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Silver micro/nanomaterials have attracted a great deal of attention due to their superior physicochemical properties. The atomic migration driven by electromigration or stress-induced migration has been demonstrated to be a promising method for the fabrication of metallic micro-/nanomaterials because of the advantage of simple processing. However, how to realize the controllable fabrication and mass production is still the critical technical problem for the method to be used in large-scale industrial applications. In this paper, the multilayered samples consisted of copper foil substrate, Ti adhesive layer, Ag film, and TiN passivation layer and with arrays of artificial holes on the passivation layer were applied to prepare arrays of Ag micro-particles. For the purpose of controllable fabrication, stress-induced migration experiments combined with finite element simulation were applied to analyze the influence of the passivation layer thickness and the heating temperature on the atom migration and Ag particles growing behavior. And the relationship between size of the fabricated Ag particles and the processing parameters of stress-induced migration experiments were also investigated. As a result, a proper structure size of the multilayered samples and heating temperature were recommended, which can be used for the Ag micro-particles controllable fabrication and mass production.

Using molecular dynamics simulations based on explicit-solvent model, we study migration of polymer-modified nanoparticles through nanochannels coated with polymers. The polymers densely grafted on the spherical nanoparticle and the channel surface form spherical polymer brush (SPB) and planar polymer brush (PPB), respectively. The migration of the neutral polymer-modified nanoparticle is driven by electroosmotic flow (EOF). The effects of the electric field strength and the SPB–PPB interaction on polymer conformations and transport dynamics of the SPB are explored. The migration velocity of the SPB reduces as the interaction between the SPB and the PPB increases. For strong SPB–PPB interaction, the directional migration of the SPB can be triggered only after the electric field strength exceeds a critical value. The high EOF velocity forces the center of mass of the spherical nanoparticle to keep near the central region of the channel due to high shear rate close to the brush–fluid interface. Unlike electrophoresis of charged polymer-grafted spherical particles, the SPB adopts a more extended conformation in the plane perpendicular to the EOF direction.

Recently, organic thermoelectric (TE) materials have attracted increasing attention in green energy conversion. However, researches on polymer nanostructured TE materials are still scarce, especially for the 1 D nanostructured polymer materials. In this work, 1D poly(3,4-ethylenedioxythiophene) (PEDOT) nanofiber was synthesized by a self-assembled micellar soft-template approach using anionic surfactant sodium dodecyl sulfate (SDS). Then, a flexible and free-standing PEDOT nanofiber film was prepared through a simple vacuum-assisted filtration method. FE-SEM and TEM characteristics real 1D configuration for all the PEDOT nanostructures. Through adjusting the molar ratio of SDS, oxidizing agent FeCl3 and EDOT monomer (nSDS: nFeCl3: nEDOT), nanofiber with different diameter (10–200 nm) and microtopography can be obtained. Electrical conductivity and Seebeck coefficient measurement indicates that the TE properties of PEDOT can be effectively tuned by adjusting its nanostructure, and a variation range as high as three orders of magnitude for the power factors (10-2–101 μW/mK2) can be realized. Due to a more ordered structure caused by the edge-on packing mode of PEDOT chain, the sample prepared with nSDS: nFeCl3: nEDOT = 30:15:7 shows the highest power factor of 7.2 μW/mK2. This value can be further enhanced to 14.4 μW/mK2 by constructing PEDOT nanofiber/SWCNTs composite.

Small organic multiamine and multihydroxyl molecules have great potential for enhancing overall properties of poly(vinyl alcohol) (PVA) through the cross-linking effect of hydrogen bonds. However, experimentally there remains a remarkable lack of insightful understanding of the cross-linking effect on a molecular level. In the work, we report molecular dynamics simulations to reveal the cross-linking effect of hydrogen bonds of tetraaminopyrimidine (4N-2456) molecules on the structure, chain dynamics and mechanical properties of the PVA matrix. It was found that the addition of 4N-2456 leads to a nonlinear decrease of the free volume of PVA. A critical concentration of 4N-2456, about 5 wt%, was identified, resulting in the formation of 4N-2456 clusters. At this concentration, the PVA chains show the relatively slow mobility, the higher glass transition temperature and elastic modulus. Further increasing the 4N-2456 concentration enhances aggregation, and conversely weakens the interactions of hydrogen bonds between the PVA chains. Our work offers an understanding of how the 4N-2456 molecules influence the PVA chain dynamics and mechanical properties of the PVA matrix on molecular level.

