Swelling behavior of submicron gel particles

We prepared submicron Poly(N-isopropylacrylamide) gel particles. Their swelling behavior was investigated by a photon correlation spectroscopy (PCS) technique. The swelling behavior of submicron gel particles showed a continuous volume phase transition for various temperatures. We combined the extended Flory-Huggins model for mixing solvent and network with a modified Flory-Rehner theory for the elastic contribution. The proposed model agreed very well with swelling behaviors of both submicron gel particles and bulk gels. A continuous volume phase transition behavior of submicron gel particles was predicted successfully by the proposed model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 109–114, 1998     

Theory of volume phase transition of slide-ring gels

Volume phase transition is a phenomenon in which gels drastically swell or shrink with an infinitesimal change in the external environment. This behavior is well explained by the Flory–Rehner–Tanaka theory. However, some assumption in the theory breaks down in a slide-ring gel composed of grand canonical chains in which the segment number between cross-linking junctions can change. The stress–strain behavior of the slide-ring gel is in a qualitative agreement with the free junction model, in which the segment number changes to maximize the entropy under the condition that the total sum of the segment number is constant. However, the model cannot work well to isotropic swelling of the slide-ring gel. To describe the volume phase transition of the slide-ring gel, we propose a new theory based on the free junction model with the effects of dangling strands, uncross-linked cyclic molecules (free rings), and high elongation. As a result, it turns out that the exchange of segments between effective and dangling strands leads to the suppression of the volume phase transition in the highly cross-linked gel and the promotion in the loosely cross-linked one. The suppression and promotion of the volume phase transition became more obvious as free rings decreased.     

Reentrant swelling behavior of thermosensitive N-isopropylacrylamide nano-sized gel particles

The closed-loop phase diagram of poly N-isopropylacrylamide (PNIPA) in a water-N,N-dimethylformamide (DMF) system was measured by thermooptical analysis (TOA). The reentrant swelling behavior of N-isopropylacrylamide (NIPA) nano-sized gel particles in the water-DMF system was measured by using photon correlation spectroscopy (PCS) technique. Theoretically, a modified double lattice model (MDL) can be used to describe the closed-loop phase behavior of linear PNIPA in water-DMF systems. For crosslinked NIPA nano-sized gel particles in a water-DMF system, we combined MDL theory for the mixing contribution and Flory-Erman theory for the elastic contribution. Molecular interaction parameters obtained from the PNIPA solution were used to directly predict the swelling-ratio curves for the NIPA gel. Using our model, the calculated results were in good agreement with the experimental data using only one adjustable parameter.     

Gel permeation chromatography using controlled-porosity glass. I. Polyacrylamide–formamide solution

The process of characterizing polyacrylamide and its partially hydrolyzed materials by gel permeation chromatography was examined. The use of controlled-porosity glass and formamide as the stationary phase and the eluent, respectively, resulted in chromatographic behavior in accord with the hydrodynamic volume concept for polyacrylamide fractions. The addition of a salt (KCl) to the eluent was found to retard the elution of the hydrolyzed polyacrylamide.     

The effects of interaction energy on the volume phase transition of N-isopropylacrylamide-co-N-isopropylmethacrylamide nano-sized gel particles: Applicability of molecular simulation technique

We investigated the volume phase transition temperatures of N-isopropylmethacrylamide (NIPMA)-co-N-isopropylacrylamide (NIPA) gels with various mole ratios. Nanometer-sized NIPA-co-NIPMA gel particles were prepared by precipitation polymerization and their swelling behaviors were measured using photon correlation spectroscopy (PCS). After applying the interaction energies found using the molecular simulation technique, we predicted the swelling equilibria for the hydrogels in a water system. For studying cross-linked hydrogel particles in water, we have combined the modified double-lattice theory with Flory and Erman's theory of elasticity. To correct for the deviation of the volume transition temperature, we considered the additional energy parameter (?_h) between the cross-linker and solvent molecules. We used the corrected model to describe the swelling behavior of the hydrogel and the volume transition temperature. The corrected model was agreed well with their experimental data with no fitting parameters.     

