The vibrational spectra of (CH3)3SiX (S=H, F, Br) molecules, revisited Transferable scale factor sets for methylsilane derivatives

The joint experimental and theoretical study of the vibrational spectra of the molecular series (CH3)3SiX (with X=H, F and Br) is carried out. Data from newly recorded IR and Raman spectra for the bromo derivative, experimental data obtained previously for the remaining species, DFT theoretical calculations and the use of the SQMFF procedure have allowed us to propose common patterns and to unify criteria in their assignment. In addition, two sets of averaged scale factors for the B3LYP force field obtained with two different basis sets (6-31G* and DZP+diff) have been proposed for the common bulky moiety of that molecular series. These parameters were used successfully in order to reproduce the frequency of the bands assigned to the (CH3)3Si- group in the vibrational spectra of the corresponding silanolic and methoxy derivatives, i.e., trimethylsilanol and methoxytrimethylsilane, proving their transferability.     

Use of a MDI-functionalized reactive polymer for the manufacture of modified bitumen with enhanced properties for roofing applications

In this study, the suitability of a reactive polymer, synthesized by reaction of 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polyethylene-glycol (PEG), as a modifying agent for the manufacture of bitumen-based waterproof membranes, was evaluated. With that purpose, rheological and thermal analysis tests, and microstructural observations by AFM were carried out on different samples of modified bitumen having a MDI–PEG content ranging from 0 to 10 wt.%, cured at room temperature for a period of time within 0–30 days. The results obtained demonstrate that the addition of the reactive polymer proposed in this work to bitumen is very suitable at high in-service temperatures, because a noticeable increase in the values of viscosity, at 60 °C, of the resulting modified bitumen samples is observed on a time-scale of days. AFM observations, carried out at 50 °C, evidenced that the reactive polymer MDI–PEG leads to a new microstructure, displaying a higher level of stiffness. Therefore, this polymer should be seriously taken into consideration as a modifier of bituminous coatings for the waterproofing industry.     

Terpenes in the gas phase: The Far-IR spectrum of perillaldehyde

The far infrared spectrum of S-(-)-perillaldehyde, a monoterpene containing an aldehyde functional group, has been recorded in the gas phase using FTIR spectroscopy. The vibration signature of the three most populated rotamers has been observed and identified in the 30–650 cm^?1 range. The vibration assignment was based on the scaled B3LYP/cc-pVDZ harmonic force field of Partal Ureña et al., 2008 [10]. Anharmonic contributions calculated at the HF/6–31+G^? level were found negligible.     

Process rheokinetics and microstructure of recycled EVA/LDPE-modified bitumen

Knowledge of the kinetics of the manufacturing process of polymer–bitumen blends is of great interest because it provides information on the behaviour of the binder at different stages of the mixing operation, which is useful for the establishment of the optimum processing conditions, involving temperature and operation time. The purpose of this research was to study the evolution of the rheological properties and microstructure of a polymer-modified bitumen during its processing. A 60/70-penetration grade bitumen and recycled EVA/LDPE were mixed under different processing conditions. Measurements of the evolution of viscosity with time, at different temperatures and agitation speeds, were carried out with an experimental device known as ‘rheomixer’, that is, a helical ribbon impeller inside a mixing vessel coupled with the transducer and motor of a conventional rheometer. Under the experimental conditions selected (within the laminar region, Re<10), temperature is the most important processing variable. Hence, low agitation speeds and a processing temperature of around 180°C should be chosen for bitumen modification with the polymer used.     

