Effect of m‐nitroaniline doping on the optical humidity‐sensing characteristics of cobalt/poly(vinyl alcohol) nanocomposites

Cobalt (Co) nanoparticles (with different loadings, 1 and 2 wt %, of Co) were synthesized in situ in a poly(vinyl alcohol) (PVA) matrix with and without meta‐nitroaniline (m‐NA) as a dopant (2.5 wt %). The obtained nanocomposite films were characterized with various physicochemical techniques, including ultraviolet–visible spectrophotometry, X‐ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared analysis. To study the effect of the humidity, the nanocomposite solutions were coated on planar glass substrates. The beam of an He–Ne laser was incident normal to the film surface and was subjected to variable relative humidities (RHs; 4–93%); the transmitted intensity was measured on a photovoltaic diode. Variations in the intensity of light caused by the changes in RH within the range 3–93% were recorded. We optimized the response by varying the film thickness by coating the solution layer by layer. We generated the RH (4–100%) by passing wet water vapors. The neat PVA film of similar thickness gave humidity sensing in the range 78–93% RH. The sensors with m‐NA‐doped Co/PVA gave better sensitivity (6.4 mV/% RH) than the undoped samples (1.78–2.45 mV/% RH), exhibiting a fast response of 3 s (2–93% RH) and a recovery of 10 s (93 to 2% RH). These samples also showed reversible behavior and long‐term stability (for nearly a year) with a good sensitivity and a large dynamic range (2–95% RH). An attempt was made to explain the results on the basis of a bulk mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Cationic water‐soluble poly(p‐phenylene vinylene) for fluorescence sensors and electrostatic self‐assembly nanocomposites with quantum dots

Novel phthalocyanine amide polymers (Pc) based on 1,8-naphthalenediamine (Ar) as an aromatic amine and 1,4-diaminobutane (Al) as an aliphatic amine, were synthesized to improve the limited stabilization modes of conventional phthalocyanines. The metal-free phthalocyanines polymers (MF-Pc) were moderately soluble in DMSO only while the metalized forms (Cu&Ni-Pc) were completely insoluble. The structure of the samples was confirmed using Fourier transform infrared (FTIR), ultraviolet–visible spectrometry (UV–vis) and nuclear magnetic resonance (NMR). Additionally, the thermal stability and glass transition temperatures (T_g) were investigated by thermal gravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The intercalation of the metal-free phthalocyanines, based on the aliphatic amine (MF-PcAl) and aromatic amine (MF-PcAr), into laponite from DMSO solution, was proved by X-ray diffraction (XRD). The basal space of laponite increased from 1.2 to 1.36 nm upon intercalation of MF-PcAl and extended more to 1.91 nm on using MF-PcAr as intercalant while the quaternized forms of MF-Pcs behaved likewise and could not widen the basal space of laponite to more than 1.43 nm which was attributed to the random distribution of the positive charges over the Pc chains which imposed confined arrangement inside the basal space and consequently narrower space than the attained one in the case of nonquaternized phthalocyanines. The plasticized PVC composites based on laponite treated with either MF-PcAl or MF-PcAr exhibited improved resistance to the UV radiation as revealed by the retention of the tensile strength and elongation at rupture after exposure to UV radiation for different time intervals. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Designing of fullers‐earth‐containing poly(vinyl alcohol)‐g‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) nanocomposites: Swelling and deswelling behaviors

In this study, polymer–clay nanocomposites (PCNs) composed of poly(vinyl alcohol)s (PVAs), poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid), and fullers earth were prepared by the effective dispersal of inorganic nanoclays in the organic PVA matrix via in situ free‐radical polymerization with potassium persulfate as an initiator and N,N‐methylene bisacrylamide as a crosslinker. The monomer, 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid, was grafted onto the PVA backbone, and at the same time, fullers earth layers were intercalated and exfoliated into the grafted copolymer, especially at a low or moderate loading of the fullers earth. The synthesized PCN materials were characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction techniques. The morphological features of the synthesized materials were studied by scanning electron microscopy; this revealed that the swelling ratio of this nanocomposite increased with increasing fullers earth content. The X‐ray diffraction results indicated that the fullers earth was exfoliated in the nanocomposite matrix, and its introduction into the polymer matrix enhanced the percentage crystallinity of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hyperbranched polyesters with internal and exo‐presented hydrogen‐bond acidic sensor groups for surface acoustic wave sensors

