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1.
ACS Polym Au ; 4(2): 128-139, 2024 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-38618004

RESUMO

Strategic customization of crystalline forms of poly(vinylidene fluoride) (PVDF) aerogels is of great importance for a variety of applications, from energy harvesters to thermal and acoustic insulation. Here, we report sustainable strategies to prepare crystalline pure α, ß, and γ forms of PVDF aerogels from their respective gels using a solvent exchange strategy with green solvents, followed by a freeze-drying technique. The crucial aspect of this process was the meticulous choice of appropriate solvents to enable the formation of thermoreversible gels of PVDF by crystallization-induced gelation. Depending on the polymer-solvent interactions, the chain conformation of PVDF can be modulated to obtain gels and aerogels with specific crystalline structures. The crystalline pure α-form and piezoelectric ß-form aerogels were readily obtained by using cyclohexanone and γ-butyrolactone as gelation solvents. On the other hand, the γ-form aerogel was obtained using a binary solvent system consisting of dimethylacetamide and water. These aerogels with distinct crystalline structures exhibit different morphologies, mechanical properties, hydrophobicities, acoustic properties, and electrical properties. Measurement of thermal conductivity for these aerogels showed exceptionally low thermal conductivity values of ∼0.040 ± 0.003 W m-1 K-1 irrespective of their crystal structures. Our results showcase the fabrication approaches that enable PVDF aerogels with varied physicochemical properties for multifunctional applications.

2.
ACS Appl Mater Interfaces ; 15(42): 49567-49582, 2023 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-37842998

RESUMO

Polymer hybrid materials that contain reinforcements with a preferred orientation have received growing attention because of their unique properties and promising applications in multifunctional fields. Herein, anisotropic poly(vinylidene fluoride) (PVDF)/MXene hybrid aerogels with highly ordered delaminated MXene nanosheets and anisotropic porous structures were successfully fabricated by unidirectional freezing of thermoreversible gels followed by a freeze-drying process. The strong interfacial interactions between PVDF chains and abundant functional groups on the surface of MXene enabled the orientation of MXene nanosheets at the boundaries of ice crystals as the semicrystalline PVDF and delaminated MXene nanosheets are squeezed along the freezing direction. These aerogels display distinct properties along the freezing and perpendicular to the freezing (transverse) directions. These anisotropic aerogels are flexible and flame-retardant and possess an anisotropic compression performance, heat transfer, electrical conductivity, and electromagnetic interference (EMI) shielding. Further, by increasing the MXene loadings, the electrical conductivity and EMI shielding performances of hybrid aerogels were significantly improved. The PVDF aerogel showed sticky hydrophobicity with a contact angle of 139°, whereas the contact angle increased significantly in hybrid aerogels (153°) with low water adhesion, making them suitable as self-cleaning materials. The combination of the above characteristics makes these hybrid aerogels potential candidates for a wide range of electronic applications.

3.
Soft Matter ; 19(35): 6671-6682, 2023 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-37609667

RESUMO

The development of biodegradable and biocompatible fluorescent materials with tunable emission in the solid state has become increasingly relevant for smart packaging and biomedical applications. Molecular packing and conformations play a critical role in tuning the solid-state photophysical properties of fluorescent materials. In this work, tunable emission of bioactive curcumin was achieved through the manipulation of the crystallization conditions and the polymorphic form of covalently linked poly(L-lactide) in the curcumin-embedded poly(L-lactide) (curcumin-PLLA). In the melt-crystallized curcumin-PLLA, with the increase in the isothermal crystallization temperature, a bathochromic shift in the fluorescence of curcumin-PLLA was observed due to the change in the intramolecular conjugation length of curcumin. The change in the isothermal crystallization temperature of curcumin-PLLA resulted in the rotation of the terminal phenyl rings of curcumin with respect to the central keto-enol group due to the covalently linked helical PLLA chains. In addition, solvent-induced single crystals and a gel of curcumin-PLLA were prepared and the influence of the polymorphic form of PLLA on the emission behavior of curcumin-PLLA was investigated. The results suggest that the polymer chain packing, crystallization conditions, morphology, and polymorphic form could play an influential role in dictating the fluorescence properties of fluorophore-embedded polymers.

