Self-Organization in Electrospun Polymer Solutions: From Dissipative Structures to Ordered Fiber Structures through Fluctuations

Self-organization in nonequilibrium systems is a research topic in the statistical physics universally important for formation of patterns or orders in various systems, including nature. In this work, we investigated the self-organization processes of ordered structures via cascade evolutions of various dissipative structures through fluctuations in electrospun poly­(vinyl alcohol) aqueous solutions in both mesoscopic and macroscopic length scales. The flowing jets were investigated both <i>in situ</i>, <i>macroscopically</i> with a high speed video imaging and <i>ex situ</i>, <i>mesoscopically</i> under optical and electron microscopies as a function of the polymer concentration. In the semidilute unentangled solutions, the main jet evolved a self-similar, cascade network composed of a set of the bulge and the branched subjets issued from the bulge as a building block of the network. In the semidilute entangled solutions, the main jet evolved a series of bulges elongated along the jet axis without formation of the branched subjets. We propose that the bulges were formed in the jet by the orientation-fluctuations-induced concentration fluctuations (OFICF) and the resultant phase separation, triggered by the chain stretching in the jet. The <i>ex situ</i> investigations unveiled the deformed bulges contained remarkable internal structures driven by phase separation into polymer-rich stringlike structures, which comprised the finer elongated bulges interconnected with bundles of oriented chains (finer jets), in the matrix of polymer-lean solution. These bulges and their internal structures are dissipative structures which were developed as a consequence of the dissipation of the increased free energy due to the conformational entropy loss of the chains in the solutions. Further stretching of the jet solution resulted in creation of the finer deformed bulge(s) and the finer jet(s): the finer jet(s) in turn further developed even finer deformed bulges via the OFICF through the consequent cascade energy dissipation mechanism. The cascade transformation of the dissipative structures from the micro- to nanosized scales, during which solvents were squeezed out to the jet surface and removed later, eventually yielded the beaded fibers deposited on the collectors. At higher concentrations, the elongated bulges were self-assembled into highly elongated strings, i.e., fine fibers composed of bundles of the stretched chains, embedded in the uniform nonbeaded fibers

Core–Shell Fibers Electrospun from Phase-Separated Blend Solutions: Fiber Formation Mechanism and Unique Energy Dissipation for Synergistic Fiber Toughness

Through single-tube electrospinning, the biodegradable core–shell fibers of poly­(3-hydroxybutyrate) (PHB) and poly­(d,l-lactic acid) (PDLLA) were obtained from blend solutions with different compositions at a total polymer concentration of 7 wt %. Regardless whether PHB is the major or minor component (PHB/PDLLA = 90/10, 75/25, 50/50, and 25/75 wt. ratio), these phase-separated solutions all yielded core–shell fibers with PHB as core and PDLLA as shell. A new scenario of core–shell fiber formation was proposed on the basis of the relative magnitude of the intrinsic relaxation rate of fluids and external extension rate during electrospinning. The effects of blend compositions on the morphologies of the Taylor cone, whipping jet, and as-spun fibers were investigated. The diameters of core–shell fibers can be tailored by simply varying the PHB/PDLLA ratios. Two scaling laws describing the apparent viscosity (η_o) dependence of the outer fiber diameter (<i>d</i>_fo) and core fiber diameter (<i>d</i>_fc) were derived. That is, <i>d</i>_fo ∼ η_o^0.38 and <i>d</i>_fc ∼ η_o^0.86. The microstructures of the as-spun fibers were determined by differential scanning calorimetry, Fourier transform infrared spectroscopy, and synchrotron wide-angle and small-angle X-ray scatterings. Results showed that the PDLLA component was in the amorphous state, and the crystallizability of PHB component remained unchanged, except the amorphous 10/90 fibers electrospun from a miscible solution state. The synergistic mechanical properties of the core–shell fibers were obtained, along with the ductile PDLLA shell enclosing the brittle PHB core. The enhanced toughness was attributed to the fragmentation of the brittle PHB core and necking fracture of the ductile PDLLA shell, which served as an effective route for energy dissipation. Compared with the neat PHB fiber, the 90/10 and 75/25 core–shell fibers possessed larger elastic moduli, which was attributed to the high PHB crystal orientation in their core sections despite the reduced PHB crystallinity. By contrast, the crystal <i>c</i>-axis of PHB in the 25/75 core–shell fibers was preferentially perpendicular to the fiber axis, suggesting the significant stretching of developing PHB crystals during electrospinning

