Influence Of Glass Transition Temperature Research Articles

The Influence of Glass Transition Temperature of PMMA-Based Nanoparticles on the Release Profile of Praziquantel as a Strategy for Controlling Drug Release

The Influence of Glass Transition Temperature of PMMA-Based Nanoparticles on the Release Profile of Praziquantel as a Strategy for Controlling Drug Release

Low viscosity versus high viscosity PMMA bone cement for total joint arthroplasty: Influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups, and crystallinity index on quasi-static flexural strength

The commercially available low viscosity (LV) PMMA bone cement has higher mechanical properties than high viscosity (HV) PMMA bone cement. However, the influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups and crystallinity index on flexural strength is yet to be unveiled. The present study is aimed to investigate the influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups and crystallinity index that contributed to the higher flexural strength of LV bone cement compared to HV bone cement. The thermal behavior analysis indicated higher glass transition temperature and residual content for LV bone cement (87.5 ± 1.80 °C and 15.56±0.62%, respectively) as compared to HV bone cement (81±2.64 °C and 13.69±0.38%, respectively). Moreover, the chemical parameters such as relatively low residual monomer content computed using Raman spectroscopy and low transmittance of chemical functional groups found in FTIR spectra for LV bone cement imply better flexural strength compared to that of HV bone cement. Results indicated the crystallinity index was higher for LV (42.78 ± 0.54%) bone cement than HV bone cement (36.41 ± 0.18%). The difference in flexural strength between LV and HV bone cements governed by glass transition temperature, crystallinity index, residual monomer content and transmittance of chemical functional groups assists in the improvement and applications of PMMA bone cement.

Strong Variation of Micelle-Unimer Coexistence as a Function of Core Chain Mobility.

Polymeric micelles coexist in solution with unassembled chains (unimers). We have investigated the influence of glass transition temperature (T g) (i.e., chain mobility) of the micelle core-forming blocks on micelle-unimer coexistence. We synthesized a series of seven PEG-b-P(nBA-ran-tBA) amphiphilic block copolymers (PEG = poly(ethylene glycol), nBA = n-butyl acrylate, tBA = tert-butyl acrylate) with similar molecular weights (12 kg/mol). Varying the nBA/tBA molar ratio enabled broad modulation of core block T g with no significant change in core hydrophobicity or micelle size. NMR diffusometry revealed increasing unimer populations from 0% to 54% of total polymer concentration upon decreasing core block T g from 25 to -46 °C. Additionally, unimer population at fixed polymer composition (and thus core T g) increased with temperature. This study demonstrates the strong influence of core-forming block mobility on polymer self-assembly, providing information toward designing drug delivery systems and suggesting the need for new dynamical theory.

Influence of glass transition temperature of crosslinked unsaturated polyester resin/styrene formulations on the final conversion after an isothermal curing at 100°C

SMC (sheet molding compound) is a composite based on fibers‐reinforced unsaturated polyester (UP) resin molded usually at 140°C to 170°C under a pressure of 60 to 100 bars. In order to develop new SMC formulations that can be molded at lower temperature (100°C) for economic and environmental reasons, the formulation of the composite had to be completely modified, both to allow a rapid reaction at 100°C, but also to avoid a vitrification phenomenon due to the fact that the glass transition temperature (Tg) of the SMC parts becomes, during the molding process, higher than the mold temperature. In this paper, the relation between the molding temperature, the glass transition temperature, and the final conversion of UP resin/styrene formulations has been underlined. The Tg of the cured resin was decreased by two different ways. The first way involved the reduction of the crosslinking density of the UP resin by using a blend of two resins, a pure maleic and a more flexible one. This blend allows to adjust the Tg over a temperature range from 197°C (Tg of the pure UP resin) to 75°C (Tg of the pure flexible resin). The second way consisted in the addition of butyl methacrylate (BuMA), a reactive plasticizer, to the formulation, allowing a decrease of the final material's Tg from 197°C to 130°C by replacing 35 wt% of styrene by BuMA. These two methods allow to obtain a final conversion of 99% after 8 minutes of molding at 100°C.

