Storage Plateau modulus, determined

The plateau modulus (Gp ) for starch-POClg gel was determined by mechanical oscillation measurements. Figure 16 represents the values of the storage moduli in the plateau region as a function of the reaction rate of starch-POClg gel. Gel formation takes several hours to reach completion this time requirement points to a very slow condensation during phosphate formation. 

It is clear from Figs. 4, 6, 8 that, for all samples, a finite interphase must be presumed in order to achieve even order-of-magnitude agreement between model and G data. The sharp-interface approximation is extremely bad. Sensitivity of G" to c()j(x) is reflected in obvious deficiencies of the linear profile in most cases. Interestingly, the storage modulus G is insensitive to interphase character Figs. 3,5,7 show the plateau level and shape to be almost independent of and (()j(x), respectively. Thus, the G plateau is determined primarily by this permits G data to be used to find while G data... 

The physical properties of the acid- and ion-containing polymers are quite interesting. The storage moduli vs. temperature behavior (Figure 8) was determined by dynamic mechanical thermal analysis (DMTA) for the PS-PIBMA diblock precursor, the polystyrene diblock ionomer and the poly(styrene)-b-poly(isobutyl methacrylate-co-methacrylic acid) diblock. The last two samples were obtained by the KC>2 hydrolysis approach. It is important to note that these three curves are offset for clarity, i.e. the modulus of the precursor is not necessarily higher than the ionomer. In particular, one should note the same Tg of the polystyrene block before and after ionomer formation, and the extension of the rubbery plateau past 200°C. In contrast, flow occurred in... 

The nanocomposites were elastic at temperatures above the Tg of PDLLA-domains as determined by DMTA measurements. The SMPU/POSS nanocomposites had storage tensile moduli greater than 2GPa at low temperatures (see Fig. 15a). The modulus dropped to a value of about lOMPa upon heating above Tg of the switching domains. This rubbery plateau bridged the temperature range from PDLLA domains associated T and POSS related Tm. Pure SMPU without POSS... 

A good PSA can be made if we understand the rubber-resin compatibility. The compatibility of natural rubber with various resins is explained in papers published by Class and Chu.GO-13) The compatibility of resin and rubber can be determined by measuring viscoelastic properties of the blend. Compatibility is identified (in the G vs. temperature plot) by a pronounced shift of the tan 8 peak maximum temperature (Tg), associated with a decrease in the storage modulus in the plateau. An incompatible system is confirmed by a minimal shift of the tan 8 peak maximum temperature along with an increase in the storage modulus in the plateau (Figure 21). A second peak in tan 8 may be apparent in the incompatible system. Compatibility of rubber-resin systems depends on the structure, molecular weight, and concentration of the resin in the blends. The compatible systems exhibit pressure-sensitive adhesive performance at some ratio of rubber to resin. The incompatible systems, on the other... 

Typical behavior is shown in Fig. 3.12(a), where the storage modulus in the plateau and terminal regions for a commercial polystyrene melt is plotted against frequency at several temperatures [17]. A reference temperature is selected, in this case To = 160 °C, and best-fit scale factors for data obtained at other temperatures are determined empirically to form Fig. 3.12(b). The timescale can shift very rapidly, as indicated by the plot of ar versus T in Fig. 3.13 [17]. The Williams-Landel-Ferry (WLF) equation, introduced in Chapter 2 and shown for this particular sample and choice of reference temperature in Fig. 3.13, describes rather well the temperature dependence of aj for most polymer melts and concentrated solutions. 

Due to the degradation the rubbery plateau is narrower as samples are more degraded, since the crystallization ends at lower temperatures [3]. In DMA, the mechanical relaxation spectrum shows that the storage modulus increases again after the glass transition, at a determined temperature named onset crystallization temperature (T), which is in... 

Small-amplitude oscillatory shear is the technique most often used to determine the linear viscoelastic characteristics of a molten polymer. Figure 5.5 shows the storage modulus for the samples whose relaxation moduli are shown in Fig. 5.2. Note that logarithmic scales have been used for both axes. The same features are present as in a plot of G(f), but the terminal zone is now found at the left end of the curve, while the short-time response corresponds to high-frequency behavior. And here again it is the behavior in the plateau and terminal zones that is sensitive to molecular structure and is thus of primary interest in this book. 

As an example of the behavior of such nanocomposites. Figure 30a shows storage modulus G measured for blends of single-wall carbon nanombe (SWNT) in a matrix of poly(methyl methacrylate) (PMMA M = 1.0 x 10 ). ° The nanotubes are uniformly dispersed in the range of the nanotube content Wf examined, but the blends exhibit elastic (solid-like) response, cu-insensitive G plateau at low cu, as Wf is inaeased beyond a threshold value Wf c (=0.12wt.% determined from percolation analysis ). This plateau is attributable to the motional constraint on the polymer chains due to a nanotube network formed through these chains. The elasticity of the... 

---