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Impact of mixture composition on self-organization in concentrated solutions of stiff helical and flexible macromolecules was studied by means of molecular dynamics simulation. The macromolecules were composed of identical amphiphilic monomer units but a fraction f of macromolecules had stiff helical backbones and the remaining chains were flexible. In poor solvents the compacted flexible macromolecules coexist with bundles or filament clusters from few intertwined stiff helical macromolecules. The increase of relative content f of helical macromolecules leads to increase of the length of helical clusters, to alignment of clusters with each other, and then to liquid-crystalline-like ordering along a single direction. The formation of filament clusters causes segregation of helical and flexible macromolecules and the alignment of the filaments induces effective liquid-like ordering of flexible macromolecules. A visual analysis and calculation of order parameter relaying the anisotropy of diffraction allow concluding that transition from disordered to liquid-crystalline state proceeds sharply at relatively low content of stiff components. [ABSTRACT FROM AUTHOR]

The transitions between smectic, nematic, and isotropic phases are investigated in the framework of a unified molecular-statistical approach. The new translational order parameter is different from the one introduced in K. Kobayashi [Phys. Lett. A 31, 125 (1970)] and W. L. McMillan [Phys. Rev. A 4, 1238 (1971)]. The variance of the square sine of intermolecular shift angle along the director is introduced to take self-consistently into account the most probable location of the molecules with respect to each other, which is unique for every liquid crystal (LC) material and is mainly responsible for the order parameters and phase sequences. The mean molecular field was treated in terms of only two parameters specific to any intermolecular potential of elongated molecules: (1) its global minimum position with respect to the shift of two interacting molecules along the director and (2) its inhomogeneity/anisotropy ratio. A simple molecular model is also introduced, where the global minimum position is determined by the linking groups elongation Δ/d, while the inhomogeneity/anisotropy ratio Gβ/Gγ is determined by the ratio of electrostatic and dispersion contributions. All possible phase sequences, including abrupt/continuous transformation between the smectic and nematic states and the direct smectic-isotropic phase transition, are predicted. The theoretical prediction is in a good agreement with experimental data for some simple materials correlating with our molecular model, but it is expected to be valid for any LC material. [ABSTRACT FROM AUTHOR]

It was found first that macromolecules made of amphiphilic monomer units could form spontaneously an ultra-thin layer on the surface which the macromolecules are grafted to. The width of such layer is about double size of monomer unit consisting of hydrophilic A (repulsive) and hydrophobic (attractive) B beads. The hydrophilic A beads are connected in a polymer chain while hydrophobic B beads are attached to A beads of the backbone as side groups. Three characteristic regimes are distinguished. At low grafting density, the macromolecules form ultra-thin micelles of the shape changing with decrease of distance d between grafting points as following: circular micelles-- prolonged micelles--inverse micelles--homogeneous bilayer. Those micelles have approximately constant height and specific top-down A-BB-A structure. At higher grafting density, the micelles start to appear above the single bilayer of amphiphilic macromolecules. The thickness of grafted layer in these cases is different in different regions of grafting surface. Only at rather high density of grafting, the height of macromolecular layer becomes uniform over the whole grafting surface. The study was performed by computer modeling experiments and confirmed in framework of analytical theory. [ABSTRACT FROM AUTHOR]

An algorithm involving classical molecular dynamics simulations with mapping and reverse mapping procedure is here suggested to simulate the crosslinking of the polystyrene dissolved in dichloroethane by monochlorodimethyl ether. The algorithm comprises consecutive stages: molecular dynamics atomistic simulation of a polystyrene solution, the mapping of atomistic structure onto coarse-grained model, the crosslink formation, the reverse mapping, and finally relaxation of the structure dissolved in dichloroethane and in dry state. The calculated values of the specific volume and the elastic modulus are in reasonable quantitative correspondence with experimental data. [ABSTRACT FROM AUTHOR]

