Preparation of High-Density Polymer Brushes with a Multihelical Structure.

It is well-known that a mixture of isotactic and syndiotactic polymethyl methacrylate (PMMA) forms a stereocomplex consisting of a multihelical structure in which an isotactic chain is surrounded by a syndiotactic chain. Here, we report the basic structure of the stereocomplex formed when the syndiotactic PMMA chains are tethered to a silicon substrate and form a high-density polymer brush. The influence of geometric confinement was investigated by preparing the high-density polymer brushes on a flat and spherical substrate. In both cases, mixing the untethered isotactic PMMA with the grafted syndiotactic PMMA led to the formation of a stereocomplex with a multihelical structure. Static contact angle measurements showed a hindered surface mobility at the outermost surface of the polymer brush, indicating that the stereocomplex forms a crystalline structure. A syndiotactic polymer brush with substituted fluoroalkyl groups was prepared to increase the contrast for grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements. The GIWAXD results verified that the stereocomplex forms a crystalline structure oriented perpendicular to the substrate with a relatively low degree of orientation.

Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order.

Epoxy films containing self-assembled 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements in epoxy. The epoxy nanocomposite films are transparent and flexible and exhibit exceptionally high tensile modulus and strength. The findings have broad implications for development of multifunctional materials for engineering applications.

Large-scale self-assembled zirconium phosphate smectic layers via a simple spray-coating process.

The large-scale assembly of asymmetric colloidal particles is used in creating high-performance fibres. A similar concept is extended to the manufacturing of thin films of self-assembled two-dimensional crystal-type materials with enhanced and tunable properties. Here we present a spray-coating method to manufacture thin, flexible and transparent epoxy films containing zirconium phosphate nanoplatelets self-assembled into a lamellar arrangement aligned parallel to the substrate. The self-assembled mesophase of zirconium phosphate nanoplatelets is stabilized by epoxy pre-polymer and exhibits rheology favourable towards large-scale manufacturing. The thermally cured film forms a mechanically robust coating and shows excellent gas barrier properties at both low- and high humidity levels as a result of the highly aligned and overlapping arrangement of nanoplatelets. This work shows that the large-scale ordering of high aspect ratio nanoplatelets is easier to achieve than previously thought and may have implications in the technological applications for similar materials.

Rheology of disentangled multiwalled carbon nanotubes dispersed in uncured epoxy fluid.

The rheological behaviors of clustered and disentangled multiwalled carbon nanotubes (MWCNTs) dispersed in a stable, non-reactive Newtonian epoxy fluid have been investigated. Suspensions of untreated and chemically oxidized MWCNTs in epoxy show strong rate-dependent behavior and long-time elastic response that is characteristic of a flocculated microstructure. Suspensions of disentangled MWCNTs in epoxy were prepared by a functionalization reaction with nitrobenzene, and show distinct rheological behavior that is attributed to the motion and rotation of the individual nanoparticles. Characteristic features of the disentangled MWCNTs in epoxy are a lack of low-frequency plateau in storage modulus and shear thickening behavior at high shear rate. The rheological behavior is discussed on the basis of continuum-level predictions for the motion of individual, semiflexible fibers under shearing flows. Implications of MWCNT disentanglement on fundamental study and applications of MWCNT-filled systems are discussed.