ABSTRACT
Time- and temperature-resolved in situ birefringence measurements were applied to analyze the effect of nanoparticles on the electric field-induced alignment of a microphase separated solution of poly(styrene)-block-poly(isoprene) in toluene. Through the incorporation of isoprene-confined CdSe quantum dots the reorientation behavior is altered. Particle loading lowers the order-disorder transition temperature, and increases the defect density, favoring nucleation and growth as an alignment mechanism over rotation of grains. The temperature dependent alteration in the reorientation mechanism is analyzed via a combination of birefringence and synchrotron SAXS. The detailed understanding of the effect of nanoparticles on the reorientation mechanism is an important prerequisite for optimization of electric-field-induced alignment of block copolymer/nanoparticle composites where the block copolymer guides the nanoparticle self-assembly into anisotropic structures.
ABSTRACT
External electric fields align nanostructured block copolymers by either rotation of grains or nucleation and growth depending on how strongly the chemically distinct block copolymer components are segregated. In close vicinity to the order-disorder transition, theory and simulations suggest a third mechanism: selective disordering. We present a time-resolved small-angle X-ray scattering study that demonstrates how an electric field can indeed selectively disintegrate ill-aligned lamellae in a lyotropic block copolymer solution, while lamellae with interfaces oriented parallel to the applied field prevail. The present study adds an additional mechanism to the experimentally corroborated suite of mechanistic pathways, by which nanostructured block copolymers can align with an electric field. Our results further unveil the benefit of electric field assisted annealing for mitigating orientational disorder and topological defects in block copolymer mesophases, both in close vicinity to the order-disorder transition and well below it.
Subject(s)
Electricity , Polymers/chemistry , Quantum Theory , Rotation , TemperatureABSTRACT
External electric fields readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-field-induced alignment of a lamellae-forming polystyrene-block-poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-field-assisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such films under benign experimental conditions.
ABSTRACT
Electric fields have been shown to stabilize the disordered phase of near-critical block copolymer solutions. Here, we use in situ synchrotron small-angle X-ray scattering to examine how the initial orientation of lamellar domains with respect to the external field (φ) affects the shift in the order-disorder transition temperature (TODT) of lyotropic solutions of poly(styrene-b-isoprene) in toluene. We find a downward shift of the transition temperature, which scales with lamellar orientation as ΔTODT â¼ cos2 φ, in accordance with theory.
ABSTRACT
We investigate the kinetics of block copolymer/nanoparticle composite alignment in an electric field using in situ transmission small-angle X-ray scattering. As a model system, we employ a lamellae forming polystyrene-block-poly(2-vinyl pyridine) block copolymer with different contents of gold nanoparticles in thick films under solvent vapor annealing. While the alignment improves with increasing nanoparticle fraction, the kinetics slows down. This is explained by changes in the degree of phase separation and viscosity. Our findings provide extended insights into the basics of nanocomposite alignment.
Subject(s)
Polymers/chemistry , Butadienes/chemistry , Electricity , Pentanes/chemistry , Polystyrenes/chemistry , Temperature , ThermodynamicsABSTRACT
Smart organic-inorganic nanohybrids are formed in aqueous solution by the interaction of amphiphilic block copolymer micelles of poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA(x)-b-PAA(y) with x = 90, 100 and y = 100, 150, 300) and diglycidylaminopropyl-functional silsesquioxane nanoparticles. We investigate the structure of the complex nanohybrids in dependence on pH and salinity. The complexation preserves the original size of the micelles according to dynamic light scattering (DLS) measurements. Cryogenic transmission electron microscopy (cryo-TEM) and Fourier-transform infrared spectroscopy (FT-IR) measurements unveil the formation of organic-inorganic nanohybrids. Furthermore, cryo-TEM micrographs provide evidence for the formation of a core-shell-corona structure of the nanohybrid system. Dialysis experiments with fluorescently labeled silsesquioxane nanoparticles clearly demonstrate the interaction between the micellar system and the silsesquioxane nanoparticles.
Subject(s)
Micelles , Nanoparticles/chemistry , Nanotechnology/methods , Organic Chemicals/chemistry , Organosilicon Compounds/chemistry , Polymers/chemistry , Quaternary Ammonium Compounds/chemistry , Cryoelectron Microscopy/methods , Hydrogen-Ion Concentration , Light , Microscopy, Electron, Transmission/methods , Potentiometry/methods , Salts/chemistry , Scattering, Radiation , Solutions , Spectroscopy, Fourier Transform InfraredABSTRACT
We report on interpolyelectrolyte complexes (IPECs) formed by micelles of ionic amphiphilic diblock copolymers with polyisobutylene (PIB) and poly(sodium methacrylate) (PMANa) blocks interacting with quaternized poly(4-vinylpyridine) (P4VPQ). The interpolyelectrolyte complexation was followed by turbidimetry and small angle neutron scattering (SANS). The data obtained by means of a combination of SANS, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) provide evidence on the core-shell-corona structure of the complex species with the shell assembled from fragments of electrostatically bound PMANa and quaternized P4VPQ fragments, original PIBx-b-PMAAy micelles apparently playing a lyophilizing part. The complex formation is followed by potentiometric titration as well. This process is initially kinetically controlled. In the second step larger aggregates rearrange in favor of smaller complexes with core-shell-corona structure, which are thermodynamically more stable. An increase in ionic strength of the solution results in dissociation of the complex species as proven by SANS and analytical ultracentrifugation (AUC). This process begins at the certain threshold ionic strength and proceeds via a salt-induced gradual release of chains of the cationic polyectrolyte from the complex species.
Subject(s)
Alkenes/chemistry , Electrolytes/chemistry , Methacrylates/chemistry , Micelles , Polymers/chemistry , Water/chemistry , Macromolecular Substances/chemistry , SolubilityABSTRACT
Block copolymers consisting of incompatible components self-assemble into microphase-separated domains yielding highly regular structures with characteristic length scales of the order of several tens of nanometres. Therefore, in the past decades, block copolymers have gained considerable potential for nanotechnological applications, such as in nanostructured networks and membranes, nanoparticle templates and high-density data storage media. However, the characteristic size of the resulting structures is usually determined by molecular parameters of the constituent polymer molecules and cannot easily be adjusted on demand. Here, we show that electric d.c. fields can be used to tune the characteristic spacing of a block-copolymer nanostructure with high accuracy by as much as 6% in a fully reversible way on a timescale in the range of several milliseconds. We discuss the influence of various physical parameters on the tuning process and study the time response of the nanostructure to the applied field. A tentative explanation of the observed effect is given on the basis of anisotropic polarizabilities and permanent dipole moments of the monomeric constituents. This electric-field-induced effect further enhances the high technological potential of block-copolymer-based soft-lithography applications.
