Controlling the Formation of Polyhedral Block Copolymer Nanoparticles: Insights from Process Variables and Dynamic Modeling.

This study delves into the formation of nanoscale polyhedral block copolymer particles (PBCPs) exhibiting cubic, octahedral, and variant geometries. These structures represent a pioneering class that has never been fabricated previously. PBCP features distinct variations in curvature on the outer surface, aligning with the edges and corners of polyhedral shapes. This characteristic sharply contrasts with previous block copolymers (BCPs), which displayed a smooth spherical surface. The emergence of these cornered morphologies presents an intriguing and counterintuitive phenomenon and is linked to process parameters, such as evaporation rates and initial concentration, while keeping other variables constant. Using a system of coupled Cahn-Hillard (CCH) equations, we uncover the mechanisms driving polyhedral particle formation, emphasizing the importance of controlling relaxation parameters for shape variable u and microphase separation v. This unconventional approach, differing from traditional steepest descent method, allows for precise control and diverse polyhedral particle generation. Accelerating the shape variable u proves crucial for expediting precipitation and aligns with experimental observations. Employing the above theoretical model, we achieve shape predictions for particles and the microphase separation within them, which overcomes the limitations of ab initio computations. Additionally, a numerical stability analysis discerns the transient nature versus local minimizer characteristics. Overall, our findings contribute to understanding the complex interplay between process variables and the morphology of polyhedral BCP nanoparticles.

Identificación de dimensiones del síndrome de burnout en estudiantes de Contaduría y Finanzas / Identification of dimensions of burnout syndrome in Accounting and Finance students / Identificação das dimensões da síndrome de burnout em estudantes de Contabilidade e Finanças

El síndrome de burnout, también conocido como síndrome del desgaste o agotamiento físico y mental, constituye un problema de gran repercusión social en nuestros días. Objetivo. Identificar las dimensiones del síndrome de Burnout en estudiantes universitarios de la Carrera de Contaduría y Finanzas. Materiales y Método. Se desarrolló bajo un diseño observacional de corte transversal. En este sentido, un total de 161 estudiantes participaron en la investigación. Se utilizó el Maslach Burnout Inventory for Educators. Resultados. Los participantes al ser clasificados en las diferentes dimensiones del síndrome burnout mostraron como regularidad diferencias significativas (p<1.056e-06), (p<1.199e-10), (p<1.309e-13) con 74 (46%) y 57 (35%), 85 (53%) y 47 (29%) y 91 (56%) y 39 (24%) para los niveles bajo y alto de las dimensiones agotamiento emocional, cinismo e ineficacia profesional, respectivamente. No se encontraron asociaciones estadísticas entre las dimensiones del síndrome y las variables edad, género y estado civil de los participantes. Conclusión. Existen diferencias significativas entre los valores de las dimensiones del síndrome de burnout en estudiantes de la Carrera de Contaduría y Finanzas; la mayor cantidad de participantes clasifican en los niveles bajo y alto de las tres dimensiones. Por otro lado, no se observaron asociaciones estadísticas al clasificar a los participantes según edad, género y estado civil. Estos hallazgos brindan información relevante sobre la prevalencia de las dimensiones del síndrome de burnout en estudiantes, lo que puede ser útil para el desarrollo de estrategias de prevención y apoyo.

Burnout syndrome, also known as burnout syndrome or physical and mental exhaustion, is a problem of great social repercussion nowadays. Objective. To identify the dimensions of burnout syndrome in university students of Accounting and Finance. Materials and Method. The study was developed under a cross-sectional observational design. In this sense, a total of 161 students participated in the research. The Maslach Burnout Inventory for Educators was used. Results. The participants when classified in the different dimensions of burnout syndrome showed as regularity significant differences (p<1.056e-06), (p<1.199e-10), (p<1.309e-13) with 74 (46%) and 57 (35%), 85 (53%) and 47 (29%) and 91 (56%) and 39 (24%) for the low and high levels of the dimensions emotional exhaustion, cynicism and professional inefficacy, respectively. No statistical associations were found between the dimensions of the syndrome and the variables age, gender and marital status of the participants. Conclusion. There are significant differences between the values of the dimensions of burnout syndrome in Accounting and Finance students; most participants are classified in the low and high levels of the three dimensions. On the other hand, no statistical associations were observed when classifying participants according to age, gender and marital status. These findings provide relevant information on the prevalence of the dimensions of burnout syndrome in students, which may be useful for the development of prevention and support strategies.

