Multicompartment thermoresponsive gels: Does the length of the hydrophobic side group matter?

Multicompartment thermoresponsive gels are novel materials with fascinating self-assembly and interesting applications. The aim of this study was to investigate for the first time the effect of the length of the alkyl side group of a hydrophobic monomer on the thermoresponsive and self-assembly behaviour of terpolymers. Specifically twelve well-defined terpolymers based on the hydrophilic monomers 2-(dimethylamino)ethyl methacrylate (DMAEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA), and on the hydrophobic monomer ethyl-, n-butyl or n-hexyl methacrylate (EtMA, BuMA or HMA) of varying architectures (ABC, ACB, BAC and statistical) were synthesised using Group Transfer Polymerisation. The A, B and C blocks were based on PEGMA, the alkyl containing methacrylate monomer, and DMAEMA, respectively. The molecular weights (MWs) and compositions of the polymers were kept the same. The polymers and their precursors were characterised in terms of their MWs, MW distributions and compositions. Aqueous solutions of the polymers were studied by turbidimetry, hydrogen ion titration, light scattering and rheology to determine their cloud points, pKas, hydrodynamic diameters and thermoresponsive behaviour and investigate the effect of the architecture and the hydrophobic alkyl side group of the terpolymers. It was found that the pKas and the Tgs were mostly affected by the hydrophobicity of the side groups and not by the architecture, while the cloud points and the sol-gel transition of the polymers were affected by both the length of the alkyl side group and the polymer architecture. Interestingly the sharpest sol-gel transitions and stable multicompartment hydrogels were observed for the ABC triblock copolymers with the short alkyl-side groups even though the sol-gel transition occurred at higher temperatures

Interactions of large amplitude solitary waves in viscous fluid conduits

The free interface separating an exterior, viscous fluid from an intrusive conduit of buoyant, less viscous fluid is known to support strongly nonlinear solitary waves due to a balance between viscosity-induced dispersion and buoyancy-induced nonlinearity. The overtaking, pairwise interaction of weakly nonlinear solitary waves has been classified theoretically for the Korteweg-de Vries equation and experimentally in the context of shallow water waves, but a theoretical and experimental classification of strongly nonlinear solitary wave interactions is lacking. The interactions of large amplitude solitary waves in viscous fluid conduits, a model physical system for the study of one-dimensional, truly dissipationless, dispersive nonlinear waves, are classified. Using a combined numerical and experimental approach, three classes of nonlinear interaction behavior are identified: purely bimodal, purely unimodal, and a mixed type. The magnitude of the dispersive radiation due to solitary wave interactions is quantified numerically and observed to be beyond the sensitivity of our experiments, suggesting that conduit solitary waves behave as "physical solitons." Experimental data are shown to be in excellent agreement with numerical simulations of the reduced model. Experimental movies are available with the online version of the paper.Comment: 13 pages, 4 figure

The globalization of U.S. business investment

This paper documents some key facts about foreign direct investment flows by U.S. businesses overseas and foreign businesses in the United States. We show how the pattern of flows has evolved, examine the sources and destination of these flows, document associated employment and productivity gains, and show how investment-related sales compare with traditional exports. While the United States is a net debtor to the rest of the world, direct investment overseas by U.S. businesses exceeds direct investment in the U.S. by foreign businesses. Furthermore, U.S. businesses seem to earn more on their foreign investments than foreign firms earn on their U.S. investments. The globalization of business investment is a long-standing phenomenon, but it has accelerated in recent years and become a source of concern for some, as it is intimately related to the debate on offshore outsourcing. Yet contrary to what some think, the bulk of U.S. investment overseas is in other high-income countries. And foreign investment in the U.S. has been an important source of employment growth in recent years.Investments, Foreign - United States

Openness and inflation

This paper reviews the evidence on the relationship between openness and inflation. There is a robust negative relationship across countries, first documented by Romer (1993), between a country's openness to trade and its long-run inflation rate. However, a key part of the standard explanation for this relationship—that central banks have a smaller incentive to engineer surprise inflations in more-open economies because the Phillips curve is steeper—seems at odds with the facts. While the United States is still not a very open economy by conventional measures, there are channels through which global developments may influence the nation's inflation. We document evidence that global resource utilization may play a role in U.S. inflation and suggest avenues for future research.Inflation (Finance) ; Trade ; Phillips curve

Structural relaxation in Morse clusters: Energy landscapes

We perform a comprehensive survey of the potential energy landscapes of 13-atom Morse clusters, and describe how they can be characterized and visualized. Our aim is to detail how the global features of the funnel-like surface change with the range of the potential, and to relate these changes to the dynamics of structural relaxation. We find that the landscape becomes rougher and less steep as the range of the potential decreases, and that relaxation paths to the global minimum become more complicated.Comment: 21 pages, 3 tables, 5 figure