Thermochromic core–shell nanofibers fabricated by melt coaxial electrospinning

Microcapsule/nanocapsule and encapsulation techniques have great potential for devices of functional materials. Also, electrospinning has attracted great attention for the fabrication of microstructures and nanostructures. The fluidity after melting limits the application of phase‐transformation thermochromic materials. In this study, with the melt coaxial electrospinning technique, a phase‐transformation thermochromic material was encapsulated in poly(methyl methacrylate) nanofibers. A device of this phase‐transformation thermochromic material was realized. With a poly(methyl methacrylate) shell with good optical transmission and a thermoresponsive core made of crystal violet lactone, bisphenol A, and 1‐tetradecanol core, the fibers had good thermal energy management, fluorescent thermochromism, and reversibility. The fabrication of thermochromic core–shell nanofibers has further potential in the preparation of temperature sensors with good fluorescence signals and body‐temperature calefactive materials with intelligent thermal energy absorption, retention, and release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cationic fluorinated polyacrylate core‐shell latex with pendant long chain alkyl: Synthesis,film morphology,and its performance on cotton substrates

We synthesized a novel cationic fluorinated polyacrylate latex (FLDH) with pendant long chain alkyl by copolymerization of perfluoroalkyl ethyl acrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, and 2‐hydroxypropyl acrylate. FTIR, ¹H‐NMR, TEM, DSC, and TGA were used to characterize the as‐prepared FLDH. Then fine morphology, components, and hydrophobicity of films on silicon wafer and cotton substrates were investigated by scanning electron microscope, field emission scanning electronic microscope, atomic force microscope, X‐ray photoelectron spectroscopy (XPS), contact angle meter, etc. Results showed that the FLDH particles had quasi‐spherical core‐shell structure with an average diameter of 144 nm. The core‐shell FLDH film thus had two T_g and its thermal property was improved compared to fluorine‐free acrylate latex. FLDH could form a film on both the cotton fiber and silicon wafer substrate. At an amplification of <60,000 (of the original fiber) and the observation rule (working distance) of >100 nm, FLDH showed a smooth resin film on the treated fabric/fiber surface. However, as the observation rule decreased to 2 nm‐almost a molecular lever‐the FLDH film mostly exhibited an inhomogeneous structure and uneven morphology in its atomic force microscope images. There were many low or high peaks in FLDH topography. Consequently, in 5 μm² scanning field, the root mean square roughness of FLDH film reached to 0.506 nm. XPS analysis indicated the perfluoroalkyl groups had the tendency to enrich at the surface. In addition, water contact angle of the treated fabric could attain 146.2°. FLDH do not influence whiteness of the treated fabric but will make it slightly stiff at high doses. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013     

Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials

In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO₂) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO₂ nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO₂ loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO₂ nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Alginate–poly(vinyl alcohol) core–shell microspheres for lipase immobilization

A lipase [triacylglycerol ester hydrolase (EC 3.1.1.3)] was encapsulated in sodium alginate (AlgNa)/poly(vinyl alcohol) (PVA) microspheres. Spherical AlgNa/PVA beads were prepared by the ionotropic gelation of an AlgNa/PVA blend in the presence of calcium tetraborate (CaB₄O₇). The particles were spherical and had an average diameter of 400 μm. The microspheres were studied with differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, and water transport by the equilibrium degree of swelling. The elevation of the glass‐transition temperature of the microspheres indicated specific crosslinking reactions of the component polymers (AlgNa/PVA). FTIR spectra showed no evidence of a strong chemical interaction changing the nature of the functional groups of both AlgNa and PVA in the AlgNa/PVA blends. The water diffusion coefficients increased with increasing PVA content in the microspheres, indicating a decrease in the resistance to mass transfer through the AlgNa/PVA microsphere wall. The AlgNa/PVA microspheres were characterized by the Michaelis constant (K_M) and the maximum reaction velocity (V_max), which were determined for both free and immobilized lipases. The enzyme affinity for the substrate (K_M/V_max) remained quite good after immobilization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1553–1560, 2006     

Synthesis and characterization of poly(butyl acrylate–methyl methacrylate)/polyaniline core–shell latexes

