AUTORES: Arturo Jimenez, Jesús Bernal-Alvarado Y Francisco Alarcón

Resumen: Inspired by the importance of understanding the dynamics of contagion in the face of diseases such as the Sars Cov-2 virus (COVID-19) pandemic. This project aims to provide an alternative to classical statistical models such as the SI, giving greater degrees of freedom to the possible parameters associated with contagion dynamics such as the spatial range of the contagion, the use of masks, the recovery of the infected agents, etc.
This alternative model consists of active Brownian particles (ABP) over a fixed area. We systematically study the dynamics of contagion as a function of parameters such as the velocity of people and the density of individuals in a certain area, we also add a recovery time over the infected agents, this addition to the rules of infections is able to recover the waves observed in the contagion dynamics showed recently by several countries.

AUTORES: Isela Sicarú Regalado Alvarado and Francisco Alarcón

Resumen: The events from the last years have raised the interest in infection dynamics and models that can provide data to prevent more cases. Using active Brownian particles (ABP) as an alternative to statistical models such as the SI model to describe the infection dynamics.
Using numerical simulations to understand the contagion dynamics, focusing on the effect of masks and vaccines. To study the evolution of the evolution of the contagion dynamics we developed a model based on active Brownian particles. Where we have carried out simulations in which the number of protected agents was changed systematically. The contagion dynamics is characterized by counting the number of infected individuals during time.

 
AUTORES: Juan Manuel Molina-Jiménez*, Beatriz Morales-Cruzado, Zenaida Briceño-Ahumada, Virginia Carrasco-Fadanelli, Erick Sarmiento-Gómez

Resumen: Measuring forces at micro-scale is of paramount importance on colloidal soft matter. Among several techniques, optical trapping is suitable for this purpose as the range of forces measured are within the typical range of  interactions in colloids. Trapping is achieved by the conservation of moment of refracted photons, and thus usually requires a trapped object with a higher index of refraction than the surrounding media. Colloidal dielectric particles and individual cells fulfills such requirements, but foams, where the trapping object is usually a gas bubble in a liquid media.
In order to measure force between bubbles on a foam, Inverse Holographical Optical Trapping (IHOT) is used, where Holographic Optical Tweezers  form a circular array of high intensity discret light points to effectively trap a bubble in a liquid media. We also give a methodology for an efficient trapping calibration that includes a theoretical approach for the calculation of optical stiffness and present a first example of measuring adhesion forces between two bubbles. 

 
Autores: Etna Yáñez, Erick Sarmiento, Natalia Rincón.

Resumen: In this work, there have been built carbon Janus particles suspended in a liquid mixture of water-lutidine to study their active motion properties when placed in an optical trap. We observe experimentally that there is a critical laser power to achieve a local demixing of the liquid mixture. This gradient of local heating can be used to produce a rotatory motion in the carbon Janus dimers when trapped by the optical tweezer. We performed these experiments with different laser powers to study their relationship with the rotational velocity of the dimers.

 
Autores: Mariela P. Vargas Rico and Natalia Rincón Londoño

Resumen: This work was focused on the protocol to obtain iron (III) hydroxide nanoparticles embedded in a viscoelastic solution (CTAB-NaSal) sulfactant. In the nanoparticle synthesis were evaluated conditions of temperature, pH and iron concentration. We observed a variation in the absorption spectra, this can related directly with nanoparticles size. Absorption of the nanoparticles embedded in the viscoelastic fluid can be modified. Knowing the absorption wavelength, the system can be irradiated and heat and as the nanoparticles absorption can be modified for subsequently the system is irradiated. This absorption can heat locally viscoleastic fluid, obtaining a rheological change.

