Langmuir 2001, 17, 2683-2687
2683
Preparation and Characterization of Surface-Modified Silica-Nanoparticles Gy. Tolnai,† F. Csempesz,‡ M. Kabai-Faix,† E. Ka´lma´n,§ Zs. Keresztes,§ A. L. Kova´cs,| J. J. Ramsden,⊥ and Z. Ho´rvo¨lgyi*,† Department of Physical Chemistry, Budapest University of Technology and Economics, H-1521 Budapest, Hungary, Department of Colloid Chemistry, Lora´ nd Eo¨ tvo¨ s University, Pa´ zma´ ny Pe´ ter se´ ta´ ny 2, H-1117 Budapest, Hungary, Department of Surface Chemistry and Corrosion Research, CRC HAS, P.O. Box 17, H-1525 Budapest, Hungary, Department of General Zoology, Lora´ nd Eo¨ tvo¨ s University, H-1088 Budapest, Hungary, and Biozentrum, University of Basel, CH-4056 Basel, Switzerland Received May 30, 2000. In Final Form: January 29, 2001 Sto¨ber silica particles having diameters of ca. 100 and ca. 200 nm were prepared and silylated using trimethylsilyl N,N-dimethylcarbamate, achieving a range of surface coverage by trimethylsilyl groups by varying the amounts of silylating agent used. The efficacy of silylation was characterized in terms of hydrophobicity of the particles which was assessed by film balance investigations at water-air interfaces and additionally by imaging the long- and short-range structures of silica particulate layers at water-air interfaces and on mica supports by using Brewster-angle and atomic force microscopies.
Introduction Nanoscale silica has had great practical importance for many years.1-3 For example, silica dispersions play a significant role in the fabrication of electric and thermal insulators, catalyst supports, and membranes; silicas are used as filling materials in polymer composites. Commercial silicas (e.g., silica aerogels, Aerosil, Cab-O-Sil) have a broad size distribution and suspended particles form agglomerates due to (interparticle) hydrogen bonding. Many applications, however, require silica particles with a narrow size distribution, and with controlled size, shape, and surface properties. Sto¨ber et al. prepared monodisperse silica spheres (“Sto¨ber silica”) in alcoholic phase from silicon alkoxides.4 Using their procedure, it is possible to obtain different sized silica spheres in the whole colloidal size range (below 1 µm) simply by changing the initial concentrations of reagents. These particles are compactsespecially when above 20 nm diameter5sand also serve as good models for theoretical investigations of colloid stability6-8 as well as in developing different methodologies6,9 (static and dynamic light scattering, * Corresponding author; E-mail:
[email protected], Tel.: 36 1 463 2911; Fax: 36 1 463 3767. † Budapest University of Technology and Economics. ‡ Lora ´ nd Eo¨tvo¨s University. § Department of Surface Chemistry and Corrosion Research, CRC HAS. | Lora ´ nd Eo¨tvo¨s University. ⊥ University of Basel. (1) Iler, R. K. The Chemistry of Silica; Wiley: New York, 1979. (2) Brinker, C. J.; Scherer, G. W. Sol-Gel Science; Academic Press: Boston, MA, 1990. (3) Chen, S.-L. Colloids Surfaces, A 1998, 142, 59. (4) Sto¨ber, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62. (5) Bailey, J. K.; Mecartney, M. L. Colloids Surf. 1992, 63, 151. (6) Nyffenegger, R.; Quellet, C.; Ricka, J. J. Colloid Interface Sci. 1993, 159, 150. (7) Kira´ly, Z.; Tu´ri; L.; De´ka´ny, I.; Bean, K.; Vincent, B. Colloid Polym. Sci. 1996, 274, 779. (8) Ludwig, P.; Peschel, G. Prog. Colloid Polym. Sci. 1988, 77, 146. (9) De´ka´ny, I. In Physical adsorption: Experiment, Theory and applications; NATO ASI Series C: Mathematical and Physical Sci.; Fraissard, J., Conner, C. W., Eds.; Kluwer Academic Publishers: Dordrecht, 1997; Vol. 491, p 369.
