Rheovibron

A variety of commercial instruments are available for the determination of the viscoelastic behavior of samples. Figure 3.15 shows one such apparatus, the Rheovibron Viscoelastometer. This instrument also takes advantage of the complementarity that exists between time and temperature It operates at four frequencies over a 175°C temperature range. With accessories, both the frequency range and the temperature range can be broadened still further. 

Figure 3.15 The Rheovibron Viscoelastometer, a commercially available instrument for the determination of the dynamic moduli and compliances. [Photo courtesy of Imass, Inc, Accord (Hingham), Mass. 02018.]...

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Fig. 46. Schematic diagram of a dynamic mechanical analy2er based on the nonresonance-forced vibration principle (Rheovibron-type).

The Autovibron is the automated version of the Rheovibron (284). It can be purchased in automated form, or the automation system can be added later. Automation improves accuracy and productivity and eliminates the problems and operator dependence of results often associated with the manual instmment. Automation enables the Rheovibron to compete with the other commercial dynamic mechanical instmments. 

Measurement of dynamic mechanical properties was carried out under tension mode using a viscoelasto-meter, (Rheovibron DDV-III-EP, M/s, Orientec Corp., Tokyo, Japan). Sample size was 3.5 cm x 6.5 mm x 2 mm. Testing was carried out at a low amplitude, 0.025 mm, over a temperature range of - 100°C to +200°C. Heating rate was TC/min and frequency of oscillation was 3.5 Hz or 110 Hz. 

Characterization Methods. Stress-strain experiments were carried out with an Instron model 1122. Dogbone samples of 10mm in length were used, and the initial strain rate was 2 mm/min. Dynamic mechanical data were obtained utilizing a DDV-IIC Rheovibron Dynamic Viscoelastometer. Most samples were tested within the temperature range of -100°C to 220°C with a heating rate of 2-3°C/min. A frequency of 11 Hz was selected for all the dynamic mechanical experiments. 

Some viscoelasticity results have been reported for bimodal PDMS [120], using a Rheovibron (an instrument for measuring the dynamic tensile moduli of polymers). Also, measurements have been made on permanent set for PDMS networks in compressive cyclic deformations [121]. There appeared to be less permanent set or "creep" in the case of the bimodal elastomers. This is consistent in a general way with some early results for polyurethane elastomers [122], Specifically, cyclic elongation measurements on unimodal and bimodal networks indicated that the bimodal ones survived many more cycles before the occurrence of fatigue failure. The number of cycles to failure was found to be approximately an order of magnitude higher for the bimodal networks, at the same modulus at 10% deformation [5] ... 

Figure 4. BR + IR is a 50/50 (wt) blend of synthetic cis-1,4-polyisoprene and cis-1,4-polybutadiene. Bl copolymers are random cis-1,4-butadiene-isoprene copolymers with the same composition. Results obtained with Rheovibron on gum vulcanizates at 110 Hz frequency.

Dynamic Mechanical. The dynamic mechanical properties of the samples were measured on a Rheovibron, Model DDV-II at either 35 or 110 Hz. 

A Toyo Boldwin Rheovibron Viscoelastometer Rheo 2000/3000 machine was used for these determinations. Such measurements were performed at a frequency of 110 Hz, a heating rate of 2°C/min and an inter-chuck distance of 40mm. 

Molecular mixing via dynamic mechanical spectroscopy. While electron microscopy yields the phase size, shape, etc., as delineated above, dynamic mechanical spectroscopy (DMS) yields the composition within each phase. The DMS measurements employed a Rheovibron direct reading viscoelastometer model DDV-II (manufactured by Toyo Measuring Instruments Co., Ltd., Tokyo, Japan). The measurements were taken over a temperature range from -120°C to 140°C using a frequency of 110 Hz and a heating rate of about 1°C/ min. Sample dimensions were about 0.03 x 0.15 x 2 cms. 

Bisphthalonitrile monomers were cured neat, with nucleophilic and redox co-reactants, or in combination with a reactive diluent. Dynamic mechanical measurements on the resulting polymers from -150 to +300°C turn up several differences attributable to differences in network structure. Rheovibron results were supplemented with solvent extraction, differential scanning calorimetry (DSC), vapor pressure osmometry, and infrared spectroscopy to characterize the state of cure. 

Bulk samples were sectioned with a diamond saw to provide samples for the Rheovibron DDV II Viscoelastometer operated at 11 Hz. In some cases a thin sheet cured between aluminum plates, was heated to the rubbery state, cut while hot, then returned to the oven to complete the cure. 

In order to establish the effect of varying monomer structure on dynamic mechanical results, three films were cured as thin sheets under identical conditions. No significant differences appear in the Rheovibron plots (Figure 3). Thus the mechanical properties (and by inference, such properties as strength and toughness) appear to be insensitive to monomer structure. The dynamic mechanical properties should be regarded as influenced primarily by the network connectivity and extent of cure. 

