Activation Energy Of Viscous Flow Research Articles

Synthesis and comprehensive characterization of bio-based polyamide 56/6 Copolymer: Mechanical, Thermal, and processing properties

In this study, nylon 56/6 copolymers with different biobased contents were synthesized using biobased pentylenediamine, adipic acid, and caprolactam as the main raw materials. The structure of the synthesized copolymers was characterized using nuclear magnetic analysis (NMR) and infrared analysis (IR). The crystal structure and crystalline properties were investigated using X-ray diffraction (XRD) and differential scanning calorimeter (DSC), while the thermodynamic properties were studied through thermogravimetric analysis (TGA). Furthermore, the mechanical and rheological properties of the copolymers were investigated. The results showed that PA56/6 copolymers exhibited excellent mechanical properties. They displayed tensile strength similar to that of pure PA56 and PA6 but with improved toughness. Moreover, PA56/6 copolymers demonstrated higher thermal stability, lower melting points, and enhanced processing properties. Rheological investigations revealed that compared to PA56 and PA6, PA56/6 copolymers exhibited reduced viscous flow activation energy. As a result, they offered a wider temperature processing range in practical production. Given the numerous benefits offered by bio-based polyamide 56/6 (PA56/6), this versatile material finds extensive utility across diverse applications, including but not limited to automotive engineering, specialty clothing fabrics, and packaging engineering. Exploiting its unique properties, PA56/6 exhibits remarkable potential in addressing various industry-specific challenges, thereby contributing to sustainable and innovative solutions.

Thermal properties and thermodynamic model of lithium doped 45S5 bioglass

AbstractShakhmatkin and Vedishcheva thermodynamic model (SV TDM) of the 45S5 Bioglass® doped with three different amounts of Li2O (4.1, 9.9, and 12.3 mol%) was evaluated at T = 800 K. The 55 components of SV TDM were considered, among them 12 lithium containing compounds. Different number of components with not negligible equilibrium molar amount was found for different glass compositions (9 or 10). In all glass compositions containing nonzero amount of Li2O, the four lithium compounds with not negligible equilibrium amount were identified, i.e., Li2O·SiO2, 3Li2O·P2O5, Li2O·2CaO·2SiO2, and 2Li2O·SiO2. In the 45S5 glass composition four phosphate compounds with not negligible abundance were identified: 9Na2O·6SiO2·2P2O5, Na2O·2CaO·P2O5, 5Na2O·4SiO2·P2O5, and Na2O·CaO·P2O5. In all other glasses the 3Li2O.P2O5 was found with not negligible abundance. Moreover, in the glass with 4.1 mol% Li2O the Na2O·2CaO·P2O5 and 3Li2O·P2O5 compounds were found with not negligible abundance. For each studied glass the glass transition temperature, coefficient of thermal expansion of glass and metastable melt were measured by thermodilatometry. The low temperature viscosity was measured by thermomechanical analysis. The viscous flow activation energy was evaluated from the viscosity temperature dependence. The compositional dependence of measured thermal properties was analyzed by correlation analysis with the Q-distribution of silicate and phosphate units.

The Effect of Substituting FeO with CaO on the Rheological and Surface Properties of Silicate Melts

A comprehensive understanding of the structural impact of composition is crucial in designing converter slag to optimize its rheological and surface properties during the smelting process. In this study, glassy CaO-SiO2-FexO samples with varying CaO/FexO ratios were prepared to simulate the slag in the initial stage of converter melting. The viscosity and surface tension of the slag at 1300–1600 °C were measured, and the microscopic essence of physical properties was further analyzed using Raman spectroscopy technology. The findings reveal that as CaO replaces FeO, [SiO4]-tetrahedra gradually depolymerize from Q4(Si) to Q0(Si), while [FeO6]-octahedra gradually transform into [FeO4]-tetrahedra, resulting in a decrease in the degree of polymerization of the slag. The slag with a lower degree of polymerization exhibits reduced activation energy of viscous flow and increased surface tension. Therefore, it is of great significance to appropriately control the CaO/FexO ratio in the early stage of smelting to improve the rheological and surface properties of the slag.

