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Cluster (or island) statistics and topological statistical mechanics based properties were employed in the analyses of hydrogen bond (H-bond) networks of t-butanol, n-butanol and ammonia aqueous solutions. These networks were generated from equilibrated Monte Carlo simulations at mixture compositions covering the entire range of miscibility and a fine grid of points around the topological transitions. We found that these H-bond networks changed from a percolation regime in water rich mixtures to a non-percolating behavior at non-aqueous component rich compositions. Topological analysis of local (clustering coefficients, average degrees) semi-global (path lengths) and global (spectral densities) properties indicated the presence of small-world patterns for the H-bond networks in mixtures at mole fraction compositions larger than ca. 0.6. These small-world patterns are characterized by highly clustered networks with small path lengths. Spectral densities show high order moment contributions that correlate with small-world patterns, thus corroborating the robustness of these statistical mechanics based topological analyses. The degree distributions of these networks were partially rationalized by the differences in the water-water and solute-solute H-bonds.

Statistical mechanics based topological analysis and island (or cluster) statistics were used to study the hydrogen bond (H-bond) networks in the water-methanol mixtures with the following methanol mole fractions (x(m)): 0.00, 0.10, 0.20, 0.25, 0.28, 0.30, 0.32, 0.36, 0.38, 0.42, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00. NPT-Monte Carlo simulations were performed at room conditions using the TIP5P model potential for water and united-atoms (OPLS) for methanol to generate the H-bond networks. We have found evidence for non-ideal behavior of mixtures with x(m) ≈ 0.3. Several structural and topological properties present strong dependence with the mixture composition. Island statistics indicate a change from the percolated to non-percolate regime at x(m) ≈ 0.5. Statistical analysis of the islands' nature (homo-clusters: same type of molecules × hetero-clusters: two types of molecules) yields a preferential formation of homo-clusters that quantifies the local composition and preferential solvation ("microimmiscibility"). The topology of the hydrogen bond networks was characterized by local (clustering coefficients, average degrees), semi-global (path lengths) and global (spectral densities) properties. Small-world patterns (highly clustered and small path lengths) appear for x(m) in the range 0.40-0.70, and the momenta in the spectral densities correlate quite well with previous analysis based on rings, chains and branched chains topologies. It also seems that small quantities of methanol in water cause disruption of the continuous fully connected H-bond networks formed by water molecules.

Metropolis Monte Carlo simulations of hydrogen-bonded liquids (water and methanol) were performed with the well tested effective pair potentials TIP5P and OPLS. The Coulomb contribution for the interaction potential was damped by a factor η varied from 1 to 0.49 for water and 1 to 0.15 for methanol. As a result, the networks formed by the hydrogen-bonded molecules presented interesting properties as a function of η, including small-world patterns and percolation transitions. These complex networks were analyzed by local (clustering coefficients, average degrees), semi-global (path lengths) and global (spectral densities) properties, and islands statistics. From these properties, small-world behavior was found for η in the range 0.60-0.75 for both liquids, interestingly independent of the molecular structure of the liquid. Phase transition behavior was observed for the average degrees and the clustering coefficient curves with critical values at 0.55 for water and 0.34 for methanol. Macroscopic properties such as mass density and vaporization enthalpy were also parametrically dependent on η and they presented phase transition behavior that coincides with the critical values obtained from the topological analysis. This is probably the first time that such phase transitions are observed for these quantities and shows a direct relation between macroscopic properties and topological features of hydrogen bond networks.

The interaction of chloroform (CHCl(3)) with single-wall carbon nanotubes (SWCNT) is investigated using both first principles calculations based on Density Functional Theory and vibrational spectroscopy experiments. CHCl(3) adsorption on pristine, defective, and carboxylated SWCNTs is simulated, thereby gaining a good understanding of the adsorption process of this molecule on SWCNT surfaces. The results predict a physisorption regime in all cases. These calculations point out that SWCNTs are promising materials for extracting trihalomethanes from the environment. Theoretical predictions on the stability of the systems SWCNT-CCl(2) and SWCNT-COCCl(3) are confirmed by experimental TGA data and Fourier Transform Infrared Spectroscopy (FT-IR) experiments. Results from resonance Raman scattering experiments indicate that electrons are transferred from the SWCNTs to the attached groups and these results are in agreement with the predictions made by ab initio calculations.