Three hyperbranched aromatic polyesters carrying both internal and exo‐presented hydrogen‐bond acidic phenol, carboxylic acid, or mixed phenol/acetoxy groups were coated onto 500 MHz surface acoustic wave (SAW) sensor platforms, and sensor responses to the nerve agent simulant dimethyl methylphosphonate (DMMP) and the explosives simulant dinitrotoluene (DNT) were studied. All three hyperbranched polyesters gave strong responses to DMMP, and the hyperbranched polyester carrying carboxylic acid groups gave a particularly strong response. The hyperbranched polyester carrying phenol groups gave the best response to DNT of the three polymers studied. The DMMP and DNT responses of the three hyperbranched polyesters were also compared with hyperbranched SAW sensor polymers carrying exo‐presented phenolic sensor groups only, and also with linear SAW sensor polymers carrying phenolic sensor groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Humidity‐sensitive properties of new polyelectrolytes based on the copolymers containing phosphonium salt and phosphine function

A simple strategy was developed based on a new reactive function‐ and a salt‐containing new monomer, 4‐vinylbenzyl dimethyl 2‐(dimethylphosphino)ethyl phosphonium chloride (VDEPC), to obtain stable humidity‐sensitive membranes. The major ingredient of a humid membrane is crosslinked polyelectrolytes obtained from copolymers of VDEPC/2‐ethylhexyl acrylate (2‐EHA) = 1/0, 4/1, and 2/1. Isothermal humidity absorption experiments were performed for the estimation of humidity‐sensing materials. The crosslinked copolymers prepared from the reaction of VDEPC/2‐EHA = 4/1 with 1,4‐dichlorobutane showed an average impedance of 595, 39.1, and 3.9 KΩ at 30, 60, and 90% RH, respectively. Their hysteresis, temperature dependence, frequency dependence, and response time were measured. The reliability including water resistance and a long‐term stability were estimated for the application of the common humidity sensor. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1062–1070, 2003     

Hyperbranched polymer based on triphenylamine and pyridine: Fluorescent chemosensors for palladium ions

Two new hyperbranched fluorescent conjugated polymers containing pyridine units were synthesized via Heck coupling reaction and Sonogashira coupling reaction, respectively, and characterized by ¹H NMR, ¹³C NMR, FTIR, and GPC. The copolymers are readily soluble in common organic solvents such as chloroform, THF, and DMF. Thermal analysis revealed that the copolymers had good thermal stability. The fluorescence quenching behaviors of the hyperbranched copolymers by metal ions were studied. It was found that the fluorescence of the copolymers can be effectively quenched by Pd²⁺. Moreover, the two hyperbranched copolymers exhibited different quenching efficiency, which may be related to difference in the hindrance for the chelation of pyridine unit with metal ions of the two polymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of s‐triazine‐based hyperbranched polyurethane for novel carbon‐nanotube‐dispersed nanocomposites

s‐Triazine‐based hyperbranched polyurethanes (HBPUs) with different hard segments were synthesized by A₂ + B₃ approach. Various kinds of multiwalled carbon nanotube (MWNT) nanocomposites with HBPU were prepared to investigate an impact of hyperbranched polymer on dispersion of MWNTs in the polymer matrix and the resulting properties of nanocomposites. Synthesized HBPUs were characterized using FTIR and NMR measurements. The highly branched structures were found very effective in enhancing the pristine MWNT dispersion in the polymer matrix. As a result, the MWNT‐reinforced HBPU nanocomposites showed a steep increase in the yield stress and modulus and enhanced shape memory effect with an increase of hard segment and MWNT loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dielectric properties and solubility of multilayer hyperbranched polyimide/polyhedral oligomeric silsesquioxane nanocomposites

Multilayer hyperbranched polyimide/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by the reaction of a bromide‐hyperbranched polyether/POSS and a main‐chain polyimide containing hydroxyl‐functional groups. The first layer was formed through the direct reactions of the main‐chain hydroxyl groups with monochloroisobutyl polyhedral oligomeric silsesquioxane (POSS–Cl). The second and third layers were prepared by the repeated reactions of bromine ether branches that incorporated POSS–Cl with 3,5‐dihydroxybenzyl alcohol. Regardless of the fixed amount of POSS, the higher layers yielded lower dielectric constants. Even when the amount of the POSS loading was reduced 4‐fold, the third layer still had the lowest dielectric constants. The lowest dielectric constant of 2.54 was found in the third layer of the hyperbranched polyimide/POSS nanocomposite because of the large free volume and loose polyimide structures. The densities of the hyperbranched polyimide/POSS nanocomposite corresponded to the dielectric constants. The lower the density was, the higher the free volume was and the lower the dielectric constant was. The experimental results indicated that the hyperbranched polyimide/POSS nanocomposite exhibited increased solubility in comparison with pure polyimide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of clay on properties of polyimide‐clay nanocomposites

