Low Glass Transition Temperature Research Articles

A Novel Preparation of Special-Shaped Phosphors-in-Glass by Gel Casting with Isobam for High-Power WLEDs Lighting.

Phosphors-in-glass (PiGs) regarded as a promising phosphor-converter for white light emitting diodes (WLEDs) is being researched widely. However, there are few reports on the effect of changing the shape of PiGs on the color rendering index (CRI) and heat dissipation of WLEDs. In this paper, gel casting with Isobam was first attempted in preparing special-shaped PiGs successfully. It exhibited that 76 wt.% was the optimum solid content based on the rheological properties of slurry and the shrinkage of green bodies. The sintering rate should be kept at a low speed and glass transition temperature (Tg) of glass powders must be higher than sublimation temperatures (Ts) of APS and Isobam. The CRI of PiGs was increased by about 27% after changing the shape of PiGs from cylinder to dome. Most importantly, operating temperature also reduced effectively the increase of the surface area of PiGs. Therefore, changing the shape of PiGs by gel casting with Isobam is a creative way for high-power WLEDs lighting.

An acrylate-based quasi-solid polymer electrolyte incorporating a novel dinitrile poly(ethylene glycol) plasticizer for lithium-ion batteries

The performance of solid polymer electrolytes is characterized by lower ionic conductivity than conventional liquid electrolytes but provides advantages in terms of operational safety. A quasi-solid polymer electrolyte (QSPE) based on a new plasticizer 4,7,10,13-tetraoxahexadecane-1,16-dinitrile (bCN-PEG4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) incorporated into a polyacrylates matrix was successfully prepared via UV-induced copolymerization. The matrix consists of units of trimethylolpropane ethoxylate triacrylate (ETPTA), poly(ethylene glycol) diacrylate (PEGDA), and the monoacrylate poly(ethylene glycol) methyl ether acrylate (mPEGa). The QSPE containing 55 wt% bCN-PEG4 exhibits highly uniform morphology, thermal stability > 200 °C, ionic conductivity of 1.8 × 10−4 S cm−1 at 30 °C, and 1.3 × 10−3 S cm−1 at 80 °C, coupled with very high electrochemical stability (> 5 V vs. Li/Li+) and a low glass transition temperature (− 55.7 °C). A cycling experiment in a Li/QPSE/Li cell setup demonstrated the compatibility toward lithium metal additionally. The bCN-PEG4 offers an overall satisfying performance as a plasticizer in a poly(ethylene oxide)-based solid polymer electrolyte. The new QSPE is an alternative to dinitrile-based (e.g., succinonitrile) or glycol ether-based (e.g., tetraglyme) plasticizers with application potential in high-voltage lithium-ion batteries.Graphical abstract

Effect of Thermal-Oxygen Aging on Temperature Stability of Styrene-Butadiene-Styrene–Modified Asphalt

Abstract In order to explore the effect of aging on the temperature stability of styrene-butadiene-styrene (SBS)-modified asphalt, matrix asphalt and SBS-modified asphalt were used as the control to conduct short-term aging and long-term aging. Three indexes of asphalt with different aging degrees were tested to analyze the change rule of each index. The specific heat capacity and phase transition temperature of SBS-modified asphalt before and after aging were studied by differential scanning calorimetry (DSC). At last, the mechanism was studied by attenuated total reflection Fourier infrared spectroscopy. The results show that the penetration and ductility of matrix asphalt and SBS-modified asphalt decrease with the deepening of aging. The difference is that the softening point of matrix asphalt shows an increasing trend, whereas the softening point of SBS-modified asphalt shows a changing rule of first decreasing and then rising. The addition of SBS modifier can increase the specific heat capacity of asphalt and change the viscosity-flow conversion temperature. The degradation of SBS modifier leads to the decrease of the specific heat capacity after long-term aging, whereas the viscosity-flow conversion temperature decreases first and then rises, which is consistent with the change law of softening point. As a special block copolymer, the specific heat capacity of SBS modifier is determined by the polymer butadiene with lower glass transition temperature, whereas the softening point changes with the polymer styrene with higher glass transition temperature, which is consistent with the change rule of functional group index, softening point, and specific heat capacity of SBS-modified asphalt before and after aging.