Autores:Hector Mauricio Reynoso de la Cruz, Erasto Ortíz Ricardo, Gerardo Gutiérrez Juárez, Rigoberto Castro Beltrán

Resumen: Las micro-cavidades resonantes son útiles como herramientas para el estudio de las propiedades de emisión de diversas especies químicas, entre sus cualidades se encuentran las siguientes: i) Su capacidad intrínseca de amplificar la potencia incidente debido al alto factor de calidad de la cavidad, ii) producto de sus tamaños compactos del orden de cientos de micras las perdidas por absorción pueden llegar a ser despreciables y por ultimo iii) debido a su alto poder de confinamiento logran alcanzar altas potencias en un área pequeña incrementando la probabilidad de interacción de la luz con las moléculas activas que conforman la cavidad. En este trabajo se analiza el efecto de las propiedades de emisión en una micro-cavidad en la forma de un cilindro (pedestal) el cual tiene dimensiones de 300 micras de diámetro por 250 micras de altura fabricada mediante el proceso de escritura directa por láser, mediante este proceso hay que resaltar que la molécula ya se encuentra incorporada dentro de la micro-cavidad.[1] Las micro-cavidades fueron expuestas a una fuente de excitación en la forma de un láser pulsado (Qsmart 450 Quantel), el cual permite sintonizar la longitud de onda central en el rango (420-680nm) con paso mínimo de 1 nm, 0.7 nm de ancho de banda espectral, 10HZ de frecuencia de repetición y 8 ns de ancho temporal. Se realizaron dos experimentos con la finalidad de analizar el comportamiento con y sin cavidad resonante. Para el primer experimento se utilizó una muestra de Rhodamina a una concentración de 1E-5 M disuelta en agua destilada. Se registro el espectro de emisión a diferentes potencias y a diferentes longitudes de onda mediante un espectrómetro (Ocean Insight HR 4000). El espectro de emisión muestra el comportamiento característico asociado a la florescencia de la molécula con una envolvente espectral de 30 nm de FHWM centrada en 620 nm. En el segundo experimento se bombeo el micro-pedestal dopado con rhodamina, el espectro de emisión es el característico de una micro-cavidad el cual cuenta con múltiples picos (Frequency-comb Peine de frecuencias) dentro de la banda de emisión de la molécula. Como era de esperarse, la molécula solo responde a longitudes de onda dentro de la banda de absorción con diferente taza de eficiencias los cuales están de acuerdo con un modelo de absorción-emisión. Los posiciones de los picos espectrales de la cavidad no se modifican durante la sintonización, lo que corresponde con un comportamiento en el cual el espectro de fluorescencia es mayor que la separación entre picos individuales del peine de frecuencias.
[1]H. M. Reynoso-de la Cruz, E. Ortiz-Ricardo, V. A. Camarena-Chávez, A. Martínez-Borquez, G. Gutiérrez-Juárez, A. B. U’Ren, and R. Castro-Beltrán, "Low-cost fabrication of microlasers based on polymeric micropedestals," Appl. Opt. 60, 720-726 (2021)

 
Autores: Segura Gómez Guillermo, Álvarez Martínez Jonathan, Medina Cásares Orlando, Gutiérrez Juárez Gerardo, Castro Beltrán Rigoberto.

Resumen: El estudio de la generación de microgotas por sistemas microfluídicos tiene importantes aplicaciones en distintas áreas., por ejemplo, en óptica y fotónica las microgotas permiten la generación de láseres de tinte. Los sistemas microfluídicos que se utilizan basan su funcionamiento en una geometría denominada T-junction en la que se forma un ángulo recto entre los flujos de entrada. Para la T-junction se definen tres regímenes principales de generación de gotas (squeezing, dripping, jetting) en función de las propiedades mecánicas de los fluidos (Capilaridad). Nuestros sistemas microfluídicos, estan diseñados especificamente para trabajar en el régimen squeezing, el cual permite controlar la longitud de las microgotas producidas mediante el control de la inyección de masa. Uno de los escalones en el diseño de un sistema microfluídico es la simulación. Para poder resolver la dinámica de un sistema microfluídico se utiliza el software comercial COMSOL Multiphysics. Este trabajo presenta las generalidades en el proceso de simulación, haciendo uso de la herramienta de COMSOL para un sistema microfluídico con geometría tipo T para la generación de microgotas operando en el régimen de squeezing.

 
Autores: Daniela Cywiak, Alejandro Gil-Villegas and Alessandro Patti.

