Confined liquids setup

Figure 11 Gap measurements of the confined liquid setup. Left Some reflectivity measurements at different readbacks of the piezos. They show oscillations due to the gap size. Right Characteristics of the piezos and a sketch of the sample with the area of confinement in the center.

Thin film polymer bilayers and confined liquids have been investigated by x-ray specular reflectivity. First, it is shown that x-ray scattering on polymer bilayers can be superior to neutron scattering if special methods to analyze the data is applied, although neutrons are usually preferred. Second, confined liquids are addressed. The experimental setup for x-ray scattering is presented. I eliminary results are shown, which suggest quantized film thicknesses of the confined liquid. 

It is a challenge to design an experimental setup that works for the investigation of confined liquids especially if x-ray scattering is used. The major problem is, how to get two surfaces very close to each other and to ccmtrol the gap distance. The following list addresses the most important points iriiich have to be taken into account fix x-ray experiments on confined liquids. 

Figure 10 Realization of the experimental setup for x-ray scattering on confined liquids. Left Special designed silicon substrates (25.4mm diameter). The area of confinement is the bridge in the center. Right The sample cell.

Thin layer — A layer of -+ electrolyte solution (molten salt electrolyte, - ionic liquid) of about 2 to 100 pm thickness is commonly treated as a thin layer because of particular properties and behavior. In bulk - electrolysis methods the amount of convertible species contained in a thin layer is very limited, thus exhaustive electrolysis becomes feasible. In numerous spectroelec-trochemical setups the electrolyte solution confined between the electrode surface under investigation and the... 

In addition to SLM, which is the most commonly used three-phase extraction principle, at least in analytical chemistry, also other ways of placing an organic phase between two aqueous phases are known. In the classical bulk liquid membrane (BLM) setups, U-tubes or similar devices are used to confine bulk volumes of organic liquids between two aqueous phases. This type of devices is very little used for sample preparation in analytical chemistry, as the extraction process becomes slow and the enrichment factors possible are very limited. 

Sect. 3.2.2 we present the technique used to perform the measurements and the experimental setup. In Sect. 3.2.3, basic ideas are introduced, describing the force acting between surfaces that confine a smectic liquid crystal. In Sect. 3.2.4 we report the observations of the smectic periodic structure performed on two smectic compounds. In Sect. 3.2.5 the compressibility modulus of 8CB is estimated using a force plot. 

The SFA setup is shown in Fig. 3.16. The core of the apparatus is a curved confinement cell, defined by two cylindrical glass lenses of radius i 2 cm, facing each other in a crossed cylinders geometry. Two flexible sheets of muscovite mica are glued on the lenses and ai e in direct contact with the liquid to be examined. Mica is used because large sheets ( 1 cm ) of uniform thickness ( 5 tni) can be easily cleaved by hand, exposing the liquid to a very clean and smooth surface (roughness 0.1 nm). 

The behavior of polymers at a solid substrate is closely related to the behavior of maaomolecules in thin films. Either such a thin film can be fabricated by confining a polymer layer between two solid substrates or one can consider a polymer film that wets a solid substrate in contact with air orvacuum. As the liquid-vapor interface that constitutes the free surface of the supported film resembles the interface between a polymer liquid and a hard, nonattractive solid substrate at the coexistence pressure, both situations are qualitatively similar. The former situation is often employed in computer simulations, whereas the latter setup is of great praaical interest owing to applications of thin polymer films as protective coating layers that control wettability, adhesion, or friction. 

Figure 8 Mechanical analog of the SFA experimental setup used for measurements of friction forces Fo. A block of mass m which is confining a thin liquid film of hexadecane between atomically smooth mica is pulled laterally at velocity v. The lateral forces, F, are measured with an elastic...

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