small-angle X-ray spectroscopy (SAXS), electrophoresis, etc.). Moreover, the surface of Sto¨ber silica can be coated with octadecyl alcohol,10,11 silylating agents,5,12-14 or polymers15 which allows one to control the interparticle forces during model investigations. In most of the cases silylation is carried out in the original (reaction) phase or in aqueous medium whereby the types of suitable agents are strongly limited. In some cases multifunctional silylating agents are applied for coating which can lead to the formation of oligomer chains on the particle surface causing difficulties in the interpretation of experimental results. Usually, alkoxy-type silylating agents are used6 and the maximum degree of silylation is carried out. However, in model investigations as well as in applications it would be important to have particles with various degrees of silylation. The main purpose of this work, therefore, is to establish experimental conditions leading to a series of surfaces from high to low degrees of silylation which manifests itself in different surface hydrophobicities. We report here on the controlled surface silylation of Sto¨ber silica using monofunctional trimethylsilyl N,N-dimethylcarbamate,16 which can only be used in aprotic solvents. This compound had been previously shown to be suitable for the controlled (and very effective) silanization of microscope glass plates,17 silica microspheres,18 and glass beads19 by changing the initial concentration of the silylating agent (10) Van Halden, A. K.; Jansen, J. W.; Vrij, A. J. Colloid Interface Sci. 1981, 81 (2), 354. (11) Van Blaaderen, A.; Vrij, A. Langmuir 1992, 8, 2921. (12) Philipse, A. P.; Vrij, A. J. Colloid Interface Sci. 1989, 128 (1), 121. (13) Badley, R. D.; Ford, W. T.; McEnroe, F. J.; Assink. R. A. Langmuir 1990, 6, 792. (14) Ketelson, H. A.; Pelton, R.; Brook, M. A. Colloids Surf., A 1998, 132, 229. (15) Pathmamanoharan, C. Colloids Surf. 1990, 50, 1. (16) Knausz, D.; Meszticzky, A.; Szaka´cs, L.; Csa´kva´ri, B.; Ujsza´szy, K. J. Organomet. Chem. 1983, 265, 11. (17) Ho´rvo¨lgyi, Z.; Kiss, E Ä .; Pinte´r, J. Magy. Kem. Foly. 1986, 92, 488. (18) Ho´rvo¨lgyi, Z.; Ne´meth, S.; Fendler, J. H. Colloids Surf. A 1993, 71, 327. (19) Ho´rvo¨lgyi, Z.; Ne´meth, S.; Fendler, J. H. Langmuir 1996, 12 (4), 997.
10.1021/la0007372 CCC: $20.00 © 2001 American Chemical Society Published on Web 04/06/2001
2684
Langmuir, Vol. 17, No. 9, 2001
and/or the time of silylation. As a result of this process, surfaces were obtained with water contact angles in the range of 30°-100°. It was found previously that this agent is more effective for the silanization of glass surfaces20 and silica aerogels (Cab-O-Sil M5)21 in its hexane solution than the chlorotrimethylsilane. The reaction, using trimethylsilyl N,N-dimethylcarbamate, produces silylated derivatives with gaseous CO2 and (CH3)2NH which can be removed from the system by continuous distillation. The suggested surface modification of silica nanoparticles requires the alcoholic phase to be changed to acetonitrile in which the silylation takes place. The stability of silica sols, which should be maintained during the preparation, was checked by dynamic light scattering investigations. After the silylation, the excess of silylating agent was removed and acetonitrile was changed back to ethanol leading to the alcosol of surface modified particles. The result of surface modification was controlled by wettability determinations using the film balance technique.22,23 Additionally, we would like to show that Brewster-angle and atomic force microscopy (combining them with the film balance and the Langmuir-Blodgett technique) can provide indirect information about the particle hydrophobicities by imaging the long- and shortrange structure of monoparticulate layers at the waterair interface and on mica supports. Experimental Section Materials. Acetonitrile (puriss, >99%, Reanal), chloroform (ultraresy analyzed, >99.8%, Baker), absolute ethanol (A.R., Reanal), ammonium hydroxide (25% aqueous solution of NH3, A.R., Reanal), tetraethyl orthosilicate (TEOS) (>98%, GC grade, Merck), methoxytrimethylsilane (>97% GC grade, Fluka), and trimethylsilyl N,N-dimethylcarbamate (TDC) (>97%, GC grade, Fluka) were used as received. Water was purified with a Millipore Milli Q filtration system. Preparation of Model Particles. Preparation of Sto¨ ber Silica Particles. The alcosols of silica particles were prepared according to the Sto¨ber method.4 With the appropriate reagent concentrations spheres of diameter ca. 200 nm (batch S200) and for comparison ca. 100 nm (batch S100) were prepared. The solid