Modeling the Self-Aggregation of Small AOT Reverse Micelles from

Subscriber access provided by GEBZE YUKSEK TEKNOLOJI ENSTITUSU

Letter

Modeling the Self-Aggregation of Small AOT Reverse Micelles from First Principles Massimo Marchi, and Stephane Abel J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/jz5023619 • Publication Date (Web): 16 Dec 2014 Downloaded from http://pubs.acs.org on December 20, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Modeling the Self-Aggregation of Small AOT Reverse Micelles from First Principles Massimo Marchi* and Stéphane Abel Commissariat à l’Energie Atomique, DSV/i-BiTec-S/SB2SM/LBMS, CNRS UMR 8221, Centre d’Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, FRANCE AUTHOR INFORMATION Corresponding Author *Massimo Marchi, Commissariat à l’Energie Atomique.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 14

ABSTRACT. This Letter is the first attempt at studying the self-aggregation of AOT reverse micelles from first principles. It focuses on predicting the aggregation number, the radius of gyration and the hydrodynamic radius of a low water content reverse micelle by theoretical means. We show that molecular dynamics simulation in the μs time range combined with atomistic potentials is capable of reproducing and explaining, to a convenient degree, experimental results on the size and dimensions of reverse micelles of AOT of low water content, [H2O]⁄[AOT] ~5.

TOC GRAPHICS

KEYWORDS Molecular dynamics, AOT micelles, self-assembly, confined water, coalescence


2

Page 3 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Reverse micelles (RM) are micro-emulsions where water is confined inside a layer of detergent molecules, which in turn are in contact with oil by their hydrophobic tail side. Over the years they have been recognized as an environment where water behaves out of the ordinary1,2. Indeed, in reverse micelles water can solvate complex solutes such as protein, nucleic acids and minerals3,4, which in the bulk it cannot. In other instances, proteins structure and their reactivity change significantly going from bulk to confined water5. Experiments, such as small angle X ray6–9 and neutron spectroscopy10,11 (SAXS and SANS), dynamic light scattering12,13 (DLS) and fluorescence correlation spectroscopy14 (FCS) can reveal the size and make educated guess on the shape of the micelle and of its core, and on its aggregation number, 𝑵𝐚𝐠𝐠 , or the number of detergent molecules forming the micelle9. 𝑵𝐚𝐠𝐠 can also be obtained by light scattering, sedimentation and osmometry experiments15. The experimental literature on the structure of Aerosol OT, or Sodium Bis (2-Ethylhexyl) Sulfosuccinate (AOT), reverse micelles is considerable. Still, at low water charge6,7, W0 = H2O

AOT

≤ 15, deviations larger than the methodological uncertainty are observed in the

experimental micelle radii and aggregation numbers. In particular, for W0=5 and AOT in isooctane, the experimental gyration and hydrodynamic radii of the reverse micelle (𝑹𝒈 and 𝑹𝑯 , respectively) and the estimates of its 𝑵𝐚𝐠𝐠 are quite disparate in literature. For instance, the 𝑹𝒈 of the water core is found 11.7 Å by Amararene et al.9 and 17.8 Å by Brochette et al.11. On the other hand, 𝑵𝐚𝐠𝐠 is estimated at 37 by Udea & Schelly16, whereas the study by Amararene et al. finds 𝑵𝐚𝐠𝐠 =64. The variability of the results for RM at small W0 might be in part explained by


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 14

the experimental uncertainty on the water content of the micelles17 and by the formation of oligomers illustrated in a series of papers by Hirai et al.6,7,13. In the last few years, following from earlier molecular dynamics (MD) simulations of the inner polar core of reverse micelles18,19, more realistic molecular modeling of AOT reverse micelles have appeared in the literature20–24. All these latter investigations simulated a single reverse micelle in isooctane for given water contents. One of the main ingredients of these simulations is 𝑵𝐚𝐠𝐠 ,

the choice of which chiefly impacts the dimensions and the structure of the reverse

micelle24. In our earlier 3 ns20 simulations, we found that AOT micelles with W0 ≤ 7 were ellipsoidal, but with a small deviation from the spherical shape or eccentricity, 𝝐, between 0.12 < 𝝐

