Viscoelastic measurements, studies

The three polymers that were chosen for study, e.g. PMMA (2), BPDN (3), and Hytrel (4), were selected because they represent a wide range of viscoelastic materials. These materials were processed into plaques. The plaques were annealed at 12S°C between highly polished chrome plated flat plates and cooled slowly to minimize the effects of residual stresses. Viscoelastic measurements were made under conditions cited above on two test specimens that were cut from... 

Under viscoelastic measurements poly(cycloalkyl methacrylates) show a loss maximum (designated y), located in the very low temperature range (T <-60 °C), as illustrated in Fig. 6 in the case of poly(cyclohexyl methacrylate). Such a series of polymers has been extensively studied by Heijboer in his Ph.D. thesis [5], by performing viscoelastic studies at 1 Hz (sometimes 180 kHz) as a function of temperature and exploring quite a large number of cycloalkyls, either substituted or not. In cyclopentyl, cyclohexyl, cyclohep-tyl derivatives, the y transition was shown to occur at ca. - 185 °C (180 Hz), - 80 °C (1 Hz), - 180 °C (1 Hz), respectively. The associated activation energies, a> are 13, 47, 26kJmol 1 for the cyclopentyl, cyclohexyl, cycloheptyl derivatives, respectively. 

Viscoelasticity is studied using dynamic mechanical analysis. When we apply a small oscillatory strain and measure the resulting stress. Purely elastic materials have stress and strain in phase, so that the response of one caused by the other is immediate. In purely viscous material the phase delay between stress and strain reach 90 degree phase lag. 

Linear viscoelastic measurements using infrared dichroism on the compatible blend polyethylene oxide) and poly(methyl methacrylate) were reported by Zawada et al. [139]. Unlike Monnerie and coworkers [127], who reported seeing only orientation in the PMMA component, and none in the PEO, Zawada et al. observed alignment in the PEO. However, since the PEO was of lower molecular weight (as was the case for Monnerie and coworkers), its relaxation timescales were substantially faster than the PMMA. This may explain the lack of any measurable orientation by Monnerie and coworkers, who studied quenched samples, since their preparation may have allowed the PEO to relax prior to testing. 

Lyotropic SCLCP are far less well studied by rheology than lyotropic MCLCPs. An example is the discotic SCLCP, as mentioned in Chap. 6 (Fig. 6.15), by Franse et al. (2002-2004). Fig. 16.37 gives a schematic representation of side chain discotic polymers (Franse, 2002). In solution the polymers have a tendency to form networks due to interaction between the discotic side chains. From viscoelastic measurements (G and G" as functions of angular frequency) it appeared that the networks formed in a 13% solution in 1,1,2-trichloroethane are very fragile, with a rubber modulus of not more than IN/m2. 

Theories for the dependence of F on molecrdar parameters will be reviewed in section 3, but it should be pointed out that Eq. (2.6) coincides exactly with the results calculated for an isolated chain (76, 190) for F for X predict quantitatively rj, given o q/JVg and C which can be obtained respectively from dilute solution studies and from viscoelasticity measurements (46). 

Whereas dynamic mechanical measurements are generally preferred for viscoelastic measurements at small strains, studies at large deformations are more conveniently carried out at constant rates of extension... 

A Rheovibron DDV-OIFP (A D, Tokyo, Japan) tester has been used for DMA. In general, DMA has been accepted as a powerful method for studying the relaxation behavior of bulk samples. However, previous to these experiments, no one knew whether the technique was sensitive enough to be used with thin and ultrathin polymer films. To answer this question, a d3mamic viscoelastic measurement for thin PS films supported on substrates was conducted. 

Reinforced vulcanized samples generally present a marked viscoelastic behavior that is usually studied by dynamic viscoelastic measurements. In this experiment, a sample is subjected to periodic sinusoidal shear strain y... 

Reinforced vulcanized samples generally present a marked viscoelastic behavior that is usually studied by dynamic viscoelastic measurements. In this experiment, a sample is subjected to periodic sinusoidal shear strain y (at defined frequency (o and temperature T). Its dynamic shear modulus G is complex and can be written as the sum of the storage modulus G, and the loss modulus G". 

In this chapter, we outline the principle, measurement, and application of dynamic viscoelasticity for solid and liquid polymers. In Section II, a basic treatment of the dynamic viscoelasticity is described. Section III deals with the various dynamic viscoelastic measurements of solid and liquid polymers. Section IV reviews in detail the results of linear dynamic viscoelasticity as a function of frequency and temperature. The dynamic mechanical studies have... 

Dynamic viscoelastic measurements are useful in studying the structure of polymers, because these mechanical properties are sensitive to glass transition, crystallinity, cross-linking, filling systems (filler or plasticizer), molecular aggregation, and phase separation. To determine dynamic viscoelastic properties, such as storage modulus, loss modulus, and tan, various methods have been proposed, and recently many types of instruments are commercially available. Typical methods to measure the dynamic viscoelasticity are classified into three categories damped free vibration, resonance free vibration, and nonresonance forced vibration. These methods are standardized by the international standard ISO 6721 [3]. 

The dynamic viscoelastic properties of polymers are measured as a function of frequency or temperature. In the 1950s, a standard sample of polyisobutylene was distributed by the National Bureau of Standards, which requested that viscoelastic measurements, including stress relaxation, creep, forced vibration, and free vibration, be carried out by a number of cooperating laboratories. The data obtained from that study were compared and studied carefully, and the results contributed to the development of the science of linear viscoelastic properties of polymers [4,9]. 

It is well known that filler-filled systems have very complex rheological properties and structures which vary in different flow fields and show special phenomena accompanied by structural changes. The processability of these dispersed systems is determined not only by their viscosities but also by their elasticities. In order to clarify the nature and the reformation process of their internal structure, dynamic viscoelasticity measurements were carried out extensively [6-8,47-51,53]. For systems filled with solid particles, the viscoelastic properties especially the dynamic ones as well as the steady flow properties have been studied extensively, and it has been found that the rheological properties of the dispersed systems differ from those of polymer solutions and melts in several ways. 

One of the problems faced with polymer systems is that of equilibrium. Not only may adsorbed polymers desorb during compression, but the polymer may not be able to achieve its equilibrium configuration for a given separation over the time-scale of the experiment. Several groups have thus built modified surface force apparatuses to perform viscoelastic measurements on confined films, not only to determine relaxation rates for grafted polymers, but also to determine the effect of confinement on the physical properties of the films and to study friction and lubrication (see Section 2.5 above). Storage and loss moduli can be extracted from the response to oscillations in the frequency range of approximately 10 to 10 Hz. Montfort and co-workers, for example, have used normal oscillations to study the viscoelasticity of polybutadiene films on metal surfaces in hydrocarbons (234, 235). At such sufficiently small separations that the polymers could interact with one another, the... 

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