Showing papers on "Glass transition published in 2016"
TL;DR: In this paper, vertically aligned and interconnected graphene networks are first used as the filler, which is prepared by a controlled three-step procedure: formation of graphene oxide liquid crystals, oriented freeze casting, and high-temperature annealing reduction under Ar. The obtained composite, at an ultralow graphene loading of 0.92 vol %, exhibits a high thermal conductivity (2.13 W m−1 K−1) that is equivalent to a dramatic enhancement of 1231% compared to the pure matrix.
Abstract: Efficient removal of heat via thermal interface materials has become one of the most critical challenges in the development of modern microelectronic devices. However, traditional polymer composites present limited thermal conductivity even when highly loaded with highly thermally conductive fillers due to the lack of efficient heat transfer channels. In this work, vertically aligned and interconnected graphene networks are first used as the filler, which is prepared by a controlled three-step procedure: formation of graphene oxide liquid crystals, oriented freeze casting, and high-temperature annealing reduction under Ar. The obtained composite, at an ultralow graphene loading of 0.92 vol %, exhibits a high thermal conductivity (2.13 W m–1 K–1) that is equivalent to a dramatic enhancement of 1231% compared to the pure matrix. Furthermore, the composite also presents a much reduced coefficient of thermal expansion (∼37.4 ppm K–1) and increased glass transition temperature (135.4 °C). This strategy provide...
310 citations
TL;DR: In this paper, a change in nucleation mechanism, from heterogeneous nucleation to surface nucleation (or in extreme cases, homogeneous nucleations), was proposed, which reflected that nucleation is the rate determining step in the overall crystallization of ideally confined polymers.
257 citations
TL;DR: In this paper, a bio-based, high molecular weight poly(limonene carbonate) (PLimC) with attractive thermal (glass transition temperature, Tg = 130 °C) and optical properties (transmission 94%, haze 0.75%) was prepared by coupling bio-base limonene oxide (LO) and carbon dioxide (CO2) using a β-diiminate zinc catalyst (bdi)Zn(OAc).
226 citations
TL;DR: The authors used fifth-order dielectric susceptibility measurements to show that the real reason behind the stiffness of glass is more complicated. But the emerging amorphous order is only weakly dependent on the specific molecular properties, suggesting a more universal governing behavior for making glasses The authors.
Abstract: Glasses are often thought of as frozen liquids without long-range order. Albert et al. used fifth-order dielectric susceptibility measurements to show that the real reason behind the stiffness of glass is more complicated. Measuring the response of two traditional glass formers to very high electric fields is challenging, but reveals the growth of compact domains across the glass transition. The emerging amorphous order is only weakly dependent on the specific molecular properties, suggesting a more universal governing behavior for making glasses.
Science , this issue p. [1308][1]
[1]: /lookup/doi/10.1126/science.aaf3182
163 citations
TL;DR: TiO2 nanoparticles improved the functional properties of potato starch film and extended the potential for food packaging applications.
162 citations
TL;DR: In this article, a common amino acid, l -arginine (0.05, 0.10,0.15 and 0.20 ) was added to (Choline chloride+urea) to form ternary deep eutectic solvents, and the physical properties such as density, viscosity and refractive index were measured.
158 citations
TL;DR: In this article, the glass transition temperature (T g ) of polyhedral oligomeric silsesquioxanes (POSSs) is investigated and the dependence of T g on the composition of POSS nanomaterials can be discussed and considered in terms similar to those used for polymer blends and copolymers.
144 citations
TL;DR: In this article, the relationship between glass transition and ionic conductivity of an amorphous crosslinked polymer electrolyte membrane (PEM) was examined based on ion-dipole complexation between dissociated lithium cations and ether oxygen of poly(ethylene glycol diacrylate) and plasticization by succinonitrile (SCN).