Symmetrical electrical double layer capacitors with ionic liquid potassium hydroxide (KOH)-based poly(acrylic acid) gel polymer electrolytes and activated charcoal electrodes were constructed and characterised. The optimised composition of gel polymer electrolytes exhibits high room temperature ionic conductivity of 0.46 S cm−1 with good mechanical and dimensional stability, which is suitable for their application as electrolyte in electrical double layer capacitors. Analysis shows that the maximum value of capacitance was 0.343 F cm−2, and this value corresponds to an energy density equal to 0.111 J cm−2. Electrical double layer capacitor exhibits large capacitance and high energy density. The results indicate that the gel polymer electrolyte used in our study is promising and is suitable as a solid electrolyte for high-performance all-solid-state electrochemical devices.

Solid Al&ndash, air batteries are a promising power source for potable electronics due to their environmentally friendly qualities and high energy density. However, the solid Al&ndash, air battery suffers from anodic corrosion and it is difficult to achieve a higher specific capacity. Thus, this work aims at suppressing the corrosion of Al anode by adding an electrospun Al2O3 interlayer on to the surface of the anode. The Al2O3 interlayer effectively inhibits the self-corrosion of the Al anode. Further, the effects of the thickness of the Al2O3 film on corrosion behavior were investigated. The results showed that the Al&ndash, air battery with a 4 &mu, m Al2O3 interlayer is more suitable for a low current density discharge, which could be applied for mini-watt devices. With a proper thickness of the Al2O3 interlayer, corrosion of the anode was considerably suppressed without sacrificing the discharge voltage at a low current density. The Al&ndash, m Al2O3 interlayer provided a significantly high capacity (1255 mAh/g at 5 mA/cm2) and an excellent stability. This wo presents a promising approach for fabricating an inhibiting corrosion interlayer for solid Al&ndash, air battery designed for mini-watt devices.

We study the conformational behavior of spherical polyelectrolyte brushes in the presence of monovalent and trivalent counterions in a confined environment. The confinement is exerted by two parallel walls on the brushes. The enhancement of the confinement induces the extension of grafted chains. For the monovalent case, the increase of the charge fraction leads to extended brush conformation for different slit width (distance between two walls) but collapsed brush in the presence of trivalent counterions is observed. The confinement does not affect electrostatic correlation between trivalent counterions and charged monomers. However, it was found that narrow slit width contributes to stronger electrostatic correlation for the monovalent case. This is because more monovalent counterions are inside the brush at strong confinement, but almost all trivalent counterions are trapped into the brush independently of the slit width. The diffusion of counterions under the confinement is related to the electrostatic correlation. Our simulations also reveal that the brush thickness depends on the slit width nonlinearly.

We comprehensively illustrate a general process of fitting all-atom molecular mechanics force field (FF) parameters based on quantum mechanical calculations and experimental thermodynamic data. For common organic molecules with free dihedral rotations, this FF format is comprised of the usual bond stretching, angle bending, proper and improper dihedral rotation, and 1–4 scaling pair interactions. An extra format of 1–n scaling pair interaction is introduced when a specific intramolecular rotation is strongly hindered. We detail how the preferred order of fitting all intramolecular FF parameters can be determined by systematically generating characteristic configurations. The intermolecular Van der Waals parameters are initially taken from the literature data but adjusted to obtain a better agreement between the molecular dynamics (MD) simulation results and the experimental observations if necessary. By randomly choosing the molecular configurations from MD simulation and comparing their energies computed from FF parameters and quantum mechanics, the FF parameters can be verified self-consistently. Using an example of a platform chemical 3-hydroxypropionic acid, we detail the comparison between the new fitting parameters and the existing FF parameters. In particular, the introduced systematic approach has been applied to obtain the dihedral angle potential and 1–n scaling pair interaction parameters for 48 organic molecules with different functionality. We suggest that this procedure might be used to obtain better dihedral and 1–n interaction potentials when they are not available in the current widely used FF. © 2014 Wiley Periodicals, Inc.

