Amphiphilic diblock dendrimers: Synthesis and incorporation in Langmuir and Langmuir-Blodgett films

Article abstract of DOI:10.1021/ja010155m

A new dendron with peripheral long alkyl chains and containing five C₆₀ units in the branching shell has been prepared and attached to a Frechet-type dendron functionalized with ethylene glycol chains. The peripheral substitution of the resulti

Full text of DOI:10.1021/ja010155m

J. Am. Chem. Soc. 2001, 123, 9743-9748
9743
Amphiphilic Diblock Dendrimers: Synthesis and Incorporation in
Langmuir and Langmuir-Blodgett Films†
Jean-Franc¸ois Nierengarten,* Jean-Franc¸ois Eckert, Yannick Rio, Maria del Pilar Carreon,
Jean-Louis Gallani, and Daniel Guillon
Contribution from the Groupe des Mate´riaux Organiques, Institut de Physique et Chimie des Mate´riaux de
Strasbourg, UniVersite´ Louis Pasteur and CNRS, UMR 7504, 23 rue du Loess, 67037 Strasbourg, France
ReceiVed January 18, 2001
Abstract: A new dendron with peripheral long alkyl chains and containing five C60 units in the branching
shell has been prepared and attached to a Fre´chet-type dendron functionalized with ethylene glycol chains.
The peripheral substitution of the resulting globular dendrimer with hydrophobic chains on one hemisphere
and hydrophilic groups on the other provides the perfect hydrophobic/hydrophilic balance allowing the formation
of stable Langmuir films. Furthermore, a perfect reversibility has been observed in successive compression/
decompression cycles. The diblock structure of the dendrimer has been also crucial for the efficient transfer
of the Langmuir films in order to obtain well-ordered multilayered Langmuir-Blodgett films. This approach
appears particularly interesting since functional groups not well adapted for the preparation of Langmuir and
Langmuir-Blodgett films such as fullerenes can be attached into the branching shell of the dendritic structure
and, thus, efficiently incorporated in thin ordered films.
Introduction
one of the most widely pursued approaches toward structurally
ordered dendrimer assemblies has been the preparation of
Langmuir films at the air-water interface.3-6 For example,
successful preparation of Langmuir monolayers has been
achieved with poly(propyleneimine) dendrimers substituted with
peripheral long alkyl chains. In this case, thanks to the high
flexibility of the dendrimer, the compounds are able to adopt a
cylindrical amphoteric shape, in which the dendritic poly-
(propylene imine) part acts as a polar headgroup and the alkyl
chains packed together form a hydrophobic moiety.4 It has also
been shown that dendrimers with peripheral polar headgroups
can be used for the preparation of thin ordered films at the air-
water interface.3 Such a strategy appears limited however, since
for high generation numbers, the dendrimer should be water-
soluble due to the presence of too many polar units. Langmuir
films have also been obtained with amphiphilic dendritic
molecules with a small polar headgroup at the focal point.5
However, the stability of the films appears to be a problem due
to the difference in size between the hydrophobic and hydro-
philic groups.3b,5 Another interesting approach based on am-
phiphilic cylinders has been also recently proposed by Schlu¨ter
and co-workers.6
As part of this research, we have recently shown that fullerene
functionalized dendrons with peripheral octyl chains and a
carboxylic acid at the focal point are able to form Langmuir
films at the air-water interface.5d We also succeeded in forming
Langmuir-Blodgett (LB) films by transferring the monolayers
onto hydrophobic substrates. However, due to the difference in
size between the hydrophobic and hydrophilic groups, the
preparation of multilayered films was found to be difficult and
the transfer ratio not too good (∼0.7-0.8). We now report on
the synthesis of a diblock globular dendrimer7 and show that
the peripheral substitution of the dendrimer with hydrophobic
Growing attention is currently devoted to large dendritic
structures for applications in nanotechnology and materials
science.1 In this respect, the incorporation of such compounds
into thin ordered films appears as an important issue,1n,2-6 and
* Corresponding author. e-mail: niereng@ipcms.u-strasbg.fr.
