Issue
EPL
Volume 80, Number 5, December 2007
Article Number 58003
Number of page(s) 5
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/80/58003
Published online 31 October 2007
EPL, 80 (2007) 58003
DOI: 10.1209/0295-5075/80/58003

Polymer turbulent drag reduction near the theta point

S. T. Lim1, C. H. Hong1, H. J. Choi1, Pik-Yin Lai2 and C. K. Chan2, 3

1  Department of Polymer Science and Engineering, Inha University - Incheon, 402-751, Korea
2  Department of Physics and Center for Complex Systems, National Central University Chungli, Taiwan 320, ROC
3  Institute of Physics, Academia Sinica - Nankang, Taipei, Taiwan 115, ROC

hjchoi@inha.ac.kr
pylai@phy.ncu.edu.tw
ckchan@gate.sinica.edu.tw

received 30 May 2007; accepted in final form 10 October 2007; published December 2007
published online 31 October 2007

Abstract
Turbulent drag reduction efficiencies (%DR) of aqueous poly (ethylene oxide) solutions at various distances $\tau \equiv (T_{\theta}-T)/T_{\theta }$ away from the theta temperature ($T_{\theta }$) are studied. It is found that only the long-time behavior of %DR of the system is sensitive to $\tau $ in that %DR decays faster for systems closer to the theta-point. Usually, this faster decay is attributed to the faster mechanical molecular degradation (MMD) of polymers in bad solvents produced by turbulence. However, temperature quenches experiments close to $T_{\theta }$ show that the apparent faster decrease in %DR for polymers closer to $T_{\theta }$ is not due to MMD but rather because of the shrinking of the polymer after they have been injected into the turbulent flow. The relative insensitivity of the initial maximum %DR can be understood if $T_{\theta }$ is considered as a function of the flow.

PACS
83.10.Tv - Structural and phase changes.
83.60.Yz - Drag reduction.
83.80.Rs - Polymer solutions.

© Europhysics Letters Association 2007