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A simple technique of thermal graft copolymerization of glycidyl methacrylate (GMA) on argon plasma pretreated poly(tetrafluoroethylene) (PTFE) films or low density polyethylene (LDPE) films with simultaneous lamination of the two films was demonstrated. The effect of crosslinking agent on the adhesion strength of the PTFE/PTFE interface was also investigated. The simultaneous thermal grafting and lamination process was carried out under atmospheric conditions and in the complete absence of a polymerization initiator. The surface structure and composition of the graft copolymerized PTFE and LDPE films from either self-delamination in acetone or mechanical delamination were studied by X-ray photoelectron spectroscopy (XPS). The efficiency of surface graft copolymerization and lamination was found to be strongly dependent on the plasma pretreatment time of the substrate, graft concentration, thermal grafting/lamination temperature and time. T-peel adhesion strengths of about 0.9 and 1.7 N cm -1 were achieved for the PTFWGMA/PTFE assemblies in the absence and presence, respectively, of the crosslinking agent, triallyl-1,3,5benzenetricarboxylate (TBTC). The T-peel adhesion strength of the LDPE/GMA/LDPE assembly, on the other hand, can reach about 2.6 N cm-1 in the absence of TBTC. XPS analysis of the mechanically assembly and the PTFEIGMA + 2 ~01% TBTClPTFE delaminated surfaces suggests that the failure mode of the PTFEIGMAFTFE assembly is adhesional in nature, and that of the LDPE/GMA/LDPE assembly is cohesive

Детальніше...  

Thermally responsive hydrogels of N-isopropylacrylamide containing hydrophobic comonomers were synthesized by free radical polymerization in both toluene and water. Various hydrophobic monomers were used, i.e. methyl methacrylate, hexylacrylate, hexafluoroisopropylmethacrylate and hexafluorobutylmethacrylate. Also polymers containing hydrophilic methacrylic acid were synthesized. The swelling properties of the polymers, as well as polymers containing 30 wt% ephedrine or ibuprofen were investigated in pure water at temperatures from 20°C to 46°C. The swelling ratios of pure gels depended on the ratio of hydrophilic and hydrophobic structural units in the polymer, as well as on the network structures of the gels. The hydrophilic drug ephedrine was bound to polyacid gels causing deswelling of the gels due to electrostatic interactions. Ephedrine did not affect the swelling of the neural gels, however. Addition of hydrophobic ibuprofen made all the hydrogels collapse at room temperature no matter whether the gels were neutral or acidic. Interactions between spin probes, 4benzoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BZONO) and 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (amino-TEMPO), and the polymer gels were studied using electron paramagnetic resonance spectroscopy. The hydrophobic probe BZONO resided in the gels below the lower critical solution temperature (LCST) due to hydrophobic interactions, but dissolved, at least partially, in the aqueous phase above the critical temperature. The distribution of BZONO between the gel and the aqueous phase depended on the hydrophobicity of the polymer. Also the hydrophilic probe amino-TEMPO was partially bound into the gels.

Детальніше...  

The synthesis and characterisation of novel polyfunctional N-glycidyl epoxies are reported. N,N 0 -Bis(3-chloro-2-hydroxypropyl)-1,2,3,4tetrahydroquinoxaline underwent condensation with formaldehyde at the 6- and 7-positions to provide a mixture of the 6,6 0 -methylene and 6,6 0 /7,7 0 -dimethylene condensation products and oligomers, which were readily converted to the corresponding epoxy compounds. The product composition depended on the molar ratio of formaldehyde employed in the expected way. Enriched 13C n.m.r. spectra indicated that condensation was not completely exclusive to the 6 and 7 positions, and this was confirmed by employing N,N 0 -bis(3-chloro-2-hydroxypropyl)-1,2,3,4-tetrahydro-6-methylquinoxaline in the condensation reaction. The effect of some other substituents and a more limited exercise with the 2,3,4,5-tetrahydro-1H-1,5-benzodiazepine ring are also described. Mixed coupled systems were prepared by condensing N,N 0 -bis(3-chloro-2-hydroxypropyl)-1,2,3,4-tetrahydroquinoxaline in the presence of N,N-bis(3-chloro-2-hydroxypropyl)-3-chloroaniline and N,N-bis(3-chloro-2-hydroxypropyl)-3,5-dichloroaniline, and simple physical blends were prepared by mixing 6,6 0 -methylene[N,N 0 (2,3-epoxypropyl)-1,2,3,4-tetrahydroquinoxaline] with the corresponding dichloro and tetrachloro derivatives of bis[N,N-bis(2,3-epoxypropyl)-4-aminophenyl]methane. The glass transition temperatures and water absorptions of castings prepared from the diamine-cured epoxies are given. The effect of hygrothermal and oxidative aging on the interlaminar shear strength of the most promising systems as the matrix component in unidirectional carbon fibre reinforced composites showed no significant improvement over current high performance composites.

Детальніше...  

