Fine liquid-core polymer fibers for microhydraulic applications: A versatile process design

Miniaturization is an essential requirement to advance areas where conventional mechatronic systems may struggle. Microhydraulic devices that combine resilience and compliance could thus revolutionize microrobot applications like locomotion and manipulation. Spurred by the deformability and structural stability provided by veins in insect wings, microscale liquid-core fibers were created, comprising of a polymeric sheath and a liquid core. A microfluidic co-extrusion spinneret was designed, assisted by com-putational fluid dynamics studies, to achieve such unique liquid-core fibers. Hydraulic pressure transfer tests were successfully applied on fine, up to 10 m long, oil-filled polyamide fibers. The results showed a pressure transfer with a fiber length-dependent delay of -20-100 s for fiber lengths of -1-10 m, and a viscoelastic behavior with relaxation times that behave linearly with fiber length. These findings enable the development of resilient and deformable microhydraulic systems within restricted available space, predestined for applications in soft robotics. CO 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)

Biphasic fluid oscillator with coaxial injection and upstream mass and momentum transfer

We present model experiments with biphasic flow and computational fluid dynamics (CFD) simulations for concentric co-flow scenarios. A lower viscosity fluid is injected into an outer phase of reduced thickness. Static design modifications of the injection geometry are then studied to allow for self-adjusting upstream transfer of mass and momentum. Such static arrangement gives rise to a simple biphasic fluid oscillator that can produce individual droplets at high rates and high aspect ratios. Frequency analysis and CFD simulations are invoked to shed light on the physics of this dynamically forced jet breakup and to identify relevant control parameters. In addition, we illustrate how a terminal baffle plate at the nozzle can produce a split-up into multiple dripping or jetting threads depending on its relative rotational symmetry with the upstream mass transfer. The here-presented distinctive injection geometry bears potential for simple ways of controlled jet breakup in microfluidics devices, which currently primarily rely on Rayleigh-Taylor breakup or the costly introduction of intricate actuators or compliant elements. Most notably, this oscillatory injector has potential for application in biphasic melt-flow spinnerets to realize advanced fiber core structures during melt-spinning

Mesophase in melt-spun poly(epsilon-caprolactone) filaments: Structure-mechanical property relationship

Fine poly(epsilon-caprolactone) (PCL) filaments (diameter: 59-92 mu m) were successfully melt-spun with modified drawing setups to prevent draw instabilities. Depending on the production parameters, different mechanical properties were obtained (tensile strength: 302-456 MPa, elongation at break: 69-88%). These variations are related to subtle structural differences, which we have analyzed with wide-angle x-ray diffraction (WAXD) and small-angle x-ray scattering (SAXS). SAXS was used to determine crystal widths and the spacing between crystals along the filament axis. Additionally, 2D WAXD patterns were simulated and WAXD profiles were fitted. The detailed 2D WAXD analysis revealed that a highly-oriented non-crystalline mesophase is present in drawn PCL filaments, which is most-likely situated in-between PCL crystals. A large amount of this mesophase (>16%), combined with high crystalline orientation and perfect crystals, led to higher tensile strength values. We also confirmed that PCL chains pack with non-planar chain conformations in the unit cell

Properties, X-ray data and 2D WAXD fitting procedures of melt-spun poly(epsilon-caprolactone)

Rheological and thermal properties of the poly(epsilon-caprolactone) (PCL) polymer are presented in Section 1.1. Section 1.2 summarizes results of melt-spun PCL filaments. Specifically, we show the necking point stabilization during high-speed online drawing in Section 1.2.1, filament morphology in Section 1.2.2, wide-angle X-ray diffraction (WAXD) fitting results in Section 1.2.3, WAXD patterns of aged fibers in Section 1.2.4, crystallinity analysis in Section 1.2.5 and small-angle X-ray scattering (SAXS) analysis results in Section 1.2.6. Details about the materials, experimental and analytical methods are given in Section 2. Of particular interest may be the simulation and fitting procedures of 2D WAXD patterns, which are summarized in Section 2.7.2. For more information see the publication by Selli et al. 'Mesophase in melt-spun poly(epsilon-caprolactone) filaments: structure-mechanical property relationship' [1]. (C) 2020 The Authors. Published by Elsevier Inc

Investigation of crystalline and tensile properties of carbon nanotube-filled polyamide-12 fibers melt-spun by industry-related processes

The paper addresses the influence of carbon nanotubes (CNT) on the structure and mechanical properties of high tensile strength thermoplasticpolymer fibers. Polyamide (PA) fibers with different draw ratios, with and without CNTs as fillers, and having mechanical properties close to industrial standards were spun in a pilot melt spinning plant. The morphology of the fibers was investigated using optical microscopy, nuclear magnetic resonance (NMR) and 2-D wide angle x-ray diffraction (WAXD). Differential scanning calorimetry (DSC) was carried out to get an estimation of the crystallinity. For a concise interpretation of the results of tensile measurements performed on the fibers, a parameter was developed to account for the detrimental influence of polymer extrusion on their mechanical properties. CNTs seem to act as sites for the growth of un-oriented crystalline domains converted from oriented regions, without yielding a mechanical reinforcing effect

Investigation of crystalline and tensile properties of carbon nanotube-filled polyamide-12 fibers melt-spun by industry-related processes

The paper addresses the influence of carbon nanotubes (CNT) on the structure and mechanical properties of high tensile strength thermoplasticpolymer fibers. Polyamide (PA) fibers with different draw ratios, with and without CNTs as fillers, and having mechanical properties close to industrial standards were spun in a pilot melt spinning plant. The morphology of the fibers was investigated using optical microscopy, nuclear magnetic resonance (NMR) and 2-D wide angle x-ray diffraction (WAXD). Differential scanning calorimetry (DSC) was carried out to get an estimation of the crystallinity. For a concise interpretation of the results of tensile measurements performed on the fibers, a parameter was developed to account for the detrimental influence of polymer extrusion on their mechanical properties. CNTs seem to act as sites for the growth of un-oriented crystalline domains converted from oriented regions, without yielding a mechanical reinforcing effect