The aim of this research was to prepare pH sensor films based on litmus using the sol–gel method with tetraethoxysilane (TEOS) and phenyltrimethoxysilane (PTMS) as precursors. The pH sensor film was then applied to millireactors to evaluate its performance on the intricate geometries of static mixers commonly found in millireactor designs. Millireactors were made from Formlabs High Temp resin using stereolithography (SLA) and from Anycubic Basic resin using digital light processing (DLP) technology. The performance of the pH sensor films was evaluated by tracking color changes in the pH sensor films and analyzing RGB (red, green, blue) and hue values through a smartphone application. The experiment involved mixing solutions with different pH values at varying flow rates within the millireactor channels. Furthermore, along with analyzing the hue values, characterization techniques involved measuring contact angles with water and diiodomethane. A film combining a litmus indicator with titanium dioxide (TiO₂) displayed a color change within one minute and maintained this color throughout the study, confirming its reusability. Sensor films exhibited excellent reversibility (RSD = 2.4–3.3%) and stability. The findings demonstrate that the pH-sensitive films perform robustly across varying geometries, paving the way for their integration into advanced millireactor systems with static mixers and continuous chemical monitoring within Industry 4.0.

This study presents the development and characterization of copper microparticle‐filled cyclic olefin copolymer (COC) composites as functional filaments for fused filament fabrication. Filaments containing up to 20 wt% copper were produced via melt extrusion, maintaining consistent diameter and surface quality, demonstrating excellent processability. Thermal analysis showed negligible impact of copper on COC's glass transition temperature and only a marginal change in decomposition onset (≈459°C), while remaining over 100°C higher than polylactide/copper analogues. Melt flow rate increased with copper content, enabling high‐load extrusion without plasticizers or compatibilizers. Mechanical testing showed that at 20 wt% copper, tensile strength increased by 15% and Young's modulus by 7% relative to pure COC, while elongation at break was largely preserved, achieving a rare combination of stiffness and ductility in metal‐filled thermoplastics. Scanning electron microscopy revealed uniform dispersion of spherical copper microparticles (≤ 63 μm). Despite copper's high density (8.96 g/cm ³ ) relative to COC (1.02 g/cm ³ ), the composites remain lighter than metals, offering a favorable compromise between weight and enhanced performance. The synergy between COC's thermal stability, processability, and copper's functional contribution establishes a platform for mechanically robust and thermally stable filaments suitable for electronic housings, sensor enclosures, and biomedical devices.

Sol–gel-based optical functional sensor coatings were developed for real-time monitoring of multiphase saponification reactions in microreactors. Various pH-sensitive indicator mixtures, including bromocresol green and bromocresol purple (BCG and BCP) and methyl red–methyl orange, were incorporated into sol–gel coatings and evaluated on test plates across pH range of 2–12. Coatings with BCG and BCP 1:3 demonstrated the most pronounced color change at high pH (11–12), with distinct hue (H) transitions providing a reliable measure of local pH. These optimized coatings were integrated into microreactor channels to track the passage of oil and NaOH slugs under varying flow rates. Hue analysis produced reproducible plateaus corresponding to NaOH-rich (H = 50°) and oil-rich (H = 41°) phases, enabling droplet-level resolution of slug flow and detection of flow-regime transitions. The sensor response was fully reversible, highlighting the robustness and reusability of the coatings. Unlike previous high-resolution fluorescence-based systems, this approach relies on simple visible-light imaging and low-cost data extraction, leaving the reaction chemistry unaltered. The results demonstrate that sol–gel coatings coupled with hue-based analysis provide a practical, noninvasive, and real-time monitoring strategy for multiphase reactions in microreactors, with potential for implementation in industrial or IoT-enabled process control systems.