Difference In Glass Transition Temperature Research Articles

Fabrication of a mechanically tough and strong graphene oxide aerogel modified phenolic resin by balancing the trade-off between load transfer efficiency and chain segment mobility

In this work, a mechanically strong and tough novolac phenolic nanocomposites (GESNH) was successfully constructed by modulating its load transfer efficiency and chain segment mobility with reactive micro-sized graphene oxide aerogel (GES). DMA analysis reveals that the microstructure of GESNH can be divided into three regions including the “bricks in mortar” structure, the main phenolic networks and the constrained region, according to the significant difference in glass transition temperature (Tg) and fractional free volume (fg). Via controlling the volume fraction of three regions, load transfer efficiency and chain segment mobility of GESNH can be effectively tuned. Especially for 0.5%GESNH-5, flexural, tensile properties and fracture toughness are increased by 44.71%, 60.41% and 96.34%, compared with those of 0.5%GNH, where the volume fraction of the “bricks in mortar” structure as 0.086 and the constrained region as 0.169 facilitate the load transfer and the chain segment mobility, simultaneously.

Experimental Determination of Molecular Weight-Dependent Miscibility of PBAT/PLA Blends.

Blends of poly(butylene adipate-co-terephthalate) (PBAT) and polylactide (PLA) have attracted the attention of academia and industry as a sustainable material. Unfortunately, this combination results in problems related to poor miscibility on the molecular level. This study mainly aims to determine the influence of molecular weights on the miscibility of PBAT/PLA blends. First, polymers with various molecular weights were obtained by the hydrolysis of PBAT and methanolysis of PLA. Second, the two components were solution-blended with different molecular weights and weight ratios. Third, each blend was heated to the molten state and subsequently stored at room temperature. Finally, the samples were tested using DSC and SEM. The thermal analysis indicated that the difference in glass transition temperature between both components decreased from about 91 °C to 57 °C and 0 °C, as the number-average molecular weights (Mn) decreased from 52/127 to 9.4/9 and 6.3/6.6 kg/mol. Moreover, the morphology changed from phase-separated with dispersed large particles gradually to uniform and homogeneous. This experimental work validated the trends predicted in the previous study, namely that PBAT/PLA blends changed the state from immiscible to partially miscible to fully miscible with decreasing Mn values. Moreover, we discussed the influencing factors such as weight ratio, temperature, and molecular structure on the miscibility. Based on the results, this work contributes to developing partially miscible and compatible blends without additives.

Coarse-graining strategies for predicting properties of closely related polymer architectures: A case study of PEEK and PEKK

The ability of atomistic and coarse-grained models to discern between two polymers of very similar architecture is examined. To this end, polyether ether ketone (PEEK) and polyether ketone ketone (PEKK) are chosen. The difference in glass transition temperature and the similarity in compressive responses of the two polymers are captured by all-atom models. A coarse-graining scheme, with 6 beads per monomer and 3 types of beads, leads to a good approximation of the structure and packing of chains of PEEK and PEKK. The CG model reproduces differences in weakly rate-dependent properties such as {T}_{mathrm{g}}. Comparison between strongly rate-dependent uniaxial stress–strain responses of these two polymers requires a knowledge of the scaling between physical strain rate in one to the effective rate in the other. The scaling can be approximately determined by comparing the variation of yield strength with strain rate, obtained from small-sized simulations.Graphic abstract

In situ AFM Observation of the Movements of Isolated Isotactic Poly(methyl methacrylate) Chains in a Precursor Film of an Oligo(methyl methacrylate) Droplet Spreading on Mica.

Atomic force microscopy (AFM) is a powerful tool to observe polymer chains at the molecular level. In this study, we show that the movements of isolated linear polymer chains in a precursor film of a droplet of an oligomer spreading on a substrate could be visualized in situ at the molecular level by AFM for the first time. The system was an isotactic poly(methyl methacrylate) (it-PMMA) solubilized in an oligo(MMA) matrix (it-PMMA/oligo(MMA) = 1/10,000 w/w) spreading on mica under high humidity. Because of the limited resolution of the AFM instrument, condensed linear polymer chains could not be visualized, but a small amount of it-PMMA chains that were solubilized as isolated chains in the oligo(MMA) matrix could be visualized in the precursor film, the contrast of which came from a large difference in glass transition temperature (Tg) of it-PMMA and oligo(MMA). The it-PMMA chains in the precursor film spread in the radial direction of the droplet with vigorously changing chain conformations. The spreading rate of it-PMMA chains under 72% relative humidity was ∼1/30 of the spreading rate of the oligo(MMA) matrix, which was estimated based on the decrease in the volume of the macroscopic droplet. The spreading of the it-PMMA chains and droplet strongly depended on humidity and was suppressed with the decrease in humidity, most likely because of the increase in friction with the substrate. The difference in the spreading rate of it-PMMA and oligo(MMA) further increased under low humidity. The dynamic molecular information of a precursor film by AFM should help to elucidate the wetting dynamics on a substrate.

