High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T_(0). However, the T_(0) of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T_(0). In Ti_(50)Au_(50-x)Cr_(x) alloys, the strain glass appears at x = 25, and exhibits a T_(0) of 251 K, while in Ti_(50)Pt_(50-y)Fey alloys, the strain glass takes place at y = 30, and shows a T_(0) of 272 K. Both of them are comparable with the highest T_(0) value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T_(0) of the strain glass is limited. This work may help to design new strain glass systems with higher T_(0) above ambient temperature.

Molecular Dynamics Simulation of Glass Transition Behavior of Polyimide Ensemble

The effect of chromophores to the glass transition temperature of polyimide ensemble has been investigated by means of molecular dynamics simulation in conjunction with barrier analysis. Simulated Tg results indicated a good agreement with experimental value. This study showed the MD simulation could estimate the effect of chromophores to the Tg of polyimide ensemble conveniently and an estimation approach method had a surprising deviation of Tg from experiment. At the same time, a polyimide structure with higher barrier energy was designed and validated by MD simulation.

Understanding the alkyl effect of geminal dinitropropyl ester energetic plasticizers on hydroxyl terminated polybutadiene(HTPB):Simultaneous tuning on low temperature behavior and processability

Geminal dinitropropyl ester plasticizers(DNPEPs) possess excellent energetic performances which provide good potentials as insensitive plasticizer. In this study, we design and synthesize DNPEPs with different alkane chain parts, and systematically investigate their structure-property relationships.Results show that DNPEPs have impact sensitivities all higher than 25.2 J, thermal decomposition temperatures all higher than 254 ℃, and glass transition temperatures(T_(g)) lower than-90 ℃.Furthermore, the effects of DNPEPs as plasticizer are studied on hydroxyl terminated polybutadiene(HTPB) in detail, including the viscosity, glass transition temperatures and others. It is noteworthy that 2,2-dinitropropyl nonanoate(DNPNc) among these DNPEPs exhibits the most expected simultaneous tuning effects on both viscosity and T_(g) of HTPB systems, providing favorable potentials to replace the conventional plastizers as dioctyl sebacate(DOS) in the HTPB based propellants and explosives.

Synthesis of Bio-Plasticizer from Soybean Oil and Its Application in Poly(Vinyl Chloride) Films

Herein,epoxidized soybean oil methyl ester(ESOM)plasticizer was synthesized for the preparation of plasticized poly(vinyl chloride)(PVC)films by the alcoholysis and epoxidation.The chemical structure of ESOM was investigated by infrared spectrum and 1 H nuclear magnetic resonance.The effect of content of ESOM and petroleum based plasticizer di-2-ethylhexyl phthalate(DEHP)on the performance of plasticized PVC films was studied.The result showed that substituting DEHP with ESOM can improve the thermal stability of plasticized PVC films.When the weight ratio of ESOM and PVC is fixed at 1:2,plasticized PVC film presents higher elongation at break(350.8%vs.345.1%)and lower tensile strength(14.21 MPa vs.15.8 MPa)compared with PVC plasticized with DEHP.ESOM showed less weight loss than DEHP in all solvents.The excellent migration resistance of ESOM is helpful to improve stability of plasticized PVC films.In all,the obtained bio-based plasticizer will be potential to replace petroleum based plasticizer DEHP in flexible PVC materials.

A Study on the Properties of Resin Transfer Molding Cyanate Ester and Its T800 Grade Carbon Fiber Composites

The properties of resin transfer molding(RTM)cyanate ester and its T800 grade carbon fiber composites were studied with the rheometer,differential scanning calorimetry(DSC),FT-IR,dynamic mechanical analyzer(DMA),thermal gravimetric analysis(TGA),mechanical property testing,and scanning electron microscopy(SEM).The results showed that the temperature of cyanate ester suitable for RTM process was 70℃.Curing process of the resin was 130℃/2 h+160℃/2 h+200℃/2 h+220℃/4 h.Glass transition temperature and heat decomposition temperature of the cured resin are 289℃and 415℃,respectively.Mechanical properties of T800/RTM cyanate composites are 13.5%higher than that of T700/RTM cyanate composites and equal to that of T800/Prepreg cyanate composites.Tg of T800/RTM cyanate composites was proved to be 291℃.Fracture pattern of the composites was flat,which proved excellent interface properties between fiber and resin in this composite.

