Ekaterina B. Zhulina

Precise hierarchical self-assembly of multicompartment micelles

Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects.

Theory of steric stabilization of colloid dispersions by grafted polymers

Abstract The structure and stabilizing properties of layers of long polymer chains, grafted at one end onto the surface of colloid particles, are considered. A mean-field analytical theory describing the interaction between two colloid particles covered with densely grafted polymer chains is developed. An analytical expression for the interaction potential of colloid particles, depending on the degree of polymerization, the thermodynamic stiffness of stabilizing chains, the solvent quality and the density of grafting of the chains onto the surface, is obtained. The shape and the parameters of this potential are determined by the value of the universal parameter γ introduced, which depends on the magnitude of interparticle attraction, the total amount of grafted polymer per unit area, and relative deviation from the θ-temperature. In the case of relatively weak interparticle attraction, γ 1, with good solvents, the potential curves display primary and secondary minima separated by a maximum and the stability of dispersion is kinetic in character.

Structure and interaction of weakly charged polyelectrolyte brushes: Self-consistent field theory

A self-consistent field analytical theory is developed to analyze the equilibrium structure of weakly charged polyelectrolyte brushes in salt-free solutions. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted (“osmotic”) brushes, we consider a general case comprising both limits of weakly and strongly charged systems without any a priori assumptions about the distribution of counterions. The analytical expressions for various structural properties of free and confined polyelectrolyte brushes are obtained and compared to existing scaling predictions. The elastic response and structural rearrangement in the polyelectrolyte brush under compression are analyzed.

Sensitivity, Specificity, and the Hybridization Isotherms of DNA Chips

Competitive hybridization, at the surface and in the bulk, lowers the sensitivity of DNA chips. Competitive surface hybridization occurs when different targets can hybridize with the same probe. Competitive bulk hybridization takes place when the targets can hybridize with free complementary chains in the solution. The effects of competitive hybridization on the thermodynamically attainable performance of DNA chips are quantified in terms of the hybridization isotherms of the spots. These relate the equilibrium degree of the hybridization to the bulk composition. The hybridization isotherm emerges as a Langmuir isotherm modified for electrostatic interactions within the probe layer. The sensitivity of the assay in equilibrium is directly related to the slope of the isotherm. A simpler description is possible, in terms of c(50) values specifying the bulk composition corresponding to 50% hybridization at the surface. The effects of competitive hybridization are important for the quantitative analysis of DNA chip results, especially when used to study point mutations.

On the hybridization isotherms of DNA microarrays: the Langmuir model and its extensions

The design of DNA chip experiments utilizes hybridization isotherms relating the equilibrium hybridization at the surface to the composition of the solution. Within this family, the Langmuir isotherm is the simplest and the most frequently used. This tutorial review summarizes the domain of validity of the Langmuir isotherm and discusses the modifications necessary to allow for competitive hybridization in the bulk and at the surface, probe polydispersity and interactions between the probe sites. The equilibrium constant of hybridization at an impenetrable surface is described, as well as the relative merits of the melting temperature and c50 as design parameters. The relevance to various experimental situations, including two-colour experiments, study of point mutations for cancer diagnostics, genotyping of pooled samples and aspects of Latin square experiments, is discussed.

Self-consistent field theory of brushes of neutral water-soluble polymers

The self-consistent field theory of brushes of neutral water-soluble polymers described by two-state models is formulated in terms of the effective Flory interaction parameter χeff(T,φ) that depends on both temperature, T, and the monomer volume fraction, φ. The concentration profiles, distribution of free ends and compression force profiles are obtained in the presence and in the absence of a vertical phase separation. A vertical phase separation within the layer leads to a distinctive compression force profile and a minimum in the plot of the moments of the concentration profile versus the grafting density. The analysis is applied explicitly to the Karalstrom model. The relevance to brushes of Poly(N-isopropylacrylamide)(PNIPAM) is discussed.

Temperature-concentration diagram for a solution of star-branched macromolecules

Abstract The temperature-concentration diagram of a star-branched macromolecule solution was constructed using scaling concepts. The quality of the solvent, solution concentration, the rigidity of star branches, their number and degree of polymerization were taken into account. The diagram obtained contains three regime types: I x -isolated stars in a dilute solution; II x -a semidilute solution of star branches (subscript characterizes the volume interactions); and III-the close packed system of impermeable (or almost impermeable) stars. Quasiglobular regime III is characterized by the universal dependence of star size on the concentration of the solution c and degree of polymerization N: R ∼ ( N c ) 1 3 independently of the quality of the solvent.

Surface patterning of nanoparticles with polymer patches

Patterning of colloidal particles with chemically or topographically distinct surface domains (patches) has attracted intense research interest. Surface-patterned particles act as colloidal analogues of atoms and molecules, serve as model systems in studies of phase transitions in liquid systems, behave as ‘colloidal surfactants’ and function as templates for the synthesis of hybrid particles. The generation of micrometre- and submicrometre-sized patchy colloids is now efficient, but surface patterning of inorganic colloidal nanoparticles with dimensions of the order of tens of nanometres is uncommon. Such nanoparticles exhibit size- and shape-dependent optical, electronic and magnetic properties, and their assemblies show new collective properties. At present, nanoparticle patterning is limited to the generation of two-patch nanoparticles, and nanoparticles with surface ripples or a ‘raspberry’ surface morphology. Here we demonstrate nanoparticle surface patterning, which utilizes thermodynamically driven segregation of polymer ligands from a uniform polymer brush into surface-pinned micelles following a change in solvent quality. Patch formation is reversible but can be permanently preserved using a photocrosslinking step. The methodology offers the ability to control the dimensions of patches, their spatial distribution and the number of patches per nanoparticle, in agreement with a theoretical model. The versatility of the strategy is demonstrated by patterning nanoparticles with different dimensions, shapes and compositions, tethered with various types of polymers and subjected to different external stimuli. These patchy nanocolloids have potential applications in fundamental research, the self-assembly of nanomaterials, diagnostics, sensing and colloidal stabilization.

Field-Directed Self-Assembly with Locking Nanoparticles

A reversible locking mechanism is established for the generation of anisotropic nanostructures by a magnetic field pulse in liquid matrices by balancing the thermal energy, short-range attractive and long-range repulsive forces, and dipole-dipole interactions using a specially tailored polymer shell of nanoparticles. The locking mechanism is used to precisely regulate the dimensions of self-assembled magnetic nanoparticle chains and to generate and disintegrate three-dimensional (3D) nanostructured materials in solvents and polymers.

Theory of polymer chains tethered at interfaces

Abstract Using self-consistent field calculations and scaling analysis, we determined the property of polymers that are tethered onto impenetrable, solid surfaces or adsorbed onto penetrable interfaces. In the case of impenetrable solids, we consider homogeneous walls, as well as surfaces containing chemically distinct patterns. These findings provide guidelines for tailoring the morphology of the polymer layer and thereby controling the interaction between polymer-coated surfaces. In particular, we pinpoint routes for creating ordered arrays of polymer-coated colloidal particles. The results also yield prescriptions for creating laterally patterned polymer films, which are useful in device applications. In the case of penetrable interfaces, we examine the adsorption of polymers into layers of tethered chains. These studies yield design criteria for creating selective filtration and separation systems, and insight into how adsorbing chains interact with a soft, responsive surface.