In general, bio-macromolecules are composed of hydrophilic and hydrophobic moieties and are confined within small cavities, such as cell membranes and intracellular organelles. Here, we studied the self-organization of macromolecules having groups with different affinities to solvents under spherical nano-scale confinement by means of computer modeling. It is shown that depending on the interaction parameters of monomer units composed of side- and main-chain monomer groups along a single linear macromolecule and on cavity size, such amphiphilic polymers undergo the conformational transitions between hollow nanospheres, rod-like and folded cylindrical structures, and a necklace conformation with and without a particular ordering of beads. The diagram of the conformations in the variables the incompatibility parameter of monomer units and the cavity radius is constructed. [ABSTRACT FROM AUTHOR]

Concentrated solutions of amphiphilic macromolecules with local helical structure were studied by means of molecular dynamic simulations. It is shown that in poor solvent the macromolecules are assembled into wire-like aggregates having complex core-shell structure. The core consists of a hydrophobic backbone of the chains which intertwine around each other. It is protected by the shell of hydrophilic side groups. In racemic mixture of right-hand and left-hand helix macromolecules the wire-like complex is a chain of braid bundles of macromolecules with the same chirality stacking at their ends. The average number of macromolecules in the wire cross-section is close to that of separate bundles observed in dilute solutions of such macromolecules. The effects described here could serve as a simple model of self-organization in solutions of macromolecules with local helical structure. [ABSTRACT FROM AUTHOR]

A Flory-Huggins type lattice approach is used to describe theoretically a heterogeneous mixture composed of an ionic liquid (IL) and a nonionic liquid (nIL). It is analyzed, how the behavior of the system depends on the difference in the affinities of the cations and the anions to the neutral molecules (i.e., on the 'amphiphilicity' of the IL with respect to the nIL). It is proved that if the difference in the affinities is not large, two macrophases coexist in the mixture; if the difference exceeds a certain threshold value, the mixture becomes microheterogeneous: depending on its composition, it can turn either into ion clusters dispersed over the phase having low concentration of ions, or into clusters of neutral molecules dispersed over the phase having high concentration of ions. If the system is not close to the critical point, the ion clusters can be only small: the maximal ratio of their diameter to an ion diameter is of the order of ten; however, the clusters of nonionic molecules can be large, if the difference in the affinities has a certain value. It is predicted also that cavities can nucleate inside an IL, and clusters of ions can appear in a saturated vapor of an IL. [ABSTRACT FROM AUTHOR]

The conformational behavior of a single diblock copolymer chain with comb blocks is studied by computer simulation. The comb blocks have equal lengths of the backbones and side chains and differ only by the degree of grafting of the side chains. The collapse behavior is studied for two cases: (i) comb diblock copolymer with attracting backbones of the blocks and swollen side chains and (ii) comb diblock copolymer with attracting monomer units of the side chains of the blocks and swollen backbones. In both cases the conformation of a globule with a tail is observed when one of the block collapses while the other stays swollen. At high attraction micellar-type globules are formed. The core of the micelle consists of attracting monomeric units and the soluble segments (side chains or backbones) comprise the corona. It is shown that separation of monomeric units belonging to different blocks can take place both in the core and in the corona regions of the micelle. [ABSTRACT FROM AUTHOR]

Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt. [ABSTRACT FROM AUTHOR]

We propose a statistical mechanical model of surface pattern recognition by heteropolymers with quenched monomer sequence distribution. The chemically heterogeneous pattern consists of different adsorption sites specifically distributed on a surface. The heteropolymer sequence is complementary with respect to the pattern. The concepts of recognition probability and recognition temperature are introduced. The algorithm for calculating the recognition probability is based on efficient recurrence procedures for evaluating the single-chain partition function of a chain macromolecule consisting of multiple monomer types, which interact with multiple types of adsorption sites. The temperature dependencies of the recognition probability are discussed. We address the critical role of the commensurability between the heteropolymer sequence and the distribution of the surface adsorbing sites on the polymer adsorption. Also, we address the question of how many types of monomer units in the heteropolymer are required for unambiguous recognition of compact target patterns. It is shown that perfect pattern recognition can be achieved for the strong-adsorption regime in the case of specifically structured compact patterns with multifunctional adsorption sites and heteropolymers with multiple monomer types when the degeneracy of the ground state is suppressed. The pattern recognition ability increases with the number of different types of monomer units and complementary adsorption sites. For random heteropolymers and patterns, the free energy change associated with the recognition process decreases linearly with increasing this number. Correlated random heteropolymers are capable of recognizing related patterns on a random background. [ABSTRACT FROM AUTHOR]

