4 research outputs found
Tuning Cross-Link Density in a Physical Hydrogel by Supramolecular Self-Sorting
Cross-link
density is an important parameter for the macroscopic
mechanical properties of hydrogels. Increasing network density leads
to an increase in the storage and loss moduli of the gel and can be
accomplished by either increasing the concentration of cross-linkers,
or by reducing the fraction of mechanically inactive cross-links.
Mechanically inactive cross-links consist of loops in the network,
which do not contribute to the mechanical properties. Suppression
of loop formation is demonstrated in a system of semiflexible supramolecular
rods of polyÂ(ethylene glycol)–bisÂ(urea) bolaamphiphiles. Use
of a cross-linker which, due to self-sorting of its hydrophobic segments,
preferentially connects different rods, increases the modulus of a
hydrogel by a factor of 15 compared to a system without self-sorting.
By using statistical-mechanical calculations, it is shown that this
increase can be explained by the increased tendency of the cross-linkers
to form bridges between the semiflexible rods and thus increasing
the cross-link density in the supramolecular hydrogel
Network Formation in an Orthogonally Self-Assembling System
Many supramolecular motifs self-assemble into nanorods,
forming
the basis of the mechanical properties of supramolecular polymers.
When integrated as end-caps in a bifunctional telechelic polymer,
the motifs can phase segregate into the same or into another nanorod.
In the latter case, a functional cross-link is formed by the bridging
chain that strengthens the polymer network. This study introduces
a supramolecular polymeric system that consists of two different nanorod
forming supramolecular motifs. When end-capped to monofunctional polymers,
these supramolecular motifs self-assemble in an orthogonal fashion
in two separate types of noncross-linked nanorods, resulting in a
viscous liquid lacking macroscopic properties. The addition of 15
mol % of an α,ω-telechelic polymer containing both supramolecular
motifs, each on one end, transforms this viscous sticky liquid to
a solid material with elastomeric properties due to network formation
between the two types of nanorods