Crystalline Cavities Research Articles

Segregation of Benzoic Acid in Polymer Crystalline Cavities.

Benzoic acid (BA) and its derivatives are very attractive because of their pharmacological properties, such as antioxidant, radical-regulating, antiviral, antitumor, anti-inflammatory, antimicrobial and antifungal. Syndiotactic polystyrene (sPS) and poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting co-crystalline phases with BA were prepared and characterized by WAXD, FTIR and polarized FTIR measurements. The FTIR measurements clearly showed that BA was present mainly as a dimer in the crystalline channels of the ε form of sPS as well as in the α form of PPO, as generally occurs not only in the solid state but also in organic dilute solutions. BA was instead present as isolated molecules in the crystalline cavities of the δ form of sPS. In fact, the FTIR spectra of BA guest molecules exhibited vibrational peaks close to those of BA in its vapor phase. Hence, the nanoporous-crystalline δ form of sPS not only avoids additive aggregation but also leads to the separation of dimeric molecules and the segregation of monomeric BA.

Linear hydrogen bonded aggregates of carboxylic acids in crystalline channels of syndiotactic polystyrene

Sorption of long aliphatic carboxylic acids (lauric with 12 C atoms and stearic with 18 C atoms) and of an aliphatic dicarboxylic acid (adipic), by amorphous and nanoporous-crystalline δ-form and ε-form films of syndiotactic polystyrene (sPS), is reported. Fourier Transform Infrared (FTIR), Polarized FTIR and Wide Angle X-ray diffraction (WAXD) patterns show that the empty crystalline channels of the ε form are able to host long carboxylic acids as well as dicarboxylic acids. These acids are instead absorbed much more slowly and only from the amorphous phase for δ form sPS films, which exhibit crystalline cavities rather than crystalline channels. This selective and fast uptake of carboxylic acids in the crystalline channels of the sPS ε form is due the formation of hydrogen bonded linear dimers and linear polymers, for monocarboxylic and dicarboxylic acid guests, respectively.

Slow light frequency reference cavities—proof of concept for reducing the frequency sensitivity due to length fluctuations

Length changes due to thermo-mechanical noise originating from, for example, Brownian motion are a key limiting factor of present day state-of-the-art laser frequency stabilization using Fabry–Pérot cavities. We present a laser-frequency stabilization concept using an optical cavity with a strong slow-light effect to reduce the impact of cavity length changes on the frequency stability. The resulting noise-reduction factor is proportional to the ratio between the light phase and group velocities in the highly dispersive cavity spacer. We experimentally demonstrate a proof-of-principle implementation of this laser-frequency stabilization technique using a rare-earth doped crystalline cavity spacer in conjunction with semi-permanent spectral tailoring to achieve precise control of the dispersive properties of the cavity. Compared to the same setup in the absence of the slow-light effect a reduction in frequency sensitivity of four orders of magnitude was achieved.

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene.

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films.

Resonant Stimulated Photorefractive Scattering.

We present the first observations, and a complete theoretical explanation, of stimulated photorefractive scattering in a high- Q crystalline cavity. The standing-wave light field in the cavity induces an ultranarrow and long-lived Bragg grating through the photorefractive effect. The spatial phase of the grating is automatically matched to that of the standing wave. The scattering from the grating strengthens the standing wave, which then further reinforces the grating itself. Eventually, the mode is seen to split into a doublet, thereby disrupting the usual strict periodicity of the mode spectrum.

A Unified Model for Stress-Driven Rearrangement Instabilities

A variational model to simultaneously treat Stress-Driven Rearrangement Instabilities, such as boundary discontinuities, internal cracks, external filaments, edge delamination, wetting, and brittle fractures, is introduced. The model is characterized by an energy displaying both elastic and surface terms, and allows for a unified treatment of a wide range of settings, from epitaxially-strained thin films to crystalline cavities, and from capillarity problems to fracture models. The existence of minimizing configurations is established by adopting the direct method of the Calculus of Variations. The compactness of energy-equibounded sequences and energy lower semicontinuity are shown with respect to a proper selected topology in a class of admissible configurations that extends the classes previously considered in the literature. In particular, graph-like constraints previously considered for the setting of thin films and crystalline cavities are substituted by the more general assumption that the free crystalline interface is the boundary, consisting of an at most fixed finite number m of connected components, of sets of finite perimeter. Finally, it is shown that, as mrightarrow infty , the energy of minimal admissible configurations tends to the minimum energy in the general class of configurations without the bound on the number of connected components for the free interface.