Resumen: Colloidal liquid crystals are excellent model systems to gain insights into the behavior of their molecular counterparts, whose dynamics is generally too fast to be investigated by conventional microscopy. In this work, we perform dynamic Monte Carlo simulations to investigate the self-diffusion of colloidal rods in the nematic and smectic liquid crystal phases. By defining the rotations and displacements of the rods via the diffusion coefficient at infinite dilution and rescaling the Monte Carlo step with the corresponding acceptance rate, we have calculated the mean square displacements of rods and the self-diffusion coefficients and its temperature dependence. Simulation results show that in the nematic phase the particles exhibit a fast diffusion in the direction parallel to the nematic vector, while the opposite occurs for the smectic phase. Furthermore, we observed that in the nematic phase at short times an inversion in the MSD parallel and perpendicular to the director occurs. This method can be extended to the characterisation of the equilibrium dynamics by calculating dynamic properties such as the intermediate scattering function, which provides information of the relaxation times of the systems.

 
Autores: V. Ramírez Carpio, A. Galindo, A. Gil-Villegas

Resumen: We study the global phase behaviour of n-alkanes, applying Wertheim’s first order thermodynamic perturbation theory (TPT1). The molecules are modelled as chains comprised of m freely jointed spherical segments interacting via the Lennard-Jones potential. Vega et al. [J. Chem. Phys. 116, 17 (2002)] have shown that the TPT1 is suitable to treat solid phases as well as fluid phases when model chains are considered, but that the adoption of a fully flexible chain model leads to the under-prediction of triple point temperatures and overestimation of the fluid ranges in comparison to experiment. We propose a model, in which a different number of segments are used to treat the fluid and the solid phase. The number of segments used to model the molecules in the fluid phase m f , and the LJ monomer potential parameters σ and ε are taken from the soft-SAFT values, whereas in the case of the solid phase a reduced temperature-dependent effective chain length m s (T * ) is determined through a minimisation between theoretical and experimental liquid-solid phase equilibrium data. We refer to this model as effective-solid TPT1 (es-TPT1). We use the model proposed to calculate the solid-liquid-vapour phase diagrams of several n-alkanes and compare with experimental data. We show that with this approach, the conformation of chains in the solid phase is decoupled from the fluid phase, obtaining an excellent description of the melting properties, and accurate predictions of the triple point temperatures for the n-alkanes examined. This simple solution provides an avenue to treat the solid-liquid-vapour phase behaviour of other real substances.

 
Autores: Kevin R. Arriola-González, Alejandro Gil-Villegas, Susana Figueroa-Gerstenmaier

Resumen: Syndiotactic polystyrene (sPS) is a stereoregular semicrystalline polymer which presents complex polymorphic behavior and has been studied as an alternative to solve the hydrogen storage issue from an economic, efficient and safety point of view. Determination of adsorption isotherms for sPS in an experimental approach is possible, however, to understand the phenomena occurring at a nanoscale level (e.g. confined interactions of H2 in sPS), alternative methods such as molecular simulations are required. In this work, molecular hydrogen (H2) adsorption isotherms of δ and ε phases of sPS were determined by Grand Canonical Monte Carlo (GCMC) molecular simulations. H2 molecule was described as a 1 site model with Lennard-Jones (LJ) and Exp-6 potentials, applying a first order Wigner-Kirkwood (WK) expansion for quantum corrections. Both polymer phases were represented using atomistic models. Initial configurations were relaxed using GROMACS molecular dynamics software at T=45 K, 60 K and 77 K. Isotherm adsorptions were calculated for each potential in a classical and semiclassical form. Results were compared with experimental adsorption data (from a previous work) at 77 K.

 
Autores: Alvarez-Martinez J.U., Polo-Parada Luis, Gutierrez-Juarez G., Medina-Cazarez O., Castro-Beltran R.

