Volumetric Properties of Binary Mixtures of Isomeric Butanols and C8 Solvents at 298.15 K

Excess molar volumes, V _m ^E, over the whole composition range for binary mixtures of 1-butanol, 2-butanol, and 2-methyl-2-propanol + 1-octanol, or 2-octanol, or di-n-butyl ether, or n-hexylacetate were determined at 298.15 K from density measurements carried out with a vibrating-tube densimeter. Small V _m ^E values, both positive and negative, are displayed by mixtures containing 1- or 2-octanol, whereas positive and larger values are always found for mixtures containing dibutyl ether and hexylacetate. These results can be justified in terms of H-bonding interactions and/or steric hindrance due to the branched alkyl chains. Partial molar volumes at infinite dilution of the isomeric butanols in the C8 compounds were also calculated from the apparent molar volumes in dilute solution. The solute-solvent interactions and the effects of the local organisation of the solvent around the butanol molecules were discussed using the void and cavity volumes as different estimates of the intrinsic volume of the molecules. The volumetric behavior of butanols seems to be determined by the solute-solvent interactions rather than packaging effects.     

Thermal and structural investigation of random ethylene/1-hexene copolymers with high 1-hexene content

Random ethylene/1-hexene copolymers with the 1-hexene content in the range from 2 to 28 mol% were produced with a novel post-metallocene catalyst and analyzed by three techniques, FTIR, ¹³C NMR, and DSC. The 1-hexene content and the sequence distribution in the copolymers were determined by means of FTIR-M and ¹³C NMR. The crystallization behavior of the copolymers was studied by DSC under dynamic and isothermal conditions; the Avrami model was used to analyze the crystallization kinetics. It was found that both the 1-hexene content and the crystallization temperature affect the relative crystallinity. The bulk crystallization rate decreases with the 1-hexene content and reduces exponentially with an increase of T _c. The melting behavior of isothermally crystallized samples was also investigated and it was found that the melting temperatures of the copolymers under equilibrium conditions were related to the composition.     

Predicting physical-chemical properties of compounds from molecular structures by recursive neural networks

In this paper, we report on the potential of a recently developed neural network for structures applied to the prediction of physical chemical properties of compounds. The proposed recursive neural network (RecNN) model is able to directly take as input a structured representation of the molecule and to model a direct and adaptive relationship between the molecular structure and target property. Therefore, it combines in a learning system the flexibility and general advantages of a neural network model with the representational power of a structured domain. As a result, a completely new approach to quantitative structure-activity relationship/quantitative structure-property relationship (QSPR/QSAR) analysis is obtained. An original representation of the molecular structures has been developed accounting for both the occurrence of specific atoms/groups and the topological relationships among them. Gibbs free energy of solvation in water, Delta(solv)G degrees , has been chosen as a benchmark for the model. The different approaches proposed in the literature for the prediction of this property have been reconsidered from a general perspective. The advantages of RecNN as a suitable tool for the automatization of fundamental parts of the QSPR/QSAR analysis have been highlighted. The RecNN model has been applied to the analysis of the Delta(solv)G degrees in water of 138 monofunctional acyclic organic compounds and tested on an external data set of 33 compounds. As a result of the statistical analysis, we obtained, for the predictive accuracy estimated on the test set, correlation coefficient R = 0.9985, standard deviation S = 0.68 kJ mol(-1), and mean absolute error MAE = 0.46 kJ mol(-1). The inherent ability of RecNN to abstract chemical knowledge through the adaptive learning process has been investigated by principal components analysis of the internal representations computed by the network. It has been found that the model recognizes the chemical compounds on the basis of a nontrivial combination of their chemical structure and target property.     

Enthalpies of Solution of Organic Compounds inWater/Octan-1-ol Mixtures. A Rationale Based ona Model of Structural Organization of the SolventMedium

Limiting enthalpies of solution _solnH°(oct/w) of several monofunctionalcompounds (tetrahydropyran, diethylamine, pyrrolidine, piperidine,1-methylpiperidine) in water–octan-1-ol mixtures with water content ranging from zero tosaturation have been determined at 25°C. The observed phenomenology hasbeen interpreted by supposing that the solvent medium undergoes a microphasetransition at water mole fraction of about 0.08. In the water-poor region theexperimental behavior is consistent with the presence of water molecules inprevailingly monodispersed form, while in the water-rich region the formationof organized pseudomicellar water aggregates is suggested. Two different simplemodels have also been proposed to describe quantitatively the observed trendsof _solnH°(oct/w) vs. mole fraction of water.Deceased while this research was in progress. The coauthors wish to dedicate this work to his memory     

Analysis of physical and chemical networks by slow DSC and turbidimetry

Semicrystalline polymers are made of a crystalline phase and of an amorphous phase. Recently, NMR, Raman and FTIR experiments have identified a third phase comprised of defects such as tie-molecules, in the organization of chains. Our investigation of physical gels has led us to believe that by following the heat flow in a very slow temperature ramp (0.05 K min^?1), phasechanges, unnoticed in the usual fast ramp, could be detected. These are associated to a physical network strained in the temperature ramp. In order to obtain more information on the network phase, the polymer has been crosslinked The characteristics obtained by slow calorimetry and turbidimetry of the original and modified materials are compared.     

