Proper percolation of charges in solar cells is possible with the self‐assembled nanostructure of a block‐copolymer film (see the TEM cross section of a solar cell). A photovoltaic device made from such a block copolymer exhibits a ten‐times higher short circuit current and a considerably larger photovoltage than its polymer‐blend analogue.

We present a complete analysis of the structure of polyethylene (PE) nanoparticles synthesized and stabilized in water under very mild conditions (15°C, 40 atm) by a nickel-catalyzed polymerization in aqueous solution. Combining cryogenic transmission electron microscopy (cryo-TEM) with X-ray scattering, we demonstrate that this new synthetic route leads to a stable dispersion of individual PE nanoparticles with a narrow size distribution. Most of the semicrystalline particles have a hexagonal shape (lateral size 25 nm, thickness 9 nm) and exhibit the habit of a truncated lozenge. The combination of cryo-TEM and small-angle X-ray scattering demonstrates that the particles consist of a single crystalline lamella sandwiched between two thin amorphous polymer layers ("nanohamburgers"). Hence, these nanocrystals that comprise only ca. 14 chains present the smallest single crystals of PE ever reported. The very small thickness of the crystalline lamella (6.3 nm) is related to the extreme undercooling (more than 100°C) that is due to the low temperature at which the polymerization takes place. This strong undercooling cannot be achieved by any other method so far. Dispersions of polyethylene nanocrystals may have a high potential for a further understanding of polymer crystallization as well as for materials science as, e.g., for the fabrication of extremely thin crystalline layers.Polyethylene (PE) is a commodity polymer that has become ubiquitous over the past several decades because of its low price and good mechanical properties. 1 Hence, the number of applications of the material is huge and many millions of tons are produced worldwide annually. However, PE has hardly played any role in the field of nanotechnology. This is due to the problem that PE is produced either by free radical polymerization under high pressure and temperature or with metal-organic catalysts working exclusively under strictly water-free conditions. Polymer nanoparticles and their composites with inorganic compounds, however, are very often produced in aqueous systems. 2 Recently, it was demonstrated that ethylene can be polymerized in aqueous systems in a catalytic fashion by Ni(II) complexes. [3][4][5][6] By virtue of this novel synthesis, long chains of polyethylene can be generated in a well-controlled environment and at ambient temperature. Thus, it could be shown that aqueous PE dispersions can be produced. This novel way of polymerization hence opens the way for the creation of nanostructures made from PE. Up to now, the particles synthesized in this way were semicrystalline and for the largest part consisted of stacks of several crystalline lamellae. 6

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We investigate the surface plasma oxidation of polydimethylsiloxane (PDMS) elastomers and its implication for the morphologies attainable by wrinkling of glassy-elastomer 'bilayers'. The kinetics of glassy skin formation is found to follow a logarithmic dependence with plasma exposure time t and, for various plasma intensities I, the relevant control variable is shown to be dose (≡I × t). We model the mechanism and kinetics of glassy film formation by plasma oxidation with a frontal propagation coarse-grained model, describing the spatio-temporal evolution of a conversion order parameter (ϕ) orthogonal to the film surface. The model is validated by X-ray reflectivity experiments, which confirm the logarithmic growth and quantify the initial growth of a transient, incomplete, skin layer during the early stage of plasma exposure. Three regimes are identified as (I) induction, (II) formation and (III) propagation with a combination of X-ray and wrinkling experiments. The simultaneous increase in thickness and skin mechanical modulus is found to be responsible for an unexpected minimum wavelength λmin attainable, which depends on critical strain εc and is ultimately limited by mechanical failure of the elastomer (λmin ≃ 140 nm is demonstrated at ε = 200%). We conclude by establishing a 1D surface morphology diagram, in terms of wavelength λ and amplitude A, limitations and capabilities for producing highly ordered (sub-)micropatterns over macroscopic areas using plasma oxidised PDMS under uniaxial strain.

HVHF decreased vasopressor requirement and tended to increase urine output in septic shock patients with renal failure. However, a larger trial is required to confirm our results and perhaps to show a benefit in survival.

We report on a novel lithography-free method for obtaining chemical submicron patterns of macromolecules on flat substrates. The approach is an advancement of the well-known microcontact printing scheme: While for classical microcontact printing lithographically produced masters are needed, we show that controlled wrinkling can serve as an alternative pathway to producing such masters. These can even show submicron periodicities. We expect upscaling to larger areas to be considerably simpler than that for existing techniques, as wrinkling results in a macroscopic deformation process that is not limited in terms of substrate size. Using this approach, we demonstrate successful printing of aqueous solutions of polyelectrolytes and proteins. We study the effectiveness of the stamping process and its limits in terms of periodicities and heights of the stamps' topographical features. We find that critical wavelengths are well below 355 nm and critical amplitudes are below 40 nm and clarify the failure mechanism in this regime. This will permit further optimization of the approach in the future.

Polyelectrolytes are remarkable molecules because of their smart behavior. By altering the environmental pH value, polyelectrolytes can undergo conformational transitions, which, if controlled, enable a wide range of applications. Herein, we describe experiments whereby a polyacid gel and a polybase grafted to a silicon substrate can be used as a means of demonstrating reversible switching adhesion in aqueous solution. By changing the environmental pH value, we can control in situ whether the gel adheres to the grafted layer or whether it dissociates. Such control over adhesion may have applications in actuators, microfluidics, drug delivery, personal-care products, or even in the understanding of biological materials.If we consider nonpolyelectrolytic polymers, the adhesion between a grafted polymer layer (polymer brush) and a polymer network in the molten state is due to enthalpic interactions that force the brush into the gel as well as the entropy of the brush as it maximizes its conformations by forming a random or self-avoiding walk structure. As the brush is entangled between fixed cross-links, the only way for the brush and the network to come apart and disentangle is for the brush to diffuse along its own contour. [1][2][3][4] This is prohibited, all the more so given that all of the other grafted polymers would have to perform the same disentanglement at the same time. The only way to remove the adhesion is therefore to break bonds, leaving the system unusable.Polyelectrolytes in aqueous solution, however, often undergo a transition from a hydrophobic state, where they can collapse and fall out of solution, to an extended hydrophilic state. This property makes them useful as nanoactuators when they are attached to a surface. [5,6] The properties of hydrogels in good solvent conditions are perhaps even more dramatic, with swellings greater than an order of magnitude than in their dry state routinely observed. [7] We present herein a means of using the responsiveness to the pH value of polyelectrolytes to create reversible adhesion of two surfaces by studying the interaction of a poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA, a polybase) brush-modified surface with a poly(methacrylic acid) (PMAA) gel. The brush and gel were equilibrated in water (initially at pH 7), then brought into contact, where it was found that there was good adhesion between the brush and the gel, a result previously obtained for two oppositely charged polyelectrolyte gels.[8] (The gel will not adhere to a silicon substrate without the brush at any pH value.) At equilibrium, the PMAA gel is partially charged and swollen to 112 % of its collapsed mass at pH 2 (approximately 300 % of its dry mass). There is also expected to be some charge on the PDMAEMA [9] brush, the free polymer of which has a pK a value of approximately 7. The two components of the system should be oppositely charged at the pH value at which equilibrium was achieved (pH 5.8). However, even at pH values of between 3 and 7, there is good adhesion between the br...

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