Organization Of Polymer Chains Research Articles

Template‐free nanostructured particle growth via a one‐pot continuous gradient nanoprecipitation

AbstractEngineered nanoparticles have emerged as new types of materials for a wide range of applications from therapeutics to energy. Still, fabricating nanomaterials presenting complex inner morphologies and shapes in a simple manner remains a great challenge. Herein, we report the template‐free one‐pot continuous gradient nanoprecipitation of different types of non‐compatible polymers to spontaneously form nanostructured particles. The continuous addition of antisolvent induces precipitation and (re)organization of polymer chains at the forming particle interface, ultimately and naturally developing complex inner morphologies and shapes while particle grows. This low‐energy‐cost bottom‐up assembly approach applies to various functional polymers, possibly embedded with metal nanoparticles, for continuous growth into well‐organized nanoparticles. UV crosslinking of the particles and core removal allows both confirming the building process and leading to hollow or multivoid nanomaterials.

Influence of Nanostructuring Sensors Based on Graphene Oxide and PEDOT:PSS for Methanol Detection

Graphene oxide (GO) composites with conducting polymer poly (3,4-ethylenedioxythiophene)-poly (styrenensulfonate) (PEDOT:PSS) were applied as methanol vapor sensors. The active layer was prepared with neat polymer and its composites for different mixing ratios with GO. An optimal ratio was found with 3% (v/v) PEDOT:PSS in GO dispersion and submitted to an additional sonication treatment to change the nanostructure. Devices with treated active layers showed higher responses when applied to methanol vapor sensors. The improved responses are related to differences found on the composite surface. 2-D materials improve the organization of polymer chains, changing PEDOT availability, number of functional groups, and defects in GO. Theoretical analysis by density functional theory (DFT) simulations indicated that the average adsorption energy of methanol molecules is elevated, around −0.8 eV, and a simple mechanism was proposed to explain the response (variation of the layer electrical resistivity in the presence of methanol). The adsorption of vapor molecules on the active layer passivates the doping effect of PSS and GO on PEDOT, decreasing the number of empty states and consequently the conductivity along PEDOT chains. It was also observed that the passivation effect is much accentuated in composites than only in PEDOT:PSS, demonstrating the advantage of using GO composites for methanol vapor detection. Therefore, understanding the dependence of surface, vapor adsorption, and response signal, can improve the development of sensors to be used for gas detection in confined spaces.

Adsorption of organic dyes on macroporous melamine sponge incorporating conducting polypyrrole nanotubes

AbstractThe macropores of melamine sponge were coated with globular polypyrrole or polypyrrole nanotubes. The resulting materials have been tested for the adsorptive removal of organic dyes from aqueous medium. The nanotubes deposited on the sponge were able to remove Reactive Black 5 dye while the adsorption on analogous polypyrrole globules was marginal. For that reason, the macroporous open‐cell melamine sponge with embedded nanotubes was tested for the adsorption of five anionic and five cationic dyes. The anionic dyes were adsorbed efficiently in the contrast to cationic ones. This can be explained by the electrostatic interaction of anionic dyes with polypyrrole polycation. The fast‐starting adsorption occurred within a few minutes and was followed by a slower process extending for days. The nanotubes deposited on the sponge have always been more efficient adsorbents than free polypyrrole nanotubes or melamine sponge alone. Better organization of polymer chains in the polypyrrole nanotubes and especially those deposited on the melamine sponge is proposed to be responsible for this effect. Cationic dyes were adsorbed even by neat melamine sponge while the adsorption by polypyrrole was negligible. In this case, the indifferent role of polypyrrole can be assigned to the electrostatic repulsion of the dye.

