No abstract

Aqueous solutions of sodium polyacrylate (NaPA) have been mixed with different phases of the system water−cetyltrimethylammonium bromide (CTABr). In all mixtures, the surfactant ions (CTA+) associate to form micelles. The polyions (PA-) bind to these micelles, displace their counterions, and bridge them together. The replacement of micellar counterions changes the micellar shapes. The bridging may change the distances between micelles, and cause them to separate into a concentrated phase; in this case excess water and salt are released in a dilute aqueous phase. The structures of the concentrated phases have been determined. At low water contents, the hexagonal, nematic, and micellar phases of the polymer-containing system merge with the corresponding phases of CTABr/water. At high water content, the concentrated phases that separate are closer to the hexagonal and cubic phases of cetyltrimethylammonium acetate/water.

ABSTRACT:Delamination is a key step to obtain individual layers from inorganic layered materials needed for fundamental studies and applications. For layered van-der-Waals materials like graphene the adhesion forces are small allowing for mechanical exfoliation, whereas for ionic layered materials like layered silicates the energy to separate adjacent layers is considerably higher. Quite counter intuitively, we show for a synthetic layered silicate (Na 0.5 -hectorite) that a scalable and quantitative delamination by simple hydration is possible for high and correlated. This is indicated by fulfilling the classical Hansen-Verlet and Lindeman criteria for melting. We provide insight into the requirements for layer separation and controlling the layer distances for a broad range of materials and outline an important pathway for the integration of layers into devices for advanced applications.

Poly(tert-butyl acrylate)-block-poly(2-vinylpyridine) (PBA-b-PVP) in acidic aqueous solutions forms micelles with PBA cores and PVP shells. When this micellar solution is brought to pH higher than 4.8 , the PVP shells collapse and the copolymer precipitates. However, when a sample of acid water soluble poly(2-vinylpyridine)-block-poly(ethylene oxide) (PVP-b-PEO) is present, its PVP blocks coprecipitate with PVP blocks of PBA-b-PVP and form a dense outer core. The PEO blocks then stabilize this complex onion-type structure. Static and dynamic light scattering measurements revealed that for small values of the (PVP-b-PEO)/(PBA-b-PVP) mass ratio the resulting particles are multimicellar clusters. When the ratio is sufficiently large, the solution contains onion-type micelles. However, the outer core of these micelles can incorporate only a limited number of PVP blocks from the PVP-b-PEO copolymer. The excess PVP-b-PEO molecules then form independent smaller micelles with PVP cores and PEO shells.

We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects. In high quality single crystals of both compounds, i.e. displaying carrier mobilities between 10 3 and 10 4 cm 2 /Vs, we observed a large non-saturating magnetoresistivity (MR) which in PtTe2 at a temperature T = 1.3 K, leads to an increase in the resistivity up to 5 × 10 4 % under a magnetic field µ0H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show an excellent agreement with those resulting from band-structure calculations. Surprisingly, this is not the case for PtTe2 whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides a strong support for the existence of a Dirac type-II node in PdTe2 and probably also for PtTe2. Band structure calculations indicate that the topologically non-trivial bands of PtTe2 do not cross the Fermi-level (εF). In contrast, for PdTe2 the Dirac type-II cone does intersect εF , although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to the one of the Dirac type-II node. Therefore it should yield a trivial Berry-phase.

Poly(tert-butyl acrylate)-block-poly(2-vinylpyridine), PBA-b-PVP, was prepared by living anionic polymerization. Polymolecular spherical micelles with compact hydrophobic PBA cores and protonated PVP shells in acid water were prepared by a dialysis from organic-aqueous mixtures and are stable if the pH is less than pH 4.8. The stretching of the PVP blocks in shells depends on pH and ionic strength of the solution and decreases significantly in a narrow pH region below 4.8. Small hydrophobic molecules, such as benzene, may be solubilized into micellar core swelling the core and releasing the segmental mobility of core-forming blocks. Two fluorimetric techniques for determination of pyrene partitioning between micelles and the aqueous phase were used. The first method is based on measurements of the ratio of intensities of the first and third vibrational bands, I1/I3, in the emission spectra of pyrene solubilized in a micellar solution as a function of micellar concentration. The second method is based on the quenching of fluorescence from solubilized pyrene by thallium salts. The two experimental techniques yield close values of the apparent partition coefficient, Kapp ) 1.3 × 10 5 and 1.1 × 10 5 , respectively.

Polystyrene-block-poly(methacrylic acid) micelles were chemically attached to an activated silicon nitride surface using a 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide methiodide coupling reaction. It has been found that this attachment method is very efficient from mixed 1,4-dioxane−water solvents and less efficient in purely aqueous media. The modified surfaces were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental conditions for surface attachment have been found such that no changes in micellar size or polydispersity occur. The SEM and AFM images allow an additional method for the evaluation of size distributions of micelles. A comparison with the quasi-elastic light scattering data from solutions shows that the distribution functions based on the SEM and AFM data for dried micelles fixed on the surface correlate reasonably well with the light scattering data on micelles in solutions.

Cannabis sativa L. produces over 200 known secondary metabolites that contribute to its distinctive aroma. Studies on compounds traditionally associated with the scent of this plant have focused on those within the terpenoid class. These isoprene-derived compounds are ubiquitous in nature and are the major source of many plant odors. Nonetheless, there is little evidence that they provide the characteristic “skunk-like” aroma of cannabis. To uncover the chemical origins of this scent, we measured the aromatic properties of cannabis flowers and concentrated extracts using comprehensive two-dimensional gas chromatography equipped with time-of-flight mass spectrometry, flame ionization detection, and sulfur chemiluminescence. We discovered a new family of volatile sulfur compounds (VSCs) containing the prenyl (3-methylbut-2-en-1-yl) functional group that is responsible for this scent. In particular, the compound 3-methyl-2-butene-1-thiol was identified as the primary odorant. We then conducted an indoor greenhouse experiment to monitor the evolution of these compounds during the plant’s lifecycle and throughout the curing process. We found that the concentrations of these compounds increase substantially during the last weeks of the flowering stage, reach a maximum during curing, and then drop after just one week of storage. These results shed light on the chemical origins of the characteristic aroma of cannabis and how volatile sulfur compound production evolves during plant growth. Furthermore, the chemical similarity between this new family of VSCs and those found in garlic (allium sativum) suggests an opportunity to also investigate their potential health benefits.