Soft interfaces

The substrate was also found to influence the properties of the electrolessly deposited vertical media CoNiMnP, CoNiReMnP, and CoNiReP. The c-axis orientation had a larger degree of perpendicular orientation for films deposited on electroless NiP than for those deposited on Cu foil, presumably because of the smaller roughness of the former substrate [43]. The double-layer (magnetically soft interface, magnetically hard bulk) properties of CoNiReP deposited on a NiMoP underlayer [57] have already been discussed. 

Designing Extracellular Environments with Nanostructured Soft Interfaces.. 97... 

PU systems with hard blocks made of piperazine, have been also studied [90, 91, 92], In systems deuterated in the segments of the soft blocks, 2H NMR results show that a fraction of the soft segments have a restricted mobility, due to the connectivity to hard blocks, rather than to the adsorption on those blocks acting as filler particles [93]. To study the interface in a specific way, systems with hard blocks selectively deuterated at different positions have been synthetised. A reduction of quadrupolar interaction according to the position was observed, corresponding to an increase of the mobility in hard segments on approaching the hard-soft interface. 

Figure 19. Boundary conditions and exchange (a) hard-soft interface with common A, (b) interface between two ferromagnetic phases with different A, and (c) quasi-discontinuous magnetization due to strongly reduced exchange between grains I and II. Note that the perpendicular magnetization component m(x) can be interpreted as a magnetization angle.

Up to date, besides the SFA, several non-interferometric techniques have been developed for direct measurements of surface forces between solid surfaces. The most popular and widespread is atomic force microscopy, AFM [14]. This technique has been refined for surface forces measurements by introducing the colloidal probe technique [15,16], The AFM colloidal probe method is, compared to the SFA, rapid and allows for considerable flexibility with respect to the used substrates, taken into account that there is no requirement for the surfaces to be neither transparent, nor atomically smooth over macroscopic areas. However, it suffers an inherent drawback as compared to the SFA It is not possible to determine the absolute distance between the surfaces, which is a serious limitation, especially in studies of soft interfaces, such as, e.g., polymer adsorption layers. Another interesting surface forces technique that deserves attention is measurement and analysis of surface and interaction forces (MASIF), developed by Parker [17]. This technique allows measurement of interaction between two macroscopic surfaces and uses a bimorph as a force sensor. In analogy to the AFM, this technique allows for rapid measurements and expands flexibility with respect to substrate choice however, it fails if the absolute distance resolution is required. 

NR is a tool that has yet to capture the imaginations of bioelectrochemists despite several examples of successful implementation of the technique. NR provides a unique means to study soft interfaces under potential control and its remarkable sensitivity to water is ideally suited for structural studies of supported phospholi-... 

A key requirement for in-situ spectroscopic methods in these systems is surface specificity. At Uquid/Uquid junctions, separating interfacial signals from the overwhelmingly large bulk responses in linear spectroscopy is not a trivial issue. On the other hand, non-Unear spectroscopy is a powerful tool for investigating the properties of adsorbed species, but the success of this approach is closely linked to the choice of appropriate probe molecules (besides the remarkably sensitivity of sum frequency generation on vibrational modes of water at interfaces). This chapter presents an overview of linear and non-linear optical methods recently employed in the study of electrified liquid/liquid interfaces. Most of the discussion will be concentrated on the junctions between two bulk liquids under potentio-static control, although many of these approaches are commonly employed to study liquid/air, phospholipid bilayers, and molecular soft interfaces. 

Self-fitting modular orthosis A modular, self-fitting, mechanical orthosis with a soft interface between human body and the orthosis. 

Pickering Stabilization Adhesion of Particles to Soft Interfaces. 34... 

Interaction of a Single Spherical Particle with a Soft Interface... 

A question often asked is whether the parabolic energy wells as predicted by Pieranski have an activation barrier that prevents the particle from falling in spontaneously. One can argue that, especially for a large spherical particle, upon its approach to the soft interface, the interface needs to deform and liquid has to drain. This event adds an activation barrier that needs to be overcome for the particle not to bounce off the interface, and clearly the interfacial tension between the two soft bulk phases (liquid-liquid and liquid-air) and the viscosity of both phases play key roles. Note that a potential hydrophobic effect [28] can counterbalance such a barrier because the dewetting of the liquid between a hydrophobic particle and the hydrophobic liquid phase, or air, stimulates long-range attraction and eases the adhesion process. 