† Dedicated to Prof. Maurice Gross on the occasion of his 60th birthday.
(1) (a) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic
Molecules: Concepts, Synthesis, PerspectiVes; VCH: Weinheim, 1996. (b)
Zeng, F.; Zimmerman, S. C. Chem. ReV. 1997, 97, 1681. (c) Smith, D. K.;
Diederich, F. Chem. Eur. J. 1998, 4, 1353. (d) Archut, A.; Vo¨gtle, F. Chem.
Soc. ReV. 1998, 27, 233. (e) Frey, H. Angew. Chem., Int. Ed. Engl. 1998,
37, 2193. (f) Gorman, C. AdV. Mater. 1998, 10, 295. (g) Balzani, V.;
Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi, M. Acc. Chem.
Res. 1998, 31, 26. (h) Fischer, M.; Vo¨gtle, F. Angew. Chem., Int. Ed. 1999,
38, 884. (i) Hearshaw, M. A.; Moss, J. R. Chem. Commun. 1999, 1. (j)
Newkome, G. R.; He, E.; Moorefield, C. N. Chem. ReV. 1999, 99, 1689.
(k) Bosman, A. W.; Janssen, H. M.; Meijer, E. W. Chem. ReV. 1999, 99,
1665. (l) Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Chem. ReV. 1999, 99,
1747. (m) Nierengarten, J.-F. Chem. Eur. J. 2000, 6, 3667. (n) Tully, D.
C.; Fre´chet, J. M. J. Chem. Commun. 2001, 1229.
(2) (a) Wells, M.; Crooks, R. M. J. Am. Chem. Soc. 1996, 118, 3988.
(b) Karthaus, O.; Ijiro, K.; Shimomura, M.; Hellman, J.; Irie, M. Langmuir
1996, 12, 6714. (c) Tsukruk, V. V.; Rinderspacher, F.; Bliznyuk, V. N.
Langmuir 1997, 13, 2171. (d) Roy, R.; Kim, J. M. Angew. Chem., Int. Ed.
Engl. 1999, 38, 369. (e) Wang, J.; Chen, J.; Jia, X.; Cao, W.; Li, M. Chem.
Commun. 2000, 511. (f) Sui, G.; Micic, M.; Huo, Q.; Leblanc, R. M.
Langmuir 2000, 16, 7847.
(3) (a) Cardullo, F.; Diederich, F.; Echegoyen, L.; Habicher, T.;
Jayaraman, N.; Leblanc, R. M.; Stoddart, J. F.; Wang, S. Langmuir 1998,
14, 1955. (b) Maierhofer, A. P.; Brettreich, M.; Burghardt, S.; Vostrwsky,
O.; Hirsch, A.; Langridge, S.; Bayerl, T. M. Langmuir 2000, 16, 8884.
(4) (a) Schenning, A. P. H. J.; Elissen-Roman, C.; Weener, J.-W.; Baars,
M. W. P. L.; van der Gaast, S. J.; Meijer, E. W. J. Am. Chem. Soc. 1998,
120, 8199. (b) Weener, J.-W.; Meijer, E. W. AdV. Mater. 2000, 12, 741.
(5) (a) Saville, P. M.; White, J. W.; Hawker, C. J.; Woley, K. L.; Fre´chet,
J. M. J. J. Phys. Chem. 1993, 97, 293. (b) Mulders, S. J. E.; Brouwer, A.
J.; Kimkes, P.; Sudho¨lter, E. J. R.; Liskamp, R. M. J. J. Chem. Soc., Perkin
Trans. 2 1998, 1535. (c) Kampf, J. P.; Frank, C. W.; Malmstro¨m, E. E.;
Hawker, C. J. Langmuir 1999, 15, 227. (d) Felder, D.; Gallani, J.-L.; Guillon,
D.; Heinrich, B.; Nicoud, J.-F.; Nierengarten, J.-F. Angew. Chem., Int. Ed.
