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In this paper, the crystallization behavior of a novel poly(monothiocarbonate), poly(trimethylene monothiocarbonate) (PTMMTC), was investigated and compared with its polycarbonate analogue, poly(trimethylene carbonate) (PTMC). It is found that PTMMTC exhibits strong crystallizability, while unstretched PTMC is amorphous. DSC and DMA results reveal that PTMMTC possesses higher glass transition temperature (Tg) and β-transition temperature (Tβ) than PTMC. Simulation based on density functional theory (DFT) shows that, the bond angle of C-S-C is evidently smaller than that of C-O-C, and thus a larger dipole moment. This leads to the stronger intermolecular interaction and more rigid chain conformation in PTMMTC, which is the origin of sulfur-substitution enhanced crystallization. The crystal structure of PTMMTC was preliminarily determined for the first time. PTMMTC has an orthorhombic crystal structure with a planar zig-zag chain conformation. The parameters of unit cell are a = 10.74 A, b = 4.79 A, and c (fiber axis) = 7.74 A.

Recently, interest in lithium–sulfur batteries has surged due to rapid advances in energy-intensive electric devices. However, despite the high theoretical capacity, natural abundance, and environm...

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), ...

Recent advances in the synthesis of block copolymers have enabled the creation of smart and functional designer polymers possessing specific intermolecular interactions. The long-range nature of these interactions strongly affects the molecular packings and microstructures of such polymers, which are intimately related to their properties. In addition to various applications, their unique physicochemical properties, distinguished from conventional block copolymers, are attracting significant attention from polymer and materials scientists. In this review, we describe the current understanding of the structure-property relationship of block copolymers having long-range interactions and suggest possible directions of technological development. We particularly focus on how specific interactions, such as Coulombic, π-π stacking, hydrogen-bonding, and metal/ion-dipole interactions, affect the molecular arrangements of block copolymers on the nanometer and molecular scales. Such information could lead to block copolymers with more advanced functions for future nanotechnologies.

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-...

Advances in lithium battery technologies necessitate improved energy densities, long cycle lives, fast charging, safe operation, and environmentally friendly components. This study concerns lithium-organic batteries comprising bioinspired poly(4-vinyl catechol) (P4VC) cathode materials and single-ion conducting polymer nanoparticle electrolytes. The controlled synthesis of P4VC results in a two-step redox reaction with voltage plateaus at around 3.1 and 3.5 V, as well as a high initial specific capacity of 352 mAh g-1 . The use of single-ion nanoparticle electrolytes enables high electrochemical stabilities up to 5.5 V, a high lithium transference number of 0.99, high ionic conductivities, ranging from 0.2×10-3 to 10-3 S cm-1 , and stable storage moduli of >10 MPa at 25-90 °C. Lithium cells can deliver 165 mAh g-1 at 39.7 mA g-1 for 100 cycles and stable specific capacities of >100 mAh g-1 at a high current density of 794 mA g-1 for 500 cycles. As the first successful demonstration of solid-state single-ion polymer electrolytes in environmentally benign and cost-effective lithium-organic batteries, this work establishes a future research avenue for advancing lithium battery technologies.

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.

In the present work, we found that single-walled carbon nanotubes (SWCNTs) could be straightened by poly(9,9-dioctylfluorene) (PFO) chains with both α- and β-conformations in different solvents. UV–vis and PL spectroscopic studies confirm that there exists π-π interaction between SWCNTs and PFO. SWCNTs are helically wrapped by the adsorbed PFO chains, which is different from the coaxial interaction between SWCNTs and poly(3-hexylthiophene) (P3HT). More stretched PFO β-conformers have a stronger interaction with SWCNTs, and the interactions between SWCNTs and PFO slightly improve the conjugation length of β-conformers in turn. We proposed that the straightening of SWCNTs by adsorbed rigid conjugated polymers is irrespective of interaction mode between them.

