Micellization of Sliding Polymer Surfactants

Following up a recent paper on grafted sliding polymer layers (Macromolecules 2005, 38, 1434-1441), we investigated the influence of the sliding degree of freedom on the self-assembly of sliding polymeric surfactants that can be obtained by complexation of polymers with cyclodextrins. In contrast to the micelles of quenched block copolymer surfactants, the free energy of micelles of sliding surfactants can have two minima: the first corresponding to small micelles with symmetric arm lengths, and the second corresponding to large micelles with asymmetric arm lengths. The relative sizes and concentrations of small and large micelles in the solution depend on the molecular parameters of the system. The appearance of small micelles drastically reduces the kinetic barrier signifying the fast formation of equilibrium micelles.Comment: Submitted to Macromolecule

SELF-CONSISTENT FIELD MODEL OF BRUSHES FORMED BY ROOT-TETHERED DENDRONS

We present an analytical self-consistent field (scf) theory that describes planar brushes formed by regularly branched root-tethered dendrons of the second and third generations. The developed approach gives the possibility for calculation of the scf molecular potential acting at monomers of the tethered chains. In the linear elasticity regime for stretched polymers, the molecular potential has a parabolic shape with the parameter k depending on architectural parameters of tethered macromolecules: polymerization degrees of spacers, branching functionalities, and number of generations. For dendrons of the second generation, we formulate a general equation for parameter k and analyze how variations in the architectural parameters of these dendrons affect the molecular potential. For dendrons of the third generation, an analytical expression for parameter k is available only for symmetric macromolecules with equal lengths of all spacers and equal branching functionalities in all generations. We analyze how the thickness of dendron brush in a good solvent is affected by variations in the chain architecture. Results of the developed scf theory are compared with predictions of boxlike scaling model. We demonstrate that in the limit of high branching functionalities, the results of both approaches become consistent if the value of exponent bin boxlike model is put to unity.In conclusion, we briefly discuss the systems to which the developed scf theory is applicable. These are: planar and concave spherical and cylindrical brushes under various solvent conditions (including solvent-free melted brushes) and brush-like layers of ionic (polyelectrolyte) dendrons

Self-Consistent Field study of Polyelectrolyte Brushes

We formulate a self-consistent field theory for polyelectrolyte brushes in the presence of counterions. We numerically solve the self-consistent field equations and study the monomer density profile, the distribution of counterions, and the total charge distribution. We study the scaling relations for the brush height and compare them to the prediction of other theories. We find a weak dependence of the brush height on the grafting density.We fit the counterion distribution outside the brush by the Gouy-Chapman solution for a virtual charged wall. We calculate the amount of counterions outside the brush and find that it saturates as the charge of the polyelectrolytes increases

