Temperature, subphase

Figure 17 shows the chemical structures of anionic amphiphile sodium-1,2-bis (tetradecylcarbonyl)ethane-l-sulfonate (2Cj4SNa)[34] and poly(ethyleneimine)(PEI). A benzene/ethanol (9 1)(WV) solution of anionic amphiphile was spread on the pure water surface or the PEI-water solution (lxlO5 unit M in monomer unit, pH=3.2) surface at a subphase temperature, Tsp of 293 K. At this pH, ca. 70 % of nitrogen atom in PEI molecule was protonated[35]. Surface pressure-area(ji-A) isotherms were measured with a microprocessor controlled film balance system. 

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... 

The n-A curves were measured with a trough equipped with a moving blade and a piezoelectric device (Figure 2). Both the trough (286 mm long and 70 mm wide) and blade were coated with Teflon. The subphase temperature was kept within 0.1 °C by use of a water jacket connected with a thermostated circulation system, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate made of filter paper (25 x 25 x 0.25 mm) using a piezoelectric device. The surface pressure(ji) is defined as ... 

Figure 3. Effect of subphase on the tc-A curve of PhDA2-8 film. The subphase temperature was 5.0°C and the compression rate was 7.5(A2/molecule)/min. The subphase composition was as follows ...

Influence of subphase temperature, pH, and molecular structure of the lipids on their phase behavior can easily be studied by means of this method. The effect of chain length and structure of polymerizable and natural lecithins is illustrated in Figure 5. At 30°C distearoyllecithin is still fully in the condensed state (33), whereas butadiene lecithin (4), which carries the same numEer of C-atoms per alkyl chain, is already completely in the expanded state (34). Although diacetylene lecithin (6) bears 26 C-atoms per chain, it forms both an expanded and a condensed phase at 30°C. The reason for these marked differences is the disturbance of the packing of the hydrophobic side chains by the double and triple bonds of the polymerizable lipids. At 2°C, however, all three lecithins are in the condensed state. Chapman (27) reports about the surface pressure area isotherms of two homologs of (6) containing 23 and 25 C-atoms per chain. These compounds exhibit expanded phases even at subphase temperatures as low as 7°C. 

Figures 6 and 7 show a modem Langmuir film balance and its arrangement inside a Puffer-Hubbard temperature-controlled cabinet (63). Inside the cabinet, the film balance is protected further from circulating air currents by a Plexiglass case. At the bottom of the Teflon trough lies a serpentine glass coil through which water from a thermoregulator is circulated to help control subphase temperature.

The interfacial properties of HM - PNIPAM, including the formation and the compression - expansion reversibility of the monolayers, at different subphase temperatures were more recently studied by using the Langmuir film balance technique [90], The stability and dynamic nature of the HM - PNIPAM monolayers were also further studied by the time - dependent surface pressure measurements. All results have suggested a compression - promoted temperature - and rate - dependent conformational rearrangement of the polymer on the water surface. Increasing the level of hydrophobic modifications progressively improved the monolayer compressibility and stability, and reduced the hysteresis. 

Two methods have been proposed for the preparation of organosilane monolayers. One is chemisorption from organosilane solution [4-6], and the other one is Langmuir-Blodgett (LB) method or water-cast method [7-23], Fig. 1 shows the film formation mechanism of the organosilane by LB method (a) and chemisorption method (b). In the case of LB method (Fig. 1(a)), the toluene solution of organotrichlorosilane was spread on the water surface (pH 5.8) at a controlled subphase temperature. To attain quasi-equilibrium state of the monolayer, the monolayer was kept on the water subphase under a given... 

Fig. 3. The %-A isotherms for the OTS, DDTS, FDOPTES, and FOETS mono-layers on the water surface at a subphase temperature of 293 K, as well as the AFM images and ED patterns of the monolayers transferred onto the substrate at the surface pressure of around 20 mN m 1.

Figure 6. Evolution of KapEa as a function of subphase temperature.

Influence of Subphase Temperature. Enzymic activity at the interface increases clearly with subphase temperature (Figure 6). When comparing enzymic adsorption with enzymic activity (Figure 7), the rate of enzymic cleavage increases when the number of macromolecules of the enzyme that reaches the surface increases. The two processes are parallel but are not immediately related. 

Figure 7. Evolution of surface radioactivity from tritiated pancreatic lipase (2 mg/l) after 2.5 min of adsorption. Influence of subphase temperature. Substrate concentration 0.5 mg/m2, pH8UbphQf8e = 8.2. Surface radioactivity is in cpm (counts/minute) (fraction C5).

A number of distinct regions are immediately apparent on examining the isotherm. When the monolayer is compressed, it can pass through several different phases, which are identified as discontinuities in the isotherm, as shown in Figure 5.6. The phase behaviour of the monolayer is mainly determined by the physical and chemical properties of the amphiphile, the subphase temperature and the subphase composition. Various monolayer states exist depending on the length of the hydrocarbon chain and the magnitude of cohe-... 

