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PubMed1989

Populations of GABAergic neurons and axons in layer I of rat auditory cortex.

Neurons and axon terminals (puncta) immunostained by an antibody against glutamic acid decarboxylase were studied in layer I of adult rats in architectonically identified area 41 of auditory cortex. The borders of area 41 and the laminar subdivisions of cortex were established in normal material and in other studies of cortical connections. Vibratomed or frozen sections were immunostained. The objectives of the study were to classify the types of (i) glutamic acid decarboxylase-positive neurons and (ii) puncta, and (iii) to examine their spatial distribution within layer I. Control sections were devoid of specific immunostaining. More than 90% of layer I cells are glutamic acid decarboxylase-positive. Four types of neuron were identified in Golgi material, including small neurons with stellate dendritic fields, horizontal cells with laterally projecting arbors, medium-sized neurons with stellate, widely ramifying dendritic fields, and large neurons with broad dendritic fields spanning the depth of layer I or branching laterally. In the glutamic acid decarboxylase material, examples with a somatodendritic shape matching each of these types were found. The average somatic diameter of glutamic acid decarboxylase-positive neurons (mean = 59 microns2, S.D. = 21 microns2) suggests that the small and medium-sized neurons predominate. Glutamic acid decarboxylase-positive neurons occur throughout the depth of layer I, but are far more numerous in the deeper half (68% in layer Ib) than in the superficial part (32% in layer Ia). Glutamic acid decarboxylase-positive neurons form small clusters of three to five cells across the cortical surface, with a range of 0-9/100 microns across the cortex. Most glutamic acid decarboxylase-positive neuronal perikarya were intensely immunostained, and the dendrites of the medium-sized and large neurons were traced as far as 50-75 microns beyond their initial branching point. Glutamic acid decarboxylase-positive puncta also had variable shapes. Both small, fine puncta (less than 0.5 micron in diameter) and larger, coarser ones (greater than 1.5 micron in diameter) were present, though the former were much more common. In traverses from the pia to the layer II border, the puncta average about 40/100 microns2 (range: 20-80), and the shape of individual pia--layer II traverses is multipeaked, often with a slight trough at congruent to 80 microns depth, then rising slowly in number toward layer II.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex.

This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. Their apical dendrites do not usually extend above layer IV, and a few of these cells may be non-pyramidal. Small pyramidal cells and inverted pyramidal cells project to the opposite cortex, but not to the inferior colliculus. Medium-sized pyramidal cells project in both systems. In addition, certain callosal cells of origin in layers V and III were morphologically similar. More than one-third of the commissural cells originate in the superficial part of layer V, where only 7% of the inferior colliculus projection neurons arise. Most corticocollicular cells lie deeper in layer V, where there are fewer commissural neurons. These findings suggest that the efferent systems projecting to telencephalic and mesencephalic targets are morphologically distinct and spatially segregated in layer V. However, the commissural projection includes similar cells in different cortical layers. The types of these efferent neurons may be more closely related to their target than to their laminar origin.

Animals↗
PubMed2004

Dewetting of thin liquid films near soft elastomeric layers.

Thin liquid film instabilities driven by van der Waals forces and in the proximity of soft elastomeric layers are considered in this work through two model problems: (i) a liquid film resting on an elastomeric layer and (ii) a liquid film bounded from one side by a rigid substrate and from the other side by an elastomeric layer. The elastomeric layers are modeled as linear viscoelastic solids, van der Waals forces are assumed to act only in the liquid, and lubrication theory and linear stability analysis are applied. For a liquid film resting on an elastomeric layer, substrate deformability has a destabilizing effect, as evidenced by an increase in the maximum growth rate and range of unstable wavenumbers. The destabilization worsens for thicker solid layers and is due to a lowering of the effective liquid-air interfacial tension. For an elastomeric layer resting on a liquid film, layer deformability has a stabilizing effect for thin layers but a destabilizing effect for thicker layers, with the former due to an enhancement and the latter due to a reduction of the effective solid-air interfacial tension. The results presented here suggest the possibility of exploiting the dewetting of thin liquid films to create topographically patterned surfaces on soft polymeric solids.

