DYNAMIC LIGHT-SCATTERING-STUDIES OF THE FRACTAL AGGREGATION OF POLY(METHACRYLIC ACID) AND POLY(ETHYLENE GLYCOL)

The complexation and subsequent aggregation of poly(methacrylic acid) (PMAA) with poly (ethylene glycol) (PEG) were investigated with photon correlation spectroscopy (PCS). The influence on aggregation of hydrophobic pyrene probes covalently attached to the PEG chain ends, denoted PEG, was also studied. The effectiveness of PCS in determining average particle radius, (R), and particle radii distributions in aggregating polymer systems is demonstrated. The effect of pH on (R) and aggregation rate is examined. A critical pH of 1.9 was found, below which the system aggregates more rapidly into larger clusters. Under the proper solution conditions, the time dependence of the particle distributions can be monitored. We found a power law growth of (R) with time for both PMAA-PEG and PMAA-PEG. This type of growth behavior is consistent with a cluster-cluster type model of aggregation. The tagged system showed much more rapid aggregation and larger (R). An aggregation model assuming Smoluchowski kinetics and diffusion-limited, cluster-cluster aggregation was developed. An excellent fit between the model and data was obtained, with the aggregates showing fractal scaling with a fractal dimension of 1.7. © 1990, American Chemical Society. All rights reserved.