Dynamic processes happening during the evaporation of films of fusible materials

Optical waveguides on glass substrates are a promising area in their application in simple and cheap optoelectronic devices. As shown in [1], the highest refractive index is achieved during the formation of waveguides by oxidized film diffusion. However, realization of a number of electro-optical effects is restrained by probabilistic repeatability of wave guiding layers which holds down the development of optoelectronics [1-3]. This happens due to the fact that film formation in gas exchange mode isn't explored enough. One of the reasons of probabilistic repeatability of local thickness and film composition is dynamic processes which happen during the material evaporation. The regularities of evaporation, which were earlier found by Knudsen, Langmuir and other scientists for point sources, fail when it comes to the line where one material escape into another state. Most materials, which have three states - solid, liquid, gaseous - at ambient pressure heating, in vacuum, lose their liquid state partly or completely. Moreover, the film distribution over the substrate is quite unclear because of the poor study of molecular vapor flow and substrate interaction

Molecular dynamics under confinement to one dimension: Options of measurement and accessible information

Two types of host systems for one-dimensional molecular arrangements are considered, namely zeolites containing one- and two-dimensional arrays of channels of sub-nanometre dimension and porous silicon with channel diameters in the range of a few nanometres. After a discussion of the potential of zeolites as host systems, in particular for molecular arrangements under the conditions of single-file diffusion and of molecular traffic control, actual diffusion measurements by means of pulsed-field gradient NMR and interference/IR microscopy are shown to reveal substantial differences between the real and ideal zeolite structure. In contrast, porous silicon with one-dimensional channel arrays is successfully exploited as a host system allowing the experimental observation of such most important features of molecular confinement like hysteresis in mesoscalic systems and surface diffusion. Thus, the attainable experimental insight offers promising conditions for a comparison of the results with those of the theoretical treatment of the observed phenomena. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Molecular dynamics under confinement to one dimension: Options of measurement and accessible information

Two types of host systems for one-dimensional molecular arrangements are considered, namely zeolites containing one- and two-dimensional arrays of channels of sub-nanometre dimension and porous silicon with channel diameters in the range of a few nanometres. After a discussion of the potential of zeolites as host systems, in particular for molecular arrangements under the conditions of single-file diffusion and of molecular traffic control, actual diffusion measurements by means of pulsed-field gradient NMR and interference/IR microscopy are shown to reveal substantial differences between the real and ideal zeolite structure. In contrast, porous silicon with one-dimensional channel arrays is successfully exploited as a host system allowing the experimental observation of such most important features of molecular confinement like hysteresis in mesoscalic systems and surface diffusion. Thus, the attainable experimental insight offers promising conditions for a comparison of the results with those of the theoretical treatment of the observed phenomena. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Gas diffusion in zeolite beds: PFG NMR evidence for different tortuosity factors in the Knudsen and bulk regimes

Self-diffusion of ethane in beds of zeolite NaX is studied using Pulsed Field Gradient (PFG) NMR. The ethane diffusivities were measured for displacements, which are orders of magnitude larger than the size of individual crystals. These diffusivities were compared with those, calculated using simple gas kinetic theory. The results of the comparison indicate that for the same bed of NaX crystals the apparent tortuosity factor in the Knudsen regime (i.e. when molecule-solid collisions dominate) is significantly larger than that in the bulk regime (i.e. when molecule-molecule collisions dominate). This finding is attributed to the more pronounced geometrical trapping by the pore structure of the zeolite bed in the Knudsen than in the bulk regime

Molecular dynamics under confinement to one dimension: Options of measurement and accessible information

Two types of host systems for one-dimensional molecular arrangements are considered, namely zeolites containing one- and two-dimensional arrays of channels of sub-nanometre dimension and porous silicon with channel diameters in the range of a few nanometres. After a discussion of the potential of zeolites as host systems, in particular for molecular arrangements under the conditions of single-file diffusion and of molecular traffic control, actual diffusion measurements by means of pulsed-field gradient NMR and interference/IR microscopy are shown to reveal substantial differences between the real and ideal zeolite structure. In contrast, porous silicon with one-dimensional channel arrays is successfully exploited as a host system allowing the experimental observation of such most important features of molecular confinement like hysteresis in mesoscalic systems and surface diffusion. Thus, the attainable experimental insight offers promising conditions for a comparison of the results with those of the theoretical treatment of the observed phenomena. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Heterogeneity of polyelectrolyte diffusion in polyelectrolyte-protein coacervates: A H-1 pulsed field gradient NMR study

Proton pulsed field gradient (PFG) NMR was used to study the diffusion of poly(diallyldimethylammonium chloride) (PDADMAC) in coacervates formed from this polycation and the protein bovine serum albumin (BSA). Application of high (up to 30 T/m) magnetic field gradients in PFG NMR measurements allowed probing the diffusion of PDADMAC on a length scale of displacements as small as 100 nm in coacervates formed at different pH's and ionic strengths, i.e., conditions of varying protein-polycation interaction energy. Studies were carried out for a broad range of diffusion times and corresponding values of the mean square displacements. Several ensembles of PDADMAC polycations with different diffusivities were observed in the measured range of diffusion times. The existence of these ensembles and the pattern of their changes with increasing diffusion time support the hypothesis about the microscopic heterogeneity of PDADMAC-BSA coacervates and also provide evidence for the dynamic disintegration and reformation of dense domains