2000, 39, 201.
(7) Amphiphilic diblock globular dendrimers have been described and
used to produce stable emulsions; see: Hawker, C. J.; Wooley, K. L.;
Fre´chet, J. M. J. J. Chem. Soc., Perkin Trans. 1 1993, 1287.
(6) Bo, Z.; Rabe, J. P.; Schlu¨ter, A. D.; Angew. Chem., Int. Ed. 1999,
38, 2370.
10.1021/ja010155m CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/18/2001

9744 J. Am. Chem. Soc., Vol. 123, No. 40, 2001
Scheme 1. Preparation of Compound 7a
Nierengarten et al.
(DCC)-mediated esterification of 4 with 3 in CH2Cl2 gave bis-
(malonate) 5 in 83% yield. The functionalization of C60 was
based on the highly regioselective reaction developed in the
Diederich group,10 which led to macrocyclic bis(adducts) of C60
through a macrocyclization reaction on the fullerene sphere with
bis(malonate) derivatives in a double Bingel addition.11 Treat-
ment of C60 with 5, I2, and diazabicyclo[5.4.0]undec-7-ene
(DBU) in toluene at room temperature afforded 6 in 59% yield.
It is well established that the 1,3-benzenedimethanol-tethered
bis(malonates) yield regioselectively a cis-2 addition pattern on
the C60.10,12 Effectively, all the spectroscopic data obtained for
6 are in agreement with a cis-2 addition pattern. In particular,
the UV/visible spectra of the bis-cyclopropanated fullerene
derivative 6 shows all the characteristic features of a cis-2 bis-
(adduct).10,13 Finally, selective cleavage of the tert-butyl ester
moiety14 of 6 with CF3CO2H in CH2Cl2 afforded carboxylic
acid 7 in a quantitative yield.
Compound 8 was prepared according to a previously reported
procedure.15 DCC-mediated esterification of 4 with 8 in CH2-
Cl2 gave bis(malonate) 9 in 90% yield (Scheme 2). Treatment
of C60 with 9, I2, and DBU in toluene at room temperature
afforded the Cs symmetric cis-2 bis(adduct) 10 in 21% yield.
Cleavage of the p-methoxybenzyl (PMB) protecting groups16
with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in CH2Cl2
in the presence of a small amount of water gave tetraalcohol
11 in 85% yield.
a
Reagents and conditions: (a) K2CO3, DMF, 70 ˚C, 48 h (63%);
(b) Meldrum’s acid, 115 ˚C, 4 h (99%); (c) DCC, DMAP, CH2Cl2, 0
˚C to room temperature, 24 h (83%); (d) C60, I2, DBU, toluene, room
temperature, 15 h (59%); (e) CF3CO2H, CH2Cl2, room temperature,
35 mn (99%).
Reaction of acid 7 with 11 under esterification conditions
using DCC, 4-(dimethylamino)pyridine (DMAP), and 1-hy-
droxybenzotriazole (BtOH) afforded fullerodendron 12 in 65%
yield (Scheme 3). Selective cleavage of the tert-butyl ester
moiety with CF3CO2H in CH2Cl2 then gave 13 in 96% yield.
