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Siloxane-imide block copolymer membranes with various siloxane contents were prepared and their dynamic viscoelasticity, sorption of carbon dioxide, and permeability of carbon dioxide, oxygen and nitrogen were studied. The siloxane-imide block copolymer consists of a microphase separated structure of imide-rich and siloxane phases, and the mechanical properties of the siloxane-imide block copolymer are well retained up to a siloxane content of about 20 wt%. The amount of carbon dioxide sorbed into the siloxane-imide block copolymer decreases with the introduction of siloxane, reflecting the less-sorptive capability of the siloxane group. The sorption behaviour of the block copolymers is interpreted in terms of a dual-mode sorption theory, which is applied to glassy imide-rich phases. On the other hand, the permeability coefficients of carbon dioxide, oxygen and nitrogen are remarkably increased with siloxane content when the latter is more than 10 wt%, and the permselectivity of oxygen to nitrogen is decreased with siloxane content. These behaviours are interpreted by considering the arrangement of the two phases in the membrane.

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The morphological evolution of as-grown poly(phenylacetylene) (PPA) free standing films has been studied. Investigations performed by scanning electron microscopy show that the freshly prepared PPA films exhibit a glass-like morphology which subsequently evolves into a microsphere structure. After ageing for 3 months at room temperature, PPA films reach a stable enamel-like phase. The chemical structure of the Rh(I) catalysts does not appear to influence the morphology of PPA. However, different catalysts yield different rates of morphological evolution

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Random incorporation of pendent aryl amines on the backbone of poly(arylene ether sulphone)s was achieved by the copolymerization of a minor amount of a second activated aromatic dihalide, bis(4-fluorophenyl)-3-aminophenylphosphine oxide (amino DFTPPO), with 4,4'-dichlorodiphenylsulphone (DCDPS) and bisphenol A via aromatic nucleophilic substitution polymerization using N-methylpyrrolidone (NMP) as the solvent, toluene as the azeotroping agent and potassium carbonate as the base. The pendent amines were optionally chemically modified by conversion to maleimides and thermally cured to afford tough insoluble networks Epoxy networks were also obtained by reacting the pendent amines with liquid epoxy resin and 4,4'-diaminodiphenylsulphone (DDS). The synthesis and characterization of these novel thermosetting materials were investigated, and it was demonstrated that selected compositions could significantly improve the fracture toughness of the epoxy networks. Two important variables identified were the weight or volume fraction of the thermoplastic modifier and, importantly, the concentration of the pendent aminophenyl 'cure' sites. In this research, about 25mo1% cure sites was the optimum concentration utilized, which produced tough multiphase systems Higher aminophenyl concentrations resulted in more homogeneous morphologies and fracture toughness was about the same as the control

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Rheological studies of gelatin solutions in the concentration range 4-14% were performed through the sol-gel transition as a function of concentration, pH and ionic strength. At the gel point, a power-law frequency dependence of the viscoelastic functions G'(e~), G"(~o) and r/*(og) was observed. The power-law exponents n obtained from these dynamic measurements were confirmed by creep experiments and are in agreement with a previous study in a lower concentration range, 1-5%. Under all conditions, the n values fall between 0.64 and 0.72, a range consistent with theoretical treatments of Martin et al. and Muthukumar et al. The critical gel strength, S, increases with concentration approximately as Sac C133 in the concentration range 4-14%. Within experimental error, S is approximately consistent with an empirical relation suggested in the recent literature, S--G~-"~/~, where Ge and r/o are, respectively, the equilibrium modulus of the fully developed gel and the shear viscosity of the initial sol. The implications of these observations with respect to the structure of the critical gel are discussed.

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We have examined polypyrrole-polyester and polypyrrole-quartz fibre composite samples using time-of-flight secondary ion mass spectrometry (TOF-SIMS). This technique has allowed us to confirm that in each composite the conducting polymer overlayer of cationic polypyrrole chains is doped with 5-sulphosalicylate dopant anions, at least to a sampling depth of 10 ]~. Surprisingly there is no detectable presence of the second aromatic sulphonate dopant anion utilized in the Milliken synthetic procedure (1,5-naphthalenedisulphonic acid, disodium salt). Our Fourier transform (FT) Raman spectra of these polypyrrole-fibre composite contain strong spectral bands due to the cationic polypyrrole chains, several weak features due to the underlying fibre substrate (particularly in the case of the polyester fibres), and no bands attributable to the dopant anions. These observations suggest that the Raman scattered light from the substrate component is largely reabsorbed by the polypyrrole overlayer. Thus we conclude that there must be extensive coverage of the fibre substrate by the conducting polymer with few, if any, 'bare' patches. Finally, our FTi.r. microscopy studies on these coated composites produced good quality spectra of the underlying substrate with few features attributable to the polypyrrole overlayers

Детальніше...  

