摘要:

AbstractThe exact solution of the problem of adsorption of a long ideal polymer chain with variable degree of stiffness on a plane surface is presented. It is shown that the adsorption of stiff polymer chains is a second‐order phase transition; in the adsorbed state “train” (i.e. adsorbed) sections are relatively longer and loop sections relatively shorter than for flexible chains. This effect is very pronounced: already for moderately stiff chains the number of Kuhn segment lengths in one “train” section at the temperatureT=Tcr/2 (Tcris the critical temperature for adsorption transition) can reach several thousands, and deviation from the surface occurs only in the form of small “hairpins”. The maximum length of the chain, which at the given conditions would flatten completely on the surface,

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020201

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe thermodynamic theory of swelling and collapse of networks in the solution of linear polymers capable to form complexes with the network chains has been developed. The interaction of components is taken into account in the framework of the Flory‐Huggins approximation. It was shown that complex formation in most of the cases leads to the contraction of the network, which can be either continuous or discrete. The influence of the solvent quality for the network and for the complex on the behavior of the network has been studied. If the solvent is poor for complexes the network reswells at high concentration of linear chains in the outer solution. This reswelling is realized as a steep conformation transitio

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020202

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe mode‐mode coupling approximation (MMCA) is applied to describe the behavior of the reduced viscosity ηrfrom ternary mixtures of two weakly charged polyelectrolytes in solution. Similarly (ε = +1) as well as oppositely (ε = −1) weakly charged polyions are discussed in this work. The variation of ηrwith the total polyelectrolyte concentrationCTexhibits a peak. The position and the height of this peak show for a given concentration of added saltCSa sensitive variation with: the charge parameters (degrees of ionization)f1andf2of both polyelectrolytes, the proportion of polyelectrolyte 1 within the mixture (x=C1/CT) and the Flory interaction parameter χFbetween monomeric units of different species. This calculation is presented within the framework of the Rouse model where no hydrodynamic interactions are taken into

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020203

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe calculation of the stress tensor from molecular simulations of atomistic model polymer systems employing periodic boundary conditions is discussed. Starting from the dynamical equations governing the motion of sites, correct double summation forms of the atomic and the molecular virial equations are derived, which are valid for flexible, infinitely stiff and rigid chain models even in the presence of interactions between different images of the same parent macromolecule. A new expression for the true instantaneous stress (flux of momentum through the faces of the simulation box) is derived and shown to exhibit large fluctuations when applied in molecular dynamics simulations. A new equation for the thermodynamic stress, cast exclusively in terms of intermolecular forces on interaction sites, is also derived. Application to Monte Carlo simulations shows that the molecular virial expression exhibits the smallest fluctuations among all stress expressions discussed, and thus allows computation of the thermodynamic stress with least uncertainty. A scheme is developed for the calculation of surface tension from intermolecular forces only.

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020204

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe conformation of diblock copolymer chains in a computer simulated homogeneous melt is analyzed distinguishing the separation of ends and the end‐to‐end vector orientation of individual chains. It is demonstrated that within the cigar‐like shapes of chains the blocks A and B are spatially separated along the cigar axis constituting concentration dipoles. Consequences of such concentration correlations for the light scattering are discussed. An extra contribution to the depolarized light scattering resulting from the “form birefringence” of individual chains is p

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020205

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently it has become possible to make a series of simulations on a supercomputer of the molecular motion of a pentacontane (C50H102) crystal containing close to 10000 atoms. Such a crystal is big enough to serve as a model of a macroscopic crystal. It can also serve as a model for polyethylene. The large volume of detailed information on the structure and motion permits a new level of understanding. Information on crystal appearance, pseudo‐symmetric crystal structures, picosecond time‐scale formation of conformational defects and the beginning of the melting process is presen

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020206

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper demonstrates that changes which are seen to occur in experimental X‐ray diffraction patterns of poly(vinyl chloride) (PVC) with varying sample tacticity are indicative of a crystal structure in which both isotactic and syndiotactic sequences are incorporated within the same lattice. The isotactic sequences are in a conformation first suggested by Juijn et al. which enables them to emulate the shape of the syndiotactic chain. We present a short summary of molecular and diffraction modelling results which show how the intensities of the 200 and 110 peaks change with crystallite tacticity. The results provide a rational explanation for the long standing enigma that the observed crystallinity of atactic PVC is too high to be accounted for in terms of crystallization of syndiotactic sequences onl

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020207

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA statistical thermodynamics theory of polydisperse polymer mixtures with strong interaction between dissimilar components based on a lattice fluid model is formulated. Expressions for the free energy, equation of state, phase stability and spinodal for a polydisperse, binary polymer mixture with strong interaction are derived.

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020208

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA sensitivity analysis is performed to determine at what conditions the simplified model for swelling of latex particles by two monomers or two solvents is valid. This model proposes that, inter alia, the fractions of two monomers in the latex particles and in the monomer droplets are equal. The model is a simplified version of that proposed by Ugelstad et al. and results from the use of three assumptions, namely (1) the molar volumes of the monomers are equal, (2) the interaction parameters between the two monomers are equal and (3) the interaction parameters between each of the monomers and the polymer are equal. It is shown by simulation that these assumptions are of algebraic necessity only. The simple model is always valid when utilizing realistic values for all the appropriate parameters for partially water soluble monomers that swell the polymer.

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020209

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractFormulae to calculate the statistically caused instantaneous copolymer composition distribution as well as the chemical distribution of accumulated macromolecules, which is due to polymerization statistics and shifts in mean polymer composition during the reaction process, are derived on the basis of a universal model for free‐radical solution polymerization with any number of monomers proceeding in a batch, semi‐batch or continuous, ideally mixed vessel. The influence of the reactor type on chemical composition distributions is investigated for a copolymerization of different reactive components (methyl methacrylate/styrene/maleic anhydride), a system with nearly equal reactive monomers (methyl methacrylate/styrene), and the ternary polymerization of methyl methacrylate/styrene/maleic anhydride. Though products of constant mean composition are obtainable in a semi‐batch or steady‐state continuous reactors, considerable statistical dispersion cannot be removed in a

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020210

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY