Phase behavior and orientational ordering in block copolymers doped with anisotropic nanoparticles

A molecular field theory and coarse-grained computer simulations with dissipative particle dynamics have been used to study the spontaneous orientational ordering of anisotropic nanoparticles in the lamellar and hexagonal phases of diblock copolymers and the effect of nanoparticles on the phase behavior of these systems. Both the molecular theory and computer simulations indicate that strongly anisotropic nanoparticles are ordered orientationally mainly in the boundary region between the domains and the nematic order parameter possesses opposite signs in adjacent domains. The orientational order is induced by the boundary and by the interaction between nanoparticles and the monomer units in different domains. In simulations, sufficiently long and strongly selective nanoparticles are ordered also inside the domains. The nematic order parameter and local concentration profiles of nanoparticles have been calculated numerically using the model of a nanoparticle with two interaction centers and also determined using the results of computer simulations. A number of phase diagrams have been obtained which illustrate the effect of nanoparticle selectivity and molar fraction of the stability ranges of various phases. Different morphologies have been identified by analyzing the static structure factor and a phase diagram has been constructed in coordinates' nanoparticle concentration-copolymer composition. Orientational ordering of even a small fraction of nanoparticles may result in a significant increase of the dielectric anisotropy of a polymer nanocomposite, which is important for various applications

Molecular theory of the tilting transition and computer simulations of the tilted lamellar phase of rod-coil diblock copolymers

Symmetric rod-coil diblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter. It has been found that the tilted lamellar phase appears to be the most stable one at strong segregation. The rod-coil copolymer tilt angle and orientational order parameters have been determined as functions of the segregation strength. The density functional theory of rod-coil diblock copolymers has been generalized to the case of the tilted lamellar phase and used to study the stability of the orthogonal lamellar phase with respect to tilt. The orthogonal phase indeed appears to be unstable in the broad region of the parameter space in the case of relatively strong segregation. It has also been shown that the transition into the tilted lamellar phase is determined by a strong coupling between two independent tilt order parameters

A Method for Creating Structural Models of Text Documents Using Neural Networks.

The article describes modern neural network BERT-based models and considers their application for Natural Language Processing tasks such as question answering and named entity recognition. The article presents a method for solving the problem of automatically creating structural models of text documents. The proposed method is hybrid and is based on jointly utilizing several NLP models. The method builds a structural model of a document by extracting sentences that correspond to various aspects of the document. Information extraction is performed by using the BERT Question Answering model with questions that are prepared separately for each aspect. The answers are filtered via the BERT Named Entity Recognition model and used to generate the contents of each field of the structural model. The article proposes two algorithms for field content generation: Exclusive answer choosing algorithm and Generalizing answer forming algorithm, that are used for short and voluminous fields respectively. The article also describes the software implementation of the proposed method and discusses the results of experiments conducted to evaluate the quality of the method.The article describes modern neural network BERT-based models and considers their application for Natural Language Processing tasks such as question answering and named entity recognition. The article presents a method for solving the problem of automatically creating structural models of text documents. The proposed method is hybrid and is based on jointly utilizing several NLP models. The method builds a structural model of a document by extracting sentences that correspond to various aspects of the document. Information extraction is performed by using the BERT Question Answering model with questions that are prepared separately for each aspect. The answers are filtered via the BERT Named Entity Recognition model and used to generate the contents of each field of the structural model. The article proposes two algorithms for field content generation: Exclusive answer choosing algorithm and Generalizing answer forming algorithm, that are used for short and voluminous fields respectively. The article also describes the software implementation of the proposed method and discusses the results of experiments conducted to evaluate the quality of the method

Ordering of anisotropic nanoparticles in diblock copolymer lamellae : simulations with dissipative particle dynamics and a molecular theory

Local distribution and orientation of anisotropic nanoparticles in microphase-separated symmetric diblock copolymers has been simulated using dissipative particle dynamics and analyzed with a molecular theory. It has been demonstrated that nanoparticles are characterized by a non-trivial orientational ordering in the lamellar phase due to their anisotropic interactions with isotropic monomer units. In the simulations, the maximum concentration and degree of ordering are attained for non-selective nanorods near the domain boundary. In this case, the nanorods have a certain tendency to align parallel to the interface in the boundary region and perpendicular to it inside the domains. Similar orientation ordering of nanoparticles located at the lamellar interface is predicted by the molecular theory which takes into account that the nanoparticles interact with monomer units via both isotropic and anisotropic potentials. Computer simulations enable one to study the effects of the nanorod concentration, length, stiffness, and selectivity of their interactions with the copolymer components on the phase stability and orientational order of nanoparticles. If the volume fraction of the nanorods is lower than 0.1, they have no effect on the copolymer transition from the disordered state into a lamellar microstructure. Increasing nanorod concentration or nanorod length results in clustering of the nanorods and eventually leads to a macrophase separation, whereas the copolymer preserves its lamellar morphology. Segregated nanorods of length close to the width of the diblock copolymer domains are stacked side by side into smectic layers that fill the domain space. Thus, spontaneous organization and orientation of nanorods leads to a spatial modulation of anisotropic composite properties which may be important for various applications

Orientational ordering of nanorods of different length in diblock copolymers

Orientational and positional ordering of nanorods in the lamellae phase of diblock copolymers has been investigated using a simple theoretical model and dissipative dynamics simulations. Orientational order parameter and local concentration profiles of nanorods are calculated numerically and extracted from computer simulations data for different values of the nanoparticle length and different number of the interaction sites in the model nanorod. The predictions of the molecular theory are compared with the results of computer simulations. It has been found that the nanorods are orientationally ordered in the boundary region between the domains and the orientational order parameter changes its sign at the domain wall. At the same time there exists some quantitative discrepancy between theory and computer simulations which is partially removed when a similar model of a nanorod is employed both in the molecular theory and in coarse-grained molecular dynamics simulations

Liquid-crystal ordering and microphase separation in the lamellar phase of rod-coil-rod triblock copolymers. Molecular theory and computer simulations

A molecular model of the orientationally ordered lamellar phase exhibited by asymmetric rod-coil-rod triblock copolymers has been developed using the density-functional approach and generalizing the molecular-statistical theory of rod-coil diblock copolymers. An approximate expression for the free energy of the lamellar phase has been obtained in terms of the direct correlation functions of the system, the Flory-Huggins parameter and the Maier-Saupe orientational interaction potential between rods. A detailed derivation of several rod-rod and rod-coil density-density correlation functions required to evaluate the free energy is presented. The orientational and translational order parameters of rod and coil segments depending on the temperature and triblock asymmetry have been calculated numerically by direct minimization of the free energy. Different structure and ordering of the lamellar phase at high and low values of the triblock asymmetry is revealed and analyzed in detail. Asymmetric rod-coil-rod triblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter and for several values of the triblock asymmetry. It has been found that the lamellar phase appears to be the most stable one at strong segregation. The density distribution of the coil segments and the segments of the two different rods have been determined for different values of the segregation strength. The simulations confirm the existence of a weakly ordered lamellar phase predicted by the density-functional theory, in which the short rods separate from the long ones and are characterized by weak positional ordering