It is known that large DNA molecules exhibit a conformational change between the coil and globule states with the addition of polyethylene glycol (PEG). We investigate the coil-globule transition of T4DNA by making use of the response of the molecule to a well-defined elongational flow field, where the response was monitored by the flow-induced birefringence. The flow-induced birefringence (Δn) increases with strain rate in elongational flow field -for the solutions of low PEG concentration indicating that the DNA molecule is in an expanded coil state. There are no Δn response at high PEG concentration solutions where the DNA molecule is in a well developed globule state. The dependence of Δn on PEG concentration accords with the PEG concentration dependence of DNA size which were directly measured by fluorescence micrograph method. Comparison of the flow birefringence and the fluorescence micrograph suggested that the globule of DNA molecule near the coil-globule transition point is soft and deformed by the elongational flow field though the well developed globule is rigid and in undeformed state. It is concluded that the elongational flow technique can be a useful method to investigate the coil-globule transition of large DNA molecules.
The additions of small amounts of polymer, of which the affinity is not very strong for the particles surfaces, cause flocculation of suspensions. The size effects on the rheological properties are examined for suspensions in which the adsorption-desorption of polymer reversibly takes place by Brownian motion. The suspensions of small particles in solution of polymer with high molecular weights are flocculated by reversible bridging. Since the polymer bridges connecting particles are constantly forming, breaking, and re-forming in a quiescent state, the flow is Newtonian at low shear rates. In high shear-fields, the flow becomes shear-thinning due to desorption of polymer coils by hydrodynamic forces. When the particles are bridged by relatively large coils with high molecular weights, the suspensions show shear-thickening flow at high shear rates. On the other hand, the suspensions of large particles in solution of polymer with low molecular weights are flocculated by depletion. The suspensions are shear-thinning in a wide range of shear rates. The depletion attractions are generated by osmotic pressure and the particles can easily rotate around each other. Because of shear motion of particles in the flocs, the suspensions flocculated by depletion are viscous fluids without elasticity. The rheological properties are discussed in relation to the interaction energy and the vector nature of particle-particle bond.
A new method to measure viscoelasticity of liquids through the surface loading analysis was proposed, and performance of a rheometer based on the method was shown. An impedance head which could detect force applied on itself and its acceleration was employed, so that apparent mass could be estimated as transfer function. A small slide glass plate was suspended from a tip of the impedance head as a measuring part, and the other tip of the device was attached to a vibrator. The mechanical impedance of liquids was estimated from difference between the transfer functions when the plate immersed in the liquids and those in the air. Then, the storage and loss moduli were converted from the mechanical impedance as functions of frequency, ω, in the range of 102 to 104 rads-1. Viscosities of pure viscous liquids from 0.1 to 20 poise and also a unique viscoelasticity of an aqueous detergent system were measured rather correctly in the frequency range.
Syndiotactic polystyrene (SPS) was polymerized by a Cp* TiCl3 (Pentamethyl cyclopentadienyl titanium trichloride)/MAO (Methylaluminoxane) catalyst system, and its rheological properties in the melt state were compared with commercial atactic polystyrene (APS) in view of the tacticity effect. The rheological properties of SPS/APS blends were also investigated. The storage and loss modulus of SPS/APS blends decreased with an increasing of APS contents in the terminal region at the same temperature and frequency. To compare rheological properties of APS with those of SPS and SPS/APS blends in the fully-melted state, the shift factor, aT, of APS was estimated in the high temperature range (>Tm of SPS) by using the Arrhenius-like equation. The shift factor of SPS/APS blends decreased by increasing APS contents at 285°C and 300°C. The reason is that the sydiotactic chains have slower relaxation times due to their rotational hindrance and also more have interaction with each other. In the LogG′ vs. LogG″ plot, SPS containing samples had slopes smaller than 2 and this trend was vivid in SPS. Thus one can say that even though this system is chemically homogeneous, it is inhomogeneous in tacticity. Further work on molecular dynamics remains untouched.
The strain dependence of dynamic viscoelastic properties was measured for an electro-rheological (ER) suspension with cation exchange resin particles. The relation between the fundamental component of stress amplitude and the strain amplitude which could be applied to the ER suspension was calculated using the amplitude of the fundamental component of torque response (T1), and the storage modulus (G1′) and loss tangent (tan δ1) obtained by Markovitz method. The ER suspension showed a yield process with three steps under various electric field strengths. The measured three yield strains were almost independent of the electric field strength. The yield behavior of the ER suspension was discussed based on an induced dipole-dipole interaction model.
his paper describes the study on wall slip in a conduit for molten polymers in order to improve the efficiency of color and/or material change-over. The velocity distributions in a rectangular conduit were experimentally measured by means of a flow visualization technique with particle tracer under the various contact surface conditions such as material characteristics and roughness on the surface. The slip velocity at a conduit wall was determined by optimal fitting of the velocity distribution calculated from CAE analysis to measured one. The following results were obtained from determined slip velocities; (1) fluoride resin lining is preferable to obtain high wall slip velocity than the case of chromium plating, (2) Smaller irregularities of steel wall gives higher wall slip velocity. Taking into account of the experimentally determined condition for wall and resin temperature, the efficiency of color and/or material change-over in the blow molding machine could be improved.
Shear strain amplitude dependence of dynamic viscoelasticity (G′ and η′) and shear rate dependence of steady flow viscosity (η) of concentrated Escherichia coli culture suspension were studied. G′ showed linear behavior at strain amplitude (γ) less than 0.02 but showed large decrement at γ >0.02. η showed pre-shear dependence at high shear rate. These results suggest change in network structure of microbial flock with increase of strain amplitude and increase of shear rate.