Mie scattering theory applied to light scattering of large nonhomogeneous colloidal spheres.

Colloidal suspensions made of smart core-shell structures are of current interest in many fields. Their properties come from the possibility of varying the core and shell materials for modifying the composite particles' chemical, biological, and optical properties. These particles are formed with a material with a constant refractive index core and a shell with a refractive index decaying until it matches the solvent refractive index.

Competition among physical, chemical, and hybrid gelation mechanisms in biopolymers.

Depending on how they form their linkages, biopolymer gelatin gels are commonly classified as physical, chemical, or hybrid; in gelatin hybrid gels, the physical and chemical crosslinking mechanisms occur simultaneously. The viscoelastic behavior of gels following different gelation processes was determined around the gel point. Their gel fractal dimensions were obtained using the BST-scaling model from large amplitude oscillatory shear results.

Micellar entanglement and its relation to the elastic behavior of wormlike micelle fluids.

Hypothesis: The elastic contribution to the fluid dynamics of wormlike micellar solutions makes these fluids unique due to the distinctive self-assembled micellar network formed by tubular micelles. Measured mesoscopic scales of the micellar network related to the degree of entanglement can give guidelines for understanding the origin of elastic forces and their effect on rheological response.

Experiments: Different experiments were made as flow curves, rotating the internal or external cylinder in a Couette geometry, small and large oscillatory shear tests, and linear shear banding observations, all of them to determine how elastic forces modify the rheological behavior in systems made of different ratios of hexadecyltrimethylammonium bromide (CTAB)/sodium salicylate (NaSal) and different ratios of CTAB/NaNO.

Measuring mesoscopic scales in complex fluids embedded with giant cylindrical micelles with diffusing wave spectroscopy micro-rheology.

This review paper presents a procedure for measuring the mesoscopic scales in micellar solutions embedded with giant cylindrical micelles using the mean square displacement determined with a quasi-elastic multiple light scattering method (diffusing wave spectroscopy) and theory. The mesoscopic scales of interest are the micelles' total contour length, persistence and entanglement lengths, and the mesh size of the entangled micellar network. All of them depend on the physicochemical parameters of the solutions and determine the rheological behavior.

BDNF as a Biomarker of Cognition in Schizophrenia/Psychosis: An Updated Review.

Brain Derived Neurotrophic Factor (BDNF) has been linked to cognitive symptoms of schizophrenia, which has been documented in previous reviews by several authors. However, a trend has recently emerged in this field moving from studying schizophrenia as a disease to studying psychosis as a group. This review article focuses on recent BDNF studies in relation to cognition in human subjects during different stages of the psychotic process, including subjects at high risk of developing psychosis, patients at their first episode of psychosis, and patients with chronic schizophrenia.

Measurement of the capillary interaction force between Janus colloidal particles trapped at a flat air/water interface.

The capillary interaction force between spherical Janus particles trapped at the air-water interface is measured using a time-sharing optical tweezer (bond number ≪ 1). One face of the particles is hydrophilic, and the other one, hydrophobic. Measured force goes from almost pure quadrupolar to almost pure hexapolar interaction due to the three-phase contact line corrugation.

Mechanical Properties of DPPC-POPE Mixed Langmuir Monolayers.

The mechanical properties of lipid monolayers and their responses to shear and compression stresses play an important role in processes such as breathing and eye blinking. We studied the mechanical properties of Langmuir monolayers of a model mixture, composed of an unsaturated lipid, 1-palmitoyl-2-oleoyl--glycero-phosphoethanolamine (POPE), and a saturated lipid, 1,2-dipalmitoyl--glycero-phosphocholine (DPPC). We performed isothermal compressions and sinusoidal shear deformations of these mixed monolayers.

Alignment of worm-like micelles at intermediate and high shear rates.

Hypothesis: Rheology combined with Small-Angle Neutron Scattering (Rheo-SANS) can determine the local structural order in Worm-Like Micelle (WLM) solutions when the shear rate increases beyond the ending of the gradient shear banding. There, micelles are supposedly aligned, but viscosity reveals a transition regime as the shear rate increases.

Experiments: The mixture of 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate (TDPS), sodium dodecylsulfate (SDS) (R = [SDS]/[TDPS] = 0.