Journal Article↗
PubMed2004

Analysis of the electrophoretic mobility and viscosity of dilute Ludox solutions in terms of a spherical gel layer model.

A spherical gel layer model of colloidal particles is used to analyze the electrophoretic mobility and viscosity of a dilute suspension of the silica sol, Ludox, reported previously by Laven and Stein (J. Laven, H.N. Stein, J. Colloid Interface Sci. 238 (2001) 8-15). The colloid is modeled as a sphere with a solid inner core surrounded by a diffuse gel layer of uniform thickness and comprising a specific fraction, f, of the colloidal particle's mass. The gel layer is accessible to solvent and ions, but the gel layer retards the flow of solvent, which is assumed to obey the Brinkman equation. The colloidal charge is assumed to be spherically symmetric, but its disposition on the surface of the core particle and gel layer (alpha = fraction of charge in the gel layer) is left as an adjustable parameter. Experiments at pH 5.7 and 8.7 over a KCl concentration range of 0.3 to 80 mM are examined. At high salt and/or low pH, the thickness of the gel layer is estimated to be 1.0 to 1.6 nm depending on the assumed fraction of silica present in the gel layer. At low salt (0.3 mM) and high pH, where the net absolute charge of Ludox is large, the thickness of the gel layer is estimated to be 3.7 to 4.1 nm. Thus, the thickness of the gel layer appears to increase with decreasing salt at high pH. The net charge required to simultaneously match experimental and model mobilities and viscosities is sensitive to the choice of f and alpha. Nonetheless, for reasonable choices of these parameters (f = 0.13 and alpha approximately equal to 1.0), the estimated net absolute charges of Ludox from present modeling are in good agreement with the titration charges of Bolt (G.H. Bolt, J. Phys. Chem. 61 (1957) 1166-1169), and Milonjic (S.K. Milonjic, Colloids Surf. 23 (1987) 301-311) over the entire salt concentration range at pH 8.7. At pH 5.7, however, the estimated net absolute charge from current modeling exceeds the Bolt values by about 50%.

Journal Article↗
PubMed2005

The functional layered organosilica materials prepared with anion surfactant templates.

A novel strategy for the synthesis of layered organosilica is demonstrated. The ionic interaction between the anionic group of a surfactant (sodium dodecyl sulfate) and the cationic organic group of an organosilane (3-aminopropyltrimethoxysilane, ATMS) under acidic conditions was utilized to create a layered organosilica at room temperature. The inorganic part of the organosilica layer was an Si-O hexagonal sheet, and organofunctional groups were alternately arranged on both sides of the sheet. The layered structure of the ATMS organosilica was retained after the removal of the surfactant with chloride anion. The properties of the layered ATMS organosilica were investigated. The layered ATMS-Cl organosilica is stable and possesses a definite layer structure in water or ethanol. Various kinds of anions can be intercalated in the interlayer space of the layered ATMS organosilicas and the layer was expanded dependent on the intercalated anions. The structure of the layered ATMS organosilica was well retained during the intercalation processes.

Journal Article↗
PubMed2003

Actively shielded multi-layer gradient coil designs with improved cooling properties.

In standard cylindrical gradient coils consisting of a single layer of wires, a limiting factor in achieving very large magnetic field gradients is the rapid increase in coil resistance with efficiency. This is a particular problem in small-bore scanners, such as those used for MR microscopy. By adopting a multi-layer design in which the coil wires are allowed to spread out into multiple layers wound at increasing radii, a more favourable scaling of resistance with efficiency is achieved, thus allowing the design of more powerful gradient coils with acceptable resistance values. Previously this approach has been applied to the design of unshielded, longitudinal, and transverse gradient coils. Here, the multi-layer approach has been extended to allow the design of actively shielded multi-layer gradient coils, and also to produce coils exhibiting enhanced cooling characteristics. An iterative approach to modelling the steady-state temperature distribution within the coil has also been developed. Results indicate that a good level of screening can be achieved in multi-layer coils, that small versions of such coils can yield higher efficiencies at fixed resistance than conventional two-layer (primary and screen) coils, and that performance improves as the number of layers of increases. Simulations show that by optimising multi-layer coils for cooling it is possible to achieve significantly higher gradient strengths at a fixed maximum operating temperature. A four-layer coil of 8 mm inner diameter has been constructed and used to test the steady-state temperature model.

