arXiv subjects

Carolina Brito

Publications and source records attributed to Carolina Brito.

At least 19 recordsLinked to original sources

arXiv2025

Probing wetting properties with self-propelled droplets

Wetting phenomena are relevant in several technological applications, particularly those involving hydrophobic or hydrophilic surfaces. Many substrates support multiple wetting states depending on surface conditions or droplet history, a behavior known as metastability. This feature is crucial both for its theoretical complexity and for its relevance in practical applications that rely on controlling metastable states. While several experimental and computational techniques have been developed to study metastability, they tend to be complex or computationally expensive. In this work, we introduce an alternative approach based on concepts from active matter physics. We investigate the wetting behavior of a droplet placed on a pillared surface using a 3-state Cellular Potts model with a polarity term that mimics a self-propelled droplet. Applying this model to a pillared substrate with known metastable wetting states, we demonstrate that increasing activity enables the droplet to traverse free energy barriers, explore consecutive metastable states, and eventually suppress metastability entirely. Our results show that activity reduces the disparity between dry and wet states and provides a reliable framework for identifying and quantifying metastability through contact angle measurements.

cond-mat.soft↗

arXiv2025

Optimizing oil-water separation using fractal surfaces

Oil has become a prevalent global pollutant, stimulating the research to improve the techniques to separate oil from water. Materials with special wetting properties - primarily those that repel water while attracting oil - have been proposed as suitable candidates for this task. However, one limitation in developing efficient substrates is the limited available volume for oil absorption. In this study we investigate the efficacy of disordered fractal materials in addressing this challenge, leveraging their unique wetting properties. Using a combination of a continuous model and Monte Carlo simulations, we characterize the hydrophobicity and oleophilicity of substrates created through ballistic deposition (BD). Our results demonstrate that these materials exhibit high contact angles for water, confirming their hydrophobic nature, while allowing significant oil penetration, indicative of oleophilic behavior. The available free volume within the substrates vary from $60\%$ to $90\%$ of the total volume of the substrate depending on some parameters of the BD. By combining their water and oil wetting properties with a high availability of volume, the fractal substrates analyzed in this work achieve an efficiency in separating oil from water of nearly $98\%$, which is significantly higher compared to a micro-pillared surfaces made from the same material but lacking a fractal design.

cond-mat.stat-mech↗

arXiv2024

Tuning collective actuation of active solids by optimizing activity localization

Active solids, more specifically elastic lattices embedded with polar active units, exhibit collective actuation when the elasto-active feedback, generically present in such systems, exceeds some critical value. The dynamics then condensates on a small fraction of the vibrational modes, the selection of which obeys non trivial rules rooted in the nonlinear part of the dynamics. So far the complexity of the selection mechanism has limited the design of specific actuation. Here we investigate numerically how, localizing the activity on a fraction of modes, one can select non-trivial collective actuation. We perform numerical simulations of an agent based model on triangular and disordered lattices and vary the concentration and the localization of the active agents on the lattices nodes. Both contribute to the distribution of the elastic energy across the modes. We then introduce an algorithm, which, for a given fraction of active nodes, evolves the localization of the activity in such a way that the energy distribution on a few targeted modes is maximized -- or minimized. We illustrate on a specific targeted actuation, how the algorithm performs as compared to manually chosen localization of the activity. While, in the case of the ordered lattice, a well educated guess performs better than the algorithm, the latter outperform the manual trials in the case of the disordered lattice. Finally, the analysis of the results in the case of the ordered lattice leads us to introduce a design principle based on a measure of the susceptibility of the modes to be activated along certain activation paths.

cond-mat.soft↗

arXiv2024

Climatic Extremes in Brazil: a parallel analysis of Historical Trends and Socioeconomical Impacts

