Reformation Of Micelles Research Articles

Host–Guest Modulation of the Micellization of a Tetrathiafulvalene-Functionalized Poly(N-isopropylacrylamide)

The aqueous solution properties of amphiphilic tetrathiafulvalene (TTF) end-functionalized poly(N-isopropylacrylamide) (PNIPAM) derivative 1 have been studied. Fluorescence spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (Nano-DSC) were used to monitor the temperature-induced micellization and showed that 1 underwent two successive phase transitions corresponding to unimer-to-micelle and lower critical solution temperature (LCST) transitions, respectively. We have investigated the complexation properties of the TTF unit toward cyclobis(paraquat-p-phenylene) (CBPQT4+) or the randomly methylated β-cyclodextrin (RAMEB) to manipulate the amphiphilicity of 1 and to control the unimer-to-micelle phase transition by forming pseudorotaxane-like architectures. For the RAMEB complex with 1, the addition of a competitive guest such as 1-adamantanol resulted in the restoration of amphiphilicity of polymer 1 and consequently the reformation of micelles.

Influence of breakup and reformation of micelles on surfactant diffusion in pure and mixed micellar systems

Pulsed field gradient (PFG) NMR technique was used to study diffusion of surfactant ions in the following two micellar systems: (i) aqueous solution of an anionic surfactant sodium dodecyl sulfate (SDS), and (ii) aqueous solution of a mixture of SDS and a small amount of the cationic surfactant N-dodecyltrimethylammonium bromide (C 12TAB). PFG NMR measurements provided separate sets of data on diffusion of SDS and C 12TAB surfactant ions for a broad range of diffusion times. For each type of surfactants at least two components with different effective diffusivities were observed at sufficiently small diffusion times. The faster component was assigned to the surfactants that experience breakup or reformation of micelles during the diffusion time of the PFG NMR measurement, while the slower component was assigned to the surfactants that did not participate in such events during the diffusion time. The observed changes of the fractions and diffusivities of these components with increasing diffusion time were found to be in a qualitative agreement with such assignment. Fundamental understanding of surfactant diffusion in micellar system is important due to an increasing use of such systems for synthesis of porous materials where micelles are used as templates as well as for many other applications.

A study on Cationic Surfactants as Drag-Reducing Additives

In this study, we investigated the influence of the number of ethanol (EO) groups of cationic surfactants having one oleyl group on the drag-reducing effect (DR effect). Also the effect of mechanical pumping power on DR effect was experimentally investigated using two experimental setups, a circulation system (with pump) and a pressurized once-through system (without pump). The concluding remarks obtained in this study are: 1. The DR effect strongly depends on the re-formation rate of micelles disrupted mechanically. 2. When increasing the number of EO groups of the DR surfactants from 0 to 2, the available temperature range of large DR effect was shifted lower. But the DR surfactant having three EO groups (EO-3) barely exhibited the DR effect even at the low temperature. This is because the big hydrophilic head of EO groups probably delays the re-formation of micelles disrupted by pumping power. 3. The DR effect was more liable to be influenced by pumping power with a decrease in temperature. This is because it takes a long time to re-form micelles disrupted by pumping power at low temperature.

Irreversible Thermodynamics Approach and Modeling of Shear-Banding Flow of Wormlike Micelles

The flow in a pipe of wormlike micellar solutions is examined using a simple model that consists of the codeformational Maxwell constitutive equation and a kinetic equation that accounts for the breaking and reformation of micelles. The model needs six parameters, all of which are extracted from single independent rheological experiments. One of the parameters, the shear-banding intensity parameter is associated with the stress plateau in the shear-banding region. The stress plateau is set in our model by the criterion of equal extended Gibbs free energy of the bands. The model predicts a Newtonian (parabolic profile) flow at low-shear rates or low-pressure gradients, followed by shear thinning up to a critical rate where instabilities and long transients appear. At this critical shear rate, a shear-banding flow region arises near the pipe wall. The model indicates that tube lengths up to 400 diameters are required to obtain fully developed flow, where a pluglike profile at the center of the tube coexists...

Effects of the molecular structure of the interface and continuous phase on solubilization of water in water/oil microemulsions

micellar solutions: one may be controlled by a chemorheological process involving actual breakdown and reformation of the entanglement network, presumably by scission and re-formation of the threadlike micelles themselves, and the other by disentanglement due to diffusion of the network chains but without accompanying their breakdown. An important feature of the type I11 behavior is that the mechanism is a single relaxation time process. This result suggests that the relaxation of the entanglement network of the micellar solutions in the type I11 region is due to a chemorheological process independent of the length of the threads rather than to a diffusional process highly dependent on the thread length. The peculiar dependence of 7, on CsCD-' of this chemorheological process of entanglement relaxation should reflect the stability of the threadlike micelles under the given environment. In the micellar solutions with CsCD-' above 1, the micelles are coexisting with excess Nasal. Therefore, scission and reformation of the micelles may happen rather easily by exchange of the CTAB units of the CTAB/NaSal complexes between the threadlike micelles a t the sites of entanglement, where the threadlike micelles can pass through each other with a certain characteristic time (T,,,) reflecting the rate of this process. Scission of the threadlike micelles may also take place, especially in the highly strained portions between entanglement points by the similar mechanism of exchange of the CTAB units with free Nasal molecules in the medium. Since the solubility of CTAB is rather low in the aqueous medium, the exchange rate must be higher; hence the relaxation time is shorter in solutions with a larger excess of Nasal. Although the detailed features of the dependence of 7, on CSCD-'~~ such as seen in Figure 6 cannot be adequately explained at the moment, the general tendency of the Cs and C D dependences of 7, and J,O may be interpreted as discussed above. The type I and type I1 behavior are the results of the onset of entanglement and the fully developed entanglement network as the threadlike micelles are formed with increasing C&-' up to the critical value of approximately 1. On the other hand, the type I11 (Maxwell model) behavior is the result of actual breakdown and re-formation of the entanglement network with the rate dependent on CsCD-1'2 but with the entanglement density being practically constant after CsCD-' exceeds the critical value.

Reversible formation and disruption of micelles by control of the redox state of the surfactant tail group

Reversible disruption and re-formation of micelles is observed by following the redox reaction of the redox-active micelles formed by the bromide salt of (11-ferrocenyl)undecyltrimethylammonium having a ferrocene moiety instead of the terminal methyl proton.