A síndrome de burnout, também conhecida como síndrome de esgotamento ou exaustão física e mental, é um problema com grandes repercussões sociais nos dias de hoje. Objetivos. Identificar as dimensões da Síndrome de Burnout em estudantes universitários de Contabilidade e Finanças. Material e Método. O estudo foi realizado através de um desenho observacional transversal. Participaram da pesquisa 161 estudantes. Foi utilizado o Maslach Burnout Inventory for Educators. Resultados. Os participantes quando classificados nas diferentes dimensões da síndrome de burnout apresentaram regularmente diferenças significativas (p<1,056e-06), (p<1,199e-10), (p<1,309e-13) com 74 (46%) e 57 (35%), 85 (53%) e 47 (29%) e 91 (56%) e 39 (24%) para os níveis baixo e alto das dimensões exaustão emocional, cinismo e ineficácia profissional, respetivamente. Não foram encontradas associações estatísticas entre as dimensões da síndrome e as variáveis idade, género e estado civil dos participantes. Conclusões. Existem diferenças significativas entre os valores das dimensões da síndrome de burnout em estudantes de Contabilidade e Finanças; a maioria dos participantes está classificada nos níveis baixo e alto das três dimensões. Por outro lado, não foram observadas associações estatísticas ao classificar os participantes de acordo com a idade, o género e o estado civil. Estes resultados fornecem informações relevantes sobre a prevalência das dimensões da síndrome de burnout em estudantes, o que pode ser útil para o desenvolvimento de estratégias de prevenção e apoio.

Ashura Particles: Experimental and Theoretical Approaches for Creating Phase-Separated Structures of Ternary Blended Polymers in Three-Dimensionally Confined Spaces.

Unique morphologies were found in binary and ternary polymer blended particles, including Ashura-type phase separation, which has three different polymer components on the particle surface. The morphologies of phase-separated structures in the binary polymer blended particles are discussed in terms of the surface tensions of the blended polymers. Structural control of ternary polymer blended particles was achieved based on the combination of polymers by examining binary polymer blended particles. A theoretical approach based on the Cahn-Hilliard equations gives identical morphologies with the experimental results. This work opens the way to creating polymer particles with sophisticated nanostructures by controlling their morphologies as predicted by theoretical simulations.

Transformation of Block Copolymer Nanoparticles from Ellipsoids with Striped Lamellae into Onionlike Spheres and Dynamical Control via Coupled Cahn-Hilliard Equations.

Annealing of block copolymers has become a tool of great importance for the reconfiguration of nanoparticles. Here, we present the experimental results of annealing block copolymer nanoparticles and a theoretical model to describe the morphological transformation of ellipsoids with striped lamellae into onionlike spheres. A good correspondence between the experimental findings and predictions of the model was observed. The model based on finding the steepest direction of descent of an appropriate free energy leads to a set of Cahn-Hilliard equations that correctly describe the dynamical transformation of striped ellipsoids into onionlike spheres and reverse onionlike particles, regardless of the nature of the annealing process. This universality makes it possible to describe a variety of experimental conditions involving nanoparticles underlying a heating process. A notable advantage of the proposed approach is that it enables selective control of the interaction between the confined block copolymer and the surrounding medium. This feature endows the model with a great versatility to enable the reproduction of several combined effects of surfactants in diverse conditions, including cases with reverse affinities for the block copolymer segments. A phase diagram to describe a variety of morphologies is presented. We employ the relationship between the temperature-dependent Flory-Huggins parameter and the width of the interfaces to account for changes in temperature due to the heating process. Simulation results correctly show how the transformation evolves as the temperature increases. This increment in temperature corresponds to progressively smaller values of the interfacial width. We anticipate that the proposed approach will facilitate the design and more precise control of experiments involving various kinds of annealing processes.

Correction: Frustrated phases under three-dimensional confinement simulated by a set of coupled Cahn-Hilliard equations.

Correction for 'Frustrated phases under three-dimensional confinement simulated by a set of coupled Cahn-Hilliard equations' by Edgar Avalos et al., Soft Matter, 2016, 12, 5905-5914.

Frustrated phases under three-dimensional confinement simulated by a set of coupled Cahn-Hilliard equations.

We numerically study a set of coupled Cahn-Hilliard equations as a means to find morphologies of diblock copolymers in three-dimensional spherical confinement. This approach allows us to find a variety of energy minimizers including rings, tennis balls, Janus balls and multipods among several others. Phase diagrams of confined morphologies are presented. We modify the size of the interface between microphases to control the number of holes in multipod morphologies. Comparison to experimental observation by transmission electron microtomography of multipods in polystyrene-polyisoprene diblock copolymers is also presented.

Granular chain between asymmetric boundaries and the quasiequilibrium state.

Some 30 years have passed since we learned that any velocity perturbation develops into a propagating solitary wave in a granular chain, and over a decade has passed since we learned that these solitary waves break and reform upon collision, leaving behind small secondary solitary waves. The production of the latter eventually precipitates the quasiequilibrium state characterized by large energy fluctuations in dissipation-free granular systems. Here we present dynamical simulations on the effects of soft boundaries on solitary wave interaction in granular chains held between fixed walls. We show that at short time scales, a gradient in the distribution of kinetic energy between the boundaries is indeed sustained. At long times, however, such a gradient gets obliterated and there is no measurable difference between the average kinetic energies of the particles adjacent to walls. Our findings suggest that (i) the quasiequilibrium state can effectively erase small gradients of the average kinetic energies of the particles adjacent to walls in a system, (ii) Boltzmann distribution of grain speeds is realized in the system of interest, and (iii) time and space averages yield the same result, thus suggesting that the system is ergodic.