SYNTHESIS,CHARACTERIZATION AND PROPERTIES OF ORGANOCLAYMODIFIED POLYSULFONE/EPOXY INTERPENETRATING POLYMER NETWORK NANOCOMPOSITES

Organoclay-modified hydroxylterminated polysulfone (PSF)/epoxy interpenetrating network nanocomposites (oM-PSF/EP nanocomposites) were prepared by adding organophilic montmorillonite (oMMT) to interpenetrating polymer networks (IPNs) of polysulfone and epoxy resin (PSF/EP) using diaminodiphenylmethane (DDM) as curing agent.The mechanical properties like tensile strength,tensile modulus,flexural strength,flexural modulus and impact properties of the nanocomposites were studied as per ASTM standards.Differ...

Nanoparticle Dispersion and Glass Transition Behavior of Polyimide-grafted Silica Nanocomposites

How to control the spatial distribution of nanoparticles to meet different performance requirements is a constant challenge in the field of polymer nanocomposites.Current studies have been focused on the flexible polymer chain systems.In this study,the rigid polyimide(PI) chain grafted silica particles with different grafting chain lengths and grafting densities were prepared by "grafting to" method,and the influence of polymerization degree of grafted chains(N),matrix chains(P),and grafting density(a) on the spatial distribution of nanoparticles in the PI matrix was explored.The glass transition temperature(Tg) of PI composites was systematically investigated as well.The results show that silica particles are well dispersed in polyamic acid composite systems,while aggregation and small clusters appear in PI nanocomposites after thermal imidization.Besides,the particle size has no impact on the spatial distribution of nanoparticles.When σ·N0.5<<(N/P)2,the grafted and matrix chains interpenetrate,and the frictional resistance of the segment increases,resulting in restricted relaxation kinetics and Tg increase of the PI composite system.In addition,smaller particle size and longer grafted chains are beneficial to improving Tg of composites These results are all propitious to complete the microstructure control theory of nanocomposites and make a theoretical foundation for the high performance and multi-function of PI nanocomposites.

Synthesis of Bio-base Plasticizer Using Waste Cooking Oil and Its Performance Testing in Soft Poly(vinyl chloride)Films

Waste cooking oil was modified to prepare bio-base plasticizers(a,b and c)with terephthalic acid,adipic acid and benzoic acid by transesterification,epoxidation and ring opening reactions,respectively.The polyvinyl chloride(PVC)films(a/PVC,b/PVC and c/PVC)were prepared using a,b and c as bio-base plasticizers.The epoxidation and ring opening reactions were mainly investigated through GC-MS analysis.The structures of bio-base plasticizers(a,b and c)were confirmed by Fourier transform infrared spectroscopy(FT-IR),^(1)H NMR and ^(13)C NMR.The mechanical properties of a/PVC were as good as those of PVC films with the dioctyl phthalate(DOP)plasticizer.Meanwhile,the elongation at break of c/PVC reached 422%.The glass transition temperature(Tg)from dynamic mechanical analysis(DMA)was reduced to 30.6℃,45.3℃,23.6℃and 40.6℃,respectively when 40 phr of a,b,c and DOP plasticizer were added.Results of thermogravimetric analysis(TGA)illustrated that the thermal degradation stabilitiy of a/PVC films was better than those of c/PVC and DOP/PVC.The volatility losses of a,b and c were lower than that of the DOP.Bio-base plasticizers a and c exhibited excellent migration resistance in different solutions(distilled water,50%ethanol(w/w)).The FT-IR of PVC films showed that the downfield shifts of the—CH—Cl groups of the PVC plasticized with a and c were greater than that of b/PVC.The bio-base plasticizers b had a better plasticizing effect at low temperature.

Effect of thermo-oxidation on the dynamical and physical properties of ethylene-propylene-diene monomer elastomer

Understanding the underlying processes associated with the thermo-oxidative performance of the ethylenepropylene-diene monomer(EPDM)is essential for assessing and improving its waterproofing performance in underground infrastructures.To explore the fundamentals of EPDM degradation behavior during thermal oxidation,this paper investigates the effects of hydrocarbon free chain,carbon crosslink,chain scission,hydroxyl,and ether crosslinks,on its kinetics and mechanical properties through molecular dynamics(MD)simulations.Several EPDM thermo-oxidative models were built and verified by comparing the simulation results of oxygen diffusivity,glass transition temperature,and mechanical properties with reported experimental ones.Then the radius of gyration,free volume,density,transport,glass transition,and uniaxial compression performance were investigated via MD simulations.The results show that crosslinking in the thermal oxidation process has a significant influence on the free volume,glass transition temperature,and mechanical properties of the system;the hydroxyl and chain scission mainly interfere with the transport properties;all of these affect the structural conformation.

