Self‐assembly of pH‐responsive acrylate latex particles at emulsion droplets interface

The self‐assembly of pH‐responsive poly (methyl methacrylate‐co‐acrylic acid) latex particles at emulsion droplet interfaces was achieved. Raising pH increases the hydrophilicity of the latex particles in situ and the latex particle acts as an efficient particulate emulsifier self‐assembling at emulsion droplet interface at around pH 10–11 but exhibits no emulsifier activity at higher pH. This effect can be reversibly induced simply by varying the aqueous phase pH and thus the latex emulsifier can be reassembled. The effect factors, including the aqueous phase pH, the surface carboxyl content, ζ‐Potential of the latex particles and oil phase solvent have been investigated. Using monomer as oil phase, the latex particles could stabilize emulsion droplets during polymerization and cage‐like polymer microspheres with hollow core/porous shell structure were obtained after polymerization. The mechanism of the latex particles self‐assembly was discussed. The morphologies of emulsion and microspheres were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Adaptive Polymeric Coatings with Self‐Reporting and Self‐Healing Dual Functions from Porous Core–Shell Nanostructures

In biological system, early detection and treatment at the same moment is highly required. For synthetic materials, it is demanding to develop materials that possess self‐reporting of early damage and self‐healing simultaneously. This dual function is achieved in this work by introducing an intelligent pH‐responsive coatings based on poly(divinylbenzene)‐graft‐poly(divinylbenzene‐co‐methacrylic acid) (PDVB‐graft‐P(DVB‐co‐AA)) core–shell microspheres as smart components of the polymer coatings for corrosion protection. The key component, synthesized PDVB‐graft‐P(DVB‐co‐AA) core–shell microspheres are porous and pH responsive. The porosity allows for encapsulation of the corrosion inhibitor of benzotriazole and the fluorescent probe, coumarin. Both loading capacities can be up to about 15 wt%. The polymeric coatings doped with the synthesized microspheres can adapt immediately to the varied variation in pH value from the electrochemical corrosion reaction and release active molecules on demand onto the damaged cracks of the coatings on metal surfaces. It leads simultaneously to the dual functions of self‐healing and self‐reporting. The corrosion area can be self‐reported in 6 h, while the substrate can be protected at least for 1 month in 3.5 wt% NaCl solution. These pH‐responsive materials with self‐reporting and self‐healing dual functions are highly expected to have a bright future due to their smart, long‐lasting, recyclable, and multifunctional properties.     

Dynamic layer‐by‐layer self‐assembly of organic–inorganic composite hollow fiber membranes

Multilayer membranes constructed layer‐by‐layer (LbL) is finding increasing importance in many separation applications. The efficient construction of LbL multilayer on to hollow fiber substrates may offer many new opportunities for industrial applications. An organic–inorganic composite hollow fiber membrane has been developed using a dynamic LbL self‐assembly. This poly(acrylic acid)/poly(ethyleneimine) multilayer was dynamically assembled onto the inner surfaces of ceramic hollow fiber porous substrates pretreated by Dynasylan Ameo silane coupling agents. The hollow fibers were subsequently heat crosslinked to obtain stable permselective membranes. The formation of multilayers on the hollow fibers was characterized with a SEM, EDX, an electrokinetic analyzer and IR spectra. The effects of layer number, feed temperature and water content in the feed on the pervaporation performance have been investigated. To the best of our knowledge, this is the first report of LbL assembly of polymer building blocks onto ceramic hollow fiber porous substrates. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3176–3182, 2012     

Emulsifier‐free reversible addition–fragmentation chain transfer emulsion polymerization of alkyl acrylates mediated by symmetrical trithiocarbonates based on poly(acrylic acid)

Emulsifier‐free batch emulsion polymerization of n‐butyl acrylate and its semi‐batch copolymerization with 2,2,3,3,4,4,5,5‐octafluoropentyl acrylate and 2,2,3,4,4,4‐hexafluorobutyl acrylate both mediated by poly(acrylic acid) containing the trithiocarbonate group in the chain was employed to produce amphiphilic triblock copolymers. The polymerization‐induced self‐assembly of these copolymers in aqueous media gave rise to spherical core–shell particles. Irrespective of the experimental conditions, the polymeric product was characterized by a bimodal molecular weight distribution. The apparent violation of the reversible addition–fragmentation chain transfer polymerization mechanism may be attributed to restricted accessibility of the trithiocarbonate group in the self‐assembled block copolymers for propagating radicals that enter into the particle. Mean‐field theoretical arguments were employed to explain the exclusively spherical morphology of the particles observed in the experiment. © 2019 Society of Chemical Industry     

