Carboxylated core–shell particles: I. A system showing hindered swelling behavior

We study the swelling behavior of carboxylated core–shell particles. It is well-known that these particles swell with increasing pH due to the electrostatic repulsion between carboxylate groups. Our results reveal that the swelling behavior is affected by the preparation method. We find that the swelling is promoted in those particles which were initially in a highly swollen state (pH  10). However, the swelling is hindered for those particles which were not previously in this trigger pH. In the hindered systems, a compact conformation of the polymer shell is induced by hydrophobic attractions between the non-charged segments which compete against the swelling driving force. In addition, an interesting hysteresis behavior emerges when promoted systems are subjected to a heating–cooling cycle; a new stable system appears with a less extended polymer shell conformation. Furthermore, salt-induced swelling experiments corroborate not only polymer restructuring but also assembly among carboxylate groups which affects their ionization grade.     

Characterisation of core-shell latexes by flow field-flow fractionation with multi-angle light scattering detection

Flat channel asymmetrical flow field-flow fractionation with multi-angle light scattering (MALS) detection was used to study the swelling behaviour of core-shell particles with either carboxylated or hydroxylated shells as a function of pH and ionic strength. The equilibration time of the most heavily carboxylated core-shells appeared to be of the order of several hours. At low ionic strength (5 mM), the carboxylated core-shells showed a definite swelling response to a change in pH in the range from 5 to 10, ranging from a hydrodynamic radius increase of 24 to 118%, depending on the degree of carboxylation. A much milder response was found for the change of the root mean square (r.m.s.) radius as measured with MALS, indicating that the scattering plane is moving inwards during the swelling process due to a decreasing density of the shell. The hydroxylated core-shells appeared to be inert to a change in pH. Also the response of two expanded (pH 10) carboxylated core-shells on increasing ionic strength was studied. Comparison of the results of these ionic strength experiments with theoretical predictions based on Donnan equilibrium led us to the conclusion that a significant amount of counter-ion condensation may take place in the shells.     

Surface plasmon spectroscopy of gold-poly-N-isopropylacrylamide core-shell particles

Highly uniform, core-shell microgels consisting of single gold nanoparticle cores and cross-linked poly-N-isopropylacrylamide (PNIPAM) shells were prepared by a novel, versatile protocol. The synthetic pathway allows control over the polymer shell thickness and its swelling behavior. The core-shell structure was investigated by electron microscopy and atomic force microscopy, whereas the swelling behavior of the shell was studied by means of dynamic light scattering and UV-vis spectroscopy. Furthermore, the latter method was used to investigate the optical properties of the hybrid particles. By modeling the scattering contribution from the PNIPAM shells, the absorption spectra of the gold nanoparticle cores could be recovered. This allows the particle concentration to be determined, and this in turn permits the calculation of the molar mass of the hybrid particles as well as the refractive index of the shells.     

Rheological Modeling of Dispersion System of Nano/Microsized Polymer Particles Considering Swelling Behavior

Rheological behavior of dispersion system containing nano/microsized cross-linked polymer particle was studied considering particle hydration and swelling. Viscosity of the dispersion system depends on swelling kinetics of polymer particles. Under shear flow, dispersion of swollen polymer particles is shear thinning. According to experimental results, kinetics of particle swelling and hydration was described well by second-order kinetic equation. Relational expression between equilibrium particle size and influencing factors of swelling such as salt concentration and temperature was presented. Assume that swollen polymer particles are uniform and have a simple core-shell structure, interacting through a repulsive steric potential. The rheological modeling of such dispersion system at low shear rate was presented using the concept of effective volume fraction, which depends on swelling kinetics and interparticle potential. Cross model was introduced to describe shear-thinning behavior. The viscosity equation allows correlation of experimental data of relative viscosity versus shear rate or hydration time; accounting for effect of temperature and salt concentration on viscosity. Predictions of the model have a good agreement with experimental results.     

Influence of the surface chemistry on the structural and mechanical properties of silica‐polymer composites

Poly(vinyl alcohol) (PVA) composite films filled with nanometric, monodisperse, and spherical silica particles were prepared by the mixing of an aqueous PVA solution and SiO₂ colloidal suspension and the evaporation of the solvent. Adjusting the solution pH to 5 and 9 controlled the PVA‐SiO₂ interaction. Adsorption isotherms showed a higher PVA/surface affinity at a lower pH. This interaction influenced the composite structure and the particle distribution within the polymer matrix, which was investigated by small‐angle neutron scattering, electron microscopy, and swelling measurements. Most of the mechanical properties could be related to the composite structure, that is, the distribution of clusters within the polymer matrix. The progressive creation of a cluster network within the polymeric matrix as the silica volume fraction increased reduced the extensibility or swelling capacity of the composite. The effect was more acute at a higher pH, at which the surface interaction with PVA was weaker and promoted the interconnection between clusters. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3127–3138, 2003     

