RESUMEN
Many types of colloids, including nanoemulsions, which contain sub-100 nm droplets, are dispersed in molecular and micellar solutions, especially surfactant solutions that confer stability. Since it would be desirable to measure the droplet volume fraction Ï and surfactant concentration C of a nanoemulsion non-destructively, and since the droplet and surfactant structures are significantly smaller than the shortest wavelengths of visible light, optical refractometry could provide a simple and potentially useful approach. By diluting a silicone oil-in-water nanoemulsion having an unknown Ï and C with pure water, measuring its refractive index n(Ï,C) using an Abbé refractometer, and fitting the result using a prediction for n that treats the nanoemulsion as an effective medium, we show that Ï and C can be deduced accurately over a relatively wide range of compositions. Moreover, we generalize this approach to other types of nanoemulsions in which a molecular constituent partitions in varying degrees between the dispersed and the continuous phases.
Asunto(s)
Emulsiones/química , Nanotecnología , Refractometría , Aceites de Silicona/química , Tensoactivos/química , Agua/químicaRESUMEN
Nanoparticles can form unique cavity-like structures in core-shell type assemblies of block copolymers through the cooperative self-assembly of nanoparticles and block copolymers. We show that the self-assembly behavior is general for common as-synthesized alkyl-terminated nanoparticles for a range of nanoparticle sizes. We examined various self-assembly conditions such as solvent compositions, nanoparticle coordinating ligands, volume fraction of nanoparticles, and nanoparticle sizes in order to elucidate the mechanism of the radial assembly formation. These experiments along with strong segregation theory calculations indicated that both the enthalpic interaction and the polymer stretching energy are important factors in the coassembly formation. The slightly unfavorable interaction between the hydrophobic segment of polymers and alkyl-terminated nanoparticles causes the accumulation of nanoparticles at the interface between the polymer core and the shell, forming the unique cavity-like structure. The coassemblies were stabilized for a limited range of nanoparticle volume fractions within which the inclusion of nanoparticle layers reduces the polymer stretching. The volume fraction range yielding the well-defined radial coassembly structure was mapped out with varying nanoparticle sizes. The experimental and theoretical phase map provides the guideline for the coassembly formation of as-synthesized alkyl-terminated nanoparticles and amphiphilic block copolymers.
Asunto(s)
Acrilatos/química , Compuestos de Cadmio/química , Nanopartículas/química , Compuestos Organometálicos/síntesis química , Poliestirenos/química , Compuestos de Selenio/química , Sulfuros/química , Compuestos de Zinc/química , Compuestos Organometálicos/química , Tamaño de la Partícula , Propiedades de SuperficieRESUMEN
Micelles derived from poly(ε-caprolactone) (PCL) poly(ethylene glycol)(PEG) diblock copolymers (HO-PCLn-b-PEG32-RX, R = -O(CH2)3S(CH2)2-; X = -CO2(-), -SO3(-), -NH3(+)) show corona charge selective degradation catalyzed by P. cepacia lipase isoforms.
Asunto(s)
Proteínas Bacterianas/metabolismo , Lipasa/metabolismo , Micelas , Proteínas Bacterianas/química , Burkholderia cepacia/enzimología , Cinética , Lipasa/química , Poliésteres/química , Polietilenglicoles/química , Isoformas de Proteínas/química , Isoformas de Proteínas/metabolismoRESUMEN
The mean diameter of palladium metal particles produced by citrate reduction of the (H(+))(n) PDMAEMA/[PdCl(4)](2-) aqueous system increases from 1.4 nm to 5.0 nm as the pH decreases from 6.3 to 3.3 and the (H(+))(n) PDMAEMA/[PdCl(4)](2-) species undergo conversion from a cross linked polymer network to a single chain structure.
Asunto(s)
Cloruros/química , Iones/química , Plomo/química , Nanopartículas del Metal/química , Metacrilatos/química , Nylons/química , Paladio/química , Ácido Cítrico/química , Concentración de Iones de Hidrógeno , Tamaño de la Partícula , ProtonesRESUMEN
Diprotonic sulfuric and succinic acids react efficiently with the tertiary amine sites in polydimethylaminoethylmethacrylate (PDMAEMA) to produce polymer colloid nano-particles held together by dinegatively charged anions that cross link the partially protonated PDMAEMA homopolymer. This procedure is used to encorporate [PtCl(6)](2-) as a cross linker into the framework of well defined polymer network colloid particles that have dual roles as nanoreactors and a source of protective polymer coating. Reduction of the cross linking [PtCl(6)](2-) groups produces platinum metal nano-particles (1.12(.25)nm) that are relatively small and narrowly dispersed. Formation of colloid particles by reaction of diprotic acids with homopolymers that have proton accepting centers provides a convenient intentional route to incorporate a variety of homopolymers into self assembled polymer network materials for applications as nanoreactors and transport systems.
Asunto(s)
Coloides/química , Reactivos de Enlaces Cruzados/química , Nanopartículas/química , Platino (Metal)/química , Ácidos Polimetacrílicos/química , Aniones/químicaRESUMEN
We present a novel route to assemble perpendicular cylinders by converting an asymmetric diblock copolymer from poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA) to poly(styrene-b-acrylic acid) (PS-b-PAA) using an autocatalytic reaction. Upon exposure of the films of PS-b-PAA to water, PAA cylinders constrained by the continuous, glassy PS phase protrude 10 nm above the surface and swell laterally to form mushroom caps, rendering the entire surface hydrophilic. Upon annealing, the original nanostructures re-form demonstrating reversibility of swelling. Because of their stimuli-responsive behavior, these nanoscale materials are excellent candidates for sensors and microfluidic applications.