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

Supramolecular polymers are important within a wide range of applications including printing, adhesives, coatings, cosmetics, surgery, and nano-fabrication. The possibility to tune polymer properties through the control of supramolecular associations makes these materials both versatile and powerful. Here, we present a systematic investigation of the linear shear rheology for a series of unentangled ethylhexyl acrylate-based polymers for which the concentration of randomly distributed supramolecular side groups is systematically varied. We perform a detailed investigation of the applicability of time temperature superposition (TTS) for our polymers; small amplitude oscillatory shear rheology is combined with stress relaxation experiments to identify the dynamic range over which TTS is a reasonable approximation. Moreover, we find that the “sticky-Rouse” model normally used to interpret the rheological response of supramolecular polymers fits our experimental data well in the terminal regime, but is less successful in the rubbery plateau regime. We propose some modifications to the “sticky-Rouse” model, which includes more realistic assumptions with regard to (i) the random placement of the stickers along the backbone, (ii) the contributions from dangling chain ends, and (iii) the chain motion upon dissociation of a sticker and reassociation with a new co-ordination which involves a finite sized “hop” of the chain. Our model provides an improved description of the plateau region. Finally, we measure the extensional rheological response of one of our supramolecular polymers. For the probed extensional flow rates, which are small compared to the characteristic rates of sticker dynamics, we expect a Rouse-type description to work well. We test this by modeling the observed strain hardening using the upper convected Maxwell model and demonstrate that this simple model can describe the data well, confirming the prediction and supporting our determination of sticker dynamics based on linear shear rheology.