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NANOSYSTEMS: PHYSICS, CHEMISTRY, MATHEMATICS, 2015, 6 (2), P. 294-298
Dependence of the dimension of the associates of water-soluble tris-malonate of light fullerene — C60 [= C(COOH)2]3 in water solutions at 25 C
K.N. Semenov1, N.A. Charykov2,3, A. S. Kritchenkov1, I. A. Cherepkova2, O. S. Manyakina2, D.P. Tyurin2, A. A. Shestopalova2, V. A. Keskinov2, K. V. Ivanova2, N.M. Ivanova1, D.G. Letenko4, V.A. Nikitin5, E.L. Fokina1, M.S. Gutenev5
1St. Petersburg State University, Saint-Petersburg, Russia 2St. Petersburg State Technological Institute (Technical University), Saint-Petersburg, Russia 3St. Petersburg State Electro-Technical University (LETI), Saint-Petersburg, Russia 4 St. Petersburg State University of Architecture and Civil Engineering, Saint-Petersburg, Russia 5Peter the Great St. Petersburg Polytechnic University, Saint-Petersburg, Russia
PACS 61.48.+c DOI 10.17586/2220-8054-2015-6-2-294-298
Investigation of the concentration dependence of the size and type C6o[=C(COOH)2]3 aggregation in aqueous solutions at 25 0 C was accomplished with the help of a dynamic light scattering method. It was determined that three types of aggregates are realized in the solutions. The average number of C60[=C(COOH)2]3 molecules in smaller aggregates and all types of aggregates were calculated. One can see that over the whole concentration range, from 0.01 to 10 g/dm3, aqueous solutions of C60[=C(COOH)2]3 are characterized by sub-micro-heterogeneous behavior (because second-type aggregates with the linear dimensions - hundreds of nm are formed in all solutions). Additionally, the most concentrated solution (C = 10 g/dm3) is characterized by micro-heterogeneous or colloid behavior (because third-type aggregates with the linear dimensions on the order of ^m - are formed). In order to describe or explain such behavior, a stepwise aggregation model was invoked.
Keywords: tris-malonate of light fullerene, method of the dynamic light scattering.
Received: 10 August 2014
1. Introduction
This article further develops investigations which were initiated previously [1-4]. These
studies were devoted to the synthesis and identification of tris-malonate C6o[=C(COOH)2]3 [1]
(the original synthesis of this water soluble derivative was described earlier in [5]), the investigation of volume and refraction properties of its aqueous solutions at 25 °C [2], poly-thermal
solubility and complex thermal analysis [3], concentration dependence of electric conductivity and hydrogen ion concentration for aqueous solutions [4]. This study was undertaken to investigate the concentration dependence of C60[=C(COOH)2]3 aggregate sizes in aqueous solutions at 25 °C, and as in the earlier article [3], these studies to investigate the state of C60[=C(COOH)2]3 and its aggregation processes were performed in aqueous solutions over a wide concentration range - 0.1 ^ 10 g/dm3.
Dependence of the dimension of the associates of water-soluble tris-malonate ... 295
Table 1. Linear dimensions of C6o [=C(COOH)2]3 aggregates in aqueous solutions at 25 °C
Diameter of first type associates d1 -interval (d1) (nm) Diameter of Diameter of
Concentration Diameter of monomer d0 & 1.8 nm (nm) second type third type
of C6o tris-malonate C (g/l) associates d2-interval №) (nm) associates d3-interval (d3) (nm)
0.01 No effect 30-70 (50) 200-400 (300) No effect
0.1 No effect 40-80 (60) 300-500 (400) No effect
1.0 No effect 40-80 (60) 300-500 (400) No effect
5.0 No effect 40-80 (60) 300-500 (400) No effect
10.0 No effect 40-80 (60) 500-1000 (750) 4000-6000 (5000)
Concentration Average number of monomer molecular Average number of clusters of the Average number of clusters of the
of C6o of C60 tris-malonate first order in second order in
tris-malonate in clusters of the clusters of the clusters of the
C (g/l) first order second order third order
N0^1 (units) N1^2 (units) N2^3 (units)
0.01 1.1 ■ 104 1.1 ■ 102 No effect
0.1 1.9 ■ 104 1.6 ■ 102 No effect
1.0 1.9 ■ 104 1.6 ■ 102 No effect
5.0 1.9 ■ 104 1.6 ■ 102 No effect
10.0 1.9 ■ 104 1.0 ■ 103 1.6 ■ 102
2. Dimension of the associates of C6o[=C(COOH)2]3 in water solutions at 25 °C
To investigate the concentration dependence of C60[=C(COOH)2]3 aggregate size in aqueous solutions at 25 °C, we utilized a dynamic light scattering method in the visible wavelength region. The Malvern Zeta Nanosizer device was used. Data are represented in Table 1 and Fig. 1 and 2 (as the examples).