Специалистическая модель в условиях непрерывного профессионального образования

Fundamental changes in the Russian economy determined by the increasing role of knowledge, the revolution in information and communication technologies, the formation of the global labor market, as well as political changes, dictate new requirements for professional training. The specialist model, professiogram, qualification characteristic, sociogram of profession, sociogram of professional identity is the view options of the ideal result of students’ training. The key competence is the defining competence because it corresponds to the conditions of implementation, which are neither limited, not too specific, but are to a certain extent universal. The essence of professional competence of a specialist is the integration of knowledge, skills, experience; personal qualities that provide professional development and self-realization of a specialist, i.e. personal opportunities that allow solving professional problems independently and effectively. The perspective direction of improvement of specialists training in professional education system is development of their models giving the chance to study more deeply problems of training and use of experts, to estimate quality of educational institutions work. In recent years, research aimed at developing a specialist model has covered not only the sphere of higher education; they are conducted in the systems of basic and secondary vocational education. One of the main means of rationing and assessing the quality of professional training of students is a competence model that allows getting the clearest information about the composition of competencies that must be formed in the future specialist in the learning process. The analysis of requirements to specialists training, the contents and technologies of educational process, methodology and practice of modern educational activity allows defining a number of principles and methods of formation of specialist model as bases of a component of the Federal State Educational Standard.Los cambios fundamentales en la economía rusa, determinados por el papel cada vez mayor del conocimiento, la revolución en las tecnologías de la información y la comunicación, la formación del mercado laboral mundial, así como los cambios políticos, dictan nuevos requisitos para la formación profesional. El modelo de especialista, el profesiograma, la característica de calificación, el sociograma de la profesión, el sociograma de la identidad profesional son las opciones de visualización del resultado ideal de la formación de los estudiantes. La competencia clave es la competencia definitoria porque corresponde a las condiciones de implementación, que no son limitadas, ni demasiado específicas, pero en cierta medida son universales. La esencia de la competencia profesional de un especialista es la integración de conocimientos, habilidades, experiencia; cualidades personales que proporcionan desarrollo profesional y autorrealización de un especialista, es decir, oportunidades personales que permiten resolver problemas profesionales de manera independiente y efectiva. La dirección de la perspectiva de mejora de la formación de especialistas en el sistema de educación profesional es el desarrollo de sus modelos que brinden la oportunidad de estudiar más profundamente los problemas de formación y uso de expertos, para estimar la calidad del trabajo de las instituciones educativas. En los últimos años, la investigación dirigida a desarrollar un modelo especializado ha cubierto no solo el ámbito de la educación superior; se llevan a cabo en los sistemas de educación vocacional básica y secundaria. Uno de los principales medios para racionar y evaluar la calidad de la formación profesional de los estudiantes es un modelo de competencia que permita obtener la información más clara sobre la composición de las competencias que deben formarse en el futuro especialista en el proceso de aprendizaje. El análisis de los requisitos para la capacitación de especialistas, los contenidos y las tecnologías del proceso educativo, la metodología y la práctica de la actividad educativa moderna permite definir una serie de principios y métodos de formación de modelos especializados como bases de un componente del Estándar Educativo del Estado Federal.Фундаментальные изменения в российской экономике, обусловленные растущей ролью знаний, революцией в информационных и коммуникационных технологиях, формированием мирового рынка труда, а также политическими изменениями, диктуют новые требования к профессиональной подготовке. Модель специалиста, профессиограмма, квалификационная характеристика, социограмма профессии, социограмма профессиональной идентичности - это варианты выбора идеального результата обучения студентов. Ключевой компетенцией является определяющая компетенция, поскольку она соответствует условиям реализации, которые не являются ни ограниченными, ни слишком конкретными, но в определенной степени универсальными. Суть профессиональной компетентности специалиста - интеграция знаний, навыков, опыта; личные качества, которые обеспечивают профессиональное развитие и самореализацию специалиста, то есть личные возможности, позволяющие самостоятельно и эффективно решать профессиональные проблемы. Перспективным направлением совершенствования подготовки специалистов в системе профессионального образования является разработка их моделей, позволяющих глубже изучить проблемы подготовки и использования специалистов, оценить качество работы учебных заведений. В последние годы исследования, направленные на разработку модели специалиста, охватывали не только сферу высшего образования; они ведутся в системах начального и среднего профессионального образования. Одним из основных средств нормирования и оценки качества профессиональной подготовки студентов является модель компетенций, позволяющая получить наиболее четкую информацию о составе компетенций, которые должны быть сформированы у будущего специалиста в процессе обучения. Анализ требований к подготовке специалистов, содержания и технологий учебного процесса, методологии и практики современной образовательной деятельности позволяет определить ряд принципов и методов формирования модели специалиста как основы компонента Федерального государственного образовательного стандарта

Localization in simple multiparticle catalytic absorption model

We consider the phase transition in the system of n simultaneously developing random walks on the halfline x>=0. All walks are independent on each others in all points except the origin x=0, where the point well is located. The well depth depends on the number of particles simultaneously staying at x=0. We consider the limit n>>1 and show that if the depth growth faster than 3/2 n ln(n) with n, then all random walks become localized simultaneously at the origin. In conclusion we discuss the connection of that problem with the phase transition in the copolymer chain with quenched random sequence of monomers considered in the frameworks of replica approach.Comment: 17 pages in LaTeX, 5 PostScript figures; submitted to J.Phys.(A): Math. Ge

Validity of the scaling functional approach for polymer interfaces as a variational theory

We discuss the soundness of the scaling functional (SF) approach proposed by Aubouy Guiselin and Raphael (Macromolecules 29, 7261 (1996)) to describe polymeric interfaces. In particular, we demonstrate that this approach is a variational theory. We emphasis the role of SF theory as an important link between ground-state theories suitable to describe adsorbed layers, and "classical" theories for polymer brushes.Comment: 8 pages, 1 figure, to be published in Phys. Rev.

