Latex particles bearing hydrophilic grafted hairs with controlled chain length and functionality synthesized by reversible addition–fragmentation chain transfer

A method is described for synthesizing latex particles with anchored hairs by the grafting of hydrophilic chains, synthesized by reversible addition–fragmentation chain transfer, onto functionalized latex particles. These have the potential to bind biologically active species. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1188–1195, 2003     

Role played by the head size of some non‐ionic surfactants on their adsorption onto montmorillonite clay

Sorption behavior of polyoxethylene(n)monooleate series [Ol(EO)_n] onto montmorillonite clay was studied at 25°C to investigate the influence of the surfactant's head size on the sorption process. All the tested surfactants exhibited L‐shaped isotherms that means a strong interaction between the adsorbent and the adsorbate. Also, all the obtained isotherms ended with a drastic increase in the isotherm slope at nearly constant equilibrium concentration. This abrupt increase reflected the fairly high affinity of the tested surfactants to the clay surface at high bulk concentration region. The maximum amount adsorbed at the plateau region, Γ_max, was calculated according to the Langmuir adsorption theory and followed the order: Ol(EO)₁₄ > Ol(EO)₂₀ < Ol(EO)₄₀ < Ol(EO)₈₀. In case of short ethylene oxide (EO) chain, Γ_max decreased with the increase in the chain length; but a reverse result was obtained in case of surfactants with longer EO chain length (20 to 80 units). The free energy of adsorption, ΔG°_ad, had negative values indicating the spontaneous adsorption of surfactant molecules onto clay. The values of ΔG°_ad increased with increasing EO units from 14 to 20 units and decreased with further elongation in the EO chain from 20 to 80 units. Copyright © 2004 John Wiley & Sons, Ltd.     

An Artificial Electrode/Electrolyte Interface for CO2 Electroreduction by Cation Surfactant Self-Assembly

In this work, an artificial electrode/electrolyte (E/E) interface, made by coating the electrode surface with a quaternary ammonium cation (R₄N⁺) surfactant, was successfully developed, leading to a change in the CO₂ reduction reaction (CO₂RR) pathway. This artificial E/E interface, with high CO₂ permeability, promotes CO₂ transportation and hydrogenation, as well as suppresses the hydrogen evolution reaction (HER). Linear and branched surfactants facilitated formic acid and CO production, respectively. Molecular dynamics simulations show that the artificial interface provided a facile CO₂ diffusion pathway. Moreover, density-functional theory (DFT) calculations revealed the stabilization of the key intermediate, OCHO*, through interactions with R₄N⁺. This strategy might also be applicable to other electrocatalytic reactions where gas consumption is involved.     

Magnetic poly(N‐isopropylacrylamide) microspheres by dispersion and inverse emulsion polymerization

The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe₂O₃ nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe₂O₃, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe₂O₃ nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007     

Multiphase Polymer Dispersions and Nanocomposites by Catalytic/Free Radical Emulsion Polymerization

Summary: Free radical emulsion polymerization of styrene (S) or butyl acrylate (BA) in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization affords colloidally stable multiphase latices. Coagulation of a PE/PS latex affords nanocomposites composed of small PE phases dispersed in a PS matrix, as evidenced by the large supercoolings of PE crystallization (by DSC). TEM of PE/PBA latices indicates a PBA phase around the PE particles under the emulsion polymerization conditions investigated. Films formed from these dispersions exhibit homogeneously dispersed PE particles.

Multiphase latices are obtained by free radical emulsion polymerization of butyl acrylate in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization.     

Surfactant effects on morphology and switching of holographic PDLCs based on polyurethane acrylates.

Effects of octanoic acid (OA) on the morphology, diffraction efficiency, and electro-optic properties of the transmission mode of holographic polymer-dispersed liquid crystals (HPDLC) are studied. Droplet size decreases with increasing OA content (0-9 %), and this leads to a monotonic increase in off-state diffraction with increasing OA content. However, on-state diffraction decreases with increasing applied voltage and shows a minimum at 6 % OA, for which minimum switching voltage (5 V microm(-1)) and maximum contrast ratio (10) are obtained. Rise time and decay time decrease with increasing OA content. Interposition of OA between polymer and LC droplet is theoretically predicted by the spreading coefficient (lambda>0) calculated on the basis of the solubility parameter, while the coalescence behavior of droplets is described by a dimensionless group (gamma d rho / mu(2)) called coalescence number.     

