научный журнал по физике Высокомолекулярные соединения. Серия А ISSN: 2308-1120

ANOGIANNAKIS STEFANOS D., CHRISTOS TZOUMANEKAS, MOROZINIS ATHANASIOS K., THEODOROU DOROS N. — 2013 г.

A molecular-level understanding of cavitation in polymer networks upon imposition of mechanical stress is still lacking. Molecular Dynamics simulations of crosslinked amorphous Polyethylene (PE) were conducted in order to study cavitation as a function of the prevailing stress. We first show that the characteristic relaxation times related to tube confinement and chain connectivity can be obtained by examining the mean square displacement of middle chain monomers. Then, we present a methodology for predicting the cavitation strength and understanding its dependence on cohesive interactions and entropic elasticity. Our simulations show that experimental observations and predictions of continuum mechanics analysis, which relate the critical stress for cavitation to the Youngs modulus of the rubber, are in agreement with the observed tensile triaxial stress below which a pre-existing cavity cannot survive in a cavitated sample.

KLOS J.S., SOMMER J.-U. — 2013 г.

Dendrimers are macromolecules with a regular-treelike, branched architecture of their skeleton. In terms of the branching number and the number of terminal groups they represent an extreme case among branched polymers. Dendrimers can occur in neutral and various charged states. Due to their highly branched architecture excluded volume effects are of great importance and conformational properties and monomer distribution profiles of dendrimers differ considerably from those of linear polymers. We give an overview of the state-of-the-art knowledge of physical properties of dendrimers as seen from coarse-grained computer simulations. Our main focus is on isolated dendrimers with flexible spacers both in the neutral and in the charged state, as well as complexation of dendrimers with oppositely charged linear polyelectrolytes. We briefly address problems of adsorption and concentration effects in dendrimer solutions and outline recent progress and open questions in this field.

LYUBARTSEV A.P., RABINOVICH A.L. — 2013 г.

Rapid development of computer power during the last decade has made molecular simulations of lipid bilayers feasible for many research groups, which, together with the growing general interest in investigations of these very important biological systems has lead to tremendous increase of the number of research on the computational modeling of lipid bilayers. In this review, we give account of the recent progress in computer simulations of lipid bilayers covering mainly the period of the last 7 years, and covering only several selected subjects: methodological (development of the force fields for lipid bilayer simulations, use of coarse-grained models) and scientific (studies of the role of lipid unsaturation, and the effect of cholesterol and other inclusions on properties of the bilayer).

БАКОВА Г.М., БУБНОВА М.Л., ДАВЫДОВА Г.И., КНЕРЕЛЬМАН Е.И., КОЧНЕВА И.С., КУРМАЗ С.В., ПЕРЕПЕЛИЦИНА Е.О. — 2013 г.

Изучены закономерности трехмерной радикальной полимеризации диметакрилата триэтиленгликоля в массе в присутствии 0–40 мас. % сополимеров на основе этилакрилата различного состава и некоторые структурно-физические свойства полученных сетчатых полимеров. Методом низкотемпературной адсорбции азота определены количественные характеристики их пористой структуры – значения удельной поверхности, общий объем пор. Показано, что в ходе золь-гель-анализа полимерные добавки удаляются из сетчатых полимеров с помощью бензола, а на их месте остаются поры c размером от 4 до 500 нм. Максимальное значение удельной поверхности составляет около 17 м2/г. Установлена зависимость величины удельной поверхности и общего объема пор от содержания полимерной добавки в исходной композиции.

PREDEEP P., SREELATHA K. — 2013 г.

Iodine doping of polyethylene terephthalate (PET) has been made to develop intrinsically conducting plastic films. The doped material is investigated in terms of structure and morphology, electrical and optical characteristics. Considerable decrease in the value of the degree of crystallinity is observed on doping the samples. Further there are discernible shifts found in the energy gap and band edge towards lower energies on doping with iodine. The refractive index of the complex films is also found to increase.

HSIAO-PING HSU, KURT BINDER, WOLFGANG PAUL — 2013 г.