Abstract: The relationship between glass transition (Tg) and ionic conductivity (σ) of an amorphous crosslinked polymer electrolyte membrane (PEM) was examined based on ion–dipole complexation between dissociated lithium cations and ether oxygen of poly(ethylene glycol diacrylate) and plasticization by succinonitrile (SCN). In a binary PEM consisting of a lithium salt/polymer network, Tg increased due to a strong ion–dipole interaction, whereas σ declined due to lower ion mobility coupled to reduced chain mobility. Above the threshold salt concentration of 7 mol %, dual loss tangent peaks were observed in dynamic mechanical studies, which may be ascribed to segmental relaxations of ion–dipole complexed networks and that of polymer chains surrounding the undissociated lithium salt acting like “fillers”. Upon SCN plasticization, these two peaks merged into one that was further suppressed below Tg of the pure network, whereas σ improved to the superionic conductor level. The role of plasticization on the ionic conduct...
143 citations
TL;DR: In this article, a novel eugenol-based epoxy monomer (TEU-EP) with a branched topology and a very rich biobased retention (80 wt %) was developed.
Abstract: Harvesting biobased epoxy resins with improved thermomechanical properties (e.g., glass transition temperature Tg and storage modulus), mechanical and dielectric similar and even superior to that of bisphenol A epoxy resin (DGEBA) is vital to many applications, yet remains a substantial challenge. Here we develop a novel eugenol-based epoxy monomer (TEU-EP) with a branched topology and a very rich biobased retention (80 wt %). TEU-EP can be well cured by 3,3′-diaminodiphenyl sulfone (33DDS) and the resultant TEU-EP/33DDS system can be considered as a “single” epoxy component, exhibiting adequate reactivity at high processing temperatures. Importantly, compared with DGEBA/33DDS, TEU-EP/33DDS achieves a 33 °C, 39% and 55% increment in the glass transition temperature, Young’s modulus, and hardness, respectively, and shows the improved creep resistance and dimensional stability. TEU-EP/33DDS is also characterized by the considerably reduced permittivity, dielectric loss factor, and flammability with high yie...
143 citations
TL;DR: In this article, the luminescent properties and their applications for white light emitting diodes (w-LEDs) were investigated using X-ray diffraction (XRD) pattern confirmed the amorphous nature of the as-prepared glass.
133 citations
TL;DR: The relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) was explored in this article.
Abstract: We explore the relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI). Two SEO polymers were studied, SEO(16–16) and SEO(4.9–5.5), over the salt concentration range r = 0.03–0.55. The numbers x and y in SEO(x–y) are the molecular weights of the blocks in kg mol–1, and the r value is the molar ratio of salt to ethylene oxide moieties. Small-angle X-ray scattering was used to characterize morphology and grain size at 120 °C, differential scanning calorimetry was used to study the crystallinity and the glass transition temperature of the PEO-rich microphase, and ac impedance spectroscopy was used to measure ionic conductivity as a function of temperature. The most surprising observation of our study is that ionic conductivity in the concentration regime 0.11 ≤ r ≤ 0.21 increases in SEO electrolyte...
TL;DR: Direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former is presented, and a real-space description of this transition and of the rapidly growing time- and lengthscales that accompany it is provided.
Abstract: Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye's theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye's theory (i.e., a Boson Peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time and length scales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition.
TL;DR: The incorporation of DPPA-MWCNT to PS significantly reduced peak heat release rate, smoke production rate, and carbon monoxide and carbon dioxide release in cone calorimeter tests, and the enhanced fire-retardant properties should be ascribed to the barrier effect of carbon nanotubes.
