Synthesis and characterization of silica/poly (methyl methacrylate) nanocomposite latex particles through emulsion polymerization using a cationic azo initiator

Following a previous work (J. L. Luna-Xavier et al., Colloid Polym. Sci.279, 947 (2001)), silica-poly (methyl methacrylate) (PMMA) nanocomposite latex particles have been synthesized in emulsion polymerization using a cationic initiator, 2,2'-azobis (isobutyramidine) dihydrochloride (AIBA), and a nonionic polyoxyethylenic surfactant (NP30). Silica beads with diameters of 68, 230, and 340 nm, respectively, were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core-shell morphology, depending on the size and nature of the silica beads. The amount of surface polymer was quantified by means of ultracentrifugation and thermogravimetric analysis as extensively described in the first article of the series (see above reference). The influence of some determinant parameters such as the pH of the suspension, the initiator, silica, monomer, or surfactant concentration on the amount of coating polymer and on the efficiency of the coating reaction was investigated in details and discussed in light of the physicochemical properties of the seed mineral. Electrostatic attraction between the positive end groups of the macromolecules and the inorganic surface proved to be the driving force of the polymer assembly on the seed surface at high pH, while polymerization in adsorbed surfactant bilayers (so-called admicellar polymerization) appeared to be the predominant mechanism of coating at lower pH. Optimal conditions have been found to reach high encapsulation efficiencies and to obtain a regular polymer layer around silica.     

Initiation mechanism of ultrasonically irradiated emulsion polymerization

The emulsion polymerization of some monomers can occur without the conventional free radical initiators under ultrasonic irradiation. However, the initiation mechanism is still under controversy. In this paper, the sources of free radicals arising from ultrasonically initiated emulsion polymerization were investigated. Experimental results show that ionic surfactants play a very important role in obtaining a high polymer yield. While monomer conversion is very low in the absence of surfactants or in the presence of nonionic surfactants, it increases significantly upon addition of a little amount of ionic surfactant. FTIR and a radical trapping experiment confirm that the free radicals involved in the irradiation process originate from the decomposition of the ionic surfactants. Under ultrasonic irradiation, ionic surfactants undergo bond scission between the alkyl and ionic group, where the bond is the weakest along the chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2617–2624, 2005     

Controlled,radical reversible addition–fragmentation chain‐transfer polymerization in high‐surfactant‐concentration ionic miniemulsions

Living free‐radical polymerization of methacrylate and styrenic monomers with ionic surfactants was carried out with reversible addition–fragmentation chain transfer in miniemulsion with different surfactant types and concentrations. The previously reported problem of phase separation was found to be insignificant at higher surfactant concentrations, and control of the molar mass and polydispersity index was superior to that of published miniemulsion systems. Cationic and anionic surfactants were used to examine the validity of the argument that ionic surfactants interfere with transfer agents. Ionic surfactants were suitable for miniemulsion polymerization under certain conditions. The colloidal stability of the miniemulsions was consistent with the predictions of a specific model. The living character of the polymer that comprised the latex material was shown by its transformation into block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 960–974, 2004     

Polymer/surfactant interactions at the air/water interface

The development of neutron reflectometry has transformed the study and understanding of polymer/surfactant mixtures at the air/water interface. A critical assessment of the results from this technique is made by comparing them with the information available from other techniques used to investigate adsorption at this interface. In the last few years, detailed information about the structure and composition of adsorbed layers has been obtained for a wide range of polymer/surfactant mixtures, including neutral polymers and synthetic and naturally occurring polyelectrolytes, with single surfactants or mixtures of surfactants. The use of neutron reflectometry together with surface tensiometry, has allowed the surface behaviour of these mixtures to be related directly to the bulk phase behaviour. We review the broad range of systems that have been studied, from neutral polymers with ionic surfactants to oppositely charged polyelectrolyte/ionic surfactant mixtures. A particular emphasis is placed upon the rich pattern of adsorption behaviour that is seen in oppositely charged polyelectrolyte/surfactant mixtures, much of which had not been reported previously. The strong surface interactions resulting from the electrostatic attractions in these systems have a very pronounced effect on both the surface tension behaviour and on adsorbed layers consisting of polymer/surfactant complexes, often giving rise to significant surface ordering.     

