Langmuir 1995,11, 3656-3659
3656
Synthesis of Nanosize Latexes by Reverse Micelle Polymerization A. Hammouda,'>$Th. Gulik,§ and M. P. Pileni*>+J Laboratoire S.R.S.I., Universitk P. et M. Curie, B.P. 52, 4 Place Jussieu, 75231 Paris Cedex 05, France, C.E.A., C.E. Saclay, D.R.E.C.A.M.IS.C.M., 91191 Gif sur Yvette, France, and C.G.M., CNRS, 91198 Gif sur Yvette, France Received January 20, 1995. I n Final Form: March 29, 1995@ The synthesis and the characterization of didecyldimethylammonium methacrylate, a new polymerizable surfactant forming reverse micelles in toluene, have been performed. The reverse micelles have been characterized by small-angle X-ray, small-angle neutron, and dynamic quasi-elastic light scattering experiments. These microemulsions have been UV irradiated i n the presence of azobisbobutyronitrile), at various water contents. For t h e first time, it has been possible to make monodisperse nanosize latexes in the size range of 2-5 n m by reverse micelle polymerization.
Introduction
acrylamide18J9 in the reverse micelles. Under these conditions, the polymerization induces the formation of Polymerization of o r in organized microstructures has latexes of 30-nm diameter w i t h a narrow distribution. been largely studied these last 10 years. Polymerization The second approach uses surfactants able to form reverse has been used t o increase the stability of organized micelles and having a double bond in the polar headassemblies. They are of considerable c u r r e n t interest in g r o ~ p . In ~ ~the , ~latter ~ case, the size obtained is about the areas of biomembrane modeling, drug delivery, a n d 60-nm diameter. In neither of these approaches has it transp0rt.l It has been well demonstrated that the initial been possible t o make latexes in the range of 2-5 nm. structure of the vesicles is conserved after the polymerization, with an internal and an external w a t e r p h a ~ e , ~ - l ~ The present paper shows that this a i m c a n be achieved by using a reverse-micelle-forming surfactant w i t h a while the polymerization of micelles in water induces the polymerizable counterion: didecyldimethylammonium formation of large cylinder^.'^-'^ In the case of reverse methacrylate. The synthesis and characterization of such structures, m a n y attempts have been made t o synthesize latexes are presented. nanosize latexes, characterized by small size and a narrow distribution, by using either an emulsion or a microemulExperimental Section sion as the medium. In the case of emulsions, it has been possible t o m a k e poly(acry1amide) inverse latexes with 1. Materials. Didecyldimethylammonium bromide, CloBr, diameters in the range of 90-160 nm.I7 In the case of was purchased from Fluka, toluene from SDS, and azobisreverse micelles, two approaches have been used. The (isobutyronitrile) from Serva. first is t o solubilize a hydrophilic monomer as the 2. Apparatus. NMR experiments were performed on a Brucker apparatus at 200 MHz. The conductivity measurements Universite P. et M. Curie. were performed by using a platinum electrode and a Tacussel D.R.E.C.A.M./S.C.M. CD 810 instrument. UV irradiation was performed by using a CNRS. Schoeffel Instrument lamp (1000W). To protect the sample from Abstract aublished inAdvance ACSAbstracts. Aueust 15.1995. heat radiation, a 20-cm water filter was fixed between the lamp (1)Ringsdirf, H.; Schlarb, B.; Venzmer, J. Angeb. &em., I h . E d . and the irradiated sample. The cell used was an absorption cell. Engl. 1988,27,113-158. The intensity of the beam has been measured by using the (2) Babilis. D.; Dais, P.: Paleos. C. M. Polvm. PreDr. (Am. Chem. SOC., " Harchard and Parker method22and was found to be equal to 1.5 Diu. Polym. ChemJ 1986,26(1),'206-7. x 1014photonsh. The small-angle X-ray scattering (SAXS)and (3)Babilis, D.; Dais, P.; Margaritis, L. H.; Paleos, C. M. Polym. Sci., small-angle neutron scattering ( S A N S ) experiments were perPolym. Chem. Ed. 1985,23,1089-1098. (4)Babilis, D.; Paleos, C. M.; Dais, P. Polym. Sci., Polym. Chem. E d . formed a t the Laboratoire d'Utilisation des Rayonnements 1988,26,2141-2156. Electromagnetiques (L.U.R.E.), CNRS, C.E.A, Paris XI, Orsay, (5)Ringsdorf, H.; Schlarb, B. Polym. Prepr. (Am. Chem. SOC.,Diu. France, on the D22 diffractometer and at Orphee, C.E.N., Saclay, Polym. ChemJ 1986,27(2),195. France, respectively. The dynamic quasi-elastic light scattering (6) Regen, S . L.; Shin, J . 3 ;Yamaguchi, K. J . Am. Chem. SOC.1984, (DQELS) measurements were performed with an argon laser 106,2446-47. (7) Kukuda, H.; Diem, T.; Stefely, J.;Kezdy, F. J.;Regen, S. L. J . Am. (514.5nm), at a temperature of 25 "C and a scattering angle of Chem. SOC.1986,108,2321-27. 45". The autocorrelation functions were obtained with a 136( 8 ) Regen, S . L.; Czech, B.; Singh, A. J . A m . Chem. SOC.1980,102, channel Brookhaven digital correlator. Size-exclusion chroma6638-40. tography (SEC)was performed on two 10;um PL-Gel columns of (9)Bolikal, D.; Regen, S.L. Macromolecules 1984,17, 1287. lo2 and lo3 porosity, respectively. (10)Reboiras, M. D.; Morris, G. A.; Jones, M. N. Colloid Surf. 1990, 49,385-94. Transmission Electron Microscopy. Air-dried prepara(11)Reboiras, M.D.; Jones, M. N. Colloid Surf. 1991,57,197-204. tions of diluted toluene solutions of nanosize latexes were (12)Regen, S.L.; Singh, A.; Oehme, G.; Singh, M. J . A m . Chem. SOC.