Aliphatic poly(monothiocarbonate)s synthesized by alternating copolymerization of carbonyl sulfide (COS) and epoxides are a new type of crystalline polymers. In this work, the isothermal crystallization behavior and spherulite morphology of poly(trimethylene monothiocarbonate) (PTMMTC) and poly(ethylene monothiocarbonate) (PEMTC) are studied. PTMMTC tends to form banded spherulites, especially at low crystallization temperatures, while PEMTC forms non-banded spherulites. The overall crystallization rate and spherulitic growth rate of PTMMTC are larger than those of PEMTC at the same degree of supercooling. PTMMTC with longer alkane segment in the main chain has a higher equilibrium melting temperature (Tm0) than PEMTC. Both polymers exhibit double melting peaks, but the formation mechanisms are different for PTMMTC and PEMTC. Small-angle X-ray scattering (SAXS) result reveals that more amorphous phases are located in interlamellae of PTMMTC, leading to a larger long period (L) and a thicker amorphous layers (la), which can account for the stronger tendency of PTMMTC to form banded spherulites. The melting enthalpies of PTMMTC and PETMC crystals with 100% crystallinity (ΔHm0) are obtained by extrapolating the melting enthalpies of the samples with different crystallinities. The free energy of the folding surface (σe) of PTMMTC is larger than that of PETMC, indicating that the PTMMTC chain is stiffer. The higher Tm0 and larger ΔHm0 and σe of PTMMTC can be attributed to its stronger interchain interaction.

Effect of chelating additive on microstructure, hydration products and mechanical property of mortar under different curing conditions was investigated. The microstructure was tested by nuclear magnetic resonance and scanning electron microscope. And the chemical composition of hydration products was analyzed by X-ray diffraction. The compressive strength was measured under different curing conditions at different curing age, including standard curing, water immersion, seawater immersion and salt mist curing. After curing for 28 days in water, compared to control mortar, the reduction ratio of harmful pores whose size larger than 0.1μm in mortar with chelating additive (CA mortar) was 14.6%, followed by 8.9%, 9.2% and 2.9% which was under standard curing, seawater immersion and salt mist curing, respectively. From the scanning electron microscope image, there were more needle-like and bar-like crystals in CA mortar making it more compact, which was mainly calcium silicate hydrate through component analysis. Besides, the raising percentage of compressive strength of CA mortar under water immersion is 28.6% compared to control mortar at the age of 28 days, followed by 26.8%, 21.8% and 16.3% which was under standard curing, seawater immersion and salt mist curing, respectively. The results indicate that chelating additive can enhance compactness and compressive strength of cement-based materials especially under water immersion by promoting the formation of calcium silicate hydrate.

Because long cylindrical crystalline micelles of block copolymers (BCPs) are similar to the fibril structures related to some severe diseases to some extent, study of the disassembly process of crystalline micelles of BCPs may provide some conceptual inspiration to the therapy of these diseases. Herein the effect of amines on the fragmentation of cylindrical crystalline-polyelectrolyte polyethylene-block-poly(acrylic acid) (PE-b-PAA) micelles is investigated. It is found that long crystalline cylindrical micelles (150–400 nm) can be fractured into short stublike ones (20–50 nm) by adding monoamines like diethylamine, triethylamine, and lysine, while addition of diamines such as ethylenediamine and 2,2′-(ethylenedioxy)di(ethylamine) or inorganic base like ammonia and sodium hydroxide has little effect on the morphology of cylindrical PE-b-PAA micelles. Fourier transform infrared (FT-IR) characterization shows that the interaction between PAA and amines is electrostatic attraction. The fragmentation of PE-b...

The closed-loop phase behavior, where a lower disorder-to-order transition (LDOT) takes place first, followed by an upper order-to-disorder transition (UODT) upon heating, is seldom observed in block copolymers (BCPs). In this work, we prepared a model BCP, LiClO4-doped poly(ethylene oxide)-b-poly(tert-butyl acrylate-co-acrylic acid) (PEO-b-P(tBA-co-AA)), in which the hydrogen (H)-bonding between the PEO and AA units and the Coulombic interaction in salt-doped PEO block have opposite effects on the miscibility of BCPs. The relative strength of the H-bonding and Coulombic interaction can be easily tuned by the hydrolysis degree (DH) of the PtBA block and the amount of doped salt. Various phase behaviors are observed by changing relative strength of different forces. Especially, the closed-loop phase behavior can be achieved when H-bonding, Coulombic interaction, and mixing entropy reach a delicate balance.

