Some basics for operating and analyzing data using the thickness shear mode resonator

The promises of obtaining meaningful measurements on physical systems loading the quartz crystal microbalance are extremely bright. The two aspects of this process, namely the gathering of faithful data and reductions of these data by way of modelling, need careful consideration to avoid some very common missteps which could frustrate this effort. The experimental techniques are emphasized here but a brief introduction to the basic methodologies of modelling is also given.     

An improved system for data acquisition and analysis for viscoelastic measurements of dilute macromolecular solutions with the modified birnboim-schrag multiple lumped resonator

A new system of data acquisition and analysis has been developed for the modified Birnboim-Schrag multiple lumped resonator apparatus which is used to measure the viscoelastic properties of long-chain macromolecules in dilute solution. The modifications to the original apparatus include improved temperature control and vibration isolation. The original theory has been reworked so that each resonance mode can be characterized by a greater number of data points. The entire data acquistion/processing system is automated and placed under computer control; a correlation for mode coupling is derived. The modifications result in improved precision in the measured viscoelastic moduli and increased instrumental reliability.     

Frequency dispersion of the dynamic moduli of elasticity of electrolyte solutions

The frequency dispersion range of the dynamic bulk relaxation modulus K(ω) and shear relaxation modulus µ(ω) of electrolyte solutions has been determined in relation to the nature of stress tensor damping in the momentum and configuration spaces. Numerical calculations have been carried out for an aqueous NaCl solution in wide frequency, temperature, and density ranges using analytical expressions obtained for K(ω) and µ(ω) for the exponential-law damping of the fluxes at a certain molecular interaction potential \(\Phi \left( {\left| {\vec r} \right|} \right)\) and radial distribution function \(g\left( {\left| {\vec r} \right|} \right)\). It has been demonstrated that the frequency dispersion range of K _r (v) and µ(v) for the exponential-law damping of the corresponding fluxes is narrow (～10² Hz).     

Three-dimensional numerical simulation of viscoelastic phase separation under shear: the roles of bulk and shear relaxation moduli

The morphological, dynamic and rheological characteristics in the viscoelastic phase separation(VPS) of sheared polymer solutions are investigated by three-dimensional(3D) numerical simulations of viscoelastic model. The simulations are accelerated by graphic process unit(GPU) to break through the limitation of computation power. Firstly, the morphological and dynamic characteristics of VPS under shear are presented by comparing with those in classic phase separation(CPS). The results show that the phase inversion and phase shrink take place in VPS under shear. Then, the roles of bulk and shear relaxation moduli in VPS are investigated in details. The bulk relaxation modulus slows down the phase separation process under shear, but not affects the dynamic path of VPS. The dynamic path can be divided into three stages: freezing stage, growth stage and stable stage. The second overshoot phenomenon in the shear stress is observed, and explained by the breakdown and reform of string structures. The shear modulus affects morphology evolution in the late stage of VPS under shear.     

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

In situ light scattering measurements were performed to investigate the effect of low shear rates (0.13-3.56 s(-1)) on an aggregating colloidal system made of 20 nm polystyrene particles. The aggregating system was subjected to a shear for a short period (ca. 33 s) and only once at various times after the onset of aggregation. The effect of shear (aggregation kinetics and morphology) was studied both in a cluster dilute and in a cluster dense regime (see introduction). Our results have shown that shear can enhance the aggregation and gelation. Shear induced growth can yield hybrid superaggregates when the system is dense.     

Temperature dependence on phase evolution in the BaTiO3 polytypes studied using ab initio calculations

Identifying the forces that drive a temperature-induced phase transition is always challenging in the prospect of the first-principles methods. Herein, we perform a first-principles study of the temperature effects on structural, energetic, electronic, and vibrational properties of four BaTiO₃ polymorphs using quasi-harmonic approximations. Study of the stability between these four phases, which we break into contributions arising from the vibration of the lattice, electronic structure, and volume expansion/contraction, is helpful to confirm the sequence of phase transitions as cubic → tetragonal → orthorhombic → rhombohedral, as well as its transition temperatures. A general mechanism was proposed based on the combination between structural distortions at [TiO₆] clusters, vibrational characteristics, and electronic structure. These findings confirm the power of quasi-harmonic approximations to disclose the main fingerprints associated with both thermic and mechanical phase transitions, serving as a guide for further theoretical studies.     

Numerical assessment of the analytical models used to determine flexural and shear moduli in I-Beams when the tensile and compressive moduli are different

The different compressive and tensile moduli of fibre reinforced composites have been considered in the analysis of the flexural and shear moduli of I-beams. Firstly, the neutral axis has been determined analytically and then, assuming that location of the neutral axis, the analytical flexural modulus of I-beams has also been obtained. In order to assess the proposed procedure, virtual pure bending and three-point bending tests at different spans have been carried out using the finite element method. The compressive and tensile moduli have been taken into account by defining two parts in the numerical models. The numerical flexural and shear moduli have been determined by reducing the data obtained in the virtual tests. Analytical and numerical results are in good agreement. Therefore, the flexural modulus determined by the proposed analytical approach can be introduced as a material property in the finite element method.     

