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Abstract:
Conducting polymers enable the simultaneous transport of electrons and ions within soft, biocompatible matrices. Yet their synthesis typically relies on soluble oxidants that generate stoichiometric waste and inhibit high-resolution patterning. Nanometer-thick gold films deposited by direct-current magnetron sputtering in dilute air function concurrently as a template and intrinsic oxidant—though, owing to their discontinuous structure, not as current collectors—for the reagent-free growth of emeraldine-salt polyaniline (PANI-ES). X-ray photoelectron spectroscopy reveals that freshly sputtered films contain approximately 60% Au2O3, which is quantitatively reduced by aniline within 60 s. In situ UV–vis spectroscopy records an increase in the 750 nm polaron band that scales linearly with oxide thickness. Polymerization self-terminates once the local Au(III) reservoir is exhausted, yielding patterns precisely registered to the underlying metal mask. The resulting PANI-ES retains the optical, Raman, and electrochemical signatures of the highly conductive emeraldine salt. By replacing soluble oxidants with a solid Au2O3 underlayer, the process avoids sulfate-containing solution-phase by-products and enables aniline-to-PANI conversion at room temperature under ambient air, providing a straightforward route to patterned PANI films without post-growth wet lithography for hole-transport layers, neural microelectrodes, and chemiresistors.

Keywords:
bioelectronics, gold oxide nanofilms, polyaniline, reagent-free oxidant polymerization, site-confined growth

Abstract:
In the present paper, we provide evidence of the vital impact of inertia on the flow in microfluidic networks, which is disclosed by the appearance of nonlinear velocity–pressure coupling. The experiments and numerical analysis of microfluidic junctions within the range of moderate Reynolds number (1 < Re < 250) revealed that inertial effects are of high relevance when Re > 10. Thus, our results estimate the applicability limit of the linear relationship between the flow rate and pressure drop in channels, commonly described by the so-called hydraulic resistance. Herein, we show that neglecting the nonlinear in their nature inertial effects can make such linear resistance-based approximation mistaken for the network operating beyond Re < 10. In the course of our research, we investigated the distribution of flows in connections of three channels in two flow modes. In the splitting mode, the flow from a common channel divides between two outputs, while in the merging mode, streams from two channels join together in a common duct. We tested a wide range of junction geometries characterized by parameters such as: (1) the angle between bifurcating channels (45°, 90°, 135° and 180°); (2) angle of the common channel relative to bifurcating channels (varied within the available range); (3) ratio of lengths of bifurcating channels (up to 8). The research revealed that the inertial effects strongly depend on angles between the channels. Additionally, we observed substantial differences between the distributions of flows in the splitting and merging modes in the same geometries, which reflects the non-reversibility of the motion of an inertial fluid. The promising aspect of our research is that for some combinations of both lengths and angles of the channels, the inertial contributions balance each other in such a way that the equations recover their linear character. In such an optimal configuration, the dependence on Reynolds number can be effectively mitigated.