4.
Chem Sci ; 14(24): 6643-6653, 2023 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-37350839

RESUMO

Covalent organic frameworks (COFs) are ideal host matrices for biomolecule immobilization and biocatalysis due to their high porosity, various functionalities, and structural robustness. However, the porosity of COFs is limited to the micropore dimension, which restricts the immobilization of enzymes with large volumes and obstructs substrate flow during enzyme catalysis. A hierarchical 3D nanostructure possessing micro-, meso-, and macroporosity could be a beneficial host matrix for such enzyme catalysis. In this study, we employed an in situ CO2 gas effervescence technique to induce disordered macropores in the ordered 2D COF nanostructure, synthesizing hierarchical TpAzo COF-foam. The resulting TpAzo foam matrix facilitates the immobilization of multiple enzymes with higher immobilization efficiency (approximately 1.5 to 4-fold) than the COF. The immobilized cellulolytic enzymes, namely ß-glucosidase (BGL), cellobiohydrolase (CBH), and endoglucanase (EG), remain active inside the TpAzo foam. The immobilized BGL exhibited activity in organic solvents and stability at room temperature (25 °C). The enzyme-immobilized TpAzo foam exhibited significant activity towards the hydrolysis of p-nitrophenyl-ß-d-glucopyranoside (BGL@TpAzo-foam: Km and Vmax = 23.5 ± 3.5 mM and 497.7 ± 28.0 µM min-1) and carboxymethylcellulose (CBH@TpAzo-foam: Km and Vmax = 18.3 ± 4.0 mg mL-1 and 85.2 ± 9.6 µM min-1 and EG@TpAzo-foam: Km and Vmax = 13.2 ± 2.0 mg mL-1 and 102.2 ± 7.1 µM min-1). Subsequently, the multi-enzyme immobilized TpAzo foams were utilized to perform a one-pot tandem conversion from carboxymethylcellulose (CMC) to glucose with high recyclability (10 cycles). This work opens up the possibility of synthesizing enzymes immobilized in TpAzo foam for tandem catalysis.

5.
ACS Macro Lett ; 11(11): 1272-1277, 2022 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-36282095

RESUMO

Polymer-based multicolor emissive materials have growing demand due to their potential applications in various fields such as full-color displays, bioimaging, and light sources because of their processability and high stability. Herein, we report dual-color emissive hybrid materials based on biocompatible poly(l-lactide) and polyethylene glycol-modified two-dimensional layered double hydroxide quantum dots (PEG-LDHQDs). The morphology of polymer films tunes the spatial distribution of QDs within the polymer matrix, modulating the energy transfer between the QDs and affording the dual emission behavior in the aggregated states. The amorphous hybrid films show single emission (blue) from the finely dispersed QDs (mostly isolated) within the polymer matrix. In contrast, dual emission (blue and red) was observed when the polymer was crystallized due to the possible accumulation of QDs at the interface of crystalline and amorphous phases in the lamellar structure. Furthermore, the dual emission could be enhanced by the aggregation of QDs on the pores of the breath figure pattern constructed on the surface of the hybrid film.


Assuntos
Pontos Quânticos , Transferência de Energia , Polímeros/química , Pontos Quânticos/química
6.
ACS Appl Mater Interfaces ; 14(39): 44239-44250, 2022 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-36129836

RESUMO

In the present era of intelligent electronics and Internet of Things (IoT), the demand for flexible and wearable devices is very high. Here, we have developed a high-output flexible piezoelectric nanogenerator (PENG) based on electrospun poly(vinylidene fluoride) (PVDF)-barium titanate (BaTiO3) (ES PVDF-BT) composite nanofibers with an enhanced electroactive phase. On addition of 10 wt % BaTiO3 nanoparticles, the electroactive ß-phase of the PVDF is found to be escalated to ∼91% as a result of the synergistic interfacial interaction between the tetragonal BaTiO3 nanoparticles and the ferroelectric host polymer matrix on electrospinning. The fabricated PENG device delivered an open-circuit voltage of ∼50 V and short-circuit current density of ∼0.312 mA m-2. Also, the PVDF-BT nanofiber-based PENG device showed an output power density of ∼4.07 mW m-2, which is 10 times higher than that of a pristine PVDF nanofiber-based PENG device. Furthermore, the developed PENG has been newly demonstrated for self-powered real-time vibration sensing applications such as for mapping of mechanical vibrations from faulty CPU fans, hard disk drives, and electric sewing machines.