Abstract: Aminated multiwalled carbon nanotubes (A-MWCNT) were reacted with diphenylphosphinic chloride (DPP-Cl) to prepare the functionalized MWCNT (DPPA-MWCNT). A-MWCNT and DPPA-MWCNT were respectively mixed with polystyrene (PS) to obtain composites through the melt compounding method. SEM observations demonstrated that the DPPA-MWCNT nanofillers were more uniformly distributed within the PS matrix than A-MWCNT. PS/DPPA-MWCNT showed improved thermal stability, glass transition temperature, and tensile strength in comparison with PS/A-MWCNT, resulting from good dispersion and interfacial interactions between DPPA-MWCNT and PS matrix. The incorporation of DPPA-MWCNT to PS significantly reduced peak heat release rate, smoke production rate, and carbon monoxide and carbon dioxide release in cone calorimeter tests. The enhanced fire-retardant properties should be ascribed to the barrier effect of carbon nanotubes, which could provide enough time for DPPA-MWCNT and its functionalized groups to trap the degrading polym...
TL;DR: In this article, 3-glycidyloxypropyltrimethoxy silane (γ-MPS) was applied to Hexagonal boron nitride (h-BN) particles to improve the interface action with the polyimide matrix.
Abstract: Polyimide (PI) has been widely used as a preferred packaging matrix material due to its low dielectricity, outstanding insulation and excellent thermal stability. Hexagonal boron nitride (h-BN) microparticles were functionalized with a silane coupling agent, 3-glycidyloxypropyltrimethoxy silane (γ-MPS), to improve the interface action with the PI matrix. The modified h-BN (m-BN) particles were used to fabricate the PI/m-BN composites with enhanced thermal conductivity by in situ polymerization. The Fourier transform infrared (FTIR) spectra, thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and contact angle test proved that γ-MPS coupling agent molecules had been chemically grafted onto the h-BN surface. In addition, the effects of the m-BN content on the thermal conductivity of PI/m-BN composites were investigated. The composite obtained with 40 wt% m-BN particle loading presented a thermal conductivity of 0.748 W m−1 K−1, 4.6 times higher than that of pure PI. Meanwhile, the fabricated PI/m-BN composites retained excellent electrical insulation and thermal stability. The glass transition temperature values of the PI/m-BN composites decreased slightly while the storage modulus improved with the increase of the m-BN content. These results showed that PI/m-BN composites may offer new applications in the microelectronic industry because future substrate materials require effective heat dissipation.
TL;DR: In this paper, a polyimide aerogel (PIA) was used to synthesize low-dielectric-constant polyimides composite films, which exhibited a 3% water uptake.
Abstract: A polyimide aerogel (PIA) was used to synthesize low-dielectric-constant polyimide composite films. Unlike silica aerogel (SIA) composites, the PIA films were synthesized using polyimide. The resulting films maintained the original thermal and chemical properties of polyimide, which contribute to their homogeneity. The dielectric constant of the aerogel composite film was decreased to ~2.4, a value similar to that of a SIA composite film. The increase in dielectric constant as a result of water adsorption exhibited by SIA films was counteracted by the hydrophobicity of the polyimide in the PIA film. The PIA composite film exhibited a 3% water uptake, compared with a 29% water uptake in the SIA film, indicating that the polyimide film is the preferred choice in wet conditions. The presence of a uniformly dispersed aerogel, a 1% thermal decomposition temperature of 589 °C and a glass transition temperature of 298 °C for the PIA composite film were confirmed by field emission scanning electron microscopy, thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis, respectively. The TGA and DSC results demonstrated that the excellent thermal properties of polyimide were maintained in the PIA composite film. Polyimide aerogel (PIA) was used to synthesize low-dielectric-constant polyimide composite films. Unlike silica aerogel composites, the polyimide aerogel composite films were synthesized solely based on polyimide. The films maintained the original thermal and chemical properties of polyimide contributing to their homogeneity. The presence of uniformly dispersed aerogel, the high-thermal decomposition and glass transition temperature of the PI–PIA sample films were confirmed by field emission scanning electron microscope, TGA and DSC analysis. The FE-SEM image of the PI–PIA film samples indicates that the PIA particles were well-dispersed in the film and retained their spherical shape.
TL;DR: In this paper, a novel high sulfur content material possessing improved thermomechanical properties is reported via the inverse vulcanization of elemental sulfur (S8) and 1,3,5-triisopropenylbenzene (TIB).