Submicron Sized Hollow Polymer Particles: Preparation and Properties

The considered method for obtaining hollow polymer particles is based on the following pathway: (1) preparation of a carboxylated core latex by emulsion copolymerization of acrylic monomers with methacrylic acid, (2) synthesis of a core-shell latex comprising a styrene (co)polymer shell, (3) neutralization of the core carboxylic groups with a base followed by the core ionization and hydration to a high degree, shell expansion and formation of water-filled hollows. A number of approaches to improve the hydrophilic core – hydrophobic shell compatibility and enlarge the hollow volume are considered. The synthesized hollow particles are of a submicron size with the relative hollow volume V_hol : V_part.= 0.43 – 0.64. Methods for cationic hollow particle latex preparation by anionic latex recharging with a cationic surfactant or acidic melamine resin are discussed. Recharging with a melamine resin is shown to afford hollow particles with an external polymer shell providing a high thermal stability of the particles.     

PNIPAM-co-polystyrene core-shell microgels: structure, swelling behavior, and crystallization

The present contribution presents the single-step preparation and characterization of poly(N-isopropyl acrylamide)-co-polystyrene core-shell microgels with varying polystyrene content. The swelling behavior of the particles is investigated using dynamic light scattering and differs significantly from the swelling behavior of poly(N-isopropyl acrylamide) homopolymer particles. The lower critical solution temperature is found to be shifted to lower temperatures upon increasing the polystyrene content of the particles. The core-shell structure of the particles is revealed by means of small angle neutron scattering (SANS) using the method of contrast variation. Additionally, the formation of mesoscopic crystals of these particles is investigated by means of scanning electron microscopy and also by SANS. The particles seem to have preferable properties with respect to crystallization compared to homopolymer microgels.     

Synthesis and swelling behavior of pH-responsive polybase brushes

We synthesize polybase brushes and investigate their swelling behavior. Poly(2-(dimethylamino)ethyl methacrylate)) (PDMAEMA) brushes are prepared by the "grafting from" method using surface-initiated Atom Transfer Radical Polymerization to obtain dense brushes with relatively monodisperse chains (PDI = 1.35). In situ quaternization reaction can be performed to obtain poly(2-(trimethylamino)ethyl methacrylate)) (PTMAEMA) brushes. We determine the swollen thickness of the brushes using ellipsometry and neutron reflectivity techniques. Brushes are submitted to different solvent conditions to be investigated as neutral brushes and weak and strong polyelectrolyte brushes. The swelling of the brushes is systematically compared to scaling models. It should be pointed out that the scaling analysis of different types of brushes (neutral polymer and weak and strong polyelectrolyte brushes) is performed with identical samples. The scaling behavior of the PDMAEMA brush in methanol and the PTMAEMA brush in water is in good agreement with the predicted scaling laws for a neutral polymer brush in a good solvent and a polyelectrolyte brush in the osmotic regime. The salt-induced contraction of the quaternized brush is observed for high salt concentration, in agreement with the predicted transition between the regimes of the osmotic brush and the salted brush. From the crossover concentration, we calculate the effective charge ratio of the brush following the Manning counterion condensation. We also use PDMAEMA brushes as pH-responsive polybase brushes. The swelling behavior of the polybase brush is intermediate with respect to the behavior of the neutral polymer brush in a good solvent and the behavior of the quenched polyelectrolyte brush, as expected. The effective charge ratio of the PDMAEMA brush is determined as a function of pH using the scaling law of the polyelectrolyte brush in the osmotic regime.     

Estimation of water absorption state within ionized carboxylated polymer particles with high sensitive differential scanning calorimetry

Glass transition temperature (Tg) of submicron-sized, carboxylated polymer particles dispersed in aqueous media, which were prepared by emulsion copolymerization of styrene, iso-butyl methacrylate, or methyl methacrylate with methacrylic acid, was measured at alkali or acidic pH region with a power compensation-type high sensitive differential scanning calorimeter. The Tg of relatively hydrophilic polymer particles was obviously decreased by the neutralization of the carboxyl groups with KOH, whereas that of hydrophobic polymer particles was not changed though water was absorbed therein. These results indicate that water absorption state, which means not only the amount of water absorption but also the heterogeneity of the ionized carboxylated polymer particles, markedly depends on the hydrophilicity of their base polymers. This strongly supports the formation mechanism of multihollow particles by the stepwise alkali/acid or the alkali/cooling treatments of carboxylated polymer particles proposed by the authors.Part CCLXIX of the series, “Studies on Suspension and Emulsion.”     

