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.     

Preparation and properties of core–shell nanosilica/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) latex

A core–shell nanosilica (nano‐SiO₂)/fluorinated acrylic copolymer latex, where nano‐SiO₂ served as the core and a copolymer of butyl acrylate, methyl methacrylate, and 2,2,2‐trifluoroethyl methacrylate (TFEMA) served as the shell, was synthesized in this study by seed emulsion polymerization. The compatibility between the core and shell was enhanced by the introduction of vinyl trimethoxysilane on the surface of nano‐SiO₂. The morphology and particle size of the nano‐SiO₂/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) [P(MMA–BA–TFEMA)] core–shell latex were characterized by transmission electron microscopy. The properties and surface energy of films formed by the nano‐SiO₂/P(MMA–BA–TFEMA) latex were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, and static contact angle measurement. The analyzed results indicate that the nano‐SiO₂/P(MMA–BA–TFEMA) latex presented uniform spherical core–shell particles about 45 nm in diameter. Favorable characteristics in the latex film and the lowest surface energy were obtained with 30 wt % TFEMA; this was due to the optimal migration of fluorine to the surface during film formation. The mechanical properties of the films were significantly improved by 1.0–1.5 wt % modified nano‐SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Interfacially initiated microemulsion copolymerization: One‐stage preparation of poly(n‐butyl methacrylate)–poly(N‐vinyl pyrrolidone) core–shell nanoparticles

Interfacially initiated microemulsion copolymerizations of n‐butyl methacrylate (BMA) and N‐vinyl pyrrolidone (NVP) by the redox initiation couple of benzoyl peroxide and ferrous sulfate were carried out with Tween 80 and n‐butanol as the surfactant and cosurfactant, respectively. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy were recorded to analyze the chemical composition of the latex particles. Transmission electron microscopy was used to observe the particle morphology and dynamic light scattering to determine the particle size. The results demonstrated that interfacially initiated microemulsion polymerization prompted the copolymerization of the water‐soluble NVP monomer with the oil‐soluble BMA monomer to form core–shell nanoparticles. The influence of the surfactant concentration, BMA amount, and temperature on the particle size and polymerization rate was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3751–3757, 2006     

Impact Modification and Fracture Mechanisms of Core–Shell Particle Reinforced Thermoplastic Protein

Mechanical properties and fracture mechanisms of Novatein thermoplastic protein and blends with core–shell particles (CSPs) have been examined. Novatein is brittle with low impact strength and energy‐to‐break. Epoxy‐modified CSPs increase notched and unnotched impact strength, tensile strain‐at‐break, and energy‐to‐break, while tensile strength and modulus decrease as CSP content increases. T_g increases slightly with increasing CSP content attributed to physical crosslinking. Changes to mechanical properties are related to the critical matrix ligament thickness and rate of loading. Novatein control samples display brittle fracture characterized by large‐scale crazing. At high CSP content a large plastic zone and a slow crack propagation zone in unnotched and tensile samples are observed suggesting increased energy absorption. Notched impact samples reach critical craze stresses easily regardless of CSP content reducing impact strength. It is concluded that the impact strength of thermoplastic protein can be modified in a similar manner to traditional thermoplastics.

     

Core–shell latex particles consisting of polysiloxane–poly(styrene-methyl methacrylate-acrylic acid): Preparation and pore generation

Latexes with a poly(dimethyl siloxane) core and a poly(styrene-methyl methacrylate-acrylic acid) [poly(St-MMA-AA)] shell have been prepared in two steps in order to generate particles that have a core with a very low glass transition temperature. In the first step, poly(dimethyl siloxane) particles were obtained via the ring-opening emulsion polymerization of octamethyl tetracyclosiloxane (D₄). The polymerization was carried out using either an anionic or a cationic catalyst. In the first case, sodium hydroxide was used as catalyst and sodium dodecylbenzene sulfonate as surfactant, while in the second, the alkylbenzene sulfonic acid (ABSA) was used both as catalyst and surfactant. Using a PD₄ latex as seed, a seeded emulsion polymerization of St-MMA-AA was conducted to obtain PD₄–P(St-MMA-AA) core–shell particles. Numerous recipes were attempted and the most successful were those in which the seed was prepared with a cationic catalyst (ABSA) at a relatively low temperature (75°C). The core–shell structure of the particles was identified by transmission electron microscopy, but also via wetting angle, water absorption, and T_g measurements. Finally, pores were generated in the core–shell particles via an alkali–acid treatment. Because PD₄ has a very low glass transition temperature, it cannot be easily handled. However, protected by a shell, it could be used as a constituent of composite materials with enhanced impact strength, even at very low temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2235–2245, 1999     