Lower disorder-to-order transition (LDOT) phase behavior is seldom observed in block copolymers (BCPs). Design of LDOT BCPs is important for broadening the applications and improving the high temperature properties of BCPs. In this work, the LDOT phase behavior was first achieved in the strongly interacting BCPs consisting of poly(ethylene oxide) (PEO) and poly(ionic liquid) (PIL) blocks (EOm-b-(IL-X)n, X: counterion) by introducing two extra strong forces (hydrogen-bonding and Coulombic interaction) with different temperature dependences. It is also found that the LDOT phase behavior of the EOm-b-(IL-X)n BCPs can be regulated by molecular weight (related to mixing entropy), counterion, and salt doping. Increasing counterion size and salt content shifts the disorder-to-order transition temperature (TDOT) to higher temperature, whereas a higher molecular weight leads to a lower TDOT. Based on our findings, some general rules for design of LDOT phase behavior in the strongly interacting BCPs were proposed. ...

A series of liquid crystalline/crystalline block copolymers (BCPs) containing poly(methacrylate) block with liquid crystalline (LC) azobenzene moieties in the side chains (PMMAzo) and crystalline block poly( l -lactide) (PLLA) were prepared. The interplay of microphase separation, crystallization and LC ordering in these BCPs was investigated. It is revealed that microphase separation between two blocks is favorable to the LC ordering, which is attributed to the enhanced local concentration of LC moieties in PMMAzo microdomains. For a similar reason, crystallization of PLLA can intensify microphase separation thus facilitate LC ordering of PMMAzo. PLLA crystallization may also stabilize the LC structure, leading to phase transition temperatures of the BCPs higher than that of PMMAzo homopolymer. On the other hand, the LC ordering can conversely affect crystallization of PLLA. The crystallizability of PLLA is weakened by the chemically linked PMMAzo block. The special PLLA e-crystals, which are usually formed in the presence of organic solvents, are unexpectedly observed under suitable conditions.

Concomitant double crystallization processes widely occur in semicrystalline polymers and their blends because of structural and morphological heterogeneity. In this work, a generalized kinetics model was established for the isothermal crystallization in the presence of concomitant double crystallization processes, based on the Avrami theory for single crystallization process. The different situations of the double crystallization processes, including independent, competitive, and composite types, are considered in the model by introducing the concept of “domains”. This model was applied to crystallization of triblock terpolymer with morphological defects, polymorphic poly(vinylidene fluoride)/nanoclay nanocomposite, isotactic polypropylene with a broad isotacticity distribution, and poly(ethylene terephthalate) ultrathin film. It is found that, besides the information on crystallization kinetics, other information such as morphological defect, nucleation density, cocrystallization, and structure of ultra...

A series of poly(e-caprolactone)- b -poly( n -butyl acrylate)- b -polystyrene (PCL- b -P n BA- b -PS) triblock terpolymers with fixed PCL and P n BA block lengths but different PS block lengths were prepared. In all of these triblock terpolymers the P n BA block can be competitively dissolved in both the PCL and PS phases to form bi-phase structures in the melt, as revealed by atomic force microscopy (AFM). Due to the “competitive dissolution effect” of the P n BA middle block, the microphase separation and crystallization behaviors of these triblock terpolymers are different from those of common diblock copolymers to some extent. As revealed by the Flory-Huggins parameters, more P n BA segments tend to dissolved in the PS phase. Therefore, the volume fraction of the PS-rich phase ( f PS-rich ) is evidently larger than the calculated volume fraction of the PS block ( f PS ), and the phase boundaries between two different structures shift to lower f PS . There also exists a thick interphase layer between the PS-rich and PCL-rich phases due to competitive dissolution of the P n BA block. However, confined crystallization can only occur at a larger f PS-rich , though the measured glass transition temperature ( T g ) is high for the PS block. This can be attributed to a high fraction of the soft zone surrounding the PCL-rich phase and the lower volume fraction of the hard zone.

