Rheological Behavior of An Aluminum Nitride Nanoparticle Suspension in Poly(Amic Acid)-NMP System
- PDF / 432,175 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 42 Downloads / 164 Views
Xiaohe Chen', Kenneth Gonsalves', R.S. Rounds 'Department of Chemistry and the Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA; 2 Fluid Dynamics, Inc., I possumitown road, Piscataway, NJ 08854, USA ABSTRACT Preliminary rheological characterizations of aluminum nitride (AIN) nanoparticle suspensions in nonaqueous Newtonian fluid media, NMP and NMP/poly(amic acid) solutions, reveal marked differences in viscoelastic behavior, at relatively low dispersed phase volume fractions. Dynamic mechanical and steady shear measurements provide experimental evidence of the effective interparticle and polymer/particle interactions in a dispersion process of nonoxide nanoparticles for ceramic/polymer nanocomposites. The rheological nature of the nanoparticle suspensions corresponds to interparticle physicochemical interactions that have been previously concluded and discussed. INTRODUCTION The importance of ultrafine particle suspensions in aqueous and nonaqueous media has increased in the past years [1]. Rheological characterizations are frequently applied to these complex fluids not only to define flow properties, but also to probe suspension physical chemistry [2,3,4]. Since system rheology is dependent on the state of aggregation of the dispersed phase, governed by Brownian, van der Waals, London, electrostatic, hydrodynamic and gravitational forces, for example, these measurements provide insight into suspension structure influencing behavior during processing and handling [5,6]. In our previous study, a nanostructured AIN powder (average grain size
1.0E-02 I.OOE-01
1.0E20-0
1.00+022
1.200EO1
ShearRate(1i2)
0
Fig.3. Steady shear viscosity behavior of 30 wt% AIN in NMP at 25 C. The results show a well defined linear viscoelastic region and the progressive disturbance of the internal microstructure with increasing strain amplitude. There appears to be a critical strain of approximately .01, sufficient to disrupt the internal architecture of system components or AIN/NMP aggregates. An order of magnitude difference between G' and G" is observed, showing this dispersion to be highly elastic, forming a continuous internal network microstructure. These results are surprising, since this type of strain dependence generally occurs with systems exhibiting yield stress behavior. To verify the microstructural state, dynamic mechanical measurements as a function of oscillatory frequency with linear viscoelastic strain region are summarized in Figure 5, suggesting the presence of a low frequency plateau modulus. Throughout the frequency spectrum, 0.1G", verifying the interparticle forces within the diluted AIN-NMP system are still active. Rheologyical properties are summarized in Figure 6 and 7, as a function of oscillatory strain and frequency, respectively. As expected, there is a decrease in the complex modulus components and complex viscosity as the concentration of the dispersed phase is reduced. Note, however, that the strain and frequency dependence still shows evidence of significant orderin
Data Loading...
