Contact studies of weakly compressed PEG brushes with a quartz crystal resonator

A quartz crystal resonator was used to characterize the contact of an elastomeric polymer membrane with a grafted poly(ethylene glycol) (PEG) brush in an aqueous environment. A two-layer model of the acoustic impedance of the system was used to measure the brush thickness before and after contact with the membrane. This model was further extended to include multiple layers, allowing characterization of other monomeric density profiles along the brush thickness. The polymer brush maintains a hydrated layer between the membrane and the quartz crystal surface, the thickness of which could be determined to within 1 nm. We show that the technique is very well suited for studying the properties of highly hydrated layers with thicknesses between 0 and 100 nm at low contact pressures corresponding to a very weak compression of the PEG brush.     

Bond rupture force measurement by means of a quartz resonator

Methods to measure the bond rupture force are considered. It is proposed to use a quartz resonator as an active element rather than simply a sensor. When the surface oscillation amplitude of an AT quartz resonator increases smoothly (rupture event scanning), a particle attached to the quartz surface is removed by inertial forces, and from their values it is easy to obtain the bond dissociation value. This procedure provides reliable measurements of the rupture force of about 10 pN. As the atomic force microscopy method, the rupture event scanning does not apply electromagnetic radiation, but has simpler instrumental set-up. The scanning requires minimum sample preparation, can be performed in various media (vacuum, air, liquid), and takes only a few minutes.     

Effect of ionic surfactants on the oscillation frequency of one-electrode-separated piezoelectric quartz crystals modified with chitosan and its derivative

From the pH dependence of oscillation frequencies of one-electrode-separated piezoelectric quartz crystals (ESPQCs) modified with chitosan and N-(1,3-dicarboxypropyl) chitosan (DCPC) in buffer solutions, it was deduced that the chitosan and DCPC films on an ESPQC contained water and that the water content depended on pH. Contrary to the expectation based on the Sauerbrey equation, the binding of ionic surfactants to chitosan and DCPC films increased the frequencies. This apparently abnormal phenomenon was explained by the release of water in swollen films. The frequency of the DCPC-modified ESPQC increased on addition of sodium dodecyl sulfate and hexadecyltrimethylammonium chloride at pH lower and higher, respectively, than 7.8. A linear relationship between surfactant concentration and frequency shift, whose slope depended on only the chain length of the surfactant alkyl group, was obtained in the range 5–50 µmol dm^–3 hexadecyltrimethylammonium chloride. The DCPC-modified ESPQC can be used for a quantitative determination of cationic surfactants in this concentration range.     

Theory and application of a quartz resonator as a sensor for viscous liquids

A comprehensive analysis of the interaction between an AT-cut quartz crystal resonator and a viscous fluid is presented. The analysis, which includes peizoelectric effects, assumes a liquid of finite extent and therefore could also be used to study thin film of viscous liquids. A novel continuous flow cell system was designed and fabricated to monitor viscosity using an 11-MHz quartz crystal resonator. Measured data for frequency shifts of aqueous solutions of alcohols and sugars are in excellent agreement with theory.     

The low-temperature quartz resonator method for determination of the enthalpy of sublimation

A low-temperature quartz resonator method for determining the enthalpy of sublimation has been described. A quartz crystal cooled to the temperature of liquid nitrogen becomes a sensitive microbalance. The method permits the value of ΔH_sub to be obtained within 4–5 h and is especially useful in measuring ΔH_sub values of substances with low saturated vapour pressures. The following values of ΔH_sub were received for standard substances: benzoic acid, ΔH_sub = (90.8±0.6) kJ mol^?1 at 293–319 K: naphthalene, ΔH_sub = (72.3±0.8) kJ mol^?1at 293–331 K.     

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.     

Chemical oscillation induced periodic swelling and shrinking of a polymeric multilayer investigated with a quartz crystal microbalance

Poly(acrylic acid- co-3-azidopropyl acrylate) and poly(acrylic acid- co-propargyl acrylate) have been alternately fabricated into a multilayer via the click reaction. The layer-by-layer deposition was monitored with a quartz crystal microbalance with dissipation (QCM-D) in real time. The response of the multilayer under continuous flow of a bromate-sulfite-ferrocyanide solution with pH oscillation has also been investigated by use of QCM-D. As the pH oscillates between 3.1 and 6.6, either the frequency shift (Delta f) or the dissipation shift (Delta D) periodically varies with a constant amplitude, clearly indicating that the multilayer swells and shrinks oscillatedly. The changes of thickness, shear viscosity, and elastic shear modulus further indicate the oscillation.     