Synthesis,characterization, and in vitro release of ibuprofen from poly(MMA‐HEMA) copolymeric core–shell hydrogel microspheres for biomedical applications

This article describes the development of a new crosslinked poly(methyl methacrylate‐2‐hydroxyethyl methacrylate) copolymeric core–shell hydrogel microsphere incorporated with ibuprofen for potential applications in bone implants. Initially poly(methyl methacrylate) (PMMA) core microspheres were prepared by free‐radical initiation technique. On these core microspheres, 2‐hydroxyethyl methacrylate (HEMA) was polymerized by swelling PMMA microspheres with the HEMA monomer by using ascorbic acid and ammonium persulfate. Crosslinking monomers such as ethylene glycol dimethacrylate (EGDMA) has also been included along with HEMA for polymerization. By this technique, it was possible to obtain core–shell‐type microspheres. The core is a hard PMMA microsphere having a hydrophilic poly(HEMA) shell coat on it. These microspheres are highly hydrophilic as compared to PMMA microspheres. The size of the hydrogel microspheres almost doubled when swollen in benzyl alcohol. These microspheres were characterized by various techniques such as optical microscopy, scanning electron microscopy, Fourier‐transformed infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The particle size of both microspheres was analyzed by using Malvern Master Sizer/E particle size analyzer. The in vitro release of ibuprofen from both microspheres showed near zero‐order patterns. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3045–3054, 2002; DOI 10.1002/app.10310     

Effect of ethylene–acrylate–(maleic anhydride) terpolymer on mechanical properties and morphology of poly(ethylene terephthalate)/polyamide‐6 blends

Background: Poly(ethylene terephthalate) (PET)/polyamide‐6 (PA‐6) blends are promising for engineering and food‐packaging applications. However, their poor toughness limits their use. In this study, an ethylene–acrylate–(maleic anhydride) terpolymer (E‐AE‐MA) was added to PET/PA‐6 blends in order to improve the toughness. Results: Izod impact tests indicated an excellent toughening effect of E‐AE‐MA. E‐AE‐MA particles were observed to be selectively dispersed at the interface between PET and PA‐6 phases and in the domain of the PA‐6 phase. Fourier transform infrared spectroscopy and differential scanning calorimetry results demonstrated that the formation of E‐AE‐MA layers around PA‐6 particles cut off the interaction between PET and PA‐6, resulting in an enlarged PA‐6 phase domain. Conclusion: Based on the experimental results, a core–shell microstructure, with PA‐6 as a hard core and E‐AE‐MA as a soft shell, could be suggested. The formation of this core–shell microstructure, along with the increased PA‐6 phase domain size, is the main toughening mechanism of E‐AE‐MA in PET/PA‐6 blends. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of poly(methyl methacrylate–butyl acrylate–acrylic acid)/polyaniline core–shell nanoparticles in miniemulsion media