An important consequence of human induced climate change is the increase in extreme weather events. This study contributes to the understanding of Brazil's climate change by examining historical temperature and precipitation patterns. Extreme events of temperature and precipitation are identified using data from the Brazilian Institute of Meteorology, which includes records from 634 meteorological stations operating intermittently since 1961. Using the first 30 years (1961 to 1990) as the reference period, our results show a significant increase in warm days and a corresponding decrease in cold days over the last 30 years (1991 to 2020), in agreement with previous works. In terms of precipitation, it indicates a trend toward drier conditions in the Northeast region of Brazil, whereas the South is experiencing wetter conditions, with an increase in the number of heavy precipitation days in South and in the extremely dry periods in the Northeast. These results have been verified for consistency with several extreme climate indices measured in this study. Additionally, data from S2iD is analyzed, an official database that records natural disasters in Brazil, to estimate their impact in terms of human losses and financial costs over the past decade. Our findings indicate that drought events are the most economically costly, with multiple instances causing damages exceeding a billion USD, whereas storms have the greatest impact on people. Although it is not possible to directly attribute the natural disasters recorded in the S2iD database to the extreme weather events identified through meteorological data, discussion is done on potential implications of these events in the frequency and location of the disasters.

physics.ao-ph↗

arXiv2024

Testing theories of the glass transition with the same liquid, but many kinetic rules

We study the glass transition by exploring a broad class of kinetic rules that can significantly modify the normal dynamics of super-cooled liquids, while maintaining thermal equilibrium. Beyond the usual dynamics of liquids, this class includes dynamics in which a fraction $(1-f_R)$ of the particles can perform pairwise exchange or 'swap moves', while a fraction $f_P$ of the particles can only move along restricted directions. We find that (i) the location of the glass transition varies greatly but smoothly as $f_P$ and $f_R$ change and (ii) it is governed by a linear combination of $f_P$ and $f_R$. (iii) Dynamical heterogeneities are not governed by the static structure of the material. Instead, they are similar at the glass transition across the ($f_R$, $f_P$) diagram. These observations are negative items for some existing theories of the glass transition, particularly those reliant on growing thermodynamic order or locally favored structure, and open new avenues to test other approaches.

cond-mat.soft↗

arXiv2024

Chemical Physics of Controlled Wettability and Super Surfaces

Wetting phenomena are widespread in both natural and technological contexts. Despite the well-established nature of this scientific field and our extensive knowledge of its underlying principles, wetting remains a dynamic and vibrant area of study. It continues to pose fundamental questions while offering innovative avenues for controlling these phenomena to develop novel applications. By tailoring the wetting properties of surfaces, researchers and engineers can design materials with specific functionalities, such as self-cleaning surfaces, anti-fog coatings, and enhanced slipperiness. Recent years have witnessed significant advancements in wetting research, owing to the exquisite control achieved in surface topography and chemistry and to the development of novel experimental techniques. Additionally, simulations and theory have played a crucial role in these advancements. They provid the fundamental knowledge and quantitative tools to control wettability and design surfaces with enhanced properties. Given these recent breakthroughs, this special collection Chemical Physics of Controlled Wettability and Super Surfaces becomes particularly timely and significant. It serves as a platform to showcase some of the latest developments in the field of wetting. It highlights the exciting progress and potential applications in controlling wetting properties that are enabled by the synergy between theory, simulations, and experiments.

cond-mat.soft↗

arXiv2023

Hierarchical structured surfaces enhance the contact angle of the hydrophobic (meta-stable) state

The relation between wetting properties and geometric parameters of fractal surfaces are widely discussed on the literature and, however, there are still divergences on this topic. Here we propose a simple theoretical model to describe the wetting properties of a droplet of water placed on a hierarchical structured surface and test the predictions of the model and the dependence of the droplet wetting state on the initial conditions using simulation of the 3-spin Potts model. We show that increasing the auto-similarity level of the hierarchy -- called $n$ -- does not affect considerably the stable wetting state of the droplet but increases its contact angle. Simulations also explicit the existence of metastable states on this type of surfaces and shows that, when $n$ increases, the metastability becomes more pronounced. Finally we show that the fractal dimension of the surface is not a good predictor of the contact angle of the droplet.