Study on the gas permeabilities in styrene-butadiene rubber by molecular dynamics simulation

In this research,molecular dynamics(MD)simulations were used to study the transport properties of small gas molecules in the butadiene-styrene copolymer(SBR).The condensed-phase optimized molecular potentials for atomistic simulation studies(COMPASS)force field was applied.The diffusion coefficients were obtained from MD(NVT ensemble)and the relationship between gas permeability;the chemical structure and free volume of butadiene-styrene copolymer were investigated.The results indicated that the diffusion coefficient of oxygen declined with increasing styrene content.The fraction of free volume(FFV)in butadiene-styrene copolymer was calculated.It was concluded that diffusion coefficient increased as the FFV increases,which is in accordance with the analysis of the small molecular hop through the free volume in polymer matrix.Subsequently,the glass transition temperatures of these copolymers were calculated by MD.The result showed that the glass transition temperature increased with increasing styrene content in polymer.

Precise Pentamers with Diverse Monomer Sequences and Their Thermal Properties

Sequenced-defined oligomer has been emerged as one of the hot topics in polymer chemistry due to its capability of precisely controlling both chain length and monomer sequence.Recent efforts have focused on development of synthetic methodologies using state-ofthe-art chemistry tools.However,investigating the impact of minor changes in monomer sequence on physical properties of these materials is still underdeveloped.Herein,four sequenced pentamers are synthesized by a reversible addition-fragmentation chain transfer(RAFT)single unit monomer insertion technique,in which a base pentamer possesses a relatively rigid backbone comprising of five cyclic monomer units.One of the cyclic units in this base pentamer is replaced by an acyclic monomer at different locations(the 1st,3rd and 5th unit)to produce three modified pentamers,which leads to a significant decrease of glass transition temperature(Tg)compared to the base pentamer.Meanwhile,the modified pentamers with identical primary structures but distinct monomer sequences also present different Tg values depending on the position of the acyclic monomer unit.The middle(3rd)position of the acyclic unit causes profound decrease of Tg due to its increased molecular flexibility.These synthetic pentamers have been demonstrated to be excellent oligomeric plasticizers to modulate thermal transitions of bulk polymer materials.

Morphological and mechanical characterization of a PMMA/CdS nanocomposite

Thickfilm of poly(methyl methacrylate)(PMMA)/CdS nanocomposite have been synthesized by the solution casting process.The nanostructure of the CdS particles has been ascertained through the small angle X-ray scattering(SAXS)technique.The surface morpholo-gical characterization of the PMMA/CdS nanocomposite has been done through scanning electron microscopy(SEM)analysis.The variation of mechanical loss factor(Tanδ)with temperature and tensile properties of prepared samples have been studied using Dynamic Mechanical Analyzer(DMA).This study reveals that the glass transition temperature(Tg),Young’s modulus,and fracture energy of the PMMA/CdS nanocomposite are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanoparticles and the matrix of PMMA.

Progress in organic semiconducting materials with high thermal stability for organic light-emitting devices

Organic light-emitting devices(OLEDs)have been extensively studied over the past three decades and are still attracting attention owing to their potential use in flexible and foldable displays.To achieve highly durable OLED displays for flexible devices,constitutive OLED materials need to be stable in various environments,including those with thermally and mechanically severe conditions.To this end,the present review aims to investigate the progress of OLED material research over the past two decades with respect to thermal stability.The literature survey is first conducted using the keyword“OLEDs”and then narrowed down to“high thermal stability materials for OLEDs.”The number of search results indicates that creating OLED materials with high thermal stability is a widely studied topic in the field of OLED research and has undergone an average growth rate of approximately 15%per year over the past two decades.In this review,the OLED materials used as core layers(ie,the hole injection and transport layers,emission layers,and electron injection and transport layers)are thoroughly analyzed,and the best representative materials are discussed in detail by summarizing their major thermal and electronic characteristics.Finally,several previous reports on flexible and foldable OLED displays are analyzed to determine the importance of the stability of their constitutive materials.