Resumen: La manipulación de fluidos a escalas microscópicas, típicamente en volúmenes de picolitros, ha sido ampliamente utilizado en distintas ramas de la ciencia desde hace más de una década, esta tecnología es llamada microfluidica1. La microfluidica ha sido empleada en la manofactura de micromezcladores, microreactores y generadores de microgoras2. Además, estos en combinación con distintas técnicas de medición han sido empleados para la generación de sistemas lab-on-a-chip (LoC)3. Un ejemplo de estas es la técnica denominada foto-acústica, en la cual, un objeto absorbe luz a una frecuencia especifica y una perturbación mecánica en forma de ultrasonido, esta técnica ha sido empleada ampliamente para la formación de imágenes4 empleando transductores acústicos (TA) para ello. En este trabajo se presenta un sistema microfluidico en forma de unión en T (SM) para la generación de micro-emulsiones en forma de gotas (microgotas), en el cual, la combinación de aceite mineral y una solución acuosa con células cancerígenas inmortalizadas y suspendidas en él serán empleados para generar dichas microgotas en un microcanal de 150µm. La adaptación de una fibra óptica y un transductor acústico al sistema microfluidico nos permitió obtener señales foto-acústicas (SPA). En el experimento, se generaron las microgotas dentro del SM y a ellas se les incidió un spot láser de 532nm y a una frecuencia de 7Hz excitando las células cancerígenas dentro de las microgotas de agua, estas, generaron una SPA la cual fue medida por los TA y transducidas a señales eléctricas, las cuales, se sometieron a un método de reconstrucción de imágenes desarrollado en el laboratorio de biofotoacústica y basado en Matlab. Como resultado, se presentan más de 400 señales fotoacústicas fueron obtenidas desde las microgotas, con las cuales, se formaron imágenes delas microgotas. Estos resultados son el inicio del desarrollo de un LoC que nos permita caracterizar células cancerígenas suspendidas en distintos fluidos.
1. Yi, C., Li, C. W., Ji, S., & Yang, M. (2006). Microfluidics technology for manipulation and analysis of biological cells. Analytica chimica acta, 560(1-2), 1-23.
2. Álvarez-Martínez, J. U., Medina-Cázares, O. M., Soto-Alcaraz, M. E., Castañeda-Priego, R., Gutiérrez-Juárez, G., & Castro-Beltrán, R. (2022). Microfluidic system manufacturing by direct laser writing for the generation and characterization of microdroplets. Journal of Micromechanics and Microengineering, 32(6), 065001.
3. R. Kishor and Y. Zheng, "Surface acoustic wave RF sensing and actuation for lab-on-a-chip platforms," 2016 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), Chengdu, China, 2016, pp. 1-4, doi: 10.1109/IMWS-AMP.2016.7588459
4. Ruiz-Veloz, M., Gutiérrez-Juárez, G., Polo-Parada, L., Cortalezzi, F., Kline, D. D., Dantzler, H. A., ... & Hidalgo-Valadez, C. (2023). Image reconstruction algorithm for laser-induced ultrasonic imaging: The single sensor scanning synthetic aperture focusing technique. The Journal of the Acoustical Society of America, 153(1), 560-572.

 
Autores: Javier Alejandro Sánchez Gallegos, Néstor Enrique Valadez Pérez and Ramón Castañeda Priego

Resumen: The gravitational effects in gel-forming patchy colloidal systems are analyzed through Monte Carlo simulation in the vicinity of gel-like states recently identified by the rigidity percolation criterion [Phys. Rev. E 104, 064606 (2021)]. The influence of the gravitational field, characterized by the gravitational Péclet number Pe, on patchy colloids, is systematically studied for different values of patchy coverage. A threshold Péclet number, where the gravity starts to be taken in account for the phase behavior, is find. A reach structural scenario emerges due the systematic increase in the gravity, passing from a homogeneous gel-like structure to a multi-dense cluster.

Autores: César Solano-Cabrera, Pavel Castro-Villareal, Ramón Castañeda-Priego

Resumen: In this work, we present a covariant formulation of the Smoluchowski equation (SE) for colloidal particles confined to a surface. We start from the many-particle Langevin equation (LE) and through methods of stochastic calculus, we obtain the associated SE. Since the motion takes place on a Riemannian manifold, the probability density present in the SE is replaced by a formulation compatible with such a space leading to the covariant form of the equation. After that, with the help of reduced probability densities, we integrate the covariant SE to obtain an equation for the probability density of one particle.

Autores: Eduardo Daniel Hernandez Campos, Joselyn Guerrero Cabrera, Héctor Mauricio Reynoso De La Cruz, Erasto Ortiz Ricardo, Ignacio Raúl Rosas Román, Víctor Ulises Lev Contreras Loera, Gerardo Gutiérrez Juárez y Rigoberto Castro Beltrán