Self-consistent field theory for the interactions between keratin intermediate filaments

Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Intermediate Filaments are major components of corneocytes, nonviable horny cells of the Stratum Corneum, the outermost layer of skin. It is considered that interactions between unstructured domains of Keratin Intermediate Filaments are the key factor in maintaining the elasticity of the skin. Results: We have developed a model for the interactions between keratin intermediate filaments based on self-consistent field theory. The intermediate filaments are represented by charged surfaces, and the disordered terminal domains of the keratins are represented by charged heteropolymers grafted to these surfaces. We estimate the system is close to a charge compensation point where the heteropolymer grafting density is matched to the surface charge density. Using a protein model with amino acid resolution for the terminal domains, we find that the terminal chains can mediate a weak attraction between the keratin surfaces. The origin of the attraction is a combination of bridging and electrostatics. The attraction disappears when the system moves away from the charge compensation point, or when excess small ions and/or NMF-representing free amino acids are added. Conclusions: These results are in concordance with experimental observations, and support the idea that the interaction between keratin filaments, and ultimately in part the elastic properties of the keratin-containing tissue, is controlled by a combination of the physico-chemical properties of the disordered terminal domains and the composition of the medium in the inter-filament region. Keywords: Stratum corneum, Skin keratins, Intermediate filaments, Unstructured terminal domains, Bridging attractio

Degradation versus self-assembly of block copolymer micelles

The stability of micelles self-assembled from block copolymers can be altered by the degradation of the blocks. Slow degradation shifts the equilibrium size distribution of block copolymer micelles and change their properties. Quasi-equilibrium scaling theory shows that the degradation of hydrophobic blocks in the core of micelles destabilize the micelles reducing their size, while the degradation of hydrophilic blocks forming coronas of micelles favors larger micelles and may, at certain conditions, induce the formation of micelles from individual chains.Comment: Published in Langmuir http://pubs.acs.org/doi/pdf/10.1021/la204625

Arrested spinodal decomposition in polymer brush collapsing in poor solvent

We study the Brownian dynamics of flexible and semiflexible polymer chains densely grafted on a flat substrate, upon rapid quenching of the system when the quality of solvent becomes poor and chains attempt collapse into a globular state. The collapse process of such a polymer brush differs from individual chains, both in its kinetics and its structural morphology. We find that the resulting collapsed brush does not form a homogeneous dense layer, in spite of all chain monomers equally attracting each other via a model Lennard-Jones potential. Instead, a very distinct inhomogeneous density distribution in the plane forms, with a characteristic length scale dependent on the quenching depth (or equivalently, the strength of monomer attraction) and the geometric parameters of the brush. This structure is identical to the spinodal-decomposition structure, however, due to the grafting constraint we find no subsequent coarsening: the established random bundling with characteristic periodicity remains as the apparently equilibrium structure. We compare this finding with a recent field-theoretical model of bundling in a semiflexible polymer brush.This work was funded by the Osk. Huttunen Foundation (Finland) and the Cambridge Theory of Condensed Matter Grant from EPSRC. Simulations were performed using the Darwin supercomputer of the University of Cambridge High Performance Computing Service provided by Dell Inc. using Strategic Research Infrastructure funding from the Higher Education Funding Council for England.This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/ma501985r

Salt Dependence of the Tribological Properties of a Surface-Grafted Weak Polycation in Aqueous Solution

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in potassium halide solutions with different concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip–sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction–load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I − collapsing the brushes more than Br − and Cl − for the same salt concentration