Structural Changes in Wormlike Micelles on the Incorporation of Small Photoswitchable Molecules.

Chromophores susceptible to light-induced trans-cis isomerization embedded in cylindrical micelles can modify micelles and their light-responsive performance. A small chromophore (4-(phenylazo)benzoate ion) is embedded in cylindrical micelles made of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in water. The microstructure is examined by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR).

Measurement of the force between uncharged colloidal particles trapped at a flat air/water interface.

The radial attraction between microspheres straddling at the air/water interface (Bond number ≪1), whose origin is the irregular shape of the contact line and its concomitant distortion of the water surface, is measured using two light beams of a time-sharing optical tweezer. The colloidal particles used to make the measurements are microspheres made of hydrophobically covered silica to reduce the electrostatic interactions to a minimum. The measured radial force goes as a quadrupolar power law, r-n, with n = 5.

Early psychosis detection program in Chile: A first step for the South American challenge in psychosis research.

Aim: Early detection and intervention (EDI) is a main challenge in psychosis research. The Chilean schizophrenia (SZ) national program has universal support and treatment by law for all SZ patients, but this does not yet extend to earlier stages of illness. Therefore, we have piloted an ultra-high risk (UHR) program to demonstrate the utility and feasibility of this public health approach in Chile.

Structure, rheology, and microrheology of wormlike micelles made of PB-PEO diblock copolymers.

A diblock copolymer made of poly(1,4-butadiene)-block-polyethylene oxide, with a degree of polymerization of the polybutadiene and polyethylene oxide blocks of 37 and 57, respectively, self-assembles in water as worm-like micelles determined by small angle neutron scattering with an average diameter of ∼12.7 nm, a core radius of ∼2.7 nm, a shell radius of ∼3 nm, and an estimated persistence length of >225 nm.

Bilayers of Janus and homogeneous particle mixtures trapped at an air/water interface.

We study mixtures of amphiphilic Janus and homogeneous hydrophobic particles trapped at an air/water interface. In contrast to an expected monolayer formation, bilayers of colloidal particles are produced. Despite their strong interfacial adsorption, Janus particles form the upper layer.

Tuning the Viscoelastic-Gel Transition of Single-Wall Carbon Nanotubes Embedded in pH-Responsive Polyelectrolyte Solutions.

We present the detailed rheological changes that occur when small quantities of single-wall carbon nanotubes are dispersed in a poly(acrylic acid) water solution, around the overlap polymer concentration, up to the gel point. Here, pH is used to tune the gel formation. Suspensions of nanotubes at pH ≤ 5 are exfoliated and dispersed by the polymer.

Measuring adhesion on rough surfaces using atomic force microscopy with a liquid probe.

We present a procedure to perform and interpret pull-off force measurements during the jump-off-contact process between a liquid drop and rough surfaces using a conventional atomic force microscope. In this method, a micrometric liquid mercury drop is attached to an AFM tipless cantilever to measure the force required to pull this drop off a rough surface. We test the method with two surfaces: a square array of nanometer-sized peaks commonly used for the determination of AFM tip sharpness and a multi-scaled rough diamond surface containing sub-micrometer protrusions.

From Molecules to the Clinic: Linking Schizophrenia and Metabolic Syndrome through Sphingolipids Metabolism.

Metabolic syndrome (MS) is a prevalent and severe comorbidity observed in schizophrenia (SZ). The exact nature of this association is controversial and very often accredited to the effects of psychotropic medications and disease-induced life-style modifications, such as inactive lifestyle, poor dietary choices, and smoking. However, drug therapy and disease-induced lifestyle factors are likely not the only factors contributing to the observed converging nature of these conditions, since an increased prevalence of MS is also observed in first episode and drug-naïve psychosis populations.

Force of adhesion on supersolvophobic surfaces: The role of capillary necks.

We study theoretically the force of adhesion of pinned liquid drops in contact with supersolvophobic surfaces. We develop a method to calculate the contact and excess surface areas vs compression of the drops against surfaces characterized by an effective interfacial energy in the Cassie-Baxter wetting regime. We find that a 9° difference in contact angle can increase the force of adhesion by almost three orders of magnitude.