EFFECTIVE VISCOSITY AND GLASS TRANSITION TEMPERATURE OF Cs<sub>2</sub>O–B<sub>2</sub>O<sub>3</sub> MELTS

Effective viscosity (viscoelasticity) of cesium and boron oxides melts was measured at temperatures 900–1600 K and concentrations 0 ≤ x ≤16 mol % Cs2O by vibration viscosimetry. It was shown that vibration leads to non-Newtonian flow of melts. This means that not only configuration activation energy, the switching energy of bridging oxygen bonds but also the elastic energy of structural units of melts associated with activation energy of viscous flow. Using parameters under conditions of Newtonian and non-Newtonian flow of melts, shear viscosity η', elastic modulus G' and stored viscosity η'' were calculated. It was shown that cesium boron melts in conditions of high shear rates can be considered as liquids with viscous and elastic properties. Glass transition temperature (Tg, K) was measured by DSC, its dependence of content of cesium oxide was plotted and explained.

Film formation kinetics of polystyrene latex‐based nanocomposites with a broad particle size distribution

AbstractThe present study article aims to clarify the effect of colloidal polystyrene (PS) latexes with a broad particle size distribution on film formation kinetics of multi‐walled carbon nanotube (MWCNT)‐added polymer nanocomposites by considering theoretical film formation models. Experimentally, light transmitted from nanocomposite films, each having different weight fractions of MWCNT, was recorded at different annealing temperatures via UV–Visible spectrophotometry. Optical data set was then theoretically elaborated by taking into account void closure and Prager‐Tirrell models. Activation energies of viscous flow (ΔH) and backbone motion for reptating PS chains (ΔEB), minimum film formation (T0) and healing (Th) temperatures were then computed from optical data. Experimental results revealed that ΔH required for void closure phenomenon remained unaffected by both nanofiller and size distribution of latexes. On the other hand, it was found that ΔEB for backbone motion promoted upon the addition of nano‐fillers into latex particles. Our experimental findings suggested that film formation from MWCNT‐added latex films with a broad particle size distribution mainly originates from void closure mechanism since ΔH for viscous flow suppresses ΔEB acquired for backbone motion of repeating PS chains to a great extent.Highlights A broad size distribution effect of PS on film formation was investigated. Voids closure and Prager‐Tirrell models were applied to spectroscopic data. Activation energy of viscous flow is unaffected by size distribution of PS. Latex film formation with varying size distribution stems from void closure.

The Molecular Ocean

We report on progress in observing the hydrogen-bonded structure of water and sea water by deep-ocean Raman spectroscopy. In the normal ocean, the abundance of single H2O species is less than 20%. The principal form is the tetrahedral pentamer, and the (H2O)[Formula: see text] nH2O equilibrium plays a dominant role in controlling physicochemical processes and the speed of sound. The enthalpy of the H-bond in water is 2.624 kcal/mol, and in sea water 2.258 kcal/mol due to the quantity of non-HB water in the solvation shell of sea salt ions. The activation energy of viscous flow is 4.28 kcal/mol at one atmosphere pressure, consistent with the need to break hydrogen bonds and overcome the van der Waals intermolecular forces. The activation energy decreases exponentially with depth/pressure and is 10% less at 4,000 m depth. We suggest this is due to the pressure-induced shift in the water equilibrium to favor the less compressible quasi-planar pentamer, tetramer, and so on forms. We address the long-standing conclusion that microbial swimming by means of rotating flagella is only 1%–2% efficient. This neglects the need for microbes to overcome the activation energy of viscous flow; [Formula: see text]95% of the mechanical energy produced by the flagella must be used to break H-bonds and overcome intermolecular forces.

Viscosity of slags from joint smelting of oxidized nickel and sulfide copper ores

The work is devoted to the viscosity determination of molten slags from the joint smelting of oxidized nickel and sulfide copper ores. The model slags were synthesized close in composition and structure to real samples, and limiting the investigated composition range (wt.%): iron-containing slag (8.9 CaO, 11.8 MgO, 12.5 Al2O3, 47.4 SiO2, 13.3 FeO, and 5.0 Fe2O3) and iron-free slag formed by removing iron oxides from the iron-containing slag (12.5 CaO, 16.0 MgO, 9.4 Al2O3, and 58.3 SiO2). The experimental (vibrational method) viscosity values for iron-containing (1550−1300 °C) and iron-free (1550−1400 °C) model slags are 0.31−2.33 and 1.28−4.55 Pa·s, respectively. Viscosity estimation by the Kalmanovitch–Frank model shows a discrepancy with the experimental data for iron-containing slag. Regression analysis (by Weimann–Frenkel–Urbain formalism) of the experimental data was carried out, and original empirical models were proposed to predict the primary model slags viscosity in the considered temperature range. Reducing the basicity from 0.7 (iron-containing slag) to 0.6 (iron-free slag) increases viscous flow activation energy from 204 to 236 kJ/mol. To maintain optimal slag viscosity, joint smelting of oxidized nickel and sulfide copper ores should be carried out at a temperature not lower than 1400 °C.