content of alcosols (mg/mL) was determined from the amount of residual solids after solvent evaporation in a drying oven at 80 °C. Surface Modification of Sto¨ ber Silica Particles. Four samples with different hydrophobicities were prepared in the case of the bigger (ca. 200 nm diameter) particles. First, the alcoholic phase (30.0 mL of sol, solid content 10.0 mg/mL) was changed for acetonitrile by distillation (resultant volume is 30.0 mL) which also eliminated residual NH3. Then, silylation was carried out in acetonitrile by sonicating the mixture for 30 min at ambient temperature. After the reaction the acetonitrile was changed for ethanol by distillation. Excess silylating agent was also removed during the distillation as revealed by mass spectrometry. For preparing samples S200/1, S200/2, S200/3, and S200/4, 300, 150, 30, and 15 µL of silylating agent was added, respectively, to the acetonitrile sol of particles. The amount of silylating agent for the preparation of S200/1 was approximately 100 times greater than that necessary for reaching a complete coating of silica particles (a calculation based on an assumed 40 Å2 area for a trimethylsilyl group24). For comparison of the behavior of particles with different sizes, ca. 100 nm diameter silica spheres (S100/1), were silylated like sample S200/1. Due to the enhanced particle surface area, the (20) Ho´rvo¨lgyi, Z. M.Sc. Thesis (in Hungarian), Department of Colloid Science, Lora´nd Eo¨tvo¨s University, Budapest, l983. (21) Tolnai, Gy.; Alexander, G.; Ho´rvo¨lgyi, Z.; Juvancz, Z.; Dallos, A. Chromatographia 2001, 53 (1/2), 69. (22) Clint, J. H.; Taylor, S. E. Colloids Surf. 1992, 65, 61. (23) Aveyard, R.; Binks, B. P.; Fletcher, P. D. I.; Rutherford, C. E. Colloids Surf. A 1994, 83, 89. (24) Herzberg, W. J.; Marian, J. E.; Vermeulen, T. J. Colloid Interface Sci. 1970, 33, 164.
Tolnai et al. amount of silylating agent (300 µL) was approximately 25 times greater than necessary for reaching a complete coating of particles. Characterization Techniques. Transmission Electron Microscopy (TEM). A JEOL JEM-100 CX II transmission electron microscope was used to assess the particle size and shape. The samples were deposited on Formvar film-coated carrier grids. Particle sizes were determined by measuring the diameters of (approximately 500) spherical particles from which the number averaged particle size and its standard deviation were calculated. Dynamic Light Scattering (DLS). Mean particle size, size distribution, and polydispersity of the sols both in ethanol and in acetonitrile (and for the purpose of film balance experiments in the mixture of ethanol-chloroform, 1:2, v/v) and also the temporal evolution of these parameters were measured at 25 °C by an advanced photon correlation spectroscopy (PCS) technique using a Malvern Zetasizer 4 apparatus (Malvern Instruments, U.K.) with autosizing mode and autosample time. On the basis of the autocorrelation function of measured intensity distribution of scattered light from solid particles, the corresponding Z-average mean size, the number, and mass- or volume-average mean sizes of sol particles were calculated. Comparison of these parameters with the particle sizes from the TEM measurements gave information about the stability of sols. Samples were prepared by diluting the silica dispersions 20-fold with the appropriate liquid phases. The concentration of silica particles in the different diluted sols was the same. The sols were ultrasonicated prior to the DLS measurements for 10 min. In certain cases, the mean particle sizes were also controlled during a 10-30 min time period after the ultrasonication. Wilhelmy Film Balance. The hydrophobicities of particles were determined by film balance experiments. A laboratory-built Wilhelmy film balance was used to determine the surface pressure (Π) vs surface area (A) isotherms of monoparticulate layers at room temperature. The sols for spreading were prepared by diluting the silica suspensions with chloroform (1 volume of alcosol + 2 volumes of chloroform) then homogenizing in an ultrasonic bath for 10 min. An appropriate amount of sol (the same number of particles in every case) was spread on the surface of water in the film balance. After the evaporation of the spreading liquid, the Π-A isotherms were obtained at a rate of 3.35 cm/min of the moving barrier (corresponding to 33.5 cm2/min). The film balance experiments were repeated three to five times for each sample and an averaged Π-A isotherm was then calculated for further analysis. As was revealed previously, the “two-dimensional” gel-point of cohesive particulate layers