Abstract: The synthesis of a novel high sulfur content material possessing improved thermomechanical properties is reported via the inverse vulcanization of elemental sulfur (S8) and 1,3,5-triisopropenylbenzene (TIB). A key feature of this system was the ability to afford highly cross-linked, thermosetting materials, where the use of TIB as a comonomer enabled facile control of the network structure and dramatically improved the glass transition temperature (relative to our earlier sulfur copolymers) of poly(sulfur-random-(1,3,5-triisopropenylbenzene)) (poly(S-r-TIB)) materials over a range from T = 68 to 130 °C. This approach allowed for the incorporation of a high content of sulfur–sulfur (S–S) units in the copolymer that enabled thermomechanical scission of these dynamic covalent bonds and thermal reprocessing of the material, which we confirmed via dynamic rheological characterization. Furthermore, the high sulfur content also imparted high refractive index (n > 1.75) and IR transparency to poly(S-r-TIB) copoly...
TL;DR: In this article, different R-groups (p-position hydrogen, methyl, ethyl, and formyl groups) in homologous lignin-based methacrylate polymers are investigated.
Abstract: Softwood (guaiacylic) lignin-based methacrylate polymers (LBMPs) that exhibit excellent glass transition temperatures (Tg’s), desirable thermal stabilities (greater than 100 °C above Tg), and intermediate shear-flow resistances, in comparison to polystyrene and poly(methyl methacrylate), are reported herein. Different R-groups (p-position hydrogen, methyl, ethyl, and formyl groups) in otherwise homologous LBMPs impart distinct characteristics to the flow behavior and thermal properties of these bio-based polymers, which permit the investigation of unique structure–property relationships. More specifically, the zero-shear viscosities (η0’s) for the LBMPs span nearly 2 orders of magnitude as the R-group is varied, while the characteristic degradation temperatures differ more modestly (by ≈50 °C over the same series of polymers), and the Tg’s exhibit minimal, yet application relevant, variations between ≈110 and ≈130 °C. These property differences were probed independent of tacticity, molecular weight, and d...
TL;DR: In this article, the authors review the recent literature aiming to clarify glassy dynamics in nanostructured polymer glasses, in particular thin films, nanocomposites and nanospheres.
TL;DR: Field emission scanning electron microscopy of PLA-TPS blends with varying amounts of maleinized linseed oil suggests an increase in compatibility and the evidence of the plasticizing-compatibilizing effect provided by MLO is the change in the glass transition temperature with a decrease of about 10°C.
TL;DR: In this paper, the authors synthesized six partially or fully renewable tricyclic anhydrides and copolymerized them with propylene oxide (PO) and cyclohexene oxide (CHO).
Abstract: Renewable, biodegradable polymers, such as aliphatic polyesters, based on sustainable sources have attracted considerable interest as alternatives to petroleum-based polymers. One limiting factor in the development of aliphatic polyesters as replacements for these materials has been their relatively low glass transition temperatures (Tg). For example, commercially available poly(lactic acid) has a Tg of approximately 60 °C. Epoxide/anhydride copolymerizations offer an alternative to the ring-opening polymerization of lactones for the synthesis of aliphatic polyesters and allow for tuning of polymer properties through two distinct monomer sets. We synthesized six partially or fully renewable tricyclic anhydrides and copolymerized them with propylene oxide (PO) and cyclohexene oxide (CHO). By varying both the epoxide and the anhydride, we were able to tune the Tg of the resulting polymers over a nearly 120 °C range from 66 °C to an exceptionally high 184 °C. Polymers produced with PO had a lower range of Tg...
TL;DR: In this article, the glass transition behavior and mechanical properties of poly(ethylene terephthalate) (PET), PET/silica nanocomposite and PET/hydroxylated silica nan composite were studied through molecular dynamics (MD) simulations.
TL;DR: The relationship between the polymer concentration and the volume fraction is quantified, and it is shown that the glass transition behaviour of soft microgels can be mapped to that of hard sphere glasses once theVolume fraction is used as the control parameter.
