Acrylamide (C3H5NO), a hydrogen‐bonded amide, is an important compound from the point of view of basic and material research. It can be used as a model system for studying hydrogen bonding interactions in amides under pressure. As it is a monomer of polyacrylamide, an important polymer, high pressure investigation of polymerization in this material is also of interest. Our in‐situ high pressure Raman spectroscopic investigations of acrylamide carried out up to 17 GPa under quasi‐hydrostatic conditions indicate possible structural variations through the reconstruction of the N‐H‐‐‐O hydrogen bonds at pressures above 2.6 GPa. Emergence of several new spectral features at higher pressures indicate onset of polymerization. The characteristic polymer band becomes discernible at ~17 GPa. The increase in the relative intensity of the polymer peaks with respect to the monomer peaks on release to ambient conditions suggests that higher fraction of polymer is obtained on decompression. Copyright © 2013 John Wiley & Sons, Ltd.
Experimental and numerical studies of slurry generation using a cooling slope are presented in the paper. The slope having stainless steel body has been designed and constructed to produce semisolid A356 Al alloy slurry. The pouring temperature of molten metal, slope angle of the cooling slope and slope wall temperature were varied during the experiment. A multiphase numerical model, considering liquid metal and air, has been developed to simulate the liquid metal flow along the cooling channel using an Eulerian two-phase flow approach. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling channel following Schiel's equation. The continuity, momentum and energy equations are solved considering thin wall boundary condition approach. During solidification of the melt, based on the liquid fraction and latent heat of the alloy, temperature of the alloy is modified continuously by introducing a modified temperature recovery method. Numerical simulations has been carried out for semisolid slurry formation by varying the process parameters such as angle of the cooling slope, cooling slope wall temperature and melt superheat temperature, to understand the effect of process variables on cooling slope semisolid slurry generation process such as temperature distribution, velocity distribution and solid fraction of the solidifying melt. Experimental validation performed for some chosen cases reveals good agreement with the numerical simulations.
Recent spectroscopic investigations of various amino acids report intriguing high-pressure and low-temperature behavior of NH 3 + groups and their influence on various hydrogen bonds in the system. In particular, the variation of the intensity of NH 3 + torsional mode at different temperatures and pressures has received much attention. We report here the first in situ Raman investigations of fully deuterated α-glycine up to ∼20 GPa. The discontinuous changes in COO − and ND 3 + modes across ∼3 GPa indicate subtle structural rearrangements in fully deuterated α-glycine. The decrease in the intensity of ND 3 + torsional mode is found to be similar to that of undeuterated α-glycine. The pressure-induced stiffening of N-D and CD 2 stretching modes are discussed in the context of changes in the hydrogen-bonding interactions.
Imidazole (C3H4N2) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with ab initio calculations on crystalline imidazole suggest that C-H---X (X = N, π) and N-H---N intermolecular hydrogen bonding interactions largely influence the nature of its structural and polymeric transformations under pressure. At pressures around ∼10 GPa, the reduction in the N---N distances close to the symmetrization limit and the emergence of the spectral features of the cationic form indicate the onset of proton disorder. The pressure-induced strengthening of the "blue-shifting hydrogen bonds" C-H---X (X = N, π) in this compound is revealed by the Raman spectra and the ab initio calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.
The viscoelastic behavior of brominated isobutylene‐co‐p‐methylstyrene (BIMS) rubber/hydrocarbon resin blends and BIMS/phenol formaldehyde resin blends was studied with the use of a rubber process analyzer. Dynamic mechanical analysis and scanning electron microscopy were used to evaluate the compatibility between the BIMS/tackifier blends. Strain sweep tests at temperature below the softening point of the tackifiers showed the formation of resin–resin networks in the incompatible BIMS/phenolic resin blends. However, resin–resin network was not prominent in the case of the compatible BIMS/hydrocarbon resin blends. Frequency sweep tests were performed at the strain amplitude within the linear region at several temperatures and the variations of shear storage modulus, G′ and complex viscosity, η* against frequency were recorded. The tackifying resins modified the viscoelastic properties of the BIMS rubber by reducing the storage modulus at lower frequency and by increasing the storage modulus at higher frequencies. However, this action was found to be highly dependent on (a) rubber‐tackifier compatibility, (b) blend proportions, and (c) test temperature. Furthermore, stress relaxation measurements of the BIMS/tackifier blends at temperature below the softening point of the tackifiers showed longer period of relaxation for the incompatible BIMS/phenolic resin blends. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
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