A study of adhesion on stainless steel in an epoxy/dicyandiamide coating system: Influence of glass transition temperature on wet adhesion

Abstract A coating was developed by controlling its glass transition temperature (Tg). This coating attained its highest Tg value in wet conditions (wet Tg) of higher than 100 °C, and maintained its adhesion on stainless steel even after immersion in boiling water. When this coating material was applied to a conventional two-component epoxy structural adhesive as a metallic primer, it improved the primer adhesion durability on the stainless steel sheet in water significantly, even if it was not chemically modified (without pretreatment). This indicated that a relative weak hydrogen bond between the hydroxyl group of the epoxy network and a surface hydroxyl group of the oxide layer of the stainless steel could be sufficient to prevent water penetration into the interface if the thermal mobility of the epoxy network is restrained. An investigation by X-ray photoelectron spectroscopy (XPS) indicated an interaction between a primer amino-group component and the metallic surface accompanied by proton transfer. However, the thermal mobility of the epoxy network could be the most important factor in its adhesion in wet conditions.

Electrospinning of Styrene–Ethyl Acrylate Emulsion Copolymers: Exploring the Impact of Polymer Polarity and Glass Transition Temperature on Fiber Formation and Hydrophobicity

ABSTRACTIn this study, the spinnability of styrene–ethyl acrylate copolymers prepared via emulsion polymerization was explored with the aim to establish the influence of glass transition temperature and polymer composition on morphological features of electrospun materials with regard to their hydrophobic/hydrophilic nature. Nonwoven mats from polymer solutions in N,N′-dimethylformamide were spun using the electrospinning method (Nanospider™ device). It was demonstrated that changing the copolymer polarity and glass transition temperature by copolymer composition or utilizing different supporting materials might lead to nanofiber webs with controlled hydrophobic/hydrophilic properties, which predetermines them for a wide range of applications such as protective textiles, composites, etc.

Influence of Glass Transition Temperature of Underfill on the Stress Behavior and Reliability of Microjoints Within a Chip Stacking Architecture

In this study, the reliability performance of two capillary-type underfill materials with different glass transition temperatures (Tg) and coefficients of thermal expansion (CTE) were assessed for a chip stacking architecture. The microbumps for integrating four chips on a Si interposer were with a pitch size of 20 μm and composed of 5 μm Cu/3 μm Ni/5 μm Sn2.5Ag solder cap. A thermocompressive bonder was used to interconnect the microbumps at 280 °C for 15 s, and the microgaps between the chips and the interposer were then, respectively, sealed by the mentioned underfill materials to form a chip stacking architecture. Then, the reliability characteristics of the test vehicles were evaluated following the preconditioning and temperature cycling test (TCT). Furthermore, a numerical analysis model was established by ansys software to study the stress and strain contours of the microjoints sealed by different underfill materials. It was found that the lifetime of microjoints was highly related to the Tg points of underfills, an interfacial fracture was observed within the microjoints sealed by a lower Tg underfill after temperature cycling because the tensile strength damaged the Sn depletion zone as heated.

The influence of glass transition temperature on the critical size for deformation mode transition in metallic glassy films

The size effect on the bending deformation behaviour of magnetron-sputtered La 57 Al 25 Co 18 , Cu 50 Zr 50 and Fe 70 Y 8 B 22 glassy films was investigated. The transition of the deformation mode from highly localized to non-localized occurs as the film thickness reduces below the critical value, which does not exhibit a distinct dependence on Poisson’s ratio. By combining the already-reported critical size for deformation mode transition in various metallic glasses, it is found that the critical size is primarily proportional to the homologous temperature.

