Thermal,mechanical and electroactive shape memory properties of polyurethane (PU)/poly (lactic acid) (PLA)/CNT nanocomposites

Polymer blend nanocomposites based on thermoplastic polyurethane (PU) elastomer, polylactide (PLA) and surface modified carbon nanotubes were prepared via simple melt mixing process and investigated for its mechanical, dynamic mechanical and electroactive shape memory properties. Chemical and structural characterization of the polymer blend nanocomposites were investigated by Fourier Transform infrared (FT-IR) and wide angle X-ray diffraction (WAXD). Loading of the surface modified carbon nanotube in the PU/PLA polymer blends resulted in the significant improvement on the mechanical properties such as tensile strength, when compared to the pure and pristine CNT loaded polymer blends. Dynamic mechanical analysis showed that the glass transition temperature (T_g) of the PU/PLA blend slightly increases on loading of pristine CNT and this effect is more pronounced on loading surface modified CNTs. Thermal and electrical properties of the polymer blend composites increases significantly on loading pristine or surface modified CNTs. Finally, shape memory studies of the PU/PLA/modified CNT composites exhibit a remarkable recoverability of its shape at lower applied dc voltages, when compared to pure or pristine CNT loaded system.     

Effect of modified carbon nanotube on physical properties of thermotropic liquid crystal polyester nanocomposites

Polymer nanocomposites based on a very small quantity of carbon nanotube (CNT) and thermotropic liquid crystal polymer (TLCP) were prepared by simple melt blending using a twin-screw extruder. Morphological observations revealed that modified CNT was uniformly dispersed in the TLCP matrix and increased interfacial adhesion between the nanotubes and the polymer matrix. The enhancement of the storage and loss moduli of the TLCP nanocomposites with the introduction of CNT was more pronounced at low frequency region, and non-terminal behavior observed in the TLCP nanocomposites resulted from the nanotube-nanotube and polymer-nanotubes interactions. There is significant dependence of the mechanical, rheological, and thermal properties of the TLCP nanocomposites on the uniform dispersion of CNT and the interfacial adhesion between CNT and TLCP matrix, and their synergistic effect was more effective at low CNT content than at high CNT content. The key to improve the overall properties of the TLCP nanocomposites depends on the optimization of the unique geometry and dispersion state of CNT and the interfacial interactions in the TLCP nanocomposites during melt processing. This study demonstrate that a very small quantity of CNT substantially improved thermal stability and mechanical properties of the TLCP nanocomposites, providing a design guide of CNT-filled TLCP composites with as great potential for industrial use.     

Effect of graphene doping of holographic polymer‐dispersed liquid crystals

Doping a polymer matrix with a minute amount of graphene (0.05–0.25%) had significant effects on the grating formation kinetics and electro‐optical performance of a holographic polymer‐dispersed liquid crystal. Low graphene contents (≤0.1%) reduced the viscosity and induced rapid diffusion, curing, grating formation, and high diffraction efficiency with a diffraction overshoot of 0.05%. Conversely, high graphene contents increased the compound viscosity, and the entire process proceeded slowly. Graphene increased the polymer conductivity and local electric field, reduced the operating voltage from 65 to 25–50 V, and increased the contrast ratio from 7 to 8–23 with a concomitant decrease in rise time. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

High‐performance holographic polymer‐dispersed liquid crystals by incorporating hyperbranched polymers

A minute amount (0.01–0.3 wt %) of ally isocyanate functionalized hyperbranched 2,2‐bis (hydroxymethyl) propionic acid (bis‐MPA) polyester‐16‐hydroxyl (HBP) was incorporated covalently into polyurethane acrylate‐based holographic polymer dispersed liquid crystals (HPDLCs), and its effects on the compound viscosity, grating kinetics, morphology, diffraction efficiency (DE), and electro‐optical properties of the HPDLC films were examined. HBP at low concentrations (0.01–0.05%) reduced the compound viscosity and domain size of liquid crystal (LC) significantly and augmented the cure rate and saturation DE by up to threefold compared to the HBP‐free compound. At high concentrations (0.10 and 0.30%), HBP increased the compound viscosity and decreased the rate of grating formation, giving rise to distorted LC‐polymer interfaces, which caused a significant decrease in the threshold and operating voltages. The rise and decay time showed a minimum and maximum, respectively, when the compound viscosity was a minimum at 0.03% HBP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Three‐dimensional structure in holographic polymer‐dispersed liquid crystals