Structure evolution and magnetization properties of FeSiBCCr amorphous alloys prepared by spark plasma sintering

FeSiBCCr bulk metallic glasses were prepared via spark plasma sintering, and the effects of holding time and heating rate on the structure and magnetization properties of powder compacts were investigated by SEM, TEM, XRD, DSC and VSM. The results show that when the holding time is increased from 10 min to 20 min, the internal porosity is reduced, and the amorphous fraction is decreased from 92.0 ± 1.7 % to 82.4 ± 4.3 % accompanied by the precipitation of fine nanocrystalline grains. When the holding time is increased to 30 min, the precipitation of the ferro-boron phase and growth of nanocrystalline grains lead to a significant deterioration of magnetization properties, although the compact density is significantly increased to 6.13±0.12 g/cm3. When the heating rate is increased from 20 K/min to 100 K/min, the activation energy of viscous flow is decreased and the compact density is improved due to the enhanced mass transfer. Moreover, the thermal stability of the amorphous material is also improved, effectively suppressing the grain coarsening and the precipitation of the ferro-boron phase. As a result, the saturation magnetic flux density is increased by 10 % and the coercivity is reduced by 83 %. The FeSiBCCr bulk metallic glasses prepared at a sintering temperature of 773 K, a heating rate of 100 K/min, and a holding time of 10 min contain an amorphous matrix with fine Fe2Si grains. And the compact has a density of 5.60±0.08 g/cm3, a saturation magnetic flux density of 1.03±0.03 T, and a coercivity of 15.9 ± 1.2 A/m, exhibiting promising magnetization properties and being expected to be used in medium and high frequency electronics.

Viscosity determination of the biomass slag in the SiO2-CaO-K2O system based on the bond distribution

The slag mobility is a key factor influencing the slag tapping process during the slagging gasification of biomass. However, the viscosity model suitable for the biomass slag (relevant to the SiO2-CaO-K2O system) has not been reported yet. This study firstly proposed an Arrhenius-type viscosity model based on the bond distribution in biomass slag. The bond information of the biomass slag was determined by61 thermodynamic modelling. The quantified relation between the slag composition (SiO2, CaO, and K2O) and bond distribution (Si-Si-O-O, Si-Ca-O-O, and Si-K-O-O), and the relation between the bond distribution and activation energy of viscous flow (Ea) or pre-exponential factor (A) were established, respectively. The standard deviations of our model are 1.71 Pa·s in the 0–100 Pa·s and 0.61 Pa·s in the 2.5–25 Pa·s, respectively. The newly built viscosity model shows superior prediction performance than the empirically viscosity models, and owns better performance than the FactSage model in the optimal viscosity range (2.5–25 Pa·s) of the smooth slag tapping process.

Balancing the sustainable component of ethylene-vinyl acetate for achieved better compatibility improvement of wax-based warm mix additives in bitumen

The ethylene-vinyl acetate (EVA) polymers are always doped into waxy bitumen to inhibit network of wax crystals in bitumen. However, the compatibility improvement behaviors between wax-based warm mix (WWM) additives and bitumen by EVA are not clear, and the sustainable components of EVA for corresponding WWM additives to achieve better compatibility improvement are also not determined. This paper investigated compatibility improvement behaviors between commonly used WWM additives and bitumen after the addition of EVA to obtain sustainable components of EVA through experimental method of activation energy of viscous flow (AEVF) and density function theory-molecular dynamic (DFT-MD) calculations. The results show that the repulsions between the end of main-chain with highest electronegativity in WWM additives and polar molecules of EVA can alleviate the aggregation behaviors of WWM additives and EVA displays the best and worst compatibility improvements for additives with shortest and longest carbon chains, respectively. The dispersed asphaltenes combined with EVA can form the composite wax inhibitors (WIs) systems to increase diffusion coefficient and reduce percentage increment values of cohesive energy density (CED) to further disrupt ordered degree of WWM additives. On this basis, the sustainable carbon numbers of main-chain for EVA that are slightly less than average carbon numbers of WWM additives will help to better improve the compatibility of WWM additives. This investigation can provide the inspiration on how to choose the sustainable components of EVA to achieve high-efficiency compatibility improvement for corresponding warm mix asphalts (WMAs) with different average carbon numbers.

