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.

This work aims at establishing a link between process conditions and resulting micromechanical properties for aminoplast core/shell microcapsules. The investigated capsules were produced by the in situ polymerization of melamine formaldehyde resins, which represents a widely used and industrially relevant approach in the field of microencapsulation. Within our study, we present a quantitative morphological analysis of the capsules' size and shell thickness. The diameter of the investigated capsules ranged from 10 to 50 μm and the shell thickness was found in a range between 50 and 200 nm. As key parameter for the control of the shell thickness, we identified the amount of amino resin per total surface area of the dispersed phase. Mechanical properties were investigated using small deformations on the order of the shell thickness by atomic force microscopy with a colloidal probe setup. The obtained capsule stiffness increased with an increasing shell thickness from 2 to 30 N/m and thus showed the same trend on the process parameters as the shell thickness. A simple analytical model was adopted to explain the relation between capsules' geometry and mechanics and to estimate the elastic modulus of the shell about 1.7 GPa. Thus, this work provides strategies for a rational design of microcapsule mechanics.

Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorganic environments, as exemplified by the existence of so-called "silicacarbonate biomorphs". These peculiar objects form upon coprecipitation of barium carbonate with silica and self-assemble into aggregates of highly oriented, uniform nanocrystals, displaying intricate noncrystallographic morphologies such as flat sheets and helicoidal filaments. While the driving force steering ordered mineralization on the nanoscale has recently been identified, the factors governing the development of curved forms on global scales are still inadequately understood. In the present work, we have investigated the circumstances that lead to the expression of smooth curvature in these systems and propose a scenario that may explain the observed morphologies. Detailed studies of the growth behavior show that morphogenesis takes crucial advantage of reduced nucleation barriers at both extrinsic and intrinsic surfaces. That is, sheets grow in a quasi-two-dimensional fashion because they spread across interfaces such as walls or the solution surface. In turn, twisted forms emerge when there is no foreign surface to grow on, such that the evolving aggregates curve back on themselves in order to use their own as a substrate. These hypotheses are corroborated by experiments with micropatterned surfaces, which show that the morphological selection intimately depends on the topology of the offered substrate. Finally, we demonstrate that, with the aid of suitable template patterns, it is possible to directly mold the shape (and size) of silica biomorphs and thus gain polycrystalline materials with predefined morphologies and complex structures.

Tailoring rheological properties of colloidal suspensions with the adsorption of polyelectrolyte multilayers (PEMs) is based on the idea of controlling macroscopic mechanical properties by modifying the particle surface in a reproducible and well-understood manner. With layer-by-layer self-assembly, monodisperse polystyrene particles are coated with up to ten layers of the oppositely charged strong polyelectrolytes: poly(diallyl dimethyl ammonium chloride) and poly(styrene sulfonate). The conformation of the adsorbed polyelectrolyte is controlled by the ionic strength of the used aqueous polyelectrolyte solution. For 1M NaCl solution, a brushlike adsorption of the polyelectrolyte is expected. The ability of PEMs to serve on a nanoscale level as surface modifiers and influence macroscopic rheological properties like viscoelasticity, yield stress, and shear banding is discussed. The mechanical behavior of these suspensions is qualitatively described by the theory of Derjaguin-Landau-Verwey-Overbeek with short-range repulsion and long-range attraction. A scaling rule is proposed which distinguishes between the precusor and the multilayer regime.

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