*
@
1982,104,791-95. (13)Regen, S.L.;Yamaguchi, K.; Samuel, N. K. P.; Singh, M. J . A m . Chem. SOC.1983,105, 6354-55. (14)Cochin, D.; Zana, R.; Candau, F. Polym. Int. 1993,30,491-98. (15)Lerebours, B.; Perly, B.; Pileni, M. P. Chem. Phys. Lett. 1988, 247(5),503-508. (16)Lerebours, B.;Perly, B.; Pileni, M. P. Prog. Colloid Sci. 1989, 79,239-243. (17)Graillat, C.; Pichot, C.; Guyot, A.; El Aasser, M. S. J . Polym. Sci., Part A: Polym. Chem. 1986,24,427-49.
0743-7463/95/2411-3656$09.00/0 . ~
~
~
____
(18) Leong, Y. S.; Candau, F. J . Phys. Chem. 1982,86(13), 2269-71. (19)Candau, F.;Carver, M. T. Structure and reactivity in reverse micelles; Pileni, M. P., Ed.; Elsevier: Amsterdam, 1989. (20) Voortmans, G.; Verbeeck, A.; Jackers, C.; De Schryver, F. Macromolecules 1988,21,1977-80. (21) Voortmans, G.; Jackers, C.; De Schryver, F. Br. Polym. J . 1989,
21,161-69. (22) Parker, C. A.; Proc. R.SOC.1953,A 220,104. Hatchard, C. G.; Parker, C. Proc. R. SOC.1966,A 235,516.
0 1995 American Chemical Society
Synthesis of Nanosize Latexes observed either directly, using a Jeol JEM lOOCX I1 electron microscope, or after unidirectional shadowing with platinumcarbon (1-1.5 nm of metal deposited in a Balzers BAF freezeetching unit), using a Philip 301 electron microscope. 3. Methods. (i) Surfactant Synthesis. Didecyldimethylammonium methacrylate, CloMA, was quantitatively obtained from CloBr by ion-exchange chromatography performed on a previously methacrylated resin (AG1 X 2 , Bioradl.6 The surfactant purity was determined by titration of the residual bromide ions, and the percentage of residual bromide ions was equal to 0.03. CIOMAhas been characterized by its proton and carbon nuclear magnetic resonance (NMR) spectra. From the proton NMR spectra, the presence of the ethylenic protons (at 5.1 and 5.7 ppm) and the methylic protons of the methacrylate group (at 1.9 ppm) confirms the exchange. The integration of the methacrylate protons with respect to those of the ammonium moiety shows that the exchange is complete. In the 13CNMR spectrum, the signals a t 174, 145.5, 118.5,and 20.9 ppm correspond to the carbonyl, the ethylenic carbons, and the methylic carbon of the methacrylate moiety. By infrared spectroscopy, the characterization of CloMA shows absorption bonds centered at 1572 and 1643 cm-l corresponding to the valence vibration ofthe carbonyl and the vinylic bonds of the carboxylate groups, respectively. (ii) Micellar Solution. CloMA ([CloMAI = 0.05 and 0.1 M) was dissolved in toluene, and water was added to reach a given water content, w ,defined as the ratio of water over surfactant concentrations (in mol/mol). The sample was hand-shaken a t room temperature, and an optically clear solution was obtained. (iii) Polymerization. CloMA-water-toluene reverse micelles were irradiated at various water contents and CloMA concentrations in the presence of an initiator such as azobis(isobutyronitrile)(AIBN). The quantity ofAIBN added is chosen to be equal to 1% in weight of CloMA. The CloMA-watertoluene-AIBN solution was degassed by nitrogen bubbling and UVirradiated for 7 h. After this period oftime, the polymerization was stopped. (iv) SEC Analysis. CloBr in dimethylformamide has been used as the eluant with a flow rate equal to 1 mUmn. The ammonium salt has been added in order to prevent adsorption and exclusion phenomena. A differential refractometer was used for the detection, and the evolution of refractive index variation (dn, with the eluant refractive index as the reference) has been measured vs the elution volume. 4. Scattering Analysis. The scattered intensity, Zfq), is
Ifq) = PfqjSfq) where q is the wave vector, equal to 4n(sin @)/A (20 and 1 are the diffision angle and the radiation wavelength, respectively) and Pfq) and Sfq) are the form factor and the structure factor, respectively. From the form factor, the shape of the aggregates is deduced while the structure factors takes into account interactions between the aggregates. In dilute solutions, the intermicellar interactions can be neglected and Sfqj is assumed to be equal to 1. For spherical structures, the form factor is expressed by
Langmuir, Vol. 11, No. 10, 1995 3657 -4
1
-6 -8
E -10
= -12 -14 -16
-18
-2
-3
-I
0
In (s)
Figure 1. ln(n = ln(q) obtained from SAXS experiments (0) and from the calculated curve in the case of the hard-sphere model (-) for the CloMA/water/toluene system. [CloMA] = 0.1 M, w = 10.
-I"
I
O
h
5 cr:
0
20
10
30
W
Figure 2. Variation of the polar (01, micellar (B), and hydrodynamic (0) radii of CloMA initial reverse micelles in toluene determined respectively by SAXS, SANS, and DQELS experiments. From DQELS experiments, at low volume fraction (@ the diffusion coefficient, D, is expressed by
