<<
>>

THE BASIC MAINTENANCE OF WORK

In INTRODUCTION the urgency of dissertational work is proved: its purpose, the original positions which are taken out on protection, scientific are stated
Novelty and the practical importance. In this partition run-down of the basic ideas of the concept of multiscale modelling and the basic unresolved problems contains.

CHAPTER 1 contains results of studying of gelation in cysteine-silver a solution (TSSR) on the basis of methodology of multiscale modelling. In the beginning of the head the general laws of formation of thixotropic gels on the basis of low molecular weight substances are discussed and the basic results of experimental and theoretical studying of gelation in TSSR are stated.

On the classification hydrogels (GG) on the basis of TSSR belong to the class supramolekuljarnyh metallokompleksnyh some gels. Though researches kompleksoobrazovanija L-tsisteina with ions of metals including with silver, are conducted already for many years, gel-forming abilities L - cysteine were unknown earlier. Unique feature such GG is ability to connect a water considerable quantity small concentration of low molecular weight reagents (~0.01 %). Thus silver is a good antiseptic agent, and cysteine - amino acid which plays a key role in protective function of an organism on linkage of heavy metals and integument formation. GG on the basis of TSSR can serve as a matrix for creation of new medical drugs, and also represent rather simple and cheap systems for studying of processes of the self-organising which understanding opens a path to purposeful design of new materials a self-assemblage method.

Generalisation of the experimental data which have been saved up at research TSSR, has allowed to formulate phenomenological model of self-organising TSSR. According to this model gelation in TSSR occurs in three stages: formation of mercaptide of silver (MS), aggregation MS in small klastery and gel-grid self-assemblage on their basis. The yielded model only evolves the basic stages of gelation on features of dimensional streamlining on the basis of summation of the experimental facts, but does not yield the exact answer why are formed klastery MS and for what reason they form gel-grid fibres. For the answer to these questions (formation MS is authentically positioned) complex modelling TSSR within the limits of a consecutive number of the models constructed taking into account characteristic scales, fixed by phenomenological model of gelation TSSR has been executed.

By means of the kvantovo-mechanical calculations executed within the limits of a semiempirical method of molecular monasteries ZINDO/1 [2], two possible morphologies suprapolimernyh chains from MS (fig. 1) are revealed. They are formed for the account of formation of donor-acceptor communications sulphur-silver and hydrogen bridges between: carboxyl groups, carboxylic and an amino group of the next molecules.

The Atomistichesky model of water solution MS includes tsvitteryoiony silver mercaptide, salt AgNO3, the initiator of gelation Na2SO4 and water molecules. The obvious account of interaction between pairs atoms of sulphur and the silver, belonging to different particles MS, on donornoyoaktseptornomu to the mechanism is executed. For this purpose not divided electronic pairs have been entered into model of mercaptide of silver at atoms of sulphur, capable to interreact only with atoms of silver.

Calculations have been executed with valentno-force field use (VSP) AMBER [3] within the limits of classical molecular dynamics. Absent parametres of interaction have been calculated within the limits of method ZINDO/1.

A number of initial configurations in which particles MS settle down in a random way has been constructed, form klasternye and niteobraznye structures. The analysis of evolution of the prepared systems has allowed to track formation of the aggregates consisting of particles MS and low molecular weight ions. Are separately investigated niteobraznye the aggregates retried through periodic boundary conditions, fibres modelling a fragment grid gel-. All is positioned, that niteobraznye the aggregates constructed on the basis of a chain of molecules MS (in which molecules follow one another), show the tendency to destruction. Thus as during evolution disorder and klasternyh initial configurations, and after destruction niteobraznyh aggregates in a modelling cell aggregates of the extended form with cross diameter ~16 A.Vse new niteobraznye the aggregates constructed of doubled number of molecules MS are formed, did not collapse on reached times of modelling. The analysis of formed molecular configurations shows, that niteobraznye aggregates are stabilised at the expense of interaction-Nh3+i-C (O) the O-groups belonging to particles MS as a part of next klasterov. The similar principle of self-assemblage for the account amino - and carboxyl groups is described and in case of other systems [4] that testifies to universality of the observable mechanism of self-organising in TSSR. It is necessary to notice, that if to execute
The account of interaction of untied atoms sulphur-silver only within the limits of VSP AMBERбез obvious introduction of not divided electronic pairs, is not possible to construct stable niteobraznye aggregates. It is important to notice, that necessity of the obvious account of features of interaction of atoms of sulphur and silver has been caused by results of Km-calculations.