Influence of Cr2O3 on the Viscous Flow Behavior and Structure of Cr‐Containing Molten Titanium Slag

Herein, the influence of Cr2O3 on the viscous flow behavior and structure of Cr‐containing molten titanium slag is investigated in this work. The melting and viscosity properties are studied by hemisphere method and rotating cylinder method, respectively. In addition, the structure of Cr‐containing molten titanium slag is investigated by Raman spectroscopy. It is shown in the results that the melting temperature and viscosity both increase with the increase of Cr2O3 content. The activation energy for viscous flow increases with increasing Cr2O3 content, which is in the same trend as viscosity. When the Cr2O3 content increases from 0% to 3%, the simpler 6‐coordinated Ti4+ and TiO44− monomer unit transformed into more complex O–Ti–O deformation and Ti2O64− chain unit. Furthermore, the fraction of relatively complex silicate structural units shows an increasing trend. Cr2O3 behaves as a network former and enhances the degree of polymerization of network structure, and the variation of Cr‐containing molten titanium slag structure is consistent with the increasing trend of viscosity.

Study on rheological behavior of polystyrene‐polyisoprene‐polystyrene around viscous flow transformation: Effect of polystyrene block content and molecular weight

AbstractThe flow behavior of triblock copolymer polystyrene‐polyisoprene‐polystyrene (SIS) was different below and above the viscous flow transition temperature (Tf). The study investigated the relationship between molecular structure (molecular weight and polystyrene block content) and the macroscopic rheological properties of SIS melt around Tf via capillary rheometer. The results indicated that below the Tf, shear viscosity of SIS melt was controlled by the polystyrene (PS) block content. On the other hand, above the Tf, shear viscosity was controlled by molecular weight. The rheological phenomena were explained based on the state change of the PS domains below and above Tf. The effect of PS block content on the viscous flow activation energy (Eη) and pressure drop of SIS melt was also investigated.

Thermal hysteresis phenomena in aqueous xanthan gum solutions

The anionic hydrocolloid polysaccharide xanthan gum is widely used in the food and petroleum industries (among others) as a viscosity enhancement polymer due to its high viscosity at low concentrations and moderate temperatures. The physical properties of microbial polysaccharide xanthan gum aqueous solutions were investigated using temperature dependent viscosity measurements. Specifically, the effect of thermal history on the solution viscosity was investigated. Heating and cooling cycles were assessed in two ways, by using a “sawtooth” and “triangle” pattern, which essentially differed in the rates of cooling. The sawtooth method used a cooling rate of 2.0 °C min−1 whereas the triangle pattern had a cooling rate of 0.20 °C min−1. The sawtooth cooling rate was controlled by the speed at which the Peltier device could cool the sample, and the triangle rate was governed by the time required to measure the viscosity at each temperature on return to the initial value. Cycles measured using the sawtooth pattern for 16 mg/kg xanthan gum in water showed an 8–10% overall decrease in the viscosity over four complete cycles. Comparatively, at 320 mg/kg the xanthan gum solution showed a 25% decrease in viscosity over four cycles. The observed temperature dependent viscosity variation suggested minor modifications in the physical network structure of xanthan gum. When using a triangle heating/cooling pattern, the overall decrease in the xanthan gum solution viscosity was 5–7% for 16 mg/kg and only 10% change for 320 mg/kg solutions. The activation energy of viscous flow for the aqueous xanthan gum solutions by either method was ∼15.0 kJ/mol under all conditions. The data showed that temperature and heating cycles influence xanthan gum viscosity and thermal history, which depends more strongly on xanthan gum concentration than solution temperature.

Thermo-kinetic and structural characterization of Ce-doped glasses based on Bioglass 45S5

Thermo-kinetic behavior of Ce-doped 45S5 bioactive glass (addition of CeO2 up to 1.5 mol.%) was explored by means of calorimetry and thermomechanical analysis. The apparent activation energy of structural relaxation was estimated to vary in the 540–670 kJ mol−1 range. The relaxation process exhibited broad distribution of relaxation times and the relaxation motions were found to only weakly depend on the material's structure. The activation energy of viscous flow was found to vary in the 585–615 kJ mol−1 range; the viscosity itself showed Arrhenian behavior within 107–1011 Pa s. Thermal stability of the glasses was found to be non-monotonous and generally very low, with the most stable glass composition being 45S5 + 0.5 mol.% CeO2. The cold crystallization was found to behave autocatalytically, with the activation energy decreasing from 360 to 310 kJ mol−1 with the gradual addition of CeO2. While the bulk glasses were crystallization-resistant up to 620 °C, the powdered material with CeO2 content ≥1 mol.% was predicted to crystallize even at temperatures slightly above the glass transition temperature.