Synthesis and Thermomechanical Analysis of Some Primer Alcohol Derivatives of Maleic Anhydride/Styrene Copolymer

In this study, Maleic anhydride/Styrene (MAS) copolymer was synthesized. The synthesized copolymer was characterized and then modified with two different primary alcohols (propyl and butyl). Dissolution, FT-IR and thermo-mechanical (TMA) analyzes of the copolymer and its two modified ester derivatives were performed. The ester numbers of the obtained derivatives were calculated. Although the ester derivatives showed dissolution behavior in the same solvents as the MAS copolymer, they dissolved faster. Modification was confirmed in the FT-IR spectra. It was also found that the derivatives were more elastic than the MAS copolymer and had a lower glass transition temperatures. The calculated ester numbers were also close to each other.

Ionic Liquid-Cured Epoxy/PCL Blends with Improved Toughness and Adhesive Properties.

In this work, ionic liquid (IL)-cured epoxy resins were modified by adding poly(ε-caprolactone) (PCL). Three different ILs were used in order to study how (a) the chemical structure of the ILs and (b) the PCL content affect the phase behaviour, microstructure, mechanical and adhesive properties. Regardless of the IL used or the PCL content, the obtained materials showed a single phase. The addition of PCL to the epoxy resin resulted in plasticizing of the network blends, lower glass transition temperatures (Tg), and crosslinking densities (νe). Low PCL contents did not have a significant impact on the mechanical properties. However, the adhesive properties improved significantly at low PCL contents. Higher PCL contents led to a significant increase in toughness, especially in the case of the imidazolium-based IL. The balance achieved between the mechanical and adhesive properties of these IL-cured epoxy/PCL blends constitutes an important step towards sustainability. This is because a biodegradable polymer (PCL) was used to substitute part of the epoxy resin, and the ILs—which are non-volatile and cure effectively at much lower contents—were used instead of conventional curing agents. Given the wide use of this kind of materials in the adhesive industry, the practical significance of these results must be emphasised.

Binary Co-Gelator Strategy: Toward Highly Deformable Ionic Conductors for Wearable Ionoskins.

Stretchable ionic conductors have been actively developed due to the increasing demand for wearable electrochemical platforms. Herein, we propose a convenient and effective strategy for tailoring the mechanical deformability of ionic conductors. The mixing of poly(methyl methacrylate) (PMMA, polymer gelator) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMI][TFSI], ionic liquid) produces mechanically stiff ionic conductors. To reduce the chain entanglement of polymer gelators and induce effective dissipation of applied stresses, flexible poly(butyl acrylate) (PBA) with a low glass-transition temperature is additionally doped into the ionic conductor. An extremely stretchable (∼1500%) homogeneous ternary ionic conductor is obtained without a notable change in electrochemical characteristics, unless the content of PBA exceeds the macrophase separation limit of 3 wt %. In addition, the mechanical elasticity (1.8 × 105 Pa) and durability (e.g., recovery ratio of ∼86.3% after 1000 stretching/releasing cycles) of the conductor further support its suitability as a strain sensory platform. In contrast to conventional ionoskins that have to fit the area of target body parts, even a small piece of the ternary ionic conductor successfully monitors human motion over large areas by taking advantage of its superior deformability.