7.
Soft Matter ; 18(14): 2722-2725, 2022 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-35234247

RESUMO

Herein, vibrational circular dichroism (VCD) measurements were carried out to study the kinetics of cold-crystallized poly(D-lactide) (PDLA) at the molecular level via qualitative analysis. The amplification of the VCD signals from intra- and inter-chain chiral interactions suggests the formation of partially ordered PDLA, followed by heterogeneous nucleation for crystallization. These results were further supported by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy analyses.

8.
J Am Chem Soc ; 144(1): 400-409, 2022 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-34965101

RESUMO

Empowered by crystalline ordered structures and homogeneous fabrication techniques, covalent organic frameworks (COFs) have been realized with uniform morphologies and isotropic properties. However, such homogeneity often hinders various surface-dependent properties observed in asymmetric nanostructures. The challenge remains to induce heterogeneity in COFs by creating an asymmetric superstructure such as a Janus thin film. In this regard, we propose a versatile yet straightforward interfacial layer-grafting strategy to fabricate free-standing Janus-type COF-graphene thin films. Herein, two-dimensional graphene sheets were utilized as the suitable grafter due to the possibility of noncovalent interactions between the layers. The versatility of the approach was demonstrated by fabricating two distinct Janus-type films, with the COF surface interwoven with nanofibers and nanospheres. The Janus-type films showcase opposing surface morphologies originating from graphene sheets and COF nanofibers or nanospheres, preserving the porosity (552-600 m2 g-1). The unique surface chemistries of the constituent layers further endow the films with orthogonal mechanical properties, as confirmed by the nanoindentation technique. Interestingly, the graphene sheets favor the Janus-type assembly of COF nanofibers over the nanospheres. This is reflected in the better nanomechanical properties of COFfiber-graphene films (Egraphene = 300-1200 MPa; ECOF = 15-60 MPa) compared to the COFsphere-graphene films (Egraphene = 11-14 MPa; ECOF = 2-5 MPa). These results indicate a direct relationship between the mechanical properties and homo/heterogeneity of Janus-type COF films.

9.
J Am Chem Soc ; 143(49): 20916-20926, 2021 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-34855393

RESUMO

Synthesis of covalent organic framework (COF) thin films on different supports with high crystallinity and porosity is crucial for their potential applications. We have designed a new synchronized methodology, residual crystallization (RC), to synthesize sub 10 nm COF thin films. These residual crystallized COF thin films showcase high surface area, crystallinity, and conductivity at room temperature. We have used interfacial crystallization (IC) as a rate-controlling tool for simultaneous residual crystallization. We have also diversified the methodology of residual crystallization by utilizing two different crystallization pathways: fiber-to-film (F-F) and sphere-to-film (S-F). In both cases, we could obtain continuous COF thin films with high crystallinity and porosity grown on various substrates (the highest surface area of a TpAzo COF thin film being 2093 m2 g-1). Precise control over the crystallization allows the synthesis of macroscopic defect-free sub 10 nm COF thin films with a minimum thickness of ∼1.8 nm. We have synthesized two COF thin films (TpAzo and TpDPP) using F-F and S-F pathways on different supports such as borosilicate glass, FTO, silicon, Cu, metal, and ITO. Also, we have investigated the mechanism of the growth of these thin films on various substrates with different wettability. Further, a hydrophilic support (glass) was used to grow the thin films in situ for four-probe system device fabrication. All residual crystallized COF thin films exhibit outstanding conductivity values. We could obtain a conductivity of 3.7 × 10-2 mS cm-1 for the TpAzo film synthesized by S-F residual crystallization.

