Porod scattering study of coarsening in immiscible polymer blends

Studies of immiscible blend compatibilization often involve laborious microscopy methods to characterize changes in the particle size distribution with time in the melt. Here we explore a simple alternative approach based on Porod scattering from the two-phase structure. Although micron-sized particles in immiscible polymer blends are too large to be fully characterized by small-angle scattering, Porod scattering measurements of the interfacial area combined with knowledge of the blend volume fraction allows determination of an average particle diameter from a single scattering measurement. This technique is illustrated in experiments monitoring coarsening of particle size in polystyrene/poly(methyl methacrylate) blends prepared either by melt blending or solid-state shear pulverization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3413–3420, 2005     

Two‐dimensional liquid chromatography with active solvent modulation for studying monomer incorporation in copolymer dispersants

A pseudo‐comprehensive two‐dimensional liquid chromatography approach with size exclusion chromatography in the first dimension and gradient reversed‐phase liquid chromatography in the second dimension was successfully developed for the characterization of vinyl acetate/acrylic acid copolymers and vinyl acetate/itaconic acid/acrylic acid terpolymers. Active solvent modulation was exploited to prevent the polymer breakthrough in the second dimension separation caused by the strong solvent used in the first dimension. The conditions of the active solvent modulation valve were optimized to achieve sufficient on‐line dilution and to completely prevent polymer breakthrough without adding excessive time to the modulation cycle. Using this approach, copolymers made with different monomer ratios and processes were studied. Heterogeneous composition distribution due to insufficient monomer incorporation was detected in some of the copolymer samples. We demonstrated that with active solvent modulation, the two‐dimensional liquid chromatography approach is no longer limited to water‐soluble polymers and can be used for a broader range of polymers and copolymers.     

Fluorescence of commercial Pluronic F127 samples: Temperature-dependent micellization

We present a novel approach of using the butylated hydroxytoluene (BHT) antioxidant found in commercial Pluronic F127 samples as a marker of polymer aggregation. The BHT marker was compared to the pyrene dye and static light scattering methods as a way to measure the critical micelle concentration (CMC) and critical micelle temperature (CMT). The n→π(?) transitions of BHT are sensitive to the microenvironment as demonstrated by plotting the fractional intensities of its excitation (≈280nm) and emission (≈325nm) peaks. BHT is more sensitive to changes in temperature than concentration. The partition coefficient increases ≈40-fold for pyrene compared to ≈2-fold for BHT when the temperature is increased from 25 to 37°C. CMT values determined using the BHT fluorescence decrease with increasing F127 concentration. Our results show that BHT can be used as a reliable marker of changes in the microenvironment of Pluronic F127.     

Autoamplification of Molecular Chirality through the Induction of Supramolecular Chirality

The novel concept for the autoamplification of molecular chirality, wherein the amplification proceeds through the induction of supramolecular chirality, is presented. A solution of prochiral, ring‐open diarylethenes is doped with a small amount of their chiral, ring‐closed counterpart. The molecules co‐assemble into helical fibers through hydrogen bonding and the handedness of the fibers is biased by the chiral, ring‐closed diarylethene. Photochemical ring closure of the open diarylethene yields the ring‐closed product, which is enriched in the template enantiomer.     

The thermolysis of zirconium precipitates : Salts of organic acids

The thermal decomposition of the zirconium salts of phthalic, phenoxyacetic, cinnamic, diphenic, p-bromornandclic, benzilic, m-crcsoxyacetic, salicylic and bcnzoic acids and 8-quinolinol were studied on the thermobalancc. The precipitates exhibited varying degrees of stability with the first weight losses occurring in the temperature range of 45° to 160°. After decomposition through various intermediates, the oxide (ZrO₂) levels were obtained between 500° to 790°.     

Thermoreversible,epitaxial fcc<-->bcc transitions in block copolymer solutions

Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.     

Reduced order modeling of head related impulse responses for virtual acoustic displays

This study investigated the use of reduced order head related impulse response (HRIR) models to improve the computational efficiency in acoustic virtual displays. State space models of varying order were generated from zero-elevation HRIRs using a singular value decomposition technique. A source identification experiment was conducted under anechoic conditions in which three subjects were required to localize sounds in the front horizontal plane. The sounds were either (1) real sources (emitted by individual loudspeakers in a semi-circular array), (2) virtual sources generated from the original HRIRs, or (3) virtual sources generated using reduced order state space models. All virtual sources were created by simultaneous activation of two loudspeakers at +/- 30 degrees using a virtual source imaging technique based on either the measured or modeled HRIRs. The errors in the perceived direction of the virtual sources generated from the reduced order models were compared to errors in localization using the original HRIRs. The results demonstrate that a very significant reduction in model size can be achieved without significantly affecting the fidelity of the virtual display of horizontally placed sources.