The Liquid-Solid Interaction

The most dynamic processes are found where the exchange of energy is most dominant. That is often 

The reactions between clay minerals and ocean water were used by Sillen (1961) to explain the relative abundance of the major cations in ocean water and also pH of the ocean. Sillen used a thermodynamic approach where clay minerals and quartz are in equilibrium with each other. The following equilibria define the ratios (K )/(H ) and (Mg+)/(H+)  

In a similar way, the coexistence of kaolinite, smectite, and quartz fix the ratio (Na )/(H ). Although Sillen s predicted data agree very well with the cation ratios of ocean water, it has not been possible to prove that these reverse weathering reactions between clay minerals and quartz take place to a significant extent. The interaction between clay minerals and ambient water is complicated and therefore difficult to study under natural conditions. 

The Donnan equilibrium theory implies that dilution of a clay/water system containing monovalent and divalent cations displaces the equilibrium in such a manner that the absorption of divalent ions increases, whereas the absorption of monovalent ions decreases. The ionic charge is not the only determining factor in the absorption effect. Factors such as temperature, pH, and specific ions also play important roles. Hydration energy, which appears to be one of the most important factors for the absorption and fixation of cations, displaces the ionic equilibria in a manner opposing the Donnan equilibrium theory. According to Sawhney (1972), cations with low hydration energy such as Ca, Mg and Sr, produce expanded interlayers and are not fixed . 

---

In connection with quantifying possible changes in the structure of liquids due to confinement in pores, an old rule, known as Gurvitsch s rule ) may be mentioned. It states that for a variety of different liquids the total pore volume is within narrow limits identical, if computed on the basis of their bulk densities. For Instance, McKee l finds a maximum variation of 4% for a number of organic adsorptives on silica gel with a (Kelvin) radius of 1.7 nm. suggesting that only minor structural deviations take place. However, for more strongly associated liquids like water, and for narrower pores, the deviations may be larger. Then the liquid-solid interaction also starts to play its role. 

This is the science that deals with the interface of two materials. The interface may exist between any forms of matter, including a gas phase. However, for the purpose of understanding the interfacial reactions of coating materials, it is only necessary to analyze the liquid-solid interaction. The effect of surface interaction between a liquid coating and the surrounding air is small and may be ignored. 

The shift of the free energy due to interactions with the solid is given by the liquid-solid interaction term (30) minus the lost part of the fluid-fluid interaction term in Eq. (9). We will compute it here for a liquid layer with a sharp interface at 2 = /i parallel to the solid surface at 2 = /i (the diffuse interface theory is discussed in Section 5.2). Setting p = p/ = const at 0 < 2 < /i and neglecting the gas density, the modified free energy integral (9) can be computed by integrating the van der Waals interactions laterally as in Eq. (11). The correction due to the interaction with the solid is computed as... 

The length a belongs to the molecular scale. Usually, the ratio x/xi is of the order 10 therefore Kj in Tanner s law is around 120. The liquid-solid interaction enters in the interface profile... 

The surface roughness, r, is defined as the ratio of the actual surface area to the horizontal projection of the surface area. In the Cassie-Baxter model, the interaction of the fluid with the air trapped in the gaps of rough (or porous) surfaces is considered alongside the liquid-solid interaction. The effect is strongest in the case of water, which forms a contact angle of 180° with air. The Cassie-Baxter model introduces a surface fraction parameter, /, which represents... 

In the absence of complicating factors, such as micropore filling effects, the magnitude of is dependent oh the nature of the liquid-solid interactions and the extent of the available surface. Thus... 

The parameter Sij determines the interaction strength between particles i and j. By choosing a different parameterisation for interactions between liquid particles and liquid and solid ones, the wetting behaviour can be simulated. Kondo et al. derived by energy considerations that the liquid-solid interaction strength sis depends on the pure liquid one su and the contact angle 0 [27]... 

The liquid-solid interactions of physical (essentially van der Waals) and chemical (essentially acid-base) type can quench or put out some surface sites, so modifying their reactivity towards reagents. Therefore, in order to understand and predict the catalytic ability of given surfaces in different liquids, it is very important to measure the effective surface properties, besides the knowledge of the intrinsic properties. 

Thus, the measured contact ingle between L and S permits the use of the liquid-solid interaction as a force balance (cf. de Gennes (1990) and van Oss (1994)). It should be noted that Eq. 6.4 contains three unknowns, i.e., 7, 7 , and (assuming that the values for 7 , and aie known as they would be in a real experiment). To obtain the three 7-component values for... 

