Langmuir-Blodgett apparatus

Fig. 2 Schematic illustration of the Langmuir-Blodgett apparatus for nanorod assembly. Nanorods are generally rendered hydrophobic through surface functionalization (Reproduced with permission from Ref. [12])...

Amphiphilic materials spread at the air/water interface have been the subject of intensive study over a long period of time. The type of apparatus usually used for this purpose has much in common with the apparatus needed to form Langmuir-Blodgett films and, indeed, it is usually possible to adapt the same apparatus for both purposes. In this section the problems which must be overcome if these processes are to be carried out are discussed and the most effective solutions to these problems described. 

Alegria and Dutton used the Langmuir-Blodgett (LB) technique to deposit multiple (mono) layers of either the Rp. viridis reaction-center complex or of the corresponding chromatophores, in either case dispersed in a phospholipid matrix. The absorption spectmm of the LB-film was almost identical to that of the reaction center complex in solution, as shown in Fig. 10 (A), indicating that the in vitro properties of the photosynthetic apparatus are stable and essentially retained in the LB-films. The authors used a combination of redox potentiometry and absorption spectroscopy to identify the four Rp. viridis hemes and their redox potentials, and also determined their orientations by linear-dichroism measurements. 

Applying Langmuir-Blodgett technique, the assembly of one-dimensional nanostructures such as nanorods and nanowtres has been synthesized successfully. These ID nanostructures are rendered hydrophobic by surfactant surface functionalization before the LB experiments. Figure 2 schematically shows the experimental apparatus. 

To measure the force between lipid layers, a lipid is chosen, which at a certain concentration and temperature range forms an L phase. The L phase is a regularly spaced stack of lamellar fluid bilayers separated by water. From a symmetry point of view, the L phase can be considered a smectic-A (SmA) liquid crystal. The mean repeat distance between lipid bilayers in the L phase is measured by X-ray diffraction versus an applied osmotic pressure. Direct experiments have been carried out with the surface force apparatus. Therefore, the bilayers are formed either by spontaneous vesicle fusion [1254-1256] or by depositing two subsequent monolayers with the Langmuir-Blodgett technique [1255, 1257]. Atomic force microscope experiments, which have been carried out between two bilayers formed by spontaneous vesicle fusion, confirmed earlier results [1258]. 

Although images of single molecules clamped in a Langmuir-Blodgett-like experiment have not yet been obtained, we believe that with some modifications of the apparatus this goal is achievable. The absence of periodicity of the bulk substrate on the time scale of our experiment opens a new possibility for tunneling microscopy. The use of a liquid substrate is particularly important in view of the fact that the interfacial ad-layer can be examined in a compressed (i.e., ordered two-dimensional solid) or an expanded (i.e., disordered two-dimensiond liquid) state. 

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