Poly(butyl acrylate–methyl methacrylate) [P(BA–MMA]/polyaniline (PANI) core–shell complex particles were synthesized with a two‐step emulsion polymerization method with P(BA–MMA) as the core and PANI as the shell. The first step was to prepare P(BA–MMA) latex particles as the core via soapless emulsion polymerization. The second step was to prepare P(BA–MMA)/PANI core–shell particles. Sodium dodecyl sulfate was fed into the P(BA–MMA) emulsion as a surfactant, and this was followed by the addition of the aniline monomer. A bilayer structure of the surfactant over the surfaces of the core particles was desired so that the aniline monomer could be attracted near the outer surface of the core particles. In some cases, dodecyl benzene sulfonic acid was added after 2 h when the polymerization of aniline was started. The final product was the desired core–shell particles. The morphology of P(BA–MMA) and P(BA–MMA)/PANI particles was observed with transmission electron microscopy. The thermal properties were studied with thermogravimetric analysis and differential scanning calorimetry. Furthermore, conductive films made from the core–shell latexes were prepared, and the electrical conductivities of the films were studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 823–830, 2007     

Novel polymer composites based on a mixture of preformed nanosilica‐filled poly(methyl methacrylate) particles and a diepoxy/diamine thermoset system

In this work, a new material based on an epoxy thermoset modified with a thermoplastic filled with silica nanoparticles was investigated. When thermoplastic particles are filled with nanoparticles with unique properties such as high efficiency for absorbing ultraviolet light, electric or magnetic shielding, high electrical conductivity, and high dielectric constants, more than an enhancement of the mechanical properties is expected to be achieved for modified epoxy‐based thermosets. Particles of poly(methyl methacrylate) (PMMA) filled with silica nanoparticles were used to modify a thermoset based on a full reaction between diglycidyl ether of bisphenol A and 3‐(aminomethyl)benzylamine. When the preformed thermoplastic particles were mixed with the reactive constituents of the epoxy system under certain curing conditions in which total miscibility was avoided, uniform particle dispersions could be obtained. The relationships between the composition, morphology (nanoscale and microscale), glass‐transition temperature, mechanical properties, and fracture toughness were considered. Four main results were obtained for consideration of the potential of silica‐filled PMMA as an important modifier of brittle epoxy thermoset systems: (1) a good dispersion of the silica nanoparticles in the PMMA domains, (2) a good dispersion of the silica‐filled PMMA microparticles in the epoxy matrix, (3) the possibility of partial dissolution of the PMMA‐rich domains into the epoxy system, and (4) a slight increase in properties such as the hardness, indentation modulus, and fracture toughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interfacial aspects of adhesion in polymer nanocomposite thin‐film devices

Nanoscale polymeric composites are important in many new electronic technologies, including lightweight and flexible devices and sensors. The influence of surface chemical treatments, which particularly affect the adhesion properties of carbon–polyimide nanocomposite thin films, was studied with infrared spectroscopy, electron microscopy, atomic force microscopy, and contact angle measurements with respect to corresponding polyimide thin films. The contact angles showed that the inclusion of carbon initially increased the hydrophilicity, whereas a potassium hydroxide treatment increased the hydrophilicity of the pure polyimide film and the polyimide component of the nanocomposite surface without increasing the hydrophilicity of the carbon nanoparticle component. Friction‐force atomic force microscopy was shown to be a powerful technique for confirming the relative wetting characteristics at the nanoscale. The lower hydrophilicity and activity of the carbon nanoparticles during adhesion reactions reduced the load at break, and this suggests that this conventional modification used for polyimides is less effective for their nanocomposite counterparts. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chemical components and properties of core–shell acrylate latex containing fluorine in the shell and their films

Core–shell acrylate latices containing fluorine in the shell were prepared by semicontinuous emulsion polymerization. The chemical components of the latices were determined by Fourier transform infrared, ion‐selective electrode analysis, and differential scanning calorimetry. The average size and morphology of the latex particles were characterized by photocorrelation spectroscopy and transmission electron microscopy, respectively. The latex particles were mainly composed of a non‐fluorine core and a fluorinated shell. The dynamic water contact angles of the latex films from the Wilhelmy method indicated that the latex films containing fluorine in the shell could be wetted by water only with difficulty. The amount of the fluoromonomer played an important role in the modification on the water contact angles, water absorption, and thermal stability of the latex films. In comparison with a random structure, the core–shell structure was more effective for improving the thermal properties of the latex films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 107–114, 2006     

