摘要:

Copolymers and stirring are commonly used to produce fine dispersions of immiscible homopolymers. Recent experiments call into question the classical view that copolymers promote the mixing by reducing the interfacial tension, suggesting rather that copolymers induce repulsive interactions between droplets and thus inhibit collision‐induced coalescence events. We present a dynamical theory of the breakup and coalescence of polymer droplets in a mixing shear flow, including hydrodynamic and repulsive interactions between droplets. We find that a low surface coverage of copolymers, of the order of one chain per square radius of gyration, is sufficient to inhibit collisions between submicron‐sized droplets, while giving a negligible reduction in interfacial tension.

ISSN:0148-6055    

DOI:10.1122/1.550731

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

The rheology of a series of long‐chain randomly branched polybutadienes (PBDs) has been investigated. Branched samples were made through a hydrosilation reaction between a small difunctional crosslinker and the 1,2 groups distributed on the backbone of near‐monodisperse PBD (Mw=56 000, 137 000; Mw/Mn=1.04). The resulting samples have both dispersity in molecular weight and architecture. The species distribution has been studied using size exclusion chromatography and has been found to agree with the Flory–Stockmayer distribution for the random branching of monodisperse chains. Sinusoidal oscillation and creep/creep recovery experiments were done to determine dynamic moduli, zero shear viscosity, and equilibrium creep compliance. The observation that branching is random allows structural parameters to be calculated such as weight fractions and average molecular weights of free chains, arms, and interior chains. These parameters are used in existing rheology models whose results are compared to experimental observation. In particular, qualitative agreement is found for η0as a function of branching content by applying the model proposed by McLeish and O’Connor [Polymer34, 2998–3003 (1993)] for star/linear blends.

ISSN:0148-6055    

DOI:10.1122/1.550732

出版商:The Society of Rheology    

年代:1996

数据来源: AIP

摘要:

Complex isochoric flows in a domain of space that is long compared to its width are studied for a viscoplastic and perfectly rigid Herschel–Bulkley model. It is argued here that no continuous yield surface can exist along the flow direction in these either confined or open channel flows. A similarity analysis is performed that shows that normal stresses cannot be neglected. For open channel flows the influence of normal stresses can be estimated through comparison of the yield stress value to the hydrostatic pressure value at the channel bed. Generalized Barré de Saint Venant one‐dimensional equations are obtained. The influence of the yield stress value on wave velocity and on gradually varied flows and critical depth has been deduced.

ISSN:0148-6055    

DOI:10.1122/1.550794

出版商:The Society of Rheology    

年代:1996

数据来源: AIP