Glass transition temperature of a polymer thin film: Statistical and fitting uncertainties

The polymer glass transition is an important property in a wide variety of applications. The glass transition temperature of a polymer composite or confined thin film can be significantly different to the pure polymer. Molecular dynamics simulations are useful for providing molecular level insight and prediction, particularly at interfaces, that are not easily observable experimentally. However, there are significant methodological uncertainties in calculating the polymer glass transition temperature using molecular dynamics simulations. In this work we investigate how the cooling method, fitting range and statistical variation affects the calculated glass transition temperature of polyethylene. We found that it is necessary to perform multiple independent simulations to obtain statistically significant results, and that appropriate fitting ranges must be chosen. The methodological findings were used to investigate the difference in glass transition temperature between pure polyethylene and a polyethylene film confined between graphene surfaces. It was found that the glass transition temperature of a 9 nm thick confined film was higher than bulk polyethylene by approximately 15 K.

Switch segment and halloysite nanotube role in the phase separation behavior of shape‐memory thermoplastic polyurethane

AbstractThermoplastic polyurethane consists of hard and soft segments. The difference in glass transition temperature and thermodynamic incompatibility of these segments results in phase separation and shape memory behavior. In this study, the effect of molecular weight of polyol and the amount of nanoparticles on the phase separation and shape memory behavior of polyurethane nanocomposites were studied. Polyurethane was synthesized using poly(tetramethylene glycol) with molecular weights of 1000 and 2000 g/mol, hexamethylene diisocyanate, and 1,4‐butanediol by step polymerization. The nanocomposites were synthesized through in situ method containing 1 and 2 wt% of nanoparticle. Phase separation and shape memory behaviors were studied using attenuated total reflectance‐Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and atomic force microscopy analysis. The results indicated that higher molecular weight polyol with molecular weight of 2000 g mol−1 shows higher phase separation than the lower molecular weight sample. Also, the addition of nanoparticles results in an increased phase separation due to the halloysite nanotubes tendency to the hard segment. The shape fixity ratio (Rf) and shape recovery ratio (Rr) were in the range of 90% to 100% in all of the synthesized samples. By increasing the nanoparticles content, the shape fixity and shape recovery parameters were increased and decreased, respectively. The study of shape memory behavior also showed that the higher the polyol molecular weight, the better the nanocomposite shape memory behavior.

Investigation on compatibility of PLA/PBAT blends modified by epoxy-terminated branched polymers through chemical micro-crosslinking

Abstract In this study, a type of epoxy-terminated branched polymer (ETBP) was used as an interface compati- bilizer to modify the poly lactic acid (PLA)/poly(butylene adipate-co-butylene terephthalate) (PBAT) (70/30) blends. Upon addition of ETBP, the difference in glass transition temperature between PLA and PBAT became smaller. By adding 3.0 phr of ETBP, the elongation at break of the PLA/PBAT blends was found increased from 45.8% to 272.0%; the impact strength increased from 26.2 kJ·m−2 to 45.3 kJ·m−2. In SEM analysis, it was observed that the size of the dispersed PBAT particle decreased with the increasing of ETBP content. These results indicated that the compatibility between PLA and PBAT can be effectively enhanced by using ETBP as the modifier. The modification mechanism was discussed in detail. It proposes that both physical and chemical micro-crosslinking were formed, the latter of which was confirmed by gel content analysis.

Investigation of Azobenzene Photoisomerization Effect on Morphologies and Properties of Nanostructured Thermosets Involving Epoxy and a Diblock Copolymer.