In the present work, crystallization-driven coassembly of micrometric polymer single crystals and nanometric block copolymer micelles was achieved. The hybrid single crystals are first formed by cocrystallization of polyethylene (PE) homopolymer and polyethylene-b-poly(tert-butyl acrylate) (PE-b-PtBA) block copolymer (BCP) in DMF or DMF/o-xylene mixed solvent. The morphology of the obtained hybrid single crystals can be regulated via changing the solvent composition, crystallization temperature and mass ratio of BCP/homopolymer. Because of the difference in crystallization rate, the distribution of PE-b-PtBA BCP in the hybrid single crystals may be inhomogeneous, leading to a concave gradient surface structure. The hybrid single crystals have a double-layer structure, in which PE homopolymer chains adopt extended conformation and the PE blocks in PE-b-PtBA are probably once-folded. After the PE homopolymer is consumed, cylindrical micelles of PE-b-PtBA can further epitaxially grow on the lateral surface o...

A semicrystalline poly(trimethylene monothiocarbonate) (PTMMTC) has been synthesized via the selective and alternating copolymerization of carbonyl sulfide and oxetane. This reaction was catalyzed by (salen)CrCl accompanied by organic bases over a wide range of temperatures from 40 to 130 °C. PTMMTC is shown to exhibit similar crystallization behavior to high-density polyethylene (HDPE), i.e., being spherulite and possessing melting temperatures (Tm) up to 127.5 °C and a degree of crystallinity (Xc) of up to 71%. Moreover, PTMMTC has a wide processing temperature window of ca. 100 °C.

Hydrogen (H)-bonding interaction was introduced into a poly(ethylene oxide)- b -poly( tert -butyl acrylate) (PEO- b -P t BA) block copolymer (BCP) by partial hydrolysis of t BA units into acrylic acid (AA) ones, in order to compete with the segregation force between the PEO and P t BA blocks. It was found that, as the hydrolysis degree ( D hyd ) of the P t BA block increased, the structure of the PEO- b -P( t BA- co -AA) BCPs underwent the change from hexagonally packed cylindrical (HEX) into body-centered cubic spherical (BCC), then into HEX. The first HEX-to-BCC transition at lower D hyd arose from the enhanced compatibility between the PEO and P( t BA- co -AA) blocks induced by the H-bonding interaction. When a PEO- b -P( t BA- co -AA) BCP with a HEX structure was heated, the BCC-to-HEX order-order transition (OOT), which was opposed to that in the common BCPs with an upper critical ordering temperature (UCOT) phase diagram, could be achieved because the H-bonding interaction was weakened at higher temperature. The second BCC-to-HEX at higher D hyd was interpreted in terms of the enhanced chain rigidity and the chain arrangement approximately parallel to the microdomain interface induced by H-bonding interaction. The variation of the H-bonding interaction with temperature and the conformational change of the PEO block induced by H-bonding interaction were verified with FT-IR.

A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which ...

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.

