Brandy Pilapil - Academia.edu (original) (raw)

Papers by Brandy Pilapil

Liquid Crystals, 2010

The thermal stability, alignment and electro-optic properties of liquid crystals can be fundament... more The thermal stability, alignment and electro-optic properties of liquid crystals can be fundamentally altered by dispersing small amounts of solid nanoparticles in a liquid crystal host. In the present study, the local alignment of the liquid crystal in such dispersions is studied by means of ...

Nematic liquid crystal cells with positive dielectric anisotropy that include colloidal suspensio... more Nematic liquid crystal cells with positive dielectric anisotropy that include colloidal suspensions having nanoclusters are provided as well as methods of inducing Freedericksz transitions therein and methods of controlling the alignment of a liquid crystal.

Electrocatalytic materials have become increasingly important over the past decade owing to their... more Electrocatalytic materials have become increasingly important over the past decade owing to their broad applicability to low emission and emission-free energy technologies, including fuel cell technology. Platinum is a great electrocatalyst due its generally good stability, high surface energy, electronic structure and interfacial properties.1-5 The morphology and chemical environment of Pt can have a substantial effect on its catalytic performance.2-7 Presently, carbon (C) black (high surface area C particles) is the most commonly used support for Pt nanoparticle (NP) electrocatalysts in low temperature polymer electrolyte membrane fuel cells (PEMFCs).4 This support provides a high surface area for dispersion of the Pt NPs and good electrical conductivity. Weak interaction between Pt NPs and the C support and oxidation of the C support under harsh fuel cell operating conditions leads to a loss of Pt catalysts and subsequent decrease in fuel cell performance. Alternative supports, s...

Pickering stabilization by colloidal particles is a common strategy to disperse droplets of one f... more Pickering stabilization by colloidal particles is a common strategy to disperse droplets of one fluid into another fluid in food, cosmetics and chemical industries1-3. For over a century, this kind of stabilization has been governed by constant surface coverage concepts in which particles irreversibly attach to the fluid–fluid interface. The need to cover sufficient interfacial area to prevent coalescence typically results in large loadings of particles, uniform droplet size, creation of rigid interface and closed-cell structure with small total area4-7. Here we report a stabilization mechanism that yields hierarchically structured oil-in-brine emulsions with high interfacial area, deformability, connectivity and long-term stability at unprecedentedly low nanoparticle loadings. The hierarchy in structure is achieved via dynamic cation-particle-droplet interactions in cascaded emulsification, which consists of i) formation of submicron oil droplets (~250 nm) lightly covered by hydrop...

MRS Proceedings

ABSTRACTNanoparticles (NPs) with either plasmonic or upconverting properties have been selectivel... more ABSTRACTNanoparticles (NPs) with either plasmonic or upconverting properties have been selectively coated onto the surfaces of polystyrene (PS) spheres, imparting their optical properties to the PS colloids. These NP coated PS spheres have many potential applications, such as in medicine as drug-delivery systems or diagnostic tools. To prepare the NP coated PS spheres, gold or core-shell NaYF4Tm0.5Yb30/NaYF4 NPs were synthesized and separately combined with amino-functionalized PS spheres. The mechanism by which the NPs adhered to the PS spheres is attributed to interactions of the NP and a polyvinylpyrrolidone additive with the surfaces of the PS spheres. Two-photon fluorescence microscopy and SERS analysis demonstrate the potential applications of these NP coated PS spheres.

J. Mater. Chem. A

Arrays of PtIr alloy nanoparticle (NP) clusters are synthesized from a method using block copolym... more Arrays of PtIr alloy nanoparticle (NP) clusters are synthesized from a method using block copolymer templates, which allows for relatively narrow NP diameter distributions (∼4–13 nm) and uniform intercluster spacing (∼60 or ∼100 nm).

Soft matter, Jan 30, 2018

Emulsions are widely used in industrial applications, including in food sciences, cosmetics, and ... more Emulsions are widely used in industrial applications, including in food sciences, cosmetics, and enhanced oil recovery. For these industries, an in depth understanding of the stability and rheological properties of emulsions under both static and dynamic conditions is vital to their successful application. Presented here is a thorough assessment of a model nanoparticle (NP) stabilized dodecane-in-water emulsion as a route to improved understanding of the relationship between NP properties, microstructure and droplet-droplet interactions on the stability and rheological properties of emulsions. Emulsions are obtained here with low NP loadings without the need for added electrolyte through the use of an optimized silica NP (SNP) surface modification procedure. The prepared emulsions were characterized via optical microscopy, cryo-scanning electron microscopy (cryo-SEM), zeta potential analysis and laser scanning confocal microscopy (LSCM), enabling quantification of the emulsion dropl...

