Solid Polymer Matrix Research Articles

Fluorescence Enhancement of Nonemissive Monodeprotonated Luteolin in a Poly(vinyl alcohol) Film.

Solid polymer matrixes can modulate the electronic states of embedded chromophores and have been widely used in flexible optoelectronic and optical materials. Luteolin is one of the most common natural flavonoids, and its neutral and monodeprotonated forms are nonemissive in aqueous solution induced by ultrafast excited-state proton transfer (ESPT) followed by nonradiative relaxation. In this study, we have incorporated luteolin into poly(vinyl alcohol) (PVA) films and studied their fluorescence behaviors. Neutral and one monodeprotonated luteolin coexist in the PVA film. Weak steady-state fluorescence of neutral luteolin peaking at about 440 nm is observed for the first time. In addition, the monodeprotonated luteolin in PVA film exhibits obvious fluorescence peaking at 500 nm, with a fluorescence quantum yield of as high as 0.4 and a fluorescence lifetime of as long as 2.4 ns. Time-dependent density functional theory calculations have determined that the ESPT of neutral luteolin is barrierless but that of monodeprotonated luteolin needs to surmount a barrier, explaining their distinct emission properties. These results indicate the modulation ability of the PVA film in both ground-state deprotonation and ESPT, broadening the application areas of the solid polymer matrix.

Pfadunabhängiges mit sichtbarem Licht adressierbares orthogonales Photoschalten für Anwendungen in multi‐photochromomen Polymeren und molekularen Computern

AbstractSynthetische molekulare Photoschalter sind als hochpräzise Werkzeuge zur Einführung von Lichtadressierbarkeit auf kleinster Ebene in den Mittelpunkt der Forschung gerückt. Heute sind sie in allen Bereichen der angewandten Chemie zu finden, sei es in der Materialforschung, chemischen Biologie, Katalyse oder Nanotechnologie. Für einen nächsten Schritt in der Anwendbarkeit ist vollständig orthogonales Photoschalten besonders wünschenswert, aber bis heute ist eine solche unabhängige Adressierbarkeit verschiedener Photoschalter eine große Herausforderung. In dieser Arbeit präsentieren wir das erste Beispiel für ein vollständig durch sichtbares Licht adressierbares und pfadunabhängiges orthogonales Photoschalten. Durch die Kombination von zwei kürzlich entwickelten indigoiden Photoschaltern – ein peri‐Anthracenthioindigo und ein auf Rhodanin‐basiertes Chromophor – wird ein Schaltsystem mit vier Zuständen geschaffen, wobei jeder Zustand in hoher Ausbeute völlig unabhängig und ausnahmslos mit sichtbarem Licht angesteuert werden kann. Die vier Zustände führen zu vier verschiedenen Farben, die auf eine feste Polymermatrix übertragen werden können, wodurch ein vielseitiges photochromes Material mit multiplen Zuständen entsteht. Darüber hinaus wird die Kombination mit einem Fluoreszenzfarbstoff als dritter Komponente gezeigt, was die Anwendbarkeit dieses orthogonalen Photoschaltersystems in der molekularen Logik und Informationsverarbeitung ermöglicht.

Path-Independent All-Visible Orthogonal Photoswitching for Applications in Multi-Photochromic Polymers and Molecular Computing.

Synthetic molecular photoswitches have taken center stage as high-precision tools to introduce light-responsiveness at the smallest scales. Today they are found in all areas of applied chemistry, covering materials research, chemical biology, catalysis, or nanotechnology. For a next step of applicability truly orthogonal photoswitching is highly desirable but to date such independent addressability of different photoswitches remains highly challenging. Herein we present the first example of all-visible, all-light responsive, and path- independent orthogonal photoswitching. By combining two recently developed indigoid photoswitches - peri-anthracenethioindigo and a rhodanine-based chromophore - a four-state system is established and each state can be accessed in high yields completely independently and also with visible light irradiation only. The four states give rise to four different colors, which can be transferred to a solid polymer matrix to yield a versatile multi-state photochromic material. Further, combination with a fluorescent dye as a third component is possible, demonstrating the applicability of this orthogonal photoswitching system in all-photonic molecular logic behavior and information processing.