Journal Article↗
PubMed2006

Acute hypoxia and programmed cell death in developing CNS: Differential vulnerability of chick optic tectum layers.

The chick optic tectum displays an alternating pattern of cellular and plexiform layers and at embryonic day (ED) 12 there are mainly four cellular layers: transient cell compartment 3 (TCC3), compartment "h-i-j"(C"h-i-j"), stratum griseum centrale (SGC) and subventricular zone (SvZ). In the present work we characterized the programmed cell death (PCD) of these layers and their vulnerability to acute hypoxia at ED12, and also identified the main cellular type involved in hypoxic cell death. The colocalization of three independent markers of cell degeneration: pyknotic nuclei by Hoechst staining, fragmented DNA by TdT-mediated dUTP nick-end labeling (TUNEL), and presence of active caspase-3 by immunofluorescence, was analyzed in embryos that developed in normoxic conditions (control embryos) and embryos that were subjected to hypoxia (8% O(2)/92% N(2)) for 60 min (hypoxic embryos), followed by 0-12 h of normoxic recovery. In control embryos cell death rate within each layer was constant through time, but there were significant differences (P<0.01) in cell death rates among the different layers. In contrast, in hypoxic embryos, a significant increase (P<0.01) in cell death rate was observed in layers TCC3, C"h-i-j" and SGC. This change was evident only at 6 h post-hypoxia, and at later time points cell death rate was similar to control values. Each of these layers had a different vulnerability to the hypoxic event while the SvZ layer was not affected. In addition, the significant colocalization between the neuron specific nuclear protein (NeuN) and TUNEL signal showed that hypoxia affected primarily neurons. In conclusion, our findings demonstrate that in the chick optic tectum at ED12, PCD is layer dependent and that acute hypoxia causes a transient increase in neuronal death in a delayed fashion, which is also layer dependent. The morphological features of the neuronal death process at the light microscope level resembled apoptosis.

Analysis of Variance↗
PubMed2001

Ultrastructure of early mineral deposition during hyaline layer formation in rat molars.

There is no consensus on whether the first mineralized layer, the hyaline layer, that is juxtaposed to root dentine is a variety of dentine or cementum or even a tissue of epithelial origin. Some suggest that there is no intermediate tissue between the acellular extrinsic fibre cementum (AEFC) and the root dentine. Here, to study hyaline layer formation and mineralization we examined by transmission electron microscopy the early stages of root development in upper molars from 10 to 13 day old Wistar rats. In addition to conventionally processed material, undemineralized and unstained sections were examined, which showed the deposition of fine mineral crystals in contact with the mineralized surface of root dentine. Early mineralization of the hyaline layer occurred in the region of the inner basement membrane, which persisted between the inner cellular layer of Hertwig's epithelial root sheath and the outer mineralized root dentine. When the root sheath began its fragment, collagen fibrils from the developing periodontal ligament began to insert into the mineralising hyaline layer, which was 0.5-0.8 micron wide. As the fragmentation of the root sheath HERS increased, more collagen fibrils appeared intermingled with the mineralising hyaline layer. In more advanced stages, when the hyaline layer had become fully mineralized and the formation of the AEFC began, the hyaline layer could no longer be identified. Thus, the hyaline layer is clearly discernible at early stages of periodontal development. Subsequently, it is masked by intermingling of cementum and dentine and therefore it is not possible to detect it in the formed roots of rat molars.

Animals↗
PubMed1998

Self-assembled alpha-hemolysin pores in an S-layer-supported lipid bilayer.