Glass Transition Temperature Influence on Crosslinked and Entangled Polymer Interfaces

The influence of glass transition temperature (Tg) on crosslinked and entangled polymer interfaces was investigated using coarse grained molecular dynamics (MD). A crosslinked polymer interface and an entangled polymer interface were built and the Tg for each system were obtained by confining a thin film between two rigid walls. The physical properties of each system above and under Tg were compared. The mechanical properties were also explored by pulling the interfaces apart at different temperature. The results are qualitatively agreed with experimental observations. Furthermore, the present results show that, when under tensile loading at temperature higher than Tg, the entangled interface exhibits strain softening while the crosslinked thin film is still able to show strain hardening. The different performances may due to that, at high temperature, the high mobility of monomers tend to unravel the entangled chain in linear polymer system while in crosslinked system, monomers with high mobility tend to arrest the void and decrease the void propagation.

Temperature characteristics of the forward voltage of GaN based blue light emitting diodes

The temperature characteristics of the forward voltage of GaN based blue light emitting diodes are studied. We find that the temperature coefficient decreases with the increasing temperature when the temperatures is relatively high. There is an inflection point as the temperature coefficient deceases，then the temperature coefficient changes from negative to positive. If the temperature still increases at this moment，the forward voltage will increase dramatically，resulting in the failure of the light emitting diodes. This phenomenon is not obvious when the current is low. When the current increases，this phenomenon becomes more and more obvious，and the temperature of inflection point becomes lower and lower. Moreover, the forward voltage increases more quickly when the temperature is higher than the inflection point temperature. By comparing the test result of another group light emitting diodes with the same package epoxy, we find that the influence of glass transition temperature of the package epoxy can be neglected. The appearance of this phenomenon is due to the rapid increment of the equivalent series resistance，of which the main reason is the rapid deterioration of the p-type layers of the GaN based blue light emitting diode. The result shows that we can judge the quality of the GaN based blue light emitting diodes p-type layers quickly by measuring the variation of the forward voltage with temperature，which is a rapid method for the researchers and producers.

Conductive carbon black-filled polymethacrylate composites as gas sensing materials: Effect of glass transition temperature

To reveal the influence of glass transition temperature of matrix polymer on electric resistivity and electrical response to organic solvent vapors of carbon black (CB) -filled polymer composites, conductive CB/poly(methyl methacrylate), CB/poly(butyl methacrylate) and CB/poly(2-ethylhexyl methacrylate) composites were fabricated by polymerization filling. It is found that the composites obtained exhibit a lower percolation threshold and a slower electrical response rate when the glass transition temperature of the matrix polymer is higher. Because the dispersion status of CB particles in the composites is related to the glass transition temperature or viscosity of the matrix polymer, and influences the composite conductivity. Low viscosity of the matrix polymer would certainly benefit the diffusion of solvent molecules in the matrix polymer and decrease the response time of the composites against organic vapors. These results would help to choose a suitable polymer as the polymer matrix and to understand the electrical response behavior of the composites as promising gas-sensing materials.

The effect of temperature and strain rate on the impact performance of recyclable all-polypropylene composites

Highly oriented polypropylene (PP) tapes, with high tensile strength and stiffness achieved by molecular orientation during solid state drawing, are consolidated to create fully recyclable, high performance “all-polypropylene” (all-PP) composites. These composites possess a large processing temperature window (>30 °C) and a high volume fraction of highly oriented PP reinforcement phase (>90%). This large processing window is achieved by using co-extruded, highly drawn PP tapes. This paper investigates the relationship between the impact resistance of all-PP composite laminates based on these highly oriented co-extruded PP tapes, and the temperature and velocity of impact. Unlike isotropic PP, the highly oriented nature of all-PP composites means that a significant influence of glass transition temperature is not observed and so all-PP composites retain high impact energy absorption even at low temperatures. Finally, the ballistic impact resistance of all-PP composites is investigated and compared with current commercial anti-ballistic materials.

Cryostability of frozen concentrated orange juices produced by enzymatic process

The cryostability of frozen concentrated orange juices (FCOJ) produced by an enzymatic process (enzymatic juice) and a squeezing process (squeezed juice) was investigated. The results showed that after thawing the enzymatic juice was superior in colour stability and cloud stability to the squeezed juice. The influence of glass transition temperature and viscosity of juices on the cryostability was examined and the data showed that some physico-chemical changes/reactions in juices during storage were controlled by diffusion. The composition of carbohydrates in juices was determined by high performance liquid chromatography (HPLC). Results obtained showed that the dominant solutes (low molecular weight compounds) of FCOJ governed the glass transition temperature of juices while the smaller fractions (high molecular weight carbohydrates) of the total solids of FCOJ had significant effects on the viscosity of FCOJ.