Polymer‐dispersed liquid crystals, heterogeneous structures consisting of a liquid crystal and a polymer, are promising materials for generating holograms with switchable diffraction efficiency. The experiments presented here reveal that the generation of a face‐centered cubic structure can be achieved by exposing a liquid crystal/reactive monomer mixture to the interference pattern of four coherent laser beams under appropriate geometrical conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of organic modifiers with different chain lengths on the dispersion of clay layers in HTPB (hydroxyl terminated polybutadiene)

The series of HTPB (hydroxyl terminated polybutadiene)/organoclay nanocomposite was formed by melt blending with rotationary and revolutionary mixer which generated high shear stress. Organoclays were formed by modifying the pristine clays with organic modifiers which had different hydrophobic chain lengths. As the length of organic modifier increased, the gap size between layers of organoclay became broader. The clays modified with octadecylamine (C18) and dodecyl amine (C12) showed wider gap sizes than that modified with octyl amine (C8). This gap size affected the dispersion state of clays, exfoliation/intercalation in HTPB polymer medium. The mixtures of HTPB with C18 and C12 were transparent without sedimentation and showed almost exfoliated structure. HTPB/C18 mixture showed the higher viscosity and yield strength than HTPB/C12 due to exfoliation. HTPB/C12 showed more elastic behavior than HTPB/C18 mixture because the organoclay C12 had less content of organic modifier.     

Effects of surfactant and molecular weight of polyol on grating formation and switching of holographic PDLC

The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0 < λ₃₁) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro‐1‐butanesulfonyl fluoride) and amounts (0–9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater λ₃₁ gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time. Copyright © 2008 John Wiley & Sons, Ltd.     

Dissolving and aligning carbon nanotubes in thermotropic liquid crystals

It has been widely recognized that the combination of carbon nanotubes (CNTs) and low molar mass thermotropic liquid crystals (tLCs) not only provides a useful way to align CNTs, but also dramatically enhances the tLC performance especially in the liquid crystal display technology. Such CNT-tLC nanocomposites have ignited hopes to address many stubborn problems within the field, such as low contrast, slow response, and narrow view angle. However, this material development has been limited by the poor solubility of CNTs in tLCs. Here, we describe an effective strategy to solve the problem. Prior to integrating with tLCs, pristine CNTs are physically "coated" by a liquid crystalline polymer (LCP) which is compatible with tLCs. The homogeneous CNT-tLC composite obtained in this way is stable for over 6 months, and the concentration of CNTs in tLCs can reach 1 wt %. We further demonstrate the alignment of CNTs at high CNT concentrations by an electric field with a theory to model the impedance response of the CNT-tLC mixture.     

A feasible strategy to constructing hybrid conductive networks in PLA‐based composites modified by CNT‐d‐RGO particles and PEG for mechanical and electrical properties

Carbon nanotubes (CNTs) and reduced graphene oxide (RGO) were successfully assembled by chemical reaction to obtain CNT‐d‐RGO particles. Then, a home‐made dynamic impregnating device was used to prepare hybrid CNT‐d‐RGO/polyethylene glycol (PEG). Next, the different modifiers, including CNTs, GO, CNT‐d‐RGO, PEG, and CNT‐d‐RGO/PEG, were, respectively, added into poly‐(lactic acid) (PLA) matrix via melt‐compounding. The dispersed morphology for these different modifiers within the PLA matrix was confirmed by SEM and TEM observations. Especially, compared with the identical weight ratio of CNT‐d‐RGO, the hybrid CNT‐d‐RGO/PEG within the PLA matrix exhibited an excellent exfoliated and interconnected networks morphology. Moreover, compared with pure PLA, not only the crystallinity of all PLA‐based composites notably improved, but half‐crystallization time was also shortened. Furthermore, despite the addition of different modifiers, the crystal form of PLA‐based composites remained unchanged. Noticeably, compared with those of pure PLA, the tensile stress, strain, and modulus of PLA composite added with CNT‐d‐RGO/PEG increased by 29.4%, 4.1%, and 56.1%, respectively, and the V‐notch impact strength slightly improved. In addition, compared with pure PLA, volume resistivity of the PLA composite added with 1 wt% CNT‐d‐RGO/PEG decreased by 93.1%, and its volume conductivity increased by five orders of magnitude.     

Photoswitching of holographic polymer-dispersed liquid crystals doped with chiral dopant

Chiral dopants were added to the formulation of holographic polymer-dispersed liquid crystals and the effects studied in terms of grating formation dynamics, morphology, diffraction efficiency, contrast ratio and electro-optical properties of the films. A gradual increase of real-time diffraction efficiency, decrease of droplet size and increase of diffraction efficiency of the composite film were obtained with the addition and increasing content of chiral dopant, due to the increased viscosity of the liquid crystal (LC) doped with the chiral dopant leading to decreased droplet coalescence. The contrast ratio decreased with increasing content of chiral dopant due to the difficult orientation of LC molecules caused by the formation of a helical structure. Addition of a small amount of the chiral dopant increased the driving voltage slightly, whereas the decay time is decreased significantly as a result of the high twisting of the helical structure.     

