: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Ferromagnetism usually only occurs in materials containing elements that form covalent 3d and 4f bonds. Its occurrence in pure carbon is therefore surprising, even controversial. A systematic magnetic force microscope study indicates that ferromagnetism in graphite is the result of localized spins that arise at grain boundaries.

/pdf/room-temperature-ferromagnetism-in-graphite-driven-by-two-36ae7e3kaz.pdf

Room-temperature ferromagnetism in graphite driven by two-dimensional networks of point defects

We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of $\epsilon_L=2.4$ eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, $D'$, 2D and $2D'$ lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm$^{-1}$ range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the $2D'$ and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the $D$ and $D'$ lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal.

/pdf/theory-of-double-resonant-raman-spectra-in-graphene-55hadiikn1.pdf

Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands

We have obtained two results since leaving Chapter 3 which make this return to βℕ possible. The first of these was Corollary 4.30 in which we found, under the assumption of the Continuum Hypothesis, that ℕ* contains a dense subset of 2C P-points. The second was Corollary 6.30 in which we saw that no point of ℕ* has its own type as a relative type with respect to any copy of ℕ contained in ℕ*. Here we will make use of these two properties of ℕ* to continue the investigation of βℕ and especially of ℕ*.

β ℕ Revisited

Novel ionic liquid-type Gemini surfactants: Synthesis, surface property and antimicrobial activity

The properties of anionic-rich and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry and surface tension measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface tension reduction effectiveness(γCAC), surface excess(Γmax), and mean molecular surface area (Amin) were determined from plots of the surface tension (γ) as a function of the total surfactant concentration. The compositions of the adsorbed films (Z) and aggregates (χ) were estimated by using regular solution theory, and then the interaction parameters in the aggregates (β) and the adsorbed film phases (βσ) were calculated. The results showed that the synergism between the surfactants enhances the formation of mixed aggregates and reduces the surface tension. Further, the nature and strength of the interaction between the surfactants in the mixtures were obtained by calculating the values of...

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates.

The ability of cationic-rich and anionic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) for dispersing of carbon nanotubes (CNTs) in aqueous media has been studied through both the experimental and molecular dynamics simulation methods. Compared to the pure CTAB and SDS, these mixtures are more effective with the lower concentrations and more individual CNTs, reflecting a synergistic effect in these mixtures. The synergistic effects observed in mixed surfactant systems are mainly due to the electrostatic attractions between surfactant heads. In addition, the surface charge related to the colloidal stability of mixed surfactant-covered nanotubes has been characterized by means of ζ-potential measurements. The results indicate that the hydrophobic interactions between surfactant tails also give rise to the higher adsorption of surfactant molecules. Furthermore, molecular dynamics (MD) simulations have been performed to provide insight about the structure of surfactant aggregates onto nanotubes and to attempt an explanation of the experimental results. The MD simulation results indicate that the random and disordered adsorption of mixed surfactants onto carbon nanotubes may be preferred for a low surfactant concentration. Our research may provide experimental and theoretical bases for using mixed surfactants to disperse CNTs, which can open an avenue for new applications of mixed surfactants.

Dispersion of carbon nanotubes using mixed surfactants: experimental and molecular dynamics simulation studies.

In the present work, the adsorption behavior at the liquid–air interface and micellization characteristics of mixtures of cetyltrimethylammonium bromide (CTAB) and p -(1,1,3,3-tetramethylbutyl) polyoxyethylene (TritonX-100) in aqueous media containing different concentrations of NaBr were investigated by surface tension and potentiometry measurements. From plots of surface tension ( γ ) as a function of solution composition and total surfactant concentration, we determined the critical micelle concentration (CMC), minimum surface tension at the CMC ( γ CMC ), surface excess ( Γ max ), and mean molecular surface area ( A min ). On the basis of regular solution theory, the compositions of the adsorbed film ( Z ) and micelles ( X M ) were estimated, and then the interaction parameters in the micelles ( β M ) and in the adsorbed film phase ( β σ ) were calculated. For all mole fraction ratios, the results showed synergistically enhanced ability to form mixed micelles as well as surface tension reduction. Furthermore β was calculated by considering nonrandom mixing and head group size effects. It was observed that, for both the planar air/aqueous interface and micellar systems, the nonideality decreased as the amount of electrolyte in the aqueous medium was increased. This was attributed to a decrease of the surface charge density caused by increasing the concentration of bromide ions.

Electrolyte effect on mixed micelle and interfacial properties of binary mixtures of cationic and nonionic surfactants

Determination of the physico-chemical parameters and aggregation number of surfactant in micelles in binary alcohol–water mixtures

Superhydrophobic surfaces for broad applications in biological and biomedical sciences are good potential candidates for technological unsolved challenges. Using superhydrophobicity can supply a suitable and biocompatible strategy for making clean antibacterial surfaces, sensitive biosensors, significant methods for biocrystallization, tunable cell/platelet/blood adhesion surfaces, appropriate templates for gene/drug delivery and 3D cell engineering. Trapped air in surface roughness, surface convection and localizer effects, reduction in tissue-implant unwanted interactions and genes delivery pathways are some of the characteristics that superhydrophobic surfaces can provide to solve biological and biomedical technical restrictions. In this review, the mechanism and procedures of superhydrophobic surfaces and their impacts on biosystems have been studied and highlighted.

Beheshteh Sohrabi

Papers

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates.

Dispersion of carbon nanotubes using mixed surfactants: experimental and molecular dynamics simulation studies.

Electrolyte effect on mixed micelle and interfacial properties of binary mixtures of cationic and nonionic surfactants

Determination of the physico-chemical parameters and aggregation number of surfactant in micelles in binary alcohol–water mixtures

Superhydrophobicity: advanced biological and biomedical applications.