Chengyou Kan

Micromotor‐Based High‐Yielding Fast Oxidative Detoxification of Chemical Threats

Rapid field conversion of chemical weapons into non-toxic products is one of the most challenging tasks in weapons of mass destruction (WMD) science. This is particularly the case for eliminating stockpiles of chemical warfare agents (CWAs) in remote storage field locations, where the use of large quantities of decontaminating reagents, long reaction times, and controlled mechanical agitation is impossible or undesired. New efficient “clean” technologies and (bio)chemical processes are thus sought for detoxifying stored agents, counteracting nerve-agent attacks, and decommissioning chemical weapons. Environmentally friendly solutions of hydrogen peroxide, combined with suitable activators (e.g., bicarbonate), have been shown to be extremely useful for decontaminating a broad spectrum of CWAs to yield nontoxic products. These peroxide-based systems, which rely on the in situ generation of OOH nucleophiles, have recently replaced chlorine-based bleaching processes, which produce undesirable products, and have thus led to effective decontamination of the chemical agents GB (Sarin, isopropyl methylphosphonofluoridate), VX ((S)-[2-(diisopropylamino)ethyl] O-ethyl methylphosphonothioate), GD (Soman, pinacolyl methylphosphonofluoridate), and HD (sulfur mustard). Yet, such an oxidative treatment commonly requires high peroxide concentrations (20–30%; approaching a stoichiometry of 1:50), along with prolonged operation and/or mechanical agitation. Such reaction conditions are not suitable or not desired for eliminating stockpiles of CWAs in remote field settings or hostile storage locations, as large quantities of the reagents may not be transportable on military aircrafts and require special packaging and handling. The efficient elimination of chemical-weapon stockpiles in field locations thus remains a major challenge to the chemistry and defense communities. Herein, we describe a powerful strategy that is based on self-propelled micromotors, for a high-yielding accelerated oxidative decontamination of chemical threats using low peroxide levels and no external agitation. Functionalized synthetic micromotors have recently demonstrated remarkable capabilities in terms of isolation and transport for diverse biomedical and environmental applications, but not in connection to increasing the yield and speed of chemical reactions. The new motor-based method relies on the use of peroxide-driven microtubular engines for the efficient selfmixing of a remediation solution, which dramatically accelerates the decontamination process. Fluid mixing is extremely important for enhancing the yield and speed of a wide range of chemical processes, including decontamination reactions, where quiescent conditions lead to low reaction efficiency and long operations. The observed mixing, which is induced by the peroxide-driven micromotor, is analogous to that reported for the motility of E. coli bacteria, where a large-scale collective motion has been shown to enhance diffusion processes. Enhanced diffusion of passive tracers has also been observed in the presence of catalytic nanowire motors. Although the new micromotor strategy presented herein was applied to the accelerated, high-yielding, and simplified decontamination of organophosphate (OP) nerve agents, the concept could have broad implications for enhancing the efficiency and speed of a wide range of chemical processes in the absence of external agitation. The concept of the micromotor/peroxide-based decontamination of chemical threats is illustrated in Figure 1. This new strategy relies on micromotors without mechanical stirring (Figure 1A). A known number of micromotors were placed in a nerve-agent-contaminated solution, along with hydrogen peroxide (used as the oxidizing agent as well as the micromotor fuel), the peroxide activator (NaHCO3 or NaOH), and the surfactant sodium cholate (NaCh), which was essential for bubble generation. The oxidative conversion of the OP nerve agent into para-nitrophenol (p-NP) was achieved under mild quiescent conditions that involve the in situ generation of OOH nucleophiles with no external stirring (Figure 1B). The decrease in concentration of the OP [*] Dr. J. Orozco, G. Cheng, D. Vilela, Dr. S. Sattayasamitsathit, Prof. R. Vazquez-Duhalt, Dr. G. Vald s-Ram rez, Dr. O. S. Pak, Prof. J. Wang Departments of Nanoengineering and Mechanical Engineering University of California San Diego La Jolla, CA 92093 (USA) E-mail: josephwang@ucsd.edu G. Cheng, Prof. C. Kan Tsinghua University, Beijing, 100084 (China) D. Vilela, Prof. A. Escarpa University of Alcal 28871 Alcal de Henares (Spain)