Drawing 1 - Visualization suprapolimerov, formed of 20 molecules of mercaptide of silver at the expense of co-ordinate linkages sulphur-silver and hydrogen bridges between: carboxyl groups, carboxylic and amino groups of the next molecules

The coarse-grained model has been developed for an illustration of formation of a grid of gel from klasterov MS and specifications of the reasons of one-dimensional growth of threads of a gel-grid on the basis of a Monte-Carlo technique and molecular dynamics. In model it is supposed, that formation process klasterov from particles MS has already come to the end, and the solution of the salt initiating gelation, is already entered. For depressing of number of degrees of freedom klastery MS are considered as spherical particles of the fixed diameter with the additional power centres on a surface for modelling of functional groups-COO - and-NH3 +.

Realisation of the yielded model within the limits of a Monte-Carlo technique has allowed to illustrate visually gel-grid occurrence in TSSR on the big dimensional scales ~500A. Use coarse-grained MD modelling has shown, that the main stabilising factor for niteobraznyh aggregates from klasterov MS - localisation of functional groups on opposite poles klasterov from silver mercaptide.

During the executed calculations under the schema kvantovo-mechanical calculations—> atomisticheskoe modelling—> mezoskopicheskoe modelling was
The following schema of linking of levels of modelling is used. As a result of Km-calculations necessity of the obvious account of donor-acceptor communications between atoms of sulphur and silver has been positioned at construction atomisticheskoj models. Atomistichesky modelling has allowed to reveal features of a structure klasterov from mercaptide of silver and threads grid gel. The received information has been used for construction mezoskopicheskoj models TSSR. Also Km-calculations were used for parametrization of absent potentials of internuclear interaction in chosen version VSP for atomisticheskogo level and intermolecular interaction for mezoskopicheskogo modelling level.

CHAPTER 2 is devoted studying of operated self-assemblage in solutions strongly charged zhestkotsepnyh polyelectrolytes. Use possibility zhestkotsepnyh polyelectrolytes as building blocks nanomaterialov is discussed. Two groups of problems of the conditions of formation devoted to research are considered: 1) a conductive plating on a fragment of a molecule of DNA and 2) the ordered files from sterzhneobraznyh nanorazmernyh objects.

The first group of problems is devoted modelling of formation of a continuous plating from nanochastits gold on a single fragment of a molecule of DNA. Such systems represent the big interest as they can be used for construction of essentially new element base for electronic devices. Matrix synthesis on the basis of DNA molecules - one of perspective ways of formation metallic nanostrukturnyh materials. For last years some ways of plating of fragments of DNA from which the least study is based on use of self-assemblage at the expense of electrostatic interaction of negatively charged phosphatic groups of DNA and nanochastits metal [5] were offered. Practically all works on plating studying are experimental. Meanwhile works on studying of conditions of self-assemblage of a plating practically are absent.

Proceeding from the size of DNA and nanochastits, modelling was made in frameworks mezoskopicheskoj models on the basis of a Monte-Carlo technique. As a unit of length the scale σ = 10 A.Model has been chosen contained completely dissociated fragment of DNA and unstructured LF of gold. For construction of model of interaction of unstructured LF has been used atomistichesky modelling level.

Following problems have been solved: search of the optimum mechanism of delivery nanochastits metal to negatively charged matrix of DNA; definition of optimum conditions of formation of a continuous plating. Two possible ways of self-assemblage of a plating are considered: 1) with use of positively charged LF and 2) the neutral LF polarised in the field of polyanion. Dalnodejstvujushchee electrostatic interaction plays a role of the mechanism of delivery of LF to polyanion. Short-range van-der-vaalsovo interaction of aggregating LF with DNA nitrogen bases (or with the implanted atoms of metal) and metal interaction of the next LF provide "pasting" nanochastits in aggregate.

At a pre-award stage of researches on the basis of simple theoretical models the comparative estimation of energy of the aggregates constructed from sterzhneobraznogo of polyanion and charged/polarized nanochastits has been executed. It has allowed to evolve two possible mechanisms of self-assemblage of a plating with participation of the charged LF (the electrostatic mechanism) and not charged LF (the polarising mechanism). The received information has been used for construction of coarse-grained models of plating of DNA.

DNA model has been constructed in the form of linear sequence of 100 overlaped spherical links (rough model) and with the account of feature of a dimensional structure of DNA (detailed model). Nanochastitsy have been presented in the form of the unstructured spherical power centres of two types: with the additional power centre on a surface for positive charge modelling (funktsionalizirovannye LF), with two additional power centres on a surface, located opposite, for modelling of polarisation of LF in an electrostatic field of DNA. The account of counterions has been executed also by two ways: with the help ekranirovannogo kulonovskogo interactions and by means of obvious inclusion of counterions in model.

