Polymer Strands Research Articles

Study of polydiacetylenes and rhodamine-800 mixed film at air–water interface and onto solid support: Trace of fluorescence resonance energy transfer (FRET)

Here, we report the mixing behaviour of diacetylene monomer 10, 12-tricosadiynoic acid (TCDA) and rhodamine-800 (Rh8) using Langmuir–Blodgett (LB) technique. The presence of Rh8 affected the structures, phase behaviour as well as colorimetric properties of TCDA in the mixed films at air–water interface and onto solid support. The mixed LB films having TCDA molefraction ≥ 0.5 leads to multilayer formation, whereas multilayer formation was hardly observed for the films containing TCDA molefraction less than 0.5. It was observed that polymerization as well as phase change (blue to red) was possible only for multilayered films. Brewster angle microscopy, atomic force microscopy, and fluorescence inverted microscopy studies confirmed the formation of definite structures in the polymerized TCDA/Rh8 mixed films at air–water interface and onto solid support. Structure of TCDA polymer strands was largely influenced by the presence of Rh8 in the mixed films. Interestingly, energy transfer occurred from TCDA in red phase to Rh8 in the mixed films with TCDA molefraction greater than 0.4. Maximum energy transfer efficiency was found to be 47.3% for the mixed LB film with TCDA molefraction 0.9.

Rotation of a helical coordination polymer by mechanical grinding.

Anisotropic cell volume expansion by mechanical grinding of the solid facilitates the concerted rotation of the photo-inert helical coordination polymer, which causes the misaligned arms containing olefin functional groups in the neighbouring strands to align to undergo [2+2] cycloaddition reaction in 83% yield.

Mechanisms by Which Organic Solvent Exchange Transforms Responsive Pure Protein Hydrogels into Responsive Organogels.

Responsive pure protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of protein hydrogels with pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to protein-ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the protein secondary structure, hydration, and protein polymer morphology. Organogel proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These protein polymer morphology changes promote interprotein interactions between BSA polymer strands, which increase the effective polymer cross-link density and prevent organogel swelling as the mobile phase is exchanged back to water.

3D Printing of Supramolecular Polymers: Impact of Nanoparticles and Phase Separation on Printability.

3D printing of linear and three-arm star supramolecular polymers with attached hydrogen bonds and their nanocomposites is reported. The concept is based on hydrogen-bonded supramolecular polymers, known to form nano-sized micellar clusters. Printability is based on reversible thermal- and shear-induced dissociation of a supramolecular polymer network, which generates stable and self-supported structures after printing, as checked via melt-rheology and X-ray scattering. The linear and three-arm star poly(isobutylene)s PIB-B2 (Mn = 8500 g mol -1 ), PIB-B3 (Mn = 16 000 g mol -1 ), and linear poly(ethylene glycol)s PEG-B2 (Mn = 900 g mol-1 , 8500 g mol -1 ) are prepared and then probed by melt-rheology to adjust the viscosity to address the proper printing window. The supramolecular PIB polymers show a rubber-like behavior and are able to form self-supported 3D printed objects at room temperature and below, reaching polymer strand diameters down to 200-300 µm. Nanocomposites of PIB-B2 with silica nanoparticles (12 nm, 5-15 wt%) are generated, in turn leading to an improvement of their shape persistence. A blend of the linear polymer PIB-B2 and the three-arm star polymer PIB-B3 (ratio ≈ 3/1 mol) reaches an even higher structural stability, able to build free-standing structures.