Spectral Tuning of High Order Plasmonic Resonances in Multimodal Film‐Coupled Crystalline Cavities

AbstractSub‐micrometric and ultrathin gold cavities sustain several high order planar plasmon resonances in the visible to near‐infrared spectral window that open new perspectives for the realization of self‐assembled metasurfaces or integrated components for nano‐optics. This article investigates in detail the far‐field spectral features of these multimodal crystalline gold nanoprisms, deposited on either dielectric (glass) or metallic substrates (Au, Al) by dark‐field scattering spectroscopy. Relying on the computation of the plasmonic density of states, the signature of each planar resonance is de‐convoluted from the experimental global response of single cavities as a function of the cavity size and the substrate nature. The redshifting dispersion of each resonance is extracted from this decomposition analysis and agrees with predictions from a Green dyadic method based numerical tool. In addition, in the presence of a metallic film, a characteristic redshift or blueshift of the global response is observed for each cavity that results from a metal‐specific redistribution of the resonances. The fine spectral tuning of high order plasmonic resonances achieved here reveals the potential of the metal–insulator–metal gap geometry for a static modal engineering within ultrathin gold cavities.

Designing Plasmonic Eigenstates for Optical Signal Transmission in Planar Channel Devices

On-chip optoelectronic and all-optical information processing paradigms require compact implementation of signal transfer for which nanoscale surface plasmons circuitry offers relevant solutions. This work demonstrates the directional signal transmittance mediated by 2D plasmonic eigenmodes supported by crystalline cavities. Channel devices comprising two mesoscopic triangular input and output ports and sustaining delocalized, higher-order plasmon resonances in the visible to infra-red range are shown to enable the controllable transmittance between two confined entry and exit ports coupled over a distance exceeding 2 $\mu$m. The transmittance is attenuated by > 20dB upon rotating the incident linear polarization, thus offering a convenient switching mechanism. The optimal transmittance for a given operating wavelength depends on the geometrical design of the device that sets the spatial and spectral characteristic of the supporting delocalized mode. Our approach is highly versatile and opens the way to more complex information processing using pure plasmonic or hybrid nanophotonic architectures.

Clathrate Structure Determination by Combining Crystal Structure Prediction with Computational and Experimental 129 Xe NMR Spectroscopy.

An approach is presented for the structure determination of clathrates using NMR spectroscopy of enclathrated xenon to select from a set of predicted crystal structures. Crystal structure prediction methods have been used to generate an ensemble of putative structures of o‐ and m‐fluorophenol, whose previously unknown clathrate structures have been studied by 129Xe NMR spectroscopy. The high sensitivity of the 129Xe chemical shift tensor to the chemical environment and shape of the crystalline cavity makes it ideal as a probe for porous materials. The experimental powder NMR spectra can be used to directly confirm or reject hypothetical crystal structures generated by computational prediction, whose chemical shift tensors have been simulated using density functional theory. For each fluorophenol isomer one predicted crystal structure was found, whose measured and computed chemical shift tensors agree within experimental and computational error margins and these are thus proposed as the true fluorophenol xenon clathrate structures.

Nanoporous triclinic δ modification of syndiotactic polystyrene

For the δ form of syndiotactic polystyrene, a nanoporous triclinic modification, different from the well-established and widely used nanoporous monoclinic modification, is presented. Detailed routes to triclinic or monoclinic modifications, which involve different guest removal procedures from different δ-clathrates, are described and rationalized. Surprisingly, both triclinic and monoclinic δ modifications can be obtained by both triclinic and monoclinic δ-clathrates. The triclinic modification, with respect to the monoclinic one, presents the advantage of higher uptake of pollutants having molecular volume in the range 0.13–0.22 nm3, mainly when present only as traces in water or in air. In particular, the different molecular selectivity of triclinic and monoclinic δ modifications, favoring n-decane and n-hexane sorption, respectively, is described. This behavior is attributed to the crystalline cavities of the triclinic δ modification, which are halved in number and increased in volume with respect to those of monoclinic δ modification.