Investigation of the Influence of Copovidone Properties and Hot-Melt Extrusion Process on Level of Impurities, In Vitro Release, and Stability of an Amorphous Solid Dispersion Product.

Hot-melt extrusion (HME) is a widely used method for creating amorphous solid dispersions (ASDs) of poorly soluble drug substances, where the drug is molecularly dispersed in a solid polymer matrix. This study examines the impact of three different copovidone excipients, their reactive impurity levels, HME barrel temperature, and the distribution of colloidal silicon dioxide (SiO2) on impurity levels, stability, and drug release of ASDs and their tablets. Initial peroxide levels were higher in Kollidon VA 64 (KVA64) and Plasdone S630 (PS630) compared to Plasdone S630 Ultra (PS630U), leading to greater oxidative degradation of the drug in fresh ASD tablets. However, stability testing (50 °C, closed container, 50 °C/30% RH, open conditions) showed lower oxidative degradation impurities in ASD tablets prepared at higher barrel temperatures, likely due to greater peroxide degradation. Plasdone S630 is suitable for ASDs with drugs prone to oxidative degradation, while standard purity grades may benefit drugs susceptible to free radical degradation, as they generate fewer free radicals post-HME. ASD tablets exhibited greater physical stability than milled extrudate samples, likely due to reduced exposure to stability conditions within the tablet matrix. Including SiO2 in the extrudate composition resulted in greater physical stability of the ASD system in the tablet; however, it negatively affected chemical stability, promoting greater oxidative degradation and hydroxylation of the drug substance. No impact of the distribution of SiO2 on drug release was observed. The study also confirmed the congruent release of copovidone, the drug substance, and Tween 80 using flow NMR coupled with in-line UV/vis. This research highlights the critical roles of peroxide levels and SiO2 in influencing the dissolution and physical and chemical stability of ASDs. The findings provide valuable insights for developing stable and effective pharmaceutical formulations, emphasizing the importance of controlling reactive impurities and excipient characteristics in ASD products prepared by using HME.

A Binary Ionogel Electrolyte for the Realization of an All Solid-State Electrical Double-Layer Capacitor Performing at Low Temperature.

Over the last years, solid-state electrolytes made of an ionic liquid (IL) confined in a solid (inorganic or polymer) matrix, also known as ionogels, have been proposed to solve the leakage problems occurring at high temperatures in classical electrical double-layer capacitors (EDLCs) with an organic electrolyte, and thereof improve the safety. However, making ionogel-based EDLCs perform with reasonable power at low temperature is still a major challenge due to the high melting point of the confined IL. To overcome these limitations, the present contribution discloses ionogel films prepared in a totally oxygen/moisture-free atmosphere by encapsulating 70 wt % of an equimolar mixture of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and 1-ethyl-3-methylimidazolium tetrafluoroborate - [EMIm][BF4]0.5[FSI]0.5 - into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) network. The further called "binary ionogel" films demonstrated a high flexibility and a good ionic conductivity of 5.8 mS cm-1 at 20 °C. Contrary to the ionogels prepared from either [EMIm][FSI] or [EMIm][BF4], displaying melting at Tm=-16 °C and -7 °C, respectively, the crystallization of confined [EMIm][BF4]0.5[FSI]0.5 is quenched in the binary ionogel, which shows only a glass transition at -101 °C. This quenching enables an increased ionicity and ionic diffusion at the interface with the PVdF host network, leading the binary ionogel membrane to display higher ionic conductivity below -20 °C than the parent binary [EMIm][BF4]0.5[FSI]0.5 liquid. Laminate EDLCs were built with a 100 μm thick binary ionogel separator and electrodes made from a hierarchical micro-/mesoporous MgO-templated carbon containing a reasonable proportion of mesopores to enhance the mass transport of ions, especially at low temperature where the ionic diffusion noticeably decreases. The EDLCs operated up to 3.0 V with ideal EDL characteristics from -40 °C to room temperature. Their output specific energy under a discharge power of 1 kW kg-1 is ca. 4 times larger than with a cell implementing the same carbon electrodes together with the binary [EMIm][BF4]0.5[FSI]0.5 liquid. Hence, this binary ionogel electrolyte concept paves the road for developing safe and flexible solid-state energy storage devices operating at subambient temperatures in extreme environments.

