocromic shift for arginine. On the other hand, the broadening of the Soret peak was more important for the ZnTPP and H2TPP surfaces, but the interaction with the CuTPP interfaces decreased the width of the peaks in all cases. In addition, a quartz crystal microbalance analysis was employed to investigate the film sensing performance during amino acid exposure. From these results, positively charged amino acids were more easily adsorbed on the films in contrast with the polar (serine) molecule. DFT calculations exhibited important deformations for H2TPP, the out-of-plane displacement of the Zn atom for ZnTPP, and hydrogen bond interactions with the CuTPP molecule. DFT also showed high binding energies for the positively charged amino acids but low binding energies for serine in agreement with experimental data. From these results, porphyrin films could be used as selective detectors for various L-amino acid molecules.

Star polymer-based nanolayers with immobilized complexes of polycationic stars and DNA for deposition gene delivery and recovery of intact transfected cells.

We designed a novel thermoresponsive system of nanolayers composed of star poly[oligo(ethylene glycol) methacrylate]s (S-POEGMA) covalently bonded to a solid support and covered with polyplexes of cationic star polymers and plasmid DNA (pDNA). S-POEGMA stars were attached to the solid support via a UV-mediated "grafting to" method. To the best of our knowledge, for the first time, the conformational changes of obtained star nanolayers, occurring with changes in temperature, were studied using a quartz crystal microbalance technique. Next, the polyplexes of star poly[N,N'-dimethylaminoethyl methacrylate-ran-di(ethylene glycol) methacrylate] (S-P(DMAEMA-DEGMA)) with pDNA, exhibiting a phase transition temperature (TCP) in culture medium DMEM, were deposited on S-POEGMA layers when the temperature increased above the TCP of polyplex. The thermoresponsivity of the system was then the main mechanism for controlling the adhesion, proliferation, transfection and detachment of HT-1080 cells. The nanolayers promoted the effective cell culture and delivered nucleic acids into cells, with a transfection efficiency several times higher than that of the control. The detachment of the transfected cells was regulated only by the change of temperature. The studies demonstrated that we obtained a novel and effective system, based on a star polymer architecture, useful for gene delivery and tissue engineering applications.

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.

Thermal Atomic Layer Etching of Gallium Oxide Using Sequential Exposures of HF and Various Metal Precursors

Gallium oxide (Ga2O3) is a transparent semiconducting oxide with a large band gap that has applications for power electronics and optoelectronics. Ga2O3 device fabrication requires etching for many processing steps. In this work, the thermal atomic layer etching (ALE) of Ga2O3 was performed using hydrofluoric acid (HF) and a wide range of different metal precursors including BCl3, AlCl(CH3)2, Al(CH3)3, TiCl4, and Ga(N(CH3)2)3. Because Ga2O3 is not a particularly stable oxide, the B-, Al-, or Ti-containing metal precursors can possibly convert the surface of Ga2O3 to B2O3, Al2O3, or TiO2. These metal precursors can also provide Cl, CH3, and N(CH3)2 ligands for ligand-exchange reactions. Consequently, the thermal ALE of Ga2O3 can occur via “conversion-etch” or fluorination and ligand-exchange reaction pathways. Using sequential HF and BCl3 exposures and in situ spectroscopic ellipsometry techniques, Ga2O3 etch rates were observed to vary from 0.59 to 1.35 Å/cycle at temperatures from 150 to 200 °C, respectively. The Ga2O3 etch rates were also self-limiting versus HF and BCl3 exposure. The lack of BCl3 pressure dependence for the etch rates argued against the conversion-etch mechanism and in favor of a fluorination and ligand-exchange reaction pathway. In situ quartz crystal microbalance techniques also revealed that Ga2O3 could be etched using sequential exposures of HF and various other metal precursors. Ga2O3 etch rates at 250 °C were 1.2, 0.82, 0.85, and 0.23 Å/cycle for AlCl(CH3)2, Al(CH3)3, TiCl4, and Ga(N(CH3)2)3 as the metal precursors, respectively. The mass changes during the individual exposures of HF and the AlCl(CH3)2 and Al(CH3)3 metal precursors argued for a fluorination and ligand-exchange mechanism. The AlCl(CH3)2 and Al(CH3)3 exposures may also lead to some conversion of Ga2O3 to Al2O3. In contrast, the mass changes during the HF and TiCl4 exposures were consistent with the conversion of the surface of Ga2O3 to TiO2 and then the spontaneous removal of the TiO2 surface layer by HF. Distinctly different behavior was observed during the HF and Ga(N(CH3)2)3 exposures. The large mass gain during the Ga(N(CH3)2)3 exposures suggested that Ga(N(CH3)2)3 can adsorb on the fluorinated Ga2O3 surface prior to the ligand-exchange reaction. The wide range of metal precursors that can etch Ga2O3 argues that the ability of these precursors to convert Ga2O3 or to undergo ligand-exchange reactions provides multiple pathways for effective thermal Ga2O3 ALE.

Developing of N-(4-methylpyrimidine-2-yl)methacrylamide Langmuir-Blodgett thin film chemical sensor via quartz crystal microbalance technique.

In the present work, the characterization and gas sensing properties of newly synthesized N-(4-methylpyrimidine-2-yl)methacrylamide (N-MPMA) monomer Langmuir-Blodgett (LB) thin films were investigated. The UV-visible spectroscopy, quartz crystal microbalance (QCM), and atomic force microscopy were utilized to characterize N-MPMA LB thin films. The surface behavior of N-MPMA monolayer was stable and allowed an effective transfer at a surface pressure of 14 mN/m. The mass change/unit area value of the N-MPMA LB thin film deposited quartz crystal surfaces was investigated. The amount of N-MPMA LB thin film deposited on the substrate for bilayer was calculated as 228.72 ng (86.31 ng/mm2 ) and 12.5 Hz frequency shift was observed for each layer of the N-MPMA film. The kinetic responses of N-MPMA LB film against chloroform, dichloromethane, benzene, and toluene were measured via QCM system at room temperature. N-MPMA QCM sensor results displayed that chloroform has the largest frequency shifts compared with the other vapors used in the present work and these results can be illuminating in terms of physical properties of organic vapors.