< 0.17. Here, we define

𝝐 = 1 − 𝐼min 𝐼

with I the micelle principal moment of inertia, whereas

Imin and are its values for the smallest axis and for the average over the three directions. 𝝐 is zero for a perfect sphere and is 1 for infinitesimally thin prolate or oblate objects. Longer simulations24, 25 ns, carried out with our Abel et al. potential20, have shown a much larger deviation of micelles from a spherical model, with

𝝐

as large as 0.67 in one case. Using longer

MD simulations (400 ns in one case) and a modified version of our potential, another work23 found reverse micelles without a defined water core and spread over the simulation box, very far from the generally accepted model of RM. In this Letter, to do away with the shortcomings of simulating one single preformed reverse micelle, we present results from simulations of self-aggregation of a ternary system containing sufficient AOT, water and Na+ ions to form a few reverse micelles, in line with the estimated 𝑵𝐚𝐠𝐠 . This approach allows us to enquire into the mechanism of self-aggregation of the micelles, their geometry and their degree of polydispersity.


4

Page 5 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. The reverse micelle system at three different stages of the trajectory SiM3: a) After 0.2 ns b) after 200 ns c) after 700 ns. In magenta are the water molecules. To avoid cluttering the iso-octane molecules are not displayed.

We have carried out molecular dynamics (MD) simulations of three all-atoms independent systems composed of AOT, water, iso-octane and Na+ ions. Each system was composed of 140 AOT and Na+, 700 waters (W0=5) and 10,147 iso-octane molecules for a total of 275,162 atoms each. Trajectory SiM1 and SiM2 lasted 1 µs, whereas SiM3 was run for 0.9 µs. The three runs differ only in the initial conditions. Indeed, they were all generated by arranging randomly AOT, Na+ and water in a cubic box of 150 Å of sides and then by adding an identical number of isooctane molecules. After an initial equilibration, each of the systems was run in the NPT ensemble at T=298 K and P=0.1 MPa with GROMACS25 (see the supporting information (SI) for details on the runs). The final concentration in AOT for the three runs was 0.08 M. We used the same potential as in Abel et al.20, except an SPC/E26 model for water. We point out that this force field is of the CHARMM type and can be readily used to investigate the association of peptides and proteins to AOT reverse micelles. All statistics discussed here were computed from the last 400 ns of each simulation. In all simulations, from the initial randomly arranged molecules, a sizable number of molecular clusters are formed and grow rapidly, within a few hundreds of picoseconds, by seizing the surrounding isolated molecules. Within a few tens of nanoseconds, these clusters begin to coalesce in larger units. Then, fully formed inverse micelles with a well-defined


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 14

detergent protected water core are observed in less than 50 ns, but at least 500 ns are necessary to form four stable micelles. In all three simulations, we find that for 15-24 % of the trajectory the RM’s forms oligomers, in particular dimers, where the tails of two micelles are in bonding contact for a certain time. This finding agrees well with SAXS experiments6,7. We have also computed the micelles translational diffusion coefficient, D=1.38±0.05 x 10-6 cm2/s (see supporting information) and found it very close to the experimental Dexp=1.5 x 10-6 cm2/s12. Based on our D, each micelle diffuses on average 9 Å per ns of simulation. The extent of such diffusion in the last 400 ns of each simulation is quantified by the micelles root mean square distance from their average positions, which is found between 51 to 76 Å. These results insure an exhaustive sampling of the cubic simulation box of side 𝑎 =142.3 Å, within the simulation time frame. Figure 2. The function G(t) for the three trajectories. To distinguish from the three results, in the figure an offset of 0.1 and 0.2 are added to G(t) for SiM2 and SiM3, respectively. In the inset a factor of 1.3 and 1.7 multiply the function for SiM2 and SiM3, respectively.