Dynamic Mechanical Measurements. Films were prepared by casting the acetone solution of sample No. 2 onto a Teflon sheet after adding curing agents. The sample was allowed to stand at room temperature for one day, and then cured at 130°C for 2 hours. The dynamic mechanical spectroscopic data were measured in tension with a Rheovibron DDV-II (Toyo Baldwin Co. Ltd.) at a frequency of 110 Hz with a heating rate of about l°C/min. 

To increase the knowledge of these pure graft copolymers, we determined the temperature dependence of the dynamic mechanical properties of such a product. These measurements were made with the Rheovibron apparatus at a frequency of 110 Hz. 

Figure 9. Temperature dependence of the loss moduli E"(Rheovibron,...

All these tests are in common use to measure the tensile stiffness of polymers. For example, tests at constant extension rate are often carried out on an Instron tensile testing machine. Tensile creep is used in many cases while stress relaxation is not so common. Dynamic testing is commonly performed using the Rheovibron or other commercial equipment32 or home made equipment33,... 

Dynamic loads are most commonly carried out using commercial equipment (e.g. Rheovibron details of the many problems associated with the use of the Rheovibron can be found in the article by Wedgewood and Seferis36 ) but for specific applications... 

The latexes were cleaned by ion exchange and serum replacement, and the number and type of surface groups were determined by conductometric titration. The molecular weight distributions of the polymers were determined by gel permeation chromatography. The stability of the latexes to added electrolyte was determined by spectrophotometry. The compositional distribution was determined by dynamic mechanical spectroscopy (Rheovibron) and differential scanning calorimetry, and the sequence distribution by C13 nuclear magnetic resonance. 

Dynamic Mechanical Testing - Film properties such as impact resistance and the cure response of thermosetting resins are conveniently investigated by dynamic measurements in which an oscillatory or torsional strain is applied to the sample with the stress and phase difference between the applied strain and measured stress being determined. In the present study, a Rheovibron Viscoelastometer was used which employed a sinusoidal strain at a... 

Characterization. Film samples about 0.25-mm thick were prepared by compression molding the polyurethanes under dry nitrogen at 180°C and 3 MPa pressure. After molding for 20 min, the samples were allowed to cool slowly in the press under dry nitrogen flow. Figure 2 shows the thermal history of the 180°C-molded films. No discoloration was observed when the samples were removed from the mold. The two soft-segment polyurethanes were compression molded at 120°C. The films were allowed to stand at least one week at room temperature in a dessicator before being evaluated with the Rheovibron DDV-IIB Dynamic Visco-... 

Viscoelastic experiments were conducted on a Rheovibron DDV-II-C apparatus and on a Rheometrics Mechanical Spectrometer. The Rheovibron studies were carried out in tension on cured samples at 3.5, 11,... 

Figure 5. Location of tan 8 peak as a function of composition for BR-IR homopolymers and diblocks Rheovibron,...

Figure 8 presents the storage and loss-modulus master curves obtained on all five samples of interest. The dashed lines indicate extensions of the master curves, using appropriately reduced data from the Rheovibron experiments in tension. Storage-modulus data in the rubbery plateau region vary systematically with composition, i.e., the... 

Dynamic Mechanical Measurements. A Rheovibron DDV-II was used to measure mechanical properties at frequencies of 3.5 and 110 Hz. Heating rates were approximately l°C/min. Films of 5-mil thickness were compression molded at 260°C from dried powders for these studies. No annealing treatments were applied to the films. Complex, storage, and loss moduli as well as tan 8 were calculated over a — 160° to 240°C range. For clarity, all of the data are not shown in the figures. 

Dynamic mechanical properties were measured on some PS/PMMA blends, using a Rheovibron model DDV-II system previously described (13). These measurements are a sensitive indicator of phase separation and can be used to obtain semiquantitative information about phase morphology as well (14). 

The dynamic elastic modulus (E ), the loss modulus (E"), and the tan 8 were measured simultaneously by the Rheovibron dynamic visco-elastometer model DDV-II (Toyo Measuring Instruments Co., Ltd.). Measurements were made at a frequency of 110 Hz, starting from —140°C and heating at 1°-2°C per minute until the samples became too soft to be tested. The readings were taken every 4°-8°C except in the transition zone when the readings were taken every 2°C. The sample chamber was kept dry by a stream of moisture-free nitrogen. 

Within measurement precision ( 10%) the various peaks gave linear Arrhenius plots with activation energies between 15 and 40 kcal/ mole. Assuming an average 25 kcal/mole, a reasonable 5 kHz impact frequency at room temperature (25°C) would extrapolate to ca. 10°C at 11 Hz, one of the Rheovibron measuring frequencies. Therefore the magnitude of the dissipation factor subsequently used for the correlation was 10°C, 11 Hz. 

Fig. 3. Typical Rheovibron data for polystyrene. Note that tan 8 always peaks at a higher temperature than E ...

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