Encapsulation of calcium carbonate by styrene polymerization

WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW In order to obtain composites of calcium carbonate (CaCO3) encapsulated by polystyrene (PS), soapless polymerization of styrene (S) in aqueous phase in the presence of CaCO3 was carried out. Influences on the encapsulation and on monomer conversion were studied. Results showed that monomer conversion higher than 52% can be achieved by increasing the stirring speed of polymerization to 1000 rpm. In order to remove the polymer adsorbed on the surface of the inorganic powder, the crude PS/CaCO3 composite obtained was treated by Soxhlet extractor, and the PS/CaCO3 ratio after the extraction was measured and defined as the real encapsulation ratio. A maximum real encapsulation ratio of 6.4% was obtained regardless of variations in experimental conditions such as monomer/CaCO3 ratios, monomer and initiator concentrations. The presence of PS on the surface of CaCO3 was tested by scanning electron microscopy and zeta potential (x) measurement of CaCO3 particles encapsulated by PS. With an increase in monomer conversion, x approached the value obtained from particles of pure PS prepared by soapless emulsion polymerization in the absence of CaCO3 powder.

Electrostatic-Driven Lamination and Untwisting of β-Sheet Assemblies.

Peptides or peptide conjugates capable of assembling into one-dimensional (1D) nanostructures have been extensively investigated over the past two decades due to their implications in human diseases and also their interesting applications as biomaterials. While many of these filamentous assemblies contain a β-sheet-forming sequence as the key design element, their eventual morphology could assume a variety of shapes, such as fibrils, ribbons, belts, or cylinders. Deciphering the key factors that govern the stacking fashion of individual β-sheets will help understand the polymorphism of peptide assemblies and greatly benefit the development of functional materials from customized molecular design. Herein, we report the decisive role of electrostatic interactions in the lamination and untwisting of 1D assemblies of short peptides. We designed and synthesized three short peptides containing only six amino acids (EFFFFE, KFFFFK, and EFFFFK) to elucidate the effective control of β-sheet stacking. Our results clearly suggest that electrostatic repulsions between terminal charges reduce the pitch of the twisting β-sheet tapes, thus leading to highly twisted, intertwined fibrils or twisted ribbons, whereas reducing this repulsion, either through molecular design of peptide with opposite terminal charges or through coassembly of two peptides carrying opposite charges, results in formation of infinite assemblies such as belt-like morphologies. We believe these observations provide important insight into the generic design of β-sheet assemblies.

Synthesis of silicone–acrylate copolymer latexes and their film properties

Emulsion copolymerization of silicones (octomethyl tetracyclosiloxane, D4 and methacryloxypropyl trimethoxy silane, MATS) and acrylics was carried out using three different polymerization processes: semicontinuous monomer emulsion addition, batch and initiator solution addition. Results showed that only the semicontinuous process led to a stable latex with monodisperse particles. Various polymerizations were carried out through this process with varying silicone/acrylic ratios and MATS content. Films were obtained from different latexes: their properties are significantly influenced by silicone and MATS contents in copolymers.

Synthesis and Characterization of Hollow Polymer Latex Particles

Latex particles with a multihollow structure were prepared by seeded emulsion polymerizatoin. Thus seed latexes Sn, consisting of styrene(St) and methyl methacrylate (MMA) copolymer, and Sa, consisting of St‐MMA‐AA (acrylic acid) copolymers, were first prepared, then a series of core‐ shell composite latexes SnCa, SnCn, SaCa and SaCn were synthesized with or without AA in the absence of emulsifiers in the second step. Final latexes were then treated by alkali and acid subsequently at 90°C for 3 h. TEM observation showed that only SnCa and SaCa (prepared with AA in the second polymerization, suffix “a” means with AA, “n” means without AA) produced multihollow structures in the particles, and their particle volumes increased 42% for SnCa and 23% for SaCa after the treatment in comparison with original latex particles. No hollows were observed for SnCn and SaCn particles prepared without AA and new particles were formed for the SaCn latex in the second step polymerization.