Fig. 1 provides a Pymol27 graphic representation aggregation

as

of

the

it

was

RM’s observed

selffor

simulation SIM3. More quantitatively, we investigated the evolution of the number of clusters in the system, 𝑁! 𝑡 , as a function of simulation time. Here, a cluster is defined as the ensemble of non-solvent molecules that can be traversed by travelling only through occupied molecular contacts (percolation). We considered that

a molecular contact is occupied between two molecules if any of the their inter-atomic distances


6

Page 7 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is less or equal to the atomic Van der Walls diameter, as defined by the force field. For the three simulations we show in Fig. 2 the function 𝐺 𝑡 defined as:

𝐺 𝑡 =

𝑁! 𝑡 − 𝑁! ∞ , (1) 𝑁! 0 − 𝑁! ∞

where 𝑁! ∞ is the number of cluster at equilibrium, 4 in all cases. To eliminate oligomer effects from 𝐺 𝑡 , we included only contributions from the first 2 carbon groups of the AOT alkyl chain in the percolation. We find that the best fit for the 𝐺 𝑡 of the three trajectories is not a bi-exponential function, but rather, as we found previously2>, a stretched exponential defined !

as 𝜙 𝑡 = 𝑒 ! ! ! . Stretched exponential relaxation is often found in disordered systems such as glasses, macromolecules and proteins. The average relaxation time, 𝑡 , is similar for the three trajectories and is 16.7, 21.7 and 24.0 ns for SiM1, SiM2 and SiM3, respectively. Attempts to address the coalescence of non-cationic micelles have been presented in the past29. For our system, the coalescence of fully formed micelles into larger ones occurs with a qualitatively similar mechanism in all trajectories. At the beginning of the process, hydrophobic

𝒎 Table 1. Structural parameters of the simulated reverse micelles. Here, 𝑹𝒘 𝒈 and 𝑹𝒈 are the gyration radii for the water core and for the whole micelle. The radii reported here are volume-weighted averages over the micelles (see SI). Polydispersities are shown in parenthesis next to the computed parameter. All distances are in Å. The statistical error on the radii and the eccentricity is around 3 %.

SiM1

SiM2

SiM3

𝐍𝐚𝐠𝐠

50 46 25 19

46 39 29 26

45 36 34 26

35 (28 %)

𝑾𝟎

5.45 5.27 4.57 3.74

5.46 4.29 5.52 4.65

5.46 4.77 4.96 4.54

4.89

𝝐

0.17 0.18 0.07 0.060

0.13 0.16 0.07 0.06

0.12 0.09 0.07 0.08

0.105

𝑹𝒘 𝒈

13.8 16.2 19.3

12.4 15.0 18.5

12.2 14.8 18.5

12.8 (14 %) 15.3 (11 %) 18.8 (10 %)

𝑹𝒎 𝒈 𝑹𝑯

Average


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 14

Table 2. Reverse micelles hydrodynamic and gyration radii. 𝑹𝑯 and 𝑹𝒎 𝒈 are computed including oligomer effects, which are not take into account in 𝑹𝒘 . The concentration in iso𝒈 octane is indicated within brackets when it is not 0.1 M. SiM1

SiM2

SiM3

Total

Exp.

𝑹𝒘 𝒈

13.8

12.4

12.2

12.8

11.79 14.58 17.811

𝑹𝒎 𝒈

21.7

20.4

18.1

20.1

18.46(0.05M) 21.96

𝑹𝑯

21.7

20.5

20.0

20.7

27.012(0.25M) 25.714 24.210

interactions between the tails of the detergents of the two micelles are formed. After a few nanoseconds, a water molecule forms an initial bridge between the two micelles. A channel is then formed and water molecules exchange rapidly until after 2-3 ns the two micelles coalesce. In all cases we have examined a sodium ion was involved at the beginning of the water molecule exchange, interacting with waters on the two micelles - see the three videos in the SI. We point out that a different mechanism might be at play when reverse micelles with large water content or especially water-free micelles are considered. This will be the topic of further investigations. The main structural findings of this Letter are given in Tables 1 and 2. We point out that only 4 micelles are formed and are stable after at most 600 ns of the three simulations. This implies that, within the boundaries of the explored time scale, 𝑁! ∞ = 4 in Eq. 1. Accordingly, Tables 1 and Figure 3. 𝝐 (eccentricity) vs. time for the largest micelle of trajectory SiM2. We show a pictorial representation of the reverse micelle structures at a low and high value of e separated by ~ 50 ns.

