(418c) Locally Triggered Nanoparticle Aggregation by Interfacial Colloidal Destabilization

A classic indispensible technique to study transport and flow involves injecting small-molecule tracers into a fluid stream. But unexpected challenges emerge when this method is adapted to investigate colloidal nanomaterials (i.e., nanofluids) because the delicate balance among physiochemical interactions governing suspension stability is easily disrupted by these additives. Failure to consider these effects can lead to conflicting and erroneous interpretations about the observed phenomena. Here we introduce a microfluidic probe that enables these interactions to be examined by locally imposing steep chemical gradients in a laminar flow, mimicking the environment created during tracer injection. Unexpectedly, we find that localized aggregation can be readily triggered in low concentration (< 1 vol%) Al₂O₃ nanoparticle suspensions that would otherwise appear to be highly stable based on conventional bulk characterization. In addition to providing a new straightforward method to assess suspension stability, interfacial colloidal destabilization can also be exploited to deposit uniform lines of dense nanoparticle aggregates along the interface between co-flowing streams, potentially laying the foundation for a robust non-lithographic method to precisely pattern particulate-based nanomaterials on surfaces.