The effect of cosolvent (ethane-1,2-diol and dimethyl sulfoxide) on the self-assembly of three surfactants, N,N,N-trimethyl-1-dodecanaminium bromide (DTAB), sodium [dodecanoyl(methyl)amino]acetate (SDDS), and polyoxyethylene (20) sorbitan monolaurate (Tween-20) in aqueous solution have been investigated by conductometric, tensiometric, and viscometric techniques at 298 K. The main focus was on the effect of solvent on critical micelle concentration (cmc), free energy contribution to micellization (ΔG m 0 ), tail transfer Gibbs free energy (ΔG trans 0 ), Gibbs adsorption energy (ΔG ads 0 ), and some micellar interfacial parameters, for example, Gibbs surface excess (Γ max ), minimum area per surfactant molecule (A min ), surface pressure (Π cmc ), and pC 20 (= −log(C 20 ), where C 20 is the surfactant molar concentration required to reduce the surface tension of mixed solvent by 20 mN m −1 ). With increasing concentration of cosolvent in the binary mixture, the cohesive force decreases, and surfactant molecules are more soluble in mixed solvent. As a result, micellization process becomes less favorable, and an increase in cmc was obtained. Steady state fluorescence spectroscopy was used to determine the aggregation number (N agg ) of the surfactants in organic solvent−water binary mixture and also the micropolarity of the mixed solvent. It was observed that N agg decreased with the increase of organic solvent concentration. The micropolarity of the mixed solvent and packing parameter (P) were also determined.

The cultural makeup of the United States continues to change rapidly, and as minority groups continue to grow, these groups' beliefs and customs must be taken into account when examining death, grief, and bereavement. This article discusses the beliefs, customs, and rituals of Latino, African American, Navajo, Jewish, and Hindu groups to raise awareness of the differences health care professionals may encounter among their grieving clients. Discussion of this small sample of minority groups in the United States is not intended to cover all of the degrees of acculturation within each group. Cultural groups are not homogeneous, and individual variation must always be considered in situations of death, grief, and bereavement. However, because the customs, rituals, and beliefs of the groups to which they belong affect individuals' experiences of death, grief, and bereavement, health care professionals need to be open to learning about them to better understand and help.

The micellar properties of gemini surfactant, tetramethylene-1,4-bis(dimethyltetradecylammonium bromide) (14-4-14) in binary aqueous mixtures of isopropanol (IP) and 1,4-dioxane (DO) were investigated by tensiometric, conductometric and microcalorimetric methods in the temperature range of 298 to 323 K. The values of both critical micelle concentration (cmc) and degree of dissociation increase with increasing temperature and concentration of cosolvent. The energetics of micellization was determined from the temperature dependence of critical micelle concentration values. The standard Gibbs free energy of micellization (ΔG) was found to be negative and the negative value decreases with both temperature and concentration of cosolvent. The Gibbs free energy of micellization (ΔG) is mainly controlled by tail transfer free energy. The enthalpy of micellization obtained from direct calorimetry, Gibbs-Helmholtz equation and van't Hoff methods are presented and compared. Entropic contribution is found to be larger than the enthalpy and for all the systems, an enthalpy-entropy compensation phenomenon was obtained. Some interfacial parameters, e.g., Gibbs surface excess (Γmax), minimum area per surfactant molecule (Amin), surface pressure (Πcmc) were been calculated. The fluorimetric technique was used to understand the microenvironment of the solution under the influence of cosolvent. The micellar aggregation number of 14-4-14 in a binary mixed solvent was also determined from fluorimetry using pyrene as a probe. Two fluorophores, fluorescein and curcumin delivered the information of the peripheral region of the micellar interface and palisade region. The self-diffusion coefficients of the micellar media were evaluated using the cyclic voltammetry (CV) method. Such multi-technique investigation provides a new look into the role of solvation in micellization.

Introduction:

The monolayers of semiconducting transition metal dichalcogenides host strongly bound excitonic complexes and are an excellent platform for exploring many-body physics. Here we demonstrate a controlled kinetic manipulation of the five-particle excitonic complex, the charged biexciton, through a systematic dependence of the biexciton peak on excitation power, gate voltage, and temperature using steady-state and time-resolved photoluminescence (PL). With the help of a combination of the experimental data and a rate equation model, we argue that the binding energy of the charged biexciton is less than the spectral separation of its peak from the neutral exciton. We also note that while the momentum-direct radiative recombination of the neutral exciton is restricted within the light cone, such restriction is relaxed for a charged biexciton recombination due to the presence of near-parallel excited and final states in the momentum space.