Abstract: We explore the influence of particle softness on the state diagram of well characterized polyelectrolyte microgel suspensions using dynamic light scattering and rheology. Upon increasing the polymer concentration, we cross successively the well defined glass and jamming transitions which delimit four different states: dilute colloidal suspension, entropic glass, jammed glass, and dense glass. Each state has a specific dynamical fingerprint dictated by two key ingredients related to particle softness: elastic contact interactions, and osmotic or steric deswelling. Soft interactions control yielding and flow of the jammed glasses. The shrinkage of the microgels makes the glass transition look smoother than in hard sphere suspensions. We quantify the relationship between the polymer concentration and the volume fraction, and show that the glass transition behaviour of soft microgels can be mapped to that of hard sphere glasses once the volume fraction is used as the control parameter.
TL;DR: In this paper, the phase change and state change behaviors of polyols are better understood in order to use these as PCM; e.g. the state change glass transition which many polyols at pure state are found to undergo.
TL;DR: A small amount of MWCNT fillers can significantly increase all three key mechanical properties at temperatures close to Tg, the recovery rate, and the repetition stability of the shape memory cycles, which make the materials good candidates for the applications in aerospace and other important fields.
Abstract: A series of shape memory nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) E51/methylhexahydrophthalic anhydride (MHHPA)/multiwalled carbon nanotube (MWCNT) with various stoichiometric ratios (rs) of DGEBA/MHHPA from 0.5 to 1.2 and filler contents of 0.25 and 0.75 wt % are fabricated. Their morphology, curing kinetics, phase transition, mechanical properties, thermal conduction, and shape memory behaviors are systematically investigated. The prepared materials show a wide range of glass transition temperatures (Tg) of ca. 65–140 °C, high flexural modulus (E) at room temperature up to ca. 3.0 GPa, high maximum stress (σm) up to ca. 30 MPa, high strain at break (eb) above 10%, and a fast recovery of 32 s. The results indicate that a small amount of MWCNT fillers (0.75 wt %) can significantly increase all three key mechanical properties (E, σm, and eb) at temperatures close to Tg, the recovery rate, and the repetition stability of the shape memory cycles. All of these remarkable advantages make...
TL;DR: Results demonstrate that the glass transitions of the interphase and matrix will be asynchronous when the interfacial bonding ratio is not 5.8% and that interfacial covalent bonding mainly restricts the volume thermal expansion of the model at temperatures near or larger than Tg.
Abstract: Atomistic molecular dynamics simulations have been performed to explore the effect of interfacial bonding on the interphase properties of a nanocomposite system that consists of a silica nanoparticle and the highly cross-linked epoxy matrix. For the structural properties, results show that interfacial covalent bonding can broaden the interphase region by increasing the radial effect range of fluctuated mass density and oriented chains, as well as strengthen the interphase region by improving the thermal stability of interfacial van der Waals excluded volume and reducing the proportion of cis conformers of epoxy segments. The improved thermal stability of the interphase region in the covalently bonded model results in an increase of ∼21 K in the glass transition temperature (Tg) compared to that of the pure epoxy. It is also found that interfacial covalent bonding mainly restricts the volume thermal expansion of the model at temperatures near or larger than Tg. Furthermore, investigations from mean-square ...
TL;DR: Spray‐drying was investigated as a scale up preparation method for co‐amorphous indomethacin (IND)–amino acid mixtures and the physico‐chemical properties of the different co‐morphous systems were investigated with respect to the amino acids' ability towards co-amorphous salt formation.
Abstract: Objectives
Recently, co-amorphous drug–amino acid mixtures were introduced as a promising alternative to other amorphous stabilization approaches such as the use of polymers to form glass solutions. So far, these co-amorphous mixtures have been mainly prepared via vibrational ball milling on a lab scale. In this study, spray-drying was investigated as a scale up preparation method for co-amorphous indomethacin (IND)–amino acid mixtures. In addition, the physico-chemical properties of the different co-amorphous systems were investigated with respect to the amino acids' ability towards co-amorphous salt formation.