Facile fabrication of double‐walled polymeric hollow spheres with independent temperature and pH dual‐responsiveness for synergetic drug delivery

A dual‐responsive double‐walled polymeric hollow sphere (PHS) serving as a candidate for synergetic drug delivery platform is prepared by a simple and green template polymerization in aqueous medium. The PHS, comprised of thermo‐responsive crosslinked poly(N‐isopropylacrylamide) (PNIPAM) as the inner shell and pH‐responsive crosslinked poly(methacrylic acid) (PMAAc) as the outer shell, is assembled through self‐removal of the thermo‐responsive template from a core‐triple shell structure by free radical polymerization with sequential addition of reactants. The discrete double‐shell structure renders the PHS independent temperature and pH‐controlled swelling/shrinking capability. Taking the advantage of two compartmentalized internal spaces (the core and the interlayer spaces) with independent temperature‐ and pH‐dependent behaviors, two model drugs representing the small molecule and the macromolecule are loaded in selective locations of the PHS. Two drugs show dramatically different release profiles according to environmental temperature and pH, due to the localization of drugs and the stimuli‐dependent property of its protective shells. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44335.     

Microcapsules prepared from a polycondensate‐based cement dispersant via layer‐by‐layer self‐assembly on melamine‐formaldehyde core templates

Novel microcapsules were prepared from colloidal core–shell particles by acid dissolution of the organic core. Weakly crosslinked, monodisperse and spherical melamine‐formaldehyde polycondensate particles (diameter ～ 1 μm) were synthesized as core template and coated with multilayers of an anionic polyelectrolyte via layer‐by‐layer deposition technique. As polyelectrolytes, an anionic naphthalenesulfonate formaldehyde polycondensate that is a common concrete superplasticizer and thus industrially available, and cationic poly(allylamine hydrochloride) were used. Core removal was achieved by soaking the core–shell particles in aqueous hydrochloric acid at pH 1.6, resulting in hollow microcapsules consisting of the polyelectrolytes. Characterization of the template, the core–shell particles, and the microcapsules plus tracking of the layer‐by‐layer polyelectrolyte deposition was performed by means of zeta potential measurement and scanning electron microscopy. The microcapsules might be useful as microcontainers for cement additives. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Controlled heparinase‐catalyzed degradation of polyelectrolyte multilayer capsules with heparin as responsive layer

This work describes the enzymatic degradation of combined hollow capsules via layer‐by‐layer (LbL) self‐assembly technique. They previously showed the build‐up and characterization of capsules composed of synthetic [Poly(sodium 4‐styrene‐sulfonate)/Poly(allylamine hydrochloride)] and biodegradable (Heparin/Chitosan) polyelectrolytes. Biocatalytic response of assembled multilayer capsules provides a more functional and oriented approach in controlled release of encapsulated molecules: in this case multilayer capsule was disassembled by heparinase. Morphological change of individual capsule was assessed with Atomic Force Microscopy and Confocal Laser Scanning Microscopy. The sustained release of encapsulated FITC‐Dextran model was realized under enzymatic degradation of the capsule shells by heparinase. The release profile of FITC‐Dextran indicated the successful control in a concentration‐dependent manner, which shows the applicability as smart drug delivery system. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44916.     

A highly efficient dispersant from black liquor for carbendazim suspension concentrate: Preparation,self‐assembly behavior and investigation of dispersion mechanism

Compared with traditional approaches using synthetic amphiphilic block copolymers, alkyl chain cross‐linked lignosulfonate (ASL) with high molecular weight (Mw) from black liquor was synthesized and characterized by GPC, functional group content, FTIR, and ¹H‐NMR measurement, and then used as water soluble amphiphilic biopolymer to prepare polymersomes via solution self‐assembly. DLS illustrated the solution assembly behavior. The hollow nature of nanospheres was revealed by TEM. Moreover, the element analysis and XPS results revealed the hollow sphere structure with a hydrophilic core and a hydrophobic shell. It facilitated the efficient encapsulation of pesticide carbendazim into the hollow sphere via electrostatic interaction, which was investigated by SEM, TEM, elemental analysis and XPS. In our study, ASLs with different Mw from 20 kDa to 200 kDa all could exhibit the similar self‐assembly behavior, which suggests that the hollow spheres and the encapsulation experiment were easily duplicated from ASL polymers without structure dependence. Furthermore, the dispersion properties of ASL in the carbendazim suspension concentrate (SC) system were also investigated, which showed that SC with ASL exhibited better dispersion property and rheological performance than that of NSF and commercial LS. Preparation and application of polymersomes via self‐assembly from modified‐lignin from black liquor provide a promising and effective scaffold which can be conveniently obtained from cheap and renewable bioresource. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43067.     