Influence of multiple extrusions of blends made of polyethylene terephthalate and an oxygen scavenger on processing and packaging-related properties

We investigated the influence of multiple extrusions of poly-(ethylene terephthalate) (PET) blended with a polymer-based oxygen scavenger. PET and PET blended with an oxygen scavenger additive were extruded up to four times to polymer strands. They were chilled in a water bath and cut to granules. Between the extrusions, the granules were dried at (only) 60°C to avoid the oxygen scavenger losing its reactivity. The water content was up to 0.5 wt.-% and therefore up to factor 100 higher than the recommended water content for PET extrusion. For further analysis, films were extruded and bottles were stretch-blow-molded. Due to polymer degradation and the recycled PET blend viscosity being too low, this material had to be blended with virgin PET in order to be processable. We used 33 wt.-% recycled PET and 66 wt.-% virgin PET ratio. The impact of the thermomechanical stress by multiple extrusions was investigated by several test methods: analysis of the melt pressure in the extruder barrel during extrusion, intrinsic viscosity and melt flow rate, microscopy, differential scanning calorimetry, color value measurements (L*a*b* values), tensile testing, compression testing, and oxygen absorption measurements. The intrinsic viscosity reduced after four re-extrusions in a compounder from 0.82 dl/g to 0.35 dl/g for PET with scavenger and to 0.41 dl/g for pure PET. This, even though low, difference can be explained by the slightly higher PET degradation due to the oxygen scavenger. We found slightly better mechanical properties (yield stress, Young’s modulus) for pure PET films compared to PET blended with an oxygen scavenger. At up to three extrusions, there was little influence on these properties. The extruded material with 3 wt.-% oxygen scavenger additive has an oxygen absorption capacity of 9.5 mg oxygen per 1 g of granules, i.e., the scavenger additive absorbed about 300 mg oxygen per 1 g of additive. Our results are relevant for in-house recycling processes of PET with oxygen scavenger.

Cross-linking polymers with ease

By tethering two reactive diazirine groups together, chemists have created a compound that cross-links essentially any organic polymer, potentially improving properties like mechanical strength and corrosion resistance. The new cross-linking molecule also functions as a universal adhesive for polymers, making it possible to stick virtually any polymer to itself or a different material. Cross-linking polymers simply means adding bonds across polymer strands, explains Jeremy E. Wulff, a chemistry professor at the University of Victoria who led the work. Silicone bakeware, certain types of joint replacements, and many modern plumbing lines are made from cross-linked polymers. “There are plenty of methods available for cross-linking polymers, but each of them is custom designed for the particular polymer,” Wulff says. “What we tried to do was to come up with a way that we could cross-link pretty much any polymer using the same set of conditions.” To do so, Wulff’s team took a

Lipid-Assisted Polymerization of Nucleotides.

In addition to being one of the proponents of the “Lipid World hypothesis”, David Deamer, together with other colleagues, pioneered studies involving formation of RNA-like oligomers from their ‘non-activated’, prebiotically plausible monomeric moieties. In particular, the pioneering work in this regard was a publication from 2008 in Origins of Life and Evolution of Biospheres, The Journal of the International Astrobiology Society, wherein we described the formation of RNA-like oligomers from nucleoside 5’-monophosphates. In that study, we had simulated a terrestrial geothermal environment, a niche that is thought to have facilitated the prebiotic non-enzymatic synthesis of polynucleotides. We showed that a mixture of lipids and non-activated mononucleotides resulted in the formation of relatively long strands of RNA-like polymers when subjected to repeated cycles of dehydration and rehydration (DH-RH). Since 2008, terrestrial geothermal niches and DH-RH conditions have been explored in the context of several other prebiotic processes. In this article, we review the work that we and other researchers have carried out since then in this line of research, including the development of new apparatus to carry out the simulation of prebiotic terrestrial geothermal environments.

Brush-Like Polymers and Entanglements: From Linear Chains to Filaments.

