Collective motion in Poly(ethylene oxide)/poly(methylmethacrylate) blends

We present neutron spin echo and structural measurements on a perdeutereted miscible polymer blend: poly(ethylene oxide)[PEO]/poly(methyl methacrylate)[PMMA], characterized by a large difference in component glass transition temperatures and minimal interactions. The measurements cover the q range 0.35 to $1.66{\mathrm{\AA }}^{-1}$ and the temperature range $T_g\text{−}75$ to $T_g+89\mathrm{K}$, where $T_g$ is the blend glass transition. The spectra, obtained directly in the time domain, are very broad with stretching parameters $\beta \sim 0.30$. The relaxation times vary considerably over the spatial range considered however at none of the $q$ values do we see two distinct relaxation times. At small spatial scales relaxations are still detectable at temperatures far below $T_g$. The temperature dependence of these relaxation times strongly resembles the $\beta$-relaxation process observed in pure PMMA.

Figure 1

Static structure factor of perdeuterated pure PMMA and 10, 20, and 30 % dPEO/ dPMMA blends.

Figure 2

Dynamic structure factor of perdeuterated dPEO/dPMMA blends 30% (a), 20% (b), 10% (c), and pure dPMMA (d) at $\mathrm{Q}=1.66{\mathrm{\AA }}^{-1}$. Lines are the KWW fits with $\beta =0.3$.

Figure 3

Dynamic structure factor of perdeuterated dPEO/dPMMA blends 30% (a), 20% (b), 10% (c), and pure dPMMA (d) at $\mathrm{Q}=0.42{\mathrm{\AA }}^{-1}$. Lines are the KWW fits with $\beta =0.3$.

Figure 4

Shift factors for the 30% blend. The reference temperature is $T_0=412\mathrm{K}$.

Figure 5

Average shift factors for the blends. For the 10% blend only the three highest temperatures had measurable decay thus not giving sufficient range in $1∕T$ for a meaningful fit. Dashed lines show activation energy fits. Solid line for comparison of the slope of the PMMA $(79.4\mathrm{kJ}∕\mathrm{mol})$ activation energy and long dashed line for PEO $(15\mathrm{kJ}∕\mathrm{mol})$ from Ref. 47.

Figure 6

Rescaled data with the calculated shift factor $a_T$ of Eq. (4) for the 30% (a), 20% (b), and 10% (c) blend at $Q=1.66{\mathrm{\AA }}^{-1}$ and $T_0=352\mathrm{K}$. For clarity only some error bars (one sigma) are shown. Solid lines are the KWW fits Eq. (3) with $A\left(q\right)=1$.

Figure 7

Calculated spectra for the pure components and fitted curves for the blends at $1.66{\mathrm{\AA }}^{-1}$ at $T=352\mathrm{K}$ together with the measured data. These latters are divided by the fitted $A\left(q\right)$ prefactor of Eq. (3). Dashed and dashed-dotted lines are the fitted KWW functions as in Fig. 2 but with a prefactor $A\left(q\right)=1$.

Figure 8

Comparison of relaxation times of the blends from NSE (at $q=1.66{\mathrm{\AA }}^{-1}$) with PMMA and PEOdynamics. QENS data for PEO are from Ref. 32, dielectric data for PEO from Ref. 47, for PMMA $\alpha$ and $\beta$ relaxations from Ref. 28, and PMMA self-correlation (incoherent scattering) for pure PMMA and PEO-PMMA from Ref. 34. Only some error bars are shown.

Figure 9

Relaxation times at 413 K and static structure factors of the pure PMMA and the three blends. Missing points in the $0.8{\mathrm{\AA }}^{-1}<q<1{\mathrm{\AA }}^{-1}$ for the 10% blend gave relaxation times $>10000$ ns (not shown).

Figure 10

$q$ and temperature dependence of the prefactor $A\left(q\right)$ of Eq. (3), for the pure PMMA, 10, 20, and 30 % blends.