Preparation of monodisperse fluorescent core–shell polymer microspheres with functional groups in the shell layer by two‐stage distillation–precipitation polymerization

Monodisperse crosslinked core–shell micrometer‐sized microspheres bearing a brightly blue fluorescent dye, carbazole, and containing various functional groups in the shell layers were prepared by a two‐stage distillation–precipitation polymerization in acetonitrile in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80 vol.% of DVB, was polymerized by distillation–precipitation in acetonitrile without any stabilizer using 2,2′‐azobisisobutyronitrile (AIBN) as the initiator for the first stage of polymerization which resulted in monodisperse polyDVB microspheres used as the core. Several functional monomers, including 2‐hydroxyethyl methacrylate and acrylonitrile together with N‐vinylcarbazole blue fluorescent comonomer, were incorporated into the shell layers with AIBN as initiator during the second stage of polymerization. The resultant core–shell polymer microspheres were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, UV‐visible spectroscopy and fluorescence spectroscopy. Copyright © 2006 Society of Chemical Industry     

Enhanced Combustion Characteristics of Bismuth Trioxide‐Aluminum Nanocomposites Prepared through Graphene Oxide Directed Self‐Assembly

We present a facile, spontaneous, and surfactant‐free method to controllably self‐assemble aluminum and bismuth trioxide nanoparticles through the introduction of graphene oxide as a self‐assembly directing agent. The self‐assembled nanocomposites demonstrate significant combustion performance improvements in comparison to randomly mixed aluminum and bismuth trioxide nanoparticles with enhanced pressure generation from 60 to 200 MPa, pressurization rate from 3 to 16 MPa μs⁻¹, burning rate from 1.15 to 1.55 km s⁻¹, and specific impulse from 41 to 71 s. The sensitivity of the self‐assembled aluminum and bismuth trioxide to electrostatic discharge was reduced by four orders of magnitude, without decreasing the combustion performance. Graphene oxide directed self‐assembly can be used to synthesize nanocomposites with diverse combustion properties and controlled ignition sensitivity, which lays the foundation for preparing multi‐functional, highly‐reactive, combustion systems in the future.     

‘Bricks and mortar’ nanoparticle self‐assembly using polymers

Developments in self‐assembly methods allow access to hierarchical materials featuring a wide range of functionality and applications. Polymer‐based self‐assembly of nanoparticles opens up new avenues for the fabrication of highly structured nanocomposites that can serve as bridges between ‘bottom‐up’ and ‘top‐down’ methods. Of various interactions leading to self‐assembly of nanocomposites, hydrogen bonding and electrostatic interactions are commonly utilized. In this review, we illustrate the design and subsequent property tuning of various self‐assembled nanocomposite materials that were developed based on these interactions. Copyright © 2007 Society of Chemical Industry     

A general template for synthesis of hollow microsphere with well‐defined structure

Using chitooligosaccharides (COS) as the backbones and polycaprolactones (PCL) as the branches, a novel type of amphiphilic graft copolymers with a large amount of free ? OH and ? NH₂ groups remained on the COS backbones was synthesized. The obtained Chitooligosaccharide‐graft‐poly(ε‐caprolactone)(COS‐g‐PCL) was self‐assembled into giant vesicles which served as templates for the preparation of hollow spheres of a series of metals(Au, Ag, Cu, Pt, and Pd). The method involved the initial mixing of COS‐g‐PCL and metal‐containing groups or metal ions to generate corresponding complex, followed by adding the selective solvent of water to induce the self‐assembly of the graft copolymers into giant vesicles; Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. In addition, hybrid hollow spheres with fluorescent quantum dots and silica hollow spheres were also prepared by slightly modified procedures. A preliminary study on the trinitrotoluene sensor of CdS/vesicle hybrid hollow spheres revealed a considerable sensitivity, which exemplifies the distinct properties imparted by the hybrid hollow structure. All of the results demonstrate that the giant vesicles self‐assembled from COS‐g‐PCL could be utilized as effective templates for the synthesis of various hollow spheres. Using Chitooligosaccharide‐graft‐poly(ε‐caprolactone) vesicles as general templates, the hollow spheres of a series of metals such as Au, Ag, Cu, and Pt were produced. The method involved the initial absorption of metal ions from solution into the functional surface layer of the graft copolymer giant vesicles. Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of core–shell glass bead/polysulfone microspheres with two‐step sol–gel process