Graft Emulsion Copolymerization of Acrylates and Siloxane

Graft acrylates and siloxane copolymer latexes were prepared by batch process via simultaneous radical and ring-opening copolymerization. Vinyl septamethyl cyclotetrasiloxane (VD4) was used as a coupling agent to form chemical bonds between polyacrylates and polysiloxane. The occurrence of graft copolymerization was confirmed by Soxhlet extraction and by the dynamic mechanical properties of latex polymer. The results showed that polymerization behavior and final latex stability strongly depend on siloxane content, with increase in siloxane content monomer conversion and latex stability decreased. The mechanical properties of latex film were influenced not only by total siloxane content, but also by relative amount of VD4 to siloxane.

Preparation of polyacrylate–polysiloxane core–shell latex particles

Crosslinked polymer seed latexes of butyl acrylate, methyl methacrylate and methacrylic acid were synthesized with ethylene glycol dimethacrylate as a crosslinking agent in a first step. Three different processes of seeded emulsion polymerization were used to prepare an outlayer of polysiloxane on the above seed latex particles: (A) direct anionic polymerization of D4 (octamethyl tetracyclosiloxane) catalyzed by potassium hydroxide; (B) direct cationic polymerization of D4 onto the seed catalyzed by dodecylbenzene sulfonic acid; (C) a vinyl-containing polysiloxane prepared by copolymerization of D4 and vinyl septamethyl tetracyclosiloxane was added before the D4 cationic polymerization. Characterization by transmission electron microscopy showed that only process C provided satisfactory results. Film hardness was measured, and the latex film from process C demonstrated the lowest hardness of all the films. The mechanism of polymerization is discussed.

Influences of MAA on the porous morphology of P(St–MAA) latex particles produced by batch soap-free emulsion polymerization followed by stepwise alkali/acid post-treatment

Soap-free P(St-MAA) latex particles with variable styrene (St)/methacrylic acid (MAA) ratio were synthesized by batch emulsion copolymerization at 70 degrees C for 7h, and the particles with porous structure were obtained after stepwise alkali/acid post-treatment. The effects of MAA amount on the particle morphologies after the alkali and the stepwise alkali/acid post-treatments were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Results indicated that the alkali-treated latex particles showed anomalous structure with rough surface, and no hollow was clearly identified inside them. When these alkali-treated particles were further treated with acid solution, the particle surface became much smoother, and porous morphology appeared. It was found that when the MAA amount was less than or equal to 4mol%, no obvious morphological variation was observed; while the latex particles showed clearly porous structure as the MAA amount increased to 6mol%; with the further increase of MAA amount to 8mol%, the pore size decreased distinctly.

Synthesis and characterization of covalently colored polymer latex based on new polymerizable anthraquinone dyes

Novel polymerizable red and yellow dyes, consisting of anthraquinone chromophore, alkyl spacer, and acryloyl group, were first synthesized and then used as comonomers in the semicontinuous emulsion copolymerization of styrene, butyl acrylate, and methacrylic acid to fabricate polymer latexes. The influences of the dye monomers on the emulsion polymerization process, the latex particle size and its distribution, the molecular weight of the latex polymer, as well as the light fastness of the polymer latex films, were investigated. Results indicated that, despite of the inhibition effect of the polymerizable dyes on polymerization, stable colored polymer latexes could be prepared with high conversion of total monomers, whereas the conversion of the polymerizable dye decreased as increasing the amount of dye. The light fastness of the covalently colored polymer latex films was proved to be much better than that of the noncovalently colored polymer latex films due to the covalent bond of dye and polymer chains.

Preparation and Properties of Thermoplastic Expandable Microspheres With P(VDC-AN-MMA) Shell by Suspension Polymerization

Thermoplastic expandable microspheres (TEMs) having core/shell structure were prepared via suspension polymerization with vinylidene chloride (VDC), acrylonitrile (AN), and methyl methacrylate (MMA) as monomers and i-butane as blowing agent. TEMs were about 20 µm in diameter and had a hollow core containing i-butane. The influence of the monomer feed ratio and blowing agent content was researched. When the monomers composition of 58.4 wt% VDC, 28 wt% AN, 13.6 wt% MMA, and 32 wt% i-butane in oil phase, suspension polymerization could yield TEMs having good expansion properties. The maximum expansion volume was 25 times of original volume at about 111–120°C, the blowing agent content in microspheres was about 21.5 wt%. The Tm.e, To.e, and To.s. of the TEMs increased with the VDC content in the polymerizable monomers decreasing. GRAPHICAL ABSTRACT