2 - along with Table S1 in the SI - report the structural parameters for the final micelles obtained from the three trajectories, averaged over the final segment of each run. We first notice that of the 4 RM’s formed in the three simulations, the smallest micelles are the most spherical, with averaged eccentricity 𝝐 < 0.1. On the other end, the largest ones with


8

Page 9 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nagg > 35 have a more pronounced eccentricity with 0.091 < 𝝐 < 0.178, similar to results obtained by us from single micelles simulations of much shorter length20. In the last 400 ns of the simulations where statistics are accumulated, the instantaneous value of

𝝐

never exceeds 0.28 units for any of the micelles. The RM’s of our simulations are also

structurally stables and their forms oscillate from spherical to ellipsoidal. At variance with previous simulation results23,24, during the almost 3 μs of simulation the RM’s of our systems never experience grossly deformed or open structures. A typical example of this behavior is shown in Fig. 3, where for the largest of the micelles of SiM2 we report the time evolution of

𝝐

during the last 480 ns of simulation. The two pictorial representations of the RM on the top are a spherical (left) and an ellipsoid (right) form of the micelle, of low and high 𝝐, respectively. The two structures are separated by ~ 50 ns of simulation, which underlines the long timescale of such transformation. From our three simulations we can also extract a theoretical estimate for the micelles 𝐍𝐚𝐠𝐠 . To our knowledge, this is the first time that this quantity has been obtained from atomistic molecular simulations. Our finding, 𝐍𝐚𝐠𝐠 =35, is close to the experimental estimates by Eicke & Rehak15 and by Ueda & Schelly16, respectively 43 and 37 units, but differs from the value reported by Amararene et al.9 of 643>. From our calculations we can also extract the micelle solution polydispersity, γ, computed as the percentage of the standard deviation over the 𝒎 observable. γ is 28 % for 𝐍𝐚𝐠𝐠 , but is significantly smaller (around 10-15 %) for 𝑹𝒘 𝒈 , 𝑹𝒈 and 𝑹𝑯 ,

which compare well with experimental estimates 15 % < γ < 20 %9,14. Finally in Table 2, we compare the dimensions of our RM’s with experiments. Oligomers effects, i.e. formation of dimers during the trajectory, are included in the statistics of Table 2 only for those properties, in particular 𝑹𝒎 𝒈 and 𝑹𝑯 , whose measure is dependent of the AOT tails


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 14

or of the micelles as a whole. Computationally wise, when a dimer is formed during any trajectory, we compute the instantaneous property not for the two micelles separately, but for the entire aggregate. On the three trajectories RM dimers are formed for 15 % to 24 % of the total time. The experimental results on 𝑹𝒘𝒈 are disparate. Our simulation result is in good accordance with that of Amararene et al.9 and Yano et al.8, but far away from SANS measurements of Brochette et al.11. If on one side our computed

𝑹𝒎 𝒈

is in agreement to results from Hirai’s group6,7, the

hydrodynamic radius is 3.5 Å smaller than the smallest reported value of 24.2 Å13. We underline, that our hydrodynamic radius is a coarse approximation of the true 𝑹𝑯 , and is computed as the radius of a sphere equivalent in volume to the ellipsoid defined by the three semi-axes of the original RM. To conclude, this Letter has been the first attempt at studying the self-aggregation of AOT reverse micelles by theoretical means. In particular, we have focused on the prediction of the aggregation number, the radius of gyration and the hydrodynamic radius of 𝑊! ≈ 5 reverse micelles from first principles. Molecular dynamics in the μs time range, combined with atomistic potentials, is capable of reproducing and explaining, to a convenient degree, some experimental results on the size and dimensions of AOT RM of W0=5. Computing intensive simulations such as ours are still challenging today, but the use of united atom models for the solvent or, better, of coarse grain models are being explored for future studies on RM of bigger water content and containing peptides and proteins. Also, enhanced MD sampling techniques (see for instance31) could be also be used in future investigations.