Thanks to the presence of the four hexadecyloxy substituents
per peripheral fullerene subunit, 12 and 13 are highly soluble
in common organic solvents such as CH2Cl2, CHCl3, toluene,
or THF, and complete spectroscopic characterization was easily
achieved. The matrix-assisted laser desorption/ionization time-
of-flight (MALDI-TOF) mass spectra also confirmed the
structures of 12 and 13, with no peaks corresponding to defected
dendrons being observed. For 12: m/z 10 702 (MH+, calcd for
chains on one hemisphere and hydrophilic groups on the other
provides the perfect hydrophobic/hydrophilic balance allowing
the formation of stable Langmuir films. Furthermore, transfer
experiments of the resulting monolayers onto solid substrates
have been carried out and the deposition occurs regularly with
a transfer ratio of 1. This approach appears particularly
interesting since functional groups not well suited for the
preparation of Langmuir and LB films such as fullerenes8 can
be attached into the branching shell of the diblock dendritic
structure and, thus, be efficiently incorporated in thin ordered
films.
Results and Discussion
C
734H681O75: 10 702.4), 10 724 (M + Na+, calcd for C734H680O75-
Na: 10 724.4). For 13: m/z 10 647 (MH+, calcd for
Synthesis. The fullerene derivative 7 was prepared according
to the procedure we developed for the synthesis of the
corresponding derivative bearing octyl chains (Scheme 1).9 The
monoester 3 of malonic acid was prepared by alkylation of 3,5-
dihydroxybenzyl alcohol (1) with 1-bromohexadecane in DMF
at 70 °C with K2CO3 as base followed by reaction of the
resulting 3,5-dihexadecyloxybenzyl alcohol (2) with 2,2-dim-
ethyl-1,3-dioxane-4,6-dione (Meldrum’s acid) at 115 °C. Diol
4 was prepared in two steps from dimethyl 5-hydroxyisoph-
thalate as previously reported.9 N,N′-Dicyclohexylcarbodiimide
C
730H673O75: 10 646.3), 10 671 (M + Na+, calcd for C730H672O75-
Na: 10 668.3)].
Compound 14 was prepared in nine steps as previously
described.17 Treatment of 14 with 13 under DCC-mediated
esterification conditions afforded the targeted amphiphilic
dendrimer 15 in 20% yield (Scheme 4). This low yield is
certainly due to the poor accessibility of the reactive groups
(10) (a) Nierengarten, J.-F.; Gramlich, V.; Cardullo, F.; Diederich, F.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2101. (b) Nierengarten, J.-F.;
Habicher, T.; Kessinger, R.; Cardullo, F.; Diederich, F.; Gramlich, V.;
Gisselbrecht, J.-P.; Boudon, C.; Gross, M. HelV. Chim. Acta 1997, 80, 2238.
(11) Bingel, C. Chem. Ber. 1993, 126, 1957-1959.
(12) Nierengarten, J.-F.; Schall, C.; Nicoud, J.-F. Angew. Chem., Int.
Ed. Engl. 1998, 37, 1934. Woods, C. R.; Bourgeois, J.-P.; Seiler, P.;
Diederich, F. Angew. Chem., Int. Ed. 2000, 39, 3813.
(13) (a) Hirsch, A.; Lamparth, I. S.; Karfunkel, H. R. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 437. (b) Armaroli, N.; Boudon, C.; Felder, D.;
Gisselbrecht, J.-P.; Gross, M.; Marconi, G.; Nicoud, J.-F.; Nierengarten,
J.-F.; Vicinelli, V. Angew. Chem., Int. Ed. 1999, 38, 3730.
(14) Nierengarten, J.-F.; Nicoud, J.-F. Tetrahedron Lett. 1997, 38, 7737.
(15) Felder, D.; Nierengarten, H.; Gisselbrecht, J.-P.; Boudon, C.; Leize,
E.; Nicoud, J.-F.; Gross, M.; Van Dorsselaer, A.; Nierengarten, J.-F. New
J. Chem. 2000, 24, 687.
(8) (a) Obeng, Y. S.; Bard, A. J.; J. Am. Chem. Soc. 1991, 113, 6279.