AN INFORMATION-THEORETIC FILTER SINGLE-STEP SEQUENTIAL MONTE CARLO METHOD IN PRACTICE. AN EXPERIMENTAL CASE STUDY FOR THE PARTICLE SIZE DISTRIBUTION ESTIMATION

In this article, we implement an extended version of a Monte Carlo methodology making use of a Sampling/Mapping/Filtering (SMF) strategy, to estimate the Particle Size Distribution (PSD) of a particle system. The methodological difference is shown by the use of a filter, based on information theory, which computes a cut-off level using an optimization scheme following the principle of relevant information (PRI). The practical application of the full strategy considers the fusion between scanning electron microscope (SEM) data and static light scattering (SLS) measurements. The two models are utilized, assuming spherical particles represented as hard spheres: the so-called local monodisperse approximation (LMA) and the Vrij’s finite mixtures model (VFMM). We analyze the resulting estimates for different configurations of both prior information and SLS models, where final results are compared to those obtained in previous studies for a polymeric particle system embedded in a solid polymer matrix.

Quasi-Solid-State Electrolyte Induced by Metallic MoS2 for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are a promising high-energy-density technology for next-generation energy storage but suffer from an inadequate lifespan. The poor cycle life of Li-S batteries stems from their commonly adopted catholyte-mediated operating mechanism, where the shuttling of dissolved polysulfides results in active material loss on the sulfur cathode and surface corrosion on the lithium anode. Here, we report in situ formation of a quasi-solid-state electrolyte (QSSE) on the metallic 1T phase molybdenum disulfide (MoS2) host that extends the lifetime of Li-S batteries. We find that the metallic 1T phase MoS2 host is able to initiate the ring-opening polymerization of 1,3-dioxolane (DOL), forming an integrated QSSE inside batteries. Nuclear magnetic resonance analysis reveals that the QSSE consists of ∼13% liquid DOL in a solid polymer matrix. The QSSE efficiently mediates sulfur redox reactions through dissolution-conversion chemistry while simultaneously suppressing polysulfide shuttling. Therefore, while ensuring high sulfur utilization, it avoids degradation of both electrodes, as well as the concomitant electrolyte consumption, leading to enhanced cycling stability. Under a practical lean electrolyte condition (electrolyte-to-sulfur ratio = 2 μL mg-1), Li-S pouch cell batteries with the QSSE demonstrate a capacity retention of 80.7% after 200 cycles, much superior to conventional liquid electrolyte cells that fail within 70 cycles. The QSSE also enables Li-S pouch cell batteries to operate across a wider temperature range (5 to 45 °C), together with improved safety under mechanical damage.

Sensitized Triplet-Triplet Annihilation in Nanostructured Polymeric Scintillators Allows for Pulse Shape Discrimination.