Fabrication and properties of core‐shell structure P(LLA‐CL) nanofibers by coaxial electrospinning

In this article, core‐shell structure nanofibers were fabricated by coaxial electrospinning with biodegradable copolymer Poly(L ‐Lactic‐ε‐Caprolactone) [P(LLA‐CL) 50 : 50] as shell and bovine serum albumin (BSA) as core. Morphology and microstructure of the nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. The mechanical properties were investigated by stress‐strain tests. In vitro degradation rates of the nanofibrous membranes were determined by measuring their weight loss when immersed in phosphate‐buffered saline (pH 7.4) for a maximum of 14 days. Release behavior of BSA was measured by an ultraviolet‐visible spectroscopy, and the results demonstrated that BSA could release from P(LLA‐CL) nanofibers in a steady manner. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Narrow‐disperse or monodisperse crosslinked and functional core–shell polymer particles prepared by two‐stage precipitation polymerization

Narrow‐disperse and monodisperse cross‐linked core–shell polymer particles containing different functional groups, such as esters, hydroxyls, chloromethyls, carboxylic acids, amides, cyanos, and glycidyls, in the shell layers in the micrometer size range were prepared by a two‐stage precipitation polymerization in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80% DVB, was precipitation polymerized in acetonitrile without any stabilizer as the first‐stage polymerization and was used as the core. Several functional monomers, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2‐hydroxyethyl methacrylate, glycidyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, t‐butyl acrylate, i‐octyl acrylate, acrylic acid, acrylamide, acrylonitrile, styrene, and p‐chloromethyl styrene, were incorporated into the shells during the second‐stage polymerization. The resulting core–shell polymer particles were characterized with scanning electron microscopy and Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1776–1784, 2006     

Preparation of polystyrene/poly(vinyl acetate) nanocomposites with a core–shell structure via emulsifier‐free emulsion polymerization

Polystyrene/poly(vinyl acetate) latex nanoparticles with a core–shell morphology in an emulsifier‐free emulsion polymerization system were prepared with purified styrene and vinyl acetate (VAc) as monomers and 2,2′‐azo bis(2‐amino propane) dihydrochloride (ABA,2HCl) as the initiator and emulsifier. The optimized conditions of polymerization of VAc, on top of the already‐formed polystyrene as a core polymer, with a core–shell morphology were obtained using various parameters such as volume ratio of the first and second stages, type of process, and reaction time. The morphologic structure of the nanoparticles was studied by scanning electron microscopy and transmission electron microscopy. The latex nanoparticles and polymers were characterized by differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2409–2414, 2006     

The characteristic properties of poly(methyl methacrylate)/polystyrene core‐shell composite polymer latex

In this study, the poly(methyl methacrylate/polystyrene (PMMA/PS) core‐shell composite latex was synthesized by the method of soapless seeded emulsion polymerization. The morphology of the PMMA/PS composite latex was core‐shell structure, with PMMA as the core and PS as the shell. The core‐shell morphology of the composite polymer latex was found to be thermally unstable. Under the effect of thermal annealing, the PS shell region first dispersed into the PMMA core region, and later separated out to the outside of the PMMA core region. This was explained on the basis of lowing interfacial tension between the PMMA and PS phases owing to the interpenetration layer. The interpenetration layer, which was located at the interface of the core and shell region, contained graft copolymer and entangled polymer chains. Both the graft copolymer and entangled polymer chains had the ability to lower the interfacial tension between the PMMA and PS phases. Also, the effect of thermal annealing on the morphology of commercial polymer/composite latex polymer blends was examined. The result showed that the core‐shell composite latex had the ability to enhance the compatibility of the components of polymer blends. The compatibilizing ability of the core‐shell composite latex was better than that of a random copolymer. Moreover, the effect of the amount of core‐shell composite latex on the morphology of the polymer blend was investigated. The polymer blends, which contained composite latex above 50% wt, showed the morphology of a double sea‐island structure. In addition, the composite latex was completely dissolved in solvent to destroy the core‐shell structure and release the entangled polymer chains, and then dried to form the entangled free composite polymer. The entangled free composite polymer had the ability to enhance the compatibility of the components of the polymer blend as usual. The weight ratio 3/7 commercial polymer/entangled free composite polymer blend showed the morphology of the phase inversion structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 312–321, 2003     