DataSheet1_Lagged response of summer precipitation to solar activity in the mid-lower reaches of the Yangtze River.ZIP

In the context of more frequent extreme precipitation worldwide, the Sun’s influence on global or regional rainfall patterns has attracted much attention. Due to its vital importance to Chinese industrial and agricultural production, the precipitation property in the mid-lower reaches of the Yangtze River (MLRYR) remains a hot issue. Although previous works have implied the plausible influence of solar activity on precipitation in the mid-lower reaches of the Yangtze River, the time-lagged effect is still an open question. In this paper, we adopt the China-Z index (CZI) to represent the original precipitation data, which is proposed to monitor moisture conditions over China and is more sensitive to solar activity. We explore the lagged correlations between summer precipitation in the mid-lower reaches of the Yangtze River and solar activity. The China-Z index in June-July is negatively correlated with the sunspot number in July of the preceding year, giving a time lag of 11 months. Based on the composite analysis, we suggest that solar activity possibly modulates the precipitation by influencing the local moisture and its vertical movement through the sea-land thermal contrast and the associated East Asian summer monsoon on a much larger scale.</p

Impact of Entanglement Density on Solution Electrospinning: A Phenomenological Model for Fiber Diameter

The rheological properties of poly­(<i>N</i>-isopropylacrylamide, PNIPAM) in dimethyl­formamide solvent were investigated and correlated with solution electrospinnability. The jet diameter was measured by using the light scattering technique during the electrospinning in the straight jet region prior to the jet whipping. The diameter of the straight jet end is independent of the solution concentration (or viscosity within the range of 15–2000 mPa·s). Thus, the final fiber diameter <i>d</i>_f observed on the grounded collector is dominantly controlled by the jet-whipping process. According to the present PNIPAM solution and other different polymer solutions, <i>d</i>_f is correlated with the solution concentration ϕ. A master curve is constructed by using the following equation: <i>d</i>_f/<i>d</i>_f,e = (ϕ/ϕ_e)^2.5, where <i>d</i>_f,e is the diameter of the fibers electrospun from the solutions with an entanglement concentration of ϕ_e, above which the specific viscosity starts to increase with ϕ according to ϕ^3.7 or ϕ^4.7, depending upon the given polymer/solvent pair. The derived exponent of 2.5 is in good agreement with the theoretical exponent value of 2.3 provided that <i>d</i>_f is proportional to the entanglement density υ­(ϕ) ∼ ϕ^2.3 (entangled strands per unit volume of the solution). Our results imply that the plateau modulus (elasticity) of the entangled polymer solution rather than its viscosity plays a major role in determining the final fiber diameter. The entangled polymer solutions behave like elastic swollen gels during electrospinning because of the high deformation rates. We propose that the deformation-induced structure formation in the jet eventually results in the fiber with the concentration-dependent diameter

Additional file 1: of Weighted-SAMGSR: combining significance analysis of microarray-gene set reduction algorithm with pathway topology-based weights to select relevant genes

R codes for the weighted-SAMGSR algorithm. (DOCX 76 kb

Poly(vinyl alcohol) Fibrils with Highly Oriented Amorphous Chains Developed in Electrospun Nanofibers

Aligned poly(vinyl alcohol) (PVA) fibers with diameters of about 180 ± 22 nm were obtained by using a wire–drum collector during electrospinning of aqueous solutions of PVA with 99% hydrolysis. The fiber orientation factor, defined by the Herman’s orientation function, was about 0.95 with respect to the collecting direction. Subjected to a stepwise heating protocol, the crystal orientation and crystallinity in the aligned fibers at different annealing temperatures (Ta) were determined by using Fourier transform infrared spectroscopy (FTIR) and synchrotron 2D wide-angle X-ray diffraction (WAXD). Upon heating, FTIR results disclosed the desorption of residual water molecules at Ta < 100 °C and an increase in crystal orientation at elevated temperatures as-revealed by the decreasing dichroism of the crystal-related band at 1143 cm–1 until fiber melting, followed by thermal degradation at Ta ≳ 190 °C. The enhanced crystal orientation along the fiber axis at high Ta (≳100 °C) was also validated by the detailed analyses of the 2D WAXD patterns to extract the Herman’s orientation factor of the reciprocal lattice vectors of the (101/101̅) crystal planes from which the chain orientation factor in the crystalline phase was derived to dramatically increase from 0.57 at 35 °C to reach the highest value of 0.88 at 200 °C. Meanwhile, the fiber crystallinity was also increased upon heating from 31% at 35 °C to 35% at 100 °C and further up to 37% at 180 °C. The peculiar two-step enhancement in the crystal orientation and fiber crystallinity at elevated temperatures is attributed to the presence of the fibrils comprising the fiber, which are composed of highly oriented amorphous chains as well as the loosely packed amorphous chains existing in between the oriented crystalline domains. The presence of fibrils and fiber bundles (superstructures of the fibrils) was validated by atomic force microscopy as well as scanning and transmission electron microscopy. The highly oriented amorphous chains were disclosed by the anomalous meridional X-ray diffraction with a unique spacing of 2.44 Å, which is associated with the spacing along the chain axis in the closely packed and aligned chains with zigzag conformation. These extended amorphous chains may form strong intrachain and interchain hydrogen bonds, which firmly hold the fiber integrity for restricting orientation relaxation of chain molecules upon heating, therefore, to readily proceed the chain reorganization and develop oriented crystals directly at high Ta. The unique features of fibrils existing in the as-spun PVA fibers are relevant to the flow-induced phase separation of the electrospinning jet to produce phase-separated structure of strings with various widths. A discussion on the structures evolved from the liquid strings to the solid fibrils and subsequent heating effect is provided