Evaluation of high-frequency elastic moduli and shear relaxation time of the Lennard-Jones fluid using three known analytical expressions for radial distribution function

High-frequency elastic moduli (G_∞ and K_∞) for a Lennard-Jones (LJ) fluid have been calculated using three known analytical expressions for radial distribution function (RDF) at different temperatures and densities and compared with the corresponding values of these properties obtained from molecular dynamics (MD).     

Modeling the growth processes of polyelectrolyte multilayers using a quartz crystal resonator

The layer-by-layer buildup of chitosan/hyaluronan (CH/HA) and poly(l-lysine)/hyaluronan (PLL/HA) multilayers was followed on a quartz crystal resonator (QCR) in different ionic strengths and at different temperatures. These polyelectrolytes were chosen to demonstrate the method whereby useful information is retrieved from acoustically thick polymer layers during their buildup. Surface acoustic impedance recorded in these measurements gives a single or double spiral when plotted in the complex plane. The shape of this spiral depends on the viscoelasticity of the layer material and regularity of the growth process. The polymer layer is assumed to consist of one or two zones. A mathematical model was devised to represent the separation of the layer to two zones with different viscoelastic properties. Viscoelastic quantities of the layer material and the mode and parameters of the growth process were acquired by fitting a spiral to the experimental data. In all the cases the growth process was mainly exponential as a function of deposition cycles, the growth exponent being between 0.250 and 0.275.     

Monitoring photopolymerization of trimethylolpropane triacrylate using a quartz crystal resonator

The UV photopolymerization of trimethylolpropane triacrylate with a photoinitiator of 2‐ethylanthraquinone is monitored using the variation of resonant resistance of a quartz crystal resonator to investigate the polymerization kinetics. The roles of initiator concentration and irradiation time are experimentally examined, and it is found that two different kinetics are involved in the photopolymerization. The initiator radicals produced by the UV light proceed the polymerization as long as the monomer remains even after the UV illumination has stopped. The experimental results indicate that the photopolymerization has the first‐order kinetics at the first‐ and the zeroth‐order kinetics followed. With the high concentration of initiator the polymerization occurs in the first‐order kinetics only, and so does with long irradiation time. The polymerization constants of the first and zeroth‐order kinetics are estimated from monitoring monomer amounts at different polymerization conditions. The photopolymerization is characterized with the FTIR spectroscopy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Frequency dependence of the hyperpolarizability measured for SF6

The frequency dependence of the hyperpolarizability of SF₆ has been measured in the visible by the technique of electric-field-induced second-harmonic generation (ESHG). The results are consistent with negligible vibrational contributions at optical frequencies for this non-linear process. The relation between these results and the results for other processes is examined.     

Characterization of BSA-fouling of ion-exchange membrane systems using a subtraction technique for lumped data

Electrical impedance spectroscopy (EIS) techniques were used to gain insight into BSA fouling of the Neosepta CMX and AMX ion-exchange membranes (IEMs). EIS characterizations were made at concentrations above 0.1 M KCl because the conductance of the IEMs was higher than that of bulk solutions of concentration below 0.1 M KCl. Spectra, expressed in terms of dispersions of the conductance and capacitance with frequency, provided an enhanced indication of IEM fouling during separation processes. Bulk conductance measurements of the solution alone, membrane immersed in solution and fouled membrane immersed in solution showed good agreement with general theoretical predictions. Strong dispersions in capacitance were observed below 1 kHz for each of these configurations. Differences in the dispersions arising from fouling were identified by subtracting the impedance of the solution from those of unfouled and fouled IEMs in solution. The conductance and capacitance dispersions of fouled IEMs decreased with the accumulation of the BSA fouling layer on the surface.     

Effect of temperature on the dynamic young's and shear moduli of unidirectional carbon fiber-epoxy composite beams

The resonance frequencies of unidirectional carbon fiber reinforced/epoxy composite beams were studied over the temperature range 24–225°C. Longitudinal Young's moduli E₁₁ and longitudinal-transverse shear moduli G₁₂ were computed from the experimental data by the use of Timoshenko beam theory. The effects of transverse shear deformation (a function of E₁₁/G₁₂) were found to increase in importance with increasing temperature. Values of G₁₂ were found to be approximately proportional to the shear modulus G_m of matrix material but were about 30% lower than predicted by the theory of Hashin and Rosen. The anisotropy of the carbon filaments and voids in the composite samples were proposed to account for the discrepancy between theory and experiment.     

Temperature dependence of the free volume in polytetrafluoroethylene studied by positron annihilation spectroscopy

The temperature dependence of the free volume holes in pure polytetrafluoroethylene (PTFE) and doped with 25% glass have been studied in the temperature range (30–250 °C) using positron annihilation lifetime spectroscopy. The data clearly revealed the glass transition temperatures for pure and doped PTFE are 130 and 110 °C, respectively. As the temperature increases, the free volume distribution becomes positioned at larger free volume hole size. A good correlation between the electrical conductivity and the o-Ps parameters was achieved.     

