Materials-based process tolerances for neutron generator encapsulation.

Variations in the neutron generator encapsulation process can affect functionality. However, instead of following the historical path in which the effects of process variations are assessed directly through functional tests, this study examines how material properties key to generator functionality correlate with process variations. The results of this type of investigation will be applicable to all generators and can provide insight on the most profitable paths to process and material improvements. Surprisingly, the results at this point imply that the process is quite robust, and many of the current process tolerances are perhaps overly restrictive. The good news lies in the fact that our current process ensures reproducible material properties. The bad new lies in the fact that it would be difficult to solve functional problems by changes in the process

Introduction: Shakespeare's public spheres

Habermas’ sense of a “cultural Public Sphere” is a notoriously complex term and, when applied to Early Modern cultures, needs careful definition. This essay both introduces the variety of methods by which we might approach playtexts with a view to their public – auditory – impact and contributes to a debate about an audience's understanding of Shakespeare's plays. By selecting two words and their spread of use in one play, Twelfth Night, we might appreciate the potential for meaningful ambiguity latent in how we hear the language of live performance. If we search for how certain terms (in this case, the cluster of semes derived from repetitions of “fancy” and “play”), we might find at times incompatible senses, yet we get near to appreciating the range of Early Modern dramatic language

Autonomic Healing of Epoxy Using Micro-Encapsulated Dicyclopentadiene

The autonomic healing ability of an epoxy adhesive containing micro-encapsulated dicyclopentadiene (DCPD) was evaluated. The epoxy resin used was Epon 828 cured with either Versamid 140 or diethylenetriamine (DETA). Variables included total weight percent of microcapsules (MCs) and catalyst, as well as the catalyst to DCPD ratio. The degree of healing was determined by the fracture toughness before and after ''healing'' using double-cantilever beam analysis. It was found that the degree of self-healing was most directly related to the contact area (i.e. crack width) during healing. Temperature also played a significant role. Observed differences between the results of this study and those in literature are discussed

Stress Relaxation in Epoxy Thermosets via a Ferrocene-Based Amine Curing Agent

Physical stress relaxation in rubbery, thermoset polymers is limited by cross-links, which impede segmental motion and restrict relaxation to network defects, such as chain ends. In parallel, the cure shrinkage associated with thermoset polymerizations leads to the development of internal residual stress that cannot be effectively relaxed. Recent strategies have reduced or eliminated such cure stress in thermoset polymers largely by exploiting chemical relaxation processes, wherein temporary cross-links or otherwise transient bonds are incorporated into the polymer network. Here, we explore an alternative approach, wherein physical relaxation is enhanced by the incorporation of organometallic sandwich moieties into the backbone of the polymer network. A standard epoxy resin is cured with a diamine derivative of ferrocene and compared to conventional diamine curing agents. The ferrocene-based thermoset is clearly distinguished from the conventional materials by reduced cure stress with increasing cure temperature as well as unique stress relaxation behavior above its glass transition in the fully cured state. The relaxation experiments exhibit features characteristic of a physical relaxation process. Furthermore, the cure stress is observed to vanish precipitously upon deliberate introduction of network defects through an increasing imbalance of epoxy and amine functional groups. We postulate that these beneficial properties arise from fluxional motion of the cyclopentadienyl ligands on the polymer backbone

Multilayer co-extrusion technique for developing high energy density organic devices.

The purpose of this project is to develop multi-layered co-extrusion (MLCE) capabilities at Sandia National Laboratories to produce multifunctional polymeric structures. Multi-layered structures containing layers of alternating electrical, mechanical, optical, or structural properties can be applied to a variety of potential applications including energy storage, optics, sensors, mechanical, and barrier applications relevant to the internal and external community. To obtain the desired properties, fillers must be added to the polymer materials that are much smaller than the end layer thickness. We developed two filled polymer systems, one for conductive layers and one for dielectric layers and demonstrated the potential for using MLCE to manufacture capacitors. We also developed numerical models to help determine the material and processing parameters that impact processing and layer stability