arXiv subjects

Ekaterina B. Zhulina

Publications and source records attributed to Ekaterina B. Zhulina.

5 recordsLinked to original sources

arXiv2025

Selective colloid transport across planar polymer brushes

Polymer brushes are attractive as surface coatings for a wide range of applications, from fundamental research to everyday life, and also play important roles in biological systems. How colloids (e.g., functional nanoparticles, proteins, viruses) bind and move across polymer brushes is an important yet under-studied problem. We present a mean-field theoretical approach to analyze the binding and transport of colloids in planar polymer brushes. The theory explicitly considers the effect of solvent strength on brush conformation and of colloid-polymer affinity on colloid binding and transport. We derive the position-dependent free energy of the colloid insertion into the polymer brush which controls the rate of colloid transport across the brush. We show how the properties of the brush can be adjusted for brushes to be highly selective, effectively serving as tuneable gates with respect to colloid size and affinity to the brush-forming polymer. The most important parameter regime simultaneously allowing for high brush permeability and selectivity corresponds to a condition when the repulsive and attractive contributions to the colloid insertion free energy nearly cancel. Our theory should be useful to design sensing and purification devices with enhanced selectivity and to better understand mechanisms underpinning the functions of biopolymer brushes.

cond-mat.soft↗

arXiv2025

Theory of polyelectrolyte dendrigrafts

A mean-field approach is used to analyze equilibrium conformations of polyelectrolyte dendrigrafts comprising ionically charged dendrons attached by focal points to a flexible linear backbone. Power law dependences for local structural parameters, cross-sectional thickness and intergraft distance, are derived as a function of grafting density and degree of branching of the dendrons. The cases of quenched and pH-sensitive ionization of the dendrons are considered. The finite extensibility of the backbone is taken into account. It is demonstrated that an increase in the degree of branching of the dendrons leads to a decrease in the dendrigraft thickness compared with that of the polyelectrolyte molecular brush with the same degree of polymerization of the side chains, while intergraft distance either increases or stays close to counter length of fully extended backbone spacer. The analytical mean-field theory predictions are confirmed by results of numerical self-consistent field modelling.

cond-mat.soft↗

arXiv2025

Non-linear elasticity effects and stratification in brushes of branched polyelectrolytes

Brushes formed by arm-tethered starlike polyelectrolytes may exhibit internal segregation into weakly and strongly extended populations (stratified two-layer structure) when strong ionic intermolecular repulsions induce stretching of the tethers up to the limit of their extensibility. We propose an approximate Poisson-Boltzmann theory for analysis of the structure of the stratified brush and compare it with results of numerical self-consistent field modelling. Both analytical and numerical models point to formation of a narrow cloud of counterions (internal double electrical layer) localized inside stratified brush at the boundary between the layers.

cond-mat.soft↗

arXiv2004

Hybridization Isotherms of DNA Microarrays and the Quantification of Mutation Studies

Background: Diagnostic DNA arrays for detection of point mutations as markers for cancer usually function in the presence of a large excess of wild type DNA. This excess can give rise to false positives due to competitive hybridization of the wild type target at the mutation spot. The analysis of the DNA array data is typically qualitative aiming to establish the presence or absence of a particular point mutation. Our theoretical approach yields methods for quantifying the analysis so as to obtain the ratio of concentrations of mutated and wild type DNA. Method: The theory is formulated in terms of the hybridization isotherms relating the hybridization fraction at the spot to the composition of the sample solutions at thermodynamic equilibrium. It focuses on samples containing an excess of single stranded DNA and on DNA arrays with low surface density of probes. The hybridization equilibrium constants can be obtained by the nearest neighbor method. Results: Two approaches allow us to obtain quantitative results from the DNA array data. In one the signal of the mutation spot is compared with that of the wild type spot. The implementation requires knowledge of the saturation intensity of the two spots. The second approach requires comparison of the intensity of the mutation spot at two different temperatures. In this case knowledge of the saturation signal is not always necessary. Conclusions: DNA arrays can be used to obtain quantitative results on the concentration ratio of mutated DNA to wild type DNA in studies of somatic point mutations.

q-bio.BM↗

arXiv2003

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 $χ_{eff}(T,ϕ)$ 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 vs. the grafting density. The analysis is applied explicitly to the Karalstrom model. The relevance to brushes of Poly(N-isopropylacrylamide)(PNIPAM) is discussed.

cond-mat.soft↗