Adsorption of different amphiphilic molecules onto polystyrene latices

In order to know the influence of the surface characteristics and the chain properties on the adsorption of amphiphilic molecules onto polystyrene latex, a set of experiments to study the adsorption of ionic surfactants, nonionic surfactants and an amphiphilic synthetic peptide on different latex dispersions was performed. The adsorbed amount versus the equilibrium surfactant concentration was determined. The main adsorption mechanism was the hydrophobic attraction between the nonpolar tail of the molecule and the hydrophobic regions of the latex surface. This attraction overcame the electrostatic repulsion between chains and latex surface with identical charge sign. However, the electrostatic interactions chain-surface and chain-chain also played a role. General patterns for the adsorption of ionic chains on charged latex surfaces could be established. Regarding the shape, the isotherms presented different plateaus corresponding to electrostatic effects and conformational changes. The surfactant size also affects the adsorption results: the higher the hydrophilic moiety in the surfactant molecule the lower the adsorbed amount.     

N-异丙基丙烯酰胺对细乳液聚合制备纳米胶囊形态的影响

将N-异丙基丙烯酰胺(NIPAAm)引入小分子烃为模板的苯乙烯细乳液聚合法制备纳米胶囊的体系.水相引发形成的聚异丙基丙烯酰胺(PNIPAAm)低聚物自由基在聚合温度下(大于其最低临界溶解温度)析出并被苯乙烯细乳液液滴吸附,在热力学推动力和静电斥力的共同作用下,PNIPAAm低聚物倾向于分布在液滴和水的界面上,使液滴界面成为主要的聚合场所,单体从液滴内部向界面扩散补充消耗的单体,生成的聚合物在液滴界面上析出,包覆小分子烃液滴,最终得到纳米胶囊.通过透射电镜观察粒子形态和大小;利用接触角测定仪测定了细乳液液滴的表面张力.考察了NIPAAm用量、油溶性单体/小分子烃比例、交联剂用量及乳化剂和引发剂对的种类对胶囊形态的影响.     

Fabrication of carbon microcapsules containing silicon nanoparticles for anode in lithium ion battery

Carbon microcapsules containing silicon (Si) nanoparticles (NPs) were prepared from silicon-embedded polymer microspheres. The precursors, polymeric microspheres containing silicon nanoparticles were fabricated by a facile emulsion polymerization with surfactants, sodium dodecyl sulfate and dodecyltrimethylammonium bromide. The effects of monomer, surfactant concentration, and ionic character of surfactant on the formation of microspheres were demonstrated. The successful fabrication of polystyrene/polydivinylbenzene microspheres with Si NPs was confirmed by scanning electron microscopy. Subsequent thermal treatment produced carbon microcapsules having Si NPs. Volume shrinkage of polymer spheres during carbonization step resulting in the formation of internal free spaces in carbon microcapsules is the critical process in this experiment, which can accommodate volume changes of Si NPs during Li ion charge/discharge processes. The successful encapsulation of Si NPs with exterior carbon shell was clearly shown by transmission electron microscopy and X-ray diffraction. The change in size distribution and structure of polymer and carbon microspheres was also revealed. The cyclic performances of these Si@C microcapsules were measured with lithium battery half cell tests.     

The effect of surfactants on the pH transition interval of bromothymol blue immobilized on XAD 4

Cationic, anionic and non-ionic surfactants adsorb readily from aqueous solution on to Amberlite XAD 4. The ionic surfactants cause the pH of the solution in contact with the resin to differ from that in the bulk of solution, cationic surfactants increasing the interfacial pH and anionic surfactants decreasing it. This causes a shift in the pH transition interval of a co-adsorbed pH indicator when measured with respect to the bulk solution. The quantity of ionic surfactant adsorbed tends to a constant value (presumably monolayer coverage) with increasing solution concentration, this amount being a function of the individual surfactant, whereas non-ionic surfactants readily form multilayers. Significant adsorption occurs when the surfactant possesses at least 14 carbon atoms.     