Enhanced mechanical properties and bactericidal activity of polypropylene nanocomposite with dual‐function silica–silver core‐shell nanoparticles

Dual‐function silica–silver core‐shell (SiO₂@Ag) nanoparticles (NPs) with the core diameter of 17 ± 2 nm and the shell thickness of about 1.5 nm were produced using a green chemistry. The SiO₂@Ag NPs were tested in vitro against gram‐positive Staphylococcus aureus (S. aureus) and gram‐negative Escherichia coli (E. coli), both of which are human pathogens. Minimal inhibitory concentrations of the SiO₂@Ag NPs based on Ag content are 4 and 10 μg mL^?1 against S. aureus and E. coli, respectively. These values are similar to those of Ag NPs. SiO₂@Ag NPs were for the first time incorporated to a commodity polypropylene (PP) polymer. This yielded an advanced multifunctional polymer using current compounding technologies i.e., melt blending by twin‐screw extruder and solvent (toluene) blending. The composite containing 5 wt % SiO₂@Ag NPs (0.05 wt % Ag) exhibited efficient bactericidal activity with over 99.99% reduction in bacterial cell viability and significantly improved the flexural modulus of the PP. Anodic stripping voltammetry, used to investigate the antibacterial mechanism of the composite, indicated that a bactericidal Ag⁺ agent was released from the composite in an aqueous environment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simple method of related sensitivity range to predict the thermodynamic equilibrium morphology of a core–shell latex particle

The equilibrium morphologies of different core–shell latices are predicted, and a related sensitivity analysis is given for the predictions. This article proposes a related sensitivity range for estimating the accuracy of predictions, made with the simple method, of the thermodynamically preferred morphology of a core–shell latex particle in two‐stage seeded emulsion polymerization. The related sensitivity range of the predictions is defined and calculated, and the results show that different core–shell latices have different sensitivity ranges. The wider the sensitivity range is, the more reliable the prediction is of the morphology of the core–shell latex. The simple method of related sensitivity range has been verified in the literature and with experiments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3144–3152, 2004     

Abrasion and nanoscratch in nanostructured epoxy coatings

A series of epoxy nanostructured coatings based on diglycidyl ether of bisphenol A (DGEBA) and an isophorone diamine crosslinker was prepared. Top‐down nanocomposites (3% nanofiller) were obtained by the mechanical dispersion of nanoalumina, silanized nanoalumina, and organomodified clays. Bottom‐up hybrids were instead achieved after the silanization of the DGEBA resin and after cocrosslinking with tetraethylorthosilicate through a self‐catalyzed sol–gel process. The curing process of the nanocomposites was studied by differential scanning calorimetry and suggested an overall increase in the crosslinking kinetics in the presence of nanoparticles. Other characterization included dynamic mechanical analysis, Buchholtz indentation hardness testing, and Taber abrasion testing. Finally, atomic force microscopy (AFM) techniques were used to study the surface morphology of the coatings and to produce nanoscratches. We concluded that, in the top‐down nanocomposites, there were minor changes in the surface hardness and a slight improvement in the abrasion resistance, whereas the nanoscratch resistance assessed by AFM tests showed significantly better performances in the hybrid coatings obtained through sol–gel chemistry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self‐Assembling of SBS Block Copolymers as Templates for Conductive Silver Nanocomposites

Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.