A novel experimental technique for the fabrication of the vitamin B12 nucleus using quartz crystal microbalance: Statistical physics modeling and new microscopic properties

A novel adsorption model for the description of adsorption isotherms of cobalt nitrate on porphyrins H2TPP and H2TTPP is developed in the present paper. Experimental data were measured at five temperatures using the quartz crystal microbalance technique and were discussed to choose the most reproductive adsorbent for the achievement of the vitamin B12 nucleus. Then, the modeling treatment was established based on the grand canonical formalism in statistical physics by taking into account the lateral interaction between the adsorbate particles. This leads to a six parameter equation describing the complexation process at the molecular level. Actually, there is a good correlation between experimental data and those calculated by using the double-layer L.B.L. model. It was found that cobalt ions were adsorbed via a multi-docking mechanism onto the two adsorbents. The study of the density of receptor sites (PM) confirmed the endothermic nature of the two complexation processes. The van der Waals parameters indicated that the disturbances following the lateral interactions between the adsorbates are the highest in the case of tetraphenylporphyrin. The magnitude of the calculated adsorption energies reveals that cobalt is physisorbed onto tetraphenylporphyrin, whereas chemical forces were found in the case of porphyrins (H2TTPP). In addition, the proposed model allows the prediction of some adsorption thermodynamic functions, which govern the adsorption mechanism, such as entropy, Gibbs free enthalpy, and internal energy.

Electrochemically prepared poly(L-lysine) and 3-hydroxyphenylboronic acid composite as a conventional adhesion material for rice suspension cells

Poly(L-lysine) (PLL)-3-hydroxyphenylboronic acid (3-PBA) composite was prepared onto an Au electrode via cyclic voltammetry (CV), which was characterized by electrochemical and quartz crystal microbalance (QCM) techniques, and used to promote adhesion of plant cells. 3-PBA can interact with glycosyl compounds on the cell wall to form negatively charged covalent compounds while PLL increases the number of positively charged sites, which enhances the electrostatic interactions with the negatively charged cell wall, both promoting cell adhesion. The PLL-poly(3-PBA) composite was successfully modified on the Au electrode surface, as demonstrated by QCM and Fourier transform infrared spectrophotometry (FTIR). Moreover, we confirmed the synergistic effect of PLL and 3-PBA to adhere rice suspension cells using CV, electrochemical impedance spectroscopy (EIS), QCM and optical microscope observations. Finally, the dynamic process of rice cells’ adhesion to PLL-poly(3-PBA)/Au followed by salt stress treatment of NaCl was monitored in real-time by QCM. The cells softened at first then hardened under the action of 40 mM NaCl. This work presents a novel and conventional way to immobilize plant cells onto sensors, and has importance in the study of the structure, function and behavior of plants under various stresses at the cellular level.

Studying the effects of bismuth on the electrochemical properties of lead dioxide layers by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO2 layers doped with bismuth in contact with sulfuric acid solutions were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers (non-doped and doped with Bi) were electrodeposited on gold substrate from aqueous solutions of Pb(NO3)2 dissolved in nitric acid and they were investigated in sulfuric acid media. Based on the electrochemical and the mass change responses, it is concluded that during the electrodeposition, bismuth influences the structure of the PbO2 formed. Bi(III) also inhibits the oxidation of lead sulfate and affects the reduction kinetics of lead dioxide. During successive cyclization (aging), the presence of bismuth accelerates the hydration of PbO2.

Effects of Waxes and the Related Chemicals on Asphaltene Aggregation and Deposition Phenomena: Experimental and Modeling Studies.

Solid deposition during production, transport, and storage of crude oils leads to significant technical problems and economic losses for the oil and gas industry. The thermodynamic equilibrium between high-molecular-weight components of crude oil, such as asphaltenes, resins, and waxes, is an important parameter for the stability of crude oil. Once the equilibrium is disturbed due to variations in temperature, pressure, and oil composition during production, the solubility of high-molecular-weight waxes decreases. This results in a decrease in the wax appearance temperature (WAT) and the deposit of wax onto solid surfaces. On the other hand, under these conditions, asphaltenes do not interact sufficiently with the resins/waxes and tend to flocculate among themselves and form asphaltene nanoaggregates. The role of waxes during the asphaltene aggregation and deposition has not been appropriately explained yet. The objective of this research study is to describe the interaction of asphaltenes and waxes and subsequently address the specific example of an asphaltenic oil commingled with a wax inhibitor-containing oil during the combination of different oil streams. It is a crucial building block for the development of a suitable and cost-effective strategy for the handling of wax/asphaltene associated flow assurance problems. In this work, the quartz crystal microbalance (QCM) technique has been used for the first time to investigate the effect of waxes and related chemicals, which are used to mitigate wax deposition, on asphaltene aggregation and deposition phenomena. Asphaltene onset point and asphaltene deposition rate have been monitored using QCM at high pressure–high temperature (HPHT) conditions. This study confirms that the different wax inhibitor chemistries result in significant differences in the pour point decrease and viscosity profiles in crude oil. Different wax inhibitors also showed different outcomes regarding the asphaltene deposition tendency. A comprehensive modeling study has also been conducted for mechanistic investigation of experimental results. In this regard, the perturbed chain statistical associating fluid theory equation of state (PC-SAFT EoS) was utilized to model the systems.