Dependence of the Dynamic Mechanical Properties and Structure of Polyurethane-Clay Nanocomposites on the Weight Fraction of Clay

The effect of clay and chemical cross-linking on the dynamic mechanical properties of polyurethane reinforced with different concentrations of organically modified montmorillonite clay is investigated in this study. The polyurethane matrix is constituted of polytetrahydrofuran soft segment and 4,4′-methylenebis(phenyl isocyanate) hard segment. Glycerin was used as the chemical crosslinking agent, while Cloisite 30B clay was the reinforcing filler. The nanocomposites containing up to 1 wt.% clay showed a uniform dispersion of clay; however, the nanocomposites containing higher concentrations of clay showed the presence of heterogeneities. Dynamic mechanical spectroscopy, DMS revealed that the nanocomposites containing between 2 and 10 wt.% clay had two glass transition temperatures, Tg,1 and Tg,2. The higher-temperature glass transition temperature, Tg,2 increased with increasing clay concentration, while the low-temperature glass transition temperature, Tg,1 decreased with increasing clay concentration. The nanocomposites containing low clay concentrations up to 1 wt.% showed only one glass transition temperature with a narrow glass transition region. The crosslink density for the nanocomposites increased with increasing wt.% clay.

Experimental and numerical damage characterization of glass/polypropylene multidirectional laminates under quasi-static loading condition

Polypropylene (PP) as a commodity thermoplastic, when reinforced with continuous glass fibers provides cost-effective composites. However, the low glass transition temperature and fabrication induced semi-crystalline morphology of PP set challenges for the experimental characterization especially when the quantification of damage mechanisms in multidirectional laminates is concerned. This paper is aimed at performing in-situ experimental observation, quantification and theoretical modeling of damage mechanisms in glass fiber reinforced polypropylene multidirectional laminates subjected to uniaxial quasi-static loading conditions. Two Stereo Digital Image Correlation systems (3D-DIC) are applied to measure the full-field strains and quantify the extent of damage mechanisms from the specimen's edge. The effects of ply thickness, off-axis ply orientation and location on damage initiation and growth are studied by testing different lay-ups. To validate the experimental measurements, a recent physics-based modeling technique is implemented that can predict the evolution of damage modes as well as their effects on the laminate properties. Good agreements are observed between the experimental measurements and simulation results which verify the accuracy of both analyses.

Controlling Morphology and Physio-Chemical Properties of Stimulus-Responsive Polyurethane Foams by Altering Chemical Blowing Agent Content.

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is a function of physio-chemical material properties. In this study, concentrations of the chemical blowing agent for the foam were altered and the resulting effects on morphology, thermal and chemical properties, and actuation rates were studied. Lower concentration of chemical blowing agent yielded foams with thick foam struts due to less bubble formation during the foaming process. Foams with thicker struts also had high tensile modulus and lower strain at break values compared to the foams made with higher blowing agent concentration. Additionally, less blowing agent resulted in foams with a lower glass transition temperature due to less urea formation during the foaming reaction. This exploratory study provides an approach to control thermo-mechanical foam properties and morphology by tuning concentrations of a foaming additive. This work aims to broaden the applications of shape memory polymer foams for medical use.

Viscosity of fluoride glass fibers for fused component fabrication.

Fluoride glasses show great promise for mid-IR fiber-based applications. Their brittleness and low glass transition temperature have thus far been obstacles towards obtaining low-loss fused components. Here, we suggest a simple method to measure glass viscosity over a range of process temperatures of interest for fused coupler fabrication. We achieved tapers of inverse taper ratio (ITR) 0.12 in multimode fluoroindate fibers. Tapers with loss <0.1dB at ITR 0.3 and no visible defects were fabricated with high repeatability. This work paves the way towards low-loss fused optical couplers in fluoride glass fiber.