Scintillating materials emit light when exposed to ionizing radiation or particles and are used for the detection of nuclear threats, medical imaging, high-energy physics, and other usages. For some of these applications, it is vital to distinguish neutrons and charged particles from γ-rays. This is achievable by pulse shape discrimination (PSD), a time-gated technique, which exploits that the scintillation kinetics can depend on the nature of the incident radiation. However, it proves difficult to realize efficient PSD with plastic scintillators, which have several advantages over liquid or crystalline scintillating materials, including mechanical robustness and shapeability. It is shown here that sensitive and rapid PSD is possible with nanostructured polymer scintillators that consist of a solid polymer matrix and liquid nanodomains in which an organic dye capable of triplet-triplet annihilation (TTA) is dissolved. The liquid nature of the nanodomains renders TTA highly efficient so that delayed fluorescence can occur at low energy density. The nanostructured polymer scintillators allow discriminating α particles, neutrons, and γ-rays with a time response that is better than that of commercial scintillators. Exploiting that the liquid nanodomains can facilitate energy transfer processes otherwise difficult to realize in solid polymers, an auxiliary triplet sensitizer is incorporated. This approach further increases the scintillator's sensitivity toward α particles and neutrons and other high-energy processes where localized interactions are involved.

Architected flexible syntactic foams: Additive manufacturing and reinforcing particle driven matrix segregation

Polymer syntactic foams are transforming materials that will shape the future of next-generation aerospace and marine structures. When manufactured using traditional processes, like compression molding, syntactic foams consist of a solid continuous polymer matrix reinforced with stiff hollow particles. However, polymer matrix segregation can be achieved during the selective laser sintering process with thermoplastic polyurethane (TPU). It is uncertain what role hollow particles play in forming this matrix segregation and its impact on the corresponding mechanical properties of syntactic foams. We show that the size of the hollow particles controls the internal microscale morphology of matrix segregation, leading to counter-intuitive macroscale mechanical responses. Particles with diameters greater than the gaps between the cell walls of the segregated matrix get lodged between and in the walls, bridging the gaps in the segregated matrix and increasing the stiffness of syntactic foams. In contrast, particles with smaller diameters with higher particle crushing strength get lodged only inside the cell walls of the segregated matrix, resulting in higher densification stresses (energy absorption). We show that stiffness and densification can be tuned while enabling lightweight syntactic foams. These novel discoveries will aid in facilitating functional and lightweight syntactic foams for cores in sandwich structures.

Controlling the Potential of Affordable Quasi‐Solid Composite Gel Polymer Electrolytes for High‐Voltage Lithium‐Ion Batteries

AbstractThis study focuses on the development of a composite gel polymer electrolyte membrane (CGPEM) as a solution to address safety concerns arising from the reactivity of lithium metal and the formation of dendrites. The CGPEM integrates a solid polymer matrix, solid‐electrolyte LSiPS (Li10SiP2S12), with a plasticizer that countering the performance decline caused by sulfide solid electrolyte (SSE) interactions with the cathode. Poly ethylene oxide (PEO) emerges as a promising polymer matrix due to its flexibility, cost‐effectiveness, eco‐friendliness, solvability for Li‐salt, mechanical processing adaptability, adhesive strength, and ionic conductivity. Conductivity and processability of CGPEM were optimized through meticulous adjustment of liquid plasticizer concentration. The CGPEM′s chemical and electrochemical stability were systematically investigated using in‐situ electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRTs). A lithium metal battery is constructed against a high voltage cathode and newly developed CGPEM. Impressively, the cell exhibited outstanding performance, maintaining a discharge capacity of around 146.22 mAh/g after 200 cycles, retaining 86.38 % of its initial capacity. The formation of a LiF‐rich interface layer near the lithium surface, a vital element in curbing CGPE degradation and dendritic growth, resulted in enhanced overall cell performance.

Novel Radiochromic Elastomer Dosimeter Based on the Self-Sensitizing Effect of Disulfide Bonds.

