Effects of shear on miscible polymer blends: in situ fluorescence studies

• Published in: Macromolecules Vol. 24; no. 19; pp. 5451 - 5458
• Main Authors: Mani, S, Malone, M. F, Winter, Henning H, Halary, J. L, Monnerie, L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.09.1991
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Thermal and thermodynamic properties; Temperature; Investigation method; Property composition relationship; Phase diagram; Shear flow; Methyl vinyl ether polymer; Styrene polymer; Critical temperature; Experimental study; Mixture; Fluorescence spectrometry
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma00019a036

The effects of shear flow on the phase behavior of a miscible blend of polystyrene with poly(vinyl methyl ether) near the lower critical solution temperature have been investigated by fluorescence measurements. For this purpose approx 1% of the polystyrene chains in the blend were labeled with anthracene and the fluorescence quenching was used as an indicator of miscibility. The modification of a Rheometrics RMS-800 rheometer for in situ fluorescence measurements along with simultaneous shear and normal stress studies under well-controlled temperature and deformation conditions is described. Following equilibration in the miscible state approx 25K below the coexistence temperature, slow heating to temperatures in the two-phase region shows that shearing at a constant rate increases the coexistence temperature. The elevation above the quiescent spinodal temperature is related to shear rate as Delta T/T sub s = (0.015 plus/minus 0.002) gamma exp 0.59 plus/minus 0.04 and this relation is independent of composition in the range of 20-60% (w/w) polystyrene, within the experimental error. Isothermal experiments in the two-phase region also show shear-induced mixing. The in situ fluorescence measurements provide a sensitive indicator of phase transitions that cannot be unambiguously identified by the measured shear stress and first normal stress difference alone. Graphs. 27 ref.--AA