Particle monolayers formed under irreversible conditions: jamming coverages and structure

The random sequential adsorption (RSA) approach was used for modelling irreversible adsorption phenomena of polyatomic particles at homogeneous interfaces. Particles of spherical and spheroidal shape, characterised by various axis ratio parameter A, were considered. In the latter case, the flat (side-on) and unoriented adsorption was discussed. The sticking probability (available surface function) was determined for various particle shapes together with “jamming” coverages for clean and precovered surfaces. The structure of adsorbed particle monolayers (under transient and jammed states) was analysed quantitatively in terms of the pair correlation functions. Methods of extrapolation of these results to interacting (soft) particle systems were also discussed. The theoretical predictions were confronted with existing experimental results derived for monodisperse spherical particles. A good agreement with theory was found both in respect of jamming coverages and the monolayer structure. These theoretical and experimental studies demonstrated that minor amounts of small particles (nanometer size range) exert decisive influence on adsorption of larger particles. This phenomenon can be treated as analogous to the surface poisoning effect occurring in heterogeneous catalytic systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

In‐situ grown silica/water‐borne epoxy shape memory composite foams prepared without blowing agent addition

Shape memory (SM) silica/epoxy composite foams were successfully synthesized via latex technology and prepared without blowing agent addition. Silica was synthesized via tetraethoxysilane (TEOS) hydrolysis. Silica/epoxy foams were obtained from the TEOS solution and water‐borne epoxy mixtures after freeze‐drying and foaming in the presence of residual moisture as the blowing agent under a vacuum at 110°C. The morphologies of the resulting foams were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compression and thermo‐mechanical cycle tests were performed to measure the mechanical and SM properties of the foams. Experimental results indicated that the micrographs and mechanical properties of the foams were closely related to freeze‐drying time. The final composite foams exhibited high shape recovery and fixity ratios and could maintain both properties at more than 90% even after five thermo‐mechanical cycles. The properties obtained in the epoxy foams may offer new opportunities for their use in future structural applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42599.     

Micron‐sized membrane reactors: Multicompartment semipermeable polymer particles containing palladium nanoparticles

Multicompartment polymer microparticles are prepared encapsulating palladium nanoparticles within closed‐shell compartments, using a double‐emulsion (W₁/O/W₂), evaporative limited coalescence process. The encapsulation efficiency in some cases is as high as 99%, and very little Pd leaches from the particles. The Pd nanoparticles dispersed in an aqueous environment within the closed‐shell compartments of the microparticles catalyze hydrogenation reactions of low molar mass substrates in water at substantial rates. The microparticle walls serve as semipermeable membranes, permitting diffusion of small molecules into the compartments while retaining the larger metal nanoparticles. The microparticles can be reused after simple filtration. The catalytic activity increases on recycling, possibly because of plasticization of polymer walls by the reactant and products, resulting in increased diffusion. In a second demonstration of catalytic activity, the microparticles efficiently decompose hydrogen peroxide. These nanoparticle‐containing microparticles serve as convenient, reusable catalyst carriers, and prevent inadvertent human and environmental contact with nanoparticles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42021.     

One‐pot preparation of multicolor polymeric nanoparticles with high brightness by single wavelength excitation

Fluorescent nanoparticles with multiplex distinct emission signatures and high brightness by a single wavelength excitation are substantially needed in multiplex bioassays and imaging. In this study, we synthesized fluorescent polymeric nanoparticles incorporated with three polymerizable organic dyes via a one‐pot miniemulsion. By altering the doping ratio of three tandem dyes, the nanoparticles display abundant multiple fluorescence such as blue, cyan, green, orange, pink, red etc., together with distinguishable emission signatures under a single wavelength excitation, which were arising from the effective fluorescence resonance energy transfer (FRET) between the three energy‐matched dyes. Meanwhile, a large Stokes shift (up to 250 nm) can be generated by taking place multiple FRET cascade mechanism between donor and acceptor fluorophores in nanoparticles, which also suggests broad applications in biological labeling and imaging. Moreover, these nanoparticles are uniform in size, highly bright, excellently photostable, and shown prominent longterm stability. Overall, the novel multicolor fluorescent polymeric nanoparticles augur well for their potential applications in multiplexed bioanalysis and emitting displays. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41492.     

Electrostatic deposition of silica nanoparticles between E‐glass fibers and an epoxy resin

The achievement of optimum adhesion between a thermoset and an inorganic material is an important goal for the composites and coatings industries. There is a growing interest in the use of structural surface modifiers, such as nanotubes, nanoparticles, and whiskers, to improve this adhesion. Here, a method for electrostatically depositing poly(ethylene imine)‐functionalized silica nanoparticles onto E‐glass fibers was developed. The deposition of 26‐nm functionalized particles onto glycidyloxypropyltrimethoxysilane (GPS)‐functionalized E‐glass fibers and then their embedding in a resin of diglycidyl ether of bisphenol A and m‐phenylene diamine increased the interfacial shear strength (IFSS) 35% over that of bare fibers and 8% over that of GPS‐functionalized fibers. IFSS was highly dependent on the particle size; the 16‐nm functionalized particles had little effect on the IFSS. When the particles size was increased to 71 and 100 nm, this led to increasingly poor IFSS values, whereas the 26‐nm particles produced the best results. Similar results were seen with the transverse flexural strength of the unidirectional composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41516.     

