Study of the properties and structure of polyimide and bilayer fluoropolyimide films after space exposure on the Mir space station

Results of examination of bilayer polyimide and fluorinated polyimide films after their exposure to outer space on the Mir space station are reported. The polyimide films were screened by quartz plates during exposure. An increase in the surface energy and the work of adhesion indicate substantial hydrophilization of the open surface, as well as slight hydrophilization of the screened film surface. A difference in values of the surface energy and work of adhesion depending on the orientation of a sample relative to the direction of motion of the space station indicates that the surface properties of the outer surface of the unscreened film became anisotropic in character, with the anisotropy axis being aligned with the direction of motion of the spacecraft. The fact that the outer surface of the film has acquired anisotropic properties is corroborated by the results of study of scanning electron microscopic images and polar plots of brightness. The hydrophilization of the films indicates an increase in the concentration of polar groups. In the space environment, the degradation of the fluoropolymer surface layer and its removal under high-vacuum conditions take place. For the quartz-shielded polyimide films, the surface energy and the work of adhesion remained practically the same as for the unexposed films. It was concluded that solar radiation (μ > 200 nm) does not cause a significant decline in the properties of the polyimide film.     

Study of the properties and structure of fluoropolymer films after space exposure on the Mir space station

Exposure in low Earth orbits (LEO) leads to alteration in properties of both outer and inner (screened) fluoropolymer films F4-MB and FEP-100A. Space environment factors have an effect primarily on the open surface of outer films. The volume and mass of the FEP-100A films accessible to the direct impact of space environment factors underwent nonequivalent changes, indicating an increase in the average density of the polymer. The surface of these films showed contact-angle anisotropy, thereby indicating the formation of spatially oriented structures on the surface. The study of the surface properties of the films revealed that the surface tension and the work of adhesion increased and both outer and (to a lesser extent) inner films became more hydrophilic after exposure. The hydrophilization process prevalently occurred during the first 28 months of exposure in LEO.     

Reversible phase transitions in emulsified nanostructured lipid systems

Aqueous submicron-sized dispersions of the binary monolinolein/water system, which are stabilized by means of a polymer, internally possess a distinct nanostructure. Taking this as our starting point, we were able to demonstrate for the first time that the internal structure of the dispersed particles can be tuned by temperature in a reversible way. Upon increasing the temperature, the internal structure undergoes a transition from cubic via hexagonal to fluid isotropic, the so-called L2 phase, and vice versa. Intriguingly, in addition to the structural changes in topology, the particles expel (take up) water to (from) the aqueous continuous phase when increasing (decreasing) the temperature in a reversible way. At each temperature, the internal structure of the dispersed particles corresponds very well to the structure observed in nondispersed binary monolinolein with excess water. This agreement is independent of any thermal history (including phase transitions), which proves that the structures in the dispersed particles actually are in thermodynamic equilibrium with the surrounding water phase.     

Continuous-wave operation of 1.30μm GaAsSb/GaAs VCSELs

1.30 μm VCSELs using GaAsSb quantum wells, which operate continuous-wave at and above room temperature (RT), are reported. A threshold current as low as 1.2 mA at RT and a maximum CW operating temperature of 70°C are demonstrated     

Low-threshold operation of 1.3-μm GaAsSb quantum-well lasersdirectly grown on GaAs substrates

GaAsSb quantum-well (QW) edge-emitting lasers grown on GaAs substrates were demonstrated. The optical quality of the QW was improved by optimizing the growth conditions and introducing a multi-QW to increase the gain. As a result, 1.27-μm lasing of a GaAs_0.66 Sb_0.34-GaAs double-QW laser was obtained with a low-threshold current density of 440 A/cm², which is comparable to that in conventional InP-based long-wavelength lasers. 1.30 μm lasing with a threshold current density of 770 A/cm² was also obtained by increasing the antimony content to 0.36. GaAsSb QW was found to be a suitable material for use in the active layer of a 1.3-μm vertical-cavity surface-emitting lasers     

A Synthesis of the Control of Dynamical Systems on the Basis of the Method of Lyapunov Functions

We consider the problem of the synthesis of a bounded control reducing a dynamical system to the given terminal state in a finite time. Two approaches to solve the problem, based on methods of the theory of stability of motion, are provided. One of them is applicable to nonlinear Lagrange mechanical systems with undetermined parameters, while another is applicable to linear systems. The characteristic property is that the Lyapunov functions are defined implicitly in both cases. We make a comparison between these approaches.     

Any component of moduli of polarized hyperkähler manifolds is dense in its deformation space

Let M be a compact hyperkähler manifold, and W the coarse moduli of complex deformations of M. Every positive integer class v   in H²(M)$H^2(M)$ defines a divisor _Dv$D_v$ in W consisting of all algebraic manifolds polarized by v. We prove that every connected component of this divisor is dense in W.     

Synthesis and Structural Diversity of Lanthanum and Neodymium Triphenylacetate Complexes with Trimethyltriazacyclohexane and Crown Ether

Russian Journal of Coordination Chemistry - The reactions of lanthanum and neodymium triphenylacetates with polydentate 6- and 18-membered N- and O-heterocyclic ligands give various types of...     

Porous Structure of Composites

NMR and the sorption method were used to study the structure of composites based on ultra-high-molecular-weight polyethylene and peat (filler).__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 1006–1009.Original Russian Text Copyright © 2005 by Grebennikov, Smotrina, Anan’eva, Kuznetsov.