To estimate the linear size of the C60[=C(COOH)2]3 monomer, d0(monomer) was obtained from the refraction data [2]. Molar refraction of C60 tris-malonate Rtris-maionate & 201 cm3/mole, so: Rtris-maionate & 2.01 ■ 10-4/6.02 ■ 1023 & 3.0 ■ 10-27 m3/molecule, so: in the spherical approximation, the linear dimension: d0(monomer) & [18/n ■ 10-27]1/3 & 1.8 ■ 10-9 m = 1.8 nm.
3. Number of i-th type associates packed into (i + 1)-th type associates
The number of i-th type aggregates packed into (i + 1)-th type aggregates - Ni^i+1 was estimated by the following equation:
Ni^i+1 = (di+1/di)3 ■ Kpack, (1)
where: Kpack & 0.52 - is formal pack coefficients for the case of 'little spheres', packed in the 'larger sphere' (1 — Kpack & 0.48 - volume fraction, which is empty of is fulfilled by a molecular of H2O).
Size Distribution by Volume
5
25 20 15 10 5 +
- a
- .ft
- 1 1
- 't V
-i-1—1—B a ¡S --1-1---1—i, % iJ.ii A—i—i—i \ 11111 --4-j—s—I?- jji Ma-
0.1
10
100
1000
10000
Size (d.nm)
Record 10: tris-malonate 60 5 g/1 1 Record 12: tris-malonate 60 5 g/1 3
Record 11 : tris-màlonate 60 5 g/1 2
Fig. 1. Distribution according to linear dimension of C60 tris-malonate aggregates in aqueous solution at concentration of C60 tris-malonate C = 5 g/dm3 (example) - 3 signals correspond to the different times of signal sum
Fig. 2. Distribution according to linear dimension of C60 tris-malonate aggregates in aqueous solution at concentration of C60 tris-malonate C =1 g/dm3 (example) - 3 signals correspond to the different times of signal sum
Calculated, concerning Ni^i+1-values data are also represented in Table 1. From obtained data one can see the following:
1. No monomer molecular (with linear dimension-diameter d0 ~ 1.8 nm) are seen in all investigated solutions, even in the dilute solution (C = 0.1 g/dm3).
2. The diameter of first type aggregates (first order clusters of percolation) have the similar linear dimension-diameter d1 ~ 60 ± 20 nm over the whole concentration range (a slight decrease is seen only for the most dilute solution (C = 0.01 g/dm3) - d1 « 50 ± 20 nm).
3. The diameter of second type aggregates (second order clusters of percolation) also have a similar linear dimension-diameter d2 ~ 400 ± 100 nm in the concentration range 0.1 ^ 5 g/dm3 (again, a slight change is seen only for the most dilute solution at
Dependence of the dimension of the associates of water-soluble tris-malonate .. . 297
C = 0.01 g/dm3 - d2 ~ 300 ± 100 nm and for the most concentrated solution at C = 10 g/dm3 - d2 ~ 750 ± 250 nm - solution 'is preparing to become heterogeneous').
4. Third type associates (third order clusters of percolation) have not been seen at any concentrations except the most concentrated solution at C = 10 g/dm3, where clusters with extremely huge linear dimension-diameter d3 « 5000 ± 1000 nm (5 ± 1 pm) are observed - the solution 'becomes very heterogeneous' but stable as a colloid system).
5. So, to describe such facts in the aggregation process, a stepwise model of particle growth was invoked. We consider that monomer spherical molecules form the first type spherical aggregates, then, the first type spherical associates form second type spherical associates. Next, the second type spherical associates form third type spherical associates (the last ones correspond to the colloidal heterogeneous system). A similar stepwise aggregation model was used by us earlier for the description of particle growth in water-fullerenol-d systems (see, for example [6]).
To prove the formation of the micro-heterogeneity (with the linear dimensions on the order of pm) in the most concentrated solution (C = 10 g/dm3), we obtained a photo of the film this solution. An optical polarizing microscope Labo-Pol (variant 2) was used. Samples were prepared by the crystallization of C60 tris-malonate crystals from aqueous solutions under quick isothermal evaporation of water from the solution (a drop of the solution was put on the surface of silicate glass). A typical photo is represented in the Fig. 3. One can see typical spherical formations (centers of crystallization) with enough characteristic linear dimensions which were observed earlier in the dynamic light scattering investigations as third type aggregates (see Table 1). Crystal formations, proceeding from these spheres, gave the crystal-like film in the quick evaporation-crystallization process.
Fig. 3. Here is an optical polarizing microscope photo of C60 tris-malonate crystals (scale x 1000). The initial (before evaporation) solution had a concentration C of 10 g C60 tris-malonate of per dm3 H2O
Acknowledgments
Investigations were supported by Russian Foundation for Basic Research - RFBR (Project No. 15-08-08438).
References
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