Study On The Rheological Behaviour Of SIS Block Copolymers

The special micro-phase separation structure of SIS block copolymers will have an important impact on their rheological behaviour.Since polymer melts generally violate the assumption of no wall slip,the study of the rheological behaviour of SIS takes wall slip as an entry point to characterise the component distribution at the restricted interface and to analyse the different rheological properties of the two components of the SIS bulk,in order to derive the wall slip mechanism applicable to the block copolymer and to provide theoretical guidance for practical processing.In this paper,three SISs(SIS-S15,SIS-S29 and SIS-S45)with different PS contents were selected for the study of the SIS confined interface composition,wall slip mechanism analysis and non-Newtonian index using surface analysis testing and rheological methods.TEM,AFM,CA and XPS surface analysis tests were used to characterise the distribution of the PS and PI phases at the confined interface of the SIS melt.The results show that the PS and PI phases are miscible in the SIS melt near the confined metal interface and that the distribution of the two phases is gradually disordered with increasing heat treatment time.The results indicate that both components(PS and PI)are present at the confined interface of the SIS melt.Based on the characterisation of the SIS melt with the presence of both phase components at the confined interface,dynamic rheology and capillary rheology studies of the SIS were carried out and the unique wall slip behaviour of the SIS was found to be mainly related to the PS phase state,while the capillary interface state was changed to carry out the analysis and the wall slip mechanism of the SIS was proposed.With the viscous transition temperature(Tf)as the cut-off point,the adsorption force at the SIS interface competes with the cohesion force in the bulk,and at T < Tf,at low shear rates,the PS phase makes strong entanglement points in the system and does not make adsorption points on the wall,the entanglement force is greater than the adsorption force,and wall slip is generated and gradually increases;at high shear rates,the PS phase is disrupted,the activity capacity increases and makes adsorption points on the wall,the adsorption force is greater than the entanglement force,the degree of wall slip gradually decreases and the wall slip velocity decreases.At T > Tf,the SIS melt is in a viscous flow state and at different shear rates,both the PS and PI phases in the SIS act as adsorption points on the wall,with the adsorption force greater than the entanglement force,and the degree of wall slip is small.In quantifying the SIS wall slip behaviour,it was found that some of the wall slip velocities contain an important rheological parameter,the non-Newtonian index n,in the formulae,so the way n is found and the calculation results have a significant impact on the rheological properties of the studied material.Different fitting methods were used to obtain the SIS non-Newtonian index and the accuracy of n was determined by deviation analysis.The results show that,due to the different responses of the two SIS relative temperatures and shear rates,in order to improve the accuracy of n,the SIS needs to be fitted to different temperature intervals for different rate ranges according to the characteristics of the flow curve development,including segmented primary fitting,segmented secondary fitting and overall secondary fitting.The study also found the effect of n values obtained from different fitting methods on the viscoelasticity of SIS.