No abstract

The glass transition temperature (Tg) of layers of stereoregular poly(methyl methacrylate) (PMMA) spin-cast on silicon and aluminum surfaces has been investigated by ellipsometry. The interfacial specific interactions were highlighted and quantified by infrared reflection absorption spectroscopy. It was found that depending on PMMA tacticity, a strong correlation exists between the density of the polymer/surface interactions and the Tg of that polymer at the interface. Indeed, i-PMMA with a large density of interfacial interactions increases its Tg at the interface whereas s-PMMA with a lower value of bonded segments exhibits a Tg depression. It is suggested that a certain level of interfacial interactions associated with an increase of density of the layer will compensate for the increase of mobility resulting from a reduction of the entanglement density or a segregation of chain ends at an interface.

No abstract

While maintaining anatomical integrity, matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) has allowed researchers to directly probe tissue, map the distribution of analytes and elucidate molecular structure with minimal preparation. MALDI-ion mobility (IM)-orthogonal time-of-flight mass spectrometry (oTOFMS) provides an advantage by initially separating different classes of biomolecules such as lipids, peptides, and nucleotides by their IM drift times prior to mass analysis. In the present work the distribution of phosphatidlycholine and cerebroside species was mapped from 16 μm thick coronal rat brain sections using MALDI-IMoTOFMS. Furthermore, the use of gold nanoparticles as a matrix enables detection of cerebrosides, which although highly concentrated in brain tissue, are not easily observed as positive ions because of intense signals from lipids such as phosphatidlycholines and sphingomyelins.