Resumen: El desarrollo de micro cavidades láser tiene un impacto directo en sistemas ópticos integrados con aplicaciones enfocadas en dispositivos "todo ópticos". En temas de versatilidad en los procesos de fabricación utilizados para desarrollar este tipo de cavidades láser a escala micrométrica, están desde basadas en procesos fotolitográficos hasta sistema por plasma y de impresión láser directa, entre otros. Este trabajo, presenta una nueva perspectiva respecto a la implementación de un resonador acústico cómo plataforma contenedora de microgotas levitadas con funcionamiento láser. La gran oportunidad en términos de caracterización radica en que la muestra levitada, la cual es una disolución a base de agua que contiene un colorante comercial, puede ser manipulada, in situ, en su forma al cambiar las distancias relativas de la cavidad acústica resonante y/o la amplitud a las cuales trabajan los transductores. El tipo de levitador acústico utilizado es una versión pequeña del TinyLev. Este trabajo, presenta al levitador acústico, el desempeño respecto a su funcionamiento, estabilidad y presentación integral para ser utilizado cómo plataforma de soporte y generación para sistemas láser a escala micrométrica. A su vez, se presentan los resultados más sobresalientes respecto al funcionamiento de un sistema micro láser.

 
Autores: K.Gonzales-Flores, R. Castañeda-Priego, and F. Alarcón

Resumen: The viruses represent an essential role in the daily life of many people because threaten public health arrow the world, such as the 2019-nCoV pandemic generated by coronavirus 2 (SARS-CoV-2), which causes the so-called Severe Acute Respiratory Syndrome. It is well known, that the most effective route for the spread of Covid-19 is due to the airborne transmission of the virus through secretions. Thus, this work aims to study and understand the diffusion of a virus model depending on the host environment in which it is suspended. By using the numerical mesoscopic technique called Dissipative Particle Dynamics (DPD) we have studied the dynamical transport of a virus model immersed in an explicit solvent. This type of approach allows us to include the hydrodynamic effects in the diffusive properties of the virus and, therefore, helps us to understand the relevance of those effects with the degree of spread of the virus.

Autores: Juan Manuel Molina, Erick Sarmiento Gómez and Natalia Rincón Londoño

Resumen: Janus particles carbon embedded in a binary critical solvent present a self-propelled motion when they are irradiated with a homogeneous light spot. Light absorption of the carbon-covered part produces a local temperature increase, obtaining a phase separation and a concentration gradient. In this project, the Janus particles are irradiated with a periodic field formed by lines of light. The motion of the particles is studied when they interact with the light lines at different separation. Preliminary results show a directed motion of the Janus particles which dependent of the separation between lines.

 
Autores: Natalia Rincón Londoño, Ivany del Carmen Romero Sánchez, Jonathan Ulises Alvarez Martínes, Rigoberto Castro Beltrán, Erick Sarmiento Gómez.

Resumen: El fenómeno de enfoque hidrodinámico se produce cuando dos líquidos newtonianos inmiscibles se ven confinados en un canal microfluídico en forma de T. Esto produce un adelgazamiento estable del fluido central, que depende de los gastos relativos de ambos fluidos. Un fenómeno completamente diferente sucede cuando el fluido central confinado es viscoelástico, produciendo una interfaz inestable con una dinámica al parecer caótica. En este trabajo se analiza esta inestabilidad usando un fluido viscoelástico Maxwelliano, es decir que cuenta con un único tiempo de relajación del esfuerzo. Se caracteriza dicha inestabilidad a diferentes valores del caudal, encontrando un valor mínimo requerido de la razón de corte para que suceda el fenómeno. Además se discute el origen de la inestabilidad como una competencia entre el almacenamiento de energía derivado del confinamiento del fluido viscoelástico, y la tensión superficial reducida por presencia del tensioactivo que forma la estructura supramolecular viscoelástica.

 
Autores: Lourdes Bibiana Merino Solís y Francisco Sastre Carmona

Resumen: In this work we implement a new algorithm based on transitions rates between order parameter levels in the two dimensional q-state Potts model without external field. The Potts model has been widely studied and is one of the few interacting models with analytical solution, in the two dimensional case without external field. Despite its simplicity it can be used to study several systems such as magnetic dominions grow, cellular behavior or social and demographic behavior, for name a few. The algorithm is based on the determination of the transition rates of between discrete macroscopic observables. This numerical method can evaluate directly the derivative of the logarithm of the probability distribution function with respect to the order parameter. Using standard finite-size scaling theory we evaluate the critical point and the correlation length critical exponent for q = 2, 3 and 4. Our results are in good agreement with the expected theoretical value.