10.
Soft Matter ; 16(31): 7312-7322, 2020 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-32672783

RESUMO

Here, we demonstrate the three-component self-assembly of functionalized small molecules (donor and acceptor) and a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer using the supramolecular approach. The introduction of functional groups on both the donor (1-pyrenebutyric acid, PBA) and acceptor (functionalized naphthalene diimide, FNDI) molecules can form stable charge-transfer (CT) complexes within the block copolymer domains and these supramolecules exhibited a charge carrier mobility of around 1.01 × 10-4 cm2 (V s)-1. In this case, both the molecules can form H-bonding with P4VP chains, and as well as π-π stacking between the PBA and FNDI molecules is also possible within the block copolymer domains. These noncovalent interactions lead to the formation of stable hierarchical structures and CT complexes between PBA and FNDI, where bilayer donor-acceptor (D-A) stacks formed within the block copolymer microdomains. Overall, the organization of both functionalized donor and acceptor molecules within the block copolymer domain exhibits an enhanced charge carrier mobility, which is potentially useful in the fabrication of organic photovoltaic cells and organic light-emitting diodes.

11.
J Phys Chem B ; 123(40): 8599-8609, 2019 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-31525982

RESUMO

Differently functionalized boron nitride nanosheets (BNNSs) [hydroxyl (OH_BNNSs), amine (NH2_BNNSs), and poly(ethylene glycol) (PEG) (PEG_BNNSs)] were synthesized, and their effects on the structure and thermal properties of poly(l-lactic acid) (PLLA) along with those of the pristine BNNSs were studied. Highly dispersed nanocomposites were prepared using PLLA and 0.5 wt % of pristine/functionalized BNNSs via a solvent blending method. Homogeneous dispersion of BNNSs in the polymer matrix was confirmed using X-ray diffraction and scanning electron microscopy. Pristine BNNSs and OH_BNNSs accelerated the crystallization of PLLA as effective nucleating agents and favored the formation of the α form in melt-crystallized samples. On the other hand, NH2_BNNSs and PEG_BNNSs incorporated samples result in the moderate crystallization rate of PLLA and lead to the formation of a mixture of α and α' forms similar to the PLLA. It is also found that thermal stability and thermal conductivity of PLLA nanocomposites significantly depend on the type of functionalization of BNNSs. At 0.5 wt % loading, the thermal conductivity enhancement is maximum for PEG_BNNSs incorporated PLLA (∼62%), and that is only 9% for pristine BNNSs incorporated PLLA. The thermal stability of PLLA nanocomposites was significantly improved by 32-41 °C depending on the type of functionalized BNNSs compared to PLLA. It is proposed that the strong interaction between functionalized BNNSs and PLLA matrix is responsible for the improved thermal management properties.

12.
Langmuir ; 35(13): 4672-4681, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30832479

RESUMO

Incorporation of multifunctional inorganic additives into the commercial polymers still stands as the most captivating and effective way to realize new-generation electronic components. Here, we introduce a simple, cost-effective, and environmentally benign method to covalently functionalize graphene oxide (GO) with vinyl- and aminopropyl-functionalized hybrid silica spheres with a polyhedral oligomeric silsesquioxane (POSS)-siloxane composition. The reaction has been carried out in a mixture of ethanol and water (used as a medium) at ambient conditions with silane precursors. Later, the synthesized hybrid material has been tested for its dielectric properties after blending with syndiotactic polystyrene, a commercially available insulating semicrystalline polymer. It was observed that the dielectric constant decreases with the addition of GOPOSS up to 1.85 with a dielectric loss of 0.02 at 5 GHz. Significant improvements in the thermal properties of the composites were verified with minimal filler loading.