The understanding of water–polymer interactions in polymeric composite materials is critical to the prediction of their behavior in applications where they are exposed to water or humid environment. Moisture diffusion in unsaturated polyester–woodflour composites exposed to environments kept at room temperature and different relative humidities was investigated. Equations obtained from microscopic mass balances for vapor diffusion in solids were used to determine the effective diffusion coefficients of the different woodflours, neat resin and composites. The effect of the size and shape of the composite specimens used in the experimental work on the final moisture content was also evaluated. Different models were used to predict the composite effective diffusion coefficients as a function of filler concentrations.

Детальніше...  

The fracture toughness of a series of polyurethane elastomers based on polytetramethylene glycol (PTMEG) soft segment, a toluene diisocyanate (TDI) and a dimethyl-thio-toluenediamine (Ethacure E300) curative with different ratios of isocyanate to amine groups has been studied. The fracture toughness required to initiate crack growth was found to be invariant with stoichiometry but the degree of stable crack growth was found to vary with stoichiometry. This behaviour has been discussed in terms of the molecular and physical structure of the polymers, particularly the extent of cross-linking which varied with the isocyanate/amine ratio

Детальніше...  

Semi-empirical molecular orbital calculations and dielectric measurements have been conducted on DPE and DPK molecules and on PEEK films containing these molecular units. The calculations were performed using a modified-CNDO/2 method allowing us to take into account the van der Waals impenetrability zone of the electronic corona of the aromatic rings. From the analysis of the relative energy maps, it is shown, amongst other things, that the most probable route for a molecule to move is through gear rotations. The DPE molecule is also found to move more easily than the DPK molecule. Measurements of the dielectric permittivity and of the refractive index were not possible for the DPE molecule in benzene solution due to its low dipole moment, this being confirmed by theoretical calculations. For the DPK molecule, an experimental mean value of 3.15 D is found for m compared to a calculated value of 3.35 D. The analysis of the dissipation factor isochronal curves shows that the activation energy for the DPK molecule is largely dependent on its concentration in benzene. In the case of PEEK, two relaxations are seen at ¹ 106°C and ¹ 73°C for a frequency of 1 kHz. A parallel is drawn between isolated molecules of DPK in solution and DPK units that are distant from each other in a polymer chain, and between aggregated molecules of DPK in solution and DPK units that are close together in entangled chains. It is finally shown that the DPK molecular unit in a macromolecular chain is only able to reach the permitted conformations in low energy valleys, corresponding to gear rotation motions.

Детальніше...  

Polypyrrole (PPy) was electrochemically synthesized in boron trifluoride ethyl ether (BTEE) whose acidity was adjusted with additional ethyl ether (EE). A high quality PPy film can be synthesized in a wide mole ratio range of BTEE/EE and under mild conditions. The obtained film showed the highest tensile strength (90 MPa) we had ever seen and good anisotropy in electrical conductivity. The structure was investigated using surface enhanced Raman scattering (SERS).

Детальніше...  

A new technique combining Py-GC/MS with TG/MS can be used in analyzing the mechanism and kinetic modelling of pyrolysis. The results of this study show that a combined approach of Py-GC/MS and TG/MS exhibited dynamic curves of 13 evolved gases from the pyrolysis of PEEK from room temperature to 9008C. In this study we also discovered that there are two stable pyrolysis reaction regions during the pyrolysis in helium atmosphere at a heating rate of 108C/min from room temperature to 9008C. In the first pyrolysis region the ether group and ketone group from the main chain of PEEK decomposed to phenol and CO2, respectively. It also showed that the thermal stability of the ketone group was better than that of the ether group. Accompanied with the chain transfer in the first pyrolysis region, the fluorenone structure appeared in part of the carbonization scheme. Above 6508C it moved to the second reaction region. In this region the main decomposition products were CO2 from the ketone group of fluorenone and from the carbonized structure described above. From the two flat regions of the activation energy curve of pyrolysis, we have proposed a kinetic model with two pyrolysis regions. Based on this model, we compared the theoretical pyrolysis curve with the experimental curve, the two curves being quite similar.

Детальніше...  

An improved self-consistent scheme accounting for the 2D geometric arrangement of fibres within the matrix is proposed to predict the influence of the reinforcement effect of DGEBA/anhydride matrix by unidirectional raw glass fibres or coated fibres with silicone or DGEBA/silane coupling agents. This model is based on both (i) an analytical morphology approach underlying the percolation concept and (ii) the definition of an original 'representative morphological pattern’ accounting for local phase inversions owing the heterogeneous morphology of composite materials. It is shown that the nature of fibre sizing can influence the viscoelasticity of composite materials by inducing variations in morphology and then in the mechanical coupling. This could result from the more or less good wettability of fibres by the resin during the process. After removing the reinforcement effect through such a theoretical approach, microstructural changes of the polymer matrix induced by fibres, i.e a decrease in the crosslinking degree of the epoxy network, are quantified but no specific influence of the nature of the interface can be revealed

Детальніше...  

