Turbidity changes, figure

Figure 10.16 Effect of Ca + on the turbidity change upon mixing oleate vesicle solutions 0.25 ml 1 mM 60 nm radius extruded oleic acid vesicles + 0.25 ml 1 mM 200 nm radius extruded oleic acid vesicles + 1.5 ml bicine buffer. Calcium ion concentration (a) 0 mM (b) 1 irtM (c) 2.5 mM (d) 5 mM (e) added excess EDTA to (d). (Adapted from Cheng and Luisi, 2003.)...

Eor a dilute suspension containing roughly equal amounts of two particle sizes. Figure 20.11 shows the way turbidity changes with time at a distance, L, below the top of the liquid. Turbidity is usually expressed in terms of nephelometric turbidity units (NTu). This is in reference to a specific type of measurement technique. A nephelom-eter specifically measures the light reflected into the detector by the particles. 

The initial stages of the DBX-1 synthesis using Cun-purified NaNT in place of raw NaNT produced similar observations as described above. Upon addition of the initial dose of sodium ascorbate, a gel-like material was formed with no evidence of crystalline DBX-1. After an apparent induction period of several minutes, a very different phenomenon was noticed. These events included a visual change in reaction mixture turbidity (it became clear) and an almost instantaneous drop in the counts of fine particles (see Figure 1). As the fines dropped the PVM almost instantaneously identified crystalline DBX-1 (see Figure 2). The event only lasted seconds and produced the beautiful rust colored crystals indicative of DBX-1 product. The second dose of reducing agent was started (denoted by the second start on the x axis) after formation of the DBX-1 crystals was identified. 

Solutions of highly surface-active materials exhibit unusual physical properties. In dilute solution the surfactant acts as a normal solute (and in the case of ionic surfactants, normal electrolyte behaviour is observed). At fairly well defined concentrations, however, abrupt changes in several physical properties, such as osmotic pressure, turbidity, electrical conductance and surface tension, take place (see Figure 4.13). The rate at which osmotic pressure increases with concentration becomes abnormally low and the rate of increase of turbidity with concentration is much enhanced, which suggests that considerable association is taking place. The conductance of ionic surfactant solutions, however, remains relatively high, which shows that ionic dissociation is still in force. 

Figure 5.15. Turbidity-time curve for microtubule assembly.The diagram illustrates the turbidity-time changes that occur during microtubule assembly. Initially during the turbidity lag phase, tubulin monomers form rings of tubulin subunits that cause microtubule elongation during the growth phase.

In dilute aqueous solutions, surfactants have normal electrolyte or solute characteristics and are formed at the interface. As the surfactant concentration increases beyond the well-defined concentrations (i.e., critical micelle concentration, c.m.c.), the surfactant molecules become more organized aggregates and form micelles. At the c.m.c., the physicochemical characteristics of the system (osmotic pressure, turbidity, surface tension, and electrical conductivity) are suddenly changed, as shown in Figure 4.19. 

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