Computer Simulation of Bridging Flocculation Processes: The Role of Colloid to Polymer Concentration Ratio on Aggregation Kinetics

The flocculation of colloidal particles by adsorbing polymers is one of the central issues of colloid science and a very important topic in many industrial, biological, and environmental processes. We report a computer simulation study of a 2- and 3-dimensional model for bridging flocculation betweenlarge linear polymer chains and comparatively small colloidal particles,where the structure and growth kinetics of cluster formation are investigated. This model was developed within the framework of the cluster–cluster aggregation model using mass and fractal dimension dependent diffusion constants, where bridging flocculation is seen as a case of heterocoagulation in which, in addition, macromolecule configurations and lengths play an important role. The simulation of aggregate structure and formation kinetics obtained at different (i) relative particle concentrations, (ii) polymer chain conformations, and (iii) sticking probabilities are described from a qualitatively and quantitative point of view. The results suggest that the formation of large aggregates is a slow process, controlled by the reactivity of the clusters, even when the reaction between microcolloids and macrochains is very fast. Aggregation kinetics are strongly dependent on the particle/chain concentration ratio and on the configurational properties of the chains. It is shown that the scaling laws which are valid for homocoagulation processes are also applicable to the kinetics of bridging flocculation. The corresponding scaling exponents have been calculated.     

Self‐Cleaning and Next Generation Anti‐Fog Surfaces and Coatings

Due to their high surface energy, hydrophilic surfaces are susceptible to contaminations which are difficult to remove and often ruin the surface. Traditional anti‐fog coatings are especially limited by contaminants, as the prevention of fogging is enhanced as hydrophilicity increases. Thus, advanced solutions to fogging are required which incorporate some degree of self‐cleaning ability without significant losses in anti‐fog character. Potential next generation anti‐fog surfaces are characterized with particular emphasis on extended lifetime stimuli‐responsive surfaces. Surfactant‐based surfaces exhibited simultaneous hydrophilicity, necessary for anti‐fogging, and oleophobicity, necessary for contamination resistance. The combination of these features rendered the surface as self‐cleaning.

     

Effects of Acid and Base on the Inductive Efficiency of Oligonucleotide on the Vesicle Formation from Single-Chained Cationic Surfactant

Recently, we reported for the first time that oligonucleotide could induce single‐chained cationic surfactant molecules to aggregate into vesicles and the facilitative efficiency of oligonucleotide on vesicle formation was dependent on its size and sequence. In the present paper, we will continue to study the effects of acid and base on the facilitative efficiency of oligonucleotide on vesicle formation. It is found that proton ions show little effect on the facilitative efficiency while hydroxide ions make it decreased. Moreover, the percentage of oligonucleotide involved in vesicle formation in basic solution is much lower than that in acidic solution (which is almost equal to that in water). Since the structures and properties of DNA/amphiphile complex are very important for its application as nonviral gene carrier, this study may provide some helpful information for gene therapy.     

Influence of PEG‐ran‐PPG Surfactant on Vapour Phase Polymerised PEDOT Thin Films

The oxidant, Fe(III) tosylate, was used in the vapour phase polymerisation (VPP) of PEDOT. The amphiphilic co‐polymer poly(ethylene glycol‐ran‐propylene glycol) was added and its influence examined. Both the PEDOT conductivity and optical contrast range increased with the inclusion of the co‐polymer, with the maximum being recorded at 4 wt.‐%. Loadings higher than this resulted in a systematic decrease in both conductivity and optical contrast. Evidence indicates that in addition to the beneficial anti‐crystallisation effect to the oxidant layer, the co‐polymer also reduces the effective reactivity of the oxidant, as demonstrated by slower polymerisation rates. Confirmation of the change in polymerisation rate was obtained using a quartz crystal microbalance (QCM). The slower polymerisation rate results in higher conductivity and optical contrast; however, XPS data confirmed that the co‐polymer remained within the PEDOT film post‐washing and this result explains why the performance decreases at high surfactant loadings.