Interactions between inorganic pigments and rabbit skin glue in reference paint reconstructions

Journal of Thermal Analysis and Calorimetry - The thermal degradation of rabbit skin glue, a collagen-based proteinaceous material used as a paint binder in paintings, was investigated in this...     

Effect of substrate interactions on the melting behavior of thin polyethylene films

Polymer films have been known to change their physical properties when film thickness is decreased below a certain value. The cause of this phenomenon is still unclear but it has been suggested that interactions and/or chain free-volume changes at the surface of the films are largely responsible for this behavior. In this paper, the effect of substrate interactions on the behavior of polymer thin films is evaluated quantitatively. The infrared spectra of nanothin polyethylene (PE) films were recorded as a function of temperature and amount of substrate covering the surface of the film. The evolution of specific bands in the CH₂ rocking region of the spectra was used to determine the melting temperature (T _m ) of the material. Results show different variations in T _m depending on the nature of the substrate, indicating that interactions dominate free-volume considerations in PE thin films. By varying the amount of surface coverage, a quantitative estimate of the heat of interaction was determined, which confirmed the importance of surface interactions.     

Double‐helical network in amylose as seen by slow calorimetry and FTIR

The phase content and crystallinity of initially amorphous amylose–water mixtures (70/30 W/W) have been changed by slow cycles of dissolution and recrystallization from T_max with 50 °C < T_max < 120 °C. Analysis of the treatment‐induced changes is made by X‐ray diffraction, FTIR, fast T‐ramp DSC and slow calorimetry. Our interest was to follow the relaxation of the network phase and its consequence on the growth of crystallinity. The DSC technique, which gives the temperature of disappearance of long‐range order, is unable to quantitatively follow the growth of crystallinity achieved by treating the samples. In highly interactive polymer–solvent systems, order is unmeltable in a fast T‐ramp due to strain developed during the ramp. In a 6 K/h T‐ramp, the order becomes meltable and grows from 21 J/g to 147 J/g when T_max increases. The other conclusion is that strain‐melting and the network phase, characterized first in polyolefins has a more prominent role in the characterization of H‐bonded polysaccharide–water mixtures. Correlation is achieved between the concentration of bands in the C O stretching region, the fraction of single and double helices, and the three endotherms found on the slow T‐ramp dissolution traces. FTIR spectra show that chains in the network cannot be disentangled by quenching but can be organized during a slow cooling. The B and V crystalline modifications are observed in the treated samples. Quenched treated amylose and enzyme‐resistant amylose seem to contain a comparable amount of double‐helical/strainable fraction. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1662–1677, 2000     

Excess Molar Enthalpies and Excess Molar Volumes of (Water+Octan-1-ol or +Octan-2-ol) at 298.15 K

The excess molar enthalpies and volumes have been determined for the binary system (water+octan-1-ol or +octan-2-ol) by means of direct calorimetric and densimetric measurements in the miscibility range. The experimental data were described through a Redlich-Kister type equation. For excess enthalpies a sigmoidal shape is predicted,while excess volumes are negative except for a little positive queue observed for(water+octan-1-ol) system at very low water content. Also the partial molar enthalpies of solution and the partial molar volumes of water in the two isomeric octanols at infinite dilution have been evaluated and discussed. A comparison is made between excess enthalpies and excess free energies calculated by the UNIFAC method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aggregation of cesium perfluorooctanoate on poly(ethylene glycol) oligomers in water

The interaction of cesium perfluorooctanoate (CsPFO) with poly(ethylene glycol) (PEG) of different molecular weight (300 < or = MW < or = 20000 Da) has been investigated at 298.15 K by isothermal titration calorimetry (ITC), density, viscosity, and conductivity measurements. Calorimetric titrations exhibited peculiar trends analogous to those already observed for sodium dodecyl sulfate (SDS). Micelles of the perfluorosurfactant, as compared to those of SDS, yield complexes with the polymer of similar thermodynamic stability but are able to interact with shorter PEG oligomers. The average number of surfactant molecules bonded per polymer chain at the saturation is about twice that observed for SDS. ITC data at 308.15 K indicate a larger thermodynamic stability of the aggregates but an almost constant stoichiometry. The peculiar thermal effects and the viscosity trend observed during the titration of an aqueous PEG solution with the surfactant appear consistent with a conformational change of the polymer. The PEG chain would evolve from a strained to an expanded conformation, induced by the growing of the surfactant micellar clusters bonded to the polymer, as suggested in a previous study of the PEG/SDS/H2O system.