Figure 1

(a) Normalized DQ buildup curves of PB2000k at three different temperatures, on a scale relative to the total signal of entangled segments, taken on a Bruker minispec mq20 low-field spectrometer. Dashed line: fit to determine the absolute value of $C(t)$, see text. Solid lines: Power laws $\sim {\tau }_{\mathrm{DQ}}^{2}C({\tau }_{\mathrm{DQ}})\sim {\tau }_{\mathrm{DQ}}^{1.71}$, demonstrating the validity range of Eq. (1). (b) Selected correlation functions $C(t/{\tau }_e)$ measured in this work, combined with field-cycling NMR data from Ref. 15 covering the lower time range, with no relative shifts applied. The dashed lines indicate the time limits for complementary NSE spectroscopy in the studied temperature interval. (c) $C(t/{\tau }_e)$ for three samples, with fits used to extract ${\tau }_R$, ${\tau }_d$, and the scaling exponent $ϵ$. Dashed lines are the offset fits for PB87k with indicated regime transitions.Reuse & Permissions

Figure 2

(a) $M$ dependence of ${\tau }_R$ and ${\tau }_d$, and (b) the regime-II (constrained-Rouse) scaling exponent $ϵ$. Raw data from field-cycling NMR [15], solid symbols, was reanalyzed using our fitting procedures. The dotted line for $ϵ$ is merely a guide to the eye, demonstrating a very protracted approach of a value larger than the tube-model prediction of $1/4$. The critical molecular weights $M_c$ for entanglement effects on viscosity, and $M_{\mathrm{rept}}$ above which viscosity scales according to the reptation model, $\eta \sim M^3$ [26], are indicated. (c) $C(t/{\tau }_e)$ for PB55k diluted to 15 wt. % in different deuterated PBs. The respective exponents $ϵ$ plotted as triangles in (b) are demonstrated to be dependent on the matrix chains, indicated by arrows. The pure PB reference data were multiplied by 0.75 to account for lower overall values due to missing interchain dipolar couplings. The factor was determined for PB196k diluted in the same deuterated $M$, which only lead to a vertical shift of the whole $C(t/{\tau }_e)$ without changes in its shape.Reuse & Permissions