For the correct task of metal interaction between LF the problem about interaction of two LF of gold of various diameters in frameworks atomisticheskoj models (on the basis of a Monte-Carlo technique) with use of potential Gupta [6] has been considered. It is shown, that potential energy of interaction of LF can be written down in the form of the simple formula where enter a median number of atoms in a contact zone on a surface nanochastits and distance
Between surfaces of particles that allows to simplify process of carrying out of calculations in frameworks mezoskopicheskoj models.

Results of modelling testify, that in a case funktsionalizirovannyh nanochastits the plating with the best characteristics (LF have the greatest number of contacts with each other, the bed has no tearing up and lacunas) is formed, when diameter of LF makes 1 σ, and the charge is equal to unit. In case of neutral LF kvazinepreryvnoe metal the covering is formed, when their diameter is equal 1.5 σ. With growth of diameter of LF on DNA there are the radial structures interfering formation of a qualitative conducting stratum (visual comparison of formed aggregates on fig. 2 see).

On an example of research of self-assemblage nanoprovoda with use funktsionalizirovannyh nanochastits it is shown, that though as a whole increase in detailed elaboration of model (the account of counterions, spatial structure of polyanion) influences features of distribution of LF on the polyanion, the calculated area of parametres at which in system the optimum plating is formed, practically coincides for all considered models.

Drawing 2 - plating Visualization on a single molecule of DNA. Aggregates are received with use: funktsionalizirovannyh nanochastits with a diameter D = 2 σ (σ = 10) and charge Z; neutral nanochastits diameter D, DNA polarised in an electrostatic field

The received results show, that at studying of processes of self-assemblage it is possible to be limited to introduction in model only structurally
Significant the component that simplifies representation of system and reduces computing expenses. It has the important methodical value for theoretical studying of difficult polymers-colloid systems when the obvious account of all the component is impossible. Vtselom the executed research has been realised under the schema: simple theoretical model—> atomisticheskoe modelling чч mezoskopicheskoe modelling. The theoretical model has helped to choose composition mezoskopichesih models, atomisticheskaja the model has allowed to receive simple aproksimatsiju for metal potential and to prove use bezstrukturnyh LF in composition mezoskopicheskoj models. Use of several coarse-grained models with various degree of detailed elaboration has allowed to receive the interesting methodical results connected with influence of level of coarsening on results of modelling.

As a result of the decision of the second group of problems it was possible to show a way as it is possible to operate self-assemblage sterzhneobraznyh polyanions for the purpose of construction of regular files of various morphology. As prototypes of such objects many biological macromolecules, such, as DNA, F-aktin, fd-viruses etc. which can be involved for creation of some nanoustrojstv can serve. At a pre-award stage of consideration calculations have been executed within the limits of the theory of the integrated equations in so-called PRISM-approach (Polymer Reference Interaction Site Model) and with use of direct computer modelling on the basis of Mk-model. Solutions silnozarjazhennyh sterzhneobraznyh molecules with the obvious account of counterions in wide temperature range in modes of the diluted with and semidiluted with solutions are considered. It is positioned, that at temperatures below threshold Manninga the theory of the integrated equations does not provide the exact quantitative consent with results of direct computer modelling.

On the basis of the calculations executed by a Monte-Carlo technique, it is shown, that the reason of falling of accuracy of PRISM-approach in the field of low temperatures is formation locally the anisotropic structures with Zhk - streamlining. Therefore the further calculations for the asimptotical limit of the big charges on a surface of polyanions have been made in frameworks Mk - modelling. The solutions containing sterzhneobraznye polyanions in the presence of spherical cations and polycations with the anisotropic distribution of a charge in a saltfree dilute solution have been considered.

Force of electrostatic interaction was controlled by gearing parametre γ = Г-z2 (G - length Berruma, z - a charge of the power centre) Change of parametre of gearing is equivalent to change of conditions of self-assemblage (on the one hand) or scale of objects (on the other hand).

Drawing 3 - Comparison of centre specific potential energy of systems from Nсиловых the centres in a final condition at achievement 1,000,000МК modelling steps. In drawing examples of initial streamlinings of polyanions [(i) lentoobraznoe, (iiи iii) puchek, (iv) cylindrical] are shown. At system there are cationic chains of two kinds: with asymmetric localisation of a charge (it is shown by red colour) and a charge in the molecule centre. By black lines values of centre potential energies of systems in a final condition are shown. Arrows show prospective directions of evolution of systems

It is shown, that with growth of parametre of gearing at achievement of threshold value γτ in system aggregates with high degree of streamlining of polyanions are formed, and presence of polycations with the anisotropic distribution of a charge result ins to formation stable nanostruktur with various dimensional morphology (fig. 3). For example, in case of charge localisation on an endgroup can be formed lentoobraznye aggregates. It is necessary to notice, that such lentoobraznye aggregates earlier in the literature were not discussed.