γ-Irradiation is a kind of high-energy ionizing ray, which has widespread applications in material, food, and medical industries as well as in the environment. Since this irradiation is invisible, quantitatively monitoring its exposure doses is crucial to irradiated targets. As a type of dosimeter, radiochromic dosimeters can detect γ-irradiation by color changing, and its strategy to realize the radiochromic behavior basically relies on active radicals from radiolysis of an external environmental medium. However, the primary problem of this external environment-mediated sensitization strategy is that it complicates the components of dosimeters. Herein, we present a novel type of self-sensitizing radiochromic poly(urethane-urea) elastomers (PUUEs), where disulfide bonds, serving as radiation-responsive and sensitizing units, are introduced. This is the first attempt to utilize radicals generated from radiolysis of weak bonds in a solid polymer matrix to sensitize color change of dye-doped radiochromic dosimeters. Moreover, it is intriguing that the simultaneously introduced aryl hydrazone bond endows dosimeters with excellent color retention and maintains the Δa* value of 72.9% even after 1 month on the basis of the as-irradiated specimen. Besides, the metathesis of disulfide bonds not only endows dosimeters with better self-healing capability, but also accelerates the postcuring behavior and hydrogen bond reconfiguration, resulting in improved mechanical performance.

Formulation and Characterization of Solid Tablets Using Solid Dispersion Matrix Technology: A Systematic Literature Review

The formulation of solid tablet preparations using solid dispersion matrix technology involves the selection of active ingredients, polymer matrices, fillers or enhancers, and lubricants. The active ingredient is the drug component that provides a therapeutic effect to the patient. This study aimed to conduct a systematic review study to explore the formulation and characterization of solid tablet dosage forms using solid dispersion matrix technology. The literature search process was carried out on various databases (PubMed, Web of Sciences, EMBASE, Cochrane Libraries, and Google Scholar) regarding the formulation and characterization of solid tablet preparations using solid dispersion matrix technology. This study follows the preferred reporting items for systematic reviews and meta-analysis (PRISMA) recommendations. Solid dispersion matrix technology is one of the approaches used in the formulation of pharmaceutical preparations, especially solid tablets, to achieve controlled and effective drug release. In this technology, the drug is dispersed homogeneously in a solid polymeric matrix, which acts as a binding agent. The basic principle of solid dispersion matrix technology is that the drug is delivered via gradual release from the polymer matrix.

Development of a fluorescent PMMA-based polymer material through in-situ incorporation of curcuma extract

In the present work, the in situ incorporation of curcumin was carried out in a polymer matrix through bulk polymerization to improve its photostability. It was found that extraction of curcumin from turmeric extract by the precursor monomer methyl methacrylate (MMA) can be performed immediately before the polymerization in order to reduce the degradation of the fluorescent species by the initiator system, although the obtained results also showed that incorporation of the turmeric extract into monomer can retard the polymerization kinetics. Despite that, the fluorescence properties of curcumin were preserved after incorporation in a solid polymeric matrix, which also enhanced the fluorophore photostability, avoiding the rapid degradation of the fluorophore observed when it is dispersed in solvents. Furthermore, it was also observed that addition of acrylic acid (AA) as a comonomer enhanced the photochemical stability of the turmeric extract incorporated into the polymer matrix and promoted the bathochromic effect, when compared to the spectroscopic behavior of the extract obtained from MMA, both in solution and solid state. It was possible to optimize the synthesis condition with help of a standard factorial experimental design, allowing the simultaneous attainment of high monomer conversion and fluorescence properties of the obtained material.

Multicore-based ferrofluids in zero field: initial magnetic susceptibility and self-assembly mechanisms.

