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Studying the scission of rodlike micelles under mechanical forces is essential for understanding their stability and behavior in industrial applications. Mechanical stress can fragment these micelles, impacting performance. Investigating this process reveals how micelle length, flexibility, and external forces interact, guiding formulation optimization. This insight is crucial for enhancing the efficiency and control of micellar systems in processes where mechanical forces shape their dynamic response and functionality. Despite its scientific and technological significance, direct experimental observation of flow-induced micellar scission using scattering techniques has yet to be reported. We use small angle neutron scattering (SANS) to investigate the shear response of aqueous solutions of cetyltrimethylammonium bromide (CTAB) surfactants in the presence of sodium nitrate, a well-studied rodlike micellar system. Prior to the scattering experiment, pilot rheological assessments demonstrate a shear thinning behavior with no shear banding occurring within the probed range of shear rates. This absence of shear banding ensures a uniform flow field with a constant velocity gradient, establishing a reliable basis for quantitatively interpreting the scattering data. As the steady shear rate increases, the two-dimensional small angle scattering spectra from the flow-velocity gradient plane exhibit progressive angular distortion. Analyzing the spectral anisotropy with a spherical harmonic decomposition method allows us to both characterize flow-induced scission and micelle orientation distribution function providing deeper insights into micellar conformations under shear. Our approach to scattering spectral analysis consists of two critical steps, each characterized by varying levels of mathematical complexity. First, we employ a model-independent strategy rooted in spectral eigendecomposition within the framework of spherical harmonic expansion. This unbiased method reveals a decreasing trend in micellar length. Subsequently, we quantify this trend through regression analysis of the isotropic component of the angularly anisotropic scattering intensities, quantitatively characterizing the evolution of the length distribution function and the mean length as the shear rate increases. Simultaneously, the alignment of flowing rodlike micelles observed to progressively increase, is quantified by the orientational distribution function reconstructed from the anisotropic components. These findings provide pivotal experimental evidence of flow-induced alignment and scission in rodlike micelles and introduce an innovative framework for understanding the interplay between micellar thermodynamics and shear-induced phenomena. Leveraging the capability of SANS, this work advances the fundamental understanding of self-assembly systems and supports applications in colloidal materials, nanomaterials, and soft colloidal systems, where mechanical forces govern complex behavior.
Citation
Journal of Colloid and Interface Science
Pub Type
Journals
Keywords
Micellar Solutions, Small Angle Neutron Scattering, Real Spherical Harmonic Expansion
Huang, G.
, Murphy, R.
, Porcar, L.
, Tung, C.
, Do, C.
and Chen, W.
(2025),
Scattering Insights into Shear-Induced Scission of Rodlike Micelles, Journal of Colloid and Interface Science
(Accessed February 11, 2025)