Interfacial layer zones

Thus, the important features of the structural-mechanical barrier are the rheological properties (See Chapter IX,1,3) of interfacial layers responsible for thermodynamic (elastic) and hydrodynamic (increased viscosity) effects during stabilization. The elasticity of interfacial layers is determined by forces of different nature. For dense adsorption layers this may indeed be the true elasticity typical for the solid phase and stipulated by high resistance of surfactant molecules towards deformation due to changes in interatomic distances and angles in hydrocarbon chains. In unsaturated (diffuse) layers such forces may be of an entropic nature, i.e., they may originate from the decrease in the number of possible conformations of macromolecules in the zone of contact or may be caused by an increase in osmotic pressure in this zone due to the overlap between adsorption layers (i.e., caused by a decrease in the concentration of dispersion medium in the zone of contact). 

The details of the formation of the interfacial layer are the focus of this section without concurrently emphasizing the processes which generate the interface stated. This separation better allows the individual aspects to be identified, but should not imply a decoupling of the two phenomena. The interface layer can have a multiplicity of zones with a division between metallic and semiconducting regions, as depicted in Fig. 3.19. 

On the semiconducting side, the interfacial layer has two zones. The first zone lies within the evanescent tail of the metal. The second zone is the remaining region where, due to interdiffusion, a composition or doping different from the original bulk semiconductor exists. A similar description can be characterized on the metal side and the new alloyed metal zone may be of sufficient width to become the metal forming the barrier. This new interfacial metal can have different characteristics from the originally deposited metal. 

Abstract. The presence of water-soluble polymers affects the microstructure of polymer-modified cement mortar. Such effects are studied by means of SEM investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. The polymers provide an improved dispersion of the cement particles in the mixing water. The tendency of certain water-soluble polymers to retard the flocculation of the cement particles minimizes the formation of a water-rich layer around the aggregate surfaces. They also provide a more uniform distribution of unhydrated cement particles in the matrix, without significant depletion near aggregate surfaces. Both effects enable to reduce the interfacial transition zone (ITZ). The polymers also provide a more cohesive microstructure, with a reduced amount of microcracks. 

The XRD studies of the interfacial transition zone (material produced by abrasion of paste layers) [16], as well as the SEM observations with EDS analysis [16] revealed the presence of transition zone surrounding the aggregate grains, determined by Maso as an aureole [ 10]. This relates to the former water film around the aggregate. This area shows higher w/c ratio and subsequently cement components can readily dissolve, as well as the hydration products crystallize from the solution. Calcium hydroxide crystallizes in this interfacial transition zone and the crystals are oriented in such a way that their (001) axis is perpendicular to the surface of aggregate, as it was reported by Barnes et al. [17]. The C-S-H is then formed and the two products occur together as a duplex film about 1 pm thick (Fig. 6.7). 

This interfacial transition zone is enriched with portlandite crystals of hexagonal shape, with the c axis perpendicular to the surface of aggregate [49]. This layer is not continuous and there are in the formed pockets the C-S-H particles, surrounding sometimes the portlandite crystals [50, 51], as well as the ettringite is present too [52]. In Fig. 6.9 the construction of paste—reinforcement interface is shown [50]. The three zones can be noticed ... 

The thickness of interfadal transition zone is determined by the range of oriented portlandite crystals and equals 50-100 pm [16]. However, only a 10-20 pm thick layer of this zone shows clearly different mechanical properties, as compared to the bulk cement matrix. The microstmcture of interfacial transition zone is variable and depends on the type and properties of cement and reinforcement, presence of admixtures, concrete maturing regime, as well as the other factors (Fig. 6.19). 

The studies of the phase composition of interfacial transition zone were also developed. A white layer of reaction products is formed on the reactive aggregate surface, sometimes surrounded by a black gel. The crystalline thaumasite is often formed this white layer [60,71], Regourd et al. [92] found the two types of gel the... 

The difference between the microstructure of cement paste and concrete should be taken into accoimt when the diffusion conditions are compared. The paste (cement matrix in concrete)— aggregate interfacial transition zone is of special importance. This transition zone is formed of the thin layer of cement paste, about 50 pm wide, which has different microstmcture than the bulk cement matrix in this concrete (see Sect. 6.2). The porosity of this interfacial transition zone is significantly higher the portlandite content is higher as well. In the case of high performance concrete with low w/c ratio the microstructural difference between the interfacial region and the matrix is negligible or none. 

The existence of a supercritical phase in the interfacial zone, where the temperature and pressure gradients are considerable, was suggested. This attractive hypothesis was expressed by Henglein,20a "Under [these physical] conditions, does the hot interfacial region represent a very dense gas, or is it still a liquid " This hypothesis was re-examined to explain the decomposition of nitrophenyl acetate, and DMF. Actually, the structure of the interfacial layer is difficult to define (Fig. 9). 

In accordance to Gugenheim approximation the surface layer represents a zone with a certain thickness, within which the interfacial forces are not in equilibrium. Such regions appear when at least two phases interact in the following combinations liquid-gas solid-gas solid-liquid and liquid-liquid. Based on statistical physics, for the interfacial layers was defined a state function (3.224) and a probability of distribution ( 3.225 ), into a wider canonized ensamble ... 

The value of-a depends on the amount of crosslinks in the interfacial layer and its volume. Let us assume that the major fiaction of polar units of BNR is uninvolved in its formation and the value of-a was recalculated to the 100% content of butadiene units -a " (Fig. 2.1) and used to characterize the structure of the interfacial interaction zone and the amount of crosslinks contained in it. In such a manner, the effect of the interfacial layer volume could be minimized. As will be shown below, this situation may not be attained in all cases. 

The interface is a layer between two different phases of a composite material. The structure and composition of that particular layer, known as the interfacial transition zone (ITZ), depend on the properties of both neighbouring phases and also on conditions of mixing, hydration, curing and ageing of the materials. 

In the stratification strategy with a replacing air distribution in the lower zone, the height of the boundary layer between the lower and upper zones can be determined with the criteria of the contaminant interfacial level.This level, where the air mass flow in the plumes is equal to the air mass flow of the supply air, IS presented in Fig. 8,4. In this ideal case the wait and air temperatures are equal on the interfacial level. In practical cases they are not usually equal and the buoyancy flows on the walls will raise the level and decrease the gradient. 

According to Frumkin and Damaskin, A% at the air/solution interface changes linearly with composition, i.e., the interface behaves as two condensers in series. "" On a molecular basis, this model is tantamount to assuming that an adsorbate and solvent do not interact in the interfacial zone, but create two homogeneous surface layers. 

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