Enhanced Mechanical Damping in Electrospun Polymer Fibers with Liquid Cores: Applications to Sound Damping

Abstract

Multicompartmental “core–sheath” fibers composed of a poly­(caprolactone) (PCL) polymer sheath and poly­(ethylene glycol) (PEG) fluids as the core materials were designed via coaxial electrospinning. Mechanical stretching of the fibers caused a discontinuous mechanical damping or stiffening behavior when the cores were composed of a PEG fluid as a known non-Newtonian shear thickening fluid (PEG and SiO2 particles). Surprisingly, it is found that shear thickening fluids are not a requirement for mechanical damping as is evidenced by similar behavior with Newtonian viscous PEG liquids. Data from optical microscopy, thermogravimetric analysis, dynamic mechanical analysis, and rheology have been employed to gain insights into the interactions between the PCL sheath and the PEG cores. The degree of mechanical damping was found to correlate with the viscosity of the core PEGs and is discussed in terms of the interactions between the core and sheath during mechanical oscillation. In addition, the nonwoven fiber mats were tested for auditory sound attenuation (e.g., white noise, pink noise, frequency steps, and chirps). The fiber mats effectively attenuate sound, especially in the low-frequency regions where their ability to dissipate energy is most prevalent. It is also clear that the degree of sound attenuation is dependent upon the core liquid viscosity. To the best of our knowledge, the results presented here are the first report of mechanical damping behavior in electrospun core–sheath fibers that employ liquid cores to attenuate auditory sound.

Electrospinning Ethanol–Water Solutions of Poly(Acrylic Acid): Nonlinear Viscosity Variations and Dynamic Taylor Cone Behavior

“…[6,7] The diversity of properties is greatly expanded by incorporating functional liquids that are not spinnable on their own to make multifunctional composite fibers, [8][9][10][11][12][13][14][15][16][17][18] using coaxial electrospinning [19][20][21][22] or in situ phase separation. [23][24][25] Exhibiting manifold properties and significant tunability, these fibers are attractive to apply across many areas, for example, in sensing, [12,15,[26][27][28][29] sound damping, [30] dynamic patterning, [31] thermal insulation via phase-change materials, [32,33] self-healing coatings, [34] or drug release. [35][36][37][38][39] However, success in spinning multifunctional composite fibers requires careful optimization of the polymer solvent with respect to the functional additive: otherwise, phenomena such as phase separation and gelation can disrupt the electrospinning process.…”

Quantitative volatile organic compound sensing with liquid crystal core fibers

“…The LC is often incorporated as a distinct core already at the spinneret level 35 using a coaxial spinning geometry, 36 but it may also be dissolved in the polymer solution, relying on phase separation during solvent evaporation for the appearance of the coaxial geometry. 37 We refer readers interested in the details pertaining to LC-functionalized fiber spinning to the now quite rich body of prior research (see, e.g., 19 , 35 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ).

Figure 1 Concept graphic for quantitative VOC sensing using LC-functionalized electrospun fibers The key components of our horizontal electrospinning setup are shown in (A); MFCS is a pneumatic flow control unit.

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Stable Electrospinning of Core-Functionalized Coaxial Fibers Enabled by the Minimum-Energy Interface Given by Partial Core–Sheath Miscibility

“… 23 , 28 , 32 , 35 , 36 Using the different variations of core–sheath fiber electrospinning, functional composite fibers have been produced for a variety of application scenarios, such as sustained release of drugs, 11 , 40 , 43 − 52 growth factor, 53 , 54 genes, 54 , 55 or live cells; 56 − 58 enhanced thermal insulation; 17 − 19 sensing of volatile organic compounds; 25 , 29 , 32 , 59 generation of wavy polymer structures; 60 or sound damping. 37 …”

“…The original confusion remains, with different teams publishing conflicting views on the matter, both for core–sheath electrospinning and for the closely related challenge of core–sheath electrospray. Several papers reported on spinning cores and sheaths that are fully miscible, 14 , 15 , 37 , 41 , 43 − 46 , 49 , 53 , 58 , 61 , 62 some emphasizing the importance of low interfacial tension, γ cs , between the two liquids. 15 , 63 Others have maintained that cores and sheaths should be immiscible, 16 − 18 , 30 , 42 , 55 , 64 − 66 often referring to the original Li and Xia work, which even showed evidence of loss of core–sheath structure when miscible fluids were spun.…”