We have seen from the above discussion that solid particles can adhere to a soft interface, and thus to monomer droplets. The effect of Pickering stabilization protects the droplets from coalescence. The use of solid particles as stabilizers in emulsion-based polymerization techniques was first described in open literature by... 

The behavior of nanoparticles at soft interfaces and their ability to adhere to these strongly has great potential for further studies, especially in the area of solids-stabilized emulsion polymerization. The ability to control and understand mechanistically this process will allow the design of innovative hybrid polymer colloids. 

Electrochemistry of soft interfaces is a rapidly progressing interdisciplinary field. The most important systems here are as... 

Aguilella, V., Belaya, M., and Levadny, V., Ion transport through membranes with soft interfaces, the influence of the polar zone thickness. Thin Solid Film, 272 (1), 10 14, 1996. 

When the liquid-to-vapor transition is suppressed kinetically, the loosening of water structure characteristic of hydrophobic interfaces (so-called soft interfaces [51,52]) can still be inferred from the rise in compressibility, k, within the solvation layer. The increase in surface compressibility of water has been quantified from density fluctuations [36] and direct density dependence on the pressure [43], Compressibility next to hydrophilic surfaces, on the other hand, remains virtually indistinguishable from that of bulk water [43, 53], Local compressibility has also been shown to offer a viable measure of hydrophobicity at a molecular level [52, 54], The issue will be addressed in the following sections as we describe the changes in surface compressibility revealed in a simulated electrowetting experiment. 

Electrochemistry at soft interfaces is a very interesting topic, as many different types of charge transfer reactions can take place in parallel and concomitantly. The different charge reactions include (i) ion transfer reactions where the flux of ions crossing the interface gives rise to a current (ii) assisted ion transfer reactions where the extraction of, for example, an aqueous ion by an organic soluble ionophore also gives rise to an ionic current and (iii)... 

If it is accepted that an electrochemical reaction is one where the Gibbs energy of the reaction depends on the potential difference between two phases, as well as temperature and pressure (as do classical chemical reactions), then charge transfer reactions at soft interfaces are truly electrochemical reactions. Indeed, their characteristic is to be potential-dependent and controlled by the Galvani potential difference between the two phases in contact. 

Extensive studies have been carried out to derive the voltammetric response of the different types of assisted ion transfer for different techniques, such as cyclic voltammetry and differential pulse voltammetry. This part of electrochemistry at soft interfaces has found many applications, mainly for the determination of complexation constants for liquid extraction [4], and these are of interest not only for nuclear reprocessing but also for the development of amperometric ion-selective electrodes [5]. 

Electron transfer (ET) reactions at soft interfaces, similar to assisted ion transfer reactions, can occur either heterogeneously or homogeneously in the vicinity of the interface following the transfer of one of the reactants (see Eigure 16.2). 

One very interesting class of ET reactions at soft interfaces are those that are photoini-tiated. Following the pioneering studies of the Russian school, including those of Volkov [6] and Kuzmin [7], it has been shown that photosensitizers soluble in one phase are often adsorbed at the interface and can be quenched by electron donor or acceptors. This class of reaction offers interesting perspectives to design biomimetic approaches to artificial photosynthesis. Photoelectrochemistry at the interfaces between two immiscible electrolyte solutions (ITIES) is rather analogous to photoelectrochemistry at a semi-conductor electrode, where the potential drop within the semi-conductor should be considered. 

Figure 16.3 shows a schematic representation of a photoelectron transfer reaction where a sensitizer (S ) in one phase is quenched by an electron donor (Q) in the adjacent phase. A charge-transfer complex [S - Q+] is formed at the inta face. In a bulk solution, recombination often occurs due to the cage effect formed by the solvent molecules. At soft interfaces, the dissociation of the charge transfer complex into photoproducts can be favored by the presence of the static electric field, and this is still a very important point to quantify in the coming years. 

Until now, the methodology available to study charge transfer reactions at soft interfaces has been rather mature, and studies in the field have shifted to the study of catalyzed reactions such as the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), or even oxygen evolution reaction (OER). Eor this, two classes of catalysts have been used (i) molecular catalysts and (ii) nanoparticle solid catalysts. These two approaches draw their inspiration from classical molecular catalysis and from electrocatalysis, respectively. 

---