Rigid Interfaces

Tomiyama et al, 1998). The fully contaminated bubble behaves as a solid particle in fact, the accumulation of impurities at the gas-liquid interface makes the interface rigid. In contrast, in pure systems the absence of impurities allows the formation of a recirculation pattern inside the bubble, which decreases the viscous drag. For pure systems and for an isolated bubble, Hadamard (1911) proposed the following relationship ... 

W/o microemulsions have been used for many years as microreactors for the synthesis of ultrafine metallic particles [78, 79]. Since the pioneer works of Boutonnet et al. [80], who studied the production of colloidal Pt, Pd, Rh, and Ir particles by hydrogen or hydrazine (N2H4) reduction in w/o microemulsions, many studies have been made on the synthesis of this type of material. A reverse micelle (microemulsion) method, as a kind of soft technique, is a suitable way for obtaining the uniform and size controllable nanoparticles. The droplet dimension was modulated by various parameters, in particular W [81]. Some studies indicated that with the assistant of cosurfactant, the size of nanoparticles prepared in quaternary reverse micelle system is more controllable [82]. For example, compared with the anionic (AOT) ternary reverse micelle system, the droplet dimension of the quaternary cationic (cetyltrimethyl-ammonium bromide, CTAB) reverse micelles can be elaborately adjusted by changing W with the additional modulation of cosurfactant at the interface of water and oil. The microstmcture and djmamic exchange process are dominated by the influence of cosuifactant on the curvature radius and interface rigidity of the droplets in the quaternary reverse miceUe [82]. 

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

The measurement of surface forces calls for a rigid apparatus that exhibits a high force sensitivity as well as distance measurement and control on a subnanometre scale [38]. Most SFAs make use of an optical interference teclmique to measure distances and hence forces between surfaces. Alternative distance measurements have been developed in recent years—predominantly capacitive techniques, which allow for faster and simpler acquisition of an averaged distance [H, 39, 40] or even allow for simultaneous dielectric loss measurements at a confined interface. 

There are three advantages to study molecular recognition on surfaces and interfaces (monolayers, films, membranes or soHds) (175) (/) rigid receptor sites can be designed (2) the synthetic chemistry may be simplified (J) the surface can be attached to transducers which makes analysis easier and may transform the molecular recognition interface to a chemical sensor. And, which is also a typical fact, this kind of molecular recognition involves outside directed interaction sites, ie, exo-receptor function (9) (see Fig. 5b). 

Vascular access ports typically consist of a self-sealing siUcone septum within a rigid housing which is attached to a radiopaque catheter (see Radiopaques). The catheter must be fabricated from a low modulus elastomeric polymer capable of interfacing with both soft tissue and the cardiovascular environment. A low modulus polyurethane-based elastomer is preferred to ensure minimal trauma to the fragile vein. 

Pacemaker Interfaces and Leads. Problems of existing pacemaker interfaces and pacemaker lead materials made from siUcones and standard polyurethanes are environmental stress cracking, rigidity, insulation properties, and size. 

LB Films of Polymerizable Amphiphiles. Stxidies of LB films of polymerizable amphiphiles include simple olefinic amphiphiles, conjugated double bonds, dienes, and diacetylenes (4). In general, a monomeric ampbipbile can be spread and polymerization can be induced either at tbe air—water interface or after transfer to a soHd substrate. Tbe former polymerization results in a rigid layer tbat is difficult to transfer. 

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air—water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in situ This polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

This solution assumes that the beams behave elastically and that all the energy dissipation is associated with the pullout process. Typically for rigid incompatible interfaces, this fracture energy is quite low, ca. 1-5 J/m [1,20,21,61,59]. 

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