Selective CO2 gas adsorption in the narrow crystalline cavities of flexible peptide metallo-macrocycles.

Crystalline peptide Ni(ii)-macrocycles (BF4(-) salt) exhibited moderate CO2 gas adsorption (ca. 6-7 CO2 molecules per macrocycle) into very narrow cavities (narrowest part <2 Å), accompanied by the expansion of the cavities. The BF4(-) salt demonstrated selective uptake of CO2 gas in preference to CH4 and N2 gases.

Dynamics of Polar Low Mass Molecules Encapsulated in the δ-cocrystal of Syndiotactic Polystyrene

The δ-cocrystal of syndiotactic polystyrene (sPS) can capsulate various small guest molecules in the cavity of the crystalline region. We examined the rotational motion of isolated polar guest molecule, benzonitrile (BN), caged in the crystalline cavities by dielectric spectroscopy and the results were compared with the previously reported data of sPS / methyl ethyl ketone (MEK) system. The relaxation of BN in the crystalline region was specified from the comparison with the dielectric data of atactic-PS / BN system in which only the amorphous phase exists. The rotational relaxation time of BN in the crystalline cavity was 6 orders of magnitude longer, and the activation energy of BN was twice larger than those of MEK. These results suggest that spatial restriction due to the small cavity size strongly retards the rotational dynamics of the larger guest molecule, BN. Two-site model could successfully describe the temperature dependence of the dielectric intensity for sPS / BN system, revealing that there exist two stable states of BN molecules with energy difference of 7.42 kJmol-1 in the crystalline cavity.

Incidence of fluid inclusions on the chemical quality of salt produced in Sfax Saline -E.S of Tunisia

Halite–crystals produced in solar salts Works of Sfax Saline (E.S of TUNISIA), more often, contain fluid inclusions which fill inter– and intra–crystalline cavities and represent from 3 to 5 % in mass. With the sole aim of quantifying the impact of fluid inclusions on chemical quality of NaCl crystals, we proceeded by a comparison of the analytical results obtained from the analysis of primary salt samples with those obtained upon the same samples cleared out as much as possible of their inclusions by grinding in ethanol. The results obtained for bromine, potassium, magnesium and heavy metals (Cu, Mn, Pb, Zn and Cd) show that these inclusions have a chemical composition similar to that of mother brines. The decrease of salt -crystals size, by washing, using saturated brines, largely contributes to the reduction of impurities in alimentary sea salt.

Preparation of Nanofibers with Nanoporous Crystalline Phases by Electrospinning

Syndiotactic polystyrene (sPS) nanofibers with a diameter of 230–720 nm have been prepared via electrospinning of chloroform solutions. The as-spun nanofibers are characterized by an s(2/1)2 helical mesomorphic form but sorption-desorption treatments allow the obtaining of nanofibrous mats characterized by the crystalline nanoporous δ-form. Sorption studies of 1,2-dichloroethane (DCE) from 50 ppm aqueous solutions show that DCE sorption in the nanofibrous mats occurs principally in the crystalline cavities of the nanofibers at a fast rate but the DCE equilibrium uptake is lower than for other δ-form morphologies.

Low-threshold lasing of InGaN vertical-cavity surface-emitting lasers with dielectric distributed Bragg reflectors

Lasing action is achieved in InGaN vertical-cavity surface-emitting lasers (VCSELs) with dielectric distributed Bragg reflectors (DBRs). We fabricated III-nitride VCSELs by removing a SiC substrate from a III-nitride cavity with a dry etching technique and then wafer bonding the cavity and SiO2/ZrO2 DBRs. These VCSELs have a high quality factor of 460 and a spontaneous emission factor of 10−2. We observed lasing at a wavelength of 401 nm at room temperature with optical pumping. This lasing action was demonstrated at a low threshold of 5.1 mJ/cm2 by using a high-quality crystalline cavity and quantum-well layers without surface roughening or cracking.