Uniform encapsulation of fine inorganic powder with soapless emulsion polymerization

The encapsulation of inorganic powder of submicron sizes was attempted with soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder. The powders used were barium sulfate and calcium carbonate. The polymerizations were initiated by potassium persulfate and by sodium bisulfite-oxygen redox reaction. The encapsulation state of the powder with the polymer formed varied considerably with the initiators used. With potassium persulfate initiator the powder surface was partially or totally covered by polymer particles, while with redox initiator under air atmosphere the powder surface was well encapsulated with a film-like polymer layer. From the differences in the encapsulation states, an encapsulation mechanism is suggested for each initiator system. Based upon this mechanism, a new encapsulation process capable of covering uniformly fine powders with a film polymer is proposed. An important factor in the new process is the addition of an extremely small quantity of a surfactant into the reaction system prior to the polymerization.     

Surfactant fouling of nanofiltration membranes: measurements and mechanisms.

Fouling of nanofiltration membranes is studied during filtration of aqueous surfactant solutions under different conditions. To this purpose, four typical nanofiltration membranes (Desal51HL, NF270, NTR7450 and NFPES10) and three typical surfactants (nonionic neodol, anionic SDBS and cationic cetrimide) are selected. Fouling is studied as a function of the surfactant concentration, with and without addition of an electrolyte (NaCl), at different pH and when filtering a mixture of surfactants. Adsorption experiments and hydrophobicity measurements (to study the orientation of the surfactants on the membrane surface) are also performed under the different conditions. The least membrane fouling is found for the anionic surfactant SDBS, while for the cationic surfactant cetrimide very low relative fluxes are observed. Neodol shows an intermediate degree of fouling. Both hydrophobic and electrostatic interactions (in the case of ionic surfactants) between the membrane surface and the surfactant explain the degree of adsorption and hence fouling, as membrane fouling is correlated with the amount of adsorbed surfactant. The difference between cetrimide and SDBS becomes especially visible when changing the pH: increasing the pH leads not only to an opposite orientation of the adsorbed surfactants, but also to an opposite trend in adsorbed amount and membrane fouling. This study permits selection of an optimal nanofiltration membrane to recycle wastewater containing surfactants in the carwash industry. The optimal choice would be a hydrophilic membrane with a low molecular weight cut-off and a small negative surface charge at neutral pH. Cationic surfactants in the wastewater should also be avoided as much as possible.     

Electrokinetic behavior and colloidal stability of polystyrene latex coated with ionic surfactants

This work is focused on analyzing the electrokinetic behavior and colloidal stability of latex dispersions having different amounts of adsorbed ionic surfactants. The effects of the surface charge sign and value, and the type of ionic surfactant were examined. The analysis of the electrophoretic mobility (mu(e)) versus the electrolyte concentration up to really high amounts of salt, much higher than in usual studies, supports the colloidal stability results. In addition, useful information to understand the adsorption isotherms was obtained by studying mu(e) versus the amount of the adsorbed surfactant. Aggregation studies were carried out using a low-angle light scattering technique. The critical coagulation concentrations (ccc) of the particles were obtained for different surfactant coverage. For latex particles covered by ionic surfactants, the electrostatic repulsion was, in general, the main contribution to the colloidal stability of the system; however, steric effects played an important role in some cases. For latices with not very high colloidal stability, the adsorption of ionic surfactants always improved the colloidal stability of the dispersion above certain coverage, independently of the sign of both, latex and surfactant charge. This was in agreement with higher mobility values. Several theoretical models have been applied to the electrophoretic mobility data in order to obtain different interfacial properties of the complexes (i.e., zeta potential and density charge of the surface charged layer).     

Body temperature-responsive gels derived from hydroxypropylcellulose bearing lignin II: adsorption and release behavior

The lower critical solution temperature (LCST) of hydroxypropylcellulose bearing lignin (HPC-L) prepared from unbleached pulp depends on the amount of residual lignin. An HPC-L gel having thermal properties reflective of original HPC-L was prepared using ethyleneglycol diglycidylether as a crosslinker, as previously reported [Uraki et al. (2004) Carbohydr. Polym. 58:123–130], and the volume transition temperature was detected as an endothermic peak by differential scanning calorimetry (DSC). The adsorption and release behavior of the guest molecules to/from this gel was then examined. When the adsorption of cationic and anionic guests was compared, cationic methylene blue (MB) was adsorbed in larger amounts than anionic methyl orange (MO). In addition, MB adsorption into the HPC-L gel was greater than MB adsorption into the HPC gel prepared from commercially available HPC. This suggests that residual lignin affects the adsorption of organic dyes. Significant differences were not observed with respect to the release of MB from HPC-L at 38 °C and lower temperatures. In the adsorption of surfactants, marked adsorption at around the critical micelle concentration of the ionic surfactants and gel swelling were observed. Such swelling did not occur in the aqueous nonionic surfactant solution, although the nonionic surfactant was adsorbed into the gel. Gel swelling may have been caused by the electrostatic repulsion of the ionic surfactants adsorbed onto the polymer chains within the gel structure.     

