Molecular View on Supramolecular Chain and Association Dynamics

Abstract

The chain and association dynamics of supramolecular polymer ensembles decisively determines their properties. Using neutron spin echo (NSE) spectroscopy we present molecular insight into the space and time evolution of this dynamics. Studying a well characterized ensemble of linearly associating telechelic poly(ethylene glycol) melts carrying triple H-bonding end groups, we show that H-bond breaking significantly impacts the mode spectrum of the associates. The breaking affects the mode contributions and not the relaxation times as was assumed previously. NSE spectra directly reveal the so far intangible H-bond lifetimes in the supramolecular melt and demonstrate that for both the microscopic and the macroscopic dynamics of the supramolecular ensemble the instantaneous average of the M_{w} distribution governs the system response at least as long as the Rouse picture applies.

High-resolution neutron spectroscopy using backscattering and neutron spin-echo spectrometers in soft and hard condensed matter

“…Polymer relaxations have been studied with high-resolution neutron spectroscopy for at least 50 years 5,27,28 , resulting in well-established relaxation maps for, at least, linear homopolymers. Since the 2000s, interest in more complex polymer-based systems, such as polymer electrolytes 29 , polymers of complex architectures (for example, dendrimers 30 ), mixtures of two or more polymers (blends 31 ) or mixtures with hard [32][33][34] or soft 35,36 components (nanocomposites), and associating polymers 37 , has been driven primarily by the interest in possible applications. In these systems, the underlying molecular dynamics and the relationship with the macroscopic, that is, rheological behaviour, is still not fully understood.…”

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers

“…Therefore, studying hydrogen bonding interactions allows a better understanding of many biological phenomena, such as the link between structure and function of proteins. In recent years, the highly directional physical interactions based on H-bonds have been applied in a fundamentally different way to form supramolecular polymers, as a means to mimic the biological self-assembly and organization [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Indeed, in these materials, modification of low molar mass polymers with functional groups that associate via H-bonding interactions give rise to a rich variety of self-organizing structures on the mesoscale with a multiplicity of macroscopic properties [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…Due to its specific features, such as its water solubility or biocompatibility, PEG is an interesting polymer for various industrial and biomedical applications. While some of us [ 13 , 18 ] have previously investigated similar bifunctional PEG polymers end-functionalized with heterocomplementary associating thy and dat in the bulk, almost no fundamental studies exist on simple bifunctional PEG polymers end-functionalized with homocomplementary associating upy in the bulk [ 37 , 38 ]. On the one hand, though being one of the most important and extensively studied H-bonding group [ 39 , 40 , 41 , 42 , 43 , 44 , 45 ], since the first reports from the group of Meijer et al [ 38 , 46 ], the focus is mostly on water solution due to the formation of supramolecular hydrogels that show promising properties for application in regenerative medicine because of their ability to adapt to the natural environment these materials are brought into [ 16 , 47 , 48 , 49 ].…”

“…Additionally, here primarily the mechanical properties are investigated since the focus of these investigations have been also on the applications, especially supramolecular self-healing materials [ 9 , 50 , 55 , 56 ]. For PEG-thy/dat, it is known [ 13 , 18 ], that linear association and simple Rouse dynamics prevail based on small-angle neutron scattering (SANS), pulsed field gradient nuclear magnetic resonance (PFG NMR) and viscosity measurements. Moreover, a direct microscopic quantitative determination of the bond breaking relaxation time, τ b is obtained using neutron spin echo (NSE) spectroscopy [ 18 ].…”

Associating Imidazoles: Elucidating the Correlation between the Static Dielectric Permittivity and Proton Conductivity

“…Evidence of the formation of a variety of linear oligomers in imidazoles has been reported from solution infrared studies, however the formation of cyclic oligomers with less than 10 repeat molecules would result in strained hydrogen bonds and are therefore highly unlikely. [37] The transient chain mechanism, which describes the slow, Debye-like relaxation of MAs, provides an avenue to estimate an [24,27,[38][39][40] The Rouse model, which describes the dynamics of short chain polymers, reveals a temperature-independent average chain length, , of approximately seven 2-ethyl-4methylimidazole molecules (inset of FIG. 2 (b)).…”