Particle Growth and Development During the In-Situ Precipitation of Silica in a Polymeric Matrix
- PDF / 2,019,090 Bytes
- 7 Pages / 420.48 x 639 pts Page_size
- 67 Downloads / 182 Views
PARTICLE GROWTH AND DEVELOPMENT DURING THE IN-SITU PRECIPITATION OF SILICA IN A POLYMERIC MATRIX
PING XU, SHUHONG WANG, AND JAMES E. MARK University of Cincinnati, Department of Chemistry and the Polymer Research Center, Cincinnati, OH 45221-0172. ABSTRACT
The hydrolysis of tetraethoxysilane much used in the sol-gel approach to ceramics can be studied in a matrix isolation technique in which the silica thus formed precipitates within a polymeric material. This technique was applied here in the in-situ precipitation of silica particles in an elastomeric matrix of poly(dimethylsiloxane). Transmission electron microscopy and mechanical property measurements were carried out as a function of time over a period of 60 days. The equilibrium amount of silica precipitated was obtained relatively quickly, after approximately one day, but reorganization of the particles continued for several days thereafter. This "aging" process resulted in particles that are better defined and more uniform in size, but their ability to reinforce the elastomeric materials was only marginally increased. Scattering techniques are also being used to obtain additional information on this interesting process. INTRODUCTION
Elastomers in the pure state generally lack useful properties simply because of their relatively low strength. To utilize them in practical applications, it is necessary to add fillers such as carbon black or finely powdered silicas to them in order to improve their mechanical properties. The mixing of typical particulate fillers into a polymer, however, is an energy-intensive process that can cause premature gelation, and it is frequently very difficult to control the structure of the resulting material, particularly the degree of particle dispersion or agglomeration [1-5]. For these reasons a number of studies were carried out to develop an efficient and practical technique for the generation or precipitation of a filler within a polymeric matrix. It has now been demonstrated that networks of poly(dimethylsiloxane) (PDMS) [-Si(CH3)20-]x may be swollen in tetraethoxysilane (TEOS) and the TEOS then hydrolyzed in situ [6-12]. Such a chemical reaction via the "sol-gel" process [13,14] can be used for precipitating the silica filler into previously cross-linked networks of PDMS. The reaction may be described by the equation Si(OC 2H5 )4 + 2H20
Catalyst N
SiO 2 + 4C 2H5 0H
(1)
where water is obviously necesary for the in-situ hydrolysis. Filling PDMS networks using such a novel technique has been very successful in improving their mechanical properties [6-12]. A previous experiment [12] indicated that there might be an "aging" or "digestion" process in the in-situ precipitation of silica, such reorganization making the particles better defined, more uniform in size and less aggregated. Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
446
The present investigation was carried out to provide additional information on this process, particularly by means of electron microscopy, and to compare the mechanical
Data Loading...
