Honglai Liu

A molecular-thermodynamic model for polyelectrolyte solutions

Polyelectrolyte solutions are modeled as freely tangent-jointed, charged hard-sphere chains and corresponding counterions in a continuum medium with permitivity e. By adopting the sticky-point model, the Helmholtz function for polyelectrolyte solutions is derived through the r-particle cavity-correlation function (CCF) for chains of sticky, charged hard spheres. The r-CCF is approximated by a product of effective nearest-neighbor two-particle CCFs; these are determined from the hypernetted-chain and mean-spherical closures (HNC/MSA) inside and outside the hard core, respectively, for the integral equation theory for electrolytes. The colligative properties are given as explicit functions of a scaling parameter Γ that can be estimated by a simple iteration procedure. Osmotic pressures, osmotic coefficients, and activity coefficients are calculated for model solutions with various chain lengths. They are in good agreement with molecular simulation and experimental results.

New Tricks for Old Molecules: Development and Application of Porous N‐doped, Carbonaceous Membranes for CO2 Separation

A new strategy is successfully applied to old acetyl compounds. A free-standing, porous, N-doped carbonaceous membrane is facilely prepared from the thermal treatment of a pyrrole-ring-containing polymeric membrane based on the superacid-catalyzed copolymerization of acetyl monomers. An exceptional ideal CO2 /N2 permselectivity of 43.2 is achieved with a good CO2 permeability of 1149.3 Barrer, exceeding the recent upper bound for CO2 /N2 .

Polyelectrolyte solutions with stickiness between polyions and counterions

Polyelectrolyte solutions are modeled as linear tangent-jointed charged hard-sphere chains and counterions embedded in a continuum medium; the stickiness between the polyions and the counterions beyond the territorial binding is taken into account as the short-range non-Coulombic perturbation. Expressions of thermodynamic properties derived are then consisted of two contributions. The chain contribution concerns the formation of polyion chains from the monomers. The sticky contribution accounts for the additional non-Coulombic stickiness, which is derived by solving the Ornstein–Zernike integral equation through the mean-spherical approximation (MSA) and the hypernetted-chain approximation (HNC). For the model solutions without stickiness between the polyions and the counterions, effects of polyion chain lengths, counterion sizes, counterion charges, and the dielectric constants on the thermodynamic properties are extensively studied. Comparisons of the osmotic pressures for the model solutions with those...

A mutual-diffusion-coefficient model based on local composition

A mutual-diffusion-coefficient model based on local-composition concept is developed. An expression for the calculation of concentration-dependent intra-diffusion coefficients is also established by considering the formation of clusters. With the import of diffusion coefficients at infinite dilution, self-diffusion coefficients and viscosities of pure components and mixtures, mutual-diffusion-coefficients of binary fluid mixtures can be predicted. The total average relative deviation of predicted values with respect to experimental data is 6.0% for 45 binary systems including those containing associative component. Results indicate that this model is superior to some currently used methods.

Modeling Swelling Behavior of Thermoresponsive Polymer Brush with Lattice Density Functional Theory

A key problem in designing thermoresponsive polymer brushes on a solid surface is to find a relation between the targeted thermoresponsive properties and controllable conditions. Usually, a temperature-thickness curve showing the heating-induced swelling behavior of polymer brushes is chosen as the relation by either experimental or theoretical investigation. In this work, a lattice density functional theory (LDFT) developed previously is employed to investigate the temperature-thickness curves for five different types of polymer brushes, where the density profiles of polymer brushes calculated by LDFT are compared directly with simulation. It is found that the thermoresponsive behavior of a polymer brush can be characterized by the bulk phase behaviors of its corresponding polymer solution, including UCST, LCST, both UCST and LCST, closed LOOP and hourglass-shaped, which implies that the bulk phase diagram of polymer solutions can help us to find an appropriate polymer brush for a targeted thermoresponsive behavior. As an example, we show that the swelling behavior of a thermoresponsive polymer brush found in the experiment could be predicted by our LDFT results with the bulk phase diagram of real polymer solution only.