Large apparent interfacial slippage at polyelectrolyte-perfluorocarbon interfaces on a quartz crystal resonator

The apparent negative areal mass densities obtained for a polyelectrolyte multilayer on a quartz crystal resonator in contact with four different perfluorocarbon liquids are explained by the interfacial slippage between the multilayer and the liquids. It is shown that the zone of interfacial slipping can be conveniently treated as a separate layer with distinct physical parameters. Three models of slippage were taken into a closer study. In the first model, the so-called de Gennes model, a very thin gas-filled cavity is formed between the moving phase and the stationary phase. The second model is based on the slipping layer consisting of water. In the third model, the so-called "true slipping" model, it is assumed that the particle velocity has a discontinuity at the interface. In each case, the slipping admittances and slippage lengths as well as the corrected areal mass densities were calculated from the experimental data. Although no unambiguous experimental evidence was found to favor strongly any of these three models, the slightly smaller variation in the slipping admittance and the areal mass density seems to give more credibility to the de Gennes model.     

The change in thickness of the solidified liquid layer rather than the immobilized mass determines the frequency response of a quartz crystal microbalance

The "solidified liquid layer" model has been examined using a quartz crystal microbalance(QCM) with a polymeric matrix.The model is shown to give a reasonable explanation for the following experimental observations:(i) The opposite response of the QCM and surface plasmon resonance(SPR) for the activation process;(ii) the marked difference in the responses for IgG/anti-IgG interaction between QCM and SPR.Theoretical analysis and experimental results indicated that QCM is sensitive to the thickness change of the "solidified liquid layer" but not the mass of captured biomolecules(i.e.,the immobilized mass),implying caution must be taken in interpreting QCM results.     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

The contact angles of surfactant solution on the quartz surface

Summary The contact angles formed on the quartz surface by 0,1 N NaCl aqueous solution at different pH were measured. The effect of surfactants such as anion-active sodium dodecyl sulphate (NaDS) and cation-active cetyltrimethylammonium bromide (CTAB) was investigated. The results are interpreted in terms of the Frumkin-Derjaguin theory of wetting.With 4 figures and 1 table     

Oscillating frequency of piezoelectric quartz crystal in solutions

Oscillating frequencies of a piezoelectric crystal were measured in various solutions. One side of the crystal surface was coated with a silicon sealant. This coating was useful for measuring the oscillation of crystals in solutions for a wide range of products of density (?) and viscosity (η) and in electrolyte solutions. For measurement in solutions, the frequency change depended on the circuit used, whereas for measurements in air the circuit did not influence the frequency change. All experimental data showed that the frequency change from pure water, ΔF_w, followed ΔF_w = ? K(√?η ? √?_wη_w) except for electrolyte and polymer solutions, where K is a proportionality constant, η_w the density of pure water and η_w the viscosity of water.     

The adsorption of liquid water on the surface of quartz

Conclusions Liquid water has positive adsorption on the surface of quartz; the value of the specific adsorption decreases with increasing temperature, comprising 9·10^–10 g/cm² at 0° and 4·10^–10 g/cm² at 70°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1276–1280, June, 1972.     

The high frequency dielectric response of a ferroelectric liquid crystal

Abstract

The temperature and frequency dependences of the complex dielectric susceptibility of a ferroelectric liquid crystal near the smectic C*-smectic A phase transition have been calculated using the classical and generalized Landau models. It is shown that although the dielectric response of the S*_C phase consists generally of four modes (soft, Goldstone, and two high frequency polarization modes) only three bands appear in the dielectric loss spectrum of ferroelectric liquid crystals at the S_A–S*_C phase transition. These results are in agreement with recent experimental data.     

Frequency response to liquid density of a piezoelectric quartz crystal sensor with longitudinal wave

Elimination of longitudinal wave effect is an important aspect in the detection cell design, although such consideration is ignored in most of references. Three detection cells were designed to investigate the influence of longitudinal wave effect on the frequency response of a piezoelectric quartz crystal (PQC) to liquid density. In the cell with horizontally mounted quartz crystal, the air/liquid interface acts the reflection surface for the longitudinal wave. The variation in liquid height by regent addition or solvent evaporation can result in fluctuation in the oscillating frequency of the PQC. The influence of the longitudinal wave is more obvious in a test liquid of lower density. In the cell with perpendicularly mounted quartz crystal, the longitudinal wave is mainly reflected back by the inner wall body. The fine structure of plotting of frequency shift (Δf) versus (ρη)^1/2 shows a wave shape, which is different from the well-known linear relationship between of Δf and (ρη)^1/2, where ρ and η are the density and viscosity of the liquid, respectively. And wave-shaped frequency-temperature curves were observed. The longitudinal wave was a kind of potential error source in the PQC measurements. The longitudinal wave effect can be efficiently eliminated by using a rough reflection surface. After eliminating the influence of reflected longitudinal wave, the stability of the sensor PQC was much improved.     