(b) Nakamura, T.; Tachibana, H.; Yumura, M.; Matsumoto, M.; Azumi,
R.; Tanaka, M.; Kawabata, Y. Langmuir 1992, 8, 4. (c) Back, R.; Lennox,
R. B. J. Phys. Chem. 1992, 96, 8149. (d) Milliken, J.; Dominguez, D. D.;
Nelson, H. H.; Barger, W. R. Chem. Mater. 1992, 4, 252. (e) Diederich,
F.; Effing, J.; Jonas, U.; Jullien, L.; Plesnivy, T.; Ringsdorf, H.; Thilgen,
C.; Weinstein, D. Angew. Chem., Int. Ed. Engl. 1992, 31, 1599. (f)
Goldenberg, L. M.; Williams, G.; Bryce, R. M.; Monkman, A. P.; Petty,
M. C.; Hirsch, A.; Soi, A. Chem. Commun. 1993, 1310. (g) Maggini, M.;
Karisson, A.; Pasimeni, L.; Scorrano, G.; Prato, M.; Valli, L. Tetrahedron
Lett. 1994, 35, 2985. (h) Mirkin, C. A.; Caldwell, W. B. Tetrahedron 1996,
52, 5113 and references therein. (i) Jonas, U.; Cardullo, F.; Belik, P.;
Diederich, F.; Gu¨gel, A.; Harth, E.; Herrmann, A.; Isaacs, L.; Mu¨llen, K.;
Ringsdorf, H.; Thilgen, C.; Uhlmann, P.; Vasella, A.; Waldraff, C. A. A.;
Walter, M. Chem. Eur. J. 1995, 1, 243 and references therein. (j)
Nierengarten, J.-F.; Schall, C.; Nicoud, J.-F.; Heinrich, B.; Guillon, D.
Tetrahedron Lett. 1998, 39, 5747.
(16) Kocienski, P. J. Protecting Groups; Thieme: Stuttgart, 1994; pp
52-54.
(17) (a) Rio, Y.; Nicoud, J.-F.; Rehspringer, J.-L.; Nierengarten, J.-F.
Tetrahedron Lett. 2000, 41, 10207. (b) Hannon, M. J.; Mayers, P. C.; Taylor,
P. C. J. Chem. Soc., Perkin Trans. 1 2000, 1881.
(9) Nierengarten, J.-F.; Felder, D.; Nicoud, J.-F. Tetrahedron Lett. 1999,
40, 269.

Amphiphilic Diblock Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 40, 2001 9745
Scheme 2. Preparation of Compound 11a
a Reagents and conditions: (a) 4, DCC, DMAP, BtOH, CH2Cl2, 0 ˚C to room temperature, 48 h (90%); (b) C60, I2, DBU, toluene, room temperature,
24 h (21%); (c) DDQ, CH2Cl2, H2O, room temperature, 1 h (85%).
Scheme 3. Preparation of Compound 13a
a Reagents and conditions: (a) 7, DCC, DMAP, BtOH, CH2Cl2, 0 ˚C to room temperature, 96 h (65%); (b) CF3CO2H, CH2Cl2, room temperature,
2 h (96%).
located at the focal points of both dendrons. The NMR spectra
of 15 are fully consistent with the proposed structure and show
clearly the presence of both kinds of dendritic branches. The
structure of 15 is also confirmed by MALDI-TOF mass
spectrometry, which displays the sodium molecular ion peak at
m/z 14 837 (M + Na+, calcd for C947H986O153Na: 14 839.1).
Langmuir and Langmuir-Blodgett Films. Compounds 13
and 15 are both able to form Langmuir films at the air-water
interface. The general shapes of the isotherms obtained at 25
°C for both 13 and 15 are similar and the molecular areas
extrapolated to zero pressure (610 ( 30 Å2 for 13 and 680(
30 Å2 for 15) in good agreement with the values estimated by
molecular modeling (Figure 1).
fectively, for 13, the films are not very stable and the isotherm
show poor reversibility, even when the highest pressure is kept
below the collapse value. In contrast, the Langmuir films of 15
are stable and a perfect reversibility has been observed in
successive compression/decompression cycles (Figure 2). The
onset of the surface pressure being quite progressive (Figure
2), one could have expected the existence of some liquid
condensed phase in the Langmuir film. Brewster angle micros-
copy (BAM) reveals that this is actually not the case and that
the molecules already associate to form islands at large
molecular areas, as seen in Figure 3a. Still, these islands fuse
together in a nice and reversible way and finally yield a very
homogeneous film, as clearly seen in Figure 3b.