The double hydrophobic azobenzene-containing diblock copolymers, namely, poly(L-lactide)-b-poly[6-(4-(4-methoxyphenylazo)phenoxy)hexyl methacrylate] (PLLA-b-PMMAZO), were successfully prepared by sequential atom transfer radical polymerization (ATRP) and ring opening polymerization. These block copolymers (BCPs) can self-assemble into various morphologies in aqueous solution via host–guest interaction between the azobenzene (azo) groups and methyl-β-cyclodextrin (β-CD). The complexation equilibrium between azo and β-CD can be shifted by changing the length of the hydrophobic PLLA block, the micelle concentration or the β-CD/azo molar ratio; thus the micellar morphology and the size of the PLLA-b-PMMAZO/β-CD complexes are altered. A vesicle-to-sphere-to-entrapped vesicle transition was observed at β-CD/azo = 1 as the PLLA block length increases. In addition, a large β-CD/azo ratio or higher micelle concentration leads to a vesicle-like morphology, while entrapped vesicles tend to be formed at a smaller β-CD/azo ratio or a lower micelle concentration. It is found that prolongation of the UV irradiation time can also induce a vesicle-to-sphere-to-entrapped vesicle transition of the micellar morphology. Such a transition is reversible upon irradiation of visible light. In summary, the self-assembly behavior of PLLA-b-PMMAZO/β-CD complexes can be readily regulated by different methods. Moreover, the complexation between the azo groups and β-CD is inhomogeneous, which is responsible for the formation of entrapped vesicles and the microphase separation in the core of the spherical micelles and entrapped vesicles.

A series of triblock copolymers with liquid crystalline (LC) poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate} (PMMAZO) as the end blocks and rubbery poly(n-butyl acrylate) (PnBA) as the midblock were synthesized. The effect of the interplay between the LC ordering and microphase separation on the hierarchical assembly of the triblock copolymers was studied. It is found that microphase separation at a larger scale can affect the LC ordering at a smaller scale, such as the stacking of the LC moieties, LC temperature and the domain size of the LC phase. On the other hand, alteration of the LC ordering, such as isotropization and smetic-to-nematic transition, may also lead to an order–order transition (OOT) or change in the long period of the microphase-separated structure. UV light can trigger the isomerization of the azobenzene LC moieties, which can be further amplified and exerts an effect on the microphase separation behavior, including the regularity of the microphase-separated structure and the OOT. The triblock copolymers also exhibit light-variable tensile properties. The results reveal that the phase behavior and mechanical properties of this type of triblock copolymer can be readily regulated by light, thus it may be used as smart and functional thermoplastic elastomer.

The microphase separation behavior of the hybrids of poly(e-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) with different inorganic salts at various doping ratios (r) was studied by temperature-variable SAXS. It was observed that the salts could induce microphase separation to form ordered structure in the originally miscible melt of PCL-b-PEO. The effects of the metal ion and anion were correlated with the competitive interactions of PEO/salt and PCL/salt, which were characterized by FT-IR and DSC, respectively. It was found that at lower doping ratios the salts preferentially interacted with PEO. The larger association number of the metal ion and stronger association between PEO and salt led to a lower onset doping ratio for formation of ordered structure (r0). At higher doping ratios the salt interacted with PCL as well. When the metal ion exhibited a highly selective interaction toward PEO, a more ordered structure with a higher order–order transition temperature (TODT) tended to be formed. The anio...

Effect of different aging treatments(namely AT1, AT2, AT3 and AT4) on the tensile strength(TS) and stress corrosion cracking(SCC) resistance of 7A04 aluminum alloy in 3.5% NaCl+0.5% H2O2solution was investigated using constant load tensile stress corrosion test. Electrochemical behavior of the alloy after different aging treatments was analyzed in 3.5% NaCl solution. The results show that AT1 (i.e. 135°C/16h) increases the TS but decreases the SCC resistance of 7A04. AT2 (i.e. 120°C/7h+165°C/10h) provides the highest SCC resistance and simultaneously retains the TS. AT3 (i.e. 115°C/5h+165°C/10h) decreases both the TS and SCC resistance. The electrochemical analysis indicates that the corrosion resistance of AT2 is the highest, which helps enhance the SCC resistance. The scanning electron micrographs reveal that intergranular corrosion occurs from the corrosion pits on the surface of the specimens when tested under stress, resulting in the ultimate fracture.

