CBE/ENGR 225 Faculty Seminar: Professor Jacob Israelachvili, Department of Chemical Engineering and Materials, UCSB
Tuesday, November 10, 2015
4:00 pm – 5:00 pm
*coffee & cookies served*
Jacob Israelachvili, Ph.D.
Professor, Department of Chemical Engineering and Materials
University of California, Santa Barbara
Dynamic (Non-Equilibrium, Rate, Time, and History) Dependent
Molecular Interactions in Biological and Bio-colloidal Systems
ABSTRACT: Most theories of surface and inter-particle forces or interactions are equilibrium theories. A few deal with steady-state situations, while others deal with kinetic or ‘dynamic’ aspects, such as the kinetics of aggregation, self-assembly, dissociation, etc. In the ‘steady state’ situation, there is a continuous and constant supply and expenditure of energy, ensuring that the system or ‘state’ under observation does not change with time, but it is not a state at ‘thermodynamic equilibrium’. In the latter, ‘kinetic’ situation, the system is continually changing (i.e., dynamic) and there is a definite starting state and an end state, where the kinetics depends on diffusion rates and/or viscous effects. Such dynamic systems, and more complex ones, occur throughout the colloidal and especially the bio-colloidal domains. With the increasing appreciation of the complexity of colloidal and biological systems – now also referred to ‘complex fluid’ and ‘soft material’ systems – many more types of rate, time, and history-dependent processes, including the interaction potentials themselves, have appeared whose main feature is their non-equilibrium nature. These will be reviewed, especially recent experimental studies of interactions in colloidal, soft material and biological systems. These can involve DLVO (electric double-layer and van der Waals) forces, repulsive hydrophilic (hydration) and attractive hydrophobic forces, Coulombic (electrostatic) and polymer-mediated interactions, non-covalent bio-specific (complementary, ligand-receptor) interactions, as well as deformations and structural changes of bilayer membranes, vesicles and cellular structures undergoing adhesion, coalescence or fusion. It is also useful to distinguish between those time-dependent biological interaction potentials that change monotonically (gradually or continuously) with time (cf. the Bell Theory), and those that change abruptly (discontinuously) – these latter ones are rare (cf. the Butterfly Effect), have no known interaction potential to describe them, but are often those that herald major ‘permanent’ changes, be it at the molecular level or in the conception of a new organism.