Conductive polymer particles, polyaniline (PANI)‐coated poly(methyl methacrylate–butyl acrylate–acrylic acid) [P(MMA–BA–AA)] nanoparticles, were prepared. The P(MMA–BA–AA)/PANI core–shell complex particles were synthesized with a two‐step miniemulsion polymerization method with P(MMA–BA–AA) as the core and PANI as the shell. The first step was to prepare the P(MMA–BA–AA) latex particles as the core via miniemulsion polymerization and then to prepare the P(MMA–BA–AA)/PANI core–shell particles. The aniline monomer was added to the mixture of water and core nanoparticles. The aniline monomer could be attracted near the outer surface of the core particles. The polymerization of aniline was started under the action of ammonium persulfate (APS). The final product was the desired core–shell nanoparticles. The morphology of the P(MMA–BA–AA) and P(MMA–BA–AA)/PANI particles was characterized with transmission electron microscopy. The core–shell structure of the P(MMA–BA–AA)/PANI composites was further determined by Fourier transform spectroscopy and ultraviolet–visible measurements. The conductive flakes made from the core–shell latexes were prepared, and the electrical conductivities of the flakes were studied. The highest conductivity of the P(MMA–BA–AA)/PANI pellets was 2.05 S/cm. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Poly(methyl methacrylate)/SIO2 hybrid membranes: Effect of solvents on structural and thermal properties

In this paper, hybrid organic–inorganic membranes were prepared using three different solvents and characterized. The hybrid membranes were fabricated using sol–gel technique, which had polymethyl‐methacrylate (PMMA) and tetraethyl orthosilicate (TEOS) as materials, with 80/20 ratio. The thin films were then characterized using FTIR, SEM, EDX, and mapping techniques. From the preliminary characterization, hybrid membranes were found to have nano and ultra scale tight‐pores ranges, which was influenced by the solvent used. The SEM images clearly show that hybrid membranes have homogenous and smooth surface. FTIR spectroscopy uncovered all the signature peaks characteristic of silicate structures in the near‐surface regions. Fingerprints of Si? O? Si groups in cyclic and linear molecular substructures were also present. From DSC analysis, the T_g value of the PMMA moieties in hybrids membranes was in the order H‐15‐Toluene < Pure PMMA < H‐15‐THF < H‐15‐DMF. Furthermore, from TGA analysis it was found that the hybrid membranes have higher thermal stability compared with that of pure PMMA. EDX and mapping analysis showed that the composition and distribution of particles in the membranes were different and dependent on the solvents used. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis and characterization of spinning poly(acrylonitrile‐co‐silk fibroin peptide)s

A novel spinning acrylic polymer containing silk protein was synthesized by copolymerization of acrylonitrile (AN) and silk fibroin peptide (SFP) modified by acryloyl chloride (AC) with vinyl groups. From results of the examination to the chemical compositions, we established that the modified SFP is more reactive than AN in the copolymerization. The intrinsic viscosity values of these copolymers showed that the copolymers have good spinnability, which were synthesized under the condition of adding a trace of metal ions into the synthesizing solvent. These copolymers exhibited good thermal property. The fiber based on the poly(acrylonitrile‐co‐silk fibroin peptide) was prepared and characterized by SEM, FTIR measurement of its shell and core flakes, and moisture absorption. The fiber exhibited a smooth surface and could be assumed to have excellent adhesive property between SFP and PAN. Furthermore, these fibers showed a core–shell structure and excellent moisture absorption. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1540–1547, 2004     

Effect of Silica‐Coated Poly(butyl methacrylate)‐block‐poly(methyl methacrylate) Double‐Shell Particles on the Mechanical Properties of PMMA Composites

Silica nanoparticles with an average diameter of 12 nm are grafted with PBMA‐b‐PMMA double shells through typical sequential ATRP from bromoisobutyrate initiators anchored at the silica surface using an epoxysilane. A commercially available PMMA homopolymer is used for the preparation of composites with unmodified, silane‐modified and double‐shell‐modified silica particles. Good mechanical properties are obtained for silica double shell containing systems. The silica content in double shell particle systems is varied from 0 to 2.5 wt%. A significant improvement in impact properties is observed. The surface‐modified silica particles are characterized by ATR‐FTIR, NMR, GPC, and thermal analyses. TEM analysis is used to analyze the nature of dispersion of particles in the composites.