Decoupling of the liquid response of a superhydrophobic quartz crystal microbalance

Recent reports using particle image velocimetry and cone-and-plate rheometers have suggested that a simple Newtonian liquid flowing across a superhydrophobic surface demonstrates a finite slip length. Slippage on a superhydrophobic surface indicates that the combination of topography and hydrophobicity may have consequences for the coupling at the solid--liquid interface observed using the high-frequency shear-mode oscillation of a quartz crystal microbalance (QCM). In this work, we report on the response of a 5 MHz QCM possessing a superhydrophobic surface to immersion in water--glycerol mixtures. QCM surfaces were prepared with a layer of SU-8 photoresist and lithographically patterned to produce square arrays of 5 mum diameter circular cross-section posts spaced 10 microm center-to-center and with heights of 5, 10, 15, and 18 microm. Non-patterned layers were also created for comparison, and both non-hydrophobized and chemically hydrophobized surfaces were investigated. Contact angle measurements confirmed that the hydrophobized post surfaces were superhydrophobic. QCM measurements in water before and after applying pressure to force a Cassie-Baxter (non-penetrating) to Wenzel (penetrating) conversion of state showed a larger frequency decrease and higher dissipation in the Wenzel state. QCM resonance spectra were fitted to a Butterworth-van Dyke model for the full range of water-glycerol mixtures from pure water to (nominally) pure glycerol, thus providing data on both energy storage and dissipation. The data obtained for the post surfaces show a variety of types of behavior, indicating the importance of the surface chemistry in determining the response of the quartz crystal resonance, particularly on topographically structured surfaces; data for hydrophobized post surfaces imply a decoupling of the surface oscillation from the mixtures. In the case of the 15 microm tall hydrophobized post surfaces, crystal resonance spectra become narrower as the viscosity-density product increases, which is contrary to the usual behavior. In the most extreme case of the 18 microm tall hydrophobized post surfaces, both the frequency decrease and bandwidth increase of the resonance spectra are significantly lower than that predicted by the Kanazawa and Gordon model, thus implying a decoupling of the oscillating surface from the liquid, which can be interpreted as interfacial slip.     

Study of the alkylation behaviors of antitumor agents to DNA using a quartz crystal resonator in PEG-DNA solution

 The alkylation of DNA by antitumor agents such as mechlorethamine hydrochloride (mustargen), thiophosphoramide (TSPA), mitomycin c (MMC), bleomycin-A₅ and dacarbazine (DTIC) can be detected with quartz crystal resonators (QCR). In the course of alkylation, the resonator frequency change in polyethylene glycol (PEG)-DNA solutions follows the cross-linking of DNA and the cleavage of the sugarphosphate backbone of DNA. It is at least partly attributed to the viscosity change of the PEG-DNA solution and possibly to some extent to the change of mass adsorbed on the QCR surface due to cross-linking and cleavage. Experimental results are consistent with that expected from theory. Received: 15 April 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

Frequency response of a quartz crystal microbalance loaded by liquid drops

The frequency response of a quartz crystal microbalance (QCM) in contact with a spreading liquid drop is studied in this paper. An improved model describing the frequency change of the QCM with the shape evolution of the liquid drop with time is proposed based on hydrodynamic analysis, which has not been reported in the literature. It is found that the drop spreading shape, including the base radius and height, has a significant influence on the frequency response of the QCM, resulting in an unexpected increase in the resonant frequency of the QCM. The model shows that the combination of the knowledge about the radial sensitivity of the QCM and the dynamic spreading of the liquid drop is potentially important to optimize the interpretation of the experimental results. The predicted results are verified with experimental results obtained with silicone oil.     

Nematic liquid crystal in contact with periodically patterned surfaces

Nematic liquid crystals confined between two different substrates, possessing alternating stripe patterns of planar and homeotropic anchoring, are studied within the Frank–Oseen theory, in which the anchoring energy function is given by the Rapini–Papoular expression. By numerical minimization of the free energy we determine phase transitions between uniform and distorted nematic textures. The calculations reveal that these phase transitions can be triggered by changing the shift of the stripe patterns with respect to each other. A hybrid nematic cell model together with an effective anchoring strength can be used to describe the phase behaviour for sample thicknesses larger than the periodicity of the stripe pattern. Rich phase behaviour is predicted for the case of a generalized expression for the surface free energy.     

Nematic liquid crystal in contact with periodically patterned surfaces

Nematic liquid crystals confined between two different substrates, possessing alternating stripe patterns of planar and homeotropic anchoring, are studied within the Frank-Oseen theory, in which the anchoring energy function is given by the Rapini-Papoular expression. By numerical minimization of the free energy we determine phase transitions between uniform and distorted nematic textures. The calculations reveal that these phase transitions can be triggered by changing the shift of the stripe patterns with respect to each other. A hybrid nematic cell model together with an effective anchoring strength can be used to describe the phase behaviour for sample thicknesses larger than the periodicity of the stripe pattern. Rich phase behaviour is predicted for the case of a generalized expression for the surface free energy.