10

Page 11 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information. Details of the simulations, additional results from simulations and videos of micelle coalescence. This material is available free of charge via the Internet at http://pubs.acs.org AUTHOR INFORMATION Corresponding Author *Email: [email protected]

ACKNOWLEDGMENT We would like to thank Marcel Waks for many useful discussions. We acknowledge the French organization “Grand Équipement Nationale de Calcul Intensif” (GENCI) for a generous grant of computer resources at CCRT, grant No. t20144077196. REFERENCES

(1)

Levinger, N. E. Water in Confinement. Science 2002, 298, 1722–1723.

(2)

Levinger, N. E.; Swafford, L. A. Ultrafast Dynamics in Reverse Micelles. Annu. Rev. Phys. Chem. 2009, 60, 385–406.

(3)

Luisi, P.; Giomini, M.; Pileni, M.; Robinson, B. Reverse Micelles as Hosts for Proteins and Small Molecules. Biochim. Biophys. Acta 1988, 947, 209–246.

(4)

Pileni, M. P. Reverse Micelles Used as Templates: A New Understanding in Nanocrystal Growth. J. Exp. Nanosci. 2006, 1, 13–27.

(5)

Waks, M. Proteins and Peptides in Water-Restricted Environments. Proteins Struct. Funct. Bioinforma. 1986, 1, 4–15.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 14

(6)

Hirai, M.; Kawaihirai, R.; Yabuki, S.; Takizawa, T.; Hirai, T.; Kobayashi, K.; Amemiya, Y.; Oya, M. Aerosol-Ot Reversed Micellar Formation at Low Water-Surfactant Ratio Studied by Synchrotron-Radiation Small-Angle X-Ray-Scattering. J. Phys. Chem. 1995, 99, 6652–6660.

(7)

Hirai, M.; Kawai-Hirai, R.; Sanada, M.; Iwase, H.; Mitsuya, S. Characteristics of AOT Microemulsion Structure Depending on Apolar Solvents. J. Phys. Chem. B 1999, 103, 9658–9662.

(8)

Yano, J.; Furedi-Milhofer, H.; Wachtel, E.; Garti, N. Crystallization of Organic Compounds in Reversed Micelles. II. Crystallization of Glycine and L-Phenylalanine in Water-Isooctane-AOT Microemulsions. Langmuir 2000, 16, 10005–10014.

(9)

Amararene, A.; Gindre, M.; Le Huérou, J.-Y.; Urbach, W.; Valdez, D.; Waks, M. Adiabatic Compressibility of AOT [sodium bis(2-Ethylhexyl)sulfosuccinate] Reverse Micelles: Analysis of a Simple Model Based on Micellar Size and Volumetric Measurements. Phys. Rev. E 2000, 61, 682–689.

(10)

Pileni, M. P. Reverse Micelles as Microreactors. J. Phys. Chem. 1993, 97, 6961–6973.

(11)

Brochette, P.; Petit, C.; Pileni, M. Cytochrome-C in Sodium Bis(2-Ethylhexyl) Sulfosuccinate Reverse Micelles - Structure and Reactivity. J. Phys. Chem. 1988, 92, 3505–3511.

(12)

Zulauf, M.; Eicke, H. F. Inverted Micelles and Microemulsions in the Ternary System Water/aerosol-OT/isooctane as Studied by Photon Correlation Spectroscopy. J. Phys. Chem. 1979, 83, 480–486.

(13)

Hirai, T.; Sato, H.; Komasawa, I. Mechanism of Formation of Cds and Zns Ultrafine Particles in Reverse Micelles. Ind. Eng. Chem. Res. 1994, 33, 3262–3266.

(14)

Pal, N.; Verma, S. D.; Singh, M. K.; Sen, S. Fluorescence Correlation Spectroscopy: An Efficient Tool for Measuring Size, Size-Distribution and Polydispersity of Microemulsion Droplets in Solution. Anal. Chem. 2011, 83, 7736–7744.