Enhanced phase separation and inverse order-to-order phase transition with increasing temperature was observed for a series of poly (acrylic acid)-b-poly (propylene oxide)-b-poly (acrylic acid) triblock copolymers with various block lengths by temperature-variable synchrotron small-angle X-ray scattering (SAXS). This abnormal phase behavior was attributed to the change of hydrogen (H)-bonding interaction in block copolymers upon increasing temperature and theoretically explained from thermodynamic viewpoint. The temperature-dependent FTIR analysis revealed that increasing temperature led to the weakening of overall H-bonding interactions and the increase of free C O and C–O–C groups. The Flory-Huggins interaction parameter χ of PAA and PPO blocks was positive and increased with increasing temperature as determined from the SAXS profiles of disordered block copolymer. The thermodynamic calculation indicated that the increase of ΔH was larger than the decrease of –TΔS with increasing temperature because of the relatively large value of χ, leading to the increase of overall ΔGmix and hence the enhanced phase separation at higher temperature.

This work describes the microphase separation behavior of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs), a type of new sulfur-containing block copolymer, induced by lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI). PPMTC-b-PEO BCPs with a fixed PEO block length but different PPMTC block lengths were synthesized and doped by LiTFSI. Temperature-variable small-angle X-ray scattering result indicates that microphase separation of the PPMTC-b-PEO BCPs can be induced by differential interactions with LiTFSI. However, the ability of LiTFSI to induce microphase separation in PPMTC-b-PEO BCPs does not monotonically increase with the doping ratio (r = [Li+]/([EO] + [PMTC])). It is observed that stronger microphase separation usually occurs at r = 1/12 and 1/6, but microphase separation is weaker at r = 1/24 and 1/3. In most cases, microphase-separated but disordered structures are obtained. Particularly, ordered lamellar structure is formed at suitable doping ratio and block composition. FTIR result confirms the differential complexation of LiTFSI with PEO and PPMTC. LiTFSI preferentially interacts with PEO at low rs, but also strongly interacts with PPMTC at high rs. This work provides a new method to prepare solid polymer electrolytes with double conductive nano-phases, which may be beneficial to both conducting and mechanical properties.

Poly(l-lactide)/polyacrylonitrile (PLLA/PAN) core-sheath composite fibers were fabricated by coaxial electrospinning. The crystallization behavior of PLLA within the coaxial electrospun fibers was studied by differential scanning calorimetry (DSC). The PLLA/PAN coaxial electrospun fiber with a PLLA diameter of ∼32 nm (C1) exhibits a crystallization temperature (Tc) of 22.5 °C higher but a cold-crystallization temperature (Tcc) of 10 °C lower than bulk PLLA. The crystallinity of C1 fiber is also higher than bulk PLLA. In both isothermal melt- and cold-crystallization, PLLA in C1 fiber crystallizes faster than the bulk PLLA, as revealed by the smaller half crystallization times (t1/2). The enhanced crystallizability of PLLA in the C1 fiber may be attributed to the increased nuclei number and crystal growth rate induced by the PAN surface, i.e., surface-induction effect. However, PLLA also suffers a nano-confinement effect exerted by PAN sheath in the coaxial electrospun fiber, which can suppress PLLA crystallization. When the diameter of PLLA is too small (< 32 nm), the nano-confinement effect may prevail over the surface-induction effect, leading to a slower crystallization rate and smaller crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45980.

Glassy polymer nanofibers with spatially confined poly(ethylene oxide) (PEO) were fabricated by coaxial electrospinning of PEO with polyacrylonitrile (PAN) or polystyrene. The effect of melt-annealing on the crystallization behavior of the confined PEOs was studied using differential scanning calorimetry. It is found that the crystallization behavior of the confined PEOs varies with annealing temperature (Ta), annealing time (ta), and molecular weight of PEO. Notably, it is observed that the crystallization temperature (Tc) and melting temperature (Tm) of PEO increase with prolongation of ta, for PEO600K/PAN and PEO2K/PAN coaxial electrospun fibers. This phenomenon can be interpreted by the annealing-induced demixing at the core-sheath interface. After the coaxial electrospinning, the core and sheath of the PEO/PAN coaxial fibers are partially compatible due to the miscible solvents used for the core and sheath polymers. Upon annealing, demixing occurs at the core-sheath interface, leading to improved crystallizability of PEO. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45760.