Aluminum–air (Al–air) battery is one of the most promising candidates for next-generation energy storage systems because of its high capacity and energy density, and abundance. The polyacrylic acid (PAA)-based alkaline gel electrolyte is used in all-solid-state Al–air batteries instead of aqueous electrolytes to prevent leakage. The optimal gel electrolyte exhibits an ionic conductivity of 460 mS cm −1 , which is close to that of aqueous electrolytes. The Al–air battery peak capacity and energy density considering only Al can reach 1166 mAh g −1 -Al and 1230 mWh g −1 -Al, respectively, during constant current discharge. The battery prototype also exhibits a high power density of 91.13 mW cm −2 . For the battery is a laminated structure, area densities of 29.2 mAh cm −2 and 30.8 mWh cm −2 are presented to appraise the performance of the whole cell. A novel design to inhibit anodic corrosion is proposed by separating the Al anode from the gel electrolyte when not in use, thereby effectively maintaining the available capacity of the battery.

Molecular dynamics simulations are conducted to investigate the suppression of electroosmotic flow by grafting polyampholyte brushes onto two parallel channel walls. The effects of grafting density and charge distribution of polyampholyte brushes on the electroosmotic flow velocity, salt ion distribution, and conformational characteristics of grafted brushes are studied in detail. Simulation results indicate that increasing the grafting density induces a stronger suppression of electroosmotic flow. The flow velocity is significantly influenced by the different charge distributions of polyampholyte brushes. In addition, an important flow phenomenon we have found is that the flow velocity profile shows a valley at the center of the channel. These results reveal that the flow velocity is dependent not only on the conformation of the polyampholyte brushes but also on the anion and cation distributions. The hierarchical distribution of salt ions is caused by the special properties of polyampholyte brushes.

We report an all-atom molecular dynamics study of the structures and dynamics of salty water droplets on a silicon surface under the influence of applied electric field. Our simulation results support ion-specific effects on the elongation dynamics of salty nanodroplets, induced by the field. This feature has not been explored up to now in monovalent salts. Nevertheless, the importance of ion-specific effects is widely confirmed in biological and colloidal systems. In particular, the increase of salt concentration enhances the effect of the nature of ions on the wetting properties of droplets. In the presence of electric field (0.05 V A-1), a complete spreading is implemented in a short time for different droplets at a concentration of 1 M, and the droplet morphology is stable, observed at long time scales. However, a higher salt concentration of 4 M considerably suppresses the spreading process owing to the increase of surface tension. It was found that the NaCl droplet shows deformation oscillations along the external field, but cannot fully wet the substrate surface. By contrast, the CsCl droplet reaches complete elongation rapidly and adopts a steady strip shape. The KCl droplet undergoes frequent transitions between breakup and connection. Additionally, the droplets can be elongated only when the electric field strength exceeds a threshold value. The dipole orientation of interfacial water and the ionic diffusion exhibit ion-specific dependences, but the hydrogen bond network is scarcely disturbed, excluding a concentration-dependent effect.

High-value-added recycling of hazardous waste is a key problem in environmental science and engineering. In previous reports, a hazardous-waste-derived catalyst showed better activity than a catalyst synthesised from pure reagents for the reduction of nitric oxide. The multimetallic nature of hazardous waste was speculated to increase the catalytic activity. In this work, a further investigation was conducted to confirm this speculation. It was found that bimetallic catalysts showed better activity than monometallic ones at 50–200 °C. A bimetallic catalyst removed 75.05% of nitric oxide (990 ppm) at 150 °C, whereas monometallic ones removed only 19.50%. Moreover, the bimetallic catalyst removed 11.46 mmol/g of nitric oxide after 1200 min at 300 °C, which was a much higher concentration than that removed by the monometallic catalyst (2.72 mmol/g). Experimental and simulated Raman spectroscopy revealed that enhanced activity was accompanied by a larger blue shift of the metal band (indicating catalytic centre activity) and a smaller blue shift of the carbon band (indicating reductant stability). In a theoretical calculation, a second metal changed the electron density difference of the catalytic centre and activated the distant reductant, increasing both the low-temperature activity and activity stability. The main result of this study explained the reason bimetallic catalysts outperformed the monometallic ones. Because hazardous waste usually contains bimetallic species, it can be used as a suitable resource for producing effective catalysts.

