Larisa Tsarkova

Electric Field Alignment of a Block Copolymer Nanopattern: Direct Observation of the Microscopic Mechanism

Using quasi-in-situ scanning force microscopy we study the details of nanopattern alignment in ABC terblock copolymer thin films in the presence of an in-plane electric field. Because of the surface interactions and electric field the lamellae are oriented both perpendicular to the plane of the film and parallel to the electric field. We identified two distinct defect types which govern the orientation mechanism. Ring-like (tori) and open-end defects dominate at the early stage of the orientation process, while mainly classic topological defects (disclinations and dislocations) are involved in long-range ordering at the late stages. Comparison of the time evolution of the defect density with the evolution of the orientational order parameter suggests that tori-defects are essential for the effective reorientation. Further, the quasi-in-situ SFM imaging allowed us to elucidate the influence of the electric field strength on the propagation velocity of the topological defects.

All-Silica Colloidosomes with a Particle-Bilayer Shell

We report on the preparation of all-silica colloidosomes with adjustable size, shell structure, mechanical strength, and permeability. Our approach is based on the coassembly at the water/oil interface of silica nanoparticles and a silica precursor polymer-hyperbranched polyethoxysiloxane-which acts as a binder for particles as well as an additional interfacial component. Remarkably, the shell of colloidosomes can be fine-tuned from a particle monolayer up to a bilayer bound with a sandwiched thin silica film. This method presents a facile approach toward multiscale production of microcapsules which have a high potential in encapsulation technology and in smart coating formulations.

Effect of confinement on the mesoscale and macroscopic swelling of thin block copolymer films.

We report on the swelling behavior and the corresponding morphological behavior of cylinder-forming polystyrene-b-polybutadiene diblock copolymers, which are confined to several layers of structures. The equilibration of thin films has been done under controlled atmosphere of a nonselective solvent. In situ spectroscopic ellipsometry measurements revealed more than 10% increase of the solvent uptake with decreasing film thickness. With scanning force microscopy of the microphase separated patterns in quenched films, the correlation between the degree of the long-range order of cylinder domains and the degree of the macroscopic swelling has been established. In the case of spontaneously formed micrometer-sized topographic features with discreet film thickness (terraces), the increased solvent uptake by thinner films holds true even for isolated terraces on the mesoscale. The observation of nonhomogeneous swelling of the films on the micrometer scale brings novel insights into the properties of confined soft matter, and suggests new approaches toward the fabrication of polymer-based nanostructured responsive materials.

Large scale alignment of a lamellar block copolymer thin film via electric fields: a time-resolved SFM study

We have devised a novel route towards a nanoscopically striped surface pattern with long range order the self-assembly of an ABC triblock terpolymer thin film exposed to an in-plane electric field. the interplay between surface interactions and the effect of the electric field the lamellae were oriented both perpendicular to the plane of the film and parallel to the electric field. Moreover, quasi scanning force microscopy measurements were used to follow the reorientation process as a function of time and to yield insight into the microscopic steps eventually leading to the ordered microdomain structure.

Nanopattern Evolution in Block Copolymer Films: Experiment, Simulations and Challenges

The present contribution reviews novel insights into block copolymer phase behavior and nanostructure formation in confined geometries. We focus on state-of-the-art experimental and theoretical progress in this area, with an emphasis on characterization methods and techniques that provide a quantitative framework for fundamental analysis. We discuss and compare basic system parameters that are readily controlled in simulations and in experiments, and present comparative stud- ies of increasing degree of complexity concerning the phase behavior and ordering dynamics of cylinder- and lamella-forming block copolymers in thin films.

3-dimensional control over lamella orientation and order in thick block copolymer films

The general strategies for achieving macroscopic order in thin block copolymer films typically utilize external stimuli and activation energies, which become less effective with increasing the film thickness to ∼0.5–1 µm. Here we show a facile and effective approach towards multi-level control over lamella orientation and order in thick diblock copolymer films. The novel finding concerns the reorientation of lamella domains relative to the substrate upon annealing under a selective solvent, and is combined with alignment of the lamellar director along a preferred direction by simultaneous application of an electric field. The multiple approach yields a method for the single step fabrication of a striped nanostructure with a controlled orientation and long-range order of the microdomains.

Liposomes remain intact when complexed with polycationic brushes

Anionic liposomes adsorb onto the surface of spherical polymer particles bearing grafted linear cationic macromolecules. The size, shape, and encapsulation ability of the liposomes remain unchanged upon adsorption, thus providing immobilized self-organizing containers that have potential applications in the biomedical field.

Self-templating amphiphilic polymer precursors for fabricating mesostructured silica particles: a water-based facile and universal method.

A facile and universal approach is reported for the preparation of silica particles of various mesostructures based on the self-assembly of amphiphilic precursor polymers in water and subsequent condensation. Depending on the hydrophilization degree of hyperbranched polyethoxysiloxane, various silica morphologies including mesoporous particles, hollow nanospheres and ultrasmall particles with high application potential are fabricated.

Nanoreactor-Assisted Polymerization Toward Stable Dispersions of Conductive Composite Particles

We demonstrate the functioning of a macromolecular nanoreactor which guides a reaction in a confined volume and leads toward improved functional properties of a product material. In our approach, the polymerization of aniline (ANi) is conducted within the interfacial volume of spherical polyelectrolyte brushes (SPB) which are densely affixed to colloidal particles. The SPB provide optimal conditions for matrix polymerization by the efficient confinement of ANi monomers within the finite volume of polyelectrolyte brushes and controlled delivery of the oxidizing reagent to the reaction volume. The excellent kinetic stability of the resulting core-shell particles together with the high macroscopic conductivity of the respective composite open up perspectives for novel materials (a conductive ink).

“Micro-structure–macro-response” relationship in swollen block copolymer films

We demonstrate the effect of confinement on the thickness-dependent swelling behavior of poly(styrene)-b-poly(2-vinylpyridine) diblock copolymer films as revealed by in situspectroscopic ellipsometry. “Microscopic” molecular confinement to the dimension smaller than the characteristic lamella spacing, as well as to the non-equilibrium microstructures limits the solvent up-take by the polymer film. The maximum degree of swelling (“macroscopic response”) is achieved for films with a starting thickness in a dry state hdr in the range of ∼one–two characteristic lamella dimension in bulk L0 and drops down according to ∼hdr−0.1 as the film thickness increases up to ∼μm scale (∼tens of L0). These findings bring novel fundamental insights into the stimuli-responsive behavior of confined soft matter.