Search

In materials research area, nanotechnology brings new opportunities for sustainable uses and applications of high-value bio-based materials from wood, forest, and agroindustrial residues. The merging of nanotechnology and lignocellulosic biomass utilization is expected to enhance industry’s ability to produce consumer goods from lignocellulosic-based material in an improved manner. This was demonstrated in this chapter by some Latin American research groups, which obtained lignocellulosic nanostructures using different approaches and the quite diverse natural resources of the region but considering, in most of the cases, mainly agroindustrial wastes. In this sense, although hierarchical and diverse structures were present in the starting materials, the research groups were able to develop advances in chemical and mechanical nanostructure preparation techniques. In general, considering applications, the nanostructures obtained were used as a reinforcing phase in composites and films, as well as fillers. Some of this work demonstrated important advantages and improvement on the mechanical and barrier properties of materials. Nevertheless, research on the effect of the fabrication methodology used on the morphology and degree of crystallinity of the resulting nanostructures is important to understand since these structural characteristics are important for their physicochemical function. Based on all the data presented in this chapter, we conclude that it is possible to use diverse natural resources to obtain lignocellulosic nanostructures with suitable size, shape/morphology, crystallinity, and aspect ratio and that they could become a very efficient system for designing and developing new bio-based nanomaterials.

We report a theoretical study of the properties of the molecular oxygen trimer in its state of maximum spin multiplicity. The most stable structures for the complex were found using an accurate pair potential. Independent ab initio calculations on the trimer for selected geometries demonstrate the validity of this approximation and thus the small contribution of three-body effects. The three lowest structures found can be rationalized on the basis of the most stable dimer structures and possess C 2, D 3 and C 2v point symmetries. The two lowest-lying structures are separated by only 0.6 meV and zero-point energy effects, which are sizable, reduce even further the gaps among the three structures studied. Diffusion Monte Carlo calculations indicate that the ground state vibrational wavefunction is mainly located around the C 2 structure but also explores the D 3 minimum, yielding a near oblate symmetric top with a binding energy of 32.1 meV. © 2011 Elsevier B.V. All rights reserved., Work supported by Ministerio de Ciencia e Innovación (Spain, Grant FIS2010-22064-C02-02). R.H.L. was supported by Conacyt (Mexico, Ref. 126608). J.P.-R. is a JAE CSIC predoctoral fellow. We also thank CESGA (Spain) for allocation of computing time.

A one-dimensional model was built to simulate the non-steady radial combustion propagation on thin circular samples of Fe 2 O 3 /Aluminum thermite mixtures. The model considers zero order kinetics and conductive/radiative heat transfer. All the properties of the system are assumed to vary with the temperature and composition during the propagation and phase transitions are also contemplated. These features, not yet considered in the literature, allowed the obtainment of realistic solutions, readily comparable with experimental values measured in an earlier work. The experimental combustion velocities were used to adjust the kinetic constant of the model, in order to give it a good predictive capability. The predicted combustion temperatures and reaction extents were higher than the experimental. This was justified by the heat losses due to the spraying of products away from the combustion system and the incompleteness of the reaction, observed in experimental conditions and not considered in the model.

8 pags. ; 5 figs., A new ab initio potential energy surface for the ground singlet state of the O2 þO2 system has been calculated. Good agreement with experiment is obtained for the van der Waals binding energy. The vibrational dependence of the potential, crucial for vibrational energy transfer studies, is analyzed and compared with other potential energy surfaces by performing quantum scattering calculations of the vibrational relaxation of O2ðvÞ. 2002 Elsevier Science B.V. All rights reserved., The financial support of the Ministerio de Ciencia y Tecnolog ııa (Spain) under contract BFM2001-2179 is gratefully acknowledged. We also acknowledge the support of the EC Research Network HPRN-CT-1999-00005. RHL would like to thank the Ministerio de Educacioon, Cultura y Deporte for a sabbatical scholarship and CONACYT for financial support through grant 34464-E and a sabbatical fellowship.

Several time-dependent quantum and hybrid methods are applied to study the dissociation dynamics of tri- and tetra-atomic van der Waals complexes, formed by a diatomic molecule and one or two rare gas atoms. Beginning with >exact> formulations of the wave packet propagation, using grid or channel descriptions, some approximations as reduction of dimensionality or >mean field> treatments are included. Also, hybrid procedures combining either simultaneously or sequentially Classical and Quantum Mechanics, are presented and discussed. © 2002 Elsevier Science B.V. All rights reserved., The financial support of the DGICYT (Spain) under contract PB95-0071 is gratefully acknowledged. We also acknowledge the support of the EC Research Network HPRN-CT-1999-00005.

We present a four degrees of freedom model that accounts for all possible fragmentation mechanisms in the vibrational predissociation of the Ne2I2 van der Waals cluster. Calculations are performed by wave packet propagation and results are interpreted in terms of an analytical sequential model leading to a good agreement with experimental data. © 1995., This work was supported by DGICYT Grant No. PB92-0053 and Comunidad Autonoma de Madrid Grant No. 064192.

The close coupled equations in the T-shape configuration for the collision {A figure is presented} have been solved numerically on the two lowest potential surfaces of the system Na-N2. We have taken the potential surfaces in the bibliography and the coupling was modelled by a gaussian function centered in the crossing points. Different sets of parameters for the coupling were used in order to study final distributions of the N2 molecule. We present also the vibrational probabilities as a function of the initial relative kinetic energy. © 1986.

Metastable energy levels and rates for vibrational predissociation of NeCl2 (B, v1 = 11) complex are investigated. The potential energy surface is represented by the sum of atom-atom pairwise interactions. Due to the large vibrational spacing of Cl2 (B), a diabatic distorted-wave approximation is used to describe diatomic vibrations. Discrete energy levels are then calculated by separating adiabatically the fast stretching motion in the weak bond from the slow rotational motions within the complex. Continuum states are described in the >infinite order sudden> (I.O.S.) approximation, and rates for vibrational predissociation are evaluated using the corresponding discrete-continuum potential couplings in the frame of the Fermi's golden rule. © 1988.