cond-mat.soft↗

arXiv2022

Scientific physics events in Brazil: female participation

We have carried out a partial survey on the female participation in events organized by the Brazilian Physical Society (SBF, in Portuguese) from 2005 to 2021. Our analysis shows that the participation of women has increased over the years, reaching in some areas, the same percentage as the one observed in the SBF community (always lower that 25\%). However, the participation as members of organizing committees and as keynote speakers is always lower. Some propositions to change this inequality situation are listed.

physics.soc-ph↗

arXiv2021

Can one predict a drop contact angle?

The study of wetting phenomena is of great interest due to the multifaceted technological applications of hydrophobic and hydrophilic surfaces. The theoretical approaches proposed by Wenzel and later by Cassie and Baxter to describe the behaviour of a droplet of water on a rough solid were extensively used and improved to characterize the apparent contact angle of a droplet. However, the equilibrium hypothesis implied in these models means that they are not always predictive of experimental contact angles due to strong metastabilities typically occurring on heterogeneous surfaces. A predictive scheme for contact angle is thus urgently needed both to characterise a surface by contact angle measurements and to design superhydrophobic and oleophobic surfaces with the desired properties, e.g., contact angle hysteresis. In this work a combination of Monte Carlo simulation and the string method is employed to calculate the free energy profile of a liquid droplet deposited on a pillared surface. For the analyzed surfaces, we show that there is only one minimum of the free energy that corresponds to the superhydrophobic wetting state while the wet state can present multiple minima. Furthermore, when the surface roughness decreases the amount of local minima observed in the free energy profile increases.

cond-mat.soft↗

arXiv2020

Modeling oil-water separation with controlled wetting properties

Several oil-water separation techniques have been proposed to improve the capacity of cleaning water. With the technological possibility of producing materials with antagonist wetting behavior, as for example a substrate that repeal water and absorb oil, the understanding of the properties that control this selective capacity has increased with the goal of being used as mechanism to separate mixed liquids. Besides the experimental advance in this field, less is known from the theoretical side. In this work we propose a theoretical model to predict the wetting properties of a given substrate and introduce simulations with a 4-spins cellular Potts model to study its efficiency in separating water from oil. Our results show that the efficiency of the substrates depends both on the interaction between the liquids and on the wetting behavior of the substrates itself. The water behavior of the droplet composed of both liquids is roughly controlled by the hidrophobicity of the substrate. To predict the oil behavior, however, is more complex because the substrate being oleophilic do not guarantee that the total amount of oil present on the droplet will be absorbed by the substrate. For both types of substrates considered is this work, pillared and porous with a reservoir, there is always an amount of reminiscent oil on the droplet which is not absorbed by the substrate due to the interaction with the water and the gas. Both theoretical and numerical models can be easily modified to analyse other types of substrates and liquids.

cond-mat.soft↗

arXiv2020

Jamming with tunable roughness

We introduce a new model to study the effect of surface roughness on the jamming transition. By performing numerical simulations, we show that for a smooth surface, the jamming transition density and the contact number at the transition point both increase upon increasing asphericity, as for ellipsoids and spherocylinders. Conversely, for a rough surface, both quantities decrease, in quantitative agreement with the behavior of frictional particles. Furthermore, in the limit corresponding to the Coulomb friction law, the model satisfies a generalized isostaticity criterion proposed in previous studies. We introduce a counting argument that justifies this criterion and interprets it geometrically. Finally, we propose a simple theory to predict the contact number at finite friction from the knowledge of the force distribution in the infinite friction limit.

