## Abstract

A novel pressure sensor plate (normal stress sensor (NSS) from RheoSense, Inc.) was adapted to an Advanced Rheometrics Expansion System rheometer in order to measure the radial pressure profile for a standard viscoelastic fluid, a poly(isobutylene) solution, during cone-plate and parallel-plate shearing flows at room temperature. We observed in our previous experimental work that use of the NSS in cone-and-plate shearing flow is suitable for determining the first and second normal stress differences N_{1} and N_{2} of various complex fluids. This is true, in part, because the uniformity of the shear rate at small cone angles ensures the existence of a simple linear relationship between the pressure [i.e., the vertical diagonal component of the total stress tensor (Π^{22})] and the logarithm of the radial position r (Christiansen and coworkers, Magda et al.). However, both normal stress differences can also be calculated from the radial pressure distribution measured in parallel-plate torsional flows. This approach has rarely been attempted, perhaps because of the additional complication that the shear rate value increases linearly with radial position. In this work, three different methods are used to investigate N_{1} and N_{2} as a function of shear rate in steady shear flow. These methods are: (1) pressure distribution cone-plate (PDCP) method, (2) pressure distribution parallel-plate (PDPP) method, and (3) total force cone-plate parallel-plate (TFCPPP) method. Good agreement was obtained between N_{1} and N_{2} values obtained from the PDCP and PDPP methods. However, the measured N_{1} values were 10-15% below the certified values for the standard poly(isobutylene) solution at higher shear rates. The TFCPPP method yielded N_{1} values that were in better agreement with the certified values but gave positive N_{2} values at most shear rates, in striking disagreement with published results for the standard poly(isobutylene) solution.

Original language | English |
---|---|

Pages (from-to) | 191-200 |

Number of pages | 10 |

Journal | Rheologica Acta |

Volume | 48 |

Issue number | 2 |

DOIs | |

State | Published - 2009 |

## Keywords

- Normal stresses
- Rheology
- Viscoelasticity