 
Autores: Jaime Jaramillo Gutiérrez, Jean-Pierre Simonin, José Torres Arenas, Olivier Bernard.

Resumen: In the framework of the primitive model where the solvent in a solution is modeled as a continuum, the BIMSA (binding mean spherical approximation) theory was used for a description of activity and osmotic coefficients of electrolytes at high temperatures. Solvation effects and variation of the permittivity are included in the model. Parameters are adjusted by comparison with experimental data. Futhermore, the BIMSA theory allows one to consider the formation of ion pairs. The cases without association and with association were compared by applying them to some aqueous solutions NaCl, LiCl, MgCl and CaCl at different concentration and temperature ranges.

Autores: María Eugenia Soto Alcaraz, Erick Sarmiento Gómez, Ignacio Raúl Rosas Román, Gerardo Gutiérrez Juárez, Rigoberto Castro Beltrán, Ramón Castañeda Priego

Resumen: Selective particle adsorption is an interesting phenomenon that takes place in an inhomogeneous system where the local concentration of the particles varies affecting the bulk structure. This phenomenon is produced in solid substrates or porous materials and it can be induced by the shape of the particles as the key-lock self-assembling mechanisms, external fields being applied to the system, the treatments on the surfaces by hydrophobic or hydrophilic coatings and, the geometry of the walls, which is the particular case of interest in this work. In this work we have used the Contraction of the Description formalism, from the Integral Equations Theory of Liquids to obtain effective potentials between the bigger particles and the geometrical constrictions imposed by surrounding walls that exhibit distinct morphologies. The wall-particle potential for the specific structures allowed us to predict the behaviour of the system and the adsorption that occurred near the walls. These results led us to design microstructures with different wall geometries (concave and convex curvatures) to study experimentally the adsorption of colloidal particles of a suspension when they are close to the wall through videomicroscopy.

 
Autores: M. Martínez-Jiménez; A. L. Benavides

Resumen: The liquidus temperature curve that characterizes the boundary between the liquid methanol/water mixture and its coexistence with ice Ih is determined using the direct-coexistence method. Several methanol concentrations and pressures of 0.1, 50, and 100 MPa are considered. In this study, we used the TIP4P/Ice model for water and two different models for methanol: OPLS and OPLS/2016, using the geometric rule for the Lennard-Jones cross interactions. We compared our simulation results with available experimental data and found that this combination of models reproduces the liquidus curve for methanol mole fractions reasonably well, up to xm = 0.3 at p = 0.1 MPa. The freezing point depression of these mixtures is calculated and compared to experimental results. We also analyzed the effect of pressure on the liquidus curve and found that both models also reproduce the experimental decrease of the liquidus temperatures as the pressure increases qualitatively well.

Autores: Fidencio Pérez Hernández, Claudio Contreras Aburto

Resumen: Transport phenomena are objects of study in soft matter, and we report on analyzing these phenomena in charged systems. In this work, we have focused on studying the transport of salt ions using the MCT-HI’s as the theoretical framework. On the one hand, to get the static correlation functions, we have used the HNC approximation for the electrolyte solution in the unrestricted primitive model; on the other hand, we also used simulation (Monte Carlo) results as the static inputs of the theory. We compare our results with experimental measurements.

Autores: Melissa Rojas-Romero, Orlando Medina-Cázares, Misael Ruiz-Veloz, Francisco J. García Rodríguez, Rigoberto Castro-Beltrán, y Gerardo Gutiérrez-Juarez

Resumen: When thermal and stress confinement conditions are satisfied, the generation and propagation of laser-induced ultrasound (LIU) is governed by an inhomogeneous wave equation for pressure. In this work a 1D-Cauchy boundary value problem, for the inhomogeneous wave equation, is solved in the frequency domain considering a laser pulse with finite time-width. The source term in the inhomogeneous wave equation is proportional to the optical energy of the laser pulses absorbed by the samples. It is assumed that the laser pulses have a Gaussian temporal profile. To experimentally prove our solution, we used aluminum slabs with artificial defects located in air and water mediums. This experimental data and the resolution of the 1D Cauchy model obtained information on the defect’s size and location. This result suggests that our proposal can detect sub-superficial defects in manufactured objects.