核-壳结构微球的制备进展

综述了近年来核-壳结构微球制备方面的研究进展,介绍了高分子胶束交联、模板逐层组装、模板微球表面原位引发聚合、动态溶胀法、种子聚合法以及溶胶-凝胶法等主要制备方法,并对各种方法所涉及的核-壳微球形成机理进行了必要阐述.     

Dynamics of shear-thinning suspensions of core-shell structured latex particles

The rheological behavior and microstructure of shear-thinning suspensions of core-shell structured carboxylated latex particles were examined. The steady shear viscosity of the suspension increased with increasing dissociation of the carboxyl groups or increasing particle concentration, however the critical shear stress sigma(c) and inter-particle distance xi of the microstructure did not change. With increasing particle diameter, sigma(c) increased and xi decreased. These results were consistent with a Brownian hard sphere model, in which competition exists between the bulk mass transfer due to the applied field and diffusion of the particles. We confirmed that sigma(c) depends on xi, as expressed by sigma(c) = 3kT/4pi xi3. This relationship is consistent with the dynamics of a Brownian hard sphere model with particle diameter xi. Thus the dynamics of shear-thinning suspensions of core-shell particles can be explained by a Brownian thermodynamic model.     

Polymer–polymer interactions via analog calorimetry. 2. Blends of polystyrene with bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Analog calorimetry is used as a tool to study the interaction of polystyrene, PS, with bisphenol-A polycarbonate, PC, and with tetramethyl bisphenol-A polycarbonate, TMPC. Electrostatic charge calculations were used as a guide to divide polymer repeat units and analogs into groups. A mean-field binary interaction model was used to evaluate group interaction energies. The enthalpic interaction energy obtained from this study for the PS-PC pair is 0.41 ± 0.13 cal/cm³ while that for the PS-TMPC pair is 0.19 ± 0.34 cal/cm³. The result for PS-PC blends is in good agreement with values obtained from studies using the critical molecular weight approach and the phase behavior of copolymer blends. The value for PS-TMPC does not correctly predict the phase behavior of this blend; however, its standard deviation (on both an absolute and relative basis) is large and the range of possible interaction energies includes the negative values obtained from neutron scattering. The results of this study indicate that the presence of methyl groups on the aromatic ring of TMPC repeat unit is the main factor favoring the miscibility of PS-TMPC blends. © 1997 John Wiley & Sons, Inc.     

Production of multi-hollow polymer particles by the stepwise acid/alkali method

 Recently, we reported that multi-hollow polymer particles can be prepared from carboxylated polymer particles by the stepwise alkali/acid method. In this article, an attempt was made to prepare similar particles from acid-swellable polymer particles by the stepwise treatment with acid and alkali, which was named the stepwise acid/alkali method. The acid-swellable particles were produced by emulsion terpolymerization of styrene, butyl acrylate, and dimethyl 2-amino ethyl methacrylate. The effects of initial pH value, temperature, and time in the acid and alkali treatment processes on the multi-hollow structure were examined. Received: 18 December 1996 Accepted: 11 March 1997     

微凝胶增强两性复合水凝胶的制备与性能

将核壳微凝胶包埋在两性基质中,制备了复合水凝胶(CAH)。 研究发现,利用微凝胶与聚合物链之间的物理缠结作用,可以使复合凝胶具有致密的网络结构,力学性能显著提高;复合凝胶对pH和离子强度敏感,呈现出典型的两性聚电解质凝胶的溶胀行为。 同时微凝胶的存在和特殊的复合结构,可赋予CAH两性凝胶基质所不具有的响应性,并实现在高温下快速响应。     

Influence of conducting polymers based on carboxylated polyaniline on in vitro CaCO3 crystallization

Conducting polymers are interesting materials of technological applications, while the use of polymers as additives controlling crystal nucleation and growth is a fast growing research field. In the present article, we make a first step in combining both topics and report the effect of conducting polymer derivatives, which are based on carboxylated polyanilines (c-PANIs), on in vitro CaCO3 crystallization by the Kitano and gas diffusion method. This is the first example of the mineralization control of CaCO3 by a rigid carboxylated polymer. Both the concentration of c-PANI and the presence of carboxylate groups have a strong influence on the CaCO3 crystallization behavior and crystal morphology. X-ray diffraction (XRD) analysis shows crystalline calcite particles confirmed by FTIR spectra. pH and Ca2+ measurements during CaCO3 crystallization utilizing the Kitano and a constant-pH approach show a defined nucleation period of CaCO3 particles. The measurements allow for the calculation of the supersaturation time development, and the kinetic data can be combined with time-dependent light microscopy. The presence of c-PANIs delays the time of nucleation indicative of calcite nucleation inhibition. Microscopy illustrates the morphologies of CaCO3 crystals at all crystallization stages, from homogeneous spherical amorphous CaCO3 (ACC) particles corresponding to the first steps of crystallization to transition stage calcite crystals also involving a dissolution-recrystallization process in a late stage of crystallization. The data show that it is not possible to conclude the crystallization mechanism even for a very simple additive controlled crystallization process without time-resolved microscopic data supplemented by the analysis of the species present in the solution. Finally, fluorescence analysis indicates that conducting polymer derivatives can be incorporated into precipitated calcite particles. This gives rise to CaCO3 particles with novel and interesting optical properties.     