Poly(ether ether ketone) (PEEK) composites were made by impregnation of continuous carbon fibres with aqueous suspensions of PEEK particles made by a novel precipitation process. These particles were suspended in aqueous solutions of ammonium salts of polyamic acids which performed two essential roles: as a polymeric dispersant and as a binder at the fibre-matrix interface. The resulting composite panels had properties that were comparable in some cases to those of commercially available PEEK composites. Fracture surface analysis from unidirectional panels suggests that the miscibility of the matrix and binder affects the failure mode at the fibre-matrix interface.

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The relative thermal and oxidative stabilities of N-[3-(triethoxysilyl)propyl]2,4-dinitroaniline (1), incorporated covalently into sol-gel coatings and of 2,4-dinitroaniline, incorporated non-covalently into similar coatings, showed no significant difference in relative thermal stability in sol-gel derived films under a variety of conditions: with no overcoat of SiO2; with a dense sol-gel-derived overcoat of SiO2; with a porous overcoat of SiO2; over a porous, high surface area coating of SiO2; and copolymerized with or physically incorporated into dense and porous SiO2 films derived from tetraethylorthosilicate.

Детальніше...  

Solid-state n.m.r, techniques have been used to study the microphase structure of poly(styrene-bmethylphenylsiloxane) (PS-b-PMPS) diblock copolymers with different compositions and molecular weights. The proton n.m.r, spectra display motionally narrowed lines of the PMPS component at ambient temperatures. The mobility of the segments in the copolymers is different, however, from that in the homopolymer. This can be related to the shift of the glass transition temperature (T~) for the siloxane-rich phase, not detected by d.s.c. By measuring the proton spin diffusion with 13C detection--combining a dipolar filter with line-narrowing techniques--the microdomain dimensions have been evaluated quantitatively. The results are compared with determination of the phase separation by SAXS and TEM. It is shown that solid-state n.m.r, is able to detect heterogeneities on a scale as small as 2 nm in systems that exhibit only a single Tg in the d.s.c, measurement. In addition, an interphase in the phase-separated PS-b-PMPS systems is revealed by spin diffusion measurements and confirmed by two-dimensional heteronuclear wideline separation n.m.r, spectroscopy

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The growth of interlaminar cracks from pre-existing defects under static and cyclic loading is of major concern in the application of advanced composites in primary structures. To overcome this problem, within the last few years many toughened graphite composites have been introduced by materials suppliers. Based on fundamental studies about the influence of the constituent properties, a third generation of toughened epoxy and bismaleimide prepreg systems with a well balanced property profile have been developed. Key factors influencing interlaminar fracture toughness and damage tolerance were identified in the frame of the development. Different toughening concepts of the matrix, rubber toughening as well as the incorporation of thermoplastics, have been studied in the neat resin as well as in the composite in combination with different fibre types. The multifaceted aspects of the relationship between the chemical structure of the matrix, the geometrical restrictions due to microstructure and the corresponding properties of the composite will be discussed.

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The conformation of lightly branched star polymers in the theta state is investigated. Long-range two- and three-body interactions are assumed to compensate one another exactly, whereas the screened interactions, arising from the finite width of the interatomic potential, do survive. Their repulsive potential dies off with interatomic distance r like (r2) -s/2, so that the mean-square radius of gyration is asymptotically proportional to the number of bonds N. However, the screened interactions expand the polymer above the random-walk conformation and give rise to a further topology-dependent term proportional to N 1/2. The topological index g = (S 2)star/(S2)lin decreases with increasing N for any degree of branching, becoming linear in N -1/2 and tending to the limit 9o~=(3f-2)/f 2 for large N, in agreement with Monte Carlo simulations performed at a vanishing second virial coefficient by Bruns and Carl in 1991. A similar dependence from N-t/2 is also found for the ratio of the hydrodynamic radii h= RH,star/RH,li n.

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Корисні статті

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.

Інженер-механік

Інженер-механік (від лат. Ingenium – талант, обдарованість, і mēchanicus – механік) – це технічний чи технологічний фахівець з вищою освітою, який застосовує отримані знання для конструювання, проектування, моделювання та експлуатації машин, апаратів та технічного обладнання в різних галузях сільського господарства та технічного виробництва. Першими з інженерів були саме механіки; вони розробляли і збирали різноманітні машини і механізми, в яких використовували принципи і закони механіки.

Комп'ютер для інженера

У сучасному світі комп'ютери дуже поширені. Складно уявити людину, не знайому з цим поняттям. Багато професій зобов'язані своїм виникненням саме комп'ютеру, вони б просто не з'явилися без створення електронно-обчислювальної техніки.

І хоча відносно недавно, на початку XX століття, комп'ютери були розкішшю і використовувалися лише для самих складних розрахунків, у наш час комп'ютери та комп'ютерна техніка дуже глибоко інтегрувалися у наше життя. Сучасне людство залежить від комп'ютерів, що викликає подиву, якщо розглянути, коли і в яких випадках вони використовуються.

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.

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.