     

Compartmentalized Polyampholyte Microgels by Depletion Flocculation and Coacervation of Nanogels in Emulsion Droplets

In pH-responsive drug carriers, the distribution of charges has been proven to affect delivery efficiency but is difficult to control and verify. Herein, we fabricate polyampholyte nanogel-in-microgel colloids (NiM−C) and show that the arrangement of the nanogels (NG) can easily be manipulated by adapting synthesis conditions. Positively and negatively charged pH-responsive NG are synthesized by precipitation polymerization and labelled with different fluorescent dyes. The obtained NG are integrated into microgel (MG) networks by subsequent inverse emulsion polymerization in droplet-based microfluidics. By confocal laser scanning microscopy (CLSM), we verify that depending on NG concentration, pH value and ionic strength, NiM−C with different NG arrangements are obtained, including Janus-like phase-separation of NG, statistical distribution of NG, and core–shell arrangements. Our approach is a major step towards uptake and release of oppositely charged (drug) molecules.     

Effect of Hydrophilic Polymer on Solubilization of Fenofibrate by Cyclodextrin Complexation

The present work investigates the possibility of improvement of the complexation efficiency of cyclodextrin towards a drug by adding a third auxiliary component (hydrophilic polymer). Phase solubility Analysis at 25 °C was used to investigate the interaction of the drug in both the binary systems (viz. Drug-Cyclodextrin and Drug-Polymer) and the ternary system (Drug-Cyclodextrin-Polymer). The combined use of polymer and cyclodextrin was clearly more effective in enhancing the aqueous solubility of the fenofibrate in comparison with the corresponding drug-cyclodextrin or drug-polymer binary systems. Hydrophilic polymers increased the complexation efficacy of cyclodextrin towards fenofibrate (as shown by the increased stability constants of the complexes). Polyvinyl Pyrollidone (PVP) was found to be most effective in enhancing the solubilization of fenofibrate by β-Cyclodextrin, the best results were obtained in ternary system with β-Cyclodextrin in presence of 1%w/v (PVP). Formulated ternary system with optimized drug:cyclodextrin:polymer ratio of 1:3.5:1 w/w resulted in a significant improvement in the dissolution rate of fenofibrate and showed 90% dissolution efficiency (D.E) as compared to around 15% and 83% of the plain drug and binary system respectively. DSC studies was carried out to characterize the ternary complex.     

阳离子Gemini表面活性剂3,5-双(亚甲基十八烷基二甲基溴化铵)-1,2,4-三氮唑胶束对酯碱性水解的影响

在25℃条件下,研究了乙酸乙酯和乙酸戊酯在阳离子Gemini表面活性剂3,5—双(亚甲基十八烷基二甲基溴化铵)—1,2,4—三氮唑(简称18—triazole—18)胶束中的碱性水解反应。实验结果表明．在一定的表面活性剂浓度范围内,乙酸乙酯和乙酸戊酯在Gemini表面活性剂18—triazole—18胶束溶液中的碱性水解反应速率随表面活性剂浓度的增加呈上升趋势,达到一最大值后,随着浓度的增加呈下降趋势。实验结果还表明,18—triazole—18对乙酸乙酯碱性水解的影响较对乙酸戊酯碱性水解的影响大。随着底物疏水性的增加,乙酸乙酯和乙酸戊酯的碱性水解速率在18—triazole—18胶束中表观反应速率常数最大值分别为无表面活性剂时的5．5倍和1．1倍。     

Effects of added surfactants on thermoreversible gelation of associating polymer solutions

The influence of added surfactants on physical properties of associating polymer solutions was examined by a new statistical‐mechanical theory of associating polymer solutions with multiple junctions and by computer simulation. The sol–gel transition line, the spinodal line, and the number of elastically effective chains in the mixed networks were calculated as functions of the concentration of added surfactants. All of them exhibited nonmonotonic behavior as a result of the following two competing mechanisms. One was the formation of new mixed micelles by binding surfactants onto the polymer associative groups. These micelles serve as crosslink junctions and promote gelation. The other was the replacement of polymer associative groups in the already formed network junctions by added surfactants. Such replacement lowers connectivity of junctions and destroys networks. The critical micelle concentration was also calculated. The results are compared with the reported experimental data on poly(ethylene oxide)‐based associating polymers and hydrophobically modified cellulose derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 733–751, 2004     

