Ruri Hidema

Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows

An experimental study has been performed to investigate the relationship between the extensional viscosity of polymers and the turbulent drag reduction. In order to obtain the flow which is mostly dominated by extensional flow, two-dimensional (2D) grid turbulence made by flowing soap films was used. Extensional rate added to the flow was controlled by changing the conformation of the grid. Polyethylene oxide, as a flexible polymer, and hydroxypropyl cellulose, as a rigid rod-like polymer were added to the flow. Several extensional rates affect polymer behaviors, which induce different effects. Drag reduction effects of polymers under several extensional rates were visualized and analyzed by image processing. Rheological properties of the polymer solutions were also measured by a rheometer. The results indicated that the mechanisms of energy transfer are different in the streamwise and normal directions. The critical concentration to observe drag reduction effects in 2D turbulence was changed by the extensional rate. When extensional rate is higher, the effects were started to observe from lower concentration. These results were confirmed to correspond to the drag reduction effects obtained by classical pressure drop experiments in a pipe flow.

Bulge structure in a cavity swept by a viscoelastic fluid

In order to study a bulge structure observed in a cavity swept by a viscoelastic fluid, flow visualization experiments have been performed. The cavity depth, the cavity length and the width of flow path were fixed while the water Reynolds number based on the narrow flow path was changed from 680 to 4,200. From the results, the bulge structure formed on the upstream backward-facing side wall of the cavity in the mid-range of the Reynolds number was found to lead a fresh fluid into a cavity and to sweep the fluid near the cavity bottom wall. The bulge structure fluctuates very slowly and this fluctuation induces a tonguing motion of the tip of the separation bubble formed in the downstream region of the cavity. Thus, this structure can be expected to enhance the heat transfer from the cavity bottom.

Photo-responsible gel actuator developed with scanning microscopic light scattering

Sensitive deformation of polymer gel actuator induced by various stimuli has been intensively investigated. The utilization of light however will significantly broaden their applications. Here we show that photo-responsive gels prepared from rigid poly(amide acid) chains having azobenzene moieties in main chains can undergo a macroscopic deformation induced by photo-isomerization. A rod-shape gel can sharply and swiftly bend by blue laser irradiation and reversibly straighten when exposed to visible light. By using a scanning microscopic light scattering, the optimal preparing condition of the gels was determined and the reversible change in mesh-size between 2.1 nm and 0.83 nm was observed.

Contraction behaviors of Vorticella sp. stalk investigated using high-speed video camera. II: Viscosity effect of several types of polymer additives

The contraction process of living Vorticella sp. in polymer solutions with various viscosities has been investigated by image processing using a high-speed video camera. The viscosity of the external fluid ranges from 1 to 5mPa·s for different polymer additives such as hydroxypropyl cellulose, polyethylene oxide, and Ficoll. The temporal change in the contraction length of Vorticella sp. in various macromolecular solutions is fitted well by a stretched exponential function based on the nucleation and growth model. The maximum speed of the contractile process monotonically decreases with an increase in the external viscosity, in accordance with power law behavior. The index values approximate to 0.5 and this suggests that the viscous energy dissipated by the contraction of Vorticella sp. is constant in a macromolecular environment.

Contraction behaviors of Vorticella sp. stalk investigated using high-speed video camera. I: Nucleation and growth model

The contraction process of living Vorticella sp. has been investigated by image processing using a high-speed video camera. In order to express the temporal change in the stalk length resulting from the contraction, a damped spring model and a nucleation and growth model are applied. A double exponential is deduced from a conventional damped spring model, while a stretched exponential is newly proposed from a nucleation and growth model. The stretched exponential function is more suitable for the curve fitting and suggests a more particular contraction mechanism in which the contraction of the stalk begins near the cell body and spreads downwards along the stalk. The index value of the stretched exponential is evaluated in the range from 1 to 2 in accordance with the model in which the contraction undergoes through nucleation and growth in a one-dimensional space.

