Crystallization of PNIPAM-hydrogel nanospheres inferred by static light scattering

In this paper we present a kinetic study on crystallization of a colloidal dispersion formed by thermosensitive Poly-N- Isopropylacrylamide (PNIPAM) nanospheres. The liquid-crystal transition is induced by decreasing the temperature of the dispersion and the crystallization process is monitored by measuring the evolution of the static structure factor of the dispersion by means of light scattering techniques. The measured static structure factor confirms the formation of a mesoscopic crystal array at the final equilibrium state, which is preceded by two stages: nucleation and crystal growth

Transport of light in amorphous photonic materials

Amorphous photonic materials based on dense assemblies of high refractive index spherical particles are presented. Light transmission through these photonic glasses shows a nontrivial wavelength dependence. The transmission spectra can be quantitatively reproduced by modeling the optical properties starting from their building blocks. Our results emphasize the relevance of including short range order correlations and an appropriate effective refractive index in the analysis of light transmission through amorphous photonic materials

Impact of volume transition on the net charge of poly-NN-isopropyl acrylamide microgels

We explore the electrostatic properties of poly-N-isopropyl acrylamide microgels in dilute, quasi-de-ionized dispersions and show that the apparent net charge of these thermosensitive microgels is an increasing function of their size, the size being conveniently varied by temperature. Our experimental results obtained in a combination of light scattering, conductivity, and mobility experiments are consistent with those obtained in Poisson-Boltzmann cell model calculations, effectively indicating that upon shrinking the number of counterions entrapped within the microgels increases. Remarkably, this behavior shows that the electrostatic energy per particle remains constant upon swelling or deswelling the microgel, resulting in a square root dependence of the net charge on the particle radius

Estudio de las propiedades estructurales de dispersiones de microgeles de poli(N-isopropilacrilamida) cargadas electrostáticamente en función de la fuerza iónica y la temperatura

En este trabajo se han estudiado las propiedades estructurales de suspensiones coloidales de microgeles de PNIPAM cargados electrostáticamente en función de la fuerza iónica y la temperatura. Los microgeles de PNIPAM fueron sintetizados por medio de polimerización en emulsión con surfactante, considerando una baja concentración de ionizador para que su carga electrostática no sea muy alta y así evitar la cristalización. El sistema analizado posee una concentración de partículas de PNIPAM de 6.9 pp/um³. Los factores de estructura estáticos experimentales, S(q), se obtuvieron mediante dispersión de luz estática con un dispositivo 3D-LS. Los S(q) medidos han sido modelados resolviendo las ecuaciones integrales de Ornstein-Zernike, suponiendo un potencial efectivo repulsivo tipo Yukawa, y usando la cerradura del tipo cadena híper-reticulada (HNC). Los resultados obtenidos muestran como la carga de las partículas decrece al aumentar la temperatura, comportamiento que sólo había sido reportado en sistemas con una baja concentración de partículas y baja fuerza iónica.Here we study the structural properties of charged microgel colloidal suspensions as a function of ionic strength and temperature. The PNIPAM particles have been synthesized by emulsion polymerization using a small initiator concentration to obtain low charged microgels, thus avoiding crystallization. We consider a fixed PNIPAM particle number concentration of 6.9 pp/um³. The static structure factor, S(q), has been measured by static light scattering using a 3D-LS device. The measured S(q)’s have been modeled by solving the Ornstein-Zernike equation, assuming a repulsive Yukawa type effective pair potential and using the Hypernetted-chain approximation (HNC) as a closure relation. The theoretical analysis shows that the particle charge decreases when the temperature increases, finding that only had been reported for systems at low particle concentration and low ionic strength

Dynamic arrest in charged colloidal systems exhibiting large-scale structural heterogeneities

Suspensions of charged liposomes are found to exhibit typical features of strongly repulsive fluid systems at short length scales, while exhibiting structural heterogeneities at larger length scales that are characteristic of attractive systems. We model the static structure factor of these systems using effective pair interaction potentials composed of a long-range attraction and a shorter range repulsion. Our modeling of the static structure yields conditions for dynamically arrested states at larger volume fractions, which we find to agree with the experimentally observed dynamics

Accounting for effective interactions among charged microgels

We introduce a theoretical approach to describe structural correlations among charged permeable spheres at finite particle concentrations. This theory explicitly accounts for correlations among microions and between microions and macroions and allows for the proposal of an effective interaction among macroions that successfully captures structural correlations observed in poly- N -isopropyl acrylamide microgel systems. In our description the bare charge is fixed and independent of the microgel size, the microgel concentration, and the ionic strength, which contrasts with results obtained using linear response approximations, where the bare charge needs to be adapted to properly account for microgel correlations obtained at different conditions