Effect of pH and added electrolyte on the thermal-induced transitions of egg yolk

Thermally-induced transitions of egg yolk were studied using Differential Scanning Calorimetry (DSC) and temperature-controlled Small Amplitude Oscillatory Shear (SAOS). The influence of composition (pH and electrolyte content and type) was analysed. The results obtained under DSC measurements suggest a continuous evolution in protein denaturation that depends on pH and salt content. Cure experiments performed using SAOS show dramatic increases in viscoelasticity functions. Protein gelation is affected by the pH, ionic strength and salt type. SAOS was also used to obtain the mechanical spectra of egg yolk dispersions and gels as a function of composition. The microstructures of gels were also evaluated by Scanning Electron Microscopy (SEM). SEM results reveal an increase in microstructure homogeneity and a decrease in the size of aggregates at lowered pH. The influence of pH and ionic strength on linear viscoelastic properties and microstructure may be explained in terms of the model for the formation of gel networks of globular proteins. However, the characteristic structure of native yolk must also be considered.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Protein-based bioplastics: effect of thermo-mechanical processing

Bioplastics based on glycerol and different proteins (wheat gluten, albumen, rice and albumen/gluten blends) have been manufactured to determine the effect that processing and further thermal treatments exert on different thermo-mechanical properties of the bioplastics obtained. Oscillatory shear, modulated differential scanning calorimetry, dynamic mechanical thermal analysis, thermo-gravimetric analysis and water absorption tests were carried out to study the effect of processing on the physical characteristics of the bioplastics. The protein-based bioplastics studied in this work present a high capacity for thermosetting modification because of protein denaturation that may favour the development of a wide variety of materials. The use of albumen or rice protein allows the reduction in both protein concentration and thermosetting temperature, leading to linear viscoelastic moduli values similar to those of synthetic polymers such as LDPE and HDPE. The hygroscopic characteristics of protein-glycerol bioplastics may lead to a decrease in the values of the linear viscoelasticity functions. However, hygroscopic properties depend on the protein nature and may be used for industrial applications where water absorption is required. This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006.     

Chiral terpenes in different phases: <Emphasis Type="Italic">R</Emphasis>-(−)-camphorquinone studied by IR–Raman–VCD spectroscopies and theoretical calculations

R-(−)-camphorquinone is a bicyclical terpenoid with many usages and application in different fields. Different experimental and theoretical works reveal that there is only one stable conformer of this chiral chemical species in agreement to the sterical restriction that the bicycle introduces. In the current work, from a complete assignment of the vibrational IR and Raman spectra, we are able to explain the VCD spectrum of the title compound. The recorded spectra of R-(−)-camphorquinone in different phases have been analyzed and compared: the first one in CCl₄ solution, the second one using Nujol and Fluorolube suspensions and the third one using thin films. Finally, to study the coupling between the two C=O stretching normal modes, a NBO analysis is performed. The present work reveals that IR, Raman and VCD, combined with quantum chemical calculations, are helpful complementary techniques to characterize chiral systems, as terpenes, in different phases.     

Raman and IR spectra of the unstable ionic species potassium trimethylsilanolate: The role of the counterion in its theoretical interpretation

We have accomplished a reliable assignment of the vibrational spectra of the ionic species potassium trimethylsilanolate, which is unstable towards hydrolysis and self‐condensation, by means of the combined use of experimental data and theoretical density functional theory (DFT) calculations. We report the first record of the Raman spectrum of the pure solid. Additionally, we have newly recorded its IR spectrum in Nujol mull and for the first time in Fluorolube mull, completing the experimental data available in the literature about this chemical species. Further, in order to discuss the convenience of including the counterion in the model used for the quantum‐mechanical calculations of its vibrational spectra, we have compared the performance of three different theoretical models, namely, the isolated trimethylsilanolate anion, a theoretical monomer of potassium trimethylsilanolate and a simplified ionic cluster model based on its crystalline structure. Copyright © 2007 John Wiley & Sons, Ltd.     

Rheology and microstructure of asphalt binders

The viscous and linear viscoelastic properties of different asphalt binders have been analyzed in this paper. Thus, an unmodified bitumen, a polymer-modified (SBS) bitumen, a commercial synthetic binder, and two model synthetic binders with different polymer (SBS) concentrations have been studied. The mechanical spectra of these binders are quite different, mainly influenced by SBS concentration. Thus, up to three regions may be observed for a synthetic binder with high polymer concentration. The temperature dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that depends on binder composition. These results have been discussed taking into account the development of a polymer-rich phase in SBS-modified bitumen and model synthetic binders. Received: 6 February 2000 Accepted: 8 August 2000