cond-mat.soft↗

arXiv2020

On the stability of the Brazilian presidential regime: a statistical analysis

Brazil's presidential system is characterized by the existence of many political parties that are elected for the Chamber of Deputies and unite in legislative coalitions to form a majority. Since the re-democratization in 1985, Brazil has had 8 direct presidential elections, among which there were two impeachments of the elected president. In this work we characterize the stability of the presidential regime and the periods of rupture analysing the votes that took place in the Chamber of Deputies from 1991 to 2019. We start by measuring the cohesion of the parties and the congress in the votes, quantifying the agreement between the votes of congressmen and observe that there is a stronger polarization among congressmen during legislative periods where there was no impeachment, referred to here as stable legislative periods. Using clustering algorithms, we are able to associate these polarized groups observed during the stable periods with the opposition to the government and government base. To characterize the impeachment of Dilma Roussef that happened in 2016 we analyze how the agreement between congressmen and the government evolved over time and identified, using cluster algorithms, that all the parties belonging to the majority coalition of the president, except her own party and another one, migrated to the opposition just before the impeachment. Our analyses allow us to identify some differences between stable presidential periods and Legislative terms with an impeachment.

physics.soc-ph↗

arXiv2020

Brazilian physicists community diversity, equity and inclusion: a first diagnostic

We report the results of a survey applied to students and professionals in the area of physics in Brazil, pursuing to draw a portrait of the composition of this community in terms of the social markers age, race, ethnicity, geographical origin, sex, gender, sexual orientation, and disabilities. The main goal was to quantify the representativeness of different groups in the community and to detect motivations and difficulties encountered by each group throughout their studies and career. This survey was open to the members of the Brazilian Physics Society (SBF) from July to September 2018. Our outcomes reveal that (i) the Brazilian physicists community is poorly diverse even in comparison with the population composition, (ii) the main obstacle to pursue the career is socioeconomic vulnerability and (iii) harassment is high in our society, being more pronounced among women. We hope that these results will be useful to scientific and educational institutions to develop different strategies and policies to change this current situation.

physics.ed-ph↗

arXiv2020

Direct Coupling Analysis of Epistasis in Allosteric Materials

In allosteric proteins, the binding of a ligand modifies function at a distant active site. Such allosteric pathways can be used as target for drug design, generating considerable interest in inferring them from sequence alignment data. Currently, different methods lead to conflicting results, in particular on the existence of long-range evolutionary couplings between distant amino-acids mediating allostery. Here we propose a resolution of this conundrum, by studying epistasis and its inference in models where an allosteric material is evolved in silico to perform a mechanical task. We find in our model the four types of epistasis (Synergistic, Sign, Antagonistic, Saturation), which can be both short or long-range and have a simple mechanical interpretation. We perform a Direct Coupling Analysis (DCA) and find that DCA predicts well the cost of point mutations but is a rather poor generative model. Strikingly, it can predict short-range epistasis but fails to capture long-range epistasis, in consistence with empirical findings. We propose that such failure is generic when function requires subparts to work in concert. We illustrate this idea with a simple model, which suggests that other methods may be better suited to capture long-range effects.

q-bio.QM↗

arXiv2019

Infinitesimal asphericity changes the universality of the jamming transition

The jamming transition of non-spherical particles is fundamentally different from the spherical case. Non-spherical particles are hypostatic at their jamming points, while isostaticity is ensured in the case of the jamming of spherical particles. This structural difference implies that the presence of asphericity affects the critical exponents related to the contact number and the vibrational density of states. Moreover, while the force and gap distributions of isostatic jamming present power-law behaviors, even an infinitesimal asphericity is enough to smooth out these singularities. In a recent work [PNAS 115(46), 11736], we have used a combination of marginal stability arguments and the replica method to explain these observations. We argued that systems with internal degrees of freedom, like the rotations in ellipsoids, or the variation of the radii in the case of the \textit{breathing} particles fall in the same universality class. In this paper, we review comprehensively the results about the jamming with internal degrees of freedom in addition to the translational degrees of freedom. We use a variational argument to derive the critical exponents of the contact number, shear modulus, and the characteristic frequencies of the density of states. Moreover, we present additional numerical data supporting the theoretical results, which were not shown in the previous work.

cond-mat.soft↗

arXiv2019

Mechanics of allostery: contrasting the induced fit and population shift scenarios

