Theoretical and experimental study on the coupling effects between viscosity and viscous dissipation in microscale flow of polymer melts

The coupling effects between viscosity and viscous dissipation during the polymer melt micro-molding process, influenced by microscale effects, notably impacted the melt's flow characteristics. The scarcity of theoretical exploration into these coupling effects have hindered the evolution of micro-molding. A mathematical model that coupled viscosity and viscous dissipation through temperature, a shared variable, was built using a novel microscale viscosity model. The study performed calculations and analyses on the variation of rheological parameters within microchannels of varying characteristic dimensions and validated the temperature changes of the melt along the flow direction through experimentation. Results showed that when the coupling effects were considered, the temperature rise of the melt along both the flow direction and the radial direction aligned more closely with experimentally measured values. The average temperature deviations along the flow direction and the radial direction both increase as the characteristic dimension decreased. When the characteristic dimension was 0.25 mm, the average temperature deviations along the flow direction and the radial direction were 45.19 % and 41.08 %, respectively. The influence of the coupling effect on viscosity and viscous dissipation also increased with decreasing characteristic dimension. When the characteristic dimension was 0.25 mm, the maximum deviations between considering and neglecting the coupling effects were 57.03 % and 49.61 %, respectively. These findings confirmed the necessity of considering the coupling effect in polymer melt micro-molding and validated the accuracy of the coupled mathematical model.