Sustained strong fluctuations in a nonlinear chain at acoustic vacuum: beyond equilibrium.

Here we consider dynamical problems as in linear response theory but for purely nonlinear systems where acoustic propagation is prohibited by the potential, e.g., the case of an alignment of elastic grains confined between walls. Our simulations suggest that in the absence of acoustic propagation, the system relaxes using only solitary waves and the eventual state does not resemble an equilibrium state. Further, the studies reveal that multiple perturbations could give rise to hot and cold spots in these systems. We first use particle dynamics based simulations to understand how one of the two unequal colliding solitary waves in the chain can gain energy. Specifically, we find that for head-on collisions the smaller wave gains energy, whereas when a more energetic wave overtakes a less energetic wave, the latter gains energy. The balance between the rate at which the solitary waves break down and the rate at which they grow eventually makes it possible for the system to reach a peculiar equilibriumlike phase that is characteristic of these purely nonlinear systems. The study of the features and the robustness of the fluctuations in time has been addressed next. A particular characteristic of this equilibriumlike or quasiequilibrium phase is that very large energy fluctuations are possible--and by very large, we mean that the energy can vary between zero and several times the average energy per grain. We argue that the magnitude of the fluctuations depend on the nature of the nonlinearity in the potential energy function and the feature that any energy must eventually travel as a compact solitary wave in these systems where the solitary wave energies may vary widely. In closing we address whether these fluctuations are peculiar to one dimension or can exist in higher dimensions. The study hence raises the following intriguing possibility. Are there physical or biological systems where these kinds of nonlinear forces exist, and if so, can such large fluctuations actually be seen? Implications of the study are briefly discussed.

Equation of state and liquid-vapor equilibrium of polarizable Stockmayer fluids.

In this work we develop the concept of an effective potential to obtain the equation of state of polarizable Stockmayer (PSM) fluids. This potential consists of a Lennard-Jones function with appropriate energy and distance parameters that depend on the reduced dipolar moment µ(∗) and polarizability α(∗). The approach deals accurately with polarizable SM fluids with µ(∗)≤2.0 and α(∗)≤0.1. However, prediction of second virial coefficients is reliable up to µ(∗)≤4.0. When the low-density sphericalized potential is used at moderate and large densities, the effect of the dipole-dipole attraction is overestimated in agreement with an effect previously found in the literature. This effect can be traced back to a frustration mechanism due to the interaction between three and more dipoles. We propose a model to account for this frustration effect and are able to reproduce the vapor-liquid equilibrium of polarizable SM fluids in agreement with simulated results from the literature. Molecular dynamics simulations were carried out to show that the effective SM fluid has a radial distribution function very close to that of the true SM system.

How solitary waves collide in discrete granular alignments.

Solitary waves in continuum media pass through each other with only a slight phase change. However, in an intrinsically nonlinear many-body system such solitary waves could behave differently. It was predicted and experimentally confirmed that head-on solitary wave collisions in granular alignments are followed by the formation of tiny secondary solitary waves in the vicinity of the collision point. While it remains a challenge to provide an analytical treatment of the local time evolution, we present arguments and associated simulations to address a crucial unknown, namely, why the secondary solitary waves must form. Extensive numerical investigations on solitary wave collisions at a grain center and at an edge show marked differences. The effects of softening the grain repulsion are discussed to validate the arguments.

Liquid-vapor equilibrium and surface tension of nonconformal molecular fluids.

Molecular dynamics simulations at constant temperature have been performed on the liquid-vapor interface for fluids characterized by a recently introduced three-parameter potential. This potential is a modification of the well-known spherical Kihara interaction and is termed approximate nonconformal (ANC). It has been used successfully to describe many real molecules in the gaseous phase. Besides the usual molecular energy and size, the ANC potential introduces a third parameter s, called softness, to measure the form of the potential profile. Study of these systems shows that their critical and interfacial properties follow very closely those of four selected substances: argon, methane, propane, and hexane. Deviations of the properties predicted from the experimental values are analyzed and their probable causes are determined. The critical properties of ANC fluids and their dependence on s are also obtained via first-order perturbation theory in the form of an augmented van der Waals model. Analysis of the results shows that ANC potential functions can be used as reliable effective interactions for real dense fluids.

Nonconformal interaction models and thermodynamics of polar fluids.

In this work, we develop a simple potential model for polar molecules which represents effectively and accurately the thermodynamics of dilute gases. This potential models dipolar interactions whose nonpolar part is either spherical, as in Stockmayer (SM) molecules, or diatomic, as for 2-center Lennard-Jones molecules (2CLJ). Predictions of the second virial coefficient for SM and polar 2CLJ fluids for various dipole moments and elongations agree very well with results of recent numerical calculations by C. Vega and co-workers (Phys. Chem. Chem Phys. 2002, 4, 3000). The model is used to predict the critical temperature of Stockmayer fluids for variable dipole moment and is applied to HCl as an example of a real polar molecule.