Cadmium octadecanoate

LB films of cadmium octadecanoate and other amphiphiles were transferred on a quartz-crystal microbalance (QCM, 9 MHz, AT-cut) as a substrate with a vertical dipping method. Frequencies of the QCM substrate were followed with time in air, after the QCM was raised from the interface. From the time courses of these frequency changes at each dipping cycle, the transfer amount of dry LB films (W ), the incorporated amount of water (W2), and its evaporation speed (v) could be obtained in nanogram level. 

Figure 2 Frequency changes of the QCM substrate in air during 4 cycles of vertical dipping processes of cadmium octadecanoate LB films (surface pressure 20 mN m->, 20 °C, dipping speed 100 mm min- )-...

The gradual frequency increase from points B to C is explained by the mass decrease due to the evaporation of water deposited between layers from the subphase. The amount of incorporated water (W2 / ng) and its evaporation speed (v / ng min- ) were calculated from the frequency change and the initial slope of the time course between points B and C, respectively. The cadmium octadecanoate LB films were observed to incorporate W2 = 209 5 ng of water with 4 layers of LB films (W, = 232 3 ng) at the first dipping cycle cadmium octadecanoate were transferred on a substrate with the water of almost the same mass of LB films. 

The transfer process was continued at least 10 times at different surface pressures (20, 10 and 5 mN m->)- The total transferred weight (JEW,) of dry cadmium octadecanoate LB films was plotted against the number of transfer cycle as closed circles in Figure 3. The amount of transferred films was also estimated from the conventional method calculated from a moving area of a barrier in kept the surface pressure constant, and plotted as closed triangles in Figure 3. Straight lines indicate the theoretical mass of Y-type two layers on each side of the QCM. 

Figure 4 Effect of number of layers on the amount of incorporated water (W2) and the evaporation speed of the water (v) in the transfer of cadmium octadecanoate LB films. The hydrophilic (O) and hydrophobic ( )...

W 2 and v values at the 5th transfer cycle of cadmium octadecanoate at 20 mN m-i as a function of dipping speed of the QCM substrate are summarized in Table 1. The transfer ratio of LB films (W,) was 0.95 0.05 at the dipping speeds of 40 - 100 mm min. When the dipping speed was decreased, the evaporation speed (v) was decreased the well-oriented LB films could be obtained at the low dipping speed. This is consistent with the report by Pitt, et. al. that the lower transfer speed was favorable to obtain the higher quality LB films in the first 10 layers [31]. 

Effect of dipping speeds on the transfer of cadmium octadecanoate LB films ... 

Figure 17 Frequency increases (mass decreases) of the QCM deposited with cadmium octadecanoate LB films (10 layers on each side, 1130 5 ng), when the QCM plate was lowered and raised repeatedly at arrows with a rate of 100 mm min-i through the air-water interface at 20 °C...

When the LB film-deposited QCM was lowered and raised through the air-water interface at 20 °C, the frequency of the QCM was observed to increase (the mass decrease) compared with that before soaking into the water phase. This is due to the detachment of LB films from the QCM substrate during dipping processes. Figure 17 shows the typical frequency increase (mass decrease) of the QCM deposited with cadmium octadecanoate LB films (10 layers on each side of the QCM, 1130 5 ng), when the QCM substrate was lowered and raised repeatedly through the interface at a rate of 100 mm min. Any increase in surface pressure wasn t observed during the experiments. The frequency of the QCM was... 

Effect of lowering and raising speeds on the detachment of cadmium octadecanoate LB films from a QCM substrate at the air-water interface (20 °C)a... 

The effect of the time at the interface and the time in water on the detached amount was examined separately to clarify whether LB films peeled off mainly at the air-water interface or in the water phase, and the results are summarized in Table 5. Runs 1-8 show the flaking amount of cadmium octadecanoate LB films with the constant dipping speed the constant time at the interface) and the different time in water. The results indicate the detached amount was independent of the time in water. On the contrary, when the time at the interface was increased and the time in water was kept constant, the detached amount of the LB films increased about two times larger (Runs 9 - 15). From these findings, It can be concluded that the LB films peeled off at the air-water interface but not in the water phase when the substrate is lowered slowly with the long contact time at the interface. 

The detached amounts of cadmium octadecanoate LB films at the water surface with various temperatures are shown in Figure 18. The detached amount increased linearly with increasing the subphase temperature. The detachment of LB films is concerned with equilibrium spreading pressure (ESP), which represents the equilibrium between bulk lipid crystals and a lipid monolayer on the water surface [45]. ESPs... 

Figure 18 Effect of water temperature on the detached amount of LB films at the first dipping cycle (10 layers of cadmium octadecanoate on each side of the QCM dipping speed, 100 mm min- )-... 

The detachment experiments were carried out at the different surface tension of the water surface. The surface pressure was controlled in the range of 0-10 mN m-1 with ethyl tetradecanoate monolayer that was confirmed not to be transferred onto a substrate under the experimental conditions. The detachment amounts of cadmium octadecanoate LB films at various surface pressures are shown in Figure 19. At the high surface pressure (the low surface tension) the detached amount became negligibly small, which means the surface tension of water is the driving force of the detachment of LB films at the air-water interface. 

Figure 20 Effect of number of layers of cadmium octadecanoate LB films on the QCM on the detached amount, (at 20 °C dipping speed, 100 mm min-i)-...

Figure 20 shows the effect of the number of layers of cadmium octadecanoate LB films (2-10 layers) on the detachment. The detached amount was hardly dependent on the number of layers, which indicates the LB film is peeled only from its surface layer. 

The detachment of the LB films transferred at various surface pressures was also examined. Relation between detached amounts and transfer conditions of cadmium octadecanoate LB films are summarized... 

SYNS ALAIXOLII CADMIUM(II) STEARATE CADMIUM OCTADECANOATE CADMIUM STEARATE KADMIUMSTEARAT (GERMAN) STABILISATORSCD STABIUZERSCD STEARIC ACID, CADMIUM SALT... 

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