Mechanisms of Asymmetric Membrane Formation in Nonsolvent-Induced Phase Separation

Kim

et al. 2022

Small

Electrospun polymeric piezoelectric fibers have a considerable potential for shape‐adaptive mechanical energy harvesting and self‐powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent‐induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF‐TrFE) fibers with higher surface porosity outperform their smooth‐surfaced counterparts with a higher β phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape‐adaptive energy harvesting and self‐powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self‐powered motion sensing.

\begin{matrix} Δ G_{normalm} = Δ H_{normalm} - T Δ S_{normalm} \end{matrix}

\begin{matrix} Δ G_{normalm} = R T (\begin{array}{l} N_{1} \ln φ_{1} + N_{2} \ln φ_{2} + N_{3} \ln φ_{3} + N_{1} φ_{2} g_{12} (u_{2}) \\ + N_{1} φ_{3} χ_{13} + N_{2} φ_{3} χ_{23} \end{array}) \end{matrix}

\begin{matrix} χ_{13} = - \frac{\ln (1 - φ_{3}) + φ_{3}}{φ_{3}^{2}} \end{matrix}

\begin{matrix} g_{12} (u_{2}) = α + \frac{β}{1 - γ u_{2}} \end{matrix}

\begin{matrix} χ_{23} = V {(δ_{2} - δ_{3})}^{2} / R T<...> \end{matrix}

…”

Section: Resultsmentioning

confidence: 99%

Ambient Humidity‐Induced Phase Separation for Fiber Morphology Engineering toward Piezoelectric Self‐Powered Sensing

Kim

et al. 2022

Small

“…A similar flow trend can be observed at t = 250 in cases (I) and (II) (results are not shown here due to space restriction). Although the solvent's free movement does not change any basic features of the phase separation, it becomes particularly important for the NIPS process where the solvent needs to move across the interface between the polymer solution and the water 7,9,[20][21][22] .…”

Section: Resultsmentioning

confidence: 99%

“…In reality, these parameters vary with the concentration and affect the phase separation to some degree. Indeed, some previous studies showed in simulations that the concentration dependency of L αβ and η could be crucial for the formation of the glassy polymerrich domains 28 and asymmetric polymeric membranes formed in the NIPS process 9,21,22 . It should be emphasized here that both viscous and elastic features of the polymer solution are fundamentally essential for the viscoelastic phase separation; a simple addition of the concentration-dependent parameters into the diffusion or viscous model may not be sufficient to reproduce the frozen and recovering features of the viscoelastic phase separation simultaneously.…”

Section: Discussionmentioning

confidence: 99%

Viscoelastic Phase Separation Model for Ternary Polymer Solutions

Yoshimoto,

Taniguchi

2021

Preprint

When a polymer solution undergoes viscoelastic phase separation, the polymer-rich phase forms a networklike structure even if it is a minor phase. This unique feature is induced by polymer dynamics, which are constrained by the temporal entanglement of polymer chains. The fundamental mechanisms of viscoelastic phase separation have already been elucidated by theory and experiments over the past few decades; however, it is not yet well understood how viscoelastic phase separation occurs in multicomponent polymer solutions. Here, we construct a new viscoelastic phase separation model for ternary polymer solutions that consist of a polymer, solvent, and nonsolvent. Our simulation results reveal that a network-like structure is formed in the ternary bulk system through a phase separation mechanism similar to that observed in binary polymer solutions. A difference in dynamics is also found in that the solvent, whose affinity to the polymer is similar to that to the nonsolvent, moves freely between the polymer-rich and water-rich phases during phase separation. These findings are considered important for understanding the phase separation mechanism of ternary mixtures often used in the manufacturing of polymeric separation membranes.

“…(22) 35,39 . Other approaches to capture dynamics related to glass-transition in systems, particularly with a polymer and solvent, have also been explored in the literature 40,41 . The interested reader is advised to look through the various citations included in this section for additional detail.…”

Section: Mobility Coefficientmentioning

confidence: 99%

Continuum-scale modelling of polymer blends using the Cahn–Hilliard equation: transport and thermodynamics

et al. 2021