Poly(N,N‐diethylacrylamide) microspheres by dispersion polymerization

Poly(N,N‐diethylacrylamide)‐based microspheres were prepared by ammonium persulfate (APS)‐initiated and poly(vinylpyrrolidone) (PVP)‐stabilized dispersion polymerization. The effects of various polymerization parameters, including concentration of N,N′‐methylenebisacrylamide (MBAAm) crosslinker, monomer, initiator, stabilizer and polymerization temperature on their properties were elucidated. The hydrogel microspheres were described in terms of their size and size distribution and morphological and temperature‐induced swelling properties. While scanning electron microscopy was used to characterize the morphology of the microspheres, the temperature sensitivity of the microspheres was demonstrated by dynamic light scattering. The hydrodynamic particle diameter decreased sharply as the temperature reached a critical temperature ～ 30 °C. A decrease in the particle size was observed with increasing concentration of both the APS initiator and the PVP stabilizer. The microspheres crosslinked with 2–15 wt % of MBAAm had a fairly narrow size distribution. It was found that the higher the content of the crosslinking agent, the lower the swelling ratio. High concentration of the crosslinker gave unstable dispersions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6263–6271, 2008     

Ionization by pH and Anionic Surfactant Binding Gives the Same Thickening Effects of Crosslinked Polyacrylic Acid Derivatives

Physical properties of aqueous solutions of hydrophobically modified crosslinked polyacrylic acids change quite extensively as the polymer is charged up. A study is carried out concerning the similarities between two polymer ionization processes, that is, by pH increment and anionic surfactant addition. The two processes charge the polymer by distinctly different mechanisms. At sufficiently high pH the carboxylic groups of the polymer are virtually all ionized and the polymer is, therefore, fully charged. The effective repulsion among the charged groups due to the entropy of the counterions promotes an increased stiffness as well as an expansion of the polymer particles. We investigate here how the ionization and swelling will be if, instead of high pH, the polymer is at low pH conditions but associated to ionic surfactants. Surfactants associate to the polymer both in a noncooperative way by the binding of individual surfactant molecules and in a cooperative way as micelles since the polymer promotes surfactant self-assembly. This binding leads to a highly charged polymer-surfactant complex and leads to an osmotic swelling as well. The swelling and the gelation were monitored by rheology and dynamic light scattering, of polymer solutions by varying the pHs and adding ionic surfactants at low pH. The results show that ionization by surfactants and by pH lead to approximately the same gelation degree, as can be seen by similar viscosity values. Both processes result in dramatic viscosity increases, up to 8 orders of magnitude. More hydrophobic surfactants, with longer alkyl chain, are shown to be more efficient as enhancers of swelling and gelation. The network that is formed at high pH or at sufficiently high concentration of surfactant can be weakened or even disrupted if monovalent or divalent salts are added, demonstrating the role of counterion entropy.     

Synthesis and Properties of Hydrogels Based on Chitosan and Poly(Vinyl Alcohol) Crosslinked by Genipin

Semi‐interpenetrating polymeric networks of chitosan and poly(vinyl alcohol) [PVA] were prepared by varying the ratio of the constituents. The hydrogels were crosslinked using genipin, a naturally occurring nontoxic cross‐linking agent. The swelling behavior of these hydrogels was studied by immersing the films in deionized water at various temperatures and in buffer solutions of different pH. The states of water in the hydrogels, swollen at 25°C and pH 7, were determined using Differential Scanning Calorimetry (DSC). The swelling behavior of the gels was found to be dependent on temperature and pH of the medium. The amount of freezing water in the swollen hydrogels increased, whereas the amount of nonfreezing bound water remained more or less the same with increasing PVA concentration.     

Butylene copolyesters based on aldaric and terephthalic acids. Synthesis and characterization

The synthesis, characterization, and some properties of new copolyesters analogous to poly(butylene terephthalate) (PBT), based on L ‐arabinaric and galactaric acids, are described. These copolyesters were obtained by polycondensation reaction in the melt of mixtures of methyl 2,3,4‐tri‐O‐methyl‐L ‐arabinarate or methyl 2,3,4,5‐tetra‐O‐methyl‐galactarate and dimethyl terephthalate with 1,4‐butanediol. Their weight‐average molecular weights ranged between 10,000 and 34,000, with polydispersities ranging from 1.4 to 2.2. The composition of all the copolymers was analyzed by NMR, and was found to have a statistical microstructure. All these copolyesters were thermally stable, with degradation temperatures well above 300 °C. The melting temperature and crystallinity decreased in both series, and the glass transition temperature increased and decreased respectively, for the PBTGa and PBTAr series with increasing amounts of aldaric units in the copolyester chain. Only PBT‐derived copolyesters containing a maximum of 30% aldaric units showed discrete scattering characteristic of crystalline material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1168–1177, 2009