Network Topology of the Interphase between Cross-Linked Polyurethane/Ethylene Propylene Diene Terpolymer Elastomers for Adhesion Applications

Understanding the interfacial phenomena involved in the adhesion between elastomer layers on a molecular basis is an important topic from both fundamental and applied aspects. Nevertheless, this topic has been poorly addressed experimentally. This report aims at rationalizing differences in the adhesion behavior of polyurethane (PU) elastomers cured on an ethylene–propylene–diene terpolymer (EPDM) substrate, based on a detailed description of their local network-like topology, determined thanks to 1H solid-state nuclear magnetic resonance (NMR) spectroscopy. The polyurethanes, composed of the same fraction of hydroxy-terminated poly(butadiene) and isophorone diisocyanate, were cured under different reaction conditions: nature and concentration of the catalyst as well as the cross-linking temperature. The rigid domains formed by the hard segments, the proportion of elastically active chains, and the distribution of the topological constraints in the soft domains were investigated by 1H solid-state NMR, taking advantage of the magic sandwich echoes and double quantum-based experiments. The PU network topology within 20 μm thick slices collected near the interface with the EPDM layer was systematically compared to the one observed for 60 μm thick slices, located 500 μm from the interface, corresponding to the bulk regions. Curing at a low temperature (30 °C) with a low amount of catalyst (0.02 wt %) leads to elastically active poly(butadiene) chains close to the interface with, on average, higher molecular weights between topological constraints than the ones in the bulk. Such differences between interfacial and bulk regions are not observed any longer as the catalyst concentration is increased to 0.2 wt %. These variations of the local PU network topology, occurring over several tens of micrometers, allow one to account for the adhesion testing results

Substituent Effects on the Inclusion of 1‑Alkyl-6-alkoxy-quinolinium in 4‑Sulfonatocalix[<i>n</i>]arenes

The effect of the chain length of the alkyl and alkoxy substituents on the binding characteristics of 1-alkyl-6-alkoxy-quinolinium cations was studied using 4-sulfonatocalix[4]­arene (SCX4) and 4-sulfonatocalix[6]­arene (SCX6) in neutral aqueous solutions at 298 K. Isothermal calorimetric titrations showed enthalpy-controlled inclusion with 1:1 stoichiometry. The equilibrium constants of complexation were always larger for the confinement in SCX4 than in its SCX6 homologue because the better matching between the host and guest sizes allowed more exothermic interaction. The binding affinity diminished with the lengthening of the aliphatic chain of the guests in the case of the association with SCX4, but insignificant change was found for SCX6 complexes. The most substantial change in the enthalpic and entropic contributions to the driving force of complex production occurred when the alkyl chain was linked to the heterocyclic nitrogen and the number of its carbon atoms varied between 1 and 4. ¹H NMR spectra evidenced that in SCX6, the 1-alkyl-6-alkoxy-quinolinium cations could be included within the macrocycle cavity. In the case of SCX4, the quinolinium ring is always inside the host, but the alkyl chain is included within SCX4 only for a short chain length (<i>n</i> up to 4). In contrast, the alkoxy chain displays a very weak interaction with the cavity irrespective of the length. Because of the outward orientation from the host, the lengthening of the alkoxy substituent of the quinolinium moiety barely influenced the thermodynamics of inclusion in SCX4. Distinct linear enthalpy–entropy correlations were found for the encapsulation in SCX4 and SCX6

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis­(urea)­s and tris­(urea)­s decorated by two incompatible polymer arms, namely, poly­(styrene) (PS) and poly­(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis­(urea)­s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris­(urea)­s (<i>N</i>_agg ∼ 50) which developed six cooperative hydrogen bonds per molecule. ¹H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders

Topological Connection between Vesicles and Nanotubes in Single-Molecule Lipid Membranes Driven by Head–Tail Interactions

Lipid nanotube–vesicle networks are important channels for intercellular communication and transport of matter. Experimentally observed in neighboring mammalian cells but also reproduced in model membrane systems, a broad consensus exists on their formation and stability. Lipid membranes must be composed of at least two molecular components, each stabilizing low (generally a phospholipid) and high curvatures. Strong anisotropy or enhanced conical shape of the second amphiphile is crucial for the formation of nanotunnels. Anisotropic driving forces generally favor nanotube protrusions from vesicles. In this work, we report the unique case of topologically connected nanotubes–vesicles obtained in the absence of directional forces, in single-molecule membranes, composed of an anisotropic bolaform glucolipid, above its melting temperature, Tm. Cryo-TEM and fluorescence confocal microscopy show the interconnection between vesicles and nanotubes in a single-phase region, between 60 and 90 °C under diluted conditions. Solid-state NMR demonstrates that the glucolipid can assume two distinct configurations, head–head and head–tail. These arrangements, seemingly of comparable energy above the Tm, could explain the existence and stability of the topologically connected vesicles and nanotubes, which are generally not observed for classical single-molecule phospholipid-based membranes above their Tm