Mechanical Spectroscopy DMS

DMS techniques yield the loss modulus E in addition to the storage modulus (See Section 1.5.5.) As is the case with the static mechanical tests discussed above, DMS and electron microscopy techniques provide complementary information on two-phase materials The former is a sensitive 

In all cases a frequency of 110 Hz was used such a frequency raises the glass transition of the individual components to about 18-20°C above the 10-sec modulus reported in the previous subsection. 

The advantage of the dynamic method (DMS) over the static tests (10-sec modulus) is that the loss modulus E is obtained. Some materials show important transitions with DMS that are missed with the static test for example, when a minor, discontinuous phase has a transition, the Young s modulus (and also E ) may not change appreciably, while E may exhibit a significant maximum. 

The mechanical measurements do not distinguish among molecules visiting because of true thermodynamic solubility or because of forced mechanical chain entanglements caused by the presence of crosslinks. 

It is of interest that both the PEA and PS transitions are shifted inward (PEA to a higher temperature and PS to a lower one), relative to the homopolymers under the same experimental conditions. This result can be explained in terms of a limited extent of molecular mixing (mechanical entrapment, thermodynamic equilibrium, or both). 

---

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. 

Marie et al. [49] also studied the in-situ block copolymer formation via reactive blending of functionalized homopolymers. In their work, blends were characterized by SEM, DSC and dynamic mechanical spectroscopy (DMS). It should be noted that their blends (PA-6/PDMS and PS/PDMS) were composed totally using functionalized homopolymers. The different reactions under investigation were amine(NH2)/anhydride(An), amine(NH2)/epoxy(E) and carboxylic acid(COOH)/epoxy(E) (Fig. 5). 

The relaxation properties as probed by dynamic mechanical spectroscopy (DMS) for a series of ESI are shown in Figure 26.2. In accordance with the DSC results, the tan S loss maximum or Tg for the semicrystalline ESI appears to be fairly independent of styrene content. For the essentially amorphous ESI (>45wt% S), Tg increases with increasing styrene content. When compared with the amorphous ESI, the amplitude and width of the Tg loss peak are lower in amplitude and broader, respectively, for the lower styrene ESI, as is characteristic of a semicrystalline material. The amorphous ESI exhibit an intense loss process associated with the amorphous phase Tg(ESI). The width of this loss... 

Figure 26.2 Dynamic mechanical spectroscopy (DMS) plot of tan<5 versus temperature, measured at 10rad/s, for a series of ESI with styrene incorporation ranging from 24 (ES24) to 77wt% (ES77)...

Dynamic Mechanical Spectroscopy (DMS). Rectangular bars (3 x 12 x 45 mm) were cut from the molded plaques and dynamic mechanical spectra (DMS) obtained using a Rheometrics System-4. Values of G. G" and tans at various temperatures were obtained by oscillatory torsion of the bars at 1 Hz and 0.2% shear strain temperatures were varied between -100°C and 120°C at 5°C Intervals in the transition regions and at 10°C intervals elsewhere. Thermal soak times were five minutes in all cases. 

Degree of cure. The titration results given in Table III reveal that from 98% to 100% of the functional groups had reacted. Similarly no evidence for incomplete cure was observed by DSC or by dynamic mechanical spectroscopy (DMS). However, it may be pointed out that 2% unreacted functional groups could result in detectable incoherence (see reference 29) in the networks prepared from high-MW epoxy prepolymers. 

Characterization by DMS and DSC. Although characterization of small-strain viscoelastic and stress-strain behavior is not yet complete, preliminary dynamic mechanical spectroscopy (DMS) and differential scanning calorimetry (DSC) data were obtained for the blends having the highest and lowest molecular weights. 

Figure 2 shows how glass transition temperatures (Tg) obtained by dynamic mechanical spectroscopy (DMS), percent crystallinities obtained by wide angle x-ray scattering (WAXS) or differential scanning calorimetry (DSC), experimental diffusion coefficients, and information on tortuosity obtained by studies of morphology, can be useful in applying both the theory of V D and the model of P D. The Williams-Landel-Ferry (WLF) parameters [18] c % and C2 , which can be determined by DMS, are needed as additional input for the theory of V D. Densities and thermal expansion coefficients are needed as additional input for the model of P D. 

Dynamic mechanical properties exhibit side chain or branch motions short main chain segment motions, main chain segmental motions, recrystallization, and melting. These transitions are observed as inflections in the storage modulus curve with temperature, peaks in either the loss modulus or damping factor (tan( )) curves. Figure 3.11 shows the dynamic mechanical spectroscopy (DMS) of a ZN-VLDPE at 1 Hz in tensile mode. The glass transition temperature (maxima of the loss modulus... 

In the majority of cases the compatibility of the polymers is characterized by the glass-transition temperature Tg, determined by methods such as dilatometry, differential scanning calorimetry (DSC), reversed-phase gas chromatography (RGC), radiation thermal luminescence (RTL), dynamic mechanical spectroscopy (DMS), nuclear magnetic resonance (NMR), or dielectric loss. The existence of two... 

The basic methods of detecting the secondary relaxation transitions are dynamic mechanical spectroscopy (DMS) and differential thermal analysis in some cases information can be obtained by evaluation of the dielectric characteristics, by NMR, and by DSC. 

The glass transition temperature is measured using differential scanning calorimetry (DSC) (179,284), by which a polymer sample is heated, and its enthalpic changes are measured in response. The temperature at which the heat capacity of the polymer drops is the glass transition temperature. Dynamic mechanical spectroscopy (DMS) is also used to determine the glass transition temperature. Certain mathematical equations, such as the Fox equation, relate the copolymer composition to the glass transition temperature. 

These latter experiments are sometimes referred to as dynamic mechanical spectroscopy, DMS. 

The change in the modulus with temperature has already been introduced (see Section 8.2.2). More detail about the transitions is available through dynamic mechanical measurements, sometimes called dynamic mechanical spectroscopy (DMS) (see Section 8.1.8). 

Several instruments are employed to measure the dynamic mechanical spectroscopy (DMS) behavior (see Table 8.5). The Rheovibron (30) requires a sample that is self-supporting and that yields absolute values of the storage modulus and tan S. The value of E" is calculated by equation (8.17). Typical data are shown in Figure 8.11 (31). Although the instrument operates at several fixed frequencies, 110 Hz is most often employed. The sample size is about that of a paper match stick. This method provides excellent results with thermoplastics (30) and preformed polymer networks (31). 

The of the most powerful methods in the investigation of heterogeneous polymeric systems is dynamic mechanical spectroscopy (DMS), which enables the estimation of the elastic moduli, mechanical losses, glass transition temperature, relaxation characteristics, etc., and plays a very important role both in the theoretical description of the systems and in their practical application. 

---