Solid-liquid interfacial interactions

When solid particles are dispersed in liquid medium, solid-liquid interfacial interactions will cause the formation of an adsorption layer, the so-called lyosphere, on their surface. The material content of the adsorption layer is the adsorption capacity of the solid particle, which may be determined in binary mixtures if the adsorption excess isotherm is known [45-50], Due to adsorption, the initial composition of the liquid mixture, x°, changes to the equilibrium concentration Xi. This change, x - Xi = Axi, can be determined by simple analytical methods. The relationship between the reduced adsorption excess amount calculated from... 

The parallel representation of the adsorption isotherms and heats of immersion measured in binary mixtures, presented above, gave information on solid-liquid interfacial interactions. If the stability of disperse systems is approached from the... 

The Good-Girifalco theory [77-82] was originally formulated to make an attempt to correlate the solid-liquid interfacial tension to the solid surface energy and the liquid surface tension through an interaction parameter, basic formulation of the theory is ... 

In the absence of specific interactions of the receptor - ligand type the change in the Helmholtz free energy (AFadj due to the process of adsorption is AFads = yps - ypi - Ysi, where Yps, YPi and ys, are the protein-solid, protein-liquid and solid-liquid interfacial tensions, respectively [5], It is apparent from this equation that the free energy of adsorption of a protein onto a surface should depend not only of the surface tension of the adhering protein molecules and the substrate material but also on the surface tension of the suspending liquid. Two different situations are possible. 

Referring to the form in which Yoimg s equation was finally expressed (Equation 16b), it is seen that with the information at hand it is possible to obtain estimates of the surface tensions of the bare solids. The discussion is restricted to three of the solid surfaces for which data were given in Table I. The data for the glassy fluorocarbon surface have been fully treated by the method of interaction parameters, as given in Table II. The liquids of interest for the three surfaces are those for which solid-liquid interfacial tension estimates are given in Table IV, and, in addition, water. 

It is possible, from the estimates obtained, to proceed to evaluate the interaction parameters for the systems considered. For this. Equation 19 is employed, and the results are also given in Table V. The trend of estimated solid-liquid interfacial tensions for the series of five liquids on each of the solids is roughly parallel to the trend of liquid surface tensions (Table I). Hence, the similar trends found for the interaction parameters on each of the solids are to be expected. 

Figure 7 Plots of potential energy of interaction as a function of the distance H between the surfaces of identical spherical particles with radius a = I pm. Top clasHcal DLVO theory. Bottom Exterxled DLVO approach. The following values were used for the calculations = 30 mV 1 1 electrolyte concentration 10 - M Mamaker constant = 2 X lO J acid-base component of the solid-liquid interfacial toiuon — 10 mJ/ni See text for details.

FIG. 37 The solid/liquid interfacial extensive functions and Bingham yield stress for interparticle interactions in hydrophobic Aerosil (2% m/v) suspensions in benzene (1)-n-heptane (2) mixtures in the entire composition range. 

For example, the solid can swell in contact with a certain liquid or even interact by chemical interfacial reactions it can also be partially dissolved. In the case of polymer surfaces, the molecular reorientation in the surface region under the influence of the liquid phase is assumed to be a major cause of hysteresis. This reorientation or restructuring is thermodynamically favoured at the polymer-air interface, the polar groups are buried away from the air phase, thus causing a lower solid-vapour interfacial tension. In contact with a sessile water drop, the polar groups turn over to achieve a lower solid-liquid interfacial tension. Time-dependent changes in contact angles can also be observed (33). 

Fowkes FM, Riddle FL, Pastore WE, Weber AA (1990) Interfacial interactions between self-associated polar liquids and squalane used to test equations for solid-liqirid interfacial interactions. Colloids Surf43 367-387... 

Chapter 1 is a view of the potential of surface forces apparatus (SFA) measurements of two-dimensional organized ensembles at solid-liquid interfaces. At this level, information is acquired that is not available at the scale of single molecules. Chapter 2 describes the measurement of surface interactions that occur between and within nanosized surface structures—interfacial forces responsible for adhesion, friction, and recognition. 

Although this treatment does not explicitly involve interactions at a solid-liquid interface, the application of Green s function to find the stochastic friction force may be an excellent opportunity for modeling interfacial friction and coupling, in the presence of liquid. An interesting note made by the authors is that the stochastic friction mechanism is proportional to the square of the frequency. This will likely be the case for interfacial friction as well. 

Fruitful interplay between experiment and theory has led to an increasingly detailed understanding of equilibrium and dynamic solvation properties in bulk solution. However, applying these ideas to solvent-solute and surface-solute interactions at interfaces is not straightforward due to the inherent anisotropic, short-range forces found in these environments. Our research will examine how different solvents and substrates conspire to alter solution-phase surface chemistry from the bulk solution limit. In particular, we intend to determine systematically and quantitatively the origins of interfacial polarity at solid-liquid interfaces as well as identify how surface-induced polar ordering... 

Complementing the equilibrium measurements will be a series of time resolved studies. Dynamics experiments will measure solvent relaxation rates around chromophores adsorbed to different solid-liquid interfaces. Interfacial solvation dynamics will be compared to their bulk solution limits, and efforts to correlate the polar order found at liquid surfaces with interfacial mobility will be made. Experiments will test existing theories about surface solvation at hydrophobic and hydrophilic boundaries as well as recent models of dielectric friction at interfaces. Of particular interest is whether or not strong dipole-dipole forces at surfaces induce solid-like structure in an adjacent solvent. If so, then these interactions will have profound effects on interpretations of interfacial surface chemistry and relaxation. 

The outlined problems correspond to the most typical system where three phases, e.g. liquid, gas and solid, are brought in contact. Additional wetting geometries can occur when the liquid phase consists of two subphases, e.g. mixture of incompatible polymer liquids, and/or the substrate surface exhibits variations in chemical composition. In these cases, the interfacial interactions will strongly interfere with the phase separation inside the film. Laterally ordered polymer films might be formed due to the preferential wetting of the patterned substrate by one of the liquid phases. 

Protein function at solid-liquid interfaces holds a structural and a dynamic perspective [31]. The structural perspective addresses macroscopic adsorption, molecular interactions between the protein and the surface, collective interactions between the individual adsorbed protein molecules, and changes in the conformational and hydration states of the protein molecules induced by these physical interactions. Interactions caused by protein adsorption are mostly non-covalent but strong enough to cause drastic functional transformations. All these features are, moreover, affected by the double layer and the electrode potential at electrochemical interfaces. Factors that determine protein adsorption patterns have been discussed in detail recently, both in the broad context of solute proteins at solid surfaces [31], and in specific contexts of interfacial metalloprotein electrochemistry [34]. Some important elements that can also be modelled in suitable detail would be ... 

---