Upper critical solution temperature-type thermosensitive hydrogel phase equilibrium of poly(2-hydroxyethyl methacrylate)/water/n-alkanol mixtures

We investigated the swelling behavior of upper critical solution temperature (UCST)-type nano-sized poly(2-hydroxyethylmethacrylate) (PHEMA) particle gel with n-propanol and n-butanol in the presence of water. Because PHEMA is a biocompatible hydrogel and is highly water absorptive, it is worthwhile to investigate the phase behavior between PHEMA and water. The swelling behavior of the cross-linked PHEMA particle gel and the phase miscibility of the linear PHEMA mixed with the n-alkanol/water solution were evaluated. Our experimental results showed that increasing the water fraction in the mixed solvent gradually reduces the swelling temperature. Moreover, the two phase region of the PHEMA/water/n-butanol mixture showed sudden expansion at ∼15 vol% water in the ternary diagram. In these systems, oriented interactions among each component exist, which strongly affect the chemical association. The modified double lattice (MDL) and Flory-Huggins (FH) models were employed to describe the swelling and phase behaviors of the given ternary systems. The MDL model matched our data much better than the FH model because it was able to correctly represent the oriented interactions from hydrogen bonding or other specific forces encountered in the systems. To demonstrate the model compatibility to UCST-type swelling behavior, we also examined other polymer solutions. Polyvinyl acetate (PVAc) gel/2-propanol was studied as an associating system and polystyrene (PS)/cyclohexane was evaluated as a non-associating system.     

Molecular thermodynamics approach on phase equilibria of dendritic polymer systems

We suggest a molecular thermodynamic framework to describe the phase behavior of dendritic polymer systems. The proposed model, which is based on the lattice cluster theory, contains correlations of molecular structure and specific interactions such as hydrogen bonding to the phase equilibria of branch-structured polymer systems. We examine liquid-liquid equilibria (LLE) of hyperbranched polymer solutions and vapor-liquid equilibria (VLE) of dendrimer solutions in the viewpoints of effects of a branched structure and specific interaction formations among endgroups of dendritic polymer and solvent molecules. We investigate VLE of dendrimer/solvent (Benzyl Ether Dendrimer/Toluene) systems by the combination of a new lattice-based model and atomistic simulation technique. The interaction energy parameters are obtained by the pairs method [Baschnagel et al., 1991] including Monte Carlo simulation with excluded volume constraint. In the pairs method [Baschnagel et al., 1991], we do not simulate the whole molecule as in molecular dynamics or molecular mechanics, but only monomer segments interacting with solvent molecules. The proposed model shows improvements in prediction for both phase equilibria (VLE and LLE) due to the branched structure and specific interaction due to endgroups at periphery of dendritic polymer molecule. Atomic simulation technique gives good result in prediction without fitting variables. Our results show that the specific interactions between the endgroup and the solvent molecule play an important role in phase behavior of the given systems.     

Kinetics and mechanisms of water sorption in hydrophobic,ionizable copolymer gels

The aqueous kinetic swelling properties of a class of cross-linked hydrophobic polyamine copolymer gels based on n-alkyl esters of methacrylic acid (nAMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been studied as a function of solution ionic composition (pH, ionic strength, and buffer content), gel composition, and temperature. Water uptake and swelling in these gels are driven by ionization of the DMA amine groups, which overcomes the hydrophobic tendency of these gels to exclude water in the unionized state. Sorption kinetics in initially glassy gel disks are generally biphasic, characterized by an initial phase of relatively slow water uptake followed by an accelerated phase during which significant volume expansion of the gel occurs. This sorption/swelling behavior strongly suggests a moving penetrant front mechanism. The initial rate of water sorption increases markedly as (1) solution pH decreases, (2) gel nAMA comonomer content decreases, (3) gel nAMA side-chain length decreases, and (4) temperature increases. Furthermore, the initial phase of sorption in initially glassy gels is generally non-Fickian and approaches zero-order behavior as (1) pH increases, (2) nAMA content increases, and (3) temperature decreases. In direct contrast, sorption in initially dry, rubbery gels is monophasic, but non-Fickian, and approaches zero-order behavior as temperature increases. This behavior is contrary to the Fickian sorption behavior normally observed in polymers above their glass transition temperatures. Finally, sorption kinetics critically depend upon the nature of the ions in solution: Kinetics are significantly faster in the presence of weak electrolytes than that of strong electrolytes. We discuss the importance of the rate of ion transport in determining the overall sorption kinetics and how sorption kinetics can be non-Fickian in rubbery gels. Also, we propose a mechanism for the observed enhanced kinetics in the presence of weak electrolytes.     