The effects of a supporting proteinaceous surface-layer (S-layer) from Bacillus coagulans E38-66 on a 1,2-diphytanoyl-sn-glycero-3-phosphatidylcholine (DPhPC) bilayer were investigated. Comparative voltage clamp studies on plain and S-layer supported DPhPC bilayers revealed no significant difference in the capacitance. The conductance of the composite membrane decreased slightly upon recrystallization of the S-layer. Thus, the attached S-layer lattice did not interpenetrate or rupture the DPhPC bilayer. The self-assembly of a pore-forming protein into the S-layer supported lipid bilayer was examined. Staphylococcal alpha-hemolysin formed lytic pores when added to the lipid-exposed side. The assembly was slow compared to unsupported membranes, perhaps due to an altered fluidity of the lipid bilayer. No assembly could be detected upon adding alpha-hemolysin monomers to the S-layer-faced side of the composite membrane. Therefore, the intrinsic molecular sieving properties of the S-layer lattice do not allow passage of alpha-hemolysin monomers through the S-layer pores to the lipid bilayer. In comparison to plain lipid bilayers, the S-layer supported lipid membrane had a decreased tendency to rupture in the presence of alpha-hemolysin.

Bacillus↗
PubMed2002

Effective rate models for receptors distributed in a layer above a surface: application to cells and Biacore.

In the Biacore biosensor, a widely used tool for studying the kinetics of ligand/receptor binding, receptors are commonly localized to the sensor surface through attachment to polymers that extend from the surface to form a layer. The importance of the polymeric layer in analyzing data is controversial. The question of the effect of a binding layer also arises in the case of ligands interacting with binding sites distributed in the extracellular matrix of cells. To identify and quantify the effects of a binding layer on the estimation of association and dissociation rate constants, we derived effective rate coefficients. The expressions show that rate constants determined under the standard assumption that binding takes place on a two-dimensional surface underestimate the true reaction rate constants by a factor that depends on the ratio of the height of the layer to the mean free path of the ligand within the layer. We show that, for typical biological ligands, receptors, cells, and Biacore conditions, the binding layer will affect the interpretation of data only if transport of the ligand in the layer is slowed substantially--by one or two orders of magnitude--relative to transport outside the layer. From existing experiments and theory, it is not clear which Biacore experiments, if any, have transport within the dextran layer reduced to such an extent. We propose a method, based on the effective rate coefficients we have derived, for the experimental determination of ligand diffusion coefficients in a polymeric matrix.

Binding Sites↗
PubMed2004

Static electrification of solid oxide in liquid metal and electrical double layer at the interface.

Static electrification of a solid oxide, say a semiconducting oxide in liquid metal, is mainly due to electron transfer between two phases. Excess electrons in the liquid metal phase provided by the oxide give rise to an electrical double layer at the interface. The electrical double layer may be divided into three parts, an immobile inner layer, a compressed diffuse layer, and a flat layer extending into the bulk liquid metal. Differential potential analysis and the induced emf method were used to measure the potential of the compressed diffuse layer and the excess electron density of the flat layer, respectively. Results show that most oxides in liquid metals carry positive charges on their surfaces and the potentials of the compressed diffuse layer are in the range of 3 to 42 microV. Such a low potential implies that the diffuse layer is considerably compressed. The excess electron densities of the flat layer are on the order of 10(22) electrons/m(3) of Hg and their contributions to surface charges of oxide are in the range of 10(17) to 10(18) charges/m(2) for the oxide/mercury systems with a solid density of 0.3 wt% at room temperature.

Journal Article↗
PubMed2003

The influence of porcelain layer thickness on the final shade of ceramic restorations.

STATEMENT OF PROBLEM: Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. By means of CAD/CAM layering technology such as CICERO, it is feasible to produce all-ceramic crowns with porcelain layers of predetermined thickness. However, it is not yet known whether changes in thickness of these porcelain layers within the clinically available space can perceivably influence the overall shade of the restoration. PURPOSE: The purpose of this study was to determine, quantitatively, the effect of different thickness ratios of opaque porcelain (OP) and translucent porcelain (TP) layers on the overall shade of all-ceramic specimens. MATERIAL AND METHODS: The CIELAB values of 5 assembled specimens, each consisting of 2 or 3 discs (CORE 0.70 mm/OP--0, 0.25, 0.50, 0.75, or 1.00 mm/TP 1.00, 0.75, 0.50, 0.25, or 0 mm) were determined with a spectrophotometer for the Vita shades A1, A2, and A3. Distilled water was used to attain optical contact between the layers. Black or white backgrounds were used to assess the influence of the background on the final shade. Color differences (DeltaE) between layered specimens were determined. Correlation between the thickness ratio and the L*, a*, and b* values was calculated by 2-tailed Spearman correlation analysis. RESULTS: The results indicated that small changes in OP/TP thickness ratio can perceivably influence the final shade of the layered specimens (DeltaE>1). Redness a* and yellowness b* increased with the thickness of OP for all shades. Redness a* (P<.01 for all shades) correlated more strongly with thickness than yellowness b* (P<.01 for A1 and A3; P<.05 for A2). The lightness (L*) was shade dependent. The correlation (r) between OP/TP thickness and L* was 0.975 (P<.01) for shade A1, 0.700 (not statistically significant) for shade A2, and 0.900 (P<.05) for shade A3. CONCLUSION: Small changes in thickness and shade of opaque and translucent porcelain layers can influence the final shade of the layered porcelain specimen.