Fig.2). At high density, the surface film is in a state thought of as a homogeneous liquid condensed or gel-like phase, LC, and finall) at ks,As a second-order phase transition to a solid condensed state SC occurs. Depending on the subphase temperature, not all of the phases shown in the schematic, Fig.2, are actually observed in the measurement, Fig.l. Rather, at low temperatures (T < 20 C) a transition from the gaseous to the condensed state (an ogous to a three-dimensional sublimation) occurs, whereas at high temperatures (T > 50 °C) the surface film remains in the expanded state,and no condensation occurs at all.

The LB-Layers were prepared with a commercial Lauda film balance, installed in a class 1000 clean room under yellow light. Merck Uvasol quality chloroform and ethanol were used. Water was purified in a Milli-Q-System (Millipore) to 18 MO cm. Commercial Bixin (C25H3QO4, Fa. Roth) was purified by chromatography on ODS-phase (MeOH/Acetone=95 5). Two different substrates, i.e. Au and Si were used. Glass slides (75 10 1 mm) were coated with layers of 200 A Cr and 2000 A Au by thermal evaporation. The gold substrates were coated immediately after vacuum deposition of the metals. Si substrates (FZ (111), p(B), 1000 X cm) were etched in 30 % HF and rinsed in Mili-Q water prior to use. For Bixin, the subphase contained 5-10"" mol/1 CdCl2 and was buffered with KOH to pH 7.5. The subphase temperature was 19 C. (7) was spread... 

A Millipore Milll-Q purification system was used for subphase preparation, and a constant temperature bath was used to control the subphase temperature. The mixed spreading solutions were dispersed at the air-water Interface and then slowly compressed at speeds of about 5 A2 mol min-" to surface pressures of 10-15 mN/m prior to deposition. Monolayers were transferred onto electron microscope grids for transmission electron microscopy and electron diffraction, using both the horizontal and vertical dipping techniques. Multilayer assemblies were prepared onto platinum-coated substrates using the vertical dipping technique for Near Edge X-Ray Absorption Fine Structure Spectroscopy (NEXAFS). 

The monolayer in a multi-component system has been attracting attention from the viewpoints of fundamental understanding on molecular self-assembly [1], as well as its applications for surface modifiers [2], biosensing [3-5], photoswitching [6] and electrical devices [7]. In this system, whether amphiphilic molecules are miscible or immiscible in the monolayer is important for its properties. Therefore, a systematic tmder-standing on the phase separation mechanism in a mixed monolayer appears to be an essential step in the design and constmction of functionalized structures in the system. The phase separation in a monolayer state depends on many factors involving electrostatic interaction, molecular chirality and so on besides thermodynamic parameters such as the subphase temperature and surface pressure. Hence, for... 

The LB film deposition was performed on a NIMA 622 alternating trough (NIMA Technology, Coventry, UK) equipped with a Wilhelmy plate surface pressure sensor. The spreading solutions were obtained by dissolving 0.9 mg/ml of substance in chloroform. The monolayers were formed by spreading 200 pi of the solution on the water subphase provided by a Milli-Q system (Millipore). The subphase temperature was held constant at 21 °C. The films were compressed with a constant barrier speed of 50 cm /min. Multilayers of 10 monolayers were deposited on cleaned silicon wafers that were hydrophobized by treatment with hexamethyldisilazane (HMDS) before the deposition. A target pressure of 28 mN/m and a dipper speed of 5 and 10 mm/min yielded an observed transfer ratio between 0.8 and 1 (Y-type transfer). 

As shown in Fig. 2, an interesting characteristic, an overshoot-hump, was observed in the n-A curves of the DNP-DPPE monolayer with a constant-speed compression. It is clear that the shape of the overshoot-hump became more marked with an increase in the subphase temperature, and that the surface pressure, at which the overshoot-hump was observed, increased from 12.7 to 31.4 mN/m. Furthermore, it was found that both the... 

Fig. 2 Surface pressure (n) vs. surface area A) curves of DNP-DPPE monolayer. Subphase temperature is (a) 10°C, (b) 20 C, and (c) 30 °C, respectively. The surface area was changed in a constant speed which was 2.71 A molecule min". The subphase component was potassium bicarbonate (50 pM) and calcium chloride (300 M)...

Figure 3B is a simulation result corresponding to the actual n-A curve in Fig. 2b. We have considered that the increase of the subphase temperature induces an increase in the critical surface pressure. In other words, the increase changes the shape of the nonlinear S -shape function. If we simulate the experimental results (Fig. 2c), it should be used as another appropriate function. In addition to this, it is clear that the rate coefficients (fcj and k-i) depend on the subphase temperature. In the present work, for convenience of calculation, we used the parameters, ki and k-i, as a constant, and estimated the value of k to be much larger than k-i which was arbitrarily determined as 1.0 X 10 . ...

It may be worth mentioning an interesting feature of the monolayer of this material the structure of the monolayer can be controlled by the subphase temperature [50,51]. The behaviour of the n-A isotherm changed at around 10°C, and different types of monolayers were obtained above and below this temperature. Moreover, the structure and electrical conductivity of the LB films fabricated from these two kinds of monolayers were different from each other. 

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