查看更多>>摘要：Polyampholyte gels,which have hierarchical structures,exhibit excellent self-healing properties and have great promise for biomateri-als and bioengineering.We investigated the relationship between microscopic structures and macroscopic viscoelastic properties of polyam-pholyte gels and found three factors influencing their viscoelastic properties,including the chemical crosslinking bonds,topological entangle-ments controlled by monomer concentration,and the ionic bonds.Ionic strength plays a major role on the strength of ionic bonds.A crossover point of elastic modulus and loss modulus was observed in the dynamic frequency sweeps at low monomer concentration or low chemical crosslinking density for gels with intermediate strength of ionic bonds.The solid-liquid transition signaled by the crossover point is a typical fea-ture of dynamic associated gels,representing the dynamical association-dissociation of the ionic bonds and full relaxation of the topological en-tanglements in the gel network.While the crossover point disappears when the ionic bonds are too weak or too strong to form"permanent"bonds.Consistently,in the non-linear yielding measurement,gels with intermediate strength of the ionic bonds are ductile and yield at very large shear strain due to the self-healing properties and the dynamic association-dissociation of the ionic bonds.But the self-healing properties disap-pear when the ionic bond strength is too weak or too strong.Our work reveals the mechanism of how the dynamic association-dissociation of ionic bonds influences both the linear and non-linear viscoelastic properties of the polyampholyte gels.
查看更多>>摘要：We present the results of molecular dynamics simulations of steady shear between a pair of neutral polymer brushes,as well as a pair of charged polymer brushes in the strongly compressed regime.The results of the molecular dynamic simulations of neutral and polyelectrolyte brushes in implicit solvent including normal forces,shear forces,viscosities and friction coefficients as a function of separation between brushes,are presented in the study.The comparison of the simulation results of neutral and charged brushes shows that the charged brushes is in the quasi-neutral regime,and the dependence of viscosity on the separation distance show the similar power law of neutral brushes.Our simulation results confirm that the implicit solvent simulations of polyelectrolyte brushes that ignore hydrodynamics interaction are in agreement with the scaling predictions qualitatively because of screening of hydrodynamic interaction and long-range electrostatic interactions on the correlation length scale.Both of neutral and charged brushes show the lubrication properties that the friction coefficient decreases with the separation de-creases at enough large loads.However,a maximum of friction coefficients is observed for polyelectrolyte brushes,which is in contrast to the neutral brushes with monotonical dependence.
查看更多>>摘要：Salt-doped block copolymers have widespread applications in batteries,fuel cells,semiconductors,and various industries,where their properties crucially depend on phase separation behavior.Traditionally,investigations into salt-doped diblock copolymers have predominantly focused on microphase separation,overlooking the segregation between ionic and polymeric species.This study employs weak segregation the-ory to explore the interplay between phase separation dominated by the polymer-modulated mode and the salt-out-modulated mode,corre-sponding to microscopic and macroscopic phase separations,respectively.By comparing diblock copolymers doped with salts to those doped with neutral solvents,we elucidate the significant role of charged species in modulating phase behavior.The phase separation mode exhibits a transition between the polymer-modulated and salt-out-modulated modes at different wavenumbers.In systems doped with neutral solvents,this transition is stepwise,while in salt-ion-doped systems,it is continuous.With a sufficiently large Flory-Huggins parameter between ions and polymers,the salt-out-modulated mode becomes dominant,promoting macrophase separation.Due to the solvation effect of salt ions,salt-doped systems are more inclined to undergo microphase separation.Furthermore,we explore factors influencing the critical wavenumber of phase separation,including doping level and the Flory-Huggins parameters between two blocks and between ions and polymeric species.Our findings reveal that in a neutral solvent environment,these factors alter only the boundary between micro-and macro-phase separations,leav-ing the critical wavenumber unchanged in microphase separation cases.However,in a salt-doped environment,the critical wavenumber of mi-crophase separation varies with these parameters.This provides valuable insights into the pivotal role of electrostatics in the phase separation of salt-doped block copolymers.
查看更多>>摘要：Polyelectrolyte(PE)gels,distinguished by their unique stimuli-responsive swelling behavior,serve as the basis of broad applications,such as artificial muscles and drug delivery.In this work,we present a theoretical model to analyze the electrostatics and its contribution to the swelling behavior of PE gels in salt solutions.By minimizing the free energy of PE gels,we obtain two distinct scaling regimes for the swelling ra-tio at equilibrium with respect to the salt concentration.We compare our predictions for the swelling ratio with experimental measurements,which show excellent agreement.In addition,we employ a finite element method to assess the applicability range of our theoretical model and assumptions.We anticipate that our model will also provide valuable insights into drug adsorption and release,deformation of red blood cells,4D printing and soft robotics,where the underlying mechanism of swelling remains enigmatic.
查看更多>>摘要：Titanium dioxide(TiO2)hollow nanoparticles present significant potential for photocatalytic applications while their straightforward preparation with precise structure control is still challenging.This work reports the approach to preparing tunable hollow TiO2 nanospheres by utilization of spherical polyelectrolyte brushes(SPB)as nanoreactors and templates.During the preparation,the evolution of the structure was characterized by small angle X-ray scattering(SAXS),and in combination with dynamic light scattering and transmission electron microscopy.The formation of TiO2 shell within the brush(SPB@TiO2)is confirmed by the significant increase of the electron density,and its internal structure has been analyzed by fitting SAXS data,which can be influenced by Titanium precursors and ammonia concentration.After calcining SPB@TiO2 in a muffle furnace,hollow TiO2 nanospheres are produced,and their transition to the anatase crystal form is triggered,as confirmed by X-ray diffraction analysis.Utilizing the advantages of their hollow structure,these TiO2 nanospheres exhibit exceptional catalytic degradation efficien-cy of methylene blue(MB),tetracycline(TC),and 2,4-dichlorophenoxyacetic acid(2,4-D),and also demonstrate excellent recyclability.
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