Use of a chain extender as a dispersing agent of the CaCO3 into PBAT matrix

This paper investigates the effect of the incorporation of chain extender on the poly(butylene adipate -co-terephthalate) (PBAT) and their mixture with calcium carbonate (CaCO3) composites. Chain extender (ADR) was used to enhance the compatibility between PBAT and CaCO3, which have poor interfacial adhesion. Mechanical, thermal, and morphological properties of PBAT, PBAT/chain extender, and their composites were studied. The incorporation of the chain extender enhanced Young’s modulus and elongation at break of the neat PBAT, which is an indicator of the interaction between both materials. These results were confirmed by 1H NMR and 13C NMR (proton – hydrogen and carbon nuclear magnetic resonance, respectively). The chain extender acted by dispersing the CaCO3 particles; however, with an increase in the filler content, there is a decrease in the mechanical properties. Thermogravimetric analysis showed that chain extender has no influence on neat PBAT thermal behavior and their composites containing CaCO3. Differential scanning calorimetric analysis showed a decrease in crystallinity values of the PBAT and its composites, which is due to the physical impediment in the organization of polymer chains. Photomicrographs, obtained by scanning electron microscopy, showed that chain extender does not influence PBAT morphology. However, in the composites, chain extender enhanced the dispersion on CaCO3 particles.

Calcium Involved Directional Organization of Polymer Chains in Polyester Nanogranules in Bacterial Cells

Soil bacteria accumulate polyesters (typically poly([R]-3-hydroxybutyrate (PHB), in which one end of the chain terminates with a carboxyl group) in the form of hydrated, amorphous nanogranules in cells. However, it is not clear what drives the structure of these biomaterials inside bacterial cells. Here, we determined that calcium guides intracellular formation of PHB nanogranules. Our systematic study using the surface zeta potential measurement and the carboxyl-specific SYTO-62 dye binding assay showed that the terminal carboxyl is not exposed to the granule surface but is buried inside native “unit-granules” comprising the mature granule. Extracellular Ca2+ was found to mediate the formation of these PHB unit-granules, with uptaken Ca2+ stored inside the granules. Comparative [Ca2+]-dependent fluorescence spectroscopy revealed that the native granules in Cupriavidus necator H16 act as a Ca2+ storage system, presumably for the regulation of its cytosolic Ca2+ level, but those from recombinant Escherichia coli do not. This study reveals intimate links between Ca2+ and native granule formation, and establishes a novel mechanism that intracellular PHB granules function as Ca2+ storage in order to relieve soil bacteria from Ca2+ stress.

Effect of organization of semi-flexible polymers on mechanical properties of its composite with single wall carbon nanotubes

Researchers have used molecular simulations to determine the mechanical properties of single walled carbon nanotube (SWCNT)-polymer nanocomposite but have not looked into composite of semi-flexible polymers. We have explored the effect of the organizations of semi-flexible polymer on mechanical properties such as elastic modulus and yield stress of the polymer-SWCNT composite. The proportions of locally ordered organization of polymer chains in a sample depend on its flexibility. For a fixed flexibility of a polymer chain, the presence of SWCNTs improves the proportion of regularly arranged polymers present in the composite. In turn, this improves the elastic modulus and yield stress of the polymer of higher rigidity. The enhancement in elastic modulus and yield stress is due to the retarded deformation of densely packed, ordered region of polymer chains in polymer/SWCNT composite. The presence of randomly oriented chains in a polymer sample containing regularly arranged polymer leads to the higher strain at yield point.

Reduced graphene oxide enhancing the photoelectrochemical properties of poly(3-hexylthiophene)

Poly(3-hexylthiophene) has been used in different photoelectrochemical devices as active material. However, its efficiency regarding photo-conversion is low and the coupling with a second compound is necessary to reduce the electron-hole recombination effect on the generation of photocurrent. The low efficiency could be related to the organization of the polymer. In this work, we propose the use of reduced graphene oxide as modifier to P3HT to enhance its photocatalytic properties. The results here obtained strong suggest, both theoretically and experimentally, an important change in the polymer chain organization from twisted to planar configuration. As consequence, an important increase in the photoelectrochemical properties were observed. In the present case an improvement of over 50% in the value of the photocurrent comparing the pure material and the binary one, processed under the same conditions. In addition, the half-life of the charge carrier increased substantially from 0.781 ms to 9.54 ms. The results are promising because they demonstrate that a higher organization level of the polymer chains increases the photocatalytic properties of the material. Furthermore, the theoretical study not only explains why the properties are improved, but also leads to new understanding of the electronic structure obtained in a binary material.