A lattice model for thermally-sensitive core-shell hydrogels

A lattice molecular thermodynamic model for describing the swelling behavior of thermally-sensitive core-shell hydrogels was developed by integrating a close-packed lattice model for mixing free energy and a Flory Gaussian chain model for the elastic free energy. The thermodynamic model is characterized with two parameters: the temperature-dependent exchange energy parameter ε and the Topology-dependent size parameter V(*). The input values of both parameters can be obtained by experimental results of pure polymer hydrogels. With the help of proposed model, swelling behaviors of two kinds of hydrogel systems were analyzed: one is a doubly thermally-sensitive core-shell hydrogels (with two LCSTs) and the other comprises a thermally-sensitive hydrogel shell with a hard internal core. We show that the calculated results are in good agreement with the experimental data.

Disclosing the distinct interfacial behaviors of structurally and configurationally diverse triazologlycolipids.

1- or 6-Triazologluco- and galactolipid derivatives bearing a lipid chain length of 16 carbons were efficiently constructed via click chemistry. The differentiation in their surface pressure-molecular area (π-A) isotherms first implies that these structurally and configurationally diverse amphiphiles adopt different distribution manner at air-water interfaces. The Langmuir-Blodgett (LB) films of the synthesized glycoconjugates on mica surface were subsequently prepared and visualized via atomic force microscopy (AFM), which exhibited diverse topographies and possess different contact angles with water. These data further suggest that the structural variation as well as epimeric identity of triazologlycolipids may result in their distinct interfacial behaviors at the air-solid interface. Furthermore, the addition of increasing amounts of 1-triazologalactolipid 2 to poly-diacetylene (PDA) was determined to impact the π-A isotherm of the latter, prompting us to further fabricate new colorimetrically detectable mixed-type vesicles containing triazologlycolipids for biochemical studies.

Lattice Monte Carlo simulation of polymer adsorption at an interface, 1. Monodisperse polymer

Competitive adsorption of polydisperse polymers at a solid-liquid interface is studied by Monte Carlo simulation (MC). The dynamic process of adsorption prior to equilibrium is traced. Changing fractionation is observed during the process of adsorption. Shorter chains are preferentially adsorbed due to the quick diffusion onto the interface at the beginning stage. However, the preadsorbed shorter chains are gradually displaced by the longer chains to enhance the stabilization of the system. At equilibrium, the distributions of total segment density and different adsorption configurations including trains, loops and tails are calculated. Segment fractions of polymers, both adsorbed and in solution, are also estimated. Comparisons with those predicted from Scheutjens-Fleer theory are further investigated. In contrast to monodisperse polymer adsorption, relatively large discrepancies are found between theoretical predictions and MC results in this mixed-polymer adsorption case.

Self-assembly nano-structure of type I collagen adsorbed on Gemini surfactant LB monolayers

The self-assembly nano-structures of type I collagen adsorbed on anionic Gemini surfactant LB monolayer were observed by using atomic force microscopy (AFM) images. It was found that the adsorption behavior and self-assembly structure of collagen could be controlled by the concentration of the collagen solution, adsorption interval and the properties of substrates. With the increase of the adsorption interval and concentration of collagen, the strands size of collagen changed. The self-assembly structures of collagen were also influenced by the interaction between collagen molecules and Gemini surfactant monolayer substrates. Finally, the adsorption behaviors of collagen molecules on cationic Gemini monolayer were compared with those on anionic Gemini monolayer.

Thermodynamic properties of aqueous solutions: Nonsymmetric sticky electrolytes with overlap between ions in the mean-spherical approximation

Based on a sticky-electrolyte model, the Ornstein–Zernike integral equation is solved for nonsymmetric electrolytes with stickiness between ions at various distances equal to or less than the collision diameter. The hypernetted chain or Percus–Yevick approximation is used for the closure inside the hard core, while the mean-spherical approximation for electrostatic interactions is used for the closure outside the hard core. Expressions for correlation functions and thermodynamic properties in term of the sticky parameters are derived. Numerical results are presented for various cases.