Whispering-gallery mode spectra in optical microcavities based on spherical silica particles coated with a thin photoluminescent shell of hydrogenated amorphous silicon carbide are studied. The spectral positions of the whispering-gallery modes for spherical microcavities with a shell are calculated. The dependence of the spectral distance between the TE and TM modes on the shell thickness is examined.

We have demonstrated that a rather weak external optical feedback with delay can lead to the mode switching of the counterpropogating modes. The delay time should be longer then any system characteristic time. The equations describing the ring resonator with the delayed optical feedback was obtained from the first principles. The analytical formula for the necessary external feedback strength was derived. Other than the regular behavior, the system demonstrates a complex chaotic behavior.

The spectrum of whispering gallery modes for resonators with a small deformation of the boundary is calculated analytically. Cylindrical resonators with two different cross sections (segment close to a circle and segment close to a semicircle) are considered. The calculation is performed for resonators with metal boundaries, but the obtained result is a good approximation for dielectric resonators as well. The applicability limits of the found expressions for the spectra are analysed. It is shown that the spectra calculated using the obtained expressions coincide well with computer-calculated spectra. The perturbation-induces changes in the field distribution are qualitatively studied using numerical simulation.

We consider the problem of the whispering gallery mode in resonators having the shape of a circular segment close to a disk or a half-disk. The calculations are performed using perturbation theory methods.

Essais de divers produits: agents de surface, ethercouronne, composes de coordination pour remplacer les classiques oxyde de zinc+acide stearique

Two series of plasticized butadiene-acrylonitrile elastomer (SKN-26M) with dibutyl phthalate or dibutyl sebacate as plasticizers were studied over the temperature interval of 77–323 K. Both plasticizers influence the storage modulus in shear, G′, most strongly in the temperature region of intensive relaxation processes and also in the state of high elasticity. For the system SKN-26M-dibutyl sebacate in the region of high elasticity the frequency dependence of G′ becomes more pronounced with increasing plasticizers concentration. In both series the modulus G′ decreases in the high elastic region exponentially with the concentration of the plasticizer; coefficients of the corresponding empirical function were determined.

Mutual diffusion processes and phase transitions in phenol-formaldehyde oligomer (PFO)-elastomer systems have been investigated at various stages of cure of PFO during the formation of adhesive bonds. The distribution of components in the adhesion contact zone has been determined. It is shown that the cure of the PFO fixes the concentrational distribution at the stage of diffusion mixing of the components. The results of electron-probe X-ray microanalysis of the adhesion contact zone between PFO and butadiene-nitrile elastomers show that phase transitions occur in this zone, and result in formation of structure that provides the bond strength. A mechanism of formation of adhesive bonds is proposed for partially compatible components.

A novolac phenolformaldehyde oligomer was used as adhesive for attaching to metal butadiene-nitrile rubber during vulcanisation. It was shown that the formation of an adhesion bond with rubber takes place as a result of the diffusion of the oligomer into the surface layer of rubber with the formation of a transition layer some dozen μm thick. The formation mechanism of the adhesion bond was described using results of diffusion and solubility of the oligomer in SKN-18, SKN-26 and SKN-40 rubbers.

When forming adhesive compounds of rubber with metal during vulcanization adsorption of adhesive on the metal surface may be of considerable significance; this process precedes adhesive interaction. The type of adsorption determines to a large extent the strength of the adhesive bond of the polymer with the substratum and the structure of boundary layers. Novolac and resole type phenolformaldehyde oligomers of different structures were synthesized and their adsorption properties examined on aluminium γ-oxide powder, which simulates the surface of the aluminium substrate.

An additive scheme is proposed for determining chemical shifts of fluorine atoms included in groups in fluorine-containing polymers. The spectra of the copolymers of vinylidene fluoride and tetrafluoroethylene and of vinylidene fluoride and tetrafluoroethylene and hexafluoropropylene are interpreted in accordance with this additive scheme. Application of the principle of alternation in changes in chemical shifts of 19F nuclei on varying the electronegativity of nearest polymer chain fragments allowed interpretation of the fine structure of spectrum lines and enabled these to be assigned in terms of tetrads and pentads.

It was shown that a globular formation of three-dimensional crosslinked oligoester acrylate of a dimension of 0·02–0·04 μm is the smallest structural element of the dispersed phase of vulcanizates based on rubber-oligomer compositions. The distribution of particles of the dispersed phase in a rubber matrix is determined by the type of rubber and has a marked effect on the tensile strength of vulcanizates.

In order to discover the effect of various functional groups in phenol-form-aldehyde oligomers on their adsorptive and adhesive properties, methylol derivatives of phenol and some other, model compounds were synthesized, and their interaction with a metal surface was examined under conditions approaching the real conditions of formation of an adhesive bond between a metal and a polymeric binder. The adsorption of methylolphenols on powdered aluminium γ-oxide was studied, and their interaction with an aluminium surface was investigated by IR-spectroscopy, using the method of attenuated total internal reflection. The adsorbability of o-methylolphenol on aluminium γ-oxide and its stronger interaction with the metal surface, in comparison with the para-derivative, is explained by the ability of o-methylolphenol to form a stable, six-membered complex with coordinately unsaturated aluminium atoms. Only weak interaction between the aluminium surface and p-methylolphenol or 2,2′-dihydroxydiphenylmethane was found, either at room or higher temperatures.

A study has been made of the curing of polydimethylvinylsiloxane rubber and its vulcanizates, using different silicon hydrides (hydro-organosilanes, hydro-organosiloxanes and hydro-organosilazanes) with H2PtCl6·6H2O as catalyst. The reaction kinetics were investigated by infrared and by an analysis of degree of swelling of the vulcanizates. It is shown that the silica hydrides may be placed in the following order as regards the rates and degrees of crosslinking: hydro-organosiloxanes, hydro-organosilazanes and hydro-organosilanes. The activation energy of the reaction varies within the limits of 12 and 16 kcal/mole. An analysis of strength properties of the vulcanizates shows the considerable extent to which the latter are influenced by the nature of the silicon hydrides: breaking elongation and tearing values are considerably higher for the vulcanizates containing silicon hydrides than for peroxide vulcanizates.

The general scheme by which a single steric network forms during the heterogeneous vulcanization of elastomers, using unsaturated compounds, has been evaluated. An oriented polymer layer is assumed to form at first at the interface with the dispersed particles of the curing agent, and the adsorbed macromolecules position themselves as folded structures on the surface. The crosslinking takes place as a result of chemical reaction of the curing agent with some of the loops of the adsorbed macromolecules. A single steric network will form when the chain units of a single folded macromolecule react with various particles of the curing agent. In addition to the heterogeneous network there is also some chemical union between chains due to reactions of the dissolved peroxide present.

Microscopy and electron microscopy have been used together with determinations of the crosslinking density and of the physico-mechanical properties of vulcanizates before and after the extraction of the azodicarbamide (ADCA), as well as nitrogen liberation, to show that the curing of elastomers with ADCA of differing structures is a heterogeneous reaction. A scheme is suggested for the formation of a single steric network during the curing with the azo-amide. Proof has been obtained that the heterogeneous vulcanization can result in the formation of a heterogeneous (butadiene nitrile rubbers) or homogeneous vulcanization structure (butadiene-styrene rubber, polybutadiene).