significantly depends on the hydrophobicity of the primary particles at water-air interfaces.25 Both the experimental results and computer simulations indicated that the higher the particle hydrophobicity (which determines the particle-particle adhesion) the higher the gel point.25 The “two-dimensional” gel point of a system in the above experiments was defined as a surface area at which contiguous layer formation occurred. As a first approximation, the contact cross sectional area (A*) was considered as a gel point in those experiments.18-19,25 A* can be determined from the Π-A isotherms fitting a straight line to the steepest, nearly linear (solidstate) part of the isotherm (also see the headgroup area for insoluble monomolecular films). The intersection of the fitted line and the X axes provides A* (also see Figure 1). In the present work the A* values are determined in order to assess the hydrophobicity of particles. If particles form a cohesive layer at the water-air interface, which happens for hydrophobic particles, the value of A* refers to particle hydrophobicity.18,19,25 The greater the value of A*, the higher the hydrophobicity of particles. It should be noted that hydrophobicity dependence of A* is entirely analogous to the adhesion dependence of sedimentation volume.19 According to former theoretical and experimental investigations,22 some parameters which can be determined from the isotherms can reflect quantitatively the hydrophobic character of particles. In certain cases, e.g., the product of surface pressure at collapse (Πc, also see Figure 1) and the surface area for a (25) Ho´rvo¨lgyi, Z.; Fendler, J. H.; Ma´te´, M.; Zrı´nyi, M. Prog. Colloid Polym. Sci. 1996, 102, 126.
Surface-Modified Silica Nanoparticles
Langmuir, Vol. 17, No. 9, 2001 2685
Figure 1. The Π-A isotherms of the larger silica particles (217 nm average diameter) at different hydrophobicities: (a) S200/1, (b) S200/2, (c) S200/3, (d) S200/4; A*, contact cross sectional area; Πc, surface pressure at collapse; Ac, the total surface area at collapse. particle at collapse (Ac′) can relate to the contact angle (Θ) as
ΠcAc′ ) γr2π(1 ( cos Θ)2
(1)
where γ is the surface tension of the subphase (72 mN m-1 for water), r is the radius of spherical particles, and π is the Ludolph number (3.14). Θ refers to advancing contact angles if particles move into the liquid phase during the collapse (-) and it refers to receding contact angles in the opposite case (+). It should be noted that the direction of particle removal can be controlled by visual observations even in the case of nanoparticles. The collapse manifests itself in whitish folds in the case of (very) hydrophobic particles demonstrating that particles come to the air.
Ac′ ) Ac/N
(2)
where Ac is the collapse area for all particles (also see Figure 1) and N is the number of particles in the film balance. N was calculated as
N ) m/(dV)
(3)
where m is the mass of the spread particles in the film balance, d is the particle density (2.06 × 103 kg m-3),26 and V is the volume of a silica sphere. We calculated the contact angles from the isotherms and compared their values with the silylation conditions. The receding contact angles were determined by an extrapolation method which was suggested in our previous work.27 Brewster Angle Microscopy (BAM). A laboratory-built Brewster angle microscope28,29 was used to obtain in situ information about the long-range structure of silica particulate layer formed at the water surface in a film balance. Illumination was provided by a plane-polarized He-Ne laser (Melles Griot, λ ) 632.8 nm, 17 mW) used in p-polarized mode at ≈53° angle of incidence, which is the Brewster angle for the water-air interface. The beam reflected from the nanolayer was detected by a black and white CCD video camera which was coupled to a computer via an Adobe digitizing card for image processing. The videomicroscope was supplied with an objective lens having a 2.5-fold magnification. The images were taken at zero surface pressure after spreading. Atomic Force Microscopy (AFM). For the AFM investigations the silica particulate layer was transferred onto a mica support by the Langmuir-Blodgett technique.28 A mica plate was dipped perpendicularly into the water prior to spreading the particles. At a few mN m-1 below the collapse pressure, the mica plate was (26) Kabai-Faix, M. Magy. Kem. Foly. 1996, 102 (1), 33. (27) Ma´te´, M.; Fendler, J. H.; Ramsden, J. J.; Szalma, J.; Ho´rvo¨lgyi, Z. Langmuir 1998, 14, 6501. (28) Fendler, J. H.; Meldrum, F. C. Adv. Mater. 1995, 7, 607. (29) Meunier, J.; Henon, S. Prog. Colloid Polym. Sci. 1991, 84, 194.