A coarse-grained model is used to study the conformational properties of semiflexible polymers with amphiphilic monomer units containing both hydrophilic and hydrophobic interaction sites. The hydrophobically driven conformational transitions are studied using molecular dynamics simulations for the chains of varying stiffness, as characterized by intrinsic Kuhn segment lengths that vary over a decade. It is shown that the energy of hydrophobic attraction required for the realization of the coil-to-globule transition increases with increasing chain stiffness. For rather stiff backbone, the coil-to-globule transition corresponds to a first order phase transition. We find that depending on the chain stiffness, a variety of thermodynamically stable anisometric chain morphologies are possible in a solvent selectively poor for hydrophobic sites of amphiphilic monomer units. For flexible chains, the amphiphilic polymer forms a cylindrical globule having blob structure with nearly spherical blobs. With increasing stiffness, the number of blobs composing the globule decreases and the shape of blobs transforms into elongated cylinder. Further increase in stiffness leads to compaction of macromolecules into a collagenlike structure when the chain folds itself several times and different strands wind round each other. In this state, the collagenlike structures coexist with toroidal globules, both conformations having approximately equal energies. [ABSTRACT FROM AUTHOR]

We present a statistical mechanical model, which is used to investigate the adsorption behavior of two-letter (AB) copolymers on chemically heterogeneous surfaces. The surfaces with regularly distributed stripes of two types (A and B) and periodic multiblock copolymers (AℓBℓ)x are studied. It is assumed that A(B)-type segments selectively adsorb onto A(B)-type stripes. It is shown that the adsorption strongly depends on the copolymer sequence distribution and the arrangement of selectively adsorbing regions on the surface. The polymer-surface binding proceeds as a two-step process. At the first step, the copolymer having short blocks adsorbs onto the surface as an effective homopolymer, which does not feel chemical pattern. At the second step, when the polymer-surface attraction is sufficiently strong, the adsorbed chain adjusts its equilibrium conformation to reach the perfect bound state, thereby demonstrating ability for pattern recognition. The key element of this mechanism is the redistribution of strongly adsorbed copolymer diblocks AℓBℓ, which behave as surfactants, between multiple AB interfaces separating A and B stripes on the adsorbing surface. Such redistribution is accompanied by a well-pronounced decrease in the system entropy. We have found that marked pattern recognition is possible for copolymers with relatively short blocks at high polymer/surface affinities, beyond the adsorption threshold. [ABSTRACT FROM AUTHOR]

The collapse behavior of a single comblike copolymer chain has been studied by Monte Carlo simulations. It has been supposed that the solvent is good for the side chains but the solvent quality for the backbone chain changes. It has been shown that depending on the structural parameters of the comb copolymer (the lengths of the backbone and side chains, grafting density of the side chains) various thermodynamically stable morphologies of the collapsed backbone chain can be realized. In addition to ordinary spherical globule we have observed elongated structures as well as necklacelike conformations. The proposed model can be used to describe conformational behavior of stoichiometric complexes between block copolymers with a polyelectrolyte short block and oppositely charged linear homopolymers. [ABSTRACT FROM AUTHOR]