Mononuclear rearrangement of heterocycles in zwitterionic micelles of amine oxide surfactants

The pH-induced swelling of poly(2-vinylpyridine) microgel particles was studied using dynamic light scattering. The increase in particle diameter with decreasing pH was modeled using a well-established thermodynamic model for microgel swelling. The Maxwell construction was applied to extend the model and yield a prediction for a pH-responsive microgel across the entire pH range. The model predicts a first order phase transition for polymer-solvent combinations with a Flory interaction parameter, χ, greater than a critical value χ(c). The modified theory compared favorably to the dynamic light scattering data for the hydrodynamic diameter of microgel particles based on 2-vinylpyridine at different pH values. In particular, the swelling transition is both predicted theoretically and observed experimentally to occur at a pH lower than the pK(a) of the polymer.     

Emulsifier-free emulsion copolymerization of styrene with methacrylic acid as a method of preparing building blocks for photonic crystals

Monodisperse polymer particles with diameters from 230 to 420 nm have been synthesized by the emulsifier-free emulsion copolymerization of styrene with methacrylic acid. It has been shown that an initiator, chain regulators, comonomer ratio, and pH of a medium influence the dispersity of latexes, the distribution of carboxyl groups in polymer particles, as well as their swelling behavior and electrophoretic mobility. These characteristics of polymer particles are substantial for designing perfect lattices of three-dimensional photonic crystals on their basis.     

Effects of high-concentration salt solutions and pH on swelling behavior of physically and chemically cross-linked hybrid hydrophobic association hydrogels with good mechanical strength

New physically and chemically cross-linked hybrid hydrophobic association hydrogels (Hybrid HA-gels) were prepared by radical copolymerization. The effect of salinity on the swelling behavior of Hybrid HA-gels was studied. Hybrid HA-gels, like ampholytic hydrogels, displayed antipolyelectrolyte behavior in high-concentration NaCl and MgCl₂ solutions. According to the analysis of experimental data, the antipolyeletrolyte behavior of Hybrid HA-gels should be attributed to the rapid hydrolysis of amide groups on polymer, and the hydrolysis reaction can be promoted by high concentrations of salt solutions. Also, the results of swelling tests verified also the reversibility of complexing action of Ca²⁺ with carboxylate groups within the Hybrid HA-gels. In addition, the effect of pH values on the swelling behavior of the Hybrid HA-gels was also studied in detail.     

Swelling of ultrathin crosslinked polyamide water desalination membranes

We study the water swelling behavior of semiaromatic crosslinked polyamide (PA) ultrathin films to characterize the network properties of the polymer. Specifically, we use X-ray reflectivity to measure film thickness increase and polymer density decrease of the PA films due to swelling. With the aid of a modified Flory–Rehner theory used to describe the constrained swelling behavior of polymer networks, we are able to extract the Flory interaction parameter and the monomer units between crosslinks by performing the swelling experiments at different levels of hydration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Syntheses of N,N′-Bis(salicylideneiminoethyl)oxamidatodicopper(II), N,N′-Bis(salicylideneiminoisopropyl)-oxamidatodicopper(II), and N,N′-Bis(2-pyridylideneiminopropyl)oxamidatodicopper(II) Nitrate and Corresponding Perchlorate

Reactions of coordinated functional groups were carried out as follows: The product formed by reaction of A-1a

1 The four new complexes are shown as A-3a, A-3b, B-3a, and B-3b (cf. Fig. 1), and other related complexes are shown as A-1a, A-1b, A-2a, A-2b, B-n, B-1, B-4, and B-5 (cf. Fig. 2)

or A-1b with copper(II), reacts with salicylaldehyde to give A-3a or A-3b, respectively. And the product formed by reaction of B-1 with copper(II), reacts with pyridine-2-aldehyde to give B-3a or B-3b. The four binuclear copper(II) complexes thus isolated as the new compounds have been characterized by elemental analyses, u.v. and i.r. spectra, magnetic susceptibility, and electronic conductivity measurements. Attempts to exchange the reactants with one another were unsuccessful.