Figure 2. TEM image of sample S100. carefully pulled out at a constant linear velocity of a few mm min-1. The silica films were dried at room temperature. A Nanoscope III Multimode atomic force microscope (Digital Instruments, Santa Barbara, CA) was used in tapping mode to characterize the distribution and morphology of the differently treated SiO2 spheres. Cantilevers (Digital Instruments) produced for tapping mode in air with a spring constant of 50 N/m and estimated tip diameter of 10 nm were used in the measurements. Imaging in contact mode AFM measurements was unsuccessful due to the weak adhesion of the particles: as a consequence of the relatively high lateral component of the applied imaging force, the tip has swept away the small silica spheres even at the smallest possible forces.
Results and Discussion Particle Sizes (TEM Analysis). A typical TEM image of sample S100 (unmodified) particles is shown in Figure 2. As can be seen, the particles are spherical and the polydispersity is small. The mean diameters (number average) and standard deviations of silica particles taken at different stages of preparation are given in Table 1. The S200/1 particles are roughly twice as big as the S100/1 particles. The larger particles are more monodisperse than the smaller ones according to the criterion of coefficient of variation. Stability of Organosols (DLS Measurements). The hydrodynamic diameters of particles (or clusters) are also given in Table 1. From the closeness of these values to the TEM results, we infer that there is little aggregation: the values of hydrodynamic diameters only exceed the individual particle diameters determined by TEM analysis by 10-30%, which is close to the error limit of measurements. Therefore, neither medium exchange nor surface modification cause destabilization of the silica sols. It should be noted that in some cases slight sedimentation of particles is observed after silylation, but the sediment can be easily redispersed by ultrasonication. According to the light scattering investigations, the silica particles in the used liquids do not aggregate and settle during a time period of 30 min after ultrasonication. Characterization of Particle Hydrophobicities (Film Balance Investigations). The averaged Π-A isotherms for samples S200/1, S200/2, S200/3, and S200/4 (for the larger particles) are shown in Figure 1 and the A* values in Table 2. As expected, the higher the concentration of silylating agent during the surface modifications, the higher the A* values (i.e., hydrophobicities) are. During the collapse, whitish folds were observed for samples S200/1 and S200/2, also indicating that these particles are indeed rather hydrophobic. Receding contact angles calculated from the isotherms of
2686
Langmuir, Vol. 17, No. 9, 2001
Tolnai et al.
Table 1. Mean Diameters (Number Average) and Standard Deviations of Surface Modified and Unmodified (Spherical) Silica Particles Dispersed in Different Liquid Phases Obtained by TEMa no. av of particle diameters determined by TEM analysis (nm)
particle samples
214 ( 18b 215 ( 20c 217 ( 19b 97 ( 17b 99 ( 18c 104 ( 18b
S200 (unmodified) S200/1 (modified) S100 (unmodified) S100/1 (modified) a
hydrodynamic diameters of particles obtained by DLS (nm) in ethanol or in ethanol-chloroform in acetonitrile mixture (vol. 1:2) 242 (0.2)b 282 (0.1)c 231 (0.2)b 126 (0.01)b 135 (0.1)c 117 (0.2)b
190 (0.1) 240 (0.2) 180 (1) 105 (0.5)
The polydispersity of samples is shown in parentheses. b Obtained in ethanol. c Obtained in acetonitrile.
