Rheological problems which I encountered in writing “Soft matter physics” are discussed. This includes balloon blowing, sedimentation of sand (in sand-picture) and wetting and drying. Rheology involves many challenging problems which stimulate our imagination in everyday life, and they are useful in teaching scientific thinking for young generation.
Structure and viscoelasticity were fully discussed for hybrid threadlike micelles formed between a cationic surfactant, cetyltrimethyl ammonium bromide, and a random copolymer of styrene and sodium p-styrene sulfonate in aqueous solution and supra-molecular polymers formed by low molar mass compounds such as N,N',N"- tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide in a nonpolar medium due to hydrogen bond formation between amide groups. Moreover, high frequency molecular dynamics, i.e. nano-rheology, of hydrated water molecules and polymer chains dissolved in water such as collagen model polypeptides were also discussed based on the results obtained by extremely high frequency dielectric relaxation measurements up to 50 GHz.
A commercially available drag-reducing additive, LSP-01, was developed in 1995. Since then, LSP-01 has been used at more than 180 sites in building air conditioning systems throughout Japan. The technique was adopted recently for air conditioning systems in skyscraper in the metropolitan area. In this paper, measurement of the velocity for a drag-reducing surfactant solution was carried out with the use of Particle Image Velocimetry (PIV) to provide a better understanding of the drag-reducing flows. The analogy between momentum and heat transfer for a surfactant solution is also discussed.
Diffusion of cyclic and linear polymers at interfaces was studied. Interdiffusion of cyclic polystyrene/cyclic deuterated polystyrene was measured by dynamic secondary ion mass spectroscopy as functions of temperature and molecular weight. Diffusion coefficient of cyclic polystyrene with weight-average molecular weight of 113k is twice as large as that of the corresponding linear one at all the temperatures employed. This result clearly shows that both the linear and cyclic polystyrenes have the same temperature dependence of segmental frictional coefficient. At an iso-free volume condition, diffusion coefficient of cyclic polystyrene is larger than that of the linear one at a given molecular weight. The short-time interdiffusion at an interface of linear polystyrene / linear deuterated polystyrene having different molecular weights was examined by time-resolved neutron reflectivity measurements. The model scattering length density profiles obtained by solving a partial differential equation for the diffusion process were used to analyze the data. The results indicate that even though the molecular weights of both components are larger than the critical molecular weight for entanglement, the initial interfacial broadening of bilayer films with different molecular weight proceeds with asymmetric mobility being inversely proportional to the molecular weight.
In this paper the unsteady helical flow of Giesekus fluid between two concentric cylinders is investigated numerically. The flow is impressed by inner cylinder's rotation and the outer cylinder's sliding or oscillating movement along its axial direction. The effects of Weissenberg number, the mobility parameter of Giesekus model, and frequency of oscillations on velocity field and shear stresses are studied. These results affirm the shear thinning behavior of Giesekus fluid. Also it was found that tangential shear stress at inner cylinder's surface, axial shear stress at outer cylinder's surface, and first normal stress difference decrease by increasing the mobility parameter and the approach of axial velocity or shear stresses to their steady periodic state values is postponed by decreasing the Reynolds number.
The upward motion and deformation of a single large-scale two-dimensional planar gas bubble rising in an otherwise quiescent viscoelastic liquid obeying the Oldroyd-B rheological model is numerically investigated using the weakly-compressible smoothed particle hydrodynamics (WC-SPH) method. It is shown that unlike the incompressible version of this mesh-less method (I-SPH), the WC-SPH method combined with the continuum surface force (CSF) idea for modelling surface tension is well capable of capturing the cusped-shape trailing edge during its rise in viscoelastic liquids. The failure of the I-SPH method for predicting the cusp is attributed to the several stages of weighted arithmetic and harmonic interpolations used for smoothing the transport parameters of the constituents. The WC-SPH code developed in the present work has enabled us to obtain results at high density and viscosity ratios not reported in similar works. The results suggest that WC-SPH is better suited than I-SPH for handling bubble rise problem in viscoelastic liquids even at large density and viscosity ratios typical of underwater explosions.
The linear stability analysis of a pulsed flow in a linear Maxwell fluid confined in the Taylor-Couette system is investigated. Both cylinders are subjected to modulated rotation in phase with equal amplitude and frequency. We show that in the limit of low frequency, the Deborah number has no effect on the stability of the basic state which tends to a stable configuration. The basic state is potentially unstable at an intermediate frequency and it becomes more unstable as Deborah number increases. At high frequency limit, the Deborah number has a strong destabilizing effect. These numerical results are in good agreement with the asymptotic solutions obtained in the limit of high and low frequencies.