Absorption effects in diffusing wave spectroscopy.

The effect of absorption in diffusing wave spectroscopy (DWS) was studied using an absorption-dependent diffusive equation for describing the light propagation within a turbid liquid where dielectric microspheres have been embedded. Here, we propose an expression for the time-averaged light intensity autocorrelation function that correctly describes the time fluctuations for the scattered light, in the regime where the diffusion approximation accurately describes the light propagation. This correction was suspected previously, but it was not formally derived from a light diffusive equation.

Worm-like micelles in water solutions of 1, 4 poly (1, 3-butadiene)-polyethylene oxide diblock copolymer.

The main purpose of this study is to determine for the first time the structure of the self-assembled aggregates in the system made of 1,4 poly(1,3-butadiene)-polyethylene oxide diblock copolymer (IUPAC name: poly(but-2-ene-1,4-diyl)-block-polyoxyethylene) and water, and the rheological behavior of the solution. The degree of polymerization of the polybutadiene and polyethylene oxide blocks is 37 and 45, respectively. The diblock copolymer concentration was limited to be ≤2.

Microenvironmentally controlled secondary structure motifs of apolipoprotein A-I derived peptides.

The structure of apolipoprotein A-I (apoA-I), the major protein of HDL, has been extensively studied in past years. Nevertheless, its corresponding three-dimensional structure has been difficult to obtain due to the frequent conformational changes observed depending on the microenvironment. Although the function of each helical segment of this protein remains unclear, it has been observed that the apoA-I amino (N) and carboxy-end (C) domains are directly involved in receptor-recognition, processes that determine the diameter for HDL particles.

Mean-square displacement of particles in slightly interconnected polymer networks.

Structural and viscoelastic properties of slightly interconnected polymer networks immersed in a solvent have been studied in two cases: when the polymer network is building up and when the polymer network is shrinking stepwise in a controlled way. To accomplish this goal, the mean square displacement (MSD) of embedded microspheres in the polymer network was measured as a function of time, with diffusive wave spectroscopy. Particle motion was analyzed in terms of a model, based on a Fokker-Planck type equation, developed for describing particles in Brownian motion within a network that constrain their movement.

Force of adhesion upon loss of contact angle hysteresis: when a liquid behaves like a solid.

The theoretically predicted vanishment of the macroscopic contact angle hysteresis is found experimentally along with a small but finite force of adhesion (F(Ad)≈-0.5 μN) that, unexpectedly, is independent of the history of the preload. Our results agree with the prediction of a model in which the surface tension of the liquid provides the counterpart of the restoring force of an elastic solid, evidencing that the dewetting of a liquid in the absence of strong pinning points is equivalent to the detachment of an elastic solid.

The cis-bis(decanoate)tin phthalocyanine/DPPC film at the air/water interface.

Films made of cis-bis-decanoate-tin(IV) phthalocyanine (PcSn10) and racemic dipalmitoylphosphatidylcholine (DPPC) are studied with compression isotherms and Brewster angle microscopy (BAM) at the air/water interface. Films enriched in PcSn10 present phase separation elliptical-shaped domains. These domains present optical anisotropy and molecular order.

Microrheology and characteristic lengths in wormlike micelles made of a zwitterionic surfactant and SDS in brine.

We study the Brownian motion of probe particles embedded in a wormlike micellar fluid made of a zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), sodium dodecyl sulfate (SDS), and salty water to get structural and dynamical information of the micellar network. The motion of the probe particles was tracked with diffusing wave spectroscopy, and the mean square displacement as a function of time for the particles was obtained. This allowed us to obtain the long-time diffusion coefficient for microspheres moving in the micellar network and the cage size where each particle is harmonically bound at short times in that network.

The wormlike micellar solution made of a zwitterionic surfactant (TDPS), an anionic surfactant (SDS), and brine in the semidilute regime.

Structural and dynamical properties of a micellar solution are studied mainly through examining its rheological behavior in the semidilute regime. The micellar solution is made of a zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, sodium dodecyl sulfate, and salty water. In particular, we are interested in how the system is affected when the ionic strength of the media is modified by adding salt.