In allosteric proteins, binding a ligand can affect function at a distant location, for example by changing the binding affinity of a substrate at the active site. The induced fit and population shift models, which differ by the assumed number of stable configurations, explain such cooperative binding from a thermodynamic viewpoint. Yet, understanding what mechanical principles constrain these models remains a challenge. Here we provide an empirical study on 34 proteins supporting the idea that allosteric conformational change generally occurs along a soft elastic mode presenting extended regions of high shear. We argue, based on a detailed analysis of how the energy profile along such a mode depends on binding, that in the induced fit scenario there is an optimal stiffness $k_a^*\sim 1/N$ for cooperative binding, where $N$ is the number of residues involved in the allosteric response. We find that the population shift scenario is more robust to mutation affecting stiffness, as binding becomes more and more cooperative with stiffness up to the same characteristic value $k_a^*$, beyond which cooperativity saturates instead of decaying. We confirm numerically these findings in a non-linear mechanical model. Dynamical considerations suggest that a stiffness of order $k_a^*$ is favorable in that scenario as well, supporting that for proper function proteins must evolve a functional elastic mode that is softer as their size increases. In consistency with this view, we find a significant anticorrelation between the stiffness of the allosteric response and protein size in our data set.

physics.bio-ph↗

arXiv2019

Geometric and chemical non-uniformity may induce the stability of more than one wetting state in the same hydrophobic surface

It is established that roughness and chemistry play a crucial role in the wetting properties of a substrate. Yet, few studies have analyzed systematically the effect of the non-uniformity in the distribution of texture and surface tension of substrates on its wetting properties. In this work we investigate this issue theoretically and numerically. We propose a continuous model that takes into account the total energy required to create interfaces of a droplet in two possible wetting states: Cassie-Baxter(CB) with air pockets trapped underneath the droplet; and the other characterized by the homogeneous wetting of the surface, the Wenzel(W) state. To introduce geometrical non-regularity we suppose that pillar heights and pillar distances are Gaussian distributed instead of having a constant value. Similarly, we suppose a heterogeneous distribution of Young's angle on the surface to take into account the chemical non-uniformity. This allows to vary the "amount" of disorder by changing the variance of the distribution. We first solve this model analytically and then we also propose a numerical version of it, which can be applied to study any type of disorder. In both versions, we employ the same physical idea: the energies of both states are minimized to predict the thermodynamic wetting state of the droplet for a given volume and surface texture. We find that the main effect of disorder is to induce the stability of both wetting states on the same substrate. In terms of the influence of the disorder on the contact angle of the droplet, we find that it is negligible for the chemical disorder and for pillar-distance disorder. However, in the case of pillar-height disorder, it is observed that the average contact angle of the droplet increases with the amount of disorder. We end the paper investigating how the region of stability of both wetting states behaves when the droplet volume changes.

cond-mat.soft↗

arXiv2019

Women in Physics: Scissors Effect from the Brazilian Olympiad of Physics to Professional Life

Despite the legislation in force in most countries and the discourse on gender equality, the observed reality, still today, shows a clear picture of inequality and restrictions for women, particularly when the issue is the choice of a career and the subsequent promotions. In many professions, although women represent the majority in the entrance to undergraduate courses, their participation is dramatically reduced as the career progresses to the highest levels. While the participation of men increases, that of women decreases as the academic levels move towards the top ranks. This kind of evolution of two groups in opposed directions is usually referred as the "scissors effect". This effect with respect to sexes also occurs in the area of physics, both in Brazil and in the rest of the world. But at what age does this effect begin? What is its intensity in the different stages of women's lives? In this article we aim to shed some light on these questions by analyzing data of the Brazilian Olympiad of Physics and of fellowships for physicists in Brazil. We observe the systematic occurrence of scissors effect throughout the full studied data, ranging from the first years of participation in the Olympiads (13 years old) to the highest stages of the scientific career.

physics.ed-ph↗