Critical micelle density

Transitions may occur in block copolymer/C02 systems, due to change in temperature and pressure. Subsequently a critical micelle density (CMD), analogous to the critical micellisation concentration (CMC) was found. The existence of a CMD was first argued by McClain et al. (47), who observed a transition from aggregates to unimers for the PS-6-PFOA/CO2 system, as solvent density was increased. Further evidence for the CMD was provided by Triolo et al. (50-52) and Zhou and Chu (53, 54). 

Samulski and J. M. DeSimone, Critical micelle density for the self-assembly ofblock copolymer surfactants in supercritical carbon dioxide, iongmihr 16(2) 416 (2000). 

MeutralSoluble Salts. So dium sulfate [7757-82-6] and, to a considerably lesser extent, sodium chloride [7647-14-5] are the principal neutral soluble salts used in laundering compositions. They are often considered to be fillers although they perform an important standardizing function enabling the formulator to manufacture powders of a desired, controlled density. Sodium sulfate, in addition, lowers the critical micelle concentration of organic surfactants and thus the concentration at which effective washing can be achieved. 

The molecular collective behavior of surfactant molecules has been analyzed using the time courses of capillary wave frequency after injection of surfactant aqueous solution onto the liquid-liquid interface [5,8]. Typical power spectra for capillary waves excited at the water-nitrobenzene interface are shown in Fig. 3 (a) without CTAB (cetyltrimethy-lammonium bromide) molecules, and (b) 10 s after the injection of CTAB solution to the water phase [5]. The peak appearing around 10-13 kHz represents the beat frequency, i.e., the capillary wave frequency. The peak of the capillary wave frequency shifts from 12.5 to 10.0kHz on the injection of CTAB solution. This is due to the decrease in interfacial tension caused by the increased number density of surfactant molecules at the interface. Time courses of capillary wave frequency after the injection of different CTAB concentrations into the aqueous phase are reproduced in Fig. 4. An anomalous temporary decrease in capillary wave frequency is observed when the CTAB solution beyond the CMC (critical micelle concentration) was injected. The capillary wave frequency decreases rapidly on injection, and after attaining its minimum value, it increases... 

The foaming propensity of surfactants generally reaches a maximum at the critical micelle concentration, beyond which there appears to be little further contribution to foam density. Foam stabilisers are also added in some cases. The two important steps in the foam treatment of textile materials are generating the foam and applying it to the substrate ... 

Polyoxyethylene (POE) (20) sorbitan monooleate (Tween 80, Lot 36218, ICI Surfactants, Inc.) was used as received with no further purification. The average molecular weight of Tween 80 is 1310 g/mole, the density is 1.07 g/cm3, the hydrophile-lipophile balance (HLB) is 15, the critical micelle... 

The characteristic effect of surfactants is their ability to adsorb onto surfaces and to modify the surface properties. Both at gas/liquid and at liquid/liquid interfaces, this leads to a reduction of the surface tension and the interfacial tension, respectively. Generally, nonionic surfactants have a lower surface tension than ionic surfactants for the same alkyl chain length and concentration. The reason for this is the repulsive interaction of ionic surfactants within the charged adsorption layer which leads to a lower surface coverage than for the non-ionic surfactants. In detergent formulations, this repulsive interaction can be reduced by the presence of electrolytes which compress the electrical double layer and therefore increase the adsorption density of the anionic surfactants. Beyond a certain concentration, termed the critical micelle concentration (cmc), the formation of thermodynamically stable micellar aggregates can be observed in the bulk phase. These micelles are thermodynamically stable and in equilibrium with the monomers in the solution. They are characteristic of the ability of surfactants to solubilise hydrophobic substances. 

Name Density (g/cm ) pH Refractive index at 20°C Surface tensian af 0.1% v//vaqueaus salutian (mN/m) Viscasity at 25°C (mPa s) Critical micelle cancentratian (%)... 

The foam centrifuge compresses the primary foam (db > 1 mm) to a flowable secondary foam (db > 0.05-0.1 mm). Preliminary experiments showed that a foam density of ca. 0.5 kg/1 is necessary [533], which was attained with a rotor tip speed of ca. 20 m/s. A similar trend of the density of the compacted foam pf as a function of the rotor tip speed u was achieved with the foam turbine [171] for which a foam density of 0.35 kg/1 was sufficient for the secondary foam to flow. Fig. 4.26 shows these measurements for both types of foam breaker and different foams and also shows the large effect the concentration of the foaming agents exerts in the range 0.2-2.0 mmol/1 = 0.073-0.73 g/L (CMC is the Critical Micelle Concentration). However, Fig, 4.26 also shows that to realize the same flowability of the foam... 

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