Ruckenstein conducts both theoretical and experimental research that not only has increased scientists' understanding of the fundamental phenomena of chemical processes, but has led to the development of enhanced research methods and new materials.
His initial interests were in transport phenomena, and two of his more important contributions have been “A generalized penetration theory” and “Scaling and physical models in transport phenomena.” In the first, he developed a new similarity transformation on the basis of which numerous unsolved transport equations could be solved, such as mass transfer in wave motion and mass transfer under pulsating flows. In the second, he showed how numerous complex problems could be solved by coupling simple solutions valid in extreme cases. An example is the “Heat transfer under combined forced and free convection.” He also suggested a physical model for turbulence near a wall, which he applied to a solid surface and to boiling heat transfer; he developed a theory of thixotropy, theories for foams, a unitary theory of phoretic motions, theories for electrokinetic phenomena involving osmosis and anomalous osmosis, and he extended the simple approach of Prandtl for Newtonian fluids to viscoelastic fluids.
After arriving in the U.S. his research diversified widely, encompassing the areas of catalysis, colloids, phase transformations, thermodynamics, and materials. In catalysis he pioneered the areas of stability of supported metal catalysts and catalytic combustion, and he suggested solid solution catalysts for CO₂ reforming of CH₄. He developed also a theory for the mechanism of oxidation by mixed oxides, proposed a kinetics for the selectivity of the catalytic processes and was the first to use quantum mechanics in the interpretation of catalytic reactions.
In the area of colloids and interfaces, he has introduced the concept of interaction force boundary layer in the examination of the deposition of particles on surfaces, he performed simulations to understand the collective behavior of a large number of charged colloidal particles, and he developed a theory for hydration forces, theories for specific ion effects, for steric repulsion, and for bridging forces. He has shown that hydration and double layer forces should be coupled in an unitary treatment and he changed the traditional treatment of double layers. He developed a thermodynamics of surfactant aggregation and a new kind of thermodynamics for microemulsions, lamellar liquid crystals, and phospholipids monolayers. He was concerned with the phospholipid bilayer and examined the interactions between them. He developed theories for wetting and for the stability of both Newtonian and non-Newtonian thin films.
In the area of molecular thermodynamics, he developed theories for the solubility of gases and pharmaceutics in binary and multi-component solvents and for the solubility of proteins. He developed also theories for salting in and out, and for the local composition in liquid mixtures.
In the area of kinetics of phase transformation he developed theories for nucleation for unary and binary mixtures, free of macroscopic thermodynamic concepts, based on a first passage time. He also developed unitary theories for nucleation and growth.
In the areas of polymers and materials, he suggested and implemented numerous technological approaches to prepare composites, conductive polymers, membranes for separation processes, polymers with unusual properties, pastes with high thermal conductivity, and more recently, materials for H₂ storage.
In addition to his election to the National Academy of Arts and Sciences in 2012, receiving the National Academy of Engineering Founders Award in 2004, and the 1998 National Medal of Science, Ruckenstein has been honored by the American Institute of Chemical Engineers with its most prestigious awards: the Founders Award in 2002 for outstanding contributions to the field of chemical engineering; the Alpha Chi Sigma Award in 1977 for excellence in chemical engineering research; and the Walker Award for excellence in contributions to chemical-engineering literature in 1988. He received the 1986 Kendall Award of the American Chemical Society for creative theories and experiments in colloid and surface science and, in 1994, the society's Langmuir Lecture Award. In 1996, he was awarded the American Chemical Society's E.V. Murphree Award in Industrial and Engineering Chemistry. He received the Senior Humboldt Award of the Alexander von Humboldt Foundation in West Germany in 1985 for his work related to detergents, and the Creativity Award from the National Science Foundation for his work on protein separation. The Hauptman-Woodward Medical Research Institute honored him in 2003 with inclusion in their Pioneers of Science Award. In 1990, he became a member of the National Academy of Engineering.