The stability of both films and their behavior upon successive
compression/decompression cycles is different however. Ef-
It is noteworthy that the five C60 units of 13 or 15 are buried
in the middle of the dendritic structure, which is capable of

9746 J. Am. Chem. Soc., Vol. 123, No. 40, 2001
Scheme 4. Preparation of Compound 15a
Nierengarten et al.
a Reagents and conditions: (a) 13, DCC, DMAP, BtOH, CH2Cl2, 0 ˚C to room temperature, 96 h (20%).
of 1 ( 0.05. The diblock structure of dendrimer 15 providing
the perfect hydrophilic/hydrophobic balance also appeared
crucial for efficient transfers of the Langmuir films in order to
obtain well-ordered multilayered LB films. Effectively, the
transfer of the Langmuir films of the dendrimer 13 with the
small polar headgroup was found to be difficult with a transfer
ratio of about 0.5-0.7.
The structural quality of mono- and multilayer films of 13
and 15 was investigated by grazing incidence X-ray diffraction.
The quality of the LB films made with 13 was not too good
and only allowed an estimation of their thickness, the roughness
being always in the 3-Å range. Monolayers of 13 were ∼20 Å
thick, and the average value of the layer thickness was found
to be somewhat smaller than expected for the multilayer films
(∼18 Å). This smaller value is probably the result of a partial
interpenetrating of the successive layers within the film.5d
For LB films of 15, the presence of low-angle Kiessig fringes
in the grazing X-ray patterns indicates that the overall quality
of the films is good. The best fit of the grazing X-ray pattern
obtained for a monomolecular film gives a thickness of 36 ( 1
Å and a roughness of ∼2 Å (Figure 4). For the multilayer films,
the average layer thickness was found to be ∼36 Å, indicating
no or little interpenetration of successive layers. The excellent
quality of the LB films prepared with 15 is also deduced from
the plot of their UV/visible absorbance as a function of the layer
number, which results in a straight line, indicating an efficient
stacking of the layers (Figure 5). It is worth stressing the quality
of the stacking and, as a consequence, the quality of the
multilayered films obtained with such a megamolecule.
Figure 1. Pressure-area isotherms for 13 and 15 at 20 °C.
providing a compact insulating layer around the carbon spheres,
thus preventing the irreversible three-dimensional aggregation
resulting from strong fullerene-fullerene interactions as usually
observed with amphiphilic C60 derivatives.8 For both 13 and
15, the polar headgroup causes an attractive interaction with
the aqueous subphase, forcing the molecules to a two-
dimensional arrangement on the water surface. However, for
13, due to the small size of the polar headgroup relative to the
large hydrophobic moiety, the interaction with the aqueous layer
is certainly not strong enough to stabilize the films. In contrast,
a perfect hydrophilic/hydrophobic balance is provided by the
16 peripheral long alkyl chains and 16 triethylene glycol units
in the diblock dendrimer 15, allowing the preparation of stable
Langmuir films. Therefore, the functionalization of the branch-
ing shell of a diblock dendritic structure is an efficient strategy
for the incorporation of functional groups in thin ordered films.
Transfer experiments of the Langmuir films onto solid
substrates and the preparation of LB films were investigated
for both 13 and 15. The deposition of films of 15 occurred
regularly on quartz slides or silicon wafers with a transfer ratio
Conclusion
The peripheral substitution of a globular dendrimer with
hydrophobic chains on one hemisphere and hydrophilic groups

Amphiphilic Diblock Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 40, 2001 9747
Figure 2. Four successive compression/expansion cycles with a monolayer of 15 (25 °C; compression/decompression speed, 5 mm mn-1) showing
the perfect reversibility of the process.