Social inequities in the impact of COVID-19 lockdown measures on the mental health of a large sample of the Colombian population (PSY-COVID study)

The identification of general population groups particularly vulnerable to the impact of COVID-19 lockdown measures on mental health and the development of healthcare policies are priority challenges in the current and future pandemics. This study aimed to identify the personal and social determinants of the impact of COVID-19 lockdown measures on mental health in a large sample of the Colombian population. In this cross-sectional study, an anonymous online survey was answered by 18,061 participants from the general population residing in Colombia during the first wave of the COVID-19 outbreak (from 20 May to 20 June 2020). The risk of depression, anxiety, and somatization disorders were measured using the Patient Health Questionnaire (PHQ-2), Generalized Anxiety Disorder Scale (GAD-2), and Somatic Symptom Questionnaire (SSQ-5), respectively. Overall, 35% of participants showed risk of depression, 29% of anxiety, and 31% of somatization. According to the analysis of social determinants of health, the most affected groups were people with low incomes, students, and young adults (18-29 years). Specifically, low-income young females were the most at-risk population group. These findings show how the lockdown measures affected the general population's mental health in Colombia and highlight some social risk factors in health

Vocabulario de la sociedad civil, la ruralidad y los movimientos sociales en América Latina

El Vocabulario de la Sociedad Civil, la Ruralidad y los Movimientos Sociales en América Latina tiene como objetivo desarrollar vocablos relacionados con temas de gran trascendencia para la vida colectiva de la población Latinoamericana; pretende introducir a estudiantes, personas del ámbito académico y activistas en la comprensión de estas categorías de análisis. A través de la mirada de 70 especialistas que participaron en este vocabulario, es posible comprender muchos de los términos que se utilizan dentro de la investigación social y áreas relacionadas con las ciencias políticas, ambientales y rurales, a partir de una mayor explicación y detalle. Es por ello que se inserta este trabajo desde una mirada colectiva y amplia de los conceptos que se exponen. En este libro podrá encontrar las ideas de varios autores y autoras de distintas universidades, con una visión multi, inter y transdisciplinaria. El esfuerzo que se realizó para conjuntar varios términos y analizar su compleja red de interpretaciones, permitirá que este manuscrito pueda ser consultado por estudiantes, personas del ámbito científico-académico, y ciudadanía; porque contiene el estado del arte, la historia del paulatino avance de múltiples conceptos y su vigencia en el contexto actual

Naturaleza y cultura en Ámerica Latina

La concreción del XVIII Foro de Estudiantes Latinoamericanos de Antrología y Arqueología: Cultura y naturaleza en América Latina: escenarios para un modelo de desarrollo no civilizatorio, efectuado en Quito desde el 17 al 23 de julio del 2011, se constituyó en un acontecimiento sumamente significativo para la antropología latinoamericana debido a dos motivos. Primero porque coincidió con la emergencia del movimiento universitario estudiantil latinoamericano que expresaba sus tendencias, propuestas y exigencias de cambios tanto de las prácticas académicas como de los patrones civilizatorios que rigen las relaciones actuales. Segundo, porque se inscribía en un contexto de consolidación de las nuevas democracias de los países andinos, de carácter antineoliberal y basadas en los sujetos de derecho entre los cuales se incluye la naturaleza. Estos contextos determinaron que el Foro no ponga en escena certidumbres teóricas o metodológicas, ni se preste al exhibicionismo estéril de los avances disciplinares. Más bien, la convocatoria de la antropología y la arqueología fue apenas un pretexto para hablar, con su lenguaje, de nosotros mismos, de lo que somos, de lo que pensamos, de lo que aspiramos y sentimos sobre nuestra Latinoamérica. Lo que hemos visto, oído y compartido, en realidad, no han sido solamente ideas o conceptos sino opciones y toma de posiciones respecto a múltiples encrucijadas. Posición ante situaciones que amenazan la vida, la justicia y los derechos de todos, un desafío epistemológico todavía en ciernes y que no termina de cuajar aún en nuestras prácticas académicas

Repositioning of the global epicentre of non-optimal cholesterol

High blood cholesterol is typically considered a feature of wealthy western countries(1,2). However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world(3) and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health(4,5). However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterol-which is a marker of cardiovascular riskchanged from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95% credible interval 3.7 million-4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world.Peer reviewe