Dynamics of melts and solutions of high molecular weight polymers and biopolymers is controlled by topological constraints (entanglements) imposing a sliding chain motion along an effective confining tube. For linear chains, the tube size is determined by universal packing number Pe, the number of polymer strands within a confining tube that is required for chains to entangle. Here we show that in melts of brush-like (graft) polymers, consisting of linear chain backbones with grafted side chains, Pe is not a universal number and depends on the molecular architecture. In particular, we use coarse-grained molecular dynamics simulations to demonstrate that the packing number is a nonmonotonic function of the ratio Rnsc/Rng of the size of the side chains Rnsc to that of the backbone spacer between neighboring grafting points Rng. This parameter characterizes the degree of mutual interpenetration between side chains of the same macromolecule. We show that Pe of brush-like polymers first decreases with increasing side chain grafting density in the dilute side chain regime (Rnsc < Rng), then begins to increase in the regime of overlapping side chains (Rnsc > Rng), approaching the value for linear chains in the limit of densely grafted side chains. This dependence of the packing number reflects a crossover from chain-like entanglements in systems with loosely grafted side chains (comb-like polymers) to entanglements between flexible filaments (bottlebrush-like polymers). Our simulation results are in agreement with the experimental data for the dependence of a plateau modulus on the molecular architecture of graft poly(n-butyl acrylates) and poly(norbornene)-graft-poly(lactide) melts.

Cost and environmental analyses of reinforcement alternatives for a concrete bridge

Reinforced Concrete (RC) and Prestressed Concrete (PC) structures using conventional materials in aggressive exposure conditions are susceptible to corrosion. Non-corrosive reinforcement materials such as: Glass Fiber-Reinforced Polymer (GFRP) rebars; Carbon Fiber-Reinforced Polymer (CFRP) strands; Stainless-Steel (SS); and Epoxy-coated steel (ECS) reinforcing bars, are attracting attention as more appropriate options in concrete structures. This paper addresses a Life Cycle Cost (LCC) analysis that verifies the cost performance of four different alternative reinforcement bars for the design of a demonstration FRP-RC/PC bridge in Florida, namely Halls River Bridge (HRB). The four different alternatives to be compared are namely Carbon Steel (CS), SS, FRP, and ECS, and the analysis is performed over 100-years. Additionally, a Life-Cycle Assessment (LCA) is included in the analysis to investigate the environmental credentials of the four design alternatives. Cost sensitivity analyses over specific parameters are included. The parameters analyzed are: reinforcement cost, changes in chloride concentration levels over the bridge service life, and discount rate values. Conclusions and recommendations for standard practices and design of future alternative solutions are then presented.

A new generation of star polymer: magnetic aromatic polyamides with unique microscopic flower morphology and in vitro hyperthermia of cancer therapy

In this work, a novel magnetic nanocomposite based on aromatic polyamide as a statistical star polymer was designed, characterized and studied in hyperthermia process of cancer therapy. The polymerization reaction was carried out via surface modification of magnetic nanoparticles (Fe3O4 MNPs) using polymerization process by phenylenediamine derivatives and terephthaloyl chloride. Various analytical techniques such as field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy, energy-dispersive X-ray, thermogravimetric and vibrating-sample magnetometer analyses were used to confirm the structure of the prepared nanocomposite. A unique rose flower and sphere morphologies were observed by FE-SEM images by the result of polymerization process and fabrication of the synthetic polymeric strands on the surface of the modified Fe3O4 magnetic cores. The application of this novel magnetic nanocomposite was evaluated in hyperthermia process as a potential method for cancer therapy and its exposure to an external alternating magnetic field. The highest specific absorption rate measured for 0.5 mg/mL of a sample was 191.97 w g−1, and the saturation magnetization value was 4.3 emu g−1.

Light guidance in photonic band gap guiding dual-ring light cages implemented by direct laser writing.