Effect of clay on mechanical, thermal, moisture absorption, and dielectric properties of polyimide‐clay nanocomposites was investigated. Nanocomposites of polyimide (ODA‐BSAA) hybridized with two modified clay (PK‐802 and PK‐805) were synthesized for comparison. The silicate layers in the polymer matrix were intercalated/exfoliated as confirmed by wide‐angle X‐ray diffraction and transmission electron microscopy. Thermal stability, moisture absorption, and storage modulus for these nanocomposites are improved as hybridized clay increases. Reduced dielectric constants due to the hybridization of layered silicates are observed at frequencies of 1 kHz–1 MHz and temperatures of 35–150°C. The tetrahedrally substituted smectite (PK‐805) resulted in higher mechanical strength and dielectric constants than those of octahedrally substituted smectite (PK‐802), which could be attributed to their stronger ionic bonding between clay layer and polymer matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 318–324, 2007     

Structure–property correlation of polyurethane nanocomposites: Influence of loading and nature of nanosilica and microstructure of hyperbranched polyol

New generation polyurethane nanocomposites based on toluene diisocyanate, poly(propylene glycol), hyperbranched polymers (HBPs), and nanosilica were synthesized with the aim of determining the effect of the loading and nature of nanosilica and the functionality of HBP on the structure and properties of polyurethane nanocomposites. Good dispersion of nanosilica at 4 wt % loading in the polymer was confirmed from atomic force microscopy. The properties of the polyurethane nanocomposites were a function of content and nature of the nanosilica in the matrix. The optimum silica loading was 4 wt %. At this loading, tensile strength and storage modulus at 25°C of the nanocomposites increased by 52 and 40%, respectively over the pristine polyurethane. Organo‐treated nanosilica exhibited higher physico‐mechanical properties than the untreated one. With the increase of functionality in the hyperbranched polyol, the tensile strength, thermal stability, and dynamic mechanical properties of the nanocomposites improved. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and properties of BCDA‐based polyimide–clay nanocomposites

Bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA)‐based polyimide–clay nanocomposites were prepared from their precursor, namely polyamic acid, by a solution‐casting method. The organoclay was prepared by treating sodium montmorillonite (Kunipia F) clay with dodecyltrimethylammonium bromide at 80 °C. Polyamic acid solutions containing various weight percentages of organoclay were prepared from 4,4′‐(4,4′‐isopropylidenediphenyl‐1,1′‐diyldioxy)‐dianiline and BCDA in N‐methyl‐2‐pyrrolidone containing dispersed particles of organoclay at 20 °C. These solutions were cast on a glass plate using a Doctor's blade and then heated subsequently to obtain nanocomposite films. The nanocomposites were characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal mechanical analysis, dynamic mechanical analysis, polarizing microscopy, scanning electron microscopy, transmission electron microscopy, wide‐angle X‐ray diffraction (WAXD) and thermogravimetric analysis. The glass transition temperature of the nanocomposites was found to be higher than that of pristine polymer. The coefficient of thermal expansion of the nanocomposites decreased with increasing organoclay content. WAXD studies indicated that the extent of silicate layer separation in the nanocomposite films depended upon the organoclay content. Tensile strength and modulus of the nanocomposite containing 1% organoclay were significantly higher when compared to pristine polymer and other nanocomposites. The thermal stability of the nanocomposites was found to be higher than that of pristine polymer in air and nitrogen atmosphere. Copyright © 2007 Society of Chemical Industry     

Preparation and characterization of poly(styrene butylacrylate) latex/nano‐ZnO nanocomposites