(15)

Eicke, H.-F.; Rehak, J. On the Formation of Water/Oil-Microemulsions. Helv. Chim. Acta 1976, 59, 2883–2891.

(16)

Ueda, M.; Schelly, Z. A. Mean Aggregation Number and Water Vapor Pressure of AOT Reverse Micellar Systems Determined by Controlled Partial Pressure-Vapor Pressure Osmometry (CPP-VPO). Langmuir 1988, 4, 653–655.

(17)

Waks, M. Private Communication.

(18)

Faeder, J.; Ladanyi, B. M. Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles. J. Phys. Chem. B 2000, 104, 1033–1046.


12

Page 13 of 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19)

Ladanyi, B. M. Computer Simulation Studies of Counterion Effects on the Properties of Surfactant Systems. Curr. Opin. Colloid Interface Sci. 2013, 18, 15–25.

(20)

Abel, S.; Sterpone, F.; Bandyopadhyay, S.; Marchi, M. Molecular Modeling and Simulations of AOT−Water Reverse Micelles in Isooctane: Structural and Dynamic Properties. J. Phys. Chem. B 2004, 108, 19458–19466.

(21)

Pomata, M. H. H.; Laria, D.; Skaf, M. S.; Elola, M. D. Molecular Dynamics Simulations of AOT-Water/formamide Reverse Micelles: Structural and Dynamical Properties. J. Chem. Phys. 2008, 129, 244503.

(22)

Chowdhary, J.; Ladanyi, B. M. Molecular Dynamics Simulation of Aerosol-OT Reverse Micelles. J. Phys. Chem. B 2009, 113, 15029–15039.

(23)

Vasquez, V. R.; Williams, B. C.; Graeve, O. A. Stability and Comparative Analysis of AOT/Water/Isooctane Reverse Micelle System Using Dynamic Light Scattering and Molecular Dynamics. J. Phys. Chem. B 2011, 115, 2979–2987.

(24)

Martinez, A. V.; Dominguez, L.; Malolepsza, E.; Moser, A.; Ziegler, Z.; Straub, J. E. Probing the Structure and Dynamics of Confined Water in AOT Reverse Micelles. J. Phys. Chem. B 2013, 117, 7345–7351.

(25)

Hess, B.; Kutzner, C.; van der Spoel, D.; Lindahl, E. GROMACS 4:   Algorithms for Highly Efficient, Load-Balanced, and Scalable Molecular Simulation. J. Chem. Theory Comput. 2008, 4, 435–447.

(26)

Berendsen, H. J. C.; Grigera, J. R.; Straatsma, T. P. The Missing Term in Effective Pair Potentials. J. Phys. Chem. 1987, 91, 6269–6271.

(27)

The PyMOL Molecular Graphics System, Version 1.5.0.4 Schrödinger, LLC.

(28)

Abel, S.; Dupradeau, F.-Y.; Marchi, M. Molecular Dynamics Simulations of a Characteristic DPC Micelle in Water. J. Chem. Theory Comput. 2012, 8, 4610–4623.

(29)

Agazzi, F. M.; Correa, N. M.; Rodriguez, J. Molecular Dynamics Simulation of water/BHDC Cationic Reverse Micelles. Structural Characterization, Dynamical Properties, and Influence of Solvent on Intermicellar Interactions. Langmuir 2014, 30, 9643–9653.

(30)

This Value of 64 Is Very Large Compared to the Other Experiments and Our Results. Its Derivation from R_g^w Is Based on the Assumption That in the Micelle the AOT Tails Are in a Fully Extended Conformation, Which Is at Variance with All Our Simulation Res.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(31)

Page 14 of 14

Schlick, T. Molecular Dynamics-Based Approaches for Enhanced Sampling of LongTime, Large-Scale Conformational Changes in Biomolecules. F1000 Biol. Rep. 2009, 1, 51.


14

Modeling the Self-Aggregation of Small AOT Reverse Micelles from

Recommend Documents