Efficient waveguiding inside low refractive index media is of key importance for a great variety of applications that demand strong light-matter interaction on small geometric footprints. Here, we demonstrate efficient light guidance in single-defect dual-ring light cages over millimeter distances that are integrated on silicon chips via direct laser writing. The cages consist of two rings of high aspect-ratio polymer strands (length 5mm, aspect ratio >1000) hexagonally arranged around a hollow core. Clear-core mode formation via the photonic band gap effect is observed, with the experiments showing pronounced transmission bands with fringe and polarization contrasts of >20 dB and >15 dB, respectively. Numerical simulations confirm our experiments and reveal the dual-ring arrangement to be the optimal geometry within the light cage concept. Particularly, the side-wise access to the core regions and the chip integration makes the light cage concept attractive for a great number of fields such as bioanalytics or quantum technology.

Identification of a missense variant in CLDN2 in obstructive azoospermia.

Obstructive azoospermia (OA), defined as an obstruction in any region of the male genital tract, accounts for 40% of all azoospermia cases. Of all OA cases, ~30% are thought to have a genetic origin, however, hitherto, the underlying genetic etiology of the majority of these cases remain unknown. To address this, we took a family-based whole-exome sequencing approach to identify causal variants of OA in a multiplex family with epidydimal obstruction. A novel gain-of-function missense variant in CLDN2 (c.481G>C; p.Gly161Arg) was found to co-segregate with the phenotype, consistent with the X-linked inheritance pattern observed in the pedigree. To assess the pathogenicity of this variant, the wild and mutant protein structures were modeled and their potential for strand formation in multimeric form was assessed and compared. The results showed that dimeric and tetrameric arrangements of Claudin-2 were not only reduced, but were also significantly altered by this single residue change. We, therefore, envisage that this amino acid change likely forms a polymeric discontinuous strand, which may lead to the disruption of tight junctions among epithelial cells. This missense variant is thus likely to be responsible for the disruption of the blood-epididymis barrier, causing dislodged epithelial cells to clog the genital tract, hence causing OA. This study not only sheds light on the underlying pathobiology of OA, but also provides a basis for more efficient diagnosis in the clinical setting.

On the use of the rotation minimizing frame for variational systems with Euclidean symmetry

AbstractWe study variational systems for space curves, for which the Lagrangian or action principle has a Euclidean symmetry, using the Rotation Minimizing frame, also known as the Normal, Parallel, or Bishop frame. Such systems have previously been studied using the Frenet–Serret frame. However, the Rotation Minimizing frame has many advantages, and can be used to study a wider class of examples.We achieve our results by extending the powerful symbolic invariant calculus for Lie group–based moving frames, to the Rotation Minimizing frame case. To date, the invariant calculus has been developed for frames defined by algebraic equations. By contrast, the Rotation Minimizing frame is defined by a differential equation.In this paper, we derive the recurrence formulae for the symbolic invariant differentiation of the symbolic invariants. We then derive the syzygy operator needed to obtain Noether's conservation laws as well as the Euler–Lagrange equations directly in terms of the invariants, for variational problems with a Euclidean symmetry. We show how to use the six Noether laws to ease the integration problem for the minimizing curve, once the Euler–Lagrange equations have been solved for the generating differential invariants. Our applications include variational problems used in the study of strands of proteins, nucleid acids, and polymers.

Оптимизационно-аналитическое моделирование технологических режимов производства микрокремнезема для изоляционных панелей типа VIP