Molecular dynamics simulations were performed for electro-osmotic flow (EOF) confined in a polyelectrolyte- grafted nanochannel under variable grafting density and nor- mal electric field. With decreasing the value of the normal elec- tric field, the brush undergoes a collapse transition, and the ion distribution is changed significantly. The brush thickness increases on increasing the grafting density at positive and weak negative electric fields, whereas a reduced brush thick- ness is observed at strong negative electric field. Our results further reveal that the flow velocity is not only dependent on conformational transition of the brush but also related to the cation and anion distributions. At low grafting density, the EOF is almost completely quenched at high electric field strength due to strong surface friction between ions and walls. For the case of very dense grafting, the flow velocity is influenced weakly within the brush when varying the grafting density. Additionally, a bidirectional flow occurs at an intermediate electric field. The investigation on fluid flux indicates that the fluid flux is insensitive to the grafting density, when the normal electric field is removed. For nonzero normal electric fields, a significant change in the fluid flux is observed at low grafting densities. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 805-811, 2012

The adsorption and wrapping process of a single flexible comb-like polymer to a single wall nanotube was studied by Molecular Dynamics simulation of a coarse-grained model. We varied the grafting density and length of the side chains, the radius of the nanotube and strength of interaction between the monomers of nanotube and side chains of polymer brush. We investigated the structural and dynamical characters of interactions of the nanotube-polymer composite, such as the effect of Lennard-Jones energy parameter ɛLJ and the nanotube radius on the adsorption behavior and how the wrapping conformation is affected by the structure of the polymer brush. The simulation results indicate that single comb-like polymer with flexible backbone tends to adsorb and wrap around the nanotube, when the interaction energy exceeds a critical value. The monomer adsorption ratio, interaction energy profiles and moment of inertia are obtained. The helical wrapping only occurs when the interaction energy is large enough. Also, the influence of the polymer structure on the conformational behavior is analyzed. This work underscores design elements important for engineering well-defined nanotube-polymer nanocomposite.

A hybrid particle–continuum method is used to study the shear flow confined between two opposing walls, one of which is coated with polymer chains. Molecular dynamics (MD) is used in the particle region near the brush and Navier–Stokes (NS) equations are applied in the remaining region where the continuum assumption holds. The information exchange from the continuum region to the particle region is implemented using the constrained particle dynamics. Both Couette shear flow and oscillatory flow are considered in the present work. The effect of the shear flow on the conformational characteristics of polymer brushes is analyzed. In the overlap region, the velocities obtained from MD simulations are smoothly connected with those from NS equations. Our investigations demonstrate that the hybrid particle–continuum model is valid in exploring the shear behavior of polymer brushes.

Molecular dynamics simulations were done to study the electroosmotic flow (EOF) transport in a nanochannel grafted with polyelectrolytes under the control of an electric field normal to the channel wall. This study first addresses some problems on the interplay between complex EOF and non-equilibrium conformational behavior of polyelectrolyte brushes at a molecular level. We demonstrated that changing the normal electric field has a significant impact on the conformational transition of polyelectrolytes and ion distributions, further leading to some new flow phenomena. The coupling mechanisms of polyelectrolyte chain dynamics and electrohydrodynamics were discussed. A remarkable result obtained is that fluid flux depends nonmonotonically on the normal electric field. Our work provides fundamental understanding of the EOF modulation using polyelectrolyte brushes and guidance for the design of smart nanofluidic channels.

Dissipative particle dynamics (DPD) is used to investigate solvent flow controlled by a cylindrical nanofluidic channel grafted with polymer brushes. Results for monomer and solvent beads density for different solvent quality were obtained, as well as the height and inclination angle of the polymer brushes in Poiseuille flow. The velocity profile and solvent permeability in Poiseuille flow for varying solvent quality were also examined. The polymer brushes expand and inhibit flow under good solvent conditions. However, under poor solvent conditions the chains collapse to open the channel. Additionally, the dependence of the permeability on the grafting density is given. The results indicate that the system is capable of changing the permeability and flow rate drastically upon changing the solvent quality.