交联三维网络结构PINPAm的制备及其性能研究

聚N-异丙基丙烯酰胺(PINPAm)水凝胶是一种亲水但不溶于水,具有交联三维网络结构的高分子聚合物,具有一定条件下的溶胀/退溶胀行为,同时具有输送和渗透性、能量转换、吸附分离、生物相容性等功能。本文研究了用不同量的引发剂过硫酸铵(APS)对水凝胶形成的影响;反应温度分别为低温(低于5℃、20℃、30℃、40℃对水凝胶形成的影响。所制备的PNIPAm水凝胶分别测定了相转变温度(LCST)和凝胶溶胀率(SR)。结果表明引发剂量用量增多时水凝胶形成反应时间变短;反应温度升高水凝胶外观出现由无色透明凝胶→乳白半透明凝胶→乳白色凝胶→乳白色且无固定形态凝胶的变化。低温生成的水凝胶相转变温度(LCST)在33~34℃之间,水凝胶体积发生不连续收缩现象;交联剂N,N-亚甲基双丙烯酞胺(BIS)使用量越多溶胀率越小。     

PROTON / NICKEL(II) INTERD1FFUSION COEFFICIENTS ON STRONG ACID RESINS

ABSTRACT

Ion exchange kinetics between proton and nickel(II) ions on sulfonic acid cation resins, with polystyrene-divinylbenzene matrix, type gel and macroporous, in high concentration of the external solution was studied at 298 K using a potentiometric method. The ratio between the amount of ions in the resin and in the solution phase was kept smaller than 0.1. The integral interdiffusion coefficients were determined using the quasi-homogeneous resin phase kinetic models at infinite and finite solution volume. The results were compared and discussed in terms of their range of validity. The influence of the ionic composition of the ion exchanger and matrix nature (gel or macroporous) on the integral interdiffusion coefficients was investigated and discussed. The simpler infinite solution volume kinetic model gives higher values for the integral interdiffusion coefficients than the Paterson's finite solution volume model. The numerical values of the integral interdiffusion coefficients are greater for gel than for macroporous type resin up to     

Volume changes and relaxations within the interphase domain of blendlike polymer particles

The behavior of volume changes upon solvent swelling and annealing was studied within the interphase domain of poly(methyl methacrylate) (PMMA) Particles sterically stabilized with polyisobutylene (PIB). Transient fluorescence technique was applied on these micronsized particles labeled in the PMMA phase with naphthalene (N) groups. Mean decay times 〈τ〉, obtained from fluorescence decay measurements, were used to examine volume changes within the PMMA–PIB interphase domain. The mathematical model proposed by Inokuti–Hirayama for the quenching of lifetimes was employed to quantify the individual volume changes and relaxations at this particular domain. © 1995 John Wiley & Sons, Inc.     

Reentrant phase transition of poly(N‐isopropylacrylamide) gels in polymer solutions: Thermodynamic analysis

The swelling behavior of poly(N‐isopropylacrylamide) (PNIPA) gels in polymer solutions, particularly in aqueous solutions of poly(ethylene glycol)s, was investigated using the theory of equilibrium swelling. The volume of the PNIPA gel and the partition parameter of the macromolecules between the gel and the solution phases were calculated for various extents of the energetic interactions between the components. The simulation results were compared with the experimental data reported in the literature. It was shown that the PNIPA gel has a tendency to a reentrant phase transition in an aqueous solution of low molecular weight linear polymers. In such a transition, the gel first collapses, then reswells, if the linear polymer concentration is continuously varied. The necessary condition for the reentrant behavior of PNIPA gels was predicted in terms of the interaction parameters among the PNIPA network, the linear polymer, and water. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 801– 813, 2002     

AN IMPROVED MODEL FOR THE INTERFACIAL BEHAVIOR OF CAUSTIC/CRUDE OIL SYSTEMS

The effects of crude oil acid number and brine concentration on the interfacial behavior of caustic/crude oil systems were investigated. The effect of increased brine concentration was generally to increase the minimum interfacial tension (IFT) while low IFT values were retained for longer periods of time. Varying the crude oil acid number caused the shape of the IFT versus time curve to change, while the minimum IFT remained constant. These combined results imply that Lagmuir and not Henry soption (adsorption/desorption) kinetics were operative

A phenomenological surface phase model for the IFT behavior of caustic/crude oil systems is proposed which incorporates Langmuir kinetics. The model takes into account interfacial activities of the acidic components in the crude and the detailed chemistry of the oil phase, the water phase, and the interface. To allow for realistic comparison of model results with interfacial tensiometer data, drastic interfacial volume changes which accompany the transient interfacial tensions in the system are taken into account.     