Computer-Aided Design↗
PubMed2003

Properties and immersion behavior of magnetron-sputtered multi-layered hydroxyapatite/titanium composite coatings.

A new biocompatible multi-layered coating was developed by alternately depositing Ti and HA layers on Ti6Al4V substrates using radio frequency magnetron-assisted sputter processing to improve the interface properties between the coating and the substrate. The multi-layered coating consisted of an underlying Ti bond coat, the alternating layer, and an HA top-layer. Between the bond coat and the top layer, an alternating layer was created by means of gradually increasing Ti content with increasing depth from the HA top-layer. The experimental results indicated that the as-sputtered coating had quite uniform thickness and well bonded to the substrate. The multi-layered coating exhibited a better electrochemical behavior than monolithic HA coating. The XRD and low vacuum SEM results consistently indicated that highly crystalline coating was not appreciably dissolvable in simulated body fluid. The adhesion strength higher than 60MPa did not change much even after 14 weeks of immersion. The multi-layered composite coatings had the advantages of high and non-declining adhesion strength and high resistance to SBF attack.

Biocompatible Materials↗
PubMedDate not supplied

The sublaminar organization of corticogeniculate neurons in layer 6 of macaque striate cortex.

We examined the laminar distribution of corticogeniculate neurons in the macaque striate cortex labeled by axonal transport following injections of retrograde tracers into the lateral geniculate nucleus (LGN). Large injections of retrograde tracers involving all layers of the LGN resulted in a distinctive bilaminar distribution of labeled cells in cortical layer 6. One tier of labeled neurons was located along the layer 5-6 border and a second was located near the bottom of the layer, leaving the middle of layer 6 largely free of labeled neurons. Following injections of tracers that were restricted to the magnocellular layers of the LGN, almost all of the labeled neurons were located in the lower tier. In contrast, following injections of retrograde tracers confined to the parvocellular layers of the LGN, labeled cells were found in both tiers, with the greatest number in the upper tier. Thus, layer 6 of macaque striate cortex consists of three distinct sublayers only two of which are the source of descending projections to the LGN: an upper tier that projects exclusively to the parvocellular layers and a lower tier that projects to both magnocellular and parvocellular layers.

Affinity Labels↗
PubMedDate not supplied

Ocular dominance columns and local projections of layer 6 pyramidal neurons in macaque primary visual cortex.

To study the relationship between ocular dominance columns (ODCs) and axonal projections of individual layer 6 pyramidal neurons in the primary visual cortex, neurons were intracellularly labeled with biocytin in live slices prepared from macaque monkeys that had received an intravitreal injection of tetrodotoxin (TTX). The TTX injection indirectly causes a decrease in cytochrome oxidase (CO) expression in the cortical ODCs corresponding to the treated eye (Wong-Riley & Carroll, 1984). Sections from slices with labeled layer 6 neurons were double stained for biocytin and CO, to allow visualization of neuronal processes as well as ODCs. Twenty-seven layer 6 pyramidal neurons in ODC-labeled slices were analyzed. These neurons were classified according to the criteria of Wiser and Callaway (1996). Eight of these are class I neurons, which have dense axonal projections to the monocular layer 4C. The remaining 19 are class II neurons which project primarily to the binocular layers outside 4C. Among class I neurons, two have dense axonal arbors in layer 4C alpha (type I alpha), one in layer 4C beta (type I beta), and two throughout the depth of layer 4C (type IC). None of these neurons have ODC-specific axonal arbors. The remaining three class I neurons have focused axonal projections in layers 4C beta and 4A (type I beta A). All three appear to have axonal arbors predominantly within their home ODC in layer 4C. The axonal arbors of class II neurons do not appear to relate to ODCs in any specific fashion.