Figure 4. Grazing incidence X-ray pattern of a monolayer of 15,
together with the best fit (continuous line) to the data.
Figure 5. UV-visible spectra of the LB films of derivative 10 (from
bottom to top: 3, 9, 21, 31, 41, 51, and 61 layers). The inset shows
the plot of the absorbance at 265 nm against the layer number.
Figure 3. Brewster angle microscopy images for 15: (a) A ) 1420
Å2; (b) A ) 680 Å2.
Experimental Section
on the other provides the perfect hydrophobic/hydrophilic
balance allowing the formation of stable Langmuir films. On
Langmuir and LB Films. Spreading solutions were prepared by
dissolving the compounds in CHCl3 (Analysis Grade from Carlo Erba)
one hand, this approach shows some of the fundamental
at 1.0-3.0 mg mL-1 concentrations. Stock solutions proved stable for
architectural requirements for obtaining stable films with
amphiphilic dendrimers. On the other hand, functional groups
not well adapted for the preparation of Langmuir and LB films
such as fullerenes can be attached into the branching shell of
the dendritic structure and, thus, efficiently incorporated in thin
ordered films.
several months when stored at room temperature. For a typical
experiment, 50 µL of the stock solution was spread on the water surface
with a microsyringe, and the film was then left for 15-20 min to
equilibrate before the compression started. Data were collected with a
KSV LB5000 system (KSV Instruments, Helsinki, Finland) using a
symmetrical compression Teflon trough and hydrophilic barriers in a

9748 J. Am. Chem. Soc., Vol. 123, No. 40, 2001
Nierengarten et al.
dust-free environment. The whole setup was in a Plexiglas enclosure
resting on a vibration-free table, and the trough temperature was
controlled to (0.1 °C. All isotherms were taken at 20 °C unless
otherwise specified. Ultrapure water (F ) 18.2 MΩ cm) obtained from
a Milli-RO3 Plus system combined with a Milli-Q185 Ultra Purification
system from Millipore was used for the subphase. Surface pressure
was measured with the Wilhelmy plate method. The monolayers were
and a proportional Xe detector. Nickel-filtered Cu KR line (wavelength
0.1542 nm) was used. All measurements were recorded immediately
after the LB transfer.
Acknowledgment. This work was supported by the CNRS
and the French Ministry of Research (ACI Jeunes Chercheurs).
J.-F.E. thanks the DGA for a doctoral fellowship, Y.R. thanks
the French Ministry of Research for a doctoral fellowship, and
M.d.P.C. thanks DGAPA-UNAM and CONACyT for a post-
doctoral fellowship. We further thank Dr. A. Van Dorsselaer
and H. Nierengarten for the MS spectra, M. Schmitt for the
NMR measurements, and L. Oswald for technical assistance.
compressed with speeds ranging from 1.2 to 10 Å2 molecule-1 min-1
,
with almost no incidence of the barrier velocity on the observed
behavior. LB films were obtained by transfer on quartz slides or silicon
wafers (100). Vertical dipping method was used for 13 and 15. Dipping
parameters were not very stringent and usually kept around the
following values: trough temperature T ≈ 20-30 °C; dipping speed
Vdip ≈ 0.5-4 mm min-1. Transfers were performed at surface pressures
of 22 mN m-1. BAM has been performed using a BAM2plus setup
from Nanofilm Technologies GmbH. Illumination came from an argon
laser; images were recorded on a CCD camera. The field is 620 µm
width × 500 µm height. The grazing incidence X-ray studies of LB
films were performed on a device equipped with a programmable
divergence slit (1/32°), a Soller slit collimator, a flat Ge monochromator,
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