Contributions to the thermodynamics of polymer hydrogel systems

In this work, an extended version of a quasichemical thermodynamic model is presented. The swelling behavior of crosslinked acrylamide polymer gels and N-substituted derivatives, such as N-isopropylacrylamide and N-tert-butylacrylamide has been compared to predictions from such model which takes into account the specific hydrogen bonding interactions encountered in these systems. The calculated volume transition temperature of the poly(N-isopropylacrylamide) gel is 0.8 °C lower than the experimental value and the predicted solvent volume fraction in the collapsed and swollen gel states are about 2% larger than the corresponding experimental data measured at the transition point. Applying the same energy parameters obtained from regressing poly(N-isopropylacrylamide) gel swelling pressure data, the model has also been capable to correctly represent the major features found in the swelling behavior of linear poly(N-tert-butylacrylamide) and poly(N-tert-butylacrylamide) gels, after the model parameters that characterize the molecular structure were changed in accord to each polymer repetitive unit.     

紫杉醇吸附制备动力学研究

通过考察C18 硅胶吸附分离中液固两相间的物质传递 ,建立了紫杉醇在该吸附柱上分离的速率模型 ,并用有限元方法对模型进行了求解 ,模型计算值与实验值吻合良好。研究体积超载和浓度超载两种方式对紫杉醇吸附分离过程的影响说明 ,在紫杉醇的C18 硅胶吸附制备中 ,浓度超载优于体积超载     

聚合物-溶剂体系中溶剂的活度模型

引言 GE模型与溶液的活度因子等紧密相联,在计算流体相平衡中具有重要地位.经过以van Laar、Margules方程与Wilson、NRTL关联式以及UNIQUAC和UNIFAC模型为代表的三个阶段的发展,预测准确度已达到实验误差范围,能较好地关联多组分体系的汽液平衡,在电解质溶液、高分子溶液及高度非理想体系中结果亦较满意.     

On the presence of a critical shell volume fraction leading to pseudo-pure droplet behavior in composite droplet polymer blends

During melt mixing a ternary blend system comprised of a high density polyethylene matrix containing dispersed polystyrene and poly(methyl-methacrylate) spontaneously forms a composite droplet structure where the PS encapsulates the PMMA. This study demonstrates that the PS/PMMA composite droplet exhibits pure PS droplet behavior at a critical volume fraction of encapsulating phase (PS:PMMA∼0.6:0.4). This critical volume fraction is shown to be independent of the overall dispersed phase concentration, shell thickness or dispersed phase size. Furthermore, the effect is observed even though the PMMA is significantly more viscous than the encapsulating PS phase. Interfacial slip as well as the maintenance of a complete PS shell during deformation are proposed as being important factors related to this behavior. The blends were prepared via melt mixing using an internal mixer and the morphology was examined by electron microscopy.     

Volume phase transition in poly(N‐isopropylacrylamide) gels in seawater at high pressures

The swelling behavior of poly(N‐isopropylacrylamide) (PNIPA) gels in seawater at high pressures up to ～40 MPa is examined in terms of human activity at deep sea. The neutral gel in seawater undergoes a continuous volume transition at 26°C at atmospheric pressure. Addition of the ionic group (sodium acrylate) does not have much effect on the swelling properties of the gels in seawater except that the transition temperature is somewhat increased. At high constant pressures up to ～40 MPa, the gels undergo a continuous volume transition at 26–28°C as the temperature varies. Normally, the gel takes a swollen state at deep sea. The ratio of the volume change associated with the transition is more than 10, which is 3 times larger than that obtained by changing the pressure at a constant temperature. The results suggest a possibility that the phase transition of PNIPA gels is utilized for producing mechanochemical energy at deep sea. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1069–1072, 2005     

Rheology and morphology of polyester/thermoplastic flour blends

Two maize flours (standard and waxy grades) were plasticized in an internal mixer with a constant amount of water and two glycerol contents. The resulting thermoplastic flours (TPFs) were characterized in dynamic oscillatory shear and creep/recovery rheometry. They displayed two different behaviors: the viscoelastic behavior of a high‐molecular‐weight polymer for the first one and a gel‐like behavior for the second one. The TPFs were then mixed with a copolyester [poly(butylene adipate–terephtalate)]. All of the blends contained the same volume fractions and were prepared with the same mixing conditions. The morphology and rheological behavior of each blend were characterized. Different morphologies, ranging from cocontinuous to nodular, were observed. In fixed mixing conditions, the blend morphology was shown to be governed by the rheological behavior of the starchy phase and the plasticizer content. The gel‐like behavior of the second TPF seemed to prevent droplet coalescence; this led to a very fine dispersion. The rheological behavior of each blend appeared to be linked to both the morphology and the rheological behavior of the two phases. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40222.