This work highlights the effect of azobenzene photoisomerization on the morphologies and properties of the nanostructured thermosets involving epoxy and a diblock copolymer. First, a diblock copolymer composed of poly(ethylene oxide) (PEO) and poly(6-(4-(4-cyanophenylazo)phenoxy)hexyl methacrylate) (PCPHM) was synthesized, and this diblock copolymer was composed of an epoxy-philic block (i.e., PEO) and an azobenzene moiety-beating block (viz., PCPHM). This diblock copolymer was introduced into epoxy to obtain the nanostructured thermosets via reaction-induced microphase separation approach. To control the configuration of azobenzene moieties of the PCPHM block, the curing reactions were performed in the absence and/or presence of ultraviolet (UV) irradiation, respectively. It was found that, without UV irradiation, the PCPHM microdomains were generated with the trans isomers of azobenzene. Under UV irradiation, however, the PCPHM microdomains were formed with the cis configuration of azobenzene moieties. The ultraviolet-visible light (UV-vis) spectroscopy showed that the trans and cis configurations of azobenzene moieties were significantly fixed with the occurrence of curing reactions. The photoluminescent measurements showed that the nanostructured thermosets with trans-azobenzene moieties can emit fluorescence, which was in sharp contrast to those with cis-azobenzene moieties. The results of small-angle X-ray and atomic force microscopy showed that the nanostructured thermosets with trans and cis isomers of azobenzene moieties had quite different morphologies. It was found that the sizes of the PCPHM microdomains with cis configuration of azobenzene moieties were significantly larger than those with trans configuration. The difference in configuration of azobenzene moieties also resulted in the difference in glass-transition temperatures and dielectric properties of the materials. The results suggest a new approach to modulate the morphologies and physical properties of the nanostructured thermosets by means of photoisomerization of azobenzene moieties.

Molecular dynamic in binary mixtures and polymer blends with large difference in glass transition temperatures of the two components: A critical review

The dynamics in highly asymmetric mixtures with large difference in Tg of the two components are complex. At low values of the lower-Tg2 component only the α1-relaxation and its Tgα1 were found together with a fast relaxation. Three different interpretations of the fast relaxation were given. The first one interpreted the fast relaxation as the JG β-relaxation, and the α2-relaxation is present but not resolved. The second one interpreted it as localized and noncooperative α′-relaxation of the low-Tg2 component totally confined by the frozen high-Tg1 component. The third one interpreted it also as the confined α2-relaxation, but it is liquid-like and cooperative. We review exhaustively the experimental data of many highly asymmetric mixtures and polymer blends to show unequivocally that the observed fast relaxation is the JG β-relaxation. Notwithstanding, the confined-but-cooperative α2-relaxation exists, albeit not resolved. Experimental data are exclusively considered and objectively utilized to arrive at the conclusions.

Barley β‐d‐glucan – modified starch complex as potential encapsulation agent for fish oil

The aim of the study was to examine physicochemical characteristics of fish oil microcapsules produced at different temperatures and estimate the optimal ratio of BG, CS and spray drying temperature. Only the interaction between spray drying and β‐d‐glucan content played a significant role in influencing the encapsulation efficiency and spray drying itself (p ≤ 0.001 and p ≤ 0.05). Temperature played a significant role in increasing particle size as well, but the coefficient for this parameter was lower (0.179). The observed differences in particle size of microcapsules could be caused by the differences in glass transition temperature of the polymers (β‐d‐glucan and modified starch) used as wall material. It could be seen that the lowest TBARS content was observed when the β‐d‐glucan in the wall material was at relatively high level (85%) with moderate temperature applied (154 °C) – 0.56 mg of malonaldehyde/kg of powder. The highest amount of EPA was present in the sample with 50% share of β‐d‐glucan and spray dried in 150 °C (10.22 ± 0.24). After examination of all runs of the experiment, we have made optimization study to obtain the wall material composition and spray drying temperature values which will be most appropriate for fish oil encapsulation.

Polyphosphazene polymer development for mixed matrix membranes using SIFSIX-Cu-2i as performance enhancement filler particles

Phosphazene-based polymers were synthesized by using different pendant groups such as trifluoroethoxy (TFE), phenoxy (PHO) and octafluoropentoxy (OFP). High performance methoxyethoxyethoxy/cyclohexoxy (MEE/CH) based polyphosphazene was developed for the first time in literature using a mixed-substitution method. The structural, chemical, and thermal properties of these polymers were analyzed using several techniques such as Gel Permeation Chromatography (GPC), Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Nuclear Magnetic Resonance (NMR). Significant differences in gas transport properties of gases have been observed between these pendant groups because of their differences in glass transition temperature and physical interaction with CO2. For the first time, we report on the high performance of TFE polyphophazene based mixed matrix membranes (MMMs) using a SIFSIX-Cu-2i (SIFSIX) metal organic framework (MOF) as the filler particles. These MMMs showed a significant improvement in both CO2 permeability and CO2/N2 selectivity compared to pure TFE polyphosphazene membranes. The excellent gas transport properties of these membranes make them very promising material for carbon capture applications.

