The effect of charged centers on the transport of charge carriers in molecularly doped polymers

The effect of charged centers on the mobility of charge carriers in molecularly doped polycarbonate is experimentally studied by the method of accelerated electrons for the generation of charge carriers in the surface layer and in the polymer bulk. The hypersensitivity of mobility toward the presence of charged sites that is predicted by the theory of correlated disorder (dipolar glass) is not found. With accumulation of charged centers, transformation of the time-of-flight curves with a well-pronounced plateau region, which is indicative of quasiequilibrium transport according to theory, proceeds in full agreement with the classical concepts on the role of a space charge or bimolecular recombination during high-signal irradiation. Transport of charge carriers in the molecularly doped polymer is not quasiequilibrium but dispersive.     

Scandium-containing layered hydroxides

A scandium analogue of hydtotalcite and a mixed sample containing both scandium and aluminum have been synthesized and characterized. It is known that both samples have a layered structure; the unit cell parameters of the scandium-containing samples are slightly higher than the respective values of an ordinary aluminum-containing sample. The mixed-metal scandium-aluminum sample easily regains its layered structure after a dehydration/rehydration cycle, while the scandium analogue after this treatment is restored only partially.     

On the theory of classic mesodiffusion

A simple model of the classical random walk of particles with a constant speed and anisotropic angular distribution is used to study the characteristic features of mesodiffusion, that is, of an intermediate stage between the ballistic regime (short times) and ordinary diffusion (long times). In the extreme case of anisotropy, namely, walking along a straight line, the process can be described by the telegraph equation, whose solution contains δ-functions accounting for the ballistic component. As the anisotropy becomes less pronounced, the δ-singularity transforms into a frontal burst (the quasi-ballistic component), beyond which the distribution can be satisfactorily described by the telegraph approximation. In the other extreme case of isotropic walking, the frontal burst disappears and the telegraph approximation, contrary to general belief, proves to be cruder than the diffusion approximation.     

The influence of the drift shift of electrons undergoing thermalization on the kinetic characteristics of geminate conductivity and recombination

A program for numerically solving the Smoluchowski equation with a modified initial condition taking into account the drift shift of electrons that experience thermalization in an external electric field was developed. The probability of survival and the polarization current of isolated ion pairs were calculated. Shift effects were shown to be especially strong in the region of medium electric fields on the order of 10⁷ V/m and noticeably weaker in both low and high fields. This was related to the proportional relation between the drift shift and electric field applied. The program was used to critically analyze the available experimental data on pulsed photoconductivity of polyacenes.     

1,4-Benzodiazepines and their cyclic homologs and analogs

The dependence of the IR and PMR spectral characteristics of 12 compounds of the 1,2-dihydro-3H-1,4-benzodiazepine series on structural and sterochemical factors was studied. Information in favor of concepts regarding the pseudoboat conformation as the primary one for this type of 1,4-benzodiazepine derivative was obtained.     

Theoretical Analysis of the Mechanism of Slow Reversible Degradation of the Transport Properties of Photoconducting Polymers

The dose effect in photoconducting polymers is analyzed, concerning the buildup of minority charge carriers that act as recombination sites, which leads to a noticeable decrease in the effective mobility of majority carriers and degradation of the transport properties of polymer layers. This charge degradation mechanism is universal and completely reversible and can be rationalized in terms of the Rose–Fowler–Vaisberg model. The disorder parameter plays a determining role in the manifestation of the dose effect; when it decreases (<0.4), both the magnitude of the dose effect and the time required for its annealing strongly increase.     