     

PTFE–PMMA core–shell colloidal particles as building blocks for self‐assembled opals: synthesis,properties and optical response

A seeded surfactant‐free methyl methacrylate emulsion polymerization is employed to prepare core–shell particles with predetermined size and narrow size distribution. The particle size is determined by the ratio between methyl methacrylate (MMA, shell) and polytetrafluoroethylene (PTFE, core). Monodisperse particles in the 100–350 nm range are obtained. These particles are used to grow colloidal photonic crystals (opals) of very high optical quality, thus indirectly demonstrating the excellent control of microbead size distribution achieved by this preparation technique. The optical properties of the opals are investigated by means of reflectance and polarized‐angle‐resolved transmittance spectroscopies. These data provide a rough determination of the effective refractive index of the system, which is favorably compared with values obtained by simple effective medium models. Copyright © 2012 Society of Chemical Industry     

The interfacial effect of TiO2–Ag core–shell micro‐/nanowires on poly(arylene ether nitrile)

Novel TiO₂–Ag core–shell micro‐/nanowires (TiO₂ shell coating on Ag core) have been successfully prepared via a solvent–thermal method. Energy dispersive spectroscopy and X‐ray diffraction analyses revealed that the micro‐/nanowires were composed of Ag, Ti and O elements, and Ag was face‐centered cubic whereas TiO₂ was mainly amorphous. Interestingly, scanning electron microscopy (SEM) and transmission electron microscopy results showed that most of the TiO₂ bristles were perpendicular to and uniformly studded on the surface of the Ag cores. Subsequently, TiO₂–Ag/poly(arylene ether nitrile) (PEN) composite films were prepared via a solution‐casting method in order to investigate the effect of TiO₂–Ag on the PEN matrix. SEM images showed that there was good interfacial adhesion between fillers and PEN matrix owing to the special bristle‐like structure. Thermal analysis results showed that the TiO₂–Ag/PEN composite films possessed excellent thermal properties endowed by the PEN matrix. The dielectric constant of the composite films increased to 9.3 at 100 Hz when the TiO₂–Ag loading reached 40 wt%. Rheology measurements revealed that the network formed by TiO₂–Ag was sensitive to shear stress and nearly time independent. © 2013 Society of Chemical Industry     

Fabrication of CL-20/HMX Cocrystal@Melamine–Formaldehyde Resin Core–Shell Composites Featuring Enhanced Thermal and Safety Performance via In Situ Polymerization

Safety concerns remain a bottleneck for the application of 2,4,6,8,10,12-hexanitro- 2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)/1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) cocrystal. Melamine–formaldehyde (MF) resin was chosen to fabricate CL-20/HMX cocrystal-based core–shell composites (CH@MF composites) via a facile in situ polymerization method. The resulted CH@MF composites were comprehensively characterized, and a compact core–shell structure was confirmed. The effects of the shell content on the properties of the composites were explored as well. As a result, we found that, except for CH@MF–2 with a 1% shell content, the increase in shell content led to a rougher surface morphology and more close-packed structure. The thermal decomposition peak temperature improved by 5.3 °C for the cocrystal enabled in 1.0 wt% MF resin. Regarding the sensitivity, the CH@MF composites exhibited a significantly reduced impact and friction sensitivity with negligible energy loss compared with the raw cocrystal and physical mixtures due to the cushioning and insulation effects of the MF coating. The formation mechanism of the core–shell micro-composites was further clarified. Overall, this work provides a green, facile and industrially potential strategy for the desensitization of energetic cocrystals. The CH@MF composites with high thermal stability and low sensitivity are promising to be applied in propellants and polymer-bonded explosive (PBX) formulations.     

Molecular dynamics study of TiO2/poly(acrylic acid‐co‐methyl methacrylate) and Fe3O4/polystyrene composite latex particles prepared by heterocoagulation