Organized Molecular Interface-Induced Noncrystallizable Polymer Ultrathin Nanosheets with Ordered Chain Alignment.

The orientation and state of organization of polymer chains play significant roles in determining the final properties and functions of these materials. Unlike most semicrystalline polymers, which have an inherent driving force toward crystallization, the means to control chain packing in noncrystallizable polymers is still restricted and remains a challenge. We report herein a 2D soft template-directed fabrication for ultrathin polyacrylamide nanosheets with a thickness as low as 3.5 nm and large dimensions (>20 μm). More importantly, the polymer chains in the nanosheets produced are well aligned with a clear interchain spacing. The formation of polymer nanosheets with ordered chain alignment was performed in a special solution containing a periodic sandwich structure of lamellar bilayer membranes and water layers that are hundreds of nanometers thick. It functions as a 2D orientation template to align the monomers in an orderly manner along the in-plane direction of the bimolecular membrane via hydrogen bonding.

Studies on PLA grafting onto graphene oxide and its effect on the ensuing composite films

Polylactide (PLA) with a terminal triple bond was synthesized by organocatalyzed ring-opening polymerization and coupled with azide-functionalized graphene oxide (GO) through an azide-alkyne cycloaddition “click” reaction. The functionalized graphenic species involved were analyzed by spectroscopic techniques (FT-IR, solid state 13C NMR, Raman), which confirmed the coupling of PLA and GO. Additionally, an in depth study of the prepared GO, intermediates and GO-g-PLA hybrid was carried out that sheds light on the mechanisms involved in the functionalization path. The obtained GO-g-PLA hybrid, containing at least 20% of biopolymer, presented an exfoliated graphenic structure, as established by XRD. The conditions used in the grafting of the PLA chains inhibited the crystallization and melting observed for the free polymer. Furthermore, the graphene oxide seems to be reduced during functionalization, which can also be an advantage. Nanocomposites were obtained as solvent-cast films, prepared by dispersion of the GO-g-PLA hybrid in commercial PLA. Preliminary results regarding the performance of these nanocomposites, obtained by DSC and DMA, highlighted the effect of functionalization. Loading values as low as 0.5% suffice to improve the mechanical properties over a broad temperature range due to the high surface area resulting from the good dispersibility of polymer functionalized nanofillers and/or their effect on the polymer chain organization.

ChemInform Abstract: Supramolecular Approaches Towards Ordered Polymer Materials

AbstractReview: 37 refs.

A mechanical characterization of polymer scaffolds and films at the macroscale and nanoscale

Biomaterials should be mechanically tested at both the nanoscale and macroscale under conditions simulating their working state, either in vitro or in vivo, to confirm their applicability in tissue engineering applications. In this article, polyester-urethane-based films and porous scaffolds produced by hot pressing and thermally induced phase separation respectively, were mechanically characterized at both the macroscale and nanoscale by tensile tests and indentation-type atomic force microscopy. All tests were conducted in wet state with the final aim of simulating scaffold real operating conditions. The films showed two distinct Young Moduli populations, which can be ascribed to polyurethane hard and soft segments. In the scaffold, the application of a thermal cooling gradient during phase separation was responsible for a nanoscale polymer chain organization in a preferred direction. At the macroscale, the porous matrices showed a Young Modulus of about 1.5 MPa in dry condition and 0.3 MPa in wet state. The combination of nanoscale and macroscale values as well as the aligned structure are in accordance with stiffness and structure required for scaffolds used for the regeneration of soft tissues such as muscles.