Table 2. Contact Cross Sectional Area Values (A*) and Contact Angles of the Investigated Systemsa A* (cm2)b S200/1
202.6
S200/2 S200/3 S200/4
138.5 120.5 97.4
S100/1
-
contact angles 93° (receding) ΘY ≈ 108° 89° (receding) 70° (advancing) ΘY ≈ 55° 96° (receding) ΘY ≈ 111°
a Θ , the Young contact angle (in a state of equilibrium), was Y derived supposing a contact angle hysteresis of 30°. b The percentile standard deviation is about 3%.
these samples are given in Table 2. The values of the extrapolated receding contact angles also reveal considerable hydrophobicity for these particles, and as expected, the hydrophobicity is more significant for S200/1. According to the A* values, the particles of sample S200/4 are the less hydrophobic among the investigated silica particles. The calculated advancing contact angle for this sample can be seen in Table 2. Supposing a contact angle hysteresis (H) of ca. 30° (which is the difference of the maximum advancing and the minimum receding contact angles), the hydrophobicity range of prepared surfaces in terms of Young contact angles |ΘY| (in a state of equilibrium) can be 55°-110° (if we approximate ΘY as [ΘA - H/2] or [ΘR + H/2]). The calculation for the particles of sample S200/3 leads to a false result. The determined (advancing) contact angle is greater than 90°. It means that these particles should come to air, which is in contradiction with the observation: no whitish folds were seen during the collapse. This is not in contradiction, however, with our earlier assertion19,30 that contact angles cannot be calculated for medium hydrophobic particles from Π-A isotherms by the usual way. A certain amount of such particles, as was emphasized earlier,19,30 can come to air; therefore eq 1 is not suitable for the contact angle determinations. In any case, the present results unambiguously show that samples can be assorted in order of decreasing hydrophobicity as S200/1, S200/2, S200/3, and S200/4 and hydrophobicities can be controlled in a wide range of water contact angles. Indirect Information about the Nanoparticle Hydrophobicities: Qualitative Analysis of BAM and AFM Images. Typical BAM images are shown in Figure 3. The pictures were taken before compression (at zero surface pressure). The whitish domains refer to the silica particles. These images give qualitative information about the dispersability of particles. As can be seen, the silica particles form domains (“two-dimensional” aggregates) in every case; i.e., they exist in a “condensed” phase. The
mean domain size, however, highly depends on the particle hydrophobicities. The higher the hydrophobicity of particles, the larger the size of domains formed as a result of spreading. Not surprisingly, the dispersability of particles is changing inversely with the particle hydrophobicities at water-air interfaces,31 due to the attractive, hydrophobic interparticle forces. Typical AFM images are shown in Figure 4. These photographs give qualitative information about the com-
(30) Ho´rvo¨lgyi, Z.; Ma´te´, M.; Da´niel, A.; Szalma, J. Colloids Surf. A 1999, 156, 501.
(31) Ma´te´, M.; Zrı´nyi, M.; Ho´rvo¨lgyi, Z. Colloids Surf., A 1996, 108, 147.
Figure 3. BAM images of samples S200/2 (a), S200/3 (b), and S200/4 (c) at zero surface pressure after spreading. The width of the pictures corresponds to ca. 550 µm. Sample S200/1 gave images very similar to S200/2.
Surface-Modified Silica Nanoparticles
Langmuir, Vol. 17, No. 9, 2001 2687
Figure 4. AFM images of samples S200/2 (a), S200/3 (b), and S200/4 (c). The layers were transferred onto mica support at a few mN m-1 below the collapse pressure. Images of sample S200/1 are very similar to those of S200/2.
pressibility of layers. As expected, there are some holes in the compressed film, especially for sample S200/2, indicating that the moving barrier cannot compress the particles to a well-packed layer due to the strong particleparticle adhesion, i.e., the considerable particle hydrophobicity. This finding is in a good agreement with the results of gel-point and contact angle determinations. Conclusions The controlled silanization of Sto¨ber silica particles was demonstrated in this work. The efficacy of silylation was characterized by particle hydrophobicities. It was shown that the particles could be prepared in a broad hydrophobicity range silylating them with different amounts of trimethylsilyl N,N-dimethylcarbamate. Further advan-
tage of the silylating agent used in this work is that effective silanization can be achieved under relatively mild circumstances. Considering the results of film balance, Brewster angle, and atomic force microscopy investigations, the prepared particles can be proposed as model materials for the study of “two-dimensional” colloid sability, which has an important role, e.g., in the fabrication of advanced materials.28 Acknowledgment. This work was supported by the Hungarian National Scientific Foundation for Research (OTKA T023080 and FKFP 0532/2000 to Z.H.) and by Grant AKP 98-952,4/22 to E.K. LA0007372