Synthesis and Characterization of Bio-Based Poly(amide imide)s Derived from 11-Aminoundecanoic Acid and 1,10-Diaminodecane

Three diimide diacid (DIDA) monomers possessing different rigid groups (phenyl, biphenyl and diphenyl ether group) between two imide rings were prepared through the dehydration cyclization reaction of 11-aminoundecanoic acid and aromatic dianhydride. These DIDA monomers were polymerized with 1,10-diaminodecane to produce bio-based poly(amide imide)s (PAIs) by the ecofriendly and low-cost two-step polymerization method. All the PAIs have high thermal stabilities, and their initial thermal decomposition temperatures are above 400 °C at 5% weight loss. When the rigid group between two imide rings is changed from phenyl to diphenyl ether group, the glass transition temperature of PAI shows a decreasing trend from 54.7 °C to 42.4 °C, the tensile strength also reduces from 62.4 MPa to 49.5 MPa, but elongation at break increases from 3.7% to 6.8%. Moreover, the PAI with phenyl group between two imide rings is a semicrystalline polymer, while the PAI with biphenyl or diphenyl ether group is an amorphous polymer. It is a viable way to regulate the properties of PAIs by changing the structure of rigid group between two imide rings. Such bio-based PAIs with high thermal stabilities, low glass transition temperatures and good mechanical strength will provide great promise for their wider applications.

Science and Business Developments

Science and Business Developments

One-pot synthesis of hydroxyl terminated hyperbranched semi-aromatic Poly(ester-imide)s

A new kind of hyperbranched semi-aromatic poly(ester-imide)s with hydroxyl terminated groups has been prepared from commercially available 1,2,4-benzenetricarboxylic anhydride (TMA) as the AA′-type aromatic monomer and 3-amino-1,2-propanediol (3APPD), 2-amino-1,3-propanediol (2APPD), N,N-bis(2-hydroxyethyl)ethylenediamine (BHED) as CB 2 -type aliphatic monomers via a simple one-pot melting polymerization method. The effects of synthesis conditions on the structures and properties of the products were investigated in detail. The combination of FTIR, 1 H NMR, 2D NMR, MALDI-FTICR-MS and model reactions have been used to characterize the structures of the obtained polymers. As assessed using thermal measurements, the obtained hyperbranched semi-aromatic poly(ester-imide)s possess low glass transition temperature (≤120 °C) and high thermostability with an onset decomposition temperature ranging from 355 to 420 °C in nitrogen. The products possess abundant terminal hydroxyl functional groups. Hydroxyl values vary between 198 and 248 mg KOH/g depending on the particular precursors used to generate the polymers. The synthesis of hydroxyl terminated hyperbranched semi-aromatic poly(ester-imide)s. • Hyperbranched semi-aromatic poly(ester-imide)s were prepared by one-pot melting polymerization. • HBPEIs possess low T g and high thermostability. • HBPEIs are terminated by abundant hydroxyl function groups. • This synthetic strategy exhibits good fault-tolerant ability for reaction condition.

Novel Cellulose Nanocrystals-Based Polyurethane: Synthesis, Characterization and Antibacterial Activity.

As a new type of polymer, water-driven polyurethane (PU) has attracted increasing attention of researchers; however, with the popularization of its application, the following infection problems limit their applications, especially in the biomedical field. Herein, a series of novel cellulose nanocrystals (CNCs)-based PUs were first synthesized by chemical cross-linking CNCs with triblock copolymer polylactide–poly (ethylene glycol)–polylactide (CNC-PU). After covalent binding with tannic acid (TA-CNC-PU), the silver nanoparticles (Ag NPs) were further introduced into the material by a reduction reaction (Ag/TA-CNC-PU). Finally, the prepared serial CNCs-based PU nanocomposites were fully characterized, including the microstructure, water contact angle, water uptake, thermal properties as well as antibacterial activity. Compared with CNC-PU, the obtained TA-CNC-PU and Ag/TA-CNC-PU were capable of lower glass transition temperatures and improved thermal stability. In addition, we found that the introduction of tannic acid and Ag NPs clearly increased the material hydrophobicity and antibacterial activity. In particular, the Ag/TA-CNC-PU had a better antibacterial effect on E. coli, while TA-CNC-PU had better inhibitory effect on S. aureus over a 24 h time period. Therefore, these novel CNCs-based PUs may be more beneficial for thermal processing and could potentially be developed into a new class of smart biomaterial material with good antibacterial properties by adjusting the ratio of TA or Ag NPs in their structures.