We report molecular dynamics simulations on bottle-brush polyelectrolytes end-grafted to a planar surface. For each bottle-brush polyelectrolyte, flexible charged side chains are anchored to one neutral main chain. The effects of the counterion valence and the grafting density on the density profiles and the structural characteristics of the brush were studied in this work. It is found that the electrostatic repulsion between charged monomers in the side chains leads an extended conformation of the brush in a solution containing monovalent counterions, while strong electrostatic binding of multivalent counterions to the side chains has a significant contribution to the collapse of the brush. For the trivalent case, the distribution of end monomers in the main chains becomes broader upon decreasing the grafting density, as compared with the monovalent case. However, the position of the distribution for the monovalent case is relatively insensitive to the change of the grafting density. Additionally, with increased counterion valence, enhanced electrostatic correlation between counterions and charged side chains also weakens the diffusive ability of counterions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Using Brownian dynamics simulations, we study the effect of the charge ratio, the surfactant length, and the grafting density on the conformational behavior of the complex formed by the polyelectrolyte brush with oppositely charged surfactants. In our simulations, the polyelectrolyte chains and surfactants are represented by a coarse-grained bead-spring model, and the solvent is treated implicitly. It is found that varying the charge ratio induces different morphologies of surfactant aggregates adsorbed onto the brush. At high charge ratios, the density profiles of surfactant monomers indicate that surfactant aggregates exhibit a layer-by-layer arrangement. The surfactant length has a strong effect on the adsorption behavior of surfactants. The lengthening of surfactant leads to a collapsed brush configuration, but a reswelling of the brush with further increasing the surfactant length is observed. The collapse of the brush is attributed to the enhancement of surfactants binding to polyelectrolyte chains. The reswelling is due to an increase in the volume of adsorbed surfactant aggregates. At the largest grafting density investigated, enhanced excluded volume interactions limit the adsorption of surfactant within the polyelectrolyte brush. We also find that end monomers in polyelectrolyte chains exhibit a bimodal distribution in cases of large surfactant lengths and high charge ratios.

Using coarse-grained molecular dynamics simulations, we study the behavior of a DNA-nanosphere complex in the absence and presence of an external stretching force exerted on two ends of DNA chain. In this work, we use an accurate coarse-grained model for double-stranded DNA chain recently developed by Savelyev and Papoian [Biophys. J. 96, 4044 (2009)]. Charged particles are uniformly distributed on the surface of the sphere. Without a stretching force, an ordered or disordered complex is formed depending on the surface charge density and the salt concentration. It is found that DNA wraps randomly around the sphere only at an intermediate salt concentration and high surface charge density. Additionally, the DNA folding around the sphere induces a reduced distance between DNA monomers close to the spherical surface. When an external force is applied, the force-extension relation reveals a discontinuous transition of DNA stretching during the unwrapping process. Moreover, the discrete change becomes more obvious for a higher salt concentration.

We have performed dissipative particle dynamics (DPDs) simulations of electroosmotic flow (EOF) through a polymer-grafted nanopore. In this model, charged particles including salt ions and counterions are not included explicitly, and EOF is created using an effective boundary condition. The screening effect of polymer layer on EOF is investigated in detail under different solvent qualities and boundary electroosmotic velocities. Results show that the solvent quality has a significant effect on the conformational properties of polymer chains and the flow characteristics of the solvent. The polymer layer undergoes a collapsed transition when decreasing the solvent quality from good to poor. Under different solvent qualities, enhancing the EOF leads to a different variation tendency of the layer thickness. The solvent-induced permeability change is inconsistent with the steady velocity away from the surface. The minimum value of the solvent permeability occurs at an intermediate solvent quality. However, the layer thickness drops gradually to a smallest value (corresponding to the largest effective pore radius) in the poor solvent condition. It is also found that the polymer inclination and stretching length exhibit a complex behavior under the combined effect of solvent quality and electroosmosis-induced shear.