All‐atom molecular dynamics simulations were used to study the morphology of polymer/inorganic composite particles prepared by heterocoagulation. The results were also compared to those of our previous study of the preparation of TiO₂/poly(acrylic acid‐co‐methyl methacrylate) and Fe₃O₄/polystyrene composite particles. In the simulation system, polymer or inorganic particles were simulated by surface‐charge‐modified C₆₀ or Na atoms. Through a combination of analysis of the radial distribution functions of charged atoms and snapshots of the equilibrated structure, three kinds of particle distributions were observed under different conditions. When the polymer and inorganic particles had opposite surface charges and their sizes were very different, the composite morphology showed a core–shell structure with small particles adsorbed onto the surfaces of large particles. Furthermore, when the polymer and inorganic particles had opposite surface charges but comparable sizes, the polymer and inorganic particles aggregated domain by domain. Finally, when the polymer and inorganic particles were endowed with the same surface charge, the distribution of these two types of particles was homogeneous, regardless of their size difference. The simulation results were in agreement with the experimental results. The electrostatic interaction and the size of the particles dominated the final morphology of the composite particles when the heterocoagulation method was used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Epoxy networks toughened by core–Shell particles: Influence of the particle structure and size on the rheological and mechanical properties

The core–shell particles considered were poly(butyl acrylate) core/epoxy groups functionalizing the poly(methyl methacrylate) shell. Physical and thermomechanical properties of benzyl dimethylamine (BDMA)‐catalyzed diglycidyl ether of bisphenol A (DGEBA)/dicyandiamine epoxy networks toughened with core–shell particles were studied. The blends were prepared under well‐defined processing conditions. The resulting properties were found to depend on the state of the dispersion of the particles in the prepolymer matrix before crosslinking. These particles were dispersed at different volume fractions in order to vary the interparticle distance. The relationships between the size of the core–shell particles and the level of toughening are reported. Static mechanical tests were performed in tension and compression modes on these core–shell polyepoxy blends. A slight decrease in the Young's modulus and an increase in the ability to plastic deformation were observed. Using linear fracture mechanics (LEFM), an improvement of the fracture properties (K_IC) was measured. By varying the volume fraction of core–shell particles, an optimum toughness improvement was found for an interparticle distance equal to 400 nm (with an average particle size of 600 nm). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 849–858, 1999     

Preparation of core–shell poly(acrylic acid)/polystyrene/SiO2 hybrid microspheres

Core–shell poly(acrylic acid)/polystyrene/SiO₂ (PAA/PS/SiO₂) hybrid microspheres were prepared by dispersion polymerization with three stages in ethanol and ethyl acetate mixture medium. Using vinyltriethoxysilane (VTEOS) as silane agent, functional silica particles structured vinyl groups on surfaces were prepared by hydrolysis and polycondensation of tetraethoxysilane and VTEOS in core stage. Then, the silica particles were used as seeds to copolymerize with styrene and acrylic acid sequentially in shell stage I and stage II to form PAA/PS/SiO₂ hybrid microspheres. Transmission electron microscope results show that most PAA/PS/SiO₂ hybrid microspheres are about 40 nm in diameter, and the silica cores are about 15 nm in diameter, which covered with a layer of PS about 7.5‐nm thick and a layer of PAA about 5‐nm thick. This core–shell structure is also conformed by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and differential scanning calorimetry. FTIR results show that silica core, PS shell, and PAA outermost shell are bonded by covalents. In the core–shell PAA/PS/SiO₂ hybrid microsphere, the silica core is rigidity, and the PAA outermost shell is polarity, while the PS layer may work as lubricant owning to its superior processing rheological property in polymer blending. These core–shell PAA/PS/SiO₂ hybrid microspheres have potential as new materials for polar polymer modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1729–1733, 2006     

Compatibilizing effect of diglycidyl ether of bisphenol‐A in polymer blend system: Nylon 6 combined with poly(butyl acrylate) core and poly(methyl methacrylate) shell particles

A polymeric blend system of nylon 6 and a core–shell impact modifier was studied. The modifier had a poly(butyl acrylate) core and a poly(methyl methacrylate) (PMMA) shell compatibilized with an epoxy resin, diglycidyl ether of bisphenol‐A (DGEBA). The compatibilization of DGEBA is achieved by the reaction of its glycidyl group with the amine groups of nylon 6, and hydrogen bonds may be generated between the hydroxyl groups and the carbonyl groups on PMMA. The effect of compatibilization was verified by the dramatic increase in impact strength and the finer dispersing of the core–shell particles in the nylon 6 matrix. The effects of compatibilization on other properties of the blend, such as the tensile and rheological properties, were also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 24–29, 2000