Interactions of the cationic gemini surfactant, 14-4-14 with anionic polymer, NaCMC.

Layered transition metal dichalcogenides (TMDCs) host a variety of strongly bound exciton complexes that control the optical properties in these materials. Apart from spin and valley, layer index provides an additional degree of freedom in a few-layer thick film. Here we show that in a few-layer TMDC film, the wavefunctions of the conduction and valence band edge states contributing to the ( ′ ) valley are spatially confined in the alternate layers -giving rise to direct (quasi-)intra-layer bright exciton and lower-energy inter-layer dark excitons. Depending on the spin and valley configuration, the bright exciton state is further found to be a coherent superposition of two layer-induced states, one (E-type) distributed in the even layers and the other (O-type) in the odd layers. The intra-layer nature of the bright exciton manifests as a relatively weak dependence of the exciton binding energy on the thickness of the few-layer film, and the binding energy is maintained up to 50 meV in the bulk limit -which is an order of magnitude higher than conventional semiconductors. Fast stokes energy transfer from the intra-layer bright state to the inter-layer dark states provides a clear signature in the layer-dependent broadening of the photoluminescence peak, and plays a key role in the suppression of the photoluminescence intensity observed in TMDCs with thickness beyond monolayer.

The strong light-matter interaction in monolayer transition metal dichalcogenides (TMDs) is promising for nanoscale optoelectronics with their direct band gap nature and the ultrafast radiative decay of the strongly bound excitons these materials host. However, the impeded amount of light absorption imposed by the ultra-thin nature of the monolayers impairs their viability in photonic applications. Using a layered heterostructure of a monolayer TMD stacked on top of strongly absorbing, non-luminescent, multi-layer SnSe2, we show that both single-photon and two-photon luminescence from the TMD monolayer can be enhanced by a factor of 14 and 7.5, respectively. This is enabled through inter-layer dipole-dipole coupling induced non-radiative Förster resonance energy transfer (FRET) from SnSe2 underneath which acts as a scavenger of the light unabsorbed by the monolayer TMD. The design strategy exploits the near-resonance between the direct energy gap of SnSe2 and the excitonic gap of monolayer TMD, the smallest possible separation between donor and acceptor facilitated by van der Waals heterojunction, and the inplane orientation of dipoles in these layered materials. The FRET driven uniform single-and twophoton luminescence enhancement over the entire junction area is advantageous over the local enhancement in quantum dot or plasmonic structure integrated 2D layers, and is promising for improving quantum efficiency in imaging, optoelectronic, and photonic applications. KEYWORDS: MoS2, WS2, SnSe2, van der Waals heterostructure, photoluminescence enhancement, two-photon luminescence, Förster Resonance Energy Transfer (FRET), charge transfer.transfer across WS2/MoSe2 hetero-bilayer stack through FRET across higher order exciton transitions. Nonetheless, the donor's absorption is still constrained by its physical thickness at the monolayer limit despite the high efficiency of FRET at the closest possible physical separation.Here, we demonstrate enhanced PL of monolayer MoS2 (and WS2) across its vdW heterojunction with multi-layer SnSe2 via FRET with single and two-photon excitation. Counteracting the charge transfer across highly staggered conduction bands of MoS2 and SnSe2, MoS2 single-photon luminescence (1P-PL) shows ~14-fold enhancement at room temperature with resonant excitation and ~5-fold enhancement with non-resonant excitation, while two-photon luminescence (2P-PL) of MoS2 shows up to ~7.5-fold enhancement with non-resonant excitation. Even with the insertion of few-layer hBN between MoS2 and SnSe2, the 1P-PL enhancement persists up to 5 times with resonant excitation. We demonstrate modulation of the degree of the PL enhancement by systematic parameter variation, including donor material, acceptor material, their thickness, physical separation between donor and acceptor, sample temperature, and excitation wavelength which corroborate FRET aided PL enhancement. We emphasize the intrinsic advantage of realizing FRET with SnSe2 as a donor and elucidate the impact of multiple parameters on the luminescence enhance...