Film formation from cationic electropaint systems containing resins with different glass transition temperature

Some phenomena in the deposition process of electropainting have not been well elucidated till now. In this paper, to investigate an influence of glass transition temperature ( T g) on film formation, the deposited film was observed with an atomic force microscope and the electrochemistry was investigated, using two kinds of cationic acrylate resin with different T g (methyl methacrylate system (MMAs): T g=70°C, and methyl acrylate system (MAs): T g=5°C). Electrodeposition was performed under constant voltage or current condition. At constant voltage, the deposition behavior in the two resin systems differed extremely. The MMAs, the resin with high T g, produced a high resistance film. The MAs, the resin with low T g, was deposited forming a film at a voltage lower than 20 V. At constant current, the film formation did not result in a rise in voltage. It behaved like a conductive film. When the resin with high T g was used, particulate deposits were observed by AFM even in the induction period. The resin with low T g formed flat deposits. These results suggest that paint deposition is initiated once electrolysis of water starts. In addition, there are two types of film formation on the cationic electropainting: high resistance film formation for the resin with high T g, and ion-permeable film formation for the resin with low T g. In both cases, film growth occurs at the film/bulk solution interface.

Influence of glass transition temperature on latex particle morphology

Macromolecular SymposiaVolume 151, Issue 1 p. 407-412 Article Influence of glass transition temperature on latex particle morphology Lina E. Ivarsson, Lina E. IvarssonSearch for more papers by this authorOla J. Karlsson, Ola J. KarlssonSearch for more papers by this authorDonald C. Sundberg, Donald C. SundbergSearch for more papers by this author Lina E. Ivarsson, Lina E. IvarssonSearch for more papers by this authorOla J. Karlsson, Ola J. KarlssonSearch for more papers by this authorDonald C. Sundberg, Donald C. SundbergSearch for more papers by this author First published: 14 November 2000 https://doi.org/10.1002/1521-3900(200002)151:1<407::AID-MASY407>3.0.CO;2-4Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume151, Issue1February 2000Pages 407-412 RelatedInformation

Indentation Cracking of Composite Matrix Materials

Composite restorative materials wear by a fatigue mechanism in the occlusal contact area. Here, tooth cusps and food debris cyclically indent the restoration. Modeling this phenomenon requires an understanding of material response to indentation. The question in this study was whether material response depends on indenter size and geometry, and also, whether polymers used in restorative materials should be considered elastic and brittle, or plastic and ductile for modeling purposes. Three resins used as matrices in proprietary restorative composites were the experimental materials. To ascertain the influence of glass transition temperature, liquid sorption, and small amounts of filler on indentation response, we prepared materials with various degrees of cure; some samples were soaked in a 50/50 water/ethanol solution, and 3 vol% silica was added in some cases. Indentation experiments revealed that no cracking occurred in any material after indentation by Vickers pyramid or spherical indenters with diameters equal to or smaller than 0.254 mm. Larger spherical indenters induced subsurface median and surface radial and/or ring cracks. Critical loads causing subsurface cracks were measured. Indentation with suitably large spherical indenters provoked an elastoplastic response in polymers, and degree of cure and Tg had less influence on critical load than soaking in solution. Crack morphology was correlated with yield strain. Commonly held assumptions regarding the brittle elastic behavior of composite matrix materials may be incorrect.

The universality of the density of states of low-energy excitations in glasses

Abstract Amorphous solids exhibit a variety of unusual low-temperature properties. These so-called ‘anomalies’ can be described by a phenomenological model based on the assumption that small structural entities are capable of tunnelling between different sites in the random structure. The validity and limitations of this model are discussed on the basis of new experimental results, focusing on the influence of glass-transition temperature, sample preparation and superconductivity on the density of tunnelling states.