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Abstract:The frictional drag in turbulent flow can be drastically reduced by the addition of minute amounts of suitable linear flexible high-molecular-weight polymers, and the various physical characteristics of the polymers used are known to be closely related to the drag reduction efficiency. This feature article briefly reviews polymer additives and factors in the system affecting turbulent drag reduction in external flow, more specifically in a rotating disk flow.

The conformational transition of Form II → Form I of Poly‐L‐proline and the intermolecular aggregation of the product Form I during and after the transition in the HOAc‐propanol mixture solvent were studied, the ratio of HOAc:propanol being changed as 1:9, 1:6, and 1:4 v/v. For the study, the viscosity, light scattering, and dynamic light scattering of the system were measured. The experimental results exhibit that the concentration of Form II promotes the end‐to‐end type aggregation during and after the transition Form II → I. The extent of the aggregation is reduced in the order of the ratios of HOAc/propanol 1:9, 1:6, and 1:4 v/v. The end‐to‐end type aggregation is also reduced at higher temperatures. It was also observed that the end‐to‐end type aggregation occurs abruptly and strongly after the transition of Form II → I occurred to some extent. The point of the abrupt occurrence depends on the solvents and temperature. The light scattering and translational diffusion‐coefficient measurements showed also similar phenomena. It was also observed that the side‐by‐side type aggregation occurs when the initial concentration of Form II of poly‐L‐proline is relatively small, and the transition temperature is relatively high (35 and 45°C). All the above mentioned experimental results are explained by a simple principle described in the text.

SynopsisThe non-Newtonian intrinsic viscosities [ q ] of poly(y-methyl L-glutamate) were measured in the helix-coil transition region under various conditions in this work. The helix content [H. which represents the degree of conformational transition, was obtained by using a polarimeter. Our experimental results show that the non-Newtonian behavior of the polypeptide is markedly affected by its conformation; i.e., the nowNewtonian eFfect becomes larger as fH increases.The effect of external pressure AP on 111 was studied carefully; [ T i ] increases with [H when aP < 1.5 psi, but it decreases when AP > 1.5 psi and f,, > 0.8. The reason for thls result is considered i n the text.