We perform a Monte Carlo simulation of irreversible template copolymerization near a chemically heterogeneous surface with a regular distribution of discrete adsorption sites that selectively adsorb from solution one of the two polymerizing monomers and the corresponding chain segments. In the polymerization model, the chain propagation process is simulated by adding individual monomers to the end of growing macroradical. We focus in this paper on the influence of polymerization rate, adsorption energy, and the distance between adsorption sites on the chain conformation and the primary sequence of the resulting two-letter (AB) copolymers and, specifically, on the coupling between polymerization and adsorption. The conditions for the realization of conformation-dependent copolymerization are formulated. For this regime, we observe the formation of a quasiregular copolymer with two types of alternating sections. One of them contains randomly distributed A and B segments. The second one consists mainly of strongly adsorbed A segments. It is found that the average length of the random sections is proportional to the distance between the nearest neighbor adsorption sites. The average length of the A-rich sections is determined by the “adsorption capacity” of adsorption site. By varying the strength of the effective monomer-substrate interaction and the distribution of adsorption sites on the substrate, the copolymers with different surface-induced primary sequences can be designed and synthesized in a controlled fashion. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Quantitative theory of orientational behavior of rodlike polyelectrolytes in dilute solution is developed. We find that in salt-free solutions many-body Coulomb interactions between macro- and counterions favor nematic ordering. It is shown that the orientationally isotropic phase of the solution becomes unstable toward nematic ordering at polymer concentration smaller than the overlap concentration. Our predictions are consistent with experimental observations for synthetic polyelectrolytes poly(p-phenylene)sulfonates in aqueous solutions. [ABSTRACT FROM AUTHOR]

"Swiss-cheese" polyelectrolyte gels (i.e., gels containing a regular set of closed spherical pores) are considered as a suitable system for modeling of a medium with extremely inhomogeneous distribution of charged species. It is shown that the inhomogeneous distribution of ions in Swiss-cheese polyelectrolyte gels can he reached simply by immersion of the gels in an aqueous solution of charged species (e.g., low-molecular 1 -1 salt or multivalent ions and macroions charged likely to the gel chains). If a polymer gel is kept in such a solution for a long time, the concentration of ions within relatively big voids becomes equal to that in external solution. On the other hand, due to the Donnan effect the ion's concentration in polymer matrix is always lower than that in external solution. As a result the multivalent ions distribute between water voids and polymer matrix. The extent of this distribution is characterized by partition coefficient kD (determined as ratio kD =nsvoid/nsmat of the concentrations nsvoid and nsmat of ions in water voids and in polymer matrix, correspondingly). It is shown that the partition coefficient kD can be larger than 10 for low-molecular salt, reaches 103 for bivalent ions, and is higher than 106 for tetravalent ions. In the case of polymer macroions the partition coefficient kD tends to infinity. Our calculations show that the lower limit of characteristic scales of heterogeneity (determined by water voids size starting from which the condition of total electroneutrality is fulfilled and effect of partition is the most pronounced) can he equal to tens of nanometers. [ABSTRACT FROM AUTHOR]

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson–Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Ångstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson–Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Strong segregation theory of microphase separation in dilute solutions of associating polyelectrolytes is developed. The driving force of the separation is shown to be a competition between a short-range attraction of associating groups and long-range repulsion of charged groups. We predict that with the increase of polymer concentration single chains first aggregate into spherical clusters of optimum size which can be disordered in space or arranged with the symmetry of the bcc lattice. Further increase of polymer concentration can result in the formation of hexagonal and lamellar structures which precede the physical gelation. The hexagonal and lamellar structures are stable at very small fractions of charged groups on the chains. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using the polymer integral equation method, we study the solution properties of charged quasi-random two-letter (HP) copolymers with two different types of distribution of monomer units along a copolymer chain: proteinlike copolymers and random-block copolymers. The copolymers consist of monomer units of two types: associating electroneutral hydrophobic (H) units and charged (P) units. Small mobile counterions are treated explicitly. We explore the influence of the primary structure of HP-polyelectrolyte chains on their structural behavior and aggregation in a solution, which is poor for H units and good for P units. Analysis of the static structure factors shows that there is an evident tendency to the aggregation of the hydrophobic groups belonging to different macromolecules into spatially correlated clusters. The spinodal lines and various structure diagrams are calculated for both copolymers. The characteristic temperature of counterion condensation is also estimated. The main finding is that charged proteinlike copolymers are more prone to self-organization in a poor solvent than their random-block counterparts. In particular, the apparent spinodal temperatures for proteinlike copolymers are several fold larger than for random-block copolymers with the same average block length and HP composition. The influence of the primary structure is more pronounced in the processes dominated by short-range hydrophobic interaction than in the processes mostly governed by long-range electrostatic interactions. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present the results of molecular dynamics simulations of charged proteinlike hydrophobic-hydrophilic (HP) copolymers with a fixed charge distribution under pure solvent conditions. The processes of coil-to-globule transition, aggregation of polymer globules, and counterion condensation are studied in detail as a function of temperature. Various static structure factors and pair correlation functions, that occur in polyelectrolyte solutions, are also analyzed. Our simulations show that the chains pass through strong conformational changes while changing temperature. We find three different temperature regimes which are characterized by a different behavior of Coulomb energy, chain sizes, and pair correlation functions. In the high-temperature regime, at the reduced temperature T > 3.0, the chains have an extended conformation with many hydrophobic blobs. As temperature is decreased, one observes a counterion condensation and sharp decrease in chain size. In this regime, we observe a solution of nonaggregating polymer globules which form a stable array resembling a charge-stabilized (micro)suspension or microgel phase. A further decrease in temperature (at T < 0.5) leads to an aggregation of the isolated globules which form aggregates built up from individual globules connected by a layer of counterions condensed on the globular surface. It is found that the transitions between the temperature regimes are thermodynamically reversible. [ABSTRACT FROM AUTHOR]