Рассмотрены два способа синтеза мелкозернистого микрокремнезёма из диатомитовых пород, пригодного для создания вакуумных теплоизоляционных панелей с теплопроводностью 0,002–0,02 Вт/м2к. Методом анализа детерминированных моделей переноса тепла в зернистых системах определены основные индикаторы, определя-ющие зависимость теплопроводности от физических и топологических свойств частиц диоксида кремния. Для оценки и регулирования теплопроводности зернистых систем, к основным индикаторам можно отнести: m2 – по-ристость микроструктуры; ρк – плотность кластеров, фор-мирующих микроструктуру; εпр – характеристику степени (диссипации энергии излучения) черноты частиц напол-нителя; di – диаметр пор на i-ом масштабном уровне; λТ , λГ – теплопроводность твёрдой и газовой фазы системы; a – коэффициент аккомодации; N – координационное число; D – фрактальную размерность, характеризующую топологические особенности строения частиц, агрегатов, кластеров.&#x0D; Проведён экспериментальный анализ свойств синтези­рованного микрокремнезёма. В результате проведённых исследований установлено, что оптимальные свойства дисперсного микрокремнезёма, синтезированного из опал-кристобалитовых биоморфных пород (диатомита Атемарского месторождения) путём осаждения оксида кремния из коллоидного раствора, получены при реали­зации второго способа производства. В процессе синтеза получен дисперсный микрокремнезём, представленный минералом опал, построенным из полимеризованных ни­тей аморфного кремнезёма, которые свёрнуты в глобулы, шаровые кластеры диаметром в диапазоне 2-40 нм. Топо­логия поверхности глобул характеризуется фрактальной размерностью D = 2,32; 2,64, что обеспечивает снижение значений коэффициента аккомодации и соответственно теплопроводности. Ассоциации шаровидных кластеров из частиц наноразмерного уровня формируют масштабно-ин­вариантную поровую структуру, обеспечивающую низкую теплопроводность[1].&#x0D; [1] Работа выполнена при финансовой поддержке гранта РФФИ N 18-48- 130001/18 «Оптимизационное моделирование свойств теплоизоляционных функционально-градиентных изделий на основе минеральных порошков оксида кремния, синтезированного из природного диатомита».

Fluorescence anisotropy imaging of a polydiacetylene photopolymer film

UV-illumination of phase-separated surfactant films prepared from mixtures of photopolymerizable 10,12-pentacosadiynoic acid and perfluorotetradecanoic acid results in the formation of fluorescent polydiacetylene fibers and aggregates. In this work, the orientation of polymer strands that comprise the resulting photopolymer structures has been probed using fluorescence anisotropy imaging in combination with defocused single-molecule fluorescence imaging. Imaging experiments indicate the presence of significant fiber-to-fiber heterogeneity, as well as anisotropy within each fiber (or aggregate), with both of these properties changing as a function of film preparation conditions. This anisotropy can be attributed to various alignments of the constituent polymer strands that comprise the larger fibers and aggregates. Intriguingly, when using defocused imaging, fiber images consisted of a series of discrete “doughnut” fluorescence emission patterns, which exhibited intermittent on–off blinking behavior; both of these properties are characteristic of individual emission transition dipoles (single molecules). Further, all of the individual emission transition dipoles had a uniform orientation with respect to the axis of the fiber, indicating a common orientation of discrete emitters in the larger polymer fiber. The implications of these results for future studies of the electronic properties of conjugated polymers in larger macroscopic systems are noted.

3D printing of high density polyethylene by fused filament fabrication

Polyolefin thermoplastics like high density polyethylene (HDPE) are the leaders in terms of world-scale plastics’ production, environmentally benign polymerization processes, recycling, and sustainability. However, additive manufacturing of HDPE by means of fused deposition modeling (FDM) also known as fused filament fabrication (FFF) has been problematic owing to its massive shrinkage, voiding and warpage problems accompanied by its poor adhesion to common build plates and to extruded HDPE strands. Herein we overcome these problems and improve Young’s modulus, tensile strength and surface quality of 3D printed HDPE by varying 3D printing parameters like temperature and diameter of the nozzle, extrusion rate, build plate temperature, and build plate material. Both nozzle diameter and printing speed affect surface quality but do not impair mechanical properties. Particularly, an extrusion rate gradient prevents void formation. For the first time additive manufactured HDPE and injection-molded HDPE exhibit similar mechanical properties with exception of elongation at break. Excellent fusion of the extruded polymer strands and the absence of anisotropy are achieved, as verified by microscopic imaging and measuring the tensile strength parallel and perpendicular to the 3D printing direction.