The Wilhehny Plate technique is the most versatile tool for surface characterization and wetting study. The more elaborate measurement procedure as well as sample preparation have hindered its popularity. However, it is still the best tool when it comes to studying the dynamics of the liquid-solid interactions. 

This interface is critically important in many applications, as well as in biological systems. For example, the movement of pollutants tln-ough the enviromnent involves a series of chemical reactions of aqueous groundwater solutions with mineral surfaces. Although the liquid-solid interface has been studied for many years, it is only recently that the tools have been developed for interrogating this interface at the atomic level. This interface is particularly complex, as the interactions of ions dissolved in solution with a surface are affected not only by the surface structure, but also by the solution chemistry and by the effects of the electrical double layer [31]. It has been found, for example, that some surface reconstructions present in UHV persist under solution, while others do not. 

Precipitation of niobium and tantalum compounds in forms that are suitable for separation from the aqueous media (liquid-solid interaction) ... 

In view of the importance of the particle/bubble contact, it may be assumed that the stress acting on the particles during gas sparging is determined by electrostatic interactions as well as by hydrophobic and hydrophilic interactions, which are determined by the nature of the liquid/solid system. The use of Pluronic as additive leads to the reduction of destruction process [44,47] possibly due to less bubble/floc contact which is also described by Meier et. al. [67]. 

Rubber swelling modifies the liquid/solid work of adhesion. Wo, because in addition to the initial liquid/solid interactions, liquid diffusion into the solid produces supplementary liquid/liquid interactions, hquid molecules having passed through the liquid/solid interface. Therefore, to the initial work of adhesion in the absence of swelling, Wq, an additional term corresponding to a fraction of the cohesion energy of the liquid, 2y, should be added. If / is the time of diffusion, the work of adhesion at /, Wo(t), can then be expressed as... 

To evaluate the time-dependent function, X(t), a simple model of diffusion is proposed. Starting from Langmuir adsorption theory, we consider that liquid molecules having diffused into the elastomer are localized on discrete sites (which might be free volume domains). In these conditions, we can deduce the rate of occupation of these sites by TCP with time. Only the filhng of the first layer of the sites situated below the liquid/solid interface at a distance of the order of the length of intermolecular interaction, i.e., a few nanometers, needs to be considered to estimate X(t). 

There are several isotherm models for which the isotherm shapes and peak prohles are very similar to that for the anti-Langmuir case. One of these models was devised by Fowler and Guggenheim [2], and it assumes ideal adsorption on a set of localized active sites with weak interactions among the molecules adsorbed on the neighboring active sites. It also assumes that the energy of interactions between the two adsorbed molecules is so small that the principle of random distribution of the adsorbed molecules on the adsorbent surface is not significandy affected. For the liquid-solid equilibria, the Fowler-Guggenheim isotherm has been empirically extended, and it is written as ... 

Principles and Characteristics In this most simple liquid-solid interaction a resin is washed with a solvent to (selectively) remove external components. This additive isolation procedure can be used to show that a component is applied on the surface of a polymer pellet, as opposed to blending throughout the polymer. Other LSE procedures consist in soaking the polymer in boiling solvent and cold liquids. 

Isolation may occur by liquid-solid interaction (extraction, dissolution) or heat (thermal, pyrolytic, laser). Extraction methods easily handle qualitative screening for low- to medium-MW compounds fail for high-MW components or polymer-bound functionalities and are less reliable quantitatively (analyte dependent). When applicable, dissolution methods suffer from sensitivity, because of the dilution effect on account of the polymer. In-polymer analysis performs well for qualitative screening, but is as yet not strongly performing for quantitative analysis, except for some specific questions. 

Ultrasonic extraction is a well-known commercial method to increase mass transfer rate by cavitation forces. Bubbles in the liquid-solid extraction using UE can explosively collapse and produce localized pressure, improving the interaction between the intracellular substances and the solvent to facilitate the extraction of the phytochemical. 

Although this concept was originally derived for gas-solid adsorption, it can also be successfully applied to describe a liquid-solid interaction process when using the equations... 

The above exceptions leave relatively few sensors based on integrated separation and detection, particularly of the types involving gas-liquid and liquid-liquid interfaces, which require the detector to be responsive to the gas or ion (molecule) transferred across the membrane. The scope of liquid-solid interactions is somewhat broader as it enables not only retention of the analyte and monitoring of some intrinsic property, but also to retain a product of a previous reaction, thereby substantially expanding the possibilities. 

---