Inter-crosslinking network gels having both shape memory and high ductility

Medical treatment for injuries should be easy and quick in many accidents. Plasters or bandages are frequently used to wrap and fix injured parts. If plasters or bandages have additional smart functions, such as cooling, removability and repeatability, they will be much more useful and effective. Here we propose innovative biocompatible materials, that is, nontoxic high-strength shape-memory gels as novel smart medical materials. These smart gels were prepared from two monomers (DMAAm and SA), a polymer (HPC), and an inter-crosslinking agent (Karenz-MOI). In the synthesis of the gels, 1) a shape-memory copolymer network is made from the DMAAm and the SA, and 2) the copolymer and the HPC are crosslinked by the Karenz-MOI. Thus the crosslinking points are connected only between the different polymers. This is our original technique of developing a new network structure of gels, named Inter-Crosslinking Network (ICN). The ICN gels achieve high ductility, going up to 700% strain in tensile tests, while the ICN gels contain about 44% water. Moreover the SA has temperature dependence due to its crystallization properties; thus the ICN gels obtain shape memory properties and are named ICN-SMG. While the Youngs modulus of the ICN-SMG is large below their crystallization temperature and the gels behave like plastic materials, the modulus becomes smaller above the temperature and the gels turn back to their original shape.

Diagnosis at a glance of biological non-Newtonian fluids with Film Interference Flow Imaging (FIFI)

In the human body, full of biological non-Newtonian fluids exist. For example, synovial fluids exist in our joints, which contain full of biopolymers, such as hyaluronan and mucin. It is thought that these polymers play critical roles on the smooth motion of the joint. Indeed, luck of biopolymers in synovial fluid cause joint pain. Here we study the effects of polymer in thin liquid layer by using an original experimental method called Film Interference Flow Imaging (FIFI). A vertically flowing soap film containing polymers is made as two-dimensional flow to observe turbulence. The thickness of water layer is about 4 μm sandwiched between surfactant mono-layers. The interference pattern of the soap film is linearly related to the flow velocity in the water layer through the change in the thickness of the film. Thus the flow velocity is possibly analyzed by the single image analysis of the interference pattern, that is, FIFI. The grid turbulence was made in the flowing soap films containing the long flexible polymer polyethyleneoxide (PEO, Mw=3.5x106), and rigid polymer hydroxypropyl cellulose (HPC, Mw > 1.0 x106). The decaying process of the turbulence is affected by PEO and HPC at several concentrations. The effects of PEO are sharply seen even at low concentrations, while the effects of HPC are gradually occurred at much higher concentration compared to the PEO. It is assumed that such a difference between PEO and HPC is due to the polymer stretching or polymer orientation under turbulence, which is observed and analyzed by FIFI. We believe the FIFI will be applied in the future to examine biological fluids such as synovial fluids quickly and quantitatively.

High-Strength Network Structure of Jungle-Gym Type Polyimide Gels Studied with Scanning Microscopic Light Scattering

Latest high-strength gels overcome brittleness due to the inhomogeneities built in their network structure. However, the inhomogeneities still prevent precise characterization of their network structures by scattering methods. A new concept is to take advantage of the ensemble-averaged structure characterization with scanning microscopic light scattering (SMILS), in order to study the network structure and properties of inhomogeneous high-strength gels nondestructively in wide spatio-temporal ranges. In this study, two kinds of the jungle-gym type polyimide gels that have semi-rigid main-chains or rigid main-chains were synthesized in varying the preparing concentration and studied with SMILS. The optimal concentration of polyimide achieved ten times higher Young modulus than before.

Turbulent Flow Characteristics Controlled by Polymers

An experimental study has been performed in order to investigate the relationship between the extensional viscosity of polymer solution and the turbulent drag reduction. A flexible polymer and a rigid rod-like polymer were added to the two-dimensional turbulent flow that was visualized by the interference pattern of a flowing soap film and analyzed by a single-image analysis. The power spectra of interference images were obtained, which is related to the water layer fluctuations in turbulence. The power spectra show a scaling behavior and the power components give the information of drag reduction. It was suggested that the energy transfer mechanisms are different in streamwise and normal directions. In the normal direction, the energy transfer was prohibited by the orientation of polymers, while the energy transfer in the streamwise direction was prohibited by extensional viscosity of polymers. The extensional viscosities of polymer solutions were measured by calculating pressure losses at an abrupt contraction flow.

Effects of extensional rates on characteristic scales of two-dimensional turbulence in polymer solutions

In order to study the effects of extensional viscosities on turbulent drag reduction, experimental studies using two-dimensional turbulence have been made. Anisotropic structures and variations of energy transfer induced by polymers are considered. Polyethyleneoxide and hydroxypropyl cellulose having different flexibility, which is due to different characteristics of extensional viscosity, are added to 2D turbulence. Variations of the turbulence were visualized by interference patterns of 2D flow, and were analysed by an image processing. The effects of polymers on turbulence in the streamwise and normal directions were also analysed by 2D Fourier transform. In addition, characteristic scales in 2D turbulence were analysed by wavelet transform.