Poly(3-mercapto-2-methylpropionate), a Novel α-Methylated Bio-Polythioester with Rubber-like Elasticity, and Its Copolymer with 3-hydroxybutyrate: Biosynthesis and Characterization.

A new polythioester (PTE), poly(3-mercapto-2-methylpropionate) [P(3M2MP)], and its copolymer with 3-hydroxybutyrate (3HB) were successfully biosynthesized from 3-mercapto-2-methylpropionic acid as a structurally-related precursor. This is the fourth PTE of biological origin and the first to be α-methylated. P(3M2MP) was biosynthesized using an engineered Escherichia coli LSBJ, which has a high molecular weight, amorphous structure, and elastomeric properties, reaching 2600% elongation at break. P(3HB-co-3M2MP) copolymers were synthesized by expressing 3HB-supplying enzymes. The copolymers were produced with high content in the cells and showed a high 3M2MP unit incorporation of up to 77.2 wt% and 54.8 mol%, respectively. As the 3M2MP fraction in the copolymer increased, the molecular weight decreased and the polymers became softer, more flexible, and less crystalline, with lower glass transition temperatures and higher elongations at break. The properties of this PTE were distinct from those of previously biosynthesized PTEs, indicating that the range of material properties can be further expanded by introducing α-methylated thioester monomers.

Synthesis and Enzymatic Degradation of Sustainable Levoglucosenone-Derived Copolyesters with Renewable Citronellol Side Chains.

Recently, a renewable five-membered lactone containing citronellol (HBO-citro) was synthesized from levoglucosenone (LGO). A one-pot two-step pathway was then developed to produce a mixture of 5- and 6-membered Lactol-citro molecules (5ML and 6ML, respectively) from HBO-citro. Proton nuclear magnetic resonance (1H NMR) of a mixture of 5ML and 6ML at varying temperatures showed that the chemical shifts of the hydroxyls, as well as the 5ML:6ML ratio, are temperature-dependent. Indeed, a high temperature, such as 65 °C, led to an up-field shielding of the hydroxyl protons as well as a drop in the 5ML:6ML ratio. The monomers 5ML and 6ML were then engaged in polycondensation reactions involving diacyl chlorides. Renewable copolyesters with low glass transition temperatures (as low as −67 °C) and cross-linked citronellol chains were prepared. The polymers were then hydrolyzed using a commercial lipase from Thermomyces lanuginosus (Lipopan® 50 BG). A higher degradation rate was found for the polymers prepared using Lactol-citro molecules, compared to those obtained by the polycondensation reactions of diacyl chlorides with Triol-citro—a monomer recently obtained by the selective reduction of HBO-citro.

Selectivity diversity for a single cobalt(II) precatalyst mediated butadiene polymerization

Selectivity diversity from a single catalyst not only allows for facile switch the type of product, but also helps to understand the reaction mechanism by simply varying the reaction conditions. In this research, we disclosed the capability of diversified selectivity of a cobalt complex as precatalyst to mediated 1,3-butadiene, which could produce different structures polymers under different conditions. On direct activation by EASC or MAO, such a complex was able to reveal high cis-1,4- selectivity, giving polybutadiene (PB) products with extremely low glass transition temperature; introducing PPh3 as external donor to such a system, the selectivity could switch from cis-1,4- to highly 1,2- manner, giving atactic 1,2- PBs. Moreover, the 1,2- contents of the obtained polymers were proportionally dependent on the PPh3 equivalents, gradual increasing PPh3/Co ratio was able to access cis-1,4-ran-1,2- products with gradual increased 1,2-contents. In contrast, selecting CS2 as donor could give high syndiotactic 1,2-PB products, which demonstrated melting temperatures up to 203.9 °C. Possible mechanism for such a selectivity diversity was proposed.