The necessity to improve magnetic building blocks in magnetic nano-structured soft materials stems from a fascinating potential these materials have in bio-medical applications and nanofluidics. Along with practical reasons, the interplay of magnetic and steric interactions on one hand, and entropy, on the other, makes magnetic soft matter fundamentally challenging. Recently, in order to tailor magnetic response of the magnetic particle suspensions, the idea arose to replace standard single-core nanoparticles with nano-sized clusters of single-domain nanoparticles (grains) rigidly bound together by solid polymer matrix - multicore magnetic nanoparticles (MMNPs). To pursue this idea, a profound understanding of the MMNP interactions and self-assembly is required. In this work we present a computational study of the MMNP suspensions and elucidate their self-assembly and magnetic susceptibility. We show that depending on the magnetic moment of individual grains the suspensions exhibit qualitatively distinct regimes. Firstly, if the grains are moderately interacting, they contribute to a significant decrease of the remanent magnetisation of MMNPs and as such to a decrease of the magnetic susceptibility, this way confirming previous findings. If the grains are strongly interacting, instead, they serve as anchor points and support formation of grain clusters that span through several MMNPs, leading to MMNP cluster formation and a drastic increase of the initial magnetic response. Both the topology of the clusters and their size distribution in MMNP suspensions is found to be notably different from those formed in conventional magnetic fluids or magnetorheological suspensions.

Sulfonate betaine modifiedPVDF/SiO2composite electrolyte for solid state lithium ion battery

AbstractHigh thermal stability, mechanical property and electrochemical stability of polyvinylidene fluorid (PVDF) make it a promising solid electrolyte polymer matrix. However, it also faces some challenges such as low ionic conductivity, high crystallinity degree and the absence of reactive groups. Herein, PVDF powder was modified by chemical grafting amphiprotic sulfonate betaine (SB) for solid electrolyte (SB‐PVDF) with high ionic conductivity and chemical stability. Furthermore, to improve the mechanical property and reduce the crystallinity degree of SB‐PVDF, 3%, 6% and 9% SiO2nanospheres were also incorporated into SB‐PVDF, and the resultant composite polymer solid electrolytes were marked as 3% SiO2/SB‐PVDF, 6% SiO2/SB‐PVDF, 9% SiO2/SB‐PVDF. The results showed that 6% SiO2/SB‐PVDF membrane exhibited the best overall performances, possibly due to the synergistic effect of amphiprotic SB modification and uniform dispersion of SiO2filler in PVDF matrix. For example, the solid‐state battery Li//6%SiO2/SB‐PVDF//LiFePO4delivered the initial discharge capacity of 153.0 mAh/g at 0.2 C and the reversible discharge capacity of 124.4 mAh/g at 1.0 C with the capacity retention rate of 93.8%, indicating high feasibility for solid‐state lithium ion battery.

Selectively Tunable Luminescence of Perovskite Nanocrystals Embedded in Polymer Matrix Allows Direct Laser Patterning

AbstractCesium lead halide perovskite nanocrystals (NCs) have gained enormous attention as promising light‐emitting and light‐converting materials. Most of their applications require embedding NCs in various matrices, which is a challenging task due to their low stability, especially in the case of red‐emitting CsPbI3 NCs. In this work, a new approach is proposed allowing the formation of red‐emitting perovskite NCs by anion exchange induced directly inside a solid polymer matrix using green‐emitting CsPbBr3 NCs as templates and iodododecane as an iodine source. Moreover, a simple and efficient route to photo‐assisted termination of the anion exchange reaction in the polymer composite after reaching desired optical properties is demonstrated. The findings allow the authors to pattern a thin composite film with an ultrashort UV laser resulting in a selective generation of green‐ and red‐emitting features with a 15 µm resolution.

A Review on Green Polymer Binder-based Electrodes and Electrolytes for All Solid-State Li-ion batteries