An Investigation on Vibration Welding of Amorphous and Semicrystalline Polymers

Vibration welding technique has been used to study the weld zone of thermoplastic polymers using ABS (amorphous), PC (amorphous), PMMA (amorphous), and PBT (semicrystalline). Polymers were welded using alike components and combinations of semicrystalline polymer with different amorphous polymers. Mechanical testing of welded polymers has proved that the tensile strength, elongation at break, and deformation was highest for PC–PC weld and least for ABS–ABS weld, when alike polymers were welded. However, welding of semicrystalline and amorphous polymer shows enormous reduction in its tensile strength as well as other tensile properties. Also, the tensile fracture of PBT with other amorphous polymers always occurred at weld zone which was not always in case of alike polymer welds. The weld strength of these polymers was observed to be dependent on the mechanical interlocking among the layers and not on interfacial bonding. This phenomenon may be due to the difference in glass transition temperatures of semicrystalline and amorphous polymers. XRD, FESEM, and AFM have been used in this study to observe the morphology of welded surfaces.

Non-photolithographic plastic-mold-based fabrication of cylindrical and multi-tiered poly(dimethylsiloxane) microchannels for biomimetic lab-on-a-chip applications

Cylindrical and multi-tiered PDMS microchannels were fabricated from two thermoplastic molds having large difference in glass transition temperatures, and were used for constructing LOC platforms mimicking human microvasculature and liver sinusoid.

Competition between water uptake and ice nucleation by glassy organic aerosol particles

Abstract. Organic aerosol particles play a key role in climate by serving as nuclei for clouds and precipitation. Their sources and composition are highly variable, and their phase state ranges from liquid to solid under atmospheric conditions, affecting the pathway of activation to cloud droplets and ice crystals. Due to slow diffusion of water in the particle phase, organic particles may deviate in phase and morphology from their thermodynamic equilibrium state, hampering the prediction of their influence on cloud formation. We overcome this problem by combining a novel semi-empirical method for estimation of water diffusivity with a kinetic flux model that explicitly treats water diffusion. We estimate timescales for particle deliquescence as well as various ice nucleation pathways for a wide variety of organic substances, including secondary organic aerosol (SOA) from the oxidation of isoprene, α-pinene, naphthalene, and dodecane. The simulations show that, in typical atmospheric updrafts, glassy states and solid/liquid core-shell morphologies can persist for long enough that heterogeneous ice nucleation in the deposition and immersion mode can dominate over homogeneous ice nucleation. Such competition depends strongly on ambient temperature and relative humidity as well as humidification rate and particle size. Due to differences in glass transition temperature, hygroscopicity and atomic O / C ratio of the different SOA, naphthalene SOA particles have the highest potential to act as heterogeneous ice nuclei. Our findings demonstrate that kinetic limitations of water diffusion into organic aerosol particles are likely to be encountered under atmospheric conditions and can strongly affect ice nucleation pathways. For the incorporation of ice nucleation by organic aerosol particles into atmospheric models, our results demonstrate a demand for model formalisms that account for the effects of molecular diffusion and not only describe ice nucleation onsets as a function of temperature and relative humidity but also include updraft velocity, particle size and composition.

Monoacryloyl esters of carbohydrates: Synthesis, polymerization and application in ceramic technology

The article presents the interdisciplinary research among organic synthesis, chemistry of polymers and ceramic technology. It presents the synthesis of monoacryloyl esters of fructose and glucose that is 1-O-acryloyl-d-fructose and 3-O-acryloyl-d-glucose, conditions of their polymerization and application in shaping of advanced ceramic powders by the so called gelcasting method. The paper presents the influence of carbohydrate esters on the viscosity of Al2O3 suspensions and microstructure of final ceramic samples. The results showed that synthesized esters of saccharides can play the role of organic monomers able to polymerize in situ and self-cross-linking compounds in gelcasting. The paper presents the proposed structure of polymeric network which is formed from acryloyl ester of glucose during gelcasting process. The paper describes rheological behaviour of slurries composed of synthesized substances and A2O3 powders, wetting angles of alumina substrate by synthesized compounds, differences in glass transition temperatures of polymers and the microstructure of obtained final ceramic samples.

