Multiscale Modeling Approach to Understand Mechanism of Deposit Control by Sulfonate-Based Lubricant Detergents.

Protecting the material surfaces from deposits and insoluble sludge particles extends the engine life and reduces waste. Lubricant detergents in engine oils are essential additive technologies that prevent deposit formation in internal combustion engines. In this study, the effect of sulfonate detergent on deposit formation in a passenger car engine is investigated with experimental and multiscale molecular modeling methods to present a unified approach.

Rod-climbing rheometry revisited.

The rod-climbing or "Weissenberg" effect in which the free surface of a complex fluid climbs a thin rotating rod is a popular and convincing experiment demonstrating the existence of elasticity in polymeric fluids. The interface shape and steady-state climbing height depend on the rotation rate, fluid elasticity (through the presence of normal stresses), surface tension, and inertia. By solving the equations of motion in the low rotation rate limit for a second-order fluid, a mathematical relationship between the interface deflection and the fluid material functions, specifically the first and second normal stress differences, emerges.

Three-dimensional chemical imaging of skin using stimulated Raman scattering microscopy.

Stimulated Raman scattering (SRS) microscopy is used to generate structural and chemical three-dimensional images of native skin. We employed SRS microscopy to investigate the microanatomical features of skin and penetration of topically applied materials. Image depth stacks are collected at distinct wavelengths corresponding to vibrational modes of proteins, lipids, and water in the skin.

Dynamics of hydration water in sugars and peptides solutions.

We analyzed solute and solvent dynamics of sugars and peptides aqueous solutions using extended depolarized light scattering (EDLS) and broadband dielectric spectroscopies (BDS). Spectra measured with both techniques reveal the same mechanism of rotational diffusion of peptides molecules. In the case of sugars, this solute reorientational relaxation can be isolated by EDLS measurements, whereas its contribution to the dielectric spectra is almost negligible.

Permeability of model stratum corneum lipid membrane measured using quartz crystal microbalance.

The stratum corneum (SC) is the outermost layer of the epidermis. Stacked intercellular lipid membranes found in the SC play a crucial role in regulating water transport through the skin. Despite the importance of this role of the SC lipid membranes, only a few studies have presented quantitative methods to measure the permeability of water in SC lipid membranes.

Rheology of viscoelastic mixed surfactant solutions: effect of scission on nonlinear flow and rheochaos.

The linear and nonlinear rheology of viscoelastic mixed anionic-zwitterionic surfactant solutions has been systematically investigated. In the linear viscoelastic regime, these systems display nearly Maxwellian behavior with a unique relaxation time, tau0, and a characteristic elastic plateau modulus, G0. Linear rheological data were used to calculate the repitation and breaking times of the micelles, tau(rep) and tau(b), respectively.

Dynamics of weakly aggregated colloidal particles.

We discuss the behaviour of the dynamics of colloidal particles with a weak attractive interparticle interaction that is induced through the addition of polymer to the solvent. We briefly review the description of their behaviour in terms of the jamming phase diagram, which parametrized the fluid-to-solid transition due to changes in volume fraction, attractive energy or applied stress. We focus on a discussion of ageing of the solid gels formed by these colloid-polymer mixtures.

Universal non-diffusive slow dynamics in aging soft matter.

We use conventional and multispeckle dynamic light scattering to investigate the dynamics of a wide variety of jammed soft materials, including colloidal gels, concentrated emulsions, and concentrated surfactant phases. For all systems, the dynamic structure factor f(q,t) exhibits a two-step decay. The initial decay is due to the thermally activated diffusive motion of the scatterers, as indicated by the q(-2) dependence of the characteristic relaxation time, where q is the scattering vector.