Adsorption of a cationic surfactant onto cellulosic fibers I. Surface charge effects

The adsorption of four cationic surfactants with different alkyl chain lengths on cellulose substrates was investigated. Cellulose fibers were used as model substrates, and primary alcohol groups of cellulose glycosyl units were oxidized into carboxylic groups to obtain substrates with different surface charges. The amount of surfactant adsorbed on the fiber surface, the fiber zeta-potential, and the amount of surfactant counterions (Cl(-)) released into solution were measured as a function of the surfactant bulk concentration, its molecular structure, the substrate surface charge, and the ionic strength. The contribution of each of these parameters to the shape of the adsorption isotherms was used to verify if surfactant adsorption and self-assembly models usually used to describe the behavior of surfactant/oxide systems can be applied, and with which limitations, to describe cationic surfactant adsorption onto oppositely charged cellulose substrates.     

Redox polymerization of 2-hydroxyethyl methacrylate (HEMA). I. Influence of surfactants on polymerization kinetics

Oxidation of ferrous orthophenanthroline (FeP) by peroxydiphosphate (PP) in aqueous medium at pH 1 was followed spectrophotometrically. Kinetic analysis has shown that oxidation occurs via the formation of an intermediate complex between FeP and PP. Equi-librium and rate constants were calculated. Influence of surfactants on the oxidation of FeP by PP was also Investigated. The equilibrium constant for complex formation was found to be higher in the presence of surfactants. The enhanced complex formation has been attributed to the ionic interactions between the charged surfactant and the ionic species in the reaction medium. Polymerization of HEMA initiated by the redox system,FeP/PP, was carried out in aqueous medium, under the conditions of excess reductant over oxidant and excess oxidant over reductant. The polymerization followed different mech-anisms under these conditions; with excess oxidant, the growing polymer radicals underwent oxidative termination, while with excess reductant, primary radical termination was pre-ferred. The effect of surfactants on the aqueous polymerization of HEMA using the redox system FeP/PP was also investigated. In addition to the decrease in rate, the polymerization followed a different mechanism in the presence of surfactants, the growing radicals ter-minated by mutual interaction. © 1995 John Wiley & Sons, Inc.     

Effect of interactions between the adsorbed species on the properties of single and mixed-surfactant monolayers at the air/water interface

Experimental data on surface tension available from the literature and generated in the present study are analyzed to estimate the applicability of adsorption models, based on the Frumkin equation, to nonionic and ionic surfactants and their mixtures. Optimization programs based on the least-squares method in media of Delphi V and Pascal VII are used. The effect of interactions between the adsorbed species on surface tension is considered in all cases. The results are compared to those obtained with the simpler Szyszkowski equation, employed in numerous studies of nonionic surfactants, when interactions are neglected. Cases where the Frumkin model can be successfully employed with ionic surfactants and mixtures are presented and the conditions of its applicability are analyzed. Related characteristic quantities (maximum adsorption, standard free energy of surfactant adsorption, energy of interaction between adsorbed species, standard free energy of counterion adsorption, degree of coverage by surfactant/counterion associates) are established as a function of: The properties of an adsorption layer from a mixture of nonionic and ionic surface-active species are compared to those of the single surfactants.     