Drift mobility of excess charge carriers in molecularly doped polymers upon photo-and radiation-induced charge generation

Comparative experiments on molecularly doped (with aromatic hydrazone) polycarbonate were performed to measure the drift mobility of excess charge carriers using carrier generation by exposure to light and ionizing radiation. Measurements showed practically complete coincidence of both mobility values and signal shapes. Compared were the results of measurements on polymer specimens with various thicknesses supported on substrates with different surface roughness, as well as for samples with or without an injecting amorphous-selenium layer. Dispersive carrier transport was observed in all cases. However, current transients sometimes displayed a plateau, depending on the sample preparation conditions. As the magnitude of generated (injected to the polymer layer) charge increased, a current spike appeared by the end of the transit time, thus indicating the emergence of local space-charge-limited current.     

Use of surface plasmon resonance for studies of protein-protein and protein-phospholipid membrane interactions. Application to the binding of factor VIII to von Willebrand factor and to phosphatidylserine-containing membranes.

The surface plasmon resonance phenomenon is used for real time measurements of protein-protein and protein-membrane interactions. In the present study two surface plasmon resonance-based binding assays permitting study of the interaction of coagulation factor VIII (fVIII) with von Willebrand factor (vWf) and phospholipid have been developed. These interactions of fVIII are required for maintenance of fVIII concentration in circulation and for the assembly of the functional factor Xase complex, respectively. With these binding assays, the role of the light chain (LCh) in fVIII binding to vWf and to immobilized phospholipid monolayers and intact vesicles containing 25% phosphatidylserine (PS) and 4% PS was examined. The finding that Kd of LCh binding to vWf (3.8 nM) is 9.5 times higher than that of fVIII (0.4 nM), indicates that the heavy chain (HCh) is required for the maximal affinity of fVIII for vWf. In contrast, affinities of LCh for 25/75 PS/phosphatidylcholine (PC) monolayers and 4/76/20 PSPC-phosphatidylethanolamine (PE) vesicles are similar to that of fVIII, indicating that LCh is solely responsible for these interactions. It was also examined how removal of the acidic region affects the binding affinity of the remaining part of LCh for vWf and phospholipid. It was demonstrated that the loss of the LCh acidic region upon thrombin cleavage leads to an 11 and 160-fold increase in the dissociation rate constant (k(off) value) and a 165 and 1500-fold increase in the Kd value of the binding of fVIII fragment A3-C1-C2 to vWf compared to that of LCh and fVIII, respectively. In contrast, the binding affinity of A3-C1-C2 for PS-containing membranes was 8-11-fold higher than that of LCh. Possible conformational change(s) in C2 domain upon removal of the acidic region were studied using anti-fVIII monoclonal antibody NMC-VIII/5 with an epitope within the C2 domain of LCh as a probe. The determined lower binding affinity of A3-C1-C2 for NMC-VIII/5 immobilized to a sensor chip than that of LCh, indicates that these conformational changes do occur.     

Spatial Moments for the Nonstationary One-Velocity Problem of Transport Theory with Isotropic Scattering. 2. Plane Instantaneous Source

The spatial distribution of the density of particles emitted by a plane infinite isotropic source with a unit surface particle density is reconstructed for the nonstationary one-velocity problem of transport theory by the method of polynomial expansions with the use of Legendre and Hermite polynomials. The diffusion approximation is examined and the boundaries of the spatiotemporal region in which this approximation is valid are estimated.     

Superdiffusion and stable laws

The superdiffusion equation with a fractional Laplacian Δ ^α/2 in _N-dimensional space describes the asymptotic (t→∞) behavior of a generalized Poisson process with the range (discontinuity) distribution density ∼|x|−α−1. The solutions of this equation belong to a class of spherically symmetric stable distributions. The main properties of these solutions are given together with their representations in the form of integrals and series and the results of numerical calculations. It is shown that allowance for the finite velocity of free particle motion for α>1 merely amounts to a reduction in the diffusion coefficient with the form of the distribution remaining stable. For α<1 the situation changes radically: the expansion velocity of the diffusion packet exceeds the velocity of free particle motion and the superdiffusion equation becomes physically meaningless. Zh. éksp. Teor. Fiz. 115, 1411–1425 (April 1999)