The persistence length of macromolecules is one of their basic characteristics, describing their intrinsic local stiffness. However, it is difficult to extract this length from physical properties of the polymers, different recipes may give answers that disagree with each other. Monte Carlo simulations are used to elucidate this problem, giving a comparative discussion of two lattice models, the self-avoiding walk model extended by a bond bending energy, and bottle-brush polymers described by the bond fluctuation model. The conditions are discussed under which a description of such macromolecules by Kratky-Porod worm-like chains holds, and the question to what extent the persistence length depends on external conditions (such as solvent quality) is considered. The scattering function of semiflexible polymers is discussed in detail, a comparison to various analytic treatments is given, and an outlook to experimental work is presented.

KAMESHAWARI DEVI S.H., PREETHI S., SHASHIDHARA G.M. — 2013 г.

The study involves synthesis of polypropylene grafted with glycidyl methacrylate (PP-g-GMA) using three different initiators, benzoyl peroxide, dicumyl peroxide and tertiary butyl cumyl peroxide (TBSP). Among the peroxides used, dicumyl peroxide resulted in considerable reduction of molecular weight of the resulting graft copolymer. The melting/crystallization behavior and isothermal crystallization kinetics of PP homopolymer and PP-g-GMA copolymers were studied with differential scanning calorimetry (DSC) at high undercooling (44–60°C). The results showed that the degree of crystallinity and overall crystallization rate of copolymers is greater than that of virgin PP. Among the three initiators used, TBCP exhibited lowest half crystallization time. The isothermal crystallization kinetics of the PP and copolymers was described with the Avrami equation and Sestak-Berggren (SB) equation. The Avrami exponent n of the PP and copolymers were found to be in the range 1.03 to 1.41 at high undercooling conditions employed in this study. The agreement between the values of n calculated from SB kinetics and Avrami equation is satisfactory with few exceptions. The crystallization rate of PP-g-GMA copolymer was found to be more sensitive to temperature. The isothermally crystallized samples showed a single melting peak for PP while a double peak at lower temperature was recorded for PP-g-GMA copolymer samples. The equilibrium melting point T was deduced according to Hoffman-Weeks theory. The decrease of T recorded for the PP modified with GMA suggests that the thermodynamic stability of the PP crystals is influenced by the chemical interactions.

CLAUDINE GROSS, WOLFGANG PAUL — 2013 г.

We present results for a recently introduced soft-particle type model for diblock copolymers. Our focus will be the interaction of this model with confining walls and the possibility to direct the microphase morphologies by tailoring the interactions with these walls. We begin by presenting its bulk phase diagram and our method for determination of the different phases. We interpret the phase behavior in comparison to experimental data as well as other model results. By a systematic coarse-graining of chemically realistic simulations, one can obtain the effective potential acting between the walls and the repeat units of our soft quadrumer model. We employ this coarse-grained potential then for simulations of the confined case for several strengths of attraction to the walls and demonstrate when extending the film thickness leads to nucleation of a new lamella in the center of the film and when it leads to reorientation transitions of the lamellar micro-phase.

BRUNO FAYOLLE, MARION MILLE, SVETLANA TEREKHINA, XAVIER COLIN — 2013 г.

The thermal ageing of a neat epoxy matrix has been studied at 473 K in air by three complementary analytical techniques: optical microscopy, dynamic mechanical analysis and nano-indentation. Thermal oxidation is restricted in a superficial layer of about 195 m of maximal thickness. It consists in a predominant chain scission process involving, in particular, chemical groups whose motions have the highest degree of cooperativity and thus, are responsible for the high temperature side of dissipation band. As a result, chain scissions decrease catastrophically the glass transition temperature, but also increase significantly the storage modulus at glassy plateau between T and T . This phenomenon is called “internal antiplasticization”. Starting from these observations, the Di Marzio and Gilberts theories have been used in order to establish relationships between the glass transition temperature and number of chain scissions, and between the storage modulus and transition activity respectively. The challenge is now to establish a relationship between the transition activity and the concentration of the corresponding chemical groups.