Anisotropic Diffusion of Small Penetrants in the δ Crystalline Phase of Syndiotactic Polystyrene: A Molecular Dynamics Simulation Study

The diffusional behavior of helium and carbon dioxide in crystalline syndiotactic polystyrene, in its nanoporous δ form, has been studied by means of molecular simulation. Crystallographic directions corresponding to prevailing diffusion pathways between crystalline cavities have been determined. Moreover, diffusion coefficients and their anisotropy at different temperatures have been calculated. For both gases at all temperatures, preferential diffusion pathways are parallel to the crystallographic ac planes, corresponding to rows of parallel helices with minimum interchain distances. Diffusion of carbon dioxide is slower and more anisotropic than that of helium. For both gases, the preferred diffusion pathways are along the 〈101〉 directions at low temperatures while parallel to the chain axes at high temperatures.

Ab Initio and Molecular Mechanics Study of Conformational Selectivity of Chlorinated Compounds Adsorbed in the Clathrate Phase of Syndiotactic Polystyrene. The Role of Electrostatic Host-Guest Interactions

A computational study of the conformational selectivity of some chlorinated compounds adsorbed in polymeric clathrates of syndiotactic polystyrene is pres ented. Ab initio investigation of the model complex benzene/CH 3 Cl gives information about the role of electrostatic interactions in determining the favored molecular orientations. The changes of conformational equilibria of some chlorinated compounds upon clathration have been rationalized by a molecular mechanics approach. This shed light on the nature of the host-guest interactions: although van der Waals interactions are most relevant for the sorption process, the observed conformations are essentially associated with electrostatic interactions of the guest conformers with a substantially quadrupolar electrostatic field of the crystalline cavity.

Thermoplastic Molecular Sieves

An inexpensive and reusable thermoplastic material that is promising in the field of chemical separations, and in particular of water and air purification from volatile organic compounds, is presented. This semicrystalline material based on syndiotactic polystyrene comprises a nanoporous crystalline phase where guest molecules can be clathrated. Changes of conformational equilibria of some chlorinated hydrocarbons upon clathration have been rationalized by a molecular mechanics approach. This sheds light on the nature of the host−guest interactions: although the van der Waals interactions are most relevant, the observed conformations for chlorinated guest molecules are essentially associated with electrostatic attractive interactions of quadrupolar conformers with a substantially quadrupolar electrostatic field of the crystalline cavity.

Critical Conditions for CO2 Hydrate Films To Rest on Submarine CO2 Pond Surfaces: A Mechanistic Study

The stability of hydrate films formed at the horizontal interface between seawater and denser liquid CO2 under high pressures (≳35 MPa) is considered to have an insight into the feasibility of the disposal/storage of liquid CO2 in the deep oceans. Hydrate films formed at the interface (i.e., the surface of a liquid CO2 pond on the seabed) may be denser than both liquid CO2 and seawater, may be denser than seawater but lighter than liquid CO2, or may be lighter than both liquids depending on the ambient pressure (i.e., the depth of the interface) and also on the fractional occupancy of hydrate crystalline cavities by CO2 molecules. The static force balance between the gravitational forces and the interfacial tension force acting on each hydrate film is formulated, thereby predicting the critical condition beyond which the film may sink into the CO2 pond or buoy up into the sea, or it may be broken due to an internal stress.

Consequences of the ?Pedersen papers? on crown type chemistry at W�rzburg and Bonn Universities: From heteroaromatic crowns and podands to large molecular and crystalline cavities including multisite receptors, cascade molecules, chromoionophores, siderophores, surfactant-type, and extreme ligands

Consequences of the ?Pedersen papers? on crown type chemistry at W�rzburg and Bonn Universities: From heteroaromatic crowns and podands to large molecular and crystalline cavities including multisite receptors, cascade molecules, chromoionophores, siderophores, surfactant-type, and extreme ligands