Hierarchically ordered ABA triblock copolymer with large difference in glass transition temperatures of the two blocks

ABSTRACTRod‐coil‐rod triblock copolymers, poly[4′‐(methoxy)‐2‐vinylbiphenyl‐4‐methyl ether] ‐blockpolydimethylsiloxane‐block‐poly[4′‐(methoxy)‐2‐vinylbiphenyl‐4‐methyl ether] (PMVBP‐b‐PDMS‐b‐PMVBP), were synthesized by nitroxide‐mediated radical polymerization, and their hierarchically ordered structures were studied. A difunctional TEMPO macroinitiator was first synthesized by the hydrosilylation reaction between hydride‐endcapped PDMS and allylic alkoxyamine. The polymerization of the monomer MVBP was triggered by the macroinitiator, resulting in a series of triblock copolymers. The molecular weights and polydispersity indexes were determined by gel permeation chromatography. Differential scanning calorimetry results demonstrate that the triblock copolymers exhibit two glass transition temperatures (−120 °C and 160 °C) that are markedly different. As revealed by small‐angle X‐ray scattering and transmission electron microscopy experiments, the triblock copolymers self‐assemble into hierarchical structures with the liquid crystalline phase of PMVBP in the lamellar structures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1737–1744

Mechanical Property Performance of Polymer-Modified Calcium Sulfoaluminate Cement Mortar Systems

The purpose of this study was to assess the effect of polymer glass-transition temperature (Tg) on the mechanical property performance of mortars containing calcium sulfoaluminate (CSA) cement and vinyl acetate/ethylene dispersible polymer powder (VAE DPP). Competitive products were acquired from companies A, B, and C. Company A supplied VAE DPP with glass-transition temperatures of 64°F (18°C) and 19°F (−7°C). Company B supplied VAE DPP with glass-transition temperatures of 59°F (15°C) and 5°F (−15°C). Company C provided VAE DPP with glass-transition temperatures of 68°F (20°C) and −8°F (−22°C). It is important to note that differences in glass-transition temperature result from differences in the ratio of monomers utilized for production of the liquid polymeric dispersion during reaction polymerization, where the pertinent ratio is that of ethylene to vinyl acetate for materials germane to this study. Additionally, each utilized polymer powder may also differ in constituent components comprising the polymer powder as a result of the drying process, where constituent materials should not be limited to products typically utilized for forming protective colloids or products utilized as anti-caking agents. Each polymer was tested in a standard mortar formulation with polymer/cement ratio of 2/5 and water/cement ratio of 0.48. Experimental results show that polymer modification improves the ductile performance of CSA cement mortars. Additionally, experimental results show that the glass-transition temperature of vendor-specific products influences the mechanical property performance of polymer-modified CSA cement mortars.

Reorganization of the molecular orientation at the organic/substrate interface in spirofluorene thin films

The thermal annealing treatment of an organic non-crystalline film of spirofluorene causes the randomization of the molecular orientation through molecular migration. However, the magnitude of the randomization depends on the depth in the film. The comparison of variable-angle spectroscopic ellipsometry, thermally stimulated current, and field-effect transistor characteristics measurements revealed that the molecular orientation in the bulk was randomized by annealing but was still partially maintained at the organic/substrate interface. This difference in condensed states between the interface and the bulk originates from a difference in glass transition temperature.

Preparation and properties of cyclic olefin copolymers multiwalled carbon nanotube nanocomposites

AbstractNanocomposites of cyclic olefin copolymer (COC) and two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios were prepared. The morphology, thermal behavior, and electrical conductivity of the nanocomposites were investigated by scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis, and the DC conductivity measurement. It was found that the developed nanocomposite preparation method resulted in good nanotubes dispersion in the polymer matrix for both types of MWCNTs. No appreciable differences in glass transition temperatures were observed between the pure COC and nanocomposites. On the other hand, CNTs significantly improved the thermo‐oxidative stability of the COC. The nanocomposites showed significant delay in onset of degradation and the degradation temperature was ∼ 40°C higher than that of the pure COC. The nanocomposites also showed substantially higher DC conductivity, which increased with the nanotube concentration and aspect ratio. An increase of DC electrical conductivity over 109 times can be achieved by the addition of 2 wt % CNTs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Dynamic Competition between Crystallization and Phase Separation at the Growth Interface of a PMMA/PEO Blend

We investigated the dynamic competition between crystallization and phase separation in a dynamically asymmetric blend of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO). Because of a large difference in glass transition temperatures between these two components, the phase transition dynamics is slowed down and can be observed in more detail. There is a morphological inversion from spherulitic to concentric ring patterns by adjusting the quench depth. Under deep quench, phase separation tends to be enhanced by the large concentration deviation at the growth interface of crystals, and propagates outward with convective concentration waves. Meanwhile, short needle-like crystals appear in the phase separated domains, compared with long crystal strips in a spherulitic pattern. A general dynamic competition model is proposed to qualitatively interpret the complex interplay between crystallization and phase separation. On the basis of this model, various morphologies are observed and predicted.