Chain ordering of regioregular polythiophene films through blending with a nickel bisdithiolene complex

An “annealing-free” strategy consisting of using a planar nickel bisdithiolene complex nickel bis[1,2-di(3′,4′-di-n-decyloxyphenyl)ethene-1,2-dithiolene] ([Ni(4dopedt)2]) is proposed for structuring poly(3-hexyl-thiophene) (P3HT). Photoluminescence (PL) and Raman spectroscopies, in conjunction with electronic absorption, have been used for evidencing P3HT changes due to blending. PL and absorption observations are consistent and show a correlation between polymer chain organization and increasing amounts of [Ni(4dopedt)2]. Blending with [Ni(4dopedt)2] do not modify the Raman ring-breathing modes energies indicating that blending does not induce strongly disorder in P3HT chains. Atomic force microscopic measurements show that blends nanoscale morphology presents a homogeneous matrix and small fibrils related to [Ni(4dopedt)2] concentration, especially for blends with a [Ni(4dopedt)2] weight ratio lower than 50%.

Supramolecular Approaches towards Ordered Polymer Materials

Controlled organization of polymer chains into ordered structures is highly important to tune or enhance the properties of the polymeric materials. A supramolecular approach using host-guest chemistry has allowed rational design of chain assemblies with many functional properties. Nanoporous materials with ordered channel structures are particularly useful for attaining precise assemblies of polymer chains through nanoconfinement.

Organization of polymer chains onto long, single-wall carbon nano-tubes: Effect of tube diameter and cooling method

We use molecular dynamics simulations to investigate the arrangement of polymer chains when absorbed onto a long, single-wall carbon nano-tube (SWCNT). We study the conformation and organization of the polymer chains on the SWCNT and their dependence on the tube's diameter and the rate of cooling. We use two types of cooling processes: direct quenching and gradual cooling. The radial density distribution function and bond orientational order parameter are used to characterize the polymer chain structure near the surface. In the direct cooling process, the beads of the polymer chain organize in lamella-like patterns on the surface of the SWCNT with the long axis of the lamella parallel to the axis of the SWCNT. In a stepwise, gradual cooling process, the polymer beads form a helical pattern on the surface of a relatively thick SWCNT, but form a lamella-like pattern on the surface of a very thin SWCNT. We develop a theoretical (free energy) model to explain this difference in pattern structures for the gradual cooling process and also provide a qualitative explanation for the pattern that forms from the direct cooling process.

Tuning the properties of an anthracene-based PPE-PPV copolymer by fine variation of its macromolecular parameters

The effects of a moderate variation of the molecular weight on the optical, structural, morphological and transport properties of an anthracene-containing PPE-PPV copolymer are investigated, as well as their overall implication on the photovoltaic parameters of bulk-heterojunction solar cells. Just a two-fold variation in the molecular weight is enough to induce appreciable changes in the properties of the investigated polymer films, indicating that a fine tuning of the macromolecular parameters is required for the optimization of the properties of polydispersed molecular systems. A remarkable role of the polydispersity index in the organization of polymer chains, thus reflecting in the electronic properties of the polymer films, is observed.

Polymer chain organization in tensile-stretched poly(ethylene oxide)-based polymer electrolytes

Polymer chain orientation in tensile-stretched poly(ethylene oxide)–lithium trifluoromethanesulfonate polymer electrolytes are investigated with polarized infrared spectroscopy as a function of the degree of strain and salt composition (ether oxygen atom to lithium ion ratios of 20:1, 15:1, and 10:1). The 1359 and 1352 cm −1 bands are used to probe the crystalline PEO and P(EO) 3LiCF 3SO 3 domains, respectively, allowing a direct comparison of chain orientation for the two phases. Two-dimensional correlation FT-IR spectroscopy indicates that the two crystalline domains align at the same rate as the polymer electrolytes are stretched. Quantitative measurements of polymer chain orientation obtained through dichroic infrared spectroscopy show that chain orientation predominantly occurs between strain values of 150% and 250%, regardless of salt composition investigated. There are few changes in chain orientation for either phase when the films are further elongated to a strain of 300%; however, the PEO domains are slightly more oriented at the high strain values. The spectroscopic data are consistent with stretching-induced melt-recrystallization of the unoriented crystalline domains in the solution-cast polymer films. Stretching the films pulls polymer chains from the crystalline domains, which subsequently recrystallize with the polymer helices parallel to the stretch direction. If lithium ion conduction in crystalline polymer electrolytes is viewed as consisting of two major components (facile intra-chain lithium ion conduction and slow helix-to-helix inter-grain hopping), then alignment of the polymer helices will affect the ion conduction pathways for these materials by reducing the number of inter-grain hops required to migrate through the polymer electrolyte.

