Method of studying viscoelastic properties of porous polymer films

A method is proposed for studying the viscoelasticity of polymer films with the aid of a quartz resonator. Results are reported pertaining to thin copper films.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 5, pp. 784–787, November, 1982.     

Design of a phase-locked multimode SAW oscillator

A 60-100 MHz multimode SAW (surface acoustic wave) oscillator with comb spacing Deltaf=10 MHz used a low-loss SPUDT (single-phase unidirectional transducer) comb filter in conjunction with two varactor-based control elements and two feedback loops, for mode selection and stability enhancement over long dwell times. The end aim is to reduce close-in phase noise over that of the unlocked oscillator, corresponding to improved intermediate-term time-domain stability. Frequency deviation was less than 20 Hz over two hours in each of the five comb modes.     

Determination of the properties of viscoelastic materials using spherical nanoindentation

The article is devoted to determining the properties of linearly viscoelastic isotropic materials from the experiment on the introduction of a spherical indenter at a constant-rate displacement in a viscoelastic sample. The results are based on the Lee–Radok (J. Appl. Mech. 27:438–444, 1960) solution of the viscoelastic contact problem. An exact formula is obtained for calculation of the relaxation function using indentation load–displacement data. To illustrate the application of this formula, it is used to find the relaxation function of polymethyl methacrylate (PMMA). The relaxation function found in the article is compared with data measured in a conventional test to evaluate the suitability of the proposed method.     

Electrodiffusive diagnosis of the viscoelastic properties of polymer solutions on a rotating spherical electrode

This article examines the feasibility of measuring normal stresses from data from electrochemical diagnosis over the surface of a rotating sphere.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 738–745, November, 1985.     

Viscoelastic properties of thin polymer films

Thin polymer films have been prepared by electron beam irradiation of adsorbed layers in vacuum. Electrodes have been applied so that capacitance measurements can be made in the presence of a d.c. bias. It is found that the polymer layer deforms under the influence of the electrostatic forces and that the deformation follows the extended Voigt model for viscoelastic deformation, indicating a combination of pure elastic and viscoelastic behaviour. Values of the elastic moduli and retardation time have been obtained.     

Characterization of polymer films using a slow positron beam

Polymer structures have been investigated using positron annihilation lifetime spectroscopy (PALS) with a slow positron beam as well as a conventional radioactive source (²²Na). The properties of the free volume holes near the polymer surface were studied as a function of the positron implantation energy. The longest lifetime was associated with ortho-positronium (o-Ps) annihilation in the free volume holes. In polytetrafluoroethylene film, the lifetime of o-Ps was observed to decrease with increasing positron implantation depth, and a significant change in the o-Ps lifetime was found at a short distance (about 10 nm) from the surface, while its intensity increased. This result implies that near the polymer surface the free volume holes become larger that in the bulk. The effect of temperature on the polymer sub-surface layers was also studied. For high molecular weight polystyrene, the glass transition temperature for the sub-surface was lower than that for the bulk and thermal expansion coefficient of the sub-surface layers was found to be larger than the bulk value. Electronic Publication     

Tunnel diode oscillator circuit for surface impedance measurement of thin films near 20 MHz

We describe and analyse a simple method for the measurement of thin film surface impedance in the frequency range 10–20 MHz. This method is based on the analysis of both the frequency shift and the amplitude variation of the signal in a tunnel diode oscillator circuit inductively coupled to the sample. The sensitivity of the method to the conducting properties of the thin films is a function which is greatly dependent on geometrical parameters and which can be easily optimized and included in the response calculation. The analysis is illustrated by examples with superconducting and normal metal films. The resolution of the measurements is also discussed.     

Determination of material properties of thin films and coatings using indentation tests: a review

This paper presents a review of the mechanical characterisation of thin film and coated systems using indentation tests. The potential in assessing mechanical properties of films and coatings using indentation tests has received a great deal of attention since this knowledge is vital for predicting their performance. The relevant theoretical background is discussed. Experimental work, numerical studies and data interpretation techniques for indentation on single bulk materials and thin films are discussed. Surface conditions, indentation depths and indentation size effects for indentation tests on thin films and coated systems are discussed. Data interpretation methods for indentation on films and coated systems are reviewed with a discussion on their limitations. Other studies in this field concerning the substrate effects and critical indentation depth ratios are also discussed. Suggestions for future experimental work and data interpretation are provided.     

Improved under damped oscillator properties of polymer blends for electronic applications

Mechanics of Time-Dependent Materials - Modified polymer blends demonstrated the desirable properties and performance suitable for various applications. In the present investigation, we prepared...     

