Effect of precursor-layer surface charge on the layer-by-layer assembly of polyelectrolyte/nanoparticle multilayers

In this Article, we investigate the effect of a precursor layer, which is composed of four bilayers of polyethyleneimine (PEI) and poly(sodium styrene sulfonate) (PSS), on the subsequent LBL assembly of hybrid films composed of indium tin oxide (ITO) nanoparticles and PSS. A precursor polyelectrolyte layer is usually deposited to minimize interference by the substrate. It is shown here that the "effective" surface charge of the precursor layer can significantly affect the subsequent assembly behavior of [ITO/PSS](9.5) hybrid thin films. Depending on the surface charge of the precursor layer, the subsequent LbL assembly of [ITO/PSS](9.5) hybrid films can exhibit either one or two regimes. When two growth regimes are present, the first one consists of a "recovery regime", and the second is the expected "linear growth regime." The length of the "recovery regime" is dependent on how much positive charge the precursor layer possesses and how fast this surface charge can be compensated. This work reveals for the first time that changes in the surface charge of the precursor layer can have a significant effect on the subsequent LBL assembly process. The surface charge of the precursor layer was investigated using ζ-potential measurements on model silica microspheres. These experiments showed that the surface charge of the precursor layer, [PEI/PSS](4), is dependent on the pH of the solution in which it is immersed, and that it can reverse from a negatively charged surface to a positively charged one, at sufficiently low pH due to the protonation of PEI, despite having the negatively charged PSS layer as the outermost layer.     

Reaction of β-aeylarylhydrazines with dimethylformamide in the presence of calcium hydride. A novel route to 3-pyrazolin-5-ones

Reaction of β-acylarylhydrazines with calcium hydride in refluxing dimethylformamide (DMF) was found to lead to the formation of 2-aryl-3-pyrazolin-5-ones (V). Application of this novel synthetic method resulted in fair to good yields of a series of 2,4-diaryl-3-pyra7,olin-5-ones. The infrared spectra (potassium bromide) of the products (V) showed that these compounds exist as the laetim tautomer (VI). An oxindole (IIc) was obtained when dimethylbenzamide was substituted for DMF under similar reaction conditions.     

NONCOOPERATIVE MANAGEMENT OF THE NORTHEAST ATLANTIC COD FISHERY: A FIRST MOVER ADVANTAGE

The point of departure for this analysis is Bjørndal and Lindroos [2012], who developed an empirical bioeconomic model to analyze cooperative and noncooperative management of Northeast Atlantic cod. In their analysis, only constant strategies were analyzed for noncooperative games. In this paper, nonconstant strategies are considered. Moreover, the fishery in question is characterized by cooperative management. What may happen in the real world is that one nation breaks the cooperative agreement by fishing in excess of its quota. Often, it takes time for the other agent to detect this and respond. In this paper, we allow this kind of delayed response into a two‐agent noncooperative game so that, if country 2 exceeds its quota, there will be a time lag before this is detected by country 1; moreover, there may also be a delay until country 1 is able to respond. Results show that the outcome critically depends on the length of these two lags as well as initial conditions.     

Structure and properties of PBO–PEO diblock copolymer modified epoxy

Amphiphilic poly(n‐butylene oxide)‐b‐poly(ethylene oxide) (PBO–PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO–PEO, epoxy resin, and curing agent, the copolymers formed well‐defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, worm‐like micelles, and spherical micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched worm‐like micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle‐toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the worm‐like micelle systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Chem 43: 1950–1965, 2005     

Evanescently coupled resonance in surface plasmon enhanced transmission

The optical transmission through subwavelength holes in metal films can be enhanced by several orders of magnitude by enabling interaction of the incident light with independent surface plasmon (SP) modes on either side of the film. Here, we show that this transmission is boosted by an additional factor of 10 when the energies of the SP modes on both sides are matched. These results, confirmed by a three-dimensional theoretical analysis, give a totally new understanding of the phenomenon of SP enhanced transmission. It is found that the holes behave like subwavelength cavities for the evanescent waves coupling the SPs on either side of the film. In this unusual device, the reflection at either end of the cavity is provided by the SP modes which act as frequency dependent mirrors.     

The Role of inclusion size in toughening of epoxy resins by spherical micelles

We report our finding of an optimal length scale for toughening of epoxies using spherical micelles formed by block copolymers. The amphiphilic diblock copolymer poly(hexylene oxide)‐poly(ethylene oxide) (PHO‐PEO) with 30 wt % PEO self‐assembled to form spherical micelles in a bisphenol A epoxy resin with a phenol novolac hardener. We systematically increased the size of the spherical micelles from 20–30 nm to 0.5–10 μm by swelling their PHO core using PHO homopolymer. Although all the blends were tougher than the unmodified epoxy, the largest enhancement of fracture resistance was measured in blends containing 0.1–1 μm spherical inclusions. This enhanced toughness was correlated with plastic deformation by shear banding in tensile test and greater roughness of the fracture surface. Smaller micelles neither induced plastic deformation nor contributed to surface roughness significantly whereas larger micelles acted as local defects resulting in early failure. These findings provide a framework in assessing the toughening effects of blended block copolymers on epoxy resins. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1125–1129, 2009