Examination of the flow behaviour of HEC and hmHEC solutions using structure-property relationships and rheo-optical methods

• Published in: Colloid and polymer science Vol. 282; no. 4; pp. 373 - 380
• Main Authors: LASCHET, Marc, PLOG, Jan Philip, CLASEN, Christian, KULICKE, Werner-Michael
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.02.2004; Springer Nature B.V
• Subjects: Applied sciences; Cellulose and derivatives; Colloids; Exact sciences and technology; Natural polymers; Physicochemistry of polymers; Polymers; Relaxation time; Shear viscosity; Viscosity; Shear thickening; Shear flow; Experimental study; Lateral group; Associative thickeners; Rheo-optics; Solution structure; Flow birefringence; Concentration effect; Structure-property relationships; Specific viscosity; Hydrophobic group; Aqueous solution; Flow curve; Cellulose ether; Cellulose(hydroxyethyl)
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s00396-003-0949-3

The effect of solely intermolecular interactions due to hydrophobic alkyl substituents on the flow behaviour of hmHEC solutions was determined via comparison of the structure-property relationships of hmHECs and HECs based on the overlap parameter c[η]. For this purpose the η^sub 0^-[η]-c relationship for HEC was determined to be η^sub 0^=8.91·10^sup -4^+8.91·10^sup -4^·c[η]+1.07·10^sup -3^(c[η])^sup 2^+1.83·10^sup -7^(c[η])^sup 5.56^. In addition the structure-property relationship for the longest relaxation time via the λ-[η]-c relationship λ·c^sup 1+1/a^=2.65·10^sup -8^(c[η])^sup 2^+4.25·10^sup -8^(c[η])^sup 3^+5.44·10^sup -12^(c[η])^sup 5.27^ has been determined. Although the hmHECs had a higher zero shear viscosity than HECs of comparable overlap parameters at a range of 1<c[η]<13, the flow curves could be described via the same λ-[η]-c relationship in that range, indicating a timescale of the intermolecular interactions below the longest relaxation time. The behaviour of the supramolecular structures in solution with an applied shear field was characterized by rheo-optical analysis of the shear thickening behaviour which occurs with addition of surfactant. Contrary to expectations, a slope >1 of the flow birefringence [delta]n' as a function of shear rate could be observed in double logarithmic plotting. The degree of orientation of the flow birefringence Φ primarily decreases with increasing shear rate, but increases later on at a characteristic shear rate. These two exceptional phenomena can be explained by a pronounced anisotropy of the polymer coils caused by the dilatant flow. This assumption is backed up by the occurrence of a maximum in the dichroism curves which is caused by a finite stability of the aggregated structures in solution. On a molecular basis, these observations agree with the theoretically predicted (Witten and Cohen) transition from intra- to intermolecular polymer micelles. The detected aggregates correspond with the polymer chains that are aligned in one micelle.[PUBLICATION ABSTRACT]