Core–shell microspheres made from glass beads as the core phase and polysulfone (PSf) as the shell phase can act as an absorbent in the separation process or a supporter for chemical reactions. Based on phase‐inversion principles, a two‐step sol–gel method was developed in this work in which ether was added first and H₂O was added second to a PSf‐containing dimethyformamide (DMF) solution to help PSf solidify on the surface of glass beads. The results from scanning electron microscopy, Fourier transform IR, and X‐ray photoelectron spectroscopy showed that a dense layer of PSf (thin to several microns) was coated on the glass beads and the core–shell microspheres were almost monodispersed. The utilization percentages of the glass beads and PSf were high as 100 and 80%, respectively. The thickness of the PSf membrane was calculated to be about 4.3 μm. To obtain well‐monodispersed microspheres, the practical volume ratio of ether to DMF was recommended to be larger than 4.5. The results suggested that the two‐step sol–gel method is a highly efficient process for preparation of glass bead/PSf core–shell microspheres. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3365–3369, 2006     

Self‐assembly morphology evolution of the polyamide 6 (PA6) component in the PA6/polyethylene glycol system by in situ polymerization of ϵ‐caprolactam monomer

This paper describes the morphology evolution of polyamide 6 (PA6) components in the presence of polyethylene glycol (PEG) by self‐assembly via in situ anionic ring‐opening polymerization of ?‐caprolactam (CL) monomer and expands the study of morphology changes of PA6 in the PA6/PEG system. With a fixed mass ratio of [CL]/[PEG], it was found that by simply changing the reaction conditions the morphology of PA6 components could be changed from nano‐sized microspheres to regular 3D microsphere structured polyhedrons to 3D nano‐sized particle clusters to micro‐scale microspheres. The morphologies of the PA6 components were investigated by SEM and TEM analyses. The diameter range of the PA6 nano‐sized microspheres was controlled within 400 nm. The side length of an individual polyhedron could be effectively tuned from 10 µm to 100 µm. The diameter range of micrometer microspheres was about 5–8 µm. The results suggest that this strategy for self‐assembly can be applied to design materials with complex geometric structures. © 2018 Society of Chemical Industry     

Preparation of polyaniline coated polystyrene‐poly(styrene‐co‐sodium 4‐styrenesulfonate) microparticles and the further fabrication of hollow polyaniline microspheres

In this article, the microparticles of polystyrene‐poly(styrene‐co‐sodium 4‐styrenesulfonate) (PS‐PSS) coated by polyaniline (PANI) were prepared and hollow PANI microspheres were further obtained by dissolving the core. First, surface‐sulfonated monodispersed PS was prepared by copolymerization of sodium 4‐styrenesulfonate (SSS) and styrene with dispersion polymerization method. Then aniline was polymerized on the surface of the surface‐sulfonated PS (PS‐PSS) by chemical oxidative polymerization. After purification, we prepared core‐shell (PS‐PSS)/PANI particles. Hollow PANI microspheres were prepared by dissolving the plastic PS core of the (PS‐PSS)/PANI particles in chloroform. The growth process of PANI on the surface of PS‐PSS particles was investigated and the hollow PANI microspheres were characterized. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of poly(divinylbenzene‐co‐N‐isopropylacrylamide) microspheres and their hydrogen‐bonding assembly behavior for raspberry‐like core‐corona polymer composite