Solution-Electrospun Poly(ethylene terephthalate) Fibers: Processing and Characterization

Electrospun poly­(ethylene terephthalate) (PET) fibers were prepared from a trifluoroacetic acid (TFA)-based solvent. Rheological studies revealed the concentration (ϕ) dependence of the specific viscosity (η_sp) to be η_sp ∼ ϕ^3.7 for PET/TFA solutions in the entangled regime. The determined entanglement concentration (ϕ_e) was higher using a lower-molecular-weight PET. To obtain bead-free fibers, the minimum concentration for the electrospinning was 0.8–1.0ϕ_e owing to the high volatility of TFA solvent, which significantly enhanced the chain network strength during jet whipping. The double-logarithmic plots of the jet (<i>d</i>_j) and fiber (<i>d</i>_f) diameters versus the zero-shear viscosity (η₀) revealed that two scaling laws existed for the present solutions, i.e., <i>d</i>_j ∼ η₀^0.06 and <i>d</i>_f ∼ η₀^0.77. The microstructural evolution of the electrospun PET fibers from stepwise annealing to crystal melting was investigated by simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements using synchrotron radiation sources. The conformer transformation from gauche to trans was monitored by in-situ Fourier transform infrared spectral measurement. In the absence of any WAXD reflection, the as-spun PET fibers possessed a SAXS scattering peak, indicating the presence of a mesomorphic phase with an interdomain distance of 6.8 nm. At annealing temperatures (<i>T</i>_a) higher than 100 °C, the mesomorphic phase gradually transformed into imperfect triclinic crystals and reached its saturation at 130 °C. Further increased <i>T</i>_a perfected the triclinic structure without altering fiber crystallinity until the initial crystal melting at 218 °C, at which a significantly increased long period was detected. When the electrospun PET fibers were embedded in an isotactic polypropylene (iPP) matrix, surface-induced crystallization occurred to develop a transcrsytalline layer of iPP monoclinic crystals at the interface

Integrative analysis of Mendelian randomization and gene expression profiles reveals a null causal relationship between adiponectin and diabetic retinopathy

Observational studies have been conducted to investigate the correlation between adiponectin and diabetic retinopathy (DR), but no consistent relationship has been established. In this study, we employed an integrative analysis that combined Mendelian randomization (MR) and bioinformatics analyses to comprehensively explore the association between DR and adiponectin, aiming to provide a unified answer of their relationship. Using the inverse-variance weighted (IVW) method, the odd ratio (OR) of developing DR per 1 mg/dL increment in genetically predicted log-transformed adiponectin concentration was estimated to be 0.949 (P = 0.557). Other robust MR methods produced consistent results, confirming the absence of a causal effect of adiponectin on DR. Additionally, the expression levels of the six adiponectin-related genes showed no significant differences among normal controls, individuals with diabetes but without DR, and those with DR Furthermore, the biological pathways enriched by these genes were not strongly relevant to DR. At both the individual gene and pathway levels, there were no overlaps between the adiponectin-related genes and the differentially expressed genes, indicating a lack of association between adiponectin and DR based on gene expression profiles. In summary, the integrative analysis, which combined MR and bioinformatics data mining, yielded compelling evidence supporting the notion that adiponectin is not a risk factor for DR.</p

2880206.mpg

Visual difference of simulation

2880207.mpg

Visual difference of simulation