Animals↗
PubMedDate not supplied

Inhibitory basket cell synaptic input to layer IV simple cells in cat striate visual cortex (area 17): a quantitative analysis of connectivity.

In the absence of a direct and specific marker for basket cells, the aim of this paper was to use available data to estimate the density of basket cell synaptic input to smooth and spiny neurons within layer IV of cat striate visual cortex (area 17). A linear quantitative analysis of layer IV basket cell connectivity data suggests that on average basket cells (1) comprise 25-35% of all GABAergic neurons in layer IV (3552-4736 cells mm(-3)), (2) account for 30-41% of all putative inhibitory dendritic synapses of layer IV spiny stellate cells (145-195 synapses cell(-1)) and a similar proportion of layer IV basket cells (25-37%, 71-107 synapses cell(-1)), and (3) provide each layer IV spiny cell with 13-45 axons and each layer IV basket cell with 6-29 axons. These estimates suggest that basket cells may be less common and provide a smaller proportion of the dendritic synaptic input to layer IV spiny and smooth neurons than previously thought. In addition, the analysis indicates that a layer IV spiny stellate cell may receive on average as many synapses and axons from layer IV basket cells as from lateral geniculate relay cells. Based on this potential numerical similarity, a geniculate-basket synaptic pairing in a spine-shaft microcircuit is hypothesized. This microcircuit could implement a type of local (dendritic) push-pull interaction underlying subfield antagonism.

Animals↗
PubMed2006

Enhanced diffraction efficiency in a photorefractive liquid crystal cell with poly(9-vinylcarbazole)-infiltrated mesoporous TiO2 layers.

The photorefractive effect of a layer-structured liquid crystal cell was significantly enhanced when a C60-doped poly(9-vinylcarbazole) (PVK)/TiO2 nanocomposite was used in two photoconductive layers. The C60-doped PVK/TiO2 nanocomposite film was prepared by infiltrating C60-doped PVK into a highly ordered mesoporous TiO2 layer. The addition of the TiO2 layer to the C60-doped PVK layer increased the first-order Raman-Nath diffraction efficiency from 24% to 42.9%. This enhancement of diffraction efficiency is attributed to a blocking effect of charge recombination in the composite layer. The electron transfer from the PVK layer into the TiO2 layer would decrease the recombination of photogenerated charges in the PVK layer, while charges in the PVK layer could participate in the formation of a space-charge field.

Journal Article↗
PubMed2005

Equilibrium aspects of polycation adsorption on silica surface: how the adsorbed layer responds to changes in bulk solution.

Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M(w) is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount Gamma of CPAM increases with pH for all studied electrolyte concentrations until a plateau Gamma is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount. The thickness of adsorbed polymer layers, obtained by ellipsometry, increases with electrolyte concentration and decreases with pH. At low c(s) and high pH the polyelectrolyte adsorbs in a flat conformation. An overcompensation of the surface charge (charge reversal) by the adsorbed polyelectrolyte is observed at high c(s) and low pH. To reveal the reversibility of the polyelectrolyte adsorption with respect to the adsorbed amount and layer thickness, parameters such as polyelectrolyte concentration (c(p)), c(s), and pH were changed during the experiment. Generally, similar adsorbed layer properties were obtained independent of whether adsorption was obtained directly to initially bare surface or by changing pH, c(s), or the concentration of polyelectrolyte solution in the presence of a preadsorbed layer, provided that the coverage of the preadsorbed layer was low. Once a steady state of the measured parameters (Gamma, d) was reached, experimental conditions were restored to the original values and corresponding changes in Gamma and adsorbed layer thickness were recorded. For initially low surface coverage it was impossible to restore the layer properties, and in this case we always ended up with higher coverage than the initial values. For initial high surface coverage it was usually possible to restore the initial layer properties. Thus, we concluded that polyelectrolyte appears only partially reversible to changes in the solution conditions due the slow rearrangement process within the adsorbed layer.

Journal Article↗