摘要:

AbstractUsing a molecular field approach, the effect of interaction between reversibly invertible, helical polymers is investigated theoretically. The helices are modelled by nearest‐neighbour statistical thermodynamics. If the interaction energy between two helices of common handedness is lower than that of oppositely handed ones, a critical temperatureTcexists, below which the system spontaneously must leave the racemic state, though there is no contact to any chiral centre or force. This is analogous to the second‐order phase transition of ferromagnets. The critical point increases with molecular weight and optical persistence of the helices. At the critical point the system is highly sensitive to any chiral influence. Doping with 1 ppb of a chiral additive leads to a relative optical rotation of order 10−3at the critical point. This corresponds to an intrinsic energy difference of left‐ to right‐handed monomeric units of only 10−8J/mol. The cooperative effects in chirally doped nematic poly(hexyl isocyanate) (PHIC) can be easily described without using the improbable assumption that the supramolecular cholesteric arrangement with an axis‐to‐axis rotation of only 0,001° must be the reason for the collective helix sense preference in this system. On the other hand, if the chain‐to‐chain interaction is transmitted through this supermolecular twist, the structure of the equations is altered slightly only and critical behaviour must

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040101

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe molecular weight of a Gaussian polymer chain can be obtained from the intercept of the asymptote in a plot of the inverse structure factor 1/S(q) as a function of the square of the wave vectorq2. Using an ϵ expansion and scaling arguments, we show that in a good solvent the situation is more complex and that the molecular weight determination is difficult to justify. The corrections to the asymptotic behavior of the structure factor at large wave vector involve several terms that are difficult to separate experimentally. This is qualitatively explained by the nonuniform swelling of a polymer chain in a good solvent due to the existence of the chain ends

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040102

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe static scattering properties of four‐component polymer mixtures are examined starting from the general equation extending the random phase approximation to multicomponent systems first proposed by Benoit. The results are compared with the light scattering data reported recently by Strazielle and coworkers for polystyrene/polydimethylsiloxane/poly(methyl methacrylate)/toluene mixtures. The present formalism provides a more rigorous treatment of these data, and a good agreement is obtained without adjustable parameters. This method provides a definition of the apparent interaction parameter used by Strazielle et al. and describes its correlation with various relevant quantities characterizing the mixture. It predicts in particular the variation of this parameter with the concentration of poly(methyl methacrylate), which was not possible in the earlier work. Various other important properties of the mixture are investigated such as the critical concentration for phase separation and the apparent radius of gyratio

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCross‐linked mixtures of polystyrene and poly(vinyl methyl ether) exhibit a non‐vanishing zero‐angle intensity in small‐angle neutron scattering experiments. A possible explanation is that fluctuations in composition in the mixture may be frozen by the presence of cross‐links. Assuming this, we introduce a screening lengthκby the condition that the scattered intensity should not be changed by cross‐linking. We find κ2∼C/(χ − χi), whereCis an elastic constant, χ and χi, respectively, the inverse temperature and that where cross‐linking is performed. When the temperature is varied, we find three regimes. In the first one, the scattered intensity is monotonously decreasing. In the second one, it has a finite maximum. In the last one, the maxi

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of shear flow on the excluded volume properties of bead spring chains is calculated via the perturbation expansion of the mean‐square end‐to‐end distance with respect to the excluded volume parameterz. The coefficient of the series 〈R2〉/〈R2〉0= 1 +C1·z− … vanishes for large flow rates but shows a strong dependence on the shear rate in the i

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractHere we study the dynamics and the conformational properties of Rouse polymers in random layered flows. We obtain explicit expressions for the mean squared displacement of the center of mass of the polymer as a function of time and number of beads. The averages involve both the thermal noise and the realizations of the random flows. We find also an explicit dependence of the equilibrium value of the end‐to‐end vector on the number of beads and other dimensional parameters. Our results are compared to that for Rouse polymers immersed in non‐random steady shear

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractWhen randomly branched polymers are grafted to a surface, polymer brushes are the result, similarly as well known in the case of linear grafted polymer chains. These brushes behave, however, special, as severe restrictions in the conformation of individual polymers are present. These restrictions are firstly due to the high degree of branching and secondly to the natural maximum stretching ratio of the branched molecules, that is given byHmax=aM1/D.ais the typical size of a monomeric unit,Dis the spectral dimension andMthe total mass of the branched polymer. Brushes cannot exceed this height, and limits on the grafting density as functions of the spectral dimension are investigated. For all thermodynamic situations the minimum area per chain scales as σmin=aM(D− 1)

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractWe present results of computer simulations by the method of Brownian dynamics of polymeric brushes attached to impenetrable planes. For testing both model and method we have used one polymer brush attached to a repulsive plane and compare some results with Monte Carlo results of Lai and Binder on the bond fluctuation model. We have also studied two polymeric brushes attached to two parallel planes at different distances between planes, and investigate the interplay between the interpenetration of the brushes and the configurational properties of the grafted chains.

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe shape‐asymmetry of linear and star‐branched nonreversal random walk polymers on a tetrahedral lattice is studied by means of a Monte Carlo simulation. Properties characteristic of the instantaneous shape based on the mean‐square radius of gyration and its principal components as well as based on the end‐to‐end distance are discussed. Short‐chain effects are characterized by polynomial expressions (power series ofN−1), simultaneously by extrapolation yielding a result in the limit of infinitely large c

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractWe consider numerically, in the framework of the lakes‐straits model, the mobility of a DNA chain under field‐inversion gel‐electrophoresis (FIGE). Here we investigate the role of the gel's structure on the mobility. We consider two situations: (i) a DNA chain fragment is bounded by two straits (narrow gateways) at a fixed distance, but is otherwise free, and (ii) the fragment is, in addition, confined with in a closed volume (pore). We calculate the tension on the DNA fragment in the two cases. For Gaussian chains we evaluate the corresponding statistical weights exactly, using a cellular automation algorithm. We find that the resulting tension differs drastically in the two models considered. Nonetheless this difference influences only weakly the overall FIGE mob

ISSN:1022-1344    

DOI:10.1002/mats.1995.040040110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY