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Probing nanostructure and rheology of complex fluids in complex flow histories using small angle scattering


Industrial processing of soft materials involves a wide range of processing histories that change the material’s nanostructure and, therefore, the properties of the final product. Determining the connection between processing, structure and properties represents a grand challenge that, if met, would enable the design of better processes for producing materials or the production of novel materials aided by flow-induced phenomena. Toward this aim, the primary focus of this dissertation is the development of new experimental methodologies for more comprehensive determination of the relationships between processing and structure.

In situ small angle scattering (SAS) represents an attractive technique for the measurement of complex fluid nanostructure under flow. However, SAS methodology is currently limited in terms of interpretation of the SAS measurements to infer structural details of the measured fluid and in terms of measurement sample environments that probe a wide variety of processing histories. With respect to structural inference from SAS measurements, this dissertation explores the problem of suspensions of dilute rigid non-spherical particles, where the fluid structure can be completely described by the orientation probability distribution function (i.e., the probability that a particle is oriented in some direction). For this case, a novel inference method, MAPSI, was developed that enables the model-free extraction of structural details from SAS measurements of these dilute particle systems. With respect to measurement sample environments for SAS, a new measurement methodology, FFoRM-SAS, was developed whereby the complex flow histories that soft materials experience can be manipulated and measured, in contrast with previous SAS sample environments that produce a limited range of flow histories. Within the FFoRM-SAS framework, studies probing the effect of different non-Newtonian responses yielded novel insight into the accessible flow regimes of elastic and viscoelastic fluids.

Utilizing the novel techniques toward application, studies probing the flow-induced SAS from model rodlike particle dispersions were employed to determine the effectiveness of micromechanical theories for predicting the flow-induced structure of such dispersions and the effect of interparticle interactions on their flow-induced structure. New analyses of flow-SAS measurements enable the extraction of structural details to intraparticle alignment and interparticle correlations. The flow-induced structural transitions uncovered in this work may be exploited for dynamically controlling fluid properties with flow.

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