Methods
The mixtures were characterized for their solid state properties using differential scanning calorimetry, thermogravimetric analysis and X-ray powder diffraction. Fourier-transform infrared spectroscopy was used to analyze molecular interactions. Furthermore, intrinsic dissolution behaviour, and physical stability at various storage conditions, were examined.
Key findings
Results showed that IND could be converted into an amorphous form in combination with the amino acids arginine (ARG), histidine (HIS) and lysine (LYS) by spray-drying. Solid state characterization revealed elevated glass transition temperatures for all mixtures compared with the pure amorphous drug due to co-amorphization with the amino acids. Furthermore, strong intermolecular interactions in the form of salt/partial salt formation between the drug and amino acids were seen for all blends. All mixtures were physically stable (>10 months) at room temperature and 40°C under dry conditions. Intrinsic dissolution of the co-amorphous mixtures showed an improved dissolution behaviour under intestinal pH conditions for IND–ARG compared with the crystalline and amorphous forms of the drug. On the other hand, IND–LYS and IND–HIS revealed no significant improvement in the intrinsic dissolution rate of IND due to recrystallization of IND during dissolution.
Conclusions
It could be shown that strong intermolecular interactions between drug and co-amorphous coformer that persist during the dissolution are crucial to prevent recrystallization and to enhance dissolution of a co-amorphous formulation.
TL;DR: In this article, diamine-functionalized graphene oxide, DDS-GO and HMDA-GO were synthesized by introducing 4,4′-diaminodiphenyl sulfone (DDS) or hexamethylenediamine (HMDA) into the carboxylic acid groups on graphene oxide via amide bonds.
TL;DR: In this article, a solvent-free graphene oxide nanoribbons colloid (GONRs-M2070) was achieved and evaluated by grafting organosilanes (KH560) and polyether amine (M 2070) to investigate its effect on the mechanical, thermal and tribological properties of the resulting composites.
TL;DR: In this paper, a series of biobased polyurethane-siloxane cross-linked coatings were prepared using castor oil, partially bi-obased Tolonate, and 3-aminopropyl trimethoxysilane.
Abstract: A series of biobased polyurethane–siloxane cross-linked coatings were prepared using castor oil, partially biobased Tolonate, and 3-aminopropyl trimethoxysilane. The 29Si NMR spectra was used to determine the formation of cross-linking structure of the polyurethane–siloxane system. FT-IR studies verified that a hydrogen bonding interaction existed at the interface of the castor oil-based polyurethane–siloxane moieties, thereby shifting the characteristic peak position of N–H and C═O groups to higher field values. The curing process of the dispersions was followed by means of gel content measurements. The thermal properties of neat waterborne polyurethane and its nanocomposite films were tested by thermogravimetric analysis and differential scanning calorimetric. TGA tests proved that adding silica nanoparticles increased the thermal stability of the nanocomposites. DSC measurements showed that the addition of silica nanoparticles increased the glass transition temperature. Silica nanoparticles in the poly...
TL;DR: This work finds that a concentrated solution of ring polymers can be driven to a kinetically arrested state by randomly pinning a small fraction of rings, a transition not observed in linear polymers.
Abstract: The static and dynamic properties of ring polymers in concentrated solutions remains one of the last deep unsolved questions in polymer physics. At the same time, the nature of the glass transition in polymeric systems is also not well understood. In this work, we study a novel glass transition in systems made of circular polymers by exploiting the topological constraints that are conjectured to populate concentrated solutions of rings. We show that such rings strongly interpenetrate through one another, generating an extensive network of topological interactions that dramatically affects their dynamics. We show that a kinetically arrested state can be induced by randomly pinning a small fraction of the rings. This occurs well above the classical glass transition temperature at which microscopic mobility is lost. Our work both demonstrates the existence of long-lived inter-ring penetrations and realizes a novel, topologically induced, glass transition.