The molecular interactions in poly (N-isopropylacrylamide) (PNIPAAM) aqueous solution have been quantitatively investigated by using a newly developed thermal micro attenuated total reflection/Fourier transform infrared (ATR/FT-IR) spectroscopic system. PNIPAAM was prepared by the w/o emulsion method and its lower critical solution temperature (LCST) was examined by cloud point measurement and differential scanning calorimetry. The LCST of this PNIPAAM in water was about 33°C, which was also confirmed by this thermal micro ATR/FT-IR spectroscopic system. Using this novel spectroscopic system with curve-fitting program, we found that below the LCST the molecular structure of PNIPAAM in water exhibited a predominantly intermolecular hydrogen bonding (about 50%–70% of total molecular interaction estimated from amide I band) between PNIPAAM and water. However, above LCST the intramolecular hydrogen bonded conformation was about 70% in total molecular interaction (estimated from amide II band). Moreover, the hydrophobic interaction of methyl group in PNIPAAM molecule increased 1.5 times when the temperature was above the LCST. The results quantitatively indicate that the intermolecular interactions might occur mainly between PNIPAAM molecules and water when temperature was below the LCST. When the temperature was above the LCST, however, PNIPAAM molecules in water were aggregated due to both the intramolecular interactions within PNIPAAM molecules and the hydrophobic interactions in system.

Детальніше...  

Корисні статті

Як стати інженером?

Кожна людина в процесі свідомого життя стикається з проблемою вибору професії. Найбільш актуальною ця проблема є для учнів старших класів – випускників, які добровільно або примусово здають шкільні іспити та зовнішнє незалежне оцінювання, за результатами чого приймають участь в конкурсному відборі на навчання у ВНЗ. Щоб обрана професія не стала важким випробовуванням, потрібно ще у шкільні роки зважити всі «за» і «проти», оцінити свої здібності, схильності, можливості.

Вибір професії

Кожна людина зіштовхується у своєму житті з вибором, який найсильніше вплине на все її подальше життя. Йдеться про вибір професії та вибір вищої освіти. Закінчуючи школу, молоді люди стикаються з величезним вибором професій та спеціальностей: інженер, економіст, юрист, менеджер, маркетолог, логіст, фінансист і т.д. При цьому навколо можна чути безліч стереотипних фраз: "Юристи багато заробляють", "Фінансисти працюють з грошима, тому у них хороші зарплати", "Маркетолог - основний людина в будь-якому бізнесі", а часом і просто без обґрунтування - "Менеджер - це круто ". Часом, такі "поради" впливають на вибір професії.

ВНЗ України

Вища освіта є невід'ємним елементом перспективного кар'єрного росту, тому перед кожним абітурієнтом виникає проблема, в які інститути подавати документи. Варто відзначити, що в Україні існує велика кількість вузів. Всі навчальні заклади поділяються на державні та приватні, пропонуючи різноманітні освітні програми по різних профілів. Щоб пошук інститутів дав задовільні результати, слід визначитися з найбільш прийнятними спеціальностями. Також підбір університету передбачає вибір підходящої форми навчання, наявність високої акредитації у вузу і рівень його престижності.

Інженер-машинобудівник

Ні для кого не секрет, що при сучасних умовах життя, темпах розвитку промисловості, безперервній автоматизації та оптимізації роботи механізмів та виробничих процесів, великою популярністю та попитом на ринку праці користується професія інженера, особливо інженера-машинобудівника.

Щоб відповісти на питання «Хто такий інженер-машинобудівник?», необхідно розуміти , що несе в собі кожне з цих слів окремо. Інженер – це людина, яка отримала освіту з визначеного фаху. Інженер – це творець техніки. Інженер – це особа, що професійно займається інженерією, тобто на основі поєднання прикладних наукових знань, математики та винахідництва знаходить нові рішення технічних проблем. Тобто, виходячи з цих загальновживаних визначень слова «інженер» зрозуміло, що цій професії може присвятити себе лише людина з неабиякими здібностями, які ґрунтуються на знанні точних наук, логічному мисленні, невичерпному терпінні і постійному бажанні вдосконалювати світ інженерії. Від латини ingenium — здатність, винахідливість, що є свідченням того, що інженером перш за все є людина-думаюча, яка знаходиться в безперервному пошуку відповідей на складні технічні завдання.

Полімерні матеріали

Полімер це велика молекула, або макромолекула, котра складається з багатьох субодиниць. Через їх широкий спектр властивостей, синтетичні і природні полімери відіграють найважливішу і всюдисущу роль в повсякденному житті. Полімери в діапазоні від знайомих синтетичних пластмас, таких як полістирол природний біополімер, таких як ДНК і білки, які є основоположними для біологічної структури і функцій. Полімери, як природні і синтетичні, створюються за допомогою полімеризації багатьох малих молекул, відомих як мономери.