Fabrication of flexible polymer dispersed liquid crystal films using conducting polymer thin films as the driving electrodes

Conducting polymers exhibit good mechanical and interfacial compatibility with plastic substrates. We prepared an optimized coating formulation based on poly(3,4-ethylenedioxythiophene) (PEDOT) and 3-(trimethoxysilyl)propyl acrylate and fabricated a transparent electrode on poly(ethylene terephthalate) (PET) substrate. The surface resistances and transmittance of the prepared thin films were 500-600 Ω/□ and 87% at 500 nm, respectively. To evaluate the performance of the conducting polymer electrode, we fabricated a five-layer flexible polymer-dispersed liquid crystal (PDLC) device as a PET-PEDOT-PDLC-PEDOT-PET flexible film. The prepared PDLC device exhibited a low driving voltage (15 VAC), high contrast ratio (60:1), and high transmittance in the ON state (60%), characteristics that are comparable with those of conventional PDLC film based on indium tin oxide electrodes. The fabrication of conducting polymer thin films as the driving electrodes in this study showed that such films can be used as a substitute for an indium tin oxide electrode, which further enhances the flexibility of PDLC film.     

Optical properties of pyrene doped polymer thin films

Thin films of pyrene in polystyrene matrix have been prepared by spin coating technique. The concentration of polystyrene is kept constant to 1 wt.% while that of pyrene dopant varied in the range 2.30×10⁻⁴-2.30×10⁻¹ wt.%. Thickness of the films was found to depend upon concentration of pyrene and varies from 90 to 782 nm. The results of X-ray diffraction analysis reveal the crystalline nature of the films. The optical properties were studied by absorption, excitation and fluorescence spectroscopy. The band gap energy of pyrene in polymer films was calculated from absorption results. A transition from monomer to excimer is observed with thickness variation of the films. The structured part of the spectrum is assigned to the monomer emission while the broad emission band is attributed to well known pyrene excimer-like emission.     

Determination of the plastic and viscoelastic properties of a metallic soap by a hot hardness measurement

An analysis of an indentation test in the case of mixed plastic—viscoelastic behaviour, as is met in metallic soaps, is described. The viscoelastic part of the strain is described in terms of a Burgers model whose five rheological parameters are then a yield stress, ₀, two elasticity moduli,G ₀ andG ₁, and two viscosities, ₀ and ₁. This analysis is applied to a hot hardness experiment on a compacted metallic soap, calcium stéarate, between 20 and 130° C. By fitting the model to the experimental curves, values of ₀, ₀, ₁,G ₀ andG ₁ as a function of temperature, have been derived. It is shown that plastic strain is much greater than viscous strain at low temperature, since ₀ is very high. The material is therefore a solid. It is also shown that, as temperature increases, viscous strain increases and plasticity vanishes (above a transition temperature, ₀=0, and only viscoelasticity remains). The curves ₀(T), ₁ (T),G ₀(T) andG ₁ (T) have marked slope changes at about 90° C (which is the crystal—crystal phase transition temperature of calcium stearate), and the viscosities fall at 123° C, which is the first crystal mesomorphic phase-transition temperature. This test seems to be a good simple rheological measurement for bodies exhibiting simultaneous plasticity and viscosity or viscoelasticity.     

Elastic and viscoelastic characterization of thermally-oxidized polymer resin using nanoindentation

Polymer matrix composites used in high temperature applications experience material property degradation due to thermal oxidation. In the present paper, the oxidation profiles of the isothermally aged PMR-15 specimens are studied using an optical microscope. Results show that the oxidized specimen exhibits distinguished heterogeneous structure. In addition, the spatial dependent elastic and viscoelastic properties of PMR-15 specimens isothermally aged at various environmental conditions are probed through nanoindentation tests. Results indicate that both elastic modulus and creep strain rate sensitivity of the oxidized surfaces are higher than those of the unoxidized interiors. These results are the consequences of chemical and physical changes that occur during oxidation including chemical bond breakage and outgassing of low-molecular weight species.     

Nonlinear optical properties of several siloxane polymer Langmuir-Blodgett films

The Langmuir-Blodgett film formation and the nonlinear optical properties of three polysiloxane polymer materials have been investigated. All three compounds could be built-up as Z-type layers on a variety of substrates. Experiments on the linear electrooptic (Pockels') effect revealed a second-order nonlinear susceptibility χ⁽²⁾ (−ω; ω, 0) of 10.6 pmV⁻¹ for one of the materials; the order of magnitude of this result was confirmed using second-harmonic generation. For multilayer films the second-harmonic intensity was found to increase with the thickness of the LB structure. However, a linear dependence upon film thickness was evident, rather than the expected quadratic variation.