CHE T., HU Z., LI Y.F., LIU S.L., MENG Y.L., TONG J.B., XU X.M. — 2013 г.

Quantitative structure property relationships are systematically studied for glass transition temperature simulation of polyacrylate. A newly developed descriptor-generalized correlative index is used for the expression of chemical structure of polyacrylate. A multiple linear regression model is built after screening some insignificant parameters with the stepwise multiple regression technique. The correlation coefficient Rcum and cross-validated correlation coefficient Qcum are 0.991 and 0.985, respectively. Furthermore, the superior performance of the MLR model is tested by the external set, the correlation coefficient is Qext = 0.920. In conclusion, generalized correlative index descriptor can be used for estimating and predicting glass transition temperature of polyacrylate.

2013

BASCHNAGEL J., CAVALLO A., JOHNER A., KREER T., MEYER H., SCHULMANN N., WITTMER J.P. — 2013 г.

The density crossover scaling of thermodynamic and conformational properties of solutions and melts of self-avoiding and highly flexible polymer chains without chain intersections confined to strictly two dimensions (d=2) is investigated by means of molecular dynamics and Monte Carlo simulations of a standard coarse-grained bead-spring model. We focus on properties related to the contact exponent 2 set by the intrachain subchain size distribution. With R Nv being the size of chains of length N and the monomer density, the interaction energy eint between monomers from different chains and the corresponding number nint of interchain contacts per monomer are found to scale as eint nint 1/Nv 2 with v=3/4 and 2 = 19/12 for dilute solutions and v=1/d and 2= 3/4 for N? . Irrespective of , long chains thus become compact packings of blobs of contour length L Nnint Rdp with dp=d- 2= 5/4 being the fractal line dimension. Due to the generalized Porod scattering of the compact chains, the Kratky representation of the intramolecular form factor F(q) reveals a non-monotonous behavior approaching with increasing chain length and density a power-law slope F(q)qd 1/(qR) 2 in the intermediate regime of the wavevector q. The specific intermolecular contact probability is argued to imply an enhanced compatibility for polymer blends confined to ultrathin films. We comment briefly on finite persistence length effects.

ANIKET BHATTACHARYA — 2013 г.

We study translocation dynamics of a semi-flexible polymer through a nanoscopic pore in two dimensions (2D) using Langevin dynamics simulation in presence of an external force inside the pore. We observe that for a given chain length N the mean first passage time (MFPT) increases for a stiffer chain. By repeating the calculation for various chain lengths N and bending rigidity parameter b we calculate the translocation exponent ( N ). For chain lengths N and bending rigidity b considered in this paper we find that the translocation exponent satisfies the inequality 1 + v, where v is the equilibrium Flory exponent for a given chain stiffness, as previously observed in various simulation studies for fully flexible chains. We observe that the peak position of the residence time W(s) as a function of the monomer index s shifts at a lower s-value with increasing chain stiffness b. We also monitor segmental gyration Rg(s) both at the cis and trans side during the translocation process and find that for b 0 the late time cis conformations are nearly identical to the early time trans conformations, and this overlap continues to increase for stiffer chains. Finally, we try to rationalize dependence of various quantities on chain stiffness b using Sakaues tension propagation (TP) theory [Phys. Rev. E 76, 021803 (2007)] and Brownian Dynamics Tension Propagation (BDTP) theory due to Ikonen et al. [Phys. Rev. E 85, 051803 (2012); J. Chem. Phys. 137, 085101 (2012)] originally developed for a fully flexible chain to a semi-flexible chain.

BLIZNYUK V.N., СИДОРЕНКО А.В., ТКАЧЕНКО И.М., ШЕВЧЕНКО В.В., ШЕКЕРА О.В. — 2013 г.

Рассмотрены особенности нелинейно-оптических свойств полимеров и принципы молекулярного дизайна макромолекул, содержащих в своем составе хромофорные группы. Обобщены подходы к дизайну гидроксилсодержащих азомономеров и полиуретанов с нелинейно-оптическими свойствами на их основе. Предложена классификация азосодержащих полиуретанов, основанная на их химическом строении и способе синтеза и обсуждаются особенности структуры и нелинейно-оптических свойств этих полимеров.