Influence of Zn2+ catalyst stoichiometry on curing dynamics and stress relaxation of polyester-based epoxy vitrimer

In the classical “covalent adaptive network” constructed by diglycidyl ether of bisphenol A (DGEBA) and crosslinking agent glutaric anhydride (GA), Zn-based catalyst greatly affects the curing crosslinking reaction and dynamic transesterification reaction. Herein, the crucial roles of Zn(Ac)2 catalyst in the curing dynamics and stress relaxation were studied. The results reveal that increasing the content of Zn(Ac)2 can significantly reduce the reaction activation energy (Eα) at initial stage, thus effectively promoting the curing crosslinking reaction. The analyses of dynamic properties suggest that although stress relation time (τ) can be shortened by increasing catalyst content, the high content of catalyst would lead a fast transesterification rate at relatively low temperature, which is adverse to the mechanical stability of vitrimer resin at operating temperature. By comparison, the vitrimer resin with modest catalyst content (mole ratio of 1:0.5:0.05) shows a highest viscous flow activation energy (Eτ), i.e., excellent dimensional stability and processability. Besides, the crosslinking density of resin was significantly affected by the content of catalyst. Since the competitive catalytic effects on curing cross-linking reaction and subsequent transesterification, the vitrimer resin of 1:0.5:0.05 exihits the highest crosslinking density (1855 mol/m3), so that it has highest Tg (79 °C) and tensile strength (72 MPa).

Effect of TiO2 on viscosity and structure for CaO-SiO2-Al2O3-based mold flux

The viscosity of CaO-SiO2-Al2O3-MgO-Na2O-CaF2-(TiO2) was measured by the rotating column method, and the viscosity, break temperature and viscous flow activation energy of the slag were analyzed based on the results. The effect of TiO2 content on the structure of the slag was studied by Raman spectroscopy. The results show that with the increase of TiO2 content in CaO-SiO2-Al2O3-based mold flux, the viscosity of mold flux increases, the break temperature increases from 1418 K to 1535 K, and the viscous flow activation energy changes little. At high temperature, TiO2 can depolymerize the [Si-O] and enter into the network structure as [Ti-O], which increases the frictional resistance to the viscous flow of the mold flux. At the same time, the crystallization temperature and viscosity of the slag is increased.

Effect of MgO/Al2O3 on Viscosity and Thermodynamic Properties of High-Titanium Slag Containing Chlorine

In order to study the effect of the change of MgO/Al2O3 on the viscosity and thermodynamic properties of the chlorinated blast-furnace slag, the CaO-SiO2-MgO-Al2O3-TiO2-CaCl2 slag system was taken as the research object, and the viscosity change rule of the chlorinated high-titanium slag was studied by using the rotating cylinder method. The thermal stability of the chlorinated high-titanium slag was quantitatively analyzed by calculating the extreme heat release rate (EHRS) of the chlorinated high-titanium slag. At the same time, the qualitative and quantitative analysis of the high-titanium slag containing chlorine was carried out by combining FTIR and Raman spectroscopy, and the mechanism of the influence of MgO/Al2O3 on the viscous flow characteristics of the high-titanium slag containing chlorine was revealed. The results show that when the alkalinity (R2) of the fixed slag is 1.15, when MgO/Al2O3 is in the range of 0.40–0.66, the viscosity of the high-titanium slag containing chlorine presents a significant decreasing trend with the gradual increase of MgO/Al2O3, and the viscous flow activation energy of the slag decreases from 98.75kJ · mol−1 to 95.21kJ · mol−1. The heat capacity and enthalpy change of slag decrease with the increase of MgO/Al2O3, but the change rule of slag extreme heat release is opposite to that of heat capacity and enthalpy change. When MgO/Al2O3 increases, the slag extreme heat release increases from 13.413 kJ to 15.172 kJ. The content of simple structural units Q0 and Q1 of silicate tetrahedron in the slag gradually increases, the content of complex structural units Q2 and Q3 gradually decreases, and the average amount of non-bridging oxygen decreases from 1.94 to 1.79, indicating that Al2O3 acts as a network maker in the internal network structure of the slag. The increase of MgO/Al2O3 destroys the complex silicate tetrahedron structure in the slag, reducing the degree of polymerization of the slag silicate network. In addition, the transmissivity of [SiO4]4− tetrahedron, [AlO4]4− tetrahedron and T-O-T bond bending vibration band in the slag shows a decreasing trend. Within the scope of the experiment, the increase of MgO/Al2O3 can effectively improve the fluidity of the chlorine-containing blast-furnace slag and improve the thermal stability of the chlorine-containing blast-furnace slag.

