Effect of temperature and counterion on the micelle formation process studied by positron annihilation techniques

Djermouni, Belkacem; Ache, Hans J.

doi:10.1021/j100482a011

Cited by 25 publications

(9 citation statements)

References 8 publications

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“…To confirm this, we have performed a temperature-dependent (22, 26, 30, and 34 °C) study to calculate the activation energy of the sucrose hydrolysis AOT RM and CTAB RM having the same water-pool size as well as in bulk water. In this temperature range, the size of the RMs remains almost constant. , It is clear from the Figure that with an increase in temperature the rate of hydrolysis of sucrose increases and the rate constants are summarized in Table . It is evident that at a particular temperature the rate of hydrolysis of sucrose is maximum in CTAB RM followed by bulk water and AOT RM.…”

Section: Results and Discussionmentioning

confidence: 79%

Ramping of pH Across the Water-Pool of a Reverse Micelle

et al. 2016

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In this work, we have addressed the problem of "acidity" of the water-pool of a reverse micelle (RM) through the well-known inversion of sucrose reaction as a tool of investigation. This reaction has been performed inside positively and negatively charged RM and the rates are compared with that in bulk water. We propose that the buffer-like action in a water-pool is much stronger than expected earlier. The rate of sucrose hydrolysis slowed down in the negatively charged AOT reverse micelle while it sped up for the positively charged CTAB reverse micelle. However, temperature-dependent measurements showed that the activation energy remained the same for all the cases. It has been concluded that a proton gradient exists inside the water-pool of the reverse micelle and it determines the buffer-like action of the water-pool that persists until about 2 N of HCl in AOT RM of w(0) = 10.5.

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Section: Results and Discussionmentioning

confidence: 79%

Ramping of pH Across the Water-Pool of a Reverse Micelle

et al. 2016

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“…[5][6][7][8] By their nature, a detailed understanding of the structure and properties of such systems demands combined study by several techniques, among which LS appears promising. However, it must be acknowledged that, notwithstanding the intrinsic interest of the work produced so far, particularly as concerns the behavior of the probe itself, little precise quantitative information on micelles has been extracted from experimental PAT data.…”

Section: Introductionmentioning

confidence: 99%

Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Marques¹,

Miguel

Lima

et al. 1996

J. Phys. Chem.

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Reverse micelles are studied in sodium AOT/water/isooctane mixtures as functions of AOT concentration (C AOT ), water to AOT mole ratio (w 0 ) and temperature (T), from 294 to 333 K, using positron annihilation lifetime spectroscopy (LS). By four-component analysis of the spectra, it is possible to extract the LS parameters (intensities, I i , and lifetimes, τ i ) of the triplet positronium (o-Ps) present in the aqueous (I 3 , τ 3 ) and organic (I 4 , τ 4 ) phases. The latter lifetime is constant and corresponds with the value measured in pure isooctane, while τ 3 is remarkably lower than the value for pure water. This difference is attributed to the out-diffusion of o-Ps from the water cores to isooctane. The relevant rigorous diffusion equations imply two fitting parameters, the radius of the water aggregates (r 0 ) and a transmission factor (h). Fixation of r 0 ) 3.6 nm for C AOT ) 0.1 M, w 0 ) 20, and T ) 294 K, as known from previous work, allows the quantitative derivation of the r 0 values for all other conditions. The water spheres appear to present some permeability to o-Ps, with a transmission factor h ) 0.12 nm -1 . The sphere radius increases smoothly with C AOT and w 0 and, more importantly, with T. The changes with w 0 give r 0 ) 0.181w 0 and 0.186w 0 nm at 294 and 298 K, respectively, and are in excellent agreement with previous proposals. The sum of the intensities, I tot ) I 3 + I 4 , is much lower than the o-Ps intensity in pure isooctane. In particular, at C AOT > 0.04 M, I tot appears very close to the value found for pure water. The possibility of a strong inhibition of Ps formation due to the micelles, as proposed in previous work, is ruled out because of the negligible electron or positron scavenging ability of alkyl sulfonates. It is thus concluded that Ps formation occurs primarily in the aqueous part of the micelles, the water aggregates representing efficient traps for the positrons while they are slowing down in the solutions. IntroductionPositronium (Ps), the bound state of a positron (e + ) with an electron (e -), has been used increasingly in recent decades as an efficient probe of the physical and chemical properties of matter. 1 The most commonly used positron annihilation technique (PAT) is lifetime spectroscopy (LS), which allows us to obtain both the lifetimes (τ i ) and relative abundances (or intensities, I i ) of the various positron species. Normally, in order of increasing lifetimes, these are singlet Ps (p-Ps, i ) 1), free positron (i ) 2), and triplet Ps (o-Ps, i ) 3). Because of its distinct long lifetime, the latter appears to be the most useful probe. The o-Ps decay occurs with the emission of two γ-rays through the pick-off process, i.e., the annihilation of the positron with one of the (bound) electrons of the surrounding medium. Information is obtained through two distinct, independent processes, Ps formation and annihilation, both of which depend on various characteristics of the systems under investigation. In liquids, Ps formation may occur on a very short time ...

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“…3 are present in biomembranes, for which parallel structures have been identified. 15,16 The most prolific area of research utilising PALS for self-assembled systems is in micellar 4,6,7,8,10,11,[58][59][60][61][62][63] and microemulsion systems. 24,[52][53][54] Although the exact mechanisms for the formation of such morphologies are unknown, they are widely associated with membrane re-arrangements resulting from cellular stress and are implicated for inter/intra cellular trafficking.…”

Section: Fitting Pals Spectramentioning

confidence: 99%

“…There is also some evidence that the oPs preferentially associates in the hydrophobic domain, presumably in the inter-chain regions, rather than in the aqueous phase. 15,16 The most prolific area of research utilising PALS for self-assembled systems is in micellar 4,6,7,8,10,11,[58][59][60][61][62][63] and microemulsion systems. [64][65][66][67] However, it is not always easy to interpret the findings in this area for reasons already stated above and a better understanding of the properties and behaviour of the positronium is necessary.…”

Section: Application Of Pals To Investigation Of Lipid Self-assembly ...mentioning

confidence: 99%

Positron annihilation lifetime spectroscopy (PALS): a probe for molecular organisation in self-assembled biomimetic systems

Fong

Dong

Hill

et al. 2015

Phys. Chem. Chem. Phys.

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Positron annihilation lifetime spectroscopy (PALS) has been shown to be highly sensitive to conformational, structural and microenvironmental transformations arising from subtle geometric changes in molecular geometry in self-assembling biomimetic systems. The ortho-positronium (oPs) may be considered an active probe that can provide information on intrinsic packing and mobility within low molecular weight solids, viscous liquids, and soft matter systems. In this perspective we provide a critical overview of the literature in this field, including the evolution of analysis software and experimental protocols with commentary upon the practical utility of PALS. In particular, we discuss how PALS can provide unique insight into the macroscopic transport properties of several porous biomembrane-like nanostructures and suggest how this insight may provide information on the release of drugs from these matrices to aid in developing therapeutic interventions. We discuss the potentially exciting and fruitful application of this technique to membrane dynamics, diffusion and permeability. We propose that PALS can provide novel molecular level information that is complementary to conventional characterisation techniques.

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Effect of temperature and counterion on the micelle formation process studied by positron annihilation techniques

Cited by 25 publications

References 8 publications

Ramping of pH Across the Water-Pool of a Reverse Micelle

Ramping of pH Across the Water-Pool of a Reverse Micelle

Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Positron annihilation lifetime spectroscopy (PALS): a probe for molecular organisation in self-assembled biomimetic systems

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