13.
J Phys Chem B ; 122(24): 6442-6451, 2018 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-29842779

RESUMO

This work reports on the impact of delaminated boron nitride nanosheets (BNNSs) on the crystallization behavior and crystalline structure of melt-crystallized poly-L-lactic acid (PLLA). Wide-angle X-ray diffraction and scanning electron microscopy data revealed that the addition of lower loadings of BNNSs (∼0.5 wt %) resulted in the highly dispersed PLLA nanocomposites, whereas the higher loading of BNNSs (≥1 wt %) leads to the agglomerated nanocomposites. It is shown that the presence of lower loadings of the BNNSs (∼0.5 wt %) induces the formation of ordered α form when crystallizing from the melt at a cooling rate of 10 °C/min, but the mixture of α' and α forms is formed in the presence of higher loading of BNNSs (≥1 wt %). Polarized optical microscopy images revealed that the crystallization rate of PLLA was significantly enhanced in the presence of lower loading of BNNSs (∼0.5 wt %) as corroborated by the increasing number of tiny spherulites. The strong interaction between the highly dispersed BNNSs and PLLA chains induces the conformationally ordered α form, and the various experimental techniques revealed that crystallization of PLLA occurred rapidly with the narrow distribution of crystal size and degree of crystal perfection in highly dispersed nanocomposites. Furthermore, the thermal conductivity of PLLA/BNNSs nanocomposites was found to increase significantly with BNNSs loading.

14.
Soft Matter ; 14(8): 1492-1498, 2018 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-29404553

RESUMO

The role of a nonsolvent in controlling the crystallization and morphology of solvent-crystallized poly(l-lactide) (PLLA) films was investigated using various microscopy techniques and small- and wide-angle X-ray scattering (SAXS/WAXS). PLLA films crystallized in THF and acetone had 40-80 µm spherulites. When water was present in the solvent, a completely different morphology was observed with nanosized voids and the surfaces of the films were smooth. In contrast, SEM studies revealed that the films crystallized in acetone and THF which had macroporous structures, had larger voids and film surfaces were rough because of the presence of globular structures. Voids appeared within the spherulites in the THF/water treated film, whereas crystals nucleated at the surface of the nanosized voids in acetone/water treated PLLA films. The formation of such voids is attributed to the interface-enhanced crystal nucleation in a solvent/nonsolvent system where the nonsolvent increases the polymer crystal nucleation and the subsequent evaporation of the nonsolvent. The method described in this work can be extended to other polymers to control the morphologies of polymer films during solvent-induced crystallization.

15.
ACS Omega ; 2(1): 20-31, 2017 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-31457206

RESUMO

Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50-200 nm). Such delaminated Co-Al LDH, Zn-Al LDH, and Co-Zn-Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancy and thermal stability of iPP with the type of LDH used for the preparation of nanocomposites. The thermal stability (50% weight loss temperature (T 0.5)) of the iPP nanocomposite containing three-metal LDH (Co-Zn-Al LDH) is superior to that of the nanocomposites made of two-metal LDH (Co-Al LDH and Zn-Al LDH). Preliminary studies on the flame-retardant properties of iPP/LDH nanocomposites using microscale combustion calorimetry showed that the peak heat release rate was reduced by 39% in the iPP/Co-Zn-Al LDH nanocomposite containing 6 wt % LDH, which is higher than that of the two-metal LDH containing nanocomposites, iPP/Co-Al LDH (24%) and iPP/Zn-Al LDH (31%). These results demonstrated that the nanocomposites prepared using three-metal LDH showed better thermal and flame-retardant properties compared to the nanocomposites prepared using two-metal LDH. This difference might be due to the better char formation capability of three-metal LDH compared to that of two-metal LDH.

16.
ACS Appl Mater Interfaces ; 7(34): 19474-83, 2015 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-26287385

RESUMO

Homogeneously dispersed hybrid silica/syndiotactic polystyrene composites were investigated for low-κ dielectric applications. The composites were prepared by a solution blending method, and their microstructures were analyzed by SEM, TEM, and AFM. Crystallization and phase transformation behavior of sPS were investigated using differential scanning calorimetry and wide-angle X-ray diffraction. These composites exhibited improved thermal stability and reduced thermal expansion coefficients. Promising dielectric properties were observed for the composites in the microwave frequency region with a dielectric constant (κ = 1.95) and loss (tan δ = 10(-4)) at 5 GHz.