The conformational transition of a single bottle-brush polyelectrolyte with charged and neutral side chains is studied through MD simulations. Counterions are included explicitly and no additional salt is added. The structure of the polyelectrolyte and the counterion condensation are found to depend greatly on the Bjerrum length. As the Bjerrum length increases, the neutral side chains in a poor solvent can condense into clusters with variable size. Moreover, the polyelectrolyte forms globular structures at large or very small Bjerrum lengths. This transition is quite different from that in the case of a good solvent, in which there are not observable clusters and a globular structure is only formed at large Bjerrum lengths.

We use molecular dynamics simulations to investigate the control of electroosmotic flow by grafting polymers onto two parallel channel walls. The effects of the grafting density and the electric field strength on electroosmotic flow velocity, counterion distribution and conformational characteristics of grafted chains have been studied in detail for athermal, good, and poor solvent cases. The simulation results indicate that in the range of grafting densities investigated, increasing the grafting density induces a different change tendency of electroosmotic flow velocity for three different solvent qualities. These tendencies are demonstrated to be related to counterion distribution, polymer coverage, and interactions between monomers and solvent particles. It is found that counterions tend to move toward the interface between polymer layer and solvent as the grafting density increases. Especially in the poor solvent case, most of the counterions gather near the interface at high grafting densities. A similar behavior is also observed when enhancing the electric field strength at a fixed grafting density.

We use molecular dynamics simulations to investigate centipede-like polymers with stiff charged side chains, end-grafted to a planar wall. The effect of the grafting density and the Bjerrum length on the conformational behaviour of the brush is examined in detail. In addition, we make a comparison of centipede-like polyelectrolyte (CPE) brushes with neutral centipede-like polymer (NCP) and linear polyelectrolyte (LPE) brushes. At weak electrostatic interaction, the main chains of the CPE chains adopt a strongly stretched conformation, and the monomer density profiles of side chains exhibit a clear oscillatory behaviour. With increasing Bjerrum length, the CPE brush undergoes a collapse transition. Compared to the CPE brushes, the counterion condensation effect is stronger for the LPE brushes, regardless of whether the electrostatic interaction is weak or strong and of whether the grafting density is low or high. Additionally, it is shown that the architecture of the grafted chains makes a weak contribution to the counterion condensation at strong electrostatic interaction. We also find that the electrostatic repulsion between charged side chains can enhance the stiffness of the main chains and thus limit the range of movement of the free-end monomers.

The conformational characteristics of polyelectrolytes end-grafted on two apposing walls are studied. The monovalent and multivalent counterions are explicitly treated. It is found that the polyelectrolyte brushes undergo a collapse transition in the presence of multivalent counterions at large wall separations. Moreover, the brush thickness is linearly proportional to the grafting density and independent of the counterion valence. The effects of normal compression on the density profiles of monomers and counterions, the pressure, the net charge density and the degree of interpenetration are also studied. The density profiles of counterions exhibit an asymmetrical distribution in systems with a mixture of monovalent and trivalent counterions.

We conducted coarse-grained molecular dynamics simulations to study the responsive behaviors of polyampholyte brushes (PABs) under external electric fields. The effects of charge sequence, chain rigidity and electric field strength on the conformational transition and local structures of grafted chains were addressed systematically. Without electric field, the calculations indicate that the thickness of the PABs is smaller compared to polyelectrolyte brushes (PEBs). The presence of electric field leads to inconsistency of densities between negatively and positively charged monomers except for the alternating brush. Counterions from the PABs can diffuse inside or outside the brush. Unlike the PABs, to separate the polyelectrolytes and their counterions the electric field needs to overcome the osmotic pressure of counterions. The critical field which induces the extension of the flexible PABs is much larger than the PEBs. Meanwhile, it was also found that the critical field which induces the collapse of the PABs decreases as the block length increases. In the limit of strong field studied, the chains with longer blocks are in a local extended state. For diblock brushes, once oppositely charged blocks in a single chain are separated, the chain will become straighter due to strong electrostatic repulsion in intrablock.