Polyelectrolyte-surfactant association—from fundamentals to applications

Mixed polymer-surfactant systems have broad applications, ranging from detergents, paints, pharmaceutical, and cosmetic to biotechnological. A review of the underlying polymer-surfactant association in bulk is given. While ionic surfactants bind broadly to polymers, nonionics only do so if the polymer has a lower polarity and can interact by hydrophobic interactions. Water-soluble polymers, which have hydrophobic groups, form physical cross-links, hence they may be used as thickeners. The rheological behaviour is strongly influenced by various cosolutes; especially strong effects are due to surfactants and both a decrease and an increase in viscosity can occur. When the polymer-surfactant interactions are particularly strong, an associative phase separation can occur, like in the case where there is electrostatic attraction as well as hydrophobic; this and other types of phase separation phenomena are described. Except for linear ionic and nonionic polymers, the interactions between surfactants and cross-linked polymers, microgel particles and covalent macroscopic gels are analyzed, as well as the possibility of forming gel particles of interest for encapsulation purposes. Furthermore, the behavior of these mixed systems on surfaces is discussed. In particular, we consider the adsorption of mixtures of ionic polymers and oppositely charged surfactants on polar and nonpolar surfaces. Depending on concentration, an ionic surfactant can either induce additional polyion adsorption or induce desorption. Kinetic control of adsorption and, in particular, desorption is typical. Important consequences of this include an increased adsorption on rinsing and path dependent adsorbed layers. Recently, considerable attention has been given to the interaction between DNA and cationic surfactant, both as a means to understand the behaviour of DNA in biological systems and to develop novel formulations, for example for gene therapy. Here we review aspects such as DNA compaction, DNA covalent gels and DNA soft nanoparticles.     

Dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) using siloxane-based surfactant in supercritical carbon dioxide and in compressed liquid dimethyl ether

The free radical dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) has been carried out in supercritical carbon dioxide (scCO₂) and compressed liquid DME using several surfactants. The polymerization are performed in the presence of fluorine-based poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl acrylate) [poly(HDFDA)], poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) [poly(HDFDMA)], or poly(HDFDMA-co-MMA) and siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA™) or PDMS modified surfactants, SS-5050K™ and KF6017™ as polymerization surfactants. When scCO₂ was used as a polymerization medium, the PHEMA were heavily agglomerated. However, the spherical and relatively uniform poly(2-hydroxyethyl methacrylate) (PHEMA) particles could be produced even at 20 bar, with a narrow particle size distribution in compressed liquid DME. It was observed that fluorine-based surfactants were not a good surfactant as siloxane-based surfactants for the dispersion polymerization of HEMA. The average particle size of PHEMA was shown to be dependent on the type of the surfactant, the amount of the surfactant and initiator added to the system. The effect of two continuous phases, which are scCO₂ and compressed liquid DME, as a polymerization medium, the surfactant types and the concentration, initiator concentration, and monomer concentration on the morphology and size of the polymer particles was also investigated.     

Hydrogel composites of neutral and slightly charged poly (acrylamide) gels with incorporated bentonite. Interaction with salt,linear polyelectrolytes and ionic surfactants

The swelling behavior in the solutions of sodium chloride, linear polyelectrolytes and ionic surfactants of the composites based on clay mineral bentonite (BENT) embedded in neutral and slightly charged poly(acrylamide) (PAAm) gels is studied. Negatively charged flat clay particles incorporated into polymer gel adsorb oppositely charged surfactant and linear polyelectrolyte and attract the charged chains of cationic polymer matrix. The results of SAXS study manifest the formation of lamella structure of the cationic surfactant adsorbed by the clay plates. The gels loaded with the clay show a strong response to changes in the nature and the composition of the ionic environment.     

Study of poly(St/BA/MAA) copolymer latexes with trimodal particle size distribution

A new strategy was developed for producing a polymer latex with trimodal particle size distribution by adding a second seed of polymer particles and some additional surfactants during polymerization. The polymerization was investigated by following the variation of the particle size, the size distribution, the number of particles, the surface tension and surfactant surface coverage at different stages of the polymerization process. The results showed that both the size and the size distribution can be easily controlled by varying the amount of additional surfactants and the second seed of polymer particles. The secondary nucleation was achieved when the surface coverage of particles was over 70%, and the amount of small particles formed increased with increasing amount of additional surfactants. The introduction of the additional surfactants had no significant effect on the size and number of middle particles, but reduced the size of large particles and caused the number of large particles to remain more stable because of the suppression of limited flocculation. Copyright © 1998 John Wiley & Sons, Ltd.     

选择性膜电极研究表面活性剂与大分子的相互作用

结合本实验室的工作介绍了表面活性剂选择性膜电极研究表面活性剂与大分子相互作用的实验装置和原理,并综述了表面活性剂选择性膜电极在研究离子型表面活性剂及其二元混合体系与不同类型大分子之间相互作用中的应用.讨论了大分子的分子量、外加盐和表面活性剂的结构对表面活性剂和大分子之间相互作用的影响结果.