Using a Monte Carlo simulation technique, we have modeled the process of copolymerization of hydrophobic and hydrophilic monomers in a selective (polar) solvent. The composition of an emerging polymer chain is such that macromolecule adopts a globular conformation. The preferential sorption of hydrophobic monomers in the core of the globule is explicitly taken into account. It is shown that such the copolymerization process automatically leads to the formation of the core--shell microstructure in the resulting globule and to the well-pronounced long-range correlations of the Levy-flight type in obtained sequences of monomer units. Thus, this type of synthesis provides a robust one-step method of producing of "proteinlike" copolymers, i.e., copolymers that exhibit in the globular state a microstructure with a hydrophobic core wrapped in a hydrophilic envelope. [ABSTRACT FROM AUTHOR]

In this paper we consider one of the ways to obtain HP-copolymers with specially designed "proteinlike" sequences such that in the dense globular conformation all the hydrophobic H-units form the core of this globule, while polar P-units constitute the envelope of this core. Namely, we assume that some low molecular reagent Z is added to the dilute solution of homopolymer H-globules and that it induces a polymeranalogous reaction H+Z→P. We present the full theoretical analysis of the macrokinetics of the corresponding chemical reaction and show that at a certain interrelation between the diffusion coefficient of the reagent Z and the constant of the chemical reaction it is possible to end up with a copolymer chain with proteinlike statistics in the sense described above. We analyze the statistical properties of the sequences in resulting copolymer chains for the general case. Also we consider the scattering properties and spinodal of the melts of these chains. [ABSTRACT FROM AUTHOR]

Studies the molecular dynamics of the solution of semiflexible telechelic polymer chains with strongly associating end-groups. Model and simulation technique used in the study; Equilibrium of association; System morphology; Comparative analysis of theoretical and computer simulation data.