We report a molecular dynamics study on non-equilibrium dynamics of polyelectrolyte brushes under external electric fields. In this work, the effects of chain stiffness and salt concentration on static and dynamic responses of the brushes are addressed in detail. Our simulations indicate that varying these parameters induce rich electro-responsive behavior of the brushes. The increase of salt concentration results in the enhancement of an opposite electric field formed by non-equilibrium distribution of cations and anions, which resists stretching or shrinkage of grafted chains. At strong positive electric fields, the flexible brushes are more sensitive to the change of salt concentration. When reversing the electric field, the stiff brushes undergo a conformational transition from collapse to complete stretching. At high salt concentrations, dynamic responsive magnitude of the brush thickness to added electric field is strongly reduced. It was found that the fall time for the stiff brush becomes much shorter than that for the flexible brush. Additionally, increasing ion concentration leads to an excess extension or shrinkage of flexible brushes. For strongly stiff brushes, such phenomenon occurs in the presence or absence of salt.

A polymer capillary electrophoresis chip is a novel kind of miniaturized device for biochemistry analysis. In this paper, a polymer micro hot embossing process is characterized by experiment and numerical simulation. a series of experiments were carried out with varied process conditions, including processing pressure, temperature and time. both the height and width of hot-embossed microchannel was investigated. Furthermore, a numerical simulation was developed to understand the mechanism of the hot-embossing process. Simulation results conform to related experiments. Based on these, a novel process of hot embossing is proposed, which lays the foundation for basic theories and techniques of structural design and manufactures of the polymer microchip.

A basic understanding of the transport mechanisms of nanostructures in a polymer brush-modified nanochannel as well as the brush-nanostructure interactions at molecular level is important to design and fabricate emerging smart nano/microfluidic channels. In this work, we report coarse-grained molecular dynamics simulations of the translocation of nanoparticles through a cylindrical nanochannel coated with the polymer brush. The effects of the interparticle interaction and grafting density on the distribution and electrokinetic transport of nanoparticles are addressed in detail. Analysis of the distribution and velocity profiles of nanoparticles from the simulations indicate that the location of nanoparticles along the radial direction and their migration velocity are very sensitive to the change of interparticle interaction. We find complicated transport dynamics of nanoparticles under the influence of various grafting densities. The nanoparticles show markedly different translocation behavior upon increasing the grafting density, which depends on the counterion distribution, free room within the brush, nanoparticle-polymer friction, and brush configuration. Our results may serve as a useful starting point for the transport of nanostructures in polymer-modified channels and help to guide the design of novel smart nanofluidic channels for controlling the migration behavior of nanostructures.

Recent experiments have revealed several morphologies of complexes formed by the self-assembly of bottle-brush polyelectrolytes (BPEs) and oppositely charged surfactants. We report herein a computational study of the formation and transition of self-assembled BPE/surfactant complexes with varying the backbone stiffness and amount of added surfactant. We characterize five complex shapes distinguished on the basis of BPE conformations and aggregate morphologies. Our simulations suggest that for cases of single adsorbed aggregate with an almost complete contact with the BPE, the backbone adopts a helical conformation regardless of the molecular details, while the helical fashion shows a dependence on the investigated parameters. Moreover, a spiral aggregate is observed at high backbone stiffness and BPE/surfactant charge ratio. The present results provide a valuable complement to experiment in exploring the possible structural phases of BPE/surfactant complexes at a molecular level.

We use Brownian dynamics (BD) simulations to investigate the formation and structural characteristics of the complex between a spherical polyelectrolyte brush (SPB) and oppositely charged surfactants. Increasing the amount of added surfactants leads to a collapsed conformation of the SPB and the number of adsorbed surfactants exhibits a linear dependence. Nevertheless, the surfactant uptake into the SPB does not increase with further addition of surfactants. It is found that the surfactant length has a strong influence on the SPB conformation and the adsorption properties of surfactant. Upon changing the surfactant length from 3 to 11, the SPB undergoes a swelling-deswelling-reswelling conformational transition. The brush deswelling is due to the increase in the surfactant uptake. The increasing size of adsorbed aggregates is a main reason for reswelling of the SPB. A non-linear relationship between the brush thickness and the grafting density is observed. Especially at intermediate grafting densities, increasing the number of grafted chains has a weak effect on the brush thickness. We also find that a completely collapsed brush conformation occurs at high surfactant/SPB charge ratios or large surfactant lengths, while the brush layer is in a partly collapsed or extended state at an intermediate charge ratio and surfactant length.