Narrowdisperse poly(divinylbenzene‐co‐N‐isopropylacrylamide) (poly(DVB‐co‐NIPAM)) functional microspheres with the diameter in the range of 630 nm and 2.58 μm were prepared by distillation–precipitation polymerization in neat acetonitrile in the absence of any stabilizer. The effect of N‐isopropylacrylamide (NIPAM) ratio in the comonomer feed on the morphology of the resultant polymer particles was investigated in detail with divinylbenzene (DVB) as crosslinker and 2,2′‐azobisisobutyronitrile (AIBN) as initiator. The monodisperse poly(DVB‐co‐NIPAM) microspheres with NIPAM fraction of 20 wt % were selected for the preparation of raspberry‐like core‐corona polymer composite by the hydrogen‐bonding self‐assembly heterocoagulation with poly(ethyleneglycol dimethacrylate‐co‐acrylic acid) [poly(EGDMA‐co‐AA)] nanospheres. Both of the functional poly(DVB‐co‐NIPAM) microspheres and the core‐corona particles were characterized with scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and elemental analysis (EA). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1350–1357, 2007     

Design Strategy for the Multilayer Core–Shell Bioceramics with Controlled Chemistry

New strategies for fabricating multiphase bioceramic porous scaffolds with time‐dependent biodegradation and pore network enlargement are of fundamental importance in the advancement of bioceramics. Here, we developed a one‐step preparation of core–shell bioceramic microspheres (~2 mm in diameter) with single‐ or double‐shell structure through a coaxially aligned multilayer capillary system. The Ca‐phosphate (CaP) and Ca‐silicate (CaSi) ceramic phase distribution could be also adjusted by extruding through different capillaries, and thus the biodegradation rate would be readily tailored over time. When the polystyrene (PS) microbeads of ~15 μm in diameter were premixed into the CaP‐ or CaSi‐containing alginate slurry, the tailorable porous structures could be introduced into the core or different shell layers of the microspheres. These micropores may potentially maximize the permeability for rapid exchange of guest molecules or inorganic ions from the bioceramics. Totally, such strategy is promising because the ceramic phases with different biological properties can be assembled into the core–shell bioceramic microspheres, and thus the macropore structure evolution may be readily manipulated in the closely packed microsphere systems. We believe our gradient hybrid methodology will have potential in various categories of advanced biomaterials of organic–inorganic composites.     

Silicon Carbonitride Hollow Nanospheres from a Block‐Copolymer Precursor

Nonoxide SiCN hollow nanospheres were prepared from a block‐copolymer comprising of a precursor block and a sacrificial block. The copolymer was first synthesized and then self‐assembled into core‐shell structured micelles with the sacrificial block forming the core and the precursor block forming the shell. The micelles were subsequently pyrolyzed at high temperatures to transform the shell into ceramics and to completely decompose the core to form a hole. The technique is probably applicable to other material systems.     

Polyaniline hollow microspheres constructed with their own self‐assembled nanofibers

Polyaniline (PANI) hollow microspheres constructed with their own nanofibers were prepared by inversed microemulsion polymerization associated with a template‐free method in the presence of β‐naphthalene sulfonic acid (β‐NSA) as the dopant. The hollow microspheres were 4.0–6.0 μm in outer diameter and 150–250 nm in shell thickness; they consisted of the nanofibers (20–30 nm in diameter and 150–250 nm in length). We propose that the coordination effect of the reversed emulsion and the dopant or dopant/aniline micelle might have been a driving force in the formation of the special microstructures/nanostructures, where the reversed microemulsion acted as a soft template in the formation of the microspheres and where NSA or the aniline/NSA micelle was regarded as a soft template in the formation of the nanofibers. The molar ratio of water to the aniline/NSA salt and ultrasonic irradiation were critical in the control of the formation yield and the diameter of the uniform microspheres. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3050–3054, 2006     

Preparation of polysulfone microspheres with a hollow core/porous shell structure and their application for oil spill cleanup

Polysulfone (PSF) microspheres with a hollow core/porous shell structure were prepared by a water‐in‐oil‐in‐water emulsion solvent evaporation method. The morphology of PSF could be controlled by variation of the surfactants, which included oleic acid, poly(vinyl pyrrolidone), and tween 80. The three kinds of prepared microspheres were developed as sorbents for the selective removal of oil from water. PSF microspheres with a hollow core/porous shell structure exhibited the best separation efficiency, which was 44.8 times higher than that of the pristine PSF powder. The oil‐absorbed microspheres combined with unsinkability, appropriate size, and highly hydrophobic and superoleophilic properties could be quickly distributed and collected in seconds and exhibited recyclability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013