Understanding the catch-bond kinetics of biomolecules on a\xa0one-dimensional energy landscape

In spite of extensive investigations, the force-dependent unfolding/rupturing rate k(F) of biomolecules still remains poorly understood. A famous example is the frequently observed switch from catch-bond behaviour, where force anti-intuitively decreases k(F), to slip-bond behaviour where increasing force accelerates k(F). A common consensus in the field is that the catch-to-slip switch behaviour cannot be explained in a one-dimensional energy landscape, while this view is mainly built upon assuming that force monotonically affects k(F) along each available transition pathway. In this work, by applying Kramers kinetic rate theory to a model system where the transition starts from a single native state through a pathway involving sequential peeling of a polymer strand until reaching the transition state, we show the catch-to-slip switch behaviour can be understood in a one-dimensional energy landscape by considering the structural-elastic properties of molecules during transition. Thus, this work deepens our understanding of the force-dependent unfolding/rupturing kinetics of molecules/molecular complexes.

Composite strands for prestressed concrete: State-of-the-practice and experimental investigation into mild prestressing with GFRP

An overview of available solutions and historic experiences in the state-of-the-practice of prestressing technologies with non-conventional tendons is presented to determine whether mild prestressing with Glass Fiber Reinforced Polymer (GFRP) strands may represent a solution for some of the existing challenges. The experimental portion of this project explores the potential of GFRP strands coupled with traditional steel anchors as an efficient, easy-to-deploy, and non-corrosive pre-tensioning solution in applications that require limited levels of prestress. The strands are composed of seven twisted wires and have a nominal diameter of 15.2 mm. This study on GFRP strand prototypes covers: a) mechanical and geometrical characterization; b) jacking strength of the coupled strand-anchor under instantaneous and sustained load; c) load loss during anchor setting using various pulling techniques; and, d) some flexural properties and coilability. Results should only be considered indicative of the potential of the technology given also the limited material availability. Experimental outcomes are evaluated with reference to information available in archival literature with particular reference to GFRP reinforcing bars.

Life-Cycle Cost and Life-Cycle Assessment Analysis at the Design Stage of a Fiber-Reinforced Polymer-Reinforced Concrete Bridge in Florida

Abstract To support and promote the deployment of innovative technologies in infrastructure, it is fundamental to quantify their implications in terms of both economic and environmental impacts. Glass Fiber-Reinforced Polymer (GFRP) bars and Carbon Fiber-Reinforced Polymer (CFRP) strands are validated corrosion-resistant solutions for Reinforced Concrete (RC) and Prestressed Concrete (PC) structures. Studies on the performance of Fiber-Reinforced Polymer (FRP) reinforcement in seawater and salt-contaminated concrete have been conducted and show that the technology is a viable solution. Nevertheless, the economic and environmental implications of FRP-RC/PC deployment have not been fully investigated. This article deals with the Life-Cycle Cost (LCC) and Life-Cycle Assessment (LCA) analyses of an FRP-RC/PC bridge in Florida. The bridge is designed to be entirely reinforced with FRP bars and strands and does not include any Carbon Steel (CS) reinforcement. Furthermore, the deployment of seawater concrete in some of the elements of the bridge is considered. LCC and LCA analyses are performed at the design stage. Data regarding equipment, labor rates, consumables, fuel consumption, and disposal were collected during the construction phase, and the analysis was refined accordingly. The FRP-RC/PC bridge design is compared with a traditional CS-RC/PC alternative. Salient differences are discussed to determine the least-impactful solution from both an economic and environmental perspective.

Immunomodulation: Immunostimulatory Effects Triggered by Self‐Assembled Microspheres with Tandem Repeats of Polymerized RNA Strands (Adv. Healthcare Mater. 4/2019)

Immunomodulation: Immunostimulatory Effects Triggered by Self‐Assembled Microspheres with Tandem Repeats of Polymerized RNA Strands (Adv. Healthcare Mater. 4/2019)