Annealing-free fabrication of P3HT:PCBM solar cells via simple brush painting

We report on the fabrication of efficient annealing-free polymer solar cells via simple brush painting considered as a promising method for the mass production of organic devices based on the high-speed roll-to-roll system. Higher device efficiency could be obtained compared to the spin-coated devices, resulting from the improved organization of polymer chains and better balanced carrier transport induced by more effective application of shear stress to the polymer chains during the brushing process. In addition, fully brush painted solar cells, including the brush-painted PEDOT:PSS and photoactive layer, presented a high power conversion efficiency of 3.6% without any annealing treatment and processing additives.

Highly Anisotropic Luminescence from Poly(9,9-dioctylfluorene) Nanowires Doped with Orientationally Ordered β-Phase Polymer Chains

We quantitatively assess the nature and extent of emissive polymer chain organization within individual poly(9,9-dioctylfluorene) nanowires fabricated by solution-assisted template wetting. A minority fraction of planar, extended β-phase polymer chains occurs within the nanowires, which dominates their luminescence behavior. Nanowires exhibit pronounced optical birefringence and detailed polarized optical microscopy analysis indicates preferential axial alignment of polymer chains. Polarization-resolved near-field photoluminescence imaging and spectroscopy methods are employed to probe local spatial variations in light emission intensity along individual nanowires. Data indicate strong axially polarized nanowire emission, with locally measured dichroic ratios up to 8.9, consistent with preferential axial alignment of emissive β-phase polymer chains. To visualize the extent of β-phase chain alignment within a typical nanowire, we generated image maps of the orientational order parameter, ⟨P2⟩, from measured near-field emission intensity image data. Numerous domains of long-range order up to 2 μm in size with ⟨P2⟩ values ranging from 0.47 to 0.76 are identified, indicating extensive axial alignment of emissive β-phase chains within the nanowires. Poly(9,9-dioctylfluorene) nanowires exhibiting micrometer-scale order make them attractive elements for future subwavelength organic opto-electronic devices.

Noninvasive Probing of the Spatial Organization of Polymer Chains in Hydrogels Using Fluorescence Resonance Energy Transfer (FRET)

Spatial organization of polymer chains upon ionic or covalent cross-linking to form a hydrogel is examined on the molecular scale using a fluorescent resonance energy transfer (FRET) technique. Minimal changes in the conformation in the polymer chains but significant changes of the intermolecular association of polymer chains are found when polymer chains are cross-linked with a different number of cross-links. This study provides a previously undescribed technique to analyze hydrogel structure in a noninvasive manner.

Polymerization of Supramolecular Diacetylenic Monomer Embedded in Porous Silicon Matrix

We have used a porous silicon matrix filled with polydiacetylenic derivatives to obtain new nanocomposites. The polymerization, known as a topochemical process, requires optimal packing of the diacetylenic segments to allow polymerization propagation across the assembly to give a conjugated backbone. We have explored the use of intermolecular H-bond interactions between diacetylenic diacid monomers to control the polymer chain organization after the polymerization step. Resonance Raman and IRTF spectroscopy have been used to directly probe the diacetylenic segment of the monomer and the pendent side-chain arrangement. Diacetylenic derivatives have been successfully incorporated inside the pores after a specific chemical treatment to improve the filling rate of the monomer. Polarized Raman scattering indicated that the monomers have a preferential orientation along the pore axis, probably because of the confinement effect and hydrogen bonding of the self-associated carboxylic dimeric form. After the polymerization process, resonance Raman spectroscopy shows a highly oriented ene−yne backbone characterized by a blue phase.