表面活性剂对TiO_2/CNT苯酚与碳酸二甲酯酯交换活性的影响

以表面活性剂十六烷基三甲基溴化铵（CTAB）和十二烷基硫酸钠（SDS）改性的碳纳米管为载体,制备了TiO2/CNT催化剂,用于苯酚与碳酸二甲酯酯交换合成碳酸二苯酯的反应.采用X射线衍射（XRD）、扫描电镜（SEM）和透射电镜（TEM）对改性前后催化剂的结构和形貌进行了表征,显示出负载后的催化剂中活性组分二氧化钛以无定形...     

Competition between supernucleation and plasticization in the crystallization and rheological behavior of PCL/CNT‐based nanocomposites and nanohybrids

PCL was blended with pristine multiwalled carbon nanotubes (MWCNT) and with a nanohybrid obtained from the same MWCNT but grafted with low molecular weight PCL, employing concentrations of 0.25 to 5 wt % of MWCNT and MWCNT‐g‐PCL. Excellent CNT dispersion was found in all samples leading to supernucleation of both nanofiller types. Nanohybrids with 1 wt % or less MWCNTs crystallize faster than nanocomposites (due to supernucleation), while the trend eventually reverses at higher nanotubes content (because of plasticization). Rheological results show that yield‐like behavior develops in both nanocomposites, even for the minimum content of carbon nanotubes. In addition, the MWCNT‐g‐PCL family, when compared with the neat polymer, exhibits lower values of viscosity and modulus in oscillatory shear, and higher compliance in creep. These rheological differences are discussed in terms of the plasticization effect caused by the existence of low molecular weight free and grafted PCL chains in the nanohybrids. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1310–1325     

The effect of surface coating of CNTs on the mechanical properties of CF‐filled HDPE composites

Mechanical properties of carbon fiber (CF) and carbon nanotube (CNT)‐filled thermoplastic high‐density polyethylene (HDPE) composites were studied with particular interest on the effects of filler content and fiber surface treatment by coupling agent. Surface‐treated CF‐filled HDPE composites increased their tensile strength and impact strength, which is further increased with the addition of CNT. SEM showed that CNT‐coating‐treated CF‐HDPE composites show better dispersion of the filler into the matrix, which results in better interfacial adhesion between the filler and the matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Dual effects of fullerene doped to holographic polymer dispersed liquid crystals

Doping of conductive fullerene particles to the formulation of conventional holographic polymer dispersed liquid crystal‐induced dual effects of reducing both droplet coalescence and operating voltage. Fullerene induced an induction period which otherwise does not exist, followed by a gradual increase of diffraction efficiency to a saturation value being increased with increasing fullerene content. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of LC by the fullerene particles. On the other hand, doped fullerene particles augmented the conductivity of polymer phase and hence the local electrical field imposed on LC droplet, which overcome the threshold for driving and reduced operating voltage and response times. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5590–5596, 2007     

Carbon Nanotube Immobilized Electrode Using Amphiphilic Phospholipid Polymer with Anti‐fouling and Dispersion Property for Electrochemical Analysis

A carbon nanotube (CNT)‐modified electrode was fabricated by dropping a dispersion of multi‐walled CNTs in water‐soluble and amphiphilic phospholipid polymer with both dispersing ability and anti‐biofouling property onto a Au electrode. A poly(2‐methacryloyloxyethyl phosphorylcholine‐co‐n‐butyl methacrylate) (PMB) composed from 50 mol% of 2‐methacryloxylethyl phosphorylcholine and 50 mol% of n‐butyl methacrylate (PMB50) was used as dispersing reagent for CNTs. The dispersion of water‐insoluble material by PMB50 and its antifouling effects in electrochemical analysis were investigated. The CNT‐modified electrode showed an anodic peak potential that was shifted negatively and an increase in the current value for the electrolytic oxidation of nicotinamide adenine dinucleotide. In addition, the charge on PMB50 did not inhibit the electrochemical reaction of the redox compounds K₃[Fe(CN)₆], [Ru(NH₃)₆]Cl₃, and hydroxymethylferrocene. Cyclic voltammetry of K₃[Fe(CN)₆] in 4 % bovine serum albumin (BSA) using a bare Au electrode, the anodic peak current was reduced to 47 % of that without BSA. In contrast, the antifouling effect of the PMB50‐coated electrode meant that the current was only reduced to 70 % of that without BSA.     