Effect of phosphorus on viscosity-temperature behavior of high-sodium coal ash slag

Co-gasification of P-rich fuels and coal would reduce the large-scale usage of fossil fuels and pollution emissions, and fit the “carbon neutrality” goal in 2060. However, the effect of phosphorus on the viscosity-temperature behavior and structure of high-sodium coal ash slag is not yet completely characterized. In this work, the effect of phosphorus on the viscosity and structure of slag was investigated, and the crystallization tendency was also elevated. Results indicate that the high-sodium coal ash slag has a low viscosity as the Na2O can provide O2− ions and break Si-O-Si bonds, leading to decreasing the slag viscosity. The slag viscosity gradually increases as the PO43−/Na molar ratio increases because the phosphorus acts as a network former and enhances the slag viscosity. The temperature of critical viscosity rises from 1206 °C to 1305 °C and 1127 °C to 1207 °C, respectively, for Group 1 and Group 2 when the PO43−/Na molar ratio rises from 0/0 to 2/1. With the addition of phosphorus, the cations of Na are removed from the silicate network and form Na phosphate complexes and Si-O-Si linkages, and the content of Q3(Si) and Q4(Si) units increases while the contents of Q0(Si), Q1(Si), and Q2(Si) units decrease, increasing the slag viscosity. In addition, the Si-O-P and P-O-P linkages are formed due to the phosphorus atoms being introduced into the slag structure. Resulting in decreases the content of non-bridging oxygen and rises the degree of polymerization of slag. Furthermore, the viscous flow activation energy of slag increases while reducing the crystallization tendency after the application of phosphorus.

Volumetric and viscometric properties of monoethanolamine (MEA) + 3-dimethylamino-1-propanol (3DMA1P) + H2O at T = (293.15 to 333.15) K

Densities and viscosities were measured for binary solutions MEA (monoethanolamine) + 3DMA1P (3-dimethylamino-1-propanol), 3DMA1P + H2O and ternary solutions MEA + 3DMA1P + H2O at P = 0.101 MPa, T = 293.15 K ∼ 333.15 K. Based on the experimental densities of solutions, the volume properties of the excess molar volume, partial molar volume, apparent molar volume and limiting partial molar volume were calculated. Moreover, the viscosity deviation and viscous flow activation energy were calculated based on the experimental viscosity. Additionally, the intermolecular interactions of the mixed solutions were analyzed and discussed, and the Redlich-Kister equation was used to correlate the excess molar volume and viscosity deviation of the binary solutions.

Protein-protein interactions in solutions of monoclonal antibodies probed by the dependence of the high-frequency viscosity on temperature and concentration.

Using a quartz crystal microbalance with dissipation monitoring (QCM-D), the complex high-frequency viscosity,  = η' - iη'', of concentrated solutions of a monoclonal antibody (mAb) was studied with respect to its dependence on temperature, T, and concentration, c. Lysozyme and bovine serum albumin (BSA) served as reference materials. Viscoelasticity was found for the mAb solution, while the reference materials behaved like Newtonian liquids. The QCM-D probes the solution's dynamics on the time scale of a few tens of nanoseconds. The processes of relaxation accessed with the QCM-D are not amenable to standard viscometry. The inverse loss tangent at 15 MHz (equal to η''/η' at 15 MHz, quantifying the elastic contribution to the oscillatory stress) was between 0.1 and 0.5 for the concentrated mAb solutions. It decreased with increasing temperature and decreasing pH. Activation energies of viscous flow, Ea,η, were derived from the functions η'(T). Ea,η was found to be higher for the mAb solutions than for water. No such increase was found for the reference materials. This difference evidences protein-protein interactions (PPIs) between the mAb molecules, which do not exist in the same way for lysozyme and BSA. The excipients citrate and arginine did not noticeably affect the mAb's high-frequency viscosity as determined with the QCM-D.