Showing papers by "Jun-Ting Xu published in 2020"

Simultaneous Improvement of Ionic Conductivity and Mechanical Strength in Block Copolymer Electrolytes with Double Conductive Nanophases

Abstract: The most daunting challenge of solid polymer electrolytes (SPEs) is the development of materials with simultaneously high ionic conductivity and mechanical strength. Herein, SPEs of lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI)-doped poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs) with both blocks associating with Li+ ions are prepared. It is found that the PPMTC-b-PEO/LiTFSI electrolytes with double conductive phases exhibit much higher ionic conductivity (2 × 10-4 S cm-1 at r.t.) than the BCP electrolytes with a single conductive phase. Concurrently, the storage moduli of PPMTCn -b-PEO44 /LiTFSI electrolytes are ≈1-4 orders of magnitude higher than that of the neat PEO/LiTFSI electrolytes. Therefore, simultaneous improvement of ionic conductivity and mechanical properties is achieved by construction of a microphase-separated and disordered structure with double conductive phases.

Polar crystalline phases of PVDF induced by interaction with functionalized boron nitride nanosheets

Abstract: Due to their unique structure and excellent physical properties, boron nitride nanosheets (BNNSs) are often used as nano-reinforcing fillers for polymeric composites In this work, hydroxyl-modified boron nitride nanosheets (OH-BNNSs) and amino-functionalized boron nitride nanosheets (NH2-BNNSs) were blended with poly(vinylidene fluoride) (PVDF) via a solution casting method to form PVDF/OH-BNNS and PVDF/NH2-BNNS nanocomposites Differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) show that the addition of OH-BNNSs has little influence on the crystal structure of PVDF, and non-polar α-crystals are mainly formed in the PVDF/OH-BNNS nanocomposites, whereas the incorporation of a small amount of NH2-BNNSs can cause exclusive formation of polar β- and γ-phases X-ray photoelectron spectroscopy (XPS) and FTIR reveal that there exists a stronger interaction between PVDF and NH2-BNNSs than that between PVDF and OH-BNNSs in both solid and melt states, which is responsible for the transformation of the crystalline phase and the accelerated crystallization of PVDF/NH2-BNNS nanocomposites

Mechanistic Study of the Influence of Salt Species on the Lower Disorder-to-Order Transition Behavior of Poly(ethylene oxide)-b-Poly(ionic liquid)/Salt Hybrids

Abstract: Recently, lower disorder-to-order transition (LDOT) phase behavior was observed in the poly(ionic liquid) (PIL)-containing block copolymers, poly(ethylene oxide)-b-poly(1-((2-acryloyloxy) ethyl)-3-...

Observation of Double Gyroid and Hexagonally Perforated Lamellar Phases in ABCBA Pentablock Terpolymers

Abstract: Three symmetric linear pentablock terpolymers, poly(tert-butyl acrylate-b-styrene-b-ethylene oxide-b-styrene-b-tert-butyl acrylate) (TzSyOxSyTz), with similar lengths of PS (S) and PtBA (T) blocks ...

Hierarchical Structures with Double Lower Disorder-to-Order Transition and Closed-Loop Phase Behaviors in Charged Block Copolymers Bearing Long Alkyl Side Groups

Abstract: In this work, poly(ionic liquid) (PIL)-containing block copolymers (BCPs), poly(ethylene oxide)-b-poly(1-((2-acryloyloxy)ethyl)-3-docosylimidazolium) with different counterions (PEO-b-P(AOEDIm-X), ...

Self-Assembly of Linear Amphiphilic Pentablock Terpolymer PAAx-PS48-PEO46-PS48-PAAxin Dilute Aqueous Solution.

Abstract: A series of linear amphiphilic pentablock terpolymer PAAx-b-PS48-b-PEO46-b-PS48-b-PAAx (AxS48O46S48Ax) with various lengths x of the PAA block (x = 15, 40, 60, and 90) were synthesized via a two-step atom transfer radical polymerization (ATRP) using Br-poly(ethylene oxide)-Br (Br-PEO46-Br) as the macroinitiator, styrene (St) as the first monomer, and tert-butyl acrylate (tBA) as the second monomer, followed with the hydrolysis of PtBA blocks. The AxS48O46S48Ax pentablock terpolymers formed micelles in dilute aqueous solution, of which the morphologies were dependent on the length x of the PAA block. Cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and zeta potential measurement were employed to investigate the morphologies, chain structures, size, and size distribution of the obtained micelles. The morphology of AxS48O46S48Ax micelles changed from spherical vesicles with ordered porous membranes to long double nanotubes, then to long nanotubes with inner modulated nanotubes or short nanotubes, and finally, to spherical micelles or large compound vesicles with spherical micelles inside when x increased from 15 to 90. The hydrophobic PS blocks formed the walls of vesicles and nanotubes as well as the core of spherical micelles. The hydrophilic PEO and PAA block chains were located on the surfaces of vesicle membranes, nanotubes, and spherical micelles. The PAA block chains were partially ionized, leading to the negative zeta potential of AxS48O46S48Ax micelles in dilute aqueous solutions.

Unexpected crystalline memory effect in poly(L-lactide)-based block copolymers

Abstract: The crystalline memory effect is frequently observed in polymer crystallization, but the melt structure remains unresolved. In this work, the preserved spherulites in the melt of poly(L-lactide)-based block copolymers are observed by polarized optical microscopy (POM) unexpectedly. These spherulites are not erased instantly on reaching the melting temperatures, but it takes tens of minutes at a designed melting temperature to completely erase the spherulites. These preserved spherulites in the melt, where some crystalline traces are lost but the Maltese cross appearance is still obvious, are possibly attributed to the long range of molecular orientation enhanced by microphase separation between two blocks. Moreover, these preserved spherulites have a significant effect on the subsequent crystallization, i.e. a faster radius growth rate and denser nucleation. This study highlights that a thermodynamically unstable structure can be fully preserved in a supercooled melt for a long time, which has never been reported elsewhere.