Journal of colloid and interface science, Jan 17, 2018

Microstructural and rheological properties of particle-stabilized emulsions are highly influenced... more Microstructural and rheological properties of particle-stabilized emulsions are highly influenced by the nanoparticle properties such as size and surface charge. Surface charge of colloidal particles not only influences the interfacial adsorption but also the interparticle network formed by the non-adsorbed particles in the continuous phase. We have studied oil-in-water emulsions stabilized by cellulose nanocrystals (CNCs) with two different degrees of surface charge. Surface charge was varied by means of acidic or basic desulfation. Confocal microscopy coupled with rheology as well as cryogenic scanning electron microscopy were employed to establish a precise link between the microstructure and rheological behavior of the emulsions. CNCs desulfated with hydrochloric acid (a-CNCs) were highly aggregated in water and shown to adsorb faster to the oil-water interface, yielding emulsions with smaller droplet sizes and a thicker CNC interfacial layer. CNCs desulfated using sodium hydrox...

Advanced Functional Materials

Microscopy and Microanalysis, 2016

Nanostructures of diverse materials prepared by using monodispersed colloidal spheres as template... more Nanostructures of diverse materials prepared by using monodispersed colloidal spheres as templates have found potential applications in many fields such as photonic crystals, sensors, and catalysts. Such nanostructured materials include polymers, oxides, metals, semiconductor compounds, as well as composites. Polystyrene (PS) beads are commonly used as the templates since the removal of the templates can be achieved by both calcination and dissolution [1,2]. Templates fabricated from a colloidal PS solution consist of many close-packed regions, where 26% void space can be used for filling up with functional materials [2]. After the removal of the PS spheres, the remaining nanostructures have high surface area and 74% spherical void volume, which allow efficient mass transport and further materials modification. These templated nanostructures incorporated with catalytic nanoparticles (NPs) attract a wide range of research interests, due to their potential in reducing and tuning the loading of precious catalytic metals, improving catalytic performance, as well as the scalability for mass production.

Liquid Crystals XIV, 2010

ABSTRACT It is well known that doping nematic liquid crystals with nanoparticles can alter the el... more ABSTRACT It is well known that doping nematic liquid crystals with nanoparticles can alter the electrooptic response of the nematic host as well as the alignment of the liquid crystal molecules on various substrates. In addition, nanoparticles dispersed in a nematic matrix often induce defects and defect patterns justifying the necessity for more detailed optical and electrooptic investigations including effects of nanoparticle size, coating, concentration and core material. We studied the local alignment of nematic LC molecules in such dispersions by means of fluorescence confocal polarizing microscopy. The results of two- and three-dimensional imaging indicate that frequently observed birefringent stripes, which are induced by the presence of metal nanoparticles and semiconductor quantum dots, correspond to twist disclinations located at the LC/substrate interface. The luminescence of dispersed quantum dots shows that the ends of these disclination threads are pinned to conglomerates of nanoparticles that stabilize these line defects. By performing (x,z)-scans, it can be shown that the defects are not walls extending through the entire cell gap, but lines that are located at the substrate surface. Our experiments also confirm, as hypothesized before, that the nanoparticles preferably reside at the liquid crystal/substrate interfaces. Finally, detailed electrooptic investigations also revealed that a contrast inversion observed earlier is initiated by a change from parallel to homeotropic anchoring, thereby causing an instability, which in turn leads to the appearance of convection rolls (Kapustin-Williams domains). This electrohydrodynamic instability is likely an example for the behavior of (+, -) systems predicted by de Gennes, which was only recently experimentally observed for the first time.

Emerging Liquid Crystal Technologies III, 2008

To capitalize on the unique size and shape-dependent optical and electronic properties of nanosca... more To capitalize on the unique size and shape-dependent optical and electronic properties of nanoscale particles for liquid crystal (LC) applications, detailed structure and size-property relationship studies are critical. To enhance our understanding of the thermal, optical and electro-optic effects of nanoparticles in nematic LCs we produced numerous different nematic LC mixtures containing small quantities of dispersed metal nanoparticles (i.e. gold and silver nanoclusters) or semiconductor quantum dots (i.e. CdTe nanocrystals) and studied their optical (texture, alignment, defect formation, luminescence) and electro-optic properties. Depending on several experimental parameters such as nanoparticle functionalization and concentration, as well as thermal history in combination with an applied electric field, these nanoparticle/LC mixtures with the nanoparticles differing in surface functionality, size, and core material gave rise to unique alignment effects and electro-optic responses in the two investigated nematic LC (N-LC) hosts.