CHAPTER 3 is devoted comparative studying of structural and transport properties of ion-exchange membranes on a basis sulfirovannyh weed (an aether-aether of ketones) (SPEEK, fig. 4 see) and nafiona with the help
mezoskopicheskogo, atomisticheskogo and kvantovo-mechanical levels of modelling.

Though by present time there were many experimental researches devoted to various ionomers, the interrelation between proton conductivity and their chemical structure remains not clear. The majority of the executed theoretical works are devoted studying of proton conductivity tafiona, and only in a small amount of works other ionomers are investigated.

Transport properties sulfirovannyh ion-exchange membranes are caused by features of their chemical constitution. Thanks to presence hydrophobic (nesulfirovannyh) and hydrophilic (sulfirovannyh) links in polymer in the presence of water there is a microphase division. As a result of this process the connected network of the aqueous channels which are conductors of ions is formed. Their effective diameter in a cross-section makes ~ 4 nanometers. Hydrophobic segments of polymeric chains form a skeletal skeleton which fills space between channels and provides mechanical stability of a membrane. Hydrophilic segments form walls of channels. At reduction of water content channels contract also conductivity of an ionomer falls. Below a threshold of percolation the network of aqueous channels is broken off. It means, that the membrane ceases to be a conductor of ions. The value of a threshold of percolation at which the connected network of channels is conserved there is less, the it is better operational properties of a membrane in the conditions of the big loss of water which are realised in srednetemperaturnyh combustion cells. As the structure of channels depends on specificity of conformational behaviour of macromolecules of an ionomer, from features of distribution of sulphonic-acid groups and the water volume, the captured membrane, one of possible ways of improvement of production characteristics of polymeric membranes of combustion cells is optimisation of chemical structure of ionomers.

As characteristic diameters of channels make ~ 4 nanometers, the basic calculations have been executed in frameworks mezoskopicheskoj models on the basis of the dynamic theory funktsionala density (DTFP). At the heart of a used method lay: an axiom about unequivocal conformity of local density of particles with their distribution function and model Flori-Hagginsa for calculation of parametres of intermolecular interaction [7]. Owing to that,
That the yielded technics of modelling is seldom used by the Russian groups in the yielded chapter the developed description of a used method is yielded.

Polymer structure has been presented in the form of linear sequence polar And and non-polar In mezoskopicheskih particles [AnSm] k (fig. 4). Sulphonation degree (controlled in the parametre) and a volume fraction of water φcв to system are the main parametres of the constructed model. For the task of parametres of interaction mezoskopicheskih particles experimental values of solubility parametres Gildebranda have been used.

Drawing 4 - the Illustration to display of chemical structure a component of modelling system on atomisticheskoe and mezoskopicheskoe representations. For carrying out of calculations the ionomer sulfirovannogo has been used weed (oksi-1,4-fenilenoksi-1,4-fenilenkarbonil - 1,4-phenylene)

As the first step studying of membranes on the basis of regular multiblock copolymers [∏1S1] 20 (degree of sulphonation DS = 50 %), [Π3S2] 8 (DS = 60 %) and [A3S1] 10 (DS = 75 %) has been executed. The received results testify, that in system there is a fast phase division of hydrophilic and hydrophobic links even at small water content φc

<< | >>
A source: Komarov Pavel Vyacheslavovich. MULTISCALE MODELLING NANODISPERSNYH of POLYMERIC SYSTEMS. The dissertation AUTOABSTRACT on competition of a scientific degree of the doctor of physical and mathematical sciences. Tver - 2014. 2014

More on topic THE BASIC MAINTENANCE OF WORK:

  1. THE BASIC MAINTENANCE OF WORK
  2. the Basic maintenance of work
  3. THE BASIC MAINTENANCE OF WORK
  4. THE BASIC MAINTENANCE OF WORK
  5. the BASIC MAINTENANCE of WORK
  6. THE BASIC MAINTENANCE OF WORK
  7. THE BASIC MAINTENANCE OF WORK
  8. THE BASIC MAINTENANCE OF WORK
  9. THE BASIC MAINTENANCE OF WORK
  10. II. THE BASIC MAINTENANCE OF WORK
  11. the Basic maintenance of work
  12. THE BASIC MAINTENANCE OF WORK