Stamping colors with solid-state superionic stamping (S4)

Traditional top-down approaches to producing metallic nanostructures are usually indirect; involve ultra-high vacuum processing steps and deep sub-micron lithography such as electron-beam lithography (EBL). Therefore, such pathways are difficult to scale up to high production rates. Additionally, they are too expensive to deploy in the production of single-use, low-cost products like plasmonic biological or chemical sensors, security tags or decorative patterns, all of which involve metallic nanopatterns. Hence, there is a need for more scalable and affordable manufacturing pathways for producing metallic nanostructures. In this work, we demonstrate a scalable manufacturing pathway for patterning silver nanostructures for plasmonic color generation. The pathway begins with the production of a single master pattern. We use commercially available Two-Photon Lithography (TPL) to direct-write a mask on a silicon substrate. Shallow etching of the silicon substrate with this mask by the Reactive Ion Etching (RIE) process (or Deep Reactive-Ion Etching for deeper patterns) produces a silicon master mold with the desired pattern. This master is used for hot embossing AgI-AgPO3 glass, a chemically stable, pure Ag-ion conductor with a low glass transition temperature (of about 100 °C, depending on its stoichiometry), into a stamp. This glass stamp, in turn, is used in the Solid-State Superionic Stamping (S4) process to electrochemically imprint the desired pattern into several substrates. Here, with this direct, facile, and efficient process, we report that a single nano-patterned stamp is capable of producing several high-fidelity replicas of the master.

Fire-retardant effect of titania-polyurea coating and additional enhancement via aromatic diamine and modified melamine polyphosphate

Polymeric materials and composites are well suited to support structures in marine conditions due to their corrosion resistance. However, their low glass transition temperature makes them vulnerable to softening at high temperatures. Hence, fire retardancy is a key aspect if these materials are selected to ensure stiffness under flammable conditions. In this paper, a fire-retardant polyurea coating for industrial applications is proposed. The aromatic diamine and aliphatic diisocyanate are believed to have a synergistic effect in improving flame properties. Moreover, various combinations of flame-retardant additives with aromatic and aliphatic-based polyurea are mixed to further improve fire-retardancy. Through the characterizations of their glass transition temperature and delay in the ignition, it indicates that the combination of Talc and melamine polyphosphate may provide an outstanding enhancement for the Titania-polyurea coating, and such enhancement may improve its original tensile and compression strength, and surface hardness as well.

Polymer Grafted Nanoparticle Composites with Enhanced Thermal and Mechanical Properties.

The distribution of filler particles within a polymer matrix nanocomposite has a profound influence on the properties and processability of the material. While filler aggregation and percolation can significantly enhance particular functionalities such as thermal and electrical conductivity, the formation of larger filler clusters and networks can also impair mechanical properties like strength and toughness and can also increase the difficulty of processing. Here, a strategy is presented for the preparation of functional composites that enhance thermal conductivity over polymer alone, without negatively affecting mechanical performance or processability. Thermal cross-linking of self-suspended polymer grafted nanoparticles is used to prepare highly filled (>50 vol %) macroscopic nanocomposites with homogeneously dispersed, non-percolating alumina particles in an organic matrix. The initial composites use low glass transition temperature polymer grafts and thus are flexible and easily shaped by thermoforming methods. However, after thermal aging, the resulting materials display high stiffness (>10 GPa) and enhanced thermal conductivity (>100% increase) and also possess mechanical strength similar to commodity plastics. Moreover, the covalent bonding between matrix and filler allows for the significant elevation of thermal conductivity despite the extensive interfacial area in the nanocomposite. The thermal aging of polymer grafted nanoparticles is therefore a promising method for producing easily processable, mechanically sturdy, and macroscopic nanocomposites with improved thermal conductivity.