Poly(styrene butylacrylate) latex/nano‐ZnO composites were prepared by blending poly(styrene butylacrylate) latex with a water slurry of nano‐ZnO particles, and the effects of certain parameters, such as particle size, dispersant type, dispersing time and others, on the dispersibility, mechanical properties, ultraviolet (UV) shielding and near infrared (NIR) shielding were investigated with transmission electron microscopy (TEM), an Instron testing machine, dynamic mechanical analysis and ultraviolet‐visible‐near infrared (UV‐VIS‐NIR) spectrophotometry. TEM observation showed that dispersants with long chains are better than those with short chains at enhancing the dispersibility of nano‐ZnO particles in a matrix; extending dispersing time also improves the dispersibility of nano‐ZnO particles in a matrix. Instron tests showed that the nanocomposite polymers embedded with nano‐ZnO particles had much higher tensile strength than the corresponding composite polymers with micro‐ZnO particles. As the nano‐ZnO content increased, the temperature of glass transition (T_g) of the nanocomposite polymer embedded with 60 nm ZnO particles first increased then decreased, but 100 nm ZnO and micro‐ZnO particles seemed to have no influence on the T_g of the composite polymers. The better dispersibility of nano‐ZnO particles resulted in higher T_g values. Increasing nano‐ZnO content or dispersibility could enhance the UV shielding properties of the nanocomposite polymers, and 60 nm ZnO particles could more effectively shield UV rays than 100 nm ZnO particles. Micro‐ZnO particles basically had no effect on the UV absorbance of the composite polymers. A blue‐shift phenomenon was observed at 365 nm when nano‐ZnO particles were present in the nanocomposite polymers. NIR analysis indicated that as nano‐ZnO content increased, the NIR shielding of the nanocomposite polymers increased, but the NIR shielding properties seemed to be more influenced by particle size than by the nano‐effect. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1923–1931, 2003     

Self‐Healing Rubbers Based on NBR Blends with Hyperbranched Polyethylenimines

Hyperbranched PEI and urea‐functionalized PEI amphiphiles are employed as additives in NBR compounding. Polarity design governing phase separation, PEI migration and PEI‐mediated self‐healing of NBR is demonstrated. The compatibility of PEI and NBR decreases with increasing molecular weight of PEI and with decreasing degree of substitution. Microphase‐separated NBR/PEI blends are prepared with varying PEI molecular architectures. Thermal self‐healing of NBR/PEI is monitored by applying tests combining crack initiation with annealing under compression. All PEI additives show complete crack‐healing upon annealing at 100 °C for 12 h. In contrast to neat NBR, the NBR/PEI‐2 blend afforded a self‐healing efficiency of 44% after cutting and re‐joining by compression and annealing.

     

Low‐Stress Hyperbranched Polymer/Silica Nanostructures Produced by UV Curing,Sol/Gel Processing and Nanoimprint Lithography

Nanocomposite materials based on a HBP and silica are produced using either a dual‐cure sol/gel and photopolymerization process or by mixing silica nanoparticles with the HBP. In both cases the conversion of the HBP is independent of composition and obeys a time‐intensity superposition with power‐law dependence on UV intensity. Optimization of the dual‐cure process leads to transparent sol/gel composites with ultrafine structures. These materials systematically outperform the particulate composites, including an increase of the glass transition temperature of 63 °C and a process‐induced internal stress as low as 2.5 MPa. Nano‐sized gratings are produced from the sol/gel composites by low‐pressure UV nanoimprint lithography.

     

Morphology and thermo‐mechanical properties of compatibilized polyimide‐silica nanocomposites

Polyimide‐silica nanocomposites have been prepared from an aromatic polyamic acid derived from pyromellitic dianhydride and oxydianiline and a silica network using the sol‐gel reaction. Compatibilization of the two components was achieved by modifying the silica network with imide linkages. Morphology, thermal, and mechanical properties of these composite materials were studied as a function of silica content and compared with the one in which reinforcement of the polyimide was achieved using a pure silica network. There was considerable reduction in the silica particle size with more homogeneous distribution in the matrix when imide spacer groups were introduced in the silica network. The tan δ spectra obtained from dynamic thermal mechanical analysis shows a large increase in the glass transition temperature with increasing silica content for the compatibilized system in contrast to the un‐compatibilized one. Mechanical properties of the polyimide composites improved due to better interaction between the organic and inorganic phases. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2521–2531, 2005     

Hyperbranched polyurethane/triethanolamine functionalized multi‐walled carbon nanotube nanocomposites as remote induced smart materials

Triethanolamine functionalized multi‐walled carbon nanotubes (TEA‐f‐MWCNTs)/hyperbranched polyurethane nanocomposites were prepared by the in situ polymerization technique. The functionalization of the MWCNTs was confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy studies. The homogeneous distribution and the strong interfacial interaction of TEA‐f‐MWCNTs with the polyurethane chains were confirmed by transmission electron microscopy and Fourier transform infrared spectroscopy studies, respectively. Significant enhancements of tensile strength (6.5 ? 28.5 MPa) and scratch resistance (3–7 kg) with content of TEA‐f‐MWCNTs (0–2 wt%) were observed. Thermogravimetric analysis showed an increase in thermal stability from 240 to 287 °C by the formation of nanocomposites. X‐ray diffraction and differential scanning calorimetry studies confirmed an increment in the degree of crystallinity of the nanocomposites with increase in TEA‐f‐MWCNT content. The extent of shape recovery as well as recovery speed were enhanced with increase in the output power of the microwave. Thus the studied nanocomposites could be utilized as non‐contact microwave energy tunable shape memory materials. © 2013 Society of Chemical Industry     

