Apparent Breakdown of the Stress-Optic Rule in Rigid-Rod Suspensions: A Stress-Partitioning Interpretation
Abstract
A fundamental problem in the field of anisotropic macromolecular materials concerns how the flow-induced orientational order connects microscopic structure to macroscopic rheological stress and optical anisotropy. This study considered cellulose nanocrystal suspensions as rigid-rod model systems for the purpose of isolating orientational effects from chain stretching. Simultaneous rheo-optical measurements of birefringence, orientation angle, and shear stress were combined with a Fokker-Planck orientation model and stress decomposition. Our results show that, at low values of the Peclet number, birefringence and total stress exhibit proportionality similar to the stress-optic rule. However, the concentration dependence indicates that this proportionality reflects stress partitioning rather than a unique material coefficient. With increasing flow strength, orientational saturation is accompanied by a reduced relative Brownian stress contribution and a corresponding change in the total stress-based relation. Referencing the optical response to an estimated Brownian stress contribution yields a substantially more unified response across concentrations and flow conditions, supporting a stress-partitioning interpretation of apparent stress-optic rule breakdown.
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BibTeX
@misc{worby2026apparent,
title = {{Apparent Breakdown of the Stress-Optic Rule in Rigid-Rod Suspensions: A Stress-Partitioning Interpretation}},
author = {William Kai Alexander Worby and Yuto Yokoyama and Misa Kawaguchi and Yoshiyuki Tagawa},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23080},
eprint = {2609.23080},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23080},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Apparent Breakdown of the Stress-Optic Rule in Rigid-Rod Suspensions: A Stress-Partitioning Interpretation
AU - William Kai Alexander Worby
AU - Yuto Yokoyama
AU - Misa Kawaguchi
AU - Yoshiyuki Tagawa
PY - 2026
DA - 2026/09/19
PB - arXiv
DO - 10.48550/arxiv.2609.23080
UR - https://arxiv.org/abs/2609.23080
AB - A fundamental problem in the field of anisotropic macromolecular materials concerns how the flow-induced orientational order connects microscopic structure to macroscopic rheological stress and optical anisotropy. This study considered cellulose nanocrystal suspensions as rigid-rod model systems for the purpose of isolating orientational effects from chain stretching. Simultaneous rheo-optical measurements of birefringence, orientation angle, and shear stress were combined with a Fokker-Planck orientation model and stress decomposition. Our results show that, at low values of the Peclet number, birefringence and total stress exhibit proportionality similar to the stress-optic rule. However, the concentration dependence indicates that this proportionality reflects stress partitioning rather than a unique material coefficient. With increasing flow strength, orientational saturation is accompanied by a reduced relative Brownian stress contribution and a corresponding change in the total stress-based relation. Referencing the optical response to an estimated Brownian stress contribution yields a substantially more unified response across concentrations and flow conditions, supporting a stress-partitioning interpretation of apparent stress-optic rule breakdown.
ER -