Cyro Ketzer Saul

Electrospinning of commercial guar-gum: Effects of purification and filtration

Guar gums of two different commercial sources were successfully electrospun on both mica and copper tape at several concentrations starting from 1% (w/w). The electrospun fibers formed with the raw materials were not uniform and presented aggregates and beads within the fibers. Two different purification procedures and a filtration sequence with different pore size membranes were applied to enhance galactomannan solution homogeneity and solubility. The consequence was improved fiber morphology. We observed that the precipitation step, within the purification procedure, produced changes in the molar mass distribution and yielded different fiber diameter. Furthermore, spherical aggregates between fibers and within them disappeared after the sequential filtration. The resulting electrospun fiber diameter decreased with membrane pore diameter reduction. We conclude that the filtration process is responsible for molecular disentanglement, as well as disaggregation, which leads to improved electrospun galactomannan fiber morphology.

Electrosprayed superhydrophobic PTFE: a non-contaminating surface

This paper reports on the exposure of superhydrophobic polytetrafluoroethylene (PTFE) coatings to common aqueous solutions which are used in biology, biotechnology and chemical sensor applications. Advancing contact angles as high as 173° for aqueous solutions were measured on the PTFE surface. Water drop sliding angles at 2° show a very low contact angle hysteresis. X-ray photoelectron spectroscopy measurements confirm that aqueous solutions can move or stay on the superhydrophobic surface without contamination. Owing to the chemical inertness of the polymer, these results indicate that superhydrophobic PTFE can be used in lab-on-a-chip and multi-sensor devices as well as in biological cultures, where aqueous solutions meet solid surfaces, without contaminating the interface.

Tuning Fe3O4 nanoparticle dispersion through pH in PVA/guar gum/electrospun membranes.

Polyvinyl Alcohol (PVA)/guar gum (GG) membranes with different loads of paramagnetic iron oxide Fe3O4 nanoparticles were successfully electrospun using both non-alkaline and alkaline stock solutions. The nanoparticle homogeneity distribution was clearly enhanced in fibers obtained from alkaline stock solutions. This is mainly due to the interaction between GG and the metallic ion, which also leads to further dispersion of remained uncoated nanoparticles in the mixture. It was also noticed that GG favors nanoparticle stability in the mixture and contributes to nanoparticle encapsulation. X-ray results showed that all membranes were semi-crystalline. FTIR-ATR spectra showed that Fe-O absorption band intensity improved with increasing nanoparticle load, reaching saturation at 3.5mg/ml Fe3O4 concentration under alkaline conditions. VSM analyses showed that the nanoparticles are paramagnetic and were successfully incorporated by the fibers. In vitro biocompatibility tests using L929 cells indicates adequate levels of cytotoxicity and cell adhesion/proliferation assays for both membranes obtained from non-alkaline and alkaline stock solutions. Therefore, they have potential for biomedical applications as biodegradable wound dressing.

Thick-mode resonance of a PZT/Si wafer stack investigated by X-ray diffraction in Bragg geometry

X-ray diffraction in Bragg geometry was used to investigate the effects of standing longitudinal acoustic waves on an Si(111) wafer. A PZT/Si(111) stack with a resonant frequency of 2.34 MHz was constructed. In addition to the ultrasonic vibration, a thermal effect is evident. The thermal contribution causes an angular displacement of the Bragg profile and was mapped without time resolution. The actual ultrasonic oscillation of the surface was measured using a stroboscopic system. Bulging of the Si(111) surface was mapped out and the maximum deformation near the centre of the Si wafer was determined for a given ultrasonic power. Simple modelling using finite differences was helpful in determining the acoustic and thermal contributions.

Electrospinning induced surface activation (EISA) of highly porous PMMA microfiber mats for HIV diagnosis

This work presents an Electrospray Induced Surface Activation (EISA) method generalization for electrospinning. It allows an easy way to produce surface functionalized microfiber mats for infectious disease diagnostic purposes. We present the details of both the production and characterization of surface functionalized highly porous poly methyl methacrylate (PMMA) microfiber mats produced using dry (DS) and wet substrate (WS) configurations. The characterization was performed using high-resolution scanning electron microscopy (HRSEM), Size Exclusion Chromatography (SEC), X-ray photoelectron spectroscopy (XPS) and biological essays attaching both the recombinant auto-fluorescent green fluorescent protein (GFP) and the anti-human Ig protein containing a fluorescent reporter R-phycoerythrin (AbPE). The final biological application assay was performed by positively detecting HIV contaminated human samples.

AFM characterization of spin coated carboxylated polystyrene nanospheres/xyloglucan layers on mica and silicon

Self-assembled nano-arrays have a potential application as solid-phase diagnostics in many biomedical devices. The easiness of its production is directly connected to manufacture cost reduction. In this work, we present self-assembled structures starting from spin coated thin films of carboxylated polystyrene (PSC) and xyloglucan (XG) mixtures on both mica and silicon substrates. AFM images showed PSC nanospheres on top of a homogeneous layer of XG, for both substrates. The average nanosphere diameter fluctuated for a constant speed and it was likely to be independent of the component proportions on the mixture within a range of 30-50% (v/v) PSC. It was also observed that the largest diameters were found at the center of the sample and the smallest at the border. The detected nanospheres were also more numerous at the border. This behavior presents a similarity to spin coated colloidal dispersions. We observed that the average nanosphere diameter on mica substrates was bigger than the nanosphere diameters obtained on top of silicon substrates, under the same conditions. This result seems to be possibly connected to different mixture-surface interactions.

Improved data analysis model for a diode-based microfabricated hot plate sensor

Abstract An improved model for data analysis of a hot plate gas sensor is presented. The equations derived from the model were used to fit experimental data obtained under different conditions. They allow the quantification of the different contributions to the heat dissipation process. It becomes clear that for thermal conductivity variation measurements, the small physical dimensions of the sensor play a major role, reducing the convective heat loss effects. The improved model proposed here also accounts for the N 2 /He switching results, which were not supported by the previous work model.

Spinning droplets on superhydrophobic surfaces

The study of liquid droplets on solid surfaces is a well established research area. Static measurements include contact angle determinations which allow surface energy measurement. Dynamic measurements generally are reported on vibrating drops on mechanically or sonic driven surfaces. The general analysis of the physics of vibrating drops is complicated due to the internal degrees of freedom of the liquid and the stick or slip conditions at the liquid-solid contact line. Here we propose a simple and straightforward experimental method to measure the physical properties of droplets on highly hydrophobic surfaces. The first dynamic experiments of droplets on superhydrophobic surfaces are also reported.