A polystyrene−poly(ethylene oxide) containing diblock copolymer, when spread at the air/water interface, spontaneously forms surface aggregates. This surface aggregation is shown to be neither compression-induced, associated with micellization in the spreading solvent, nor induced by the Langmuir−Blodgett film transfer process. We have previously found that such two-dimensional surface aggregation occurs for diblock copolymers with a polystyrene block and a hydrophilic block of quaternized poly(vinylpyridine), poly(tert-butyl acrylate), poly(n-butyl acrylate), or poly(dimethylsiloxane). The phenomenon has also been observed in films of polystyrene−poly(methyl methacrylate) by Rice and co-workers. Indeed, whenever an appropriate imaging technique has been used, phase-separated domains with 30−100 nm length scales have been observed, when amphiphilic diblock copolymers are spread at the air/water interface and transferred to solid substrates at appreciable surface pressures. We therefore believe that the formation of surface aggregates (often well defined) is a general phenomenon for hydrophobic−hydrophilic diblock copolymers. The implications of this phenomenon for the study of diblock copolymers at the air/water interface are discussed, particularly in relation to studies using techniques which report properties averaged over the lateral dimensions of the film in question, such as specular neutron reflectivity, specular X-ray reflectivity, and Brewster angle microscopy.

This paper examines the economics of substituting tube-hydroformed parts for stamped assemblies. Tube hydroforming has been heralded for its ability to decrease weight and increase stiffness compared with stamped solutions. The economics of this substitution question is examined in three case studies where tube-hydroformed components have replaced stampings using technical cost modeling, a technique developed at the Massachusetts Institute of Technology. The cases illustrate different factors that influence the relative cost of tube hydroforming compared to stamping.