Cynthia A. Mitchell

Templating of cylindrical and spherical block copolymer microdomains by layered silicates

The influence of a highly anisotropic layered silicate (organically modified montmorillonite) in directing the mesoscopic self-assembly of a block copolymer blend is studied as a model for the development and tailoring of templated inorganic–organic hybrid materials. The potential for nanometer thick layers to induce large-scale mesoscopic ordering of cylindrical and spherical microdomains in asymmetric block copolymers is studied using a combination of rheology, electron microscopy, and small angle neutron scattering. Spherical microdomains arranged on a bcc lattice are templated by the anisotropic layered silicate and the kinetics of their growth are dramatically accelerated by the presence of even 0.1 wt.% (0.04 vol.%) of the filler. However, for cylindrical microdomain ordering, the kinetics are essentially unaffected by the addition of layered silicates and the development of three-dimensional mesoscopic order is possibly even disrupted. These results suggest that for the development of three-dimensi...

Effect of silicate layer anisotropy on cylindrical and spherical microdomain ordering in block copolymer nanocomposites

The influence of the addition of small quantities of anisotropic layered silicates on the ordering of block copolymers is studied by a combination of linear viscoelasticity and small angle neutron scattering. Specifically, we examine the influence of varying the lateral dimensions of thermodynamically roughly equivalent layered silicates on the development of cylindrical and spherical microdomain order in a blend of a matched diblock and triblock copolymer. The kinetics for the development of spheres arranged on a bcc lattice from an initial disordered state are dramatically accelerated by the two larger layered silicates with equivalent diameters of ∼1 and 10 μm, while the incorporation of an organically modified laponite, with an equivalent diameter of ∼30 nm, has no influence on these kinetics. On the other hand, the addition of layered silicates, irrespective of layer dimensions, has no influence on the development of cylindrical ordered microdomains and the epitaxial transformation of shear-aligned c...

Thermal mismatch strains in sidewall functionalized carbon nanotube/polystyrene nanocomposites.

We present an unusual temperature dependence of thermal strains in 4-(10-hydroxy)decyl benzoate (HDB) modified SWNTPS (SWNT-single wall carbon nanotube, PS-polystyrene) nanocomposites. The strain transfer from the matrix to nanotubes in these nanocomposites, inferred from the frequency change of the Raman active tangential modes of the nanotubes, is enhanced strongly below 300 K, whereas it is vanishingly small at higher temperatures. The increased strain transfer is suggestive of reinforcement of the HDB-SWNTPS nanocomposites at low temperatures. On the other hand, the pristine SWNTs couple weakly to the PS matrix over the entire temperature range of 4.5-410 K. We argue that the strain transfer in HDB-SWNTPS is determined by the thermomechanical properties of the interface region composed of polystyrene plasticized by the tethered alkanelike modifier.