No abstract

Composite materials consisting of a polymer matrix with embedded functional modifiers (like filaments, whiskers, or nanoparticles), have potential use in chemical, biological, optical and microelectronic technology. [1][2][3][4] The properties of such hybrid materials depend on the physical properties and chemical nature of the dispersed and continuous phases, as well as morphology, which can dictate the spatial distribution of the dispersed modifiers. Control over the spatial distribution of nano-objects can be achieved using structure-guiding matrix scaffolds, such as block copolymers. [4][5][6][7][8][9][10][11][12] As an alternate method, besides the in-situ reduction technique, [13][14][15][16] the self-assembly of cadmium selenide, silica, gold and other nanoparticles into two-and three-dimensional ordered structures has been achieved recently, [5][6][7][8][9]11,12,17] led by the theoretical studies of Balazs and coworkers. [18][19][20] Kramer and coworkers [5][6][7][8] used polystyrene ligands to localize gold nanoparticles inside the polystyrene (PS) microdomains of a polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer, while mixtures of PS and P2VP ligands directed the nanoparticles to the interface between the PS and P2VP microdomains. Bockstaller, et al. have shown that the location of particles within the same domain is affected by the size of the nanoparticle.[9] Large silica nanoparticles were found to segregate to the center of one domain, whereas smaller gold nanoparticles segregated to the interface between microdomains. Here, we demonstrate a simple approach to control the spatial distributions of gold nanoparticles in a lamellar forming PS-b-P2VP diblock copolymer. Solvent and thermal annealing treatments were then applied to control the specific location of the functionalized gold nanoparticles in the diblock copolymer.Gold nanoparticles have been investigated extensively over the past decade due to their synthetic availability and advanced functionalization chemistry. [21][22][23][24][25][26] For our studies, gold nanoparticles of ca. 2-3 nm diameter were synthesized according to the Brust-Schiffrin method, [27] and functionalized with a mixture of hydrophilic and hydrophobic ligands by ligand exchange. Dodecanethiol-covered gold nanoparticles were agitated in dry dichloromethane, with 11-mercapto-1-undecanol, at room temperature for 48 h. The composition of the ligands on the nanoparticles was controlled by the concentration of 11-mercapto-1-undecanol used in the ligand exchange. The nanoparticles were then concentrated, washed repeatedly with dichloromethane and methanol to remove the unbound ligands, then dispersed in toluene. The final ratio of dodecanethiol to 11-mercapto-1-undecanol was determined by 1 H-NMR spectroscopy integrations. The solution of gold nanoparticles was aged at room temperature and centrifuged before use. The average core diameter of the gold nanoparticles was 2.4 nm, as determined by small-angle X-ray scattering, shown in Figure S1 in the Supporting...

Polymers that are thermally insulating in bulk forms have been found to exhibit higher thermal conductivities when stretched under tension. This enhanced heat transport performance is believed to arise from the orientational alignment of the polymer chains induced by tensile stretching. In this work, a novel high-sensitivity micro-device platform was employed to determine the axial thermal conductivity of individual Nylon-11 polymer nanofibers fabricated by electrospinning and post-stretching. Their thermal conductivity showed a correlation with the crystalline morphology measured by high-resolution wide-angle X-ray scattering. The relationship between the nanofiber internal structures and thermal conductivities could provide insights into the understanding of phonon transport mechanisms in polymeric systems and also guide future development of the fabrication and control of polymer nanofibers with extraordinary thermal performance and other desired properties.

Nanoporous thin films were prepared from poly(ethylene oxide)-b-poly(methyl methacrylate)-bpolystyrene (PEO-b-PMMA-b-PS) ABC triblock copolymer by solvent annealing under high relative humidity followed by UV degradation and acid washing. Ordered half-spheres at the surface that template ordering of spheres below the surface in thin films were formed as a result of the interaction between the hydrophilic PEO segments and water vapor during processing. The spherical block copolymer domains exhibit complex packing behavior on the surface and in the interior. A half-sphere "monolayer" and a half-sphere plus whole sphere "bilayer" were formed in thin films with thicknesses of 43 and 71 nm, respectively, and have hexagonal lattice symmetry. For half-sphere plus two whole sphere "trilayers" with a nominal thickness of 117 nm, coexistence of regions of hexagonal and square packing was observed by transmission electron microscopy, scanning force microscopy, scanning electron microscopy, and grazing-incidence small-angle X-ray scattering. Square packing was consistent with a surface-truncated unit cell of a body-centered cubic lattice with the (100) plane parallel to the surface.