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This article describes mild methods to directly assemble, functionalize, and pattern monolayers of undecylenic acid on hydrogen-terminated Si(111). These monolayers were assembled under very mild conditions from a neat solution of undecylenic acid containing 0.1 mol % 4-(decanoate)-2,2,6,6-tetramethylpiperidinooxy at room temperature without the need for UV light. Because of these mild conditions, monolayers exposing carboxylic acids could be assembled in one step without the need to protect the acid prior to its assembly. The monolayers were extensively characterized by horizontal attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle goniometry. The monolayers bonded to the silicon surface preferentially through the olefin with no detectable bonds between the carboxylic acids and silicon. The crystallinity of the monolayer was studied by infrared spectroscopy through the antisymmetric&sbd;va(CH2)&sbd;and symmetric&sbd;vs(CH2)&sbd;stretches for methylene. Because it is important for future applications to assemble functional surfaces, methods to react the acid-terminated monolayers with trifluoroacetic anhydride and triethylamine to yield a symmetric anhydride on the monolayer were studied. These anhydrides were reacted with a variety of milligram-quantity amines to yield amide-terminated surfaces. This method was general, and a variety of amines could be bonded to the monolayer. The stabilities of these monolayers upon exposure to ambient conditions and under a variety of solvents were described. Because patterned monolayers have found wide applications, we have developed methods to pattern 1-octadecylamine and poly(ethylenimine) on the micrometer scale using soft lithography. In addition, polymer brushes of polynorbornene with thicknesses from 32 to 150 nm were grown from monolayers patterned with the Grubbs' catalyst. The patterned surfaces were imaged by scanning electron microscopy, scanning probe microscopy, and ellipsometry to determine the thicknesses of the patterns and the fidelity of the method.

This paper describes the two-dimensional self-assembly of hexagonal plates at the interface between perfluorodecalin and water. The plates were prepared with five different permutations of hydrophobic and hydrophilic faces. The shapes and amplitudes of the menisci that form on the faces of the plates determine the magnitude of the lateral capillary forces through which they interact. The amplitudes of the menisci also influence&sbd;through their out-of-plane components&sbd;the position and orientation of the plate relative to the plane of the liquid−liquid interface. In these experiments, the plates were made of poly(dimethylsiloxane) (PDMS) (ρ = 1.05 g/cm³) containing aluminum oxide (ρ = 4.00 g/cm³); this dopant adjusted the density of the plates, the extent to which they sank into the liquid−liquid interface, and thus the structure of their menisci. The plates studied had densities of 1.05 to 1.86 g/cm³. This work complements previous papers (Bowden, N.; Choi I. S.; Grzybowski, B. A.; Whitesides, G. M. J. Am. Chem. Soc. 1999, 121, 5373. Bowden, N.; Oliver, S. R. J.; Whitesides, G. M. J. Phys. Chem. B 2000, 104, 2714.) that examined the assembly of hexagonal plates with densities at the extremes of the range studied. By following the structures of the aggregates formed at intermediate densities, it is possible to observe the way in which the self-assembling system transitions from an aggregate of one structure to that of another. The results from these studies are relevant to the design of micrometer-sized plates capable of self-assembly.

This paper reports a simple and versatile technique for generating structures on the surfaces of poly(dimethylsiloxane) (PDMS), approximately sinusoidal waves with periods between 0.1 and 10 μm, and the use of these structures to study cell contact guidance.¹ The features are generated by stretching PDMS slabs mechanically, oxidizing them in an oxygen plasma, and allowing them to relax. These surface features are similar to photolithographically fabricated grooves that have traditionally been used to investigate cell contact guidance, although their edges are rounded rather than angular. Bovine capillary endothelial cells align and elongate on these features. The morphology and cytoskeletal structure of the aligned cells are similar to those of cells described in previous studies of contact guidance on surfaces with other types of topography. These observations and comparisons indicate that sharp edges in the features defining the grooves are not essential in eliciting contact guidance. This technique provides a method for fabricating microfeatures for the studies of the interactions between cells and their environment that does not require a cleanroom or access to photolithographic tools.

Small (100−600 μm in width) hexagonal polymeric plates with faces patterned into hydrophobic and hydrophilic regions, and interacting through lateral capillary forces, were allowed to self-assemble at the perfluorodecalin/water interface. These plates were fabricated from photoresist and patterned by shadow evaporation of gold onto selected faces. The arrays that assembled from the 100 μm objects were similar in structure to those that assembled from millimeter-sized objects with analogous patterns of hydrophobic and hydrophilic faces, but with three important differences. (i) The contribution of buoyancy forces in establishing the level at which the 100 μm objects floated relative to the interface was small compared to the contribution of the vertical capillary forces. (ii) As a result, the designs of hydrophobic edges necessary to generate menisci useful in self-assembly were different for 100 μm objects than for millimeter-sized objects. (iii) The arrays that formed from the 100 μm objects had higher densities of defects than the arrays that formed from the millimeter-sized objects; these defects reflected the increase in the strength of the capillary forces (which favored assembly) relative to the shear forces (which disrupted assembly). This work adds two new elements to the study of mesoscale self-assembly:  (i) It describes a new method of fabrication of plates with faces patterned into regions of different hydrophobicity that is applicable to small (perhaps <10 μm) objects, and (ii) it describes the self-assembly of 100 μm plates made by this method into ordered arrays. The work also established the contours of the menisci on the separate 100 μm and millimeter-sized plates. The scaling of the lateral and vertical capillary forces and buoyancy forces acting on millimeter-sized objects, relative to those acting on 100 μm objects, is described.

This paper describes the spontaneous formation of patterns of aligned buckles in a thin film of gold deposited on the surface of an elastomer [poly(dimethylsiloxane), PDMS]. The surface of the elastomer is patterned photochemically into areas differing in stiffness and coefficient of thermal expansion. The gold is deposited while the surface of the patterned elastomer is warm (T ~ 100 °C). On cooling, shrinkage in the elastomer places the gold film under compressive stress. The buckles relieve this compressive stress. The distribution of stresses and buckle patterns is described during the pre- and postbuckling regimes using solutions from calculations describing a model comprising a thin stiff plate resting on a thick elastic foundation.