Preparation and properties of polypropylene filled with organo‐montmorillonite nanocomposites

Organo‐Montmorillonite (Org‐MMT)/maleic anhydride grafted polypropylene (PP‐g‐MAH)/polypropylene nanocomposites have been prepared by melt blending with twin‐screw extruder. The mechanical properties of the nanocomposites and the dispersion of Org‐MMT intercalated by the macromolecular chain were investigated by transmission electron microscopy and mechanical tests. The crystal properties of the nanocomposites have been tested by a differential scanning calorimeter. The thermal properties of the nanocomposites were investigated by thermo gravimetric analysis. The results show that not only the impact property but also the tensile property and the bending modulus of the system have been increased evidently by the added Org‐MMT. The Org‐MMT has been dispersed in the matrix in the nanometer scale. With the addition of the Org‐MMT, the melting point and the crystalling point of the nanocomposites increased; the total velocity of crystallization of the nanocomposites also increased. Thermal stability of the nanocomposites is increased by the filled Org‐MMT. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2875–2880, 2006     

Effects of the processing temperature on the nanostructure and mechanical properties of PCTG‐based nanocomposites

The influence of the processing temperature on both the dispersion level and the mechanical properties of the amorphous copolyester (PCTG)/organoclay (Cloisite® 20A) nanocomposite (NC) is studied in this article. At high processing temperatures, no change in the chemical nature of the matrix was observed, but its molecular weight decreased. Widely dispersed structures were observed by wide angle X‐ray diffraction (WAXD) and transmission electron microscopy whatever the processing temperature might be. Dispersion was greatest for the samples processed at 200°C due to the highest viscosity of these samples and decreased at higher processing temperatures (T_p). These different dispersion levels led to a large modulus increase (71%) after processing at 200°C and to lower ones (about 50%) after processing at 230 and 260°C. The ductility of the NCs decreased at lower processing temperatures. The decrease was attributed to the greater stiffness of the matrix, and was not significant enough to modify the ductile nature of the NCs, which showed clear yield points even at the lowest processing temperature (200°C). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

PMMA‐grafted‐silica/PVC nanocomposites: Mechanical performance and barrier properties

Poly(vinyl chloride) (PVC)/SiO₂ nanocomposites were prepared via melt mixture using a twin‐screw mixing method. To improve the dispersion degree of the nanoparticles and endow the compatibility between polymeric matrix and nanosilica, SiO₂ surface was grafted with polymethyl methacrylate (PMMA). The interfacial adhesion was enhanced with filling the resulting PMMA‐grafted‐SiO₂ hybrid nanoparticles characterized by scanning electron microscopy. Both storage modulus and glass transition temperature of prepared nanocomposites measured by dynamic mechanical thermal analysis were increased compared with untreated nanosilica‐treated PVC composite. A much more efficient transfer of stresses was permitted from the polymer matrix to the hybrid silica nanoparticles. The filling of the hybrid nanoparticles caused the improved mechanical properties (tensile strength, notched impact strength, and rigidity) when the filler content was not more than 3 wt %. Permeability rates of O₂ and H₂O through films of PMMA‐grafted‐SiO₂/PVC were also measured. Lower rates were observed when compared with that of neat PVC. This was attributed to the more tortuous path which must be covered by the gas molecules, since SiO₂ nanoparticles are considered impenetrable by gas molecules. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and properties of natural rubber nanocomposites with solid‐state organomodified montmorillonite

A novel organomodified montmorillonite prepared by solid‐state method and its nanocomposites with natural rubber were studied. The nanocomposites were prepared by traditional rubber mixing and vulcanizing process. The properties of solid‐state organomodified montmorillonite were investigated by Fourier‐transform infrared spectroscopy (FITR) and thermogravimetric analysis (TGA). The dispersion of the layered silicate in rubber matrix was characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the nanocomposites consisting of solid‐state organomodified montmorillonite and natural rubber are obtained. The solid‐state organomodified montmorillonite can not only accelerate the curing process, but also improve the mechanical and aging resistance properties of NR. The properties improvement caused by the fillers are attributed to partial intercalation of the organophilic clay by NR macromolecules. In addition, the dynamic mechanical analysis (DMA) results showed a decrease of tanδmax and increase of T_g when the organoclay is added to the rubber matrix, which is due to the confinement of the macromolecular segments into the organoclay nanolayers and the strong interaction between the filler and rubber matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008