Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films

Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064     

Domain size equilibration in sphere‐forming block copolymers

The kinetics of domain size equilibration were studied for asymmetric poly(ethylene‐alt‐propylene)‐b‐poly(dimethyl siloxane) (EPDMS) and polyisoprene‐b‐poly(dimethyl siloxane) (IDMS) block copolymers in the body‐centered cubic ordered phase. Small‐angle X‐ray scattering measurements of the principal peak position (q*) were made as a function of time after temperature jumps within the ordered state. The equilibration times were remarkably long, especially on cooling and for temperatures below 100 °C. For example, after a quench to 40 °C, q* for EPDMS had not fully equilibrated even after several weeks of annealing; IDMS required several days to equilibrate at the same temperature. In contrast, a lamella‐forming EPDMS sample was able to adjust q* within the timescale of the measurements (i.e., minutes) with both heating and cooling over the same temperature range. Measurements of tracer diffusion indicated that chain mobility was not the rate‐limiting step, although differences in mobility did account for the differences between EPDMS and IDMS. Rather, the limiting step was the required reduction in the number density of spheres on cooling; the disappearance of spheres, either by evaporation or by fusion, provided a large kinetic barrier. Lamellae, however, could adjust domain dimensions simply by local displacements of individual chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 715–724, 2003     

XAS investigation of tantalum and niobium in nanostructured TiO2 anatase

Sol-gel routes were used to prepare Ta 10 at% and Nb 5 at% and 10 at% doped titania nanosized powders. When fired between 410°C and 850°C the doped titania powders are in the anatase phase; further heating up to 1050°C is required to obtain the rutile phase. The presence of dopant atoms delays the rate of transformation as compared with pure titania powders. Doping also affects the rate of grain growth and increases the conductance response to gas. To better understand the role played by dopant atoms in inhibiting both phase transformation to rutile and grain growth, X-ray Absorption Spectroscopy measurements were performed at the L_III-L_I absorption edges of Ta and Nb K absorption edge. Analysis was restricted to the anatase phase because the transformation to rutile phase, obtained by firing at 1050°C, is accompanied by the formation of undesired Ta and Nb oxides (Ta₂O₅ and Nb₂TiO₇, respectively). Extended X-ray Absorption Fine Structure and X-ray Absorption Near-Edge Spectroscopy analysis results indicate that in nanostructured anatase both tantalum and niobium atoms substitute Ti cations with +5 valence state.     

Bubble nucleation and growth anomaly for a hydrophilic microheater attributed to metastable nanobubbles

Nanobubbles on a hydrophilic surface immersed in water and ethanol are inferred from the response of the surface to two consecutive heat pulses with a variable separation time. Bubble nucleation occurs at specific positions on the surface during the first heat pulse but at lower nucleation temperatures and random locations on the second. Nanobubbles are hypothesized to form on collapse of the bubble from the first pulse.     

An Ordered Nanoporous Monolith from an Elastomeric Crosslinked Block Copolymer Precursor

Summary: An ordered nanoporous monolith was prepared from a poly(isoprene‐b‐dimethylsiloxane) (PI‐PDMS) hexagonally packed cylinder precursor. The PDMS cylinders were macroscopically aligned, the PI was crosslinked with dicumyl peroxide, and the PDMS was removed using tetrabutylammonium fluoride. The stability of the pores depended on the modulus of the matrix. At high crosslink density the pores were stable, but they collapsed at a low crosslink density. The nanoporous materials could be swollen in toluene.

A scanning electron micrograph of the end‐on view of crosslinked degraded poly(isoprene‐b‐dimethylsiloxane).     

