arXiv subjects

Huaisong Yong

Publications and source records attributed to Huaisong Yong.

4 recordsLinked to original sources

arXiv2026

Cosolvency response in polymer brushes

We present the first analytic theory with elegant and closed-form analytical solutions to explore the cosolvency effect in polymer brushes, where polymer chains that are poorly soluble in two pure solvents become fully soluble in certain mixtures thereof. This effect is key to designing stimulus-responsive smart materials but has not previously been addressed by analytic theory for polymer brushes. Our theoretical framework reveals that preferential adsorption of cosolvent induces an effective repulsion between monomers solvated by cosolvent and those solvated by solvent. The equilibrium solvation of polymer chains by cosolvent gives rise to a concentration-dependent $χ$-function, which captures the effective interactions within the brush and reproduces the reentrant behavior characteristic of the cosolvency effect. The model predicts a discontinuous soluble transition followed by a re-collapse transition at higher cosolvent concentrations. Analytical treatment within a minimal free-energy model for the case of two symmetric poor solvents shows that the swelling and re-collapse transitions share the same thermodynamic origin. For low-density brushes, we derive an analytical approximation and delineate the phase diagram of parameter space in which discontinuous transitions occur. For cosolvency to take place, the theory specifies a minimum strength for preferential solvation and the associated repulsive coupling. Furthermore, it demonstrates that, contrary to previous models, repulsive interactions between cosolvent and solvent in the bulk are not required. This work lays the groundwork for the rational design of smart stimulus-responsive materials based on the cosolvency effect in polymer brushes, a capability which was not previously established.

cond-mat.soft↗

arXiv2024

Why can a hydrophilic polyelectrolyte precipitate and redissolve below the critical micelle concentration of an oppositely-charged surfactant ?

We theoretically study the reentrant condensation of a polyelectrolyte in the presence of an oppositely-charged surfactant,a phenomenon whose phase-transition mechanism remains under discussion. We focus on the adsorption and attraction effects of surfactant near/on polymer chains, and ignore their own non-essential mixing effects if surfactant molecules are far away from polymer chains. This approach allows us to construct a simple mean-field theory and solve it analytically, and finally rationalize the essential features (such as the "egg shape" of spinodal phase diagrams) of the reentrant condensation of a polyelectrolyte induced by diluted oppositely-charged surfactants. By theoretical analysis, we found that a strong electrostatic adsorption between the ionic monomers and surfactant ions is critical to understand the peculiar phenomenon that both the collapse and reentry transitions of polyelectrolytes can occur when the concentration of surfactant is lower than its bulk critical micelle concentration (CMC). The analytical solution of the theory indicates that a minimum coupling energy for the nonlinear hydrophobic-aggregation effect of adsorbed surfactant is essential for phase transition to occur,which explains why polyelectrolytes show phase transition only if the surfactant chain length is longer than a minimum length. The obtained results will shed light on a deep understanding of liquid-liquid phase separation in biological systems where ionic surfactant-like proteins/peptides bound to bio-polyelectrolytes play an important role.

cond-mat.soft↗

arXiv2024

The reentrant condensation of polyelectrolytes induced by diluted multivalent salts: A mean-field level revisiting

We study the reentrant condensation of polyelectrolytes in dilute solutions of small multivalent salts, whose phase-transition mechanism remains poorly understood. Motivated by recent full atomic simulation results reported by the Caltech group on phase behaviors of polyelectrolytes in presence of multivalent salts (DOIs: 10.1021/acs.macromol.3c02437 and 10.1021/acs.langmuir.3c03640), in this work we construct a simple but effective mean-field model which can rationalize the essential features of the reentrant condensation including the phase diagram of polyelectrolyte. The model unveils that the strong adsorption between the ionic monomers and multivalent ions can be at the origin of the peculiar phenomenon that rather low concentrations of multivalent salts trigger both collapse and re-entry transitions. For the first time, the analytical solution of the model indicates that a minimum of coupling energy due to sharing multivalent salt ions between ionic monomers is essential for a phase transition to occur, which can explain the enigmatic observation that polyelectrolytes can only show phase transition in a dilute solution of salts with selective multivalency. Our analytical calculations also show that the incompatibility of the uncharged moieties of the polyelectrolytes with water is critical to regulate phase behaviors of polyelectrolytes in aqueous solutions. This is in agreement with recent experimental investigations on solution properties of amphiphilic proteins. The obtained results will contribute to the understanding of liquid-liquid phase separation in biological systems where multivalent ions bound to bio-polyelectrolytes play an essential role.

cond-mat.soft↗

arXiv2012

Driven polymer translocation through a cylindrical nanochannel: Interplay between the channel length and the chain length

Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of polymer translocation through a nanochannel embedded in two dimensions under an applied external field. We examine the translocation time for various ratio of the channel length $L$ to the polymer length $N$. For short channels $L\ll N$, the translocation time $τ\sim N^{1+ν}$ under weak driving force $F$, while $τ\sim F^{-1}L$ for long channels $L\gg N$, independent of the chain length $N$. Moreover, we observe a minimum of translocation time as a function of $L/N$ for different driving forces and channel widths. These results are interpreted by the waiting time of a single segment.

cond-mat.soft↗