The microscopic origin of the rheology in supramolecular entangled polymer networks

Abstract

Supramolecular groups in polymeric systems lead to responsive materials which are ideally suited for applications in dynamic environments. The key to their advanced properties such as shape-memory or self-healing is the reversibility of secondary interactions which can be triggered by external stimuli such as temperature, light, or pH-value. Controlling the (mechanical) behavior of such systems requires a precise understanding of intrinsic properties. We present a multimethod study of transient polyisoprene networks that were functionalized with different amounts of hydrogen bonding urazole groups. This work aims at understanding rich rheological features on the basis of their microscopic origin. First, the thermorheological simple behavior is validated experimentally. Subsequently, we characterize the underlying microscopic processes by broadband dielectric spectroscopy (a-process and a Ã-process), differential scanning calorimetry (glass transition behavior), and Fourier-transform infrared spectroscopy (thermodynamics of group association/dissociation). Based on these results, the influence of the supramolecular groups on the rheological response is analyzed. The observed features such as the onset of elastomeric properties in the flow regime, a drastic increase in the chain relaxation time with an increasing amount of functional groups, and the occurrence of a second rheological relaxation process, which is the most prominent effect, are discussed and related to their physical origin. V

A Critical Approach to Polymer Dynamics in Supramolecular Polymers

“…45 In fact, in nearly monodisperse polymers with stickers randomly distributed along the chain the shallowing was still observed. 43,44 In another study, on the contrary, with Đ of nearly 2 with each repeating unit carrying a sticker, no shallowing was observed (Figure 10). 77 It might be tempting to conclude that the sticker distribution is rather the important parameter, but in another study on monodisperse polymers with randomly located stickers slopes of 1 and 2 were observed.…”

Bulk rheometry at high frequencies: a review of experimental approaches

“…The obtained information on local dynamics may provide insights into the microscopic mechanisms governing the viscoelastic response of the investigated systems. Importantly, for associative systems, or even for concentrated solutions in complex solvents such as ionic liquids, it is unclear whether application of time-temperature superposition is appropriate even if a master curve can be obtained, since interpretation of the shift factors is complicated (Gold et al 2017;Zhang et al 2018). Independent high-frequency measurements can be very valuable in this regard.…”

Linear shear and nonlinear extensional rheology of unentangled supramolecular side-chain polymers

“…The effect of UPy addition on the linear viscoelasticity of supramolecular polymers has previously been investigated [20,[63][64][65][66]. However, few studies exist where the rheological response is characterised for a systematic variation of supramolecular side-group density [41,66,67].…”