Scrutiny of annexin A1 mediated membrane-membrane interaction by means of a thickness shear mode resonator and computer simulations

The dissipational quartz crystal microbalance (D-QCM) technology was applied to monitor the adsorption of vesicles to membrane-bound annexin A1 by simultaneously reading out the shifts in resonance frequency and dissipation. Solid-supported membranes (SSMs) composed of a chemisorbed octanethiol monolayer and a physisorbed 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine monolayer were immobilized on the gold electrode of a 5 MHz quartz plate. Adsorption and desorption of annexin A1 to the SSM was followed by means of the QCM technique. After nonbound annexin A1 was removed from solution, the second membrane binding was monitored by the D-QCM technique, which allowed distinguishing between adsorbed and ruptured vesicles. The results show that vesicles stay always intact independent of the amount of bound annexin and the vesicle and buffer composition. It was shown that the vesicle adsorption process to membrane-bound annexin A1 is fully irreversible and is mediated by two-dimensional annexin clusters. For N-terminally truncated annexin A1, a decrease in the amount of bound vesicles was observed, which might be the result of fewer binding sites presented by the annexin A1 core. Supported by computer simulations, the results demonstrate that the vesicle adsorption process is electrostatically driven, but compared to those of sole electrostatic binding, the rate constants of adsorption are 1-2 orders of magnitude smaller, indicating the presence of a potential barrier.     

Frequency shift in smectic multiple relaxations and the effect of a flexible end chain

The low frequency (LF) dielectric constant was studied as a function of temperature in the Schiff 's base liquid crystalline compounds of N ( p - n -alkoxybenzylidene)- p - n -alkylanilines with the applied field parallel to the director to determine the phase transition temperatures and the underlying dipolar association. The low frequency (1 kHz to 10 MHz) complex dielectric spectrum systematically studied in the smectic polymorphs of these compounds implied multiple relaxations. The rotational degrees of freedom were found to be squeezed with the decrease of temperature as the low temperature smectic phases were approached. The ColeDavidson method was used to differentiate the fast dynamics of the rigid core-associated dipole from the slow component of the flexible end chain. A comparative study of the orientational dynamics of the rigid core dipole (type I) was carried out by designing a normalized scale in smectic phases. Arrehenius dependence was used in the estimation of smectic relaxation frequency at a common normalized smectic temperature scale point. The results imply the downward shift of frequency with increase in length of the flexible end chain. The distinct loss of rotational degrees of freedom of the rigid core dipole with increasing chain length suggests its solute particle behaviour in the solvent concentration.     

Reversible Melting of Semi-crystalline Polymers Frequency dependence of the reversible melting enthalpy

Modulated DSC (MDSC) has been used to study the heat flow during melting and crystallisation of some semi-crystalline polymers i.e. different grades of polyethylene (LDPE, LLDPE and HDPE), and polypropylene (PP). The heat capacities measured by MDSC are compared with the hypothetical complex heat capacities of Schawe and it is shown that numerically they are equivalent; nevertheless, the concept of the complex heat capacity is problematic on a thermodynamic basis. A reversing heat flow (proportional to the experimental heat capacity of the material) was present at all conditions used for the study. In the melting zone of the polymers it depends on the modulation frequency and on the amplitude. Higher amplitude and frequency of modulation reduce the ratio of the reversing heat flow to the total heat flow, the latter is nearly independent on these parameters. The reversible component of the melting enthalpy of polymers depends on the modulation frequency, the modulation amplitude and the type of the polymer. It increases by increasing the branching in polyethylene. The existence of the reversible heat flow during the crystallisation and melting is contrary to the current hypotheses and theories of polymer crystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Frequency dependence of hysteresis associated with the electromechanical performance of PVDF film

The thickness strains, the electric displacements, and the hysteresis exhibited by poly(vinylidene fluoride) films under sinusoidal applied electric fields were measured over a range of frequencies from 0.05 to 100 Hz. The loops of strain‐ and electric displacement versus electric field exhibit a shape and hysteresis that undergoes a continuous and reversible change with frequency. At lower frequencies (<5 Hz), the shape and large hysteresis are characteristic of a ferroelectric with degrees of remanent polarization. At higher frequencies (>5 Hz), the shape and slight hysteresis of the loops are representative of a nonremanently polarized ferroelectric. This dependence of shape and hysteresis on frequency is attributed to the difference in rates between the rapid rate by which the polarization of domains of aligned dipoles is reversed in a periodic field and the slower rate by which the polarization is made remanent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3207–3214, 2007     

Frequency dependence of the electrorheological effect in the nematic phase of pentyl cyanobiphenyl

The effect of an electric field on the viscosity, the electrorheological (ER) effect, is studied as a function of the frequency of the electric field for the nematic phase of 4-n-pentyl-4'- cyanobiphenyl (5CB). In the frequency region between 10Hz and 1kHz, a gradual change of the ER effect is observed, with its behaviour depending on the shear rate and the amplitude of the electric field. On the basis of a calculation of the orientational motion of the director and its effect on the viscosity, the observed frequency dependence is suggested to occur as a result of an orientational relaxation of the director.