     

Synthesis and characterization of temperature‐responsive poly(vinyl alcohol)‐based copolymers

A poly(vinyl alcohol) (PVA)/sodium acrylate (AANa) copolymer was synthesized to improve the water solubility of PVA at the ambient temperature. Furthermore, a series of temperature‐responsive acetalyzed poly(vinyl alcohol) (APVA)‐co‐AANa samples of various chain lengths, degrees of acetalysis (DAs), and comonomer contents were prepared via an acid‐catalysis process. Fourier transform infrared and ¹H‐NMR techniques were used to analyze the compositions of the copolymers. The measurement of the turbidity change for APVA‐co‐AANa aqueous solutions at different temperatures revealed that the lower critical solution temperature (LCST) of the copolymers could be tailored through the control of the molecular weight of the starting PVA‐co‐AANa, DA, and comonomer ratios. Lower LCSTs were observed for APVA‐co‐AANa with a longer chain length, a higher DA, and fewer acrylic acid segments. In addition, the LCSTs of the APVA‐co‐AANa aqueous solutions appeared to be salt‐sensitive. The LCSTs decreased as the concentration of NaCl increased. Moreover, atomic force microscopy images of APVA‐co‐AANa around the LCST also proved the temperature sensitivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of core‐shell latexes for paper coatings

Novel core‐shell latices with a partially crosslinked hydrophilic polymer core and a hard hydrophobic shell of polystyrene were prepared to improve optical properties of coated paper such as gloss and brightness. These core‐shell latices were prepared by sequential addition of a monomer mixture of styrene, n‐butylacrylate and methacrylic acid. Different crosslinkers were used to form the polymer core and in the second stage styrene to form the hard shell component. In addition, attempts were made to further improve optical properties by introducing a new polymerizable optical brightener, i.e., 1‐[(4‐vinylphenoxy)methyl]‐4‐(2‐phenylethylenyl)benzene during polymerization either into the core or into the shell. The prepared core‐shell latex particles were used as specialty plastic pigments for paper coating together with kaolin as the primary pigment. The runability of paper coating formulation by either using a laboratory scale Helicoater or pilot scale JET‐coating machine was very good. The produced coated papers were printed on both sides employing a heat set web offset (HSWO) printer to study the quality of image reproduction in terms of print gloss, print mottle, print through, etc. The core‐shell latices improved the overall print quality. Furthermore, the results demonstrated that by optimizing polymer composition one can significantly enhance the optical properties and surface smoothness of coated paper. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of the rubber crosslinking density of a core–shell structure modifier on the properties of toughened poly(methyl methacrylate)

Four kinds of core–shell structure acrylic impact modifiers (AIMs) with different rubber crosslinking densities were synthesized. The effects of the rubber crosslinking density of the AIMs on the crack initiation and propagation resistance and the mechanical properties of the AIM/poly(methyl methacrylate) (PMMA) blends were investigated, and we found that the maximum stress intensity factor, crack propagation energy, and Izod impact strength reached maximums when the appropriate rubber crosslinking density of AIM, 2.51 × 10²⁵ crosslinks/m³, was adopted. Transmission electron microscopy photographs of the AIM/PMMA blends showed that the AIMs dispersed uniformly in the PMMA matrix. Meanwhile, through the analysis of optical photos and scanning electron microscopy of the impact fracture surface, we found that the deformation mechanism of the AIM/PMMA blends was local matrix shear yielding initiated by rubber particle cavitation of the AIM. The rubber of the AIM, whose crosslinking density was 2.51 × 10²⁵ crosslinks/m³, was beneficial to the formation of intensive voids and initiated the local shear yielding of nearby modifiers of the PMMA matrix effectively in impact tests, which led to higher Izod impact strengths. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Spinodal dewetting–A simple method to prepare conjugated polymer array

A novel, simple method was developed to prepare conjugated polymer array in a large scale by using a spinodal dewetting technique. Mica, silicon, and glass were selected as substrates. The results show that with a suitable concentration of poly(9,9‐dihexylfluorene) (PF) in volatile organic solvent the polymer forms different sizes of array on the substrates. Atomic force microscopy measured the three‐dimensional structure of the arrays, and the relative FFT and PSD analyses reveal the detail information of the dewetting process and the array formation mechanism. The size of spots in the arrays is controlled by the evaporation speed of solvent and concentration of the PF solutions. The photoluminescence of PF arrays were also measured. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1412–1417, 2005