17.
ACS Appl Mater Interfaces ; 7(23): 12399-410, 2015 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-25741910

RESUMO

Highly dispersed isotactic polypropylene (iPP) nanocomposites were prepared by incorporating two different sized Mg-Al LDH nanoparticles with different loadings from 1 to 10 wt % using a modified solvent mixing method. Larger sized LDH nanoparticles (∼3-4 µm) were prepared from the gel form of Mg-Al LDH, and the smaller sized nanoparticles (∼50-200 nm) were prepared by sonication of as-synthesized LDH particles. Such obtained LDH nanoparticles were carefully characterized using wide-angle X-ray diffraction (WAXD), transmission electron microscopy, and scanning electron microscopy. WAXD and atomic force microscopy results indicate that the LDH nanoparticles were highly dispersed in the iPP matrix. The influence of LDH nanoparticles size and concentration on the thermal stability, spherulitic morphology, melting behavior, isothermal crystallization kinetics, and lamellar structure of iPP were investigated. Incorporation of low loadings of sonicated LDH particles (e.g., 1-2.5 wt %) show substantial effect on thermal stability, spherulite size, crystallinity, and crystallization half-time and lamellar morphology of iPP compared to the pure iPP and that of nanocomposites with larger LDH particles with same loadings. The better nucleation ability of iPP in the presence of sonicated LDH can be attributed to the high surface area of LDH nanoparticles along with its better dispersibility within the polymer matrix. The incorporation of LDH nanoparticles does not change the crystallization growth mechanism and crystal structure of iPP.

18.
ACS Appl Mater Interfaces ; 7(23): 12559-69, 2015 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-25619225

RESUMO

In this review, recent developments in the fabrication of hexagonal and parallel ordered arrays of metallic nanodomains on a substrate are described. We focus on the nanopatterning approach by means of switchable block copolymer thin films. This approach is highly advantageous, because it can lead to extremely regular patterns with metal subunits of only a few nanometers in diameter and center-to-center distances of tens of nanometers. Hence, the resulting 1D or 2D periodic arrays of metal nanodots and nanowires on silicon substrates can be fabricated with extremely high unit densities and on very large areas. The templated deposition of presynthesized metal nanoparticles on functional block copolymers is described in detail. Current challenges are discussed and an outlook for further developments is given.

19.
Soft Matter ; 10(39): 7753-61, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25142254

RESUMO

The orientation changes of perpendicular cylindrical microdomains in polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) thin films upon annealing in different solvent vapors were investigated by in situ grazing incidence small-angle X-ray scattering (GISAXS) and ex situ scanning force microscopy (SFM). The swelling of P4VP perpendicular cylinders (C⊥) in chloroform, a non-selective solvent vapor, leads to the reorientation to in-plane cylinders through a disordered state in a particular kinetic pathway in the phase diagram upon drying. On the other hand, the swelling of the P4VP perpendicular cylinders in a selective solvent vapor (i.e., 1,4-dioxane) induces a morphological transition from cylindrical to ellipsoidal as a transient structure to spherical microdomains; subsequent solvent evaporation resulted in shrinkage of the matrix in the vertical direction, merging the ellipsoidal domains into the perpendicularly aligned cylinders. In this paper, we have discussed the mechanism based on the selectivity of the solvent to the constituting blocks that is mainly responsible for the orientation changes.

20.
Phys Chem Chem Phys ; 16(32): 17008-17, 2014 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-25004950

RESUMO

Dielectric composites composed of poly(vinylidene fluoride) (PVDF) and La0.5Sr0.5CoO3-δ (LSCO) with high permittivity, low loss and high breakdown strength have been developed. The effects of particle size of LSCO (fine (∼250 nm) and coarse (∼3 µm)) on the phase crystallization of PVDF and dielectric properties of polymer-LSCO composites are studied. The inclusion of fine LSCO into PVDF readily favours the formation of polar crystals (ß and γ-phases), which makes the composite suitable for both electromechanical and high charge storage embedded capacitor applications. Moreover, the addition of fine LSCO particles also increases the overall crystallization rate as well as the melting point of PVDF. The composite containing fine LSCO particles gave a percolation threshold at about 25 volume percentage, while that with coarse particles did not show any percolation even at very high volume percentage. As a result of fine LSCO particle loading, the composite exhibited a relative permittivity (εr) of ∼600, a conductivity of 2.7 × 10(-7) S cm(-1), a dielectric loss (tan δ) of 0.7 at 1 kHz and a breakdown voltage of 100 V even at 20 volume percentage of a filler, demonstrating promising applications in the embedded capacitors.

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