ТКАЧЕНКО И.М., ШЕВЧЕНКО В.В., ШЕКЕРА О.В. — 2013 г.

Разработан метод синтеза фторированного аллилсодержащего бисфенола на основе 4,4-[(2,3,5,6-тетрафтор-1,4-фенилен)бис(окси)]дифенола. Поликонденсацией синтезированного бисфенола с декафторбифенилом получены способные к отверждению ароматические полиэфиры. Изучено влияние оснований К2СО3 и NaH на молекулярную массу полимеров и подобраны условия их отверждения по аллильным фрагментам. Механические, физико-химические и диэлектрические свойства аллилсодержащих полимеров зависят от способа их получения и отверждения.

ГОРШКОВ А.В., ЕВРЕИНОВ В.В., РОЗДИНА И.Г., ФИЛАТОВА Н.Н. — 2013 г.

Методом хроматографии в критических условиях исследована кинетика реакций полипропиленгликолей с фенилбутилизоцианатом, моделирующих процесс получения полиэфируретанов. Применение двухдетекторного варианта хроматографии позволяет следить за концентрацией начальных, промежуточных и конечных олигомеров, а также установить влияние одной концевой группы на реакционную способность другой, разделенной длинной цепью. Обработка кинетических данных позволяет определить константы скорости реакций макромолекул различной функциональности и количественно описать протекание процесса.

2013

АБРАМЕШИН А.Е., ИХСАНОВ Р.Ш., ПОЖИДАЕВ Е.Д., ТЮТНЕВ А.П. — 2013 г.

Рассмотрены общие вопросы бимолекулярной рекомбинации носителей заряда в молекулярно допированном поликарбонате. Экспериментальные исследования выполнены с использованием метода нестационарной радиационной электропроводности. Проведены численные расчеты кривых переходного тока с использованием модели многократного захвата. Достигнуто хорошее совпадение расчетных и экспериментальных кривых. Показано, что в исследованном молекулярно допированном полимере реализуется ланжевеновский механизм бимолекулярной рекомбинации.

ИХСАНОВ Р.Ш., САЕНКО В.С., ТАМЕЕВ А.Р., ТЮТНЕВ А.П. — 2013 г.

Рассмотрены общие вопросы бимолекулярной рекомбинации носителей заряда как в чистом, так и в молекулярно допированном разветвленном полифениленвинилене. Экспериментальные исследования выполнены с помощью метода нестационарной радиационной электропроводности. Проведены численные расчеты кривых переходного тока с использованием модели многократного захвата. Достигнуто хорошее совпадение расчетных и экспериментальных кривых. В исследованных полимерах реализуется ланжевеновский механизм бимолекулярной рекомбинации.

ЗАХАРОВ В.П., ЗАХАРОВА Е.М., МИНГАЛЕЕВ В.З. — 2013 г.

Исследована кинетическая неоднородность центров полимеризации изопрена на фракциях частиц титанового катализатора. Установлено, что полимеризация изопрена на катализаторе, состоящем из частиц с диаметром 0.03–0.14 мкм, протекает с участием одного типа центров, который характеризуется низкой реакционной способностью. На частицах катализатора с диаметром 0.15–4.50 мкм возможно формирование до двух типов центров полимеризации высокой реакционной способности. Введение модификаторов, понижение температуры формирования катализатора и гидродинамическое воздействие приводят к созданию узкодисперсной фракции частиц с диаметром 0.15–0.18 мкм, на которой функционирует один тип центров – генерирующий высокомолекулярный 1,4-цис-полиизопрен. Полученные результаты согласуются с представлением о частицах с диаметром 0.15–4.5 мкм как об агломератах элементарных кристаллитов -TiCl3, объединенных за счет дополнительных связей Al–Cl c поверхностным атом титана. В то же время, частицы катализатора с диаметром 0.03–0.14 мкм образованы минимальным числом элементарных кристаллитов, где атомы титана содержат меньшее число атомов хлора.