Polymer melts inside nanoscale cylindrical pores: Chain conformations, polymer diffusion and local dynamics

Polymers in composites and inside porous media are frequently confined to spaces that are comparable to or even smaller than their mean end-to-end distances in the unconfined bulk state. Understanding the impact of nanoscale confinement on both polymer structure and dynamics is critical for a variety of applications including hydraulic fracturing fluids, porous inorganic thin films in the electronics industry, and composites. To date, our work focuses on polymer melts under nanoscale cylindrical confinement. The polymer center-of-mass diffusion into cylindrical pores in anodized aluminum oxide membranes (diameters 18 – 80 nm) was measured using elastic recoil detection. This ion beam method that provides the concentration profile of deuterated polystyrene (400 kg/mol) penetrating into the AAO membranes prefilled with polystyrene (200 or 290 kg/mol). The polymer diffusion coefficient increases with decreasing pore diameter. This experimental finding is corroborated by coarse grain simulations with neutral interactions with the pore walls, although the increase is more pronounced in the simulations. The simulations previously found that chain conformations slightly elongated parallel to the cylinder axis and compressed perpendicular to the cylinder and the number of entanglements per chain decreases as the cylinder diameter decreases. It is primarily the reduction in polymer entanglements that allows polymers to diffuse faster when the pore diameter is smaller. We have also probed the local polymer dynamics using quasi-elastic neutron scattering

Anchorage Leader Training Needs Based On 1970 Youth Organization Survey

Thesis (M.Ed.) University of Alaska Fairbanks, 197

The ecology of a child\u27s day : a study of the effects of various care environments on the complexity of a preschooler\u27s play.

Observations were conducted at various care environments and preschools to determine whether environmental variables, such as setting and time of day, affect the complexity of a young child\u27s play. Twenty-four preschoolers were observed for an hour during the morning and afternoon on three separate occasions. Three males and three females, from each of the following programs, participated in the study: (1) half-day morning preschool; (2) half-day afternoon preschool; (3) full-day day care; and (4) full-day family day care. Children attending half-day programs were observed at their homes as well as at school, whereas the other children were observed in only one setting during both mornings and afternoons. Scores based on the number of instances of complex play divided by the number of instances of complex and simple play were used as a measure of complexity in the analyses. Findings indicate that setting does affect the complexity of a child\u27s play. Those children attending a half-day afternoon preschool program were found to have significantly higher complexity scores than their peers in other settings. No significant differences existed between the other groups. In addition, no differences were found in the complexity scores of males and females. In looking at the effect of the time of day, no significant differences were found between morning and afternoon complexity scores. The complexity levels of children changing settings, as compared to those attending a full-day program, were found not to differ significantly. In addition, the home play of children attending afternoon preschool was found to be significantly more complex than the home play of children attending morning preschool. Disregarding the effect of time of day, the relationship between play complexity and activities was investigated. Across programs, children were found to spend most of their time involved in the following activities: table games, art, fantasy, and blocks. The activities associated with the greatest percentage of complex play were as follows: art, sand/water play, blocks, table games, and fantasy

The Mouse Mps1p-like Kinase Regulates Centrosome Duplication

AbstractThe yeast Mps1p protein kinase acts in centrosome duplication and the spindle assembly checkpoint. We demonstrate here that a mouse Mps1p ortholog (esk, which we designate mMps1p) regulates centrosome duplication. Endogenous mMps1p and overexpressed GFP-mMps1p localize to centrosomes and kinetochores in mouse cells. Overexpression of GFP-mMps1p causes reduplication of centrosomes during S phase arrest. In contrast, a kinase-deficient mutant blocks centrosome duplication altogether. Control of centrosome duplication by mMps1p requires a known regulator of the process, Cdk2. Inhibition of Cdk2 prevents centrosome reduplication and destabilizes mMps1p, causing its subsequent loss from centrosomes, suggesting that Cdk2 promotes mMps1p's centrosome duplication function by regulating its stability during S phase. Thus, mMps1p, an in vitro Cdk2 substrate, regulates centrosome duplication jointly with Cdk2

Ionic Aggregates in Zn- and Na-neutralized Poly(ethylene-\u3cem\u3eran\u3c/em\u3e-methacrylic acid)

The morphology of ionic aggregates in semi-crystalline Zn- and Na-neutralized poly(ethylene-ran-methacrylic acid) (EMAA) ionomer blown films has been explored with scanning transmission electron microscopy (STEM) and small angle x-ray scattering (SAXS). The ionic aggregates of Zn-EMAA are spherical, monodisperse and uniformly-distributed in as-extruded pellets and blown films prepared at low and high blow-up ratio. Thus, although the biaxial stresses of film blowing are sufficient to alter the PE superstructure, the ionic aggregates in Zn-EMAA are unaffected. In contrast, the morphology of Na-EMAA as detected by STEM changes from featureless in the as-extruded pellets to a heterogeneous distribution of Na-rich aggregates in the blown films. This transformation in Na-EMAA morphology is consistent with our earlier study of quiescent annealing suggesting that the morphological change is the result of thermal processing rather than the biaxial stresses of film blowing

Polymer conformations in polymer nanocomposites containing spherical nanoparticles

We investigate the effect of various spherical nanoparticles on chain dimensions in polymer melts for high nanoparticle loading which is larger than the percolation threshold, using molecular dynamics simulations. We show that polymer chains are unperturbed by the presence of repulsive nanoparticles. In contrast polymer chains can be perturbed by the presence of attractive nanoparticles when the polymer radius of gyration is larger than the nanoparticle radius. At high nanoparticle loading, chains can be stretched and flattened by the nanoparticles, even oligomers can expand under the presence of attractive nanoparticles of very small size

Effect of nanotube alignment on percolation conductivity in carbon nanotube/polymer composites

Percolation conductivity of a stick network depends on alignment as well as concentration. We show that both dependences exhibit critical (power-law) behavior, and study the alignment threshold in detail. The highest conductivity occurs for slightly aligned, rather than isotropic, sticks. Experiments on single wall carbon nanotube composites are supported by Monte Carlo simulations. These results should be broadly applicable to percolating networks of anisotropic conductors

Production of haloperidol loaded PLGA nanoparticles for extended controlled drug release of haloperidol

This study developed an emulsion-solvent evaporation method for producing haloperidol-loaded PLGA nanoparticles with up to 2% (wt/wt. of polymer) drug content, in vitro release duration of over 13 days and less than 20% burst release. The free haloperidol is removed from the nanoparticle suspension using a novel solid phase extraction technique. This leads to a more accurate determination of drug incorporation efficiency than the typical washing methods. It was discovered that PLGA end groups have a strong influence on haloperidol incorporation efficiency and its release from PLGA nanoparticles. The hydroxyl-terminated PLGA (uncapped) nanoparticles have a drug incorporation efficiency of more than 30% as compared to only 10% with methyl-terminated PLGA (capped) nanoparticles. The in vitro release profile of nanoparticles with uncapped PLGA has a longer release period and a lower initial burst as compared to capped PLGA. By varying other processing and materials parameters, the size, haloperidol incorporation and haloperidol release of the haloperidol-loaded PLGA nanoparticles were controlled