The compactization of a single DNA molecule in polyethylene glycol (PEG) solution was investigated both theoretically and experimentally. A theory is proposed taking into account the polyelectrolyte effect and redistribution of PEG within DNA coils. This approach makes it possible to describe the dependence of critical value, c, of PEG concentration at the point of DNA collapse on the degree of PEG polymerization, P, and on the concentration of low-molecular salt, ns. Observation of single DNA molecule in solution of PEG has been carried out by means of fluorescence microscopy which allows one to observe the conformation of individual DNA directly. Direct evidence that the coil–globule transition of DNA occurs as first order phase transition was obtained. It was confirmed that the critical concentration of PEG decreases with an increase of the degree of PEG polymerization and salt concentration. The width of the coexistence region of coil and globule was found to be dependent on salt concentration and degree of polymerization of PEG. It was found that DNA undergoes re-entrant globule–coil transition in concentrated solution of high-molecular weight PEG. These experimental results correspond well to the theoretical predictions. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The adsorption of a single polymer chain onto a solid surface is investigated by molecular dynamics simulations. The chain is composed of mass points interacting via a truncated Lennard-Jones potential, i.e., the excluded volume interaction is taken into account, and grafted to the surface with one end. The average adsorption degree is calculated for various chain lengths (N = 16, 32, 64, 128) and adsorption energies. In addition, the scaling behavior of the adsorption degree and the radius of gyration is investigated. The adsorption degree and the average length of loops and tails are obtained for chains of various stiffnesses. In this context, we find that stiffer chains adsorb more easily. Moreover, the distribution of the mass points perpendicular to the surface as well as the orientation of the bonds with respect to the surface is discussed for various adsorption energies and stiffnesses. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A new simplified model is proposed to mimic some properties of the glass transition. The physical system undergoing glass transition is modeled as Brownian particle diffusing in one- or two-dimensional space with obstacles. In one dimension obstacles are points which cannot be crossed by Brownian particles, in two dimensions obstacles are randomly distributed sections of straight lines which are impenetrable for the diffusing particle. The obstacles have a finite lifetime τ. After time τ the obstacle disappears and reappears in some new random position. In another modification of the model the obstacle barrier can be opened for short time and then closed again. Both cases are studied for one-dimensional diffusion, while in two dimensions only the first modification of the model is considered. The main feature of the model is that the mean lifetime of obstacles τ is connected with the diffusion coefficient of the Brownian particle through the coupling equation Dτ=K, with K being the coupling constant. This idea is borrowed from the theory of reptations in polymer liquids. Both analytical calculations and results of computer simulations are presented. The model is shown to reflect some of the features of glass transition. It was found that a slight change in the model, i.e., opening and closing of a barrier in the same position versus transfer of a barrier to a new position, leads to a drastic change in the diffusion kinetics of the system. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An equilibrium mean-field theory for dilute polyelectrolyte solution with many associating groups per chain is presented. We have shown that in addition to physical gel formation, the aggregation of polyelectrolyte chains in dilute solution can lead to the formation of optimum size clusters. The physical reason for the stabilization of such clusters is discussed. Intramolecular optimum cluster formation (necklace conformation) becomes possible for long or charged enough chains. The study of influence of the number of stickers on phase behavior of associating polyelectrolyte solution enabled us to predict a rather unusual counterintuitive effect: The physical gel formation can be induced by the decrease of the number of stickers (anomalous physical gelation). This effect has pure polyelectrolyte nature and is connected with the translational entropy of mobile counterions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present an integral equation theory based on the polymer reference interaction site model (PRISM) formalism to describe a phase behavior of polymer containing colloidal dispersion. We focus on the thermodynamic stability of dispersed component, i.e., on the conditions of percolation and phase separation in this subsystem. Different phase diagrams for the colloid subsystem are constructed in the variables: volume fraction of the colloid component-temperature. We analyze the behavior of the spinodal line and the percolation threshold. It was shown that the spinodal lines do not exhibit a critical point. The additivity of a polymer induced and a direct attraction between the colloidal particles is examined. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using the cellular-automaton-based simulation technique, we study the processes of self-organization in the systems of comblike copolymers with strongly attracting groups located at the ends of side chains. It is found that at a certain critical association energy, dependent both on polymer volume fraction and on the chemical composition of the copolymers, a micellar phase is nucleated. For the combs with large linear grafting density, a weak extension of the macromolecules is observed as attraction between end groups is increased. We find that the micelle formation observed in the sufficiently dense systems is mainly a result of intermolecular association. From the analysis of the static structure factors and snapshot pictures, it is concluded that the system is spatially inhomogeneous on the intermediate length scales related to the average intermicellar distances. Strong attraction stabilizes the aggregates (multiplets) that serve as junction points of a temporary network (micellar gel). We observe the formation of a specific space-filling weblike network in which strongly attracting side-chain ends group into multiplets which are wrapped by neutral polymer sections connecting these multiplets. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the phase behavior of self-assembling grafted comblike copolymers with strongly attractive side chains. An off-lattice, microscopic integral equation theory is applied to investigate intermolecular correlations, collective scattering intensities, and thermally induced macro- and microphase separation transitions in the systems of different comb models having various architectures and chain stiffness. The properties of these models are analyzed as a function of molecular density, the number of side chains, the length of the side chains and backbone. Detailed calculations reveal the main factors that control micro- versus macrophase separation and thereby yield guideline for controlling the phase behavior of comblike copolymer systems in solutions and in melts. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]