Monitoring of macromolecular dynamics during a chemical cross-linking process of hydroxyethylcellulose derivatives by dynamic light scattering

• Two relaxation modes were found for HEC and HMHEC gels.
• The amplitude of the slow mode decreased during gelation.
• The ratio of the amplitudes of the relaxation modes increased after gel threshold.

We report a study where we follow a chemical crosslinking process and record the intensity autocorrelation functions for two polymer systems, hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC), by dynamic light scattering (DLS). Due to the distinct chemical structures, the measured intensity autocorrelation function shows significant difference between the two systems. Two relaxation modes were found for both systems, which were attributed to the cooperative relaxation and the structural relaxation. The decay rate for cooperative diffusion was found to decrease during the gelation for HEC, but it remains constant for HMHEC. The same trend was found for the structural relaxation where the decay rate decreased as a function of the gelation time for HEC, but not for HMHEC. By analyzing the amplitudes of both relaxation modes, we also found that during the gelation the structural relaxation was suppressed, which was caused by the decrease of the elastic modulus.

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