Alexander Ya. Malkin

Russian Academy of Sciences, Moscow

1937 – Present

Chemical Engineer

Fellow, Elected 2019

Alexander Ya. Malkin started his scientific carrier entering the laboratory of polymer rheology of the Institute of Petrochemical Synthesis of the Academy of Sciences as a PhD student in late 1962 under supervising of Professor G. V. Vinogradov. One of his first outstanding accomplishments is the concept of the flow-to-rubbery transition in strong flows of viscoelatic polymeric fluids. First, this was the observation of the spurt effect in the flow of flexible-chain monodisperse polymer melts. It consists in abrupt transition from quasi-Newtonian flow to wall slip at a critical shear stress independent of molecular weight. This effect was understood as a consequence of a relaxation transition to the rubbery state equivalent to the similar phenomenon observed in increasing frequency. For broad MWD, this transition smears along shear rate scale that can be considered as one of the dominant mechanisms of the non-Newtonian flow of polydisperse polymers. Then it was shown that calculation of MWD from a flow curve can be an incorrect problem. Macro-modeling of deformation of flexible chains demonstrated that at high deformation rates, the entanglement knots tighten because chains have not enough time for slipping out. This approach explains a mechanism of rubbery transition by creation of quasistable knots. Second, the systematic study of uniaxial extension has allowed to construct a universal envelope which presents the critical strain (at rupture) as a function of the Weissenberg Number. Then large draw ratios are completely related to reversible rubbery deformations. This understanding of polymer melts behavior in extension is now generally accepted. Latest investigation of uniaxial extension of polymer solutions demonstrated the effect of phase separation at high deformation rates and can be considered as the ground for a new process of mechanotropic spanning. Studies of the rheology of rigid-chain polymer solutions have lead to a discovery of isotropic-to-LC state transition (with V.G. Kulichikhin) which was the first experimental confirmation of the Flory theory.

Malkin’s investigations of multi-component systems developed the understanding of the yielding and for the first time demonstrated time-dependent and thixotropic nature of the yield stress as well as the absence of the limiting Newtonian flow below the yield stress. Malkin become interested in highly concentrated emulsions in the past decade. Several new experimental evidences allowed for constructing general dependencies of the rheological properties on concentration and droplet size. These works cleared up the role of interdroplet interaction in addition to the traditional effect of droplet surface energy. His current field of investigations is related to the problem of heavy oil transportation and search for ways for reducing its costineffective high viscosity. In particular, he tackles this problem through directed emulsification in water.