It is not an exaggerated fact that the whole world relies on the energy storage systems such as Li-ion batteries (LIBs). Li-ion batteries have been widely used in electric vehicles and electronic devices such as laptops, mobile phones, etc. However, the commercial Li-ion batteries have many issues associated with safety and durability including the thermal runaway and the use of toxic solvents during the construction of batteries. In order to highlight the recent developments towards addressing these issues, we have summarized the major impact in replacing the toxic solvents, which are conventionally used to dissolve the binder in the commercial Li-ion batteries, with the aqueous-based binder called green binders. Further, an emphasis has been given on the importance of shifting from flammable liquid electrolytes to non-flammable solid-electrolytes, which essentially suppress the issues such as leakage problems, mechanical failure and fire explosives in LIBs. Even though considerable works have been performed on the development of green-based solid polymer electrolytes, it still needs more effort to overcome the obstacles towards improving the properties of the solid-polymer matrix, which is their low ionic conductivity at low temperatures. Further research in this direction has been highlighted in this review, which involves improving the interfacial contacts in the solid-polymer electrolytes, where the interfacial interaction and conductive mechanisms are yet to be clearly investigated to have the solid-electrolytes with improved electrochemical property.

One-pot synthesis of concentration and excitation dual-dependency truly full-color photoluminescence carbon dots

The paper describes a kind of truly full-color photoluminescence (PL) CDs. The CDs were prepared by using one-pot hydrothermally heating citric acid and formamide at 200 °C for 2 h. The CDs have three fluorescent centers at blue, green, and red light region. Their color was regulated through two means, including changing excitation wavelengths or CDs concentrations. The emission maxima changed from blue to red with the increase of excitation wavelengths or CDs concentrations. The full-color PL behavior of the CDs was inherited and conserved in the solid polymer matrix, giving multicolor CDs/polymer films and light emitting diodes (LEDs). White-light LED (WLED) with the CIE coordinate approaching to (0.31, 0.32) were also achieved.

Laser-Induced Microstructuring of Polymers in Gaseous, Liquid and Supercritical Media.

New results are presented for laser formation—in particular, the “drawing” of microstructures in polymer films using continuous-wave (CW) laser radiation λ = 405 nm with an intensity of 0.8–3.7 kW/cm2. The laser drawing was carried out in the polymer system poly-2,2′-p-oxydiphenylene-5,5′-bis-benzimidazole (OPBI), which consists of two phases: a solid polymer matrix with formic acid (HCOOH) dissolved in it. The formation of microstructures, including the stage of foaming, was carried out in three media: air, water and a supercritical carbon dioxide medium containing dissolved molecules of the silver precursor Ag(hfac)COD. The morphological features of foam-like track structures formed in the near-surface layer of the polymer films by laser “drawing” are considered. A model of processes is presented that explains the appearance of periodic structures. The key point of this model is that it considers the participation of the photoinduced mechanism of explosive boiling of formic acid molecules dissolved in the polymer matrix. Using Raman spectroscopy, spectra were obtained and interpreted, which relate to different stages in the formation of microstructures in OPBI films. The effects associated with the peculiarities of luminescent microstructures on the surfaces of glasses in close contact with polymer films during laser “painting” in the air have been studied.

The Effect of Geometry on the Flexural Properties of Cellular Structures Reinforced with Natural Fibres: Statistical Approach

ABSTRACT New concepts of honeycomb structures were developed. These new cellular structures, known as honeycomb (HN), reentrant honeycomb (RE-HN) and silicomb (Silico) are made from new solid polymer matrix reinforced with natural fibers resulting in biocomposites that are innovative and sustainable for a variety of engineering applications. In order to elaborate these biocomposites structures, PLA (Polylactic Acid) molds were made using a 3D printer. Then, the flexural behavior of honeycomb, reentrant and silicomb structures reinforced by various natural fibers like flax, jute and sisal using various fibers volume fractions of 10, 20 and 30% was investigated. Taguchi plan (L9) experiments were conducted to determine how each factor affects bending stress, displacement and flexural modulus. Bending stress values varied from 24.66 to 36.53 MPa while flexural modulus values from 3.58 to 17.17 GPa. Moreover, it was found that fiber volume fraction had significant influence on flexural properties and on fracture resistance. The silicomb structure has a higher load capacity than the honeycomb and reentrant structures. In fact, this type of biocomposite structure with low density and good mechanical properties are intended for many packaging and furnishing applications with a lower impact on the environment.