Shape memory ionomers

This review is focused on the use of ionomers in shape memory polymers. Ionomers are polymers that contain less than ∼15% ionic groups. The incompatibility between the ion-pairs and the polymer backbone drives microphase separation producing dispersed ionic aggregates, which can physically crosslink the polymer. Shape memory polymers are responsive materials that can be deformed to program a temporary shape and then recovered on application of an external stimulus. Through the review of the main types of ionomers used in shape memory polymers, polyurethanes and polyester ionomers, polyolefin and polyaromatic ionomers, and perfluorosulfonic acid ionomers (i.e., Nafion^®) it will be shown that ionomers can produce robust thermoplastic shape memory polymers and in many cases impart unique properties which allow advanced shape memory materials to be obtained including antibacterial, high temperature, and multishape memory polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1389–1396     

Dynamic interaction effects of multiple delaminations in plates subject to cylindrical bending

The interaction of multiple delaminations in a laminated composite plate loaded dynamically under plane strain conditions (cylindrical bending) is studied by a simple but accurate model that represents the delaminated plate as a set of Timoshenko beams joined by cohesive interfaces. Behavioral maps are derived, which distinguish conditions under which multiple delaminations tend to propagate with equal lengths from those under which one of them tends to grow as a dominant crack with relatively high velocity. In homogeneous systems, equal length growth is favored when the delaminations are equally spaced through the thickness. While the behavioral maps are similar to those for static loading conditions, significant dynamic effects arise in the details of propagation: the maximum energy release rate depends strongly on the loading rate, duration and profile; dynamic effects and crack-interaction effects are generally coupled; and strong hammering effects (chaotic collisions of sub-laminates) can occur during the free wave motions that arise after the load is removed. The hammering effect can be suppressed by imposing a large-scale bridging mechanism (bridging extending far in the crack wake, as from pins or stitches), whereupon energy release rates tend to show smooth oscillations associated with waves propagating on the scale of the whole specimen. The energy absorbed during failure will depend significantly on whether conditions favor multiple delaminations propagating with equal lengths or a single delamination growing dominantly.     

Nanosecond imaging of microboiling behavior on pulsed-heated au films modified with hydrophilic and hydrophobic self-assembled monolayers

Fast transient microboiling has been characterized on modified gold microheaters using a novel laser strobe microscopy technique. Microheater surfaces of different hydrophobicity were prepared using self-assembled monolayers of hexadecane thiol (hydrophobic) and 16-mercaptohexadecanol (hydrophilic) as well as the naturally hydrophilic bare gold surface. The microheater was immersed in a pool of water, and a 5-micros voltage pulse to the heater was applied, causing superheating of the water and nucleation of a vapor bubble on the heater surface. Light from a pulsed Nd:Yag laser was configured to illuminate and image the sample through a microscope assembly. The timing of the short duration (7.5 ns) laser flash was varied with respect to the voltage pulse applied to the heater to create a series of images illuminated by the flash of the laser. These images were correlated with the transient resistance change of the heater both during and after the voltage pulse. It was found that hydrophobic surfaces produced a bubble that nucleated at an earlier time, grew more slowly to a smaller maximum size, and collapsed more rapidly than bubbles formed on hydrophilic surfaces.     

Synthesis of ω‐sulfonated polystyrene via reversible addition fragmentation chain transfer polymerization and postpolymerization modification

The synthesis of chain‐end sulfonated polystyrene [PS (ω‐sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymerization modification was investigated by two methods. In the first method, the polymer was converted to a thiol‐terminated polymer by aminolysis. This polymer was then sulfonated by oxidation of the thiol end‐group with m‐chloroperoxybenzoic acid (m‐CPBA) to produce a sulfonic acid end‐group. In the second method, the RAFT‐polymerized polymer was directly sulfonated by oxidation with m‐CPBA. After purification by column chromatography, ω‐sulfonated PS was obtained by both methods with greater than 95% end‐group functionality as measured by titration. The sulfonic acid end‐group could be neutralized with various ammonium or imidazolium counter ions through acid–base or ionic metathesis reactions. The effect of the ionic end‐groups on the glass transition temperature of the PS was found to be consistent with what is known for PS ionomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011