Effects of monovalent and multivalent ions on the stability of a polyelectrolyte complex with entrapped surfactants

In this article, we report the effects of nine different monovalent and multivalent salts on the particle size and stability of refined, positively charged polyelectrolyte complexes (PECs) with entrapped surfactant. Dynamic light scattering and ζ potential measurements of these polymeric particles as a function of various salt concentrations showed that both counter ions and co‐ions induced a concentration‐dependent increase in the particle size and a decrease in the ζ potential. We found that the anion concentration where the particle size doubled and the maximum anion concentration beyond which particle precipitation occurred (C_a,max) demonstrated a power law dependence on the anion valence. Moreover, for anions of the same valence but different hydration radio, C_a,max decreased in the following order: NO₃ → Cl → HPO₄^2? > SO₄^2? > PO₄^3?. However, unlike the case of hard colloids where co‐ions have relatively little effect on particle interactions, the co‐ions also increased the hydrodynamic radii of our PECs in the following order: K⁺ ≈ Na⁺ > Ca²⁺ > Mg²⁺ > Al³⁺. Furthermore, we found that the entrapped surfactants were shielded from the adverse effect of multivalent ions; this established that the monovalent and multivalent ions interacted with the polyelectrolyte shells of the PEC. This behavior was in contrast with the effect of salts on mixtures containing the polyelectrolyte and surfactant components, where the addition of salts typically causes an interaction with the individual components. Because several biomedical and technological applications involving PECs require saline environments, our studies provide insight into how small ions influence the PEC stability in applications involving varying salinities. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42099.     

Preparation and functional evaluation of chitosan‐EGCG conjugates

Chitosan, as a novel food additive, is proposed to conjugate with EGCG using a free radical grafting procedure. Chitosan is activated by hydroxyl free radicals produced by the redox reaction of hydrogen peroxide and ascorbic acid and subsequently react with EGCG. Chitosan‐EGCG conjugate has demonstrated by UV, FTIR, and ¹H‐NMR spectroscopy and exhibits a dramatical increase in DPPH free radical scavenging activity. In addition, the LC (low‐molecular‐weight chitosan)‐EGCG conjugate is used to prepare O/W emulsion and then monitor the average droplet size, polydispersity index, zeta‐potential and transmission changes during centrifuge process, results show that the conjugate exhibited excellent emulsifying activity and superior emulsifying stability as compared with chitosan. Therefore, LC‐EGCG conjugate could be used as an efficient natural food antioxidant and emulsifier. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39732.     

Synthesis and application of acrylic colloidal unimolecular polymers as a melamine thermoset system

Acrylic polymers were synthesized with a ratio of 1 : 7 or 1 : 8 of acrylic acid to acrylic ester monomers to produce an acid‐rich resin. The polymers were water reduced and solvent was stripped to produce colloidal unimolecular polymers (CUPs). These particles were typically 3–9 nm in diameter depending on the molecular weight. They were then formulated into a clear coating with melamine as the crosslinker with thermal curing. Compared to commercial latex films, these melamine‐cured acrylic CUPs had a distinct advantage of having a near‐zero volatile organic compound, better availability of surface functional groups , and improved water resistance. The coatings were evaluated for their methyl ethyl ketone resistance, adhesion, hardness, gloss, flexibility, abrasion , and impact resistance properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40916.     

Microwave-assisted synthesis of hybrid colloids for design of conducting films

We report synthesis of colloids with polymer core and inorganic shell consisting of silver nanoparticles (AgNPs) which can be used as building blocks for the preparation of conducting composite films. Polymer colloids based on copolymer of styrene and butyl acrylate with variable film formation temperature and functional surface have been prepared by surfactant-free emulsion polymerization. Polymer particles with average size between 140 nm and 220 nm and narrow size distribution were used as templates for deposition of AgNPs by microwave-assisted reduction of silver precursors in aqueous medium. The loading of the AgNPs on the polymer particle surface has been increased up to 60 wt.-%. Obtained hybrid colloids were used for preparation of composite films. The electrical conductivity of the composite films starts to increase if the AgNPs loading on the polymer particle surface is above 20 wt.-%.     

Influence of chromophoric electron-withdrawing groups on photoinduced deformation of azo polymer colloids

This study investigated the influence of chromophoric electron-withdrawing groups on photoinduced deformation behavior of colloidal spheres of three azo polymers. The colloidal spheres were prepared by using the epoxy-based azo polymers (BP-AZ-CA, BP-AZ-CN, and BP-AZ-NT) through gradual hydrophobic aggregation of the polymers in THF-H₂O media. The colloidal spheres were controlled to have similar average sizes by adjusting both the polymer concentrations in the initial THF solutions and water-adding rates in the preparation processes. The colloids were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The colloid deformation was investigated by irradiating the colloidal spheres in solid state with a linearly polarized Ar⁺ laser beam (488 nm, 130 mW/cm²). For comparison, the colloids were also studied by irradiation with a polarized diode solid state laser beam (532 nm, 130 mW/cm²). Upon the light irradiation, all the colloidal spheres were elongated along the polarization direction of the laser beams. The electron-withdrawing groups showed significant influence on the colloid deformation behavior related with the response to the light irradiation. The colloid deformation was more efficiently induced by irradiation with the laser beams having the intermediate wavelengths between the λ_max and the absorption band tails of the azo chromophores. When the hydrophilic carboxylic group was used as the electron-withdrawing groups, more significant deformation was induced under the same light irradiation condition, which could be attributed to the higher hydrophilicity of the polymer. Above observations can lead to a better understanding of the photoinduced deformation mechanism of azo polymer colloids.