Both the electrical conductivity and tailored mechanical characteristics—showing flexibility and structural integrity—are key properties of polymer composites. In this work, a novel, simple, and water-based strategy for synthesizing rGO-MWCNT/polymer composites was developed. Namely, carbon nanofillers in a mixture of reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) were incorporated in a waterborne methacrylic polymer matrix at loadings of 0.25, 0.5, and 1.0 wt.% nanofiller, and with rGO-to-MWCNT ratios of 10:1, 1:1, and 1:10 (w/w) at room temperature. Electrically conductive composites were obtained with all tested filler rates showing the highest conductivity (up to 8.2 × 10⁻³ Sm⁻¹) for the MWCNT-rich filler due to the formation of a segregated network of the filler in the matrix. The mechanical properties of the composites—characterized by their Young’s modulus and elongation at break—strongly depended on both the filler incorporation rate and the rGO:MWCNT ratio. For instance, soft and flexible composites were obtained by incorporating 0.25 wt.% of the MWCNT-rich filler, which increased the elongation at break from 154.2% (neat polymer) to 252.4%. Overall, this study emphasizes the sensitive interplay between carbon filler introduction incorporating conductivity and the fillers’ impact on the mechanical properties of a polymer composite, both necessitating careful optimization for applications, e.g., in flexible electronics.

Water-in-water (w-w) emulsion electrospinning combines organic solvent-free processing, tunable fiber microstructures, and the potential for the encapsulation and subsequent release of sensitive compounds in a single platform. The key challenge is maintaining stable phase-separated structures throughout the electrospinning process while ensuring spinnability. Tackling this challenge, this study explores the boundaries of spinnability of w-w emulsions of poly(ethylene oxide) (PEO) and dextran that are stabilized by cellulose nanocrystals (CNCs) to form w-w Pickering emulsions (PEs). By constructing a phase diagram, the organization and stabilization of PEs at different PEO/dextran ratios (70/30, 50/50, and 30/70), polymer concentrations, and CNC contents (0.1-2 wt%) are systematically investigated. This is followed by the translation of the droplets to fibers, whereby a combined setup of fluorescence and electron microscopy reveals the role of the particle stabilizer in fiber formation, diameter distribution and architecture. Core-shell fibers are obtained from PEO-rich and dextran-rich systems at optimized emulsion compositions (e.g., ≥1 wt% CNC), where the CNCs align with the electric field assisting the fiber core formation, as confirmed by polarized optical microscopy. The optimized PEs are easily electrospun to fiber mats suitable for further characterization by IR spectroscopy, thermogravimetry and calorimetry. Ultimately, this article demonstrates how w-w PEs as fully water-based system can be integrated into a high-end polymer processing technique. The result are multiphasic fibers with high potential for advanced applications ranging from functional foods to biomedicine.