Improvements in morphological and electro‐optical properties of polymer‐dispersed liquid crystal grating using a highly fluorine‐substituted acrylate monomer

To improve the morphological and electro‐optical properties of a polymer‐dispersed liquid crystal (PDLC) grating, a type of highly fluorine‐substituted acrylate monomer was added to the prepolymer mixture. The morphologies of the PDLC gratings were investigated using atom force microscopy and scanning electron microscopy. The grating had a very clear polymer/LC interface after addition of 3.9 wt % of fluorine‐substituted monomer. The LC droplets in this case were much larger than the sample without fluorinated monomer. This phenomenon indicated that an almost complete phase separation had occurred. However, as the content of fluorine‐substituted monomer increased, the morphologies of gratings became less defined and the volumes of LC droplets were smaller. The diffraction efficiency (DE) decreased with increasing of fluoride content and the V ₉₀ increased simultaneously, which may be ascribed to the blurry interface and the small LC droplets. The highest DE (90%) and lowest V ₉₀ (70 V) were obtained simultaneously under the condition of 3.9 wt % fluoride added in the prepolymer. In addition, it was also found that the fluorine‐substituted monomer may disorder the alignment of LCs in the grating.     

Studies on electro‐optical properties of polymer matrix/LC/ITO nanoparticles composites

In this paper, polymer‐dispersed liquid crystal (PDLC) films consisting of liquid crystal (LC)/monomers/indium tin oxide (ITO) nanoparticles with good near‐infrared absorption property had been fabricated, and the influence of the ITO nanoparticles modified with 3‐methacryloxypropyltrimethoxysilane (KH570) on the PDLC films was systematically studied. First, different liquid crystal content was studied to obtain PDLC films with good electro‐optical properties. And then, various weight ratio of ITO nanoparticles was added to samples. While the content of ITO nanoparticles was increased, the saturation voltage increased and the CR decreased. Though the electro‐optical properties of PDLC samples reduced with the addition ITO nanoparticles, the near‐infrared absorption property of films was enhanced.     

Polymorphism behavior of poly(ethylene naphthalate)/clay nanocomposites

Thermally stable organically modified clays based on 1,3‐didecyl‐2‐methylimidazolium (IM2C10) and 1‐hexadecyl‐2,3‐dimethyl‐imidazolium (IMC16) were used to prepare poly(ethylene naphthalate) (PEN)/clay nanocomposites via a melt intercalation process. The clay dispersion in the resulting hybrids was studied by a combination of X‐ray diffraction, polarizing optical microscopy, and transmission electron microscopy. It was found that IMC16 provided better compatibility between the PEN matrix and the clay than IM2C10, as evidenced by some intercalation of polymer achieved in the PEN/IMC16‐MMT hybrid. The effects of clay on the crystal structure of PEN were investigated. It was found that both pristine MMT and imidazolium‐treated MMT enhanced the formation of the β‐crystal phase under melt crystallization at 200 °C. At 180 °C, however, the imidazolium‐treated MMT was found to favor the α‐crystal form instead. The difference in clay‐induced polymorphism behavior was attributed to conformational changes experienced by the clay modifiers as the crystallization temperature changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1040–1049, 2006     

Diffraction grating in noncrosslinked polymers

The diffraction efficiency and morphology of the transmission modes of holographic polymer dispersed liquid crystals were studied with respect to the molecular structure of poly(urethane acrylate) (PUA), the film (polymer/liquid crystal) and resin (oligomer/monomer) compositions, and the cell thickness. PUA, based on N‐vinylpyrrolidone and ethyl hexyl acrylate, with low‐molecular‐weight poly(propylene glycol) at a low oligomer content, showed high diffraction efficiency. The results were interpreted in terms of the monomer reactivity and polymer elasticity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 613–620, 2004     

Ionic liquid functionalized polylactide by cationic polymerization: Synthesis and stabilization of carbon nanotube suspensions

Medium molecular weight poly(L ,L ‐lactide)s (PLA) containing at one chain end ionic group derived from imidazolium ionic liquid (IL) were synthesized by cationic polymerization using hydroxylated IL as initiator. matrix assisted laser desorption/ionization time‐of‐flight analysis confirmed the structure of products (PLA‐IL). Carbon nanotubes (CNT) were dispersed in solution of PLA‐IL in 1,4‐dioxane and significant improvement of stability of suspension was observed by measurements of suspension absorbance. Similar effect was, however, observed also for solutions of PLA which did not contain terminal IL group. CNT samples treated with PLA‐IL and PLA were isolated, thoroughly washed with 1,4‐dioxane and stability of suspensions was again measured. Sