Stress-sensing in flexible epoxy adhesives

In mechanochemistry, mechanical force causes a chemical change using small molecules, called mechanophores, by covalently connecting them into polymer materials. Stress-sensing mechanophores give a visual signal of mechanical force on the molecular level within a material. To our knowledge, stress-sensing mechanophores have never been incorporated into a commercially available epoxy kit. In this work, the characterization of two 3MTM Scotch-Weld TM Epoxy Adhesive kits: DP100 Plus Clear and DP190 Translucent have been completed through FT-IR Spectroscopy. The addition of the mechanophore spiropyran to the 3M kits will be discussed; as well as preparation and characterization of three dimerized anthracene derivatives. Our strategy is to synthesize a mechanophore crosslinker and add it into a two-part epoxy adhesive material, taking advantage of the existing cross-linking reaction to covalently incorporate it into the material; with the goal of using it to characterize the relationship between external strain and molecular-level force

More is the Same; Phase Transitions and Mean Field Theories

This paper looks at the early theory of phase transitions. It considers a group of related concepts derived from condensed matter and statistical physics. The key technical ideas here go under the names of "singularity", "order parameter", "mean field theory", and "variational method". In a less technical vein, the question here is how can matter, ordinary matter, support a diversity of forms. We see this diversity each time we observe ice in contact with liquid water or see water vapor, "steam", come up from a pot of heated water. Different phases can be qualitatively different in that walking on ice is well within human capacity, but walking on liquid water is proverbially forbidden to ordinary humans. These differences have been apparent to humankind for millennia, but only brought within the domain of scientific understanding since the 1880s. A phase transition is a change from one behavior to another. A first order phase transition involves a discontinuous jump in a some statistical variable of the system. The discontinuous property is called the order parameter. Each phase transitions has its own order parameter that range over a tremendous variety of physical properties. These properties include the density of a liquid gas transition, the magnetization in a ferromagnet, the size of a connected cluster in a percolation transition, and a condensate wave function in a superfluid or superconductor. A continuous transition occurs when that jump approaches zero. This note is about statistical mechanics and the development of mean field theory as a basis for a partial understanding of this phenomenon.Comment: 25 pages, 6 figure

Telemediations

Postprin

Muriel Rukeyser, America, and the “Melville Revival”

Whilst Muriel Rukeyser's poetic affinity with Walt Whitman is generally acknowledged, the close relation of her work and poetic sensibility to the thought and writing of Herman Melville has somehow gone relatively unnoticed, and almost wholly unexamined. In 1918, Van Wyck Brooks called for the creation of a usable past that would energize America by recasting its cultural tradition. His plea addressed the need to rebuild a national heritage via the rediscovery of culturally "great" figures. By the late 1930s, many scholars and writers had answered the call, and the new discipline of American studies was beginning to take shape, aided by a reclamation of one of the country's greatest, most neglected, writers - Herman Melville. This was also the period in which Rukeyser "came of age"; a time when political and international conflicts and economic crises generated both the stark, documentary representation of present social realities and the drive to retrieve or reconstruct a more golden age that might mobilize a dislocated nation. The following article examines the importance of Melville to Rukeyser's work, and situates her within the "Melville revival" as an important figure in the movement throughout the first half of the twentieth century to reconstruct an American cultural character

Gas-phase studies of phosphenium ions as chemical ionization reagents for the differentiation of diastereomeric organic substrates in a Fourier transform ion cyclotron resonance mass spectrometer

There exists a need in the pharmaceutical industry for a simple and rapid method to differentiate stereoisomeric compounds. As a result, a great deal of research has been devoted to developing such a method. It was once believed that mass spectrometry could not provide differentiation of stereoisomers because the most widely used ionization method, electron impact ionization (EI), is insensitive to the stereochemistry of molecules. The work presented in this thesis demonstrates that a chemical ionization (CI) method based on phosphenium ions can be used to rapidly differentiate certain diastereomeric organic substrates in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Both acyclic and cyclic phosphenium ions were used in these studies. When the phosphenium ions were allowed to react with certain substrates, unique reaction products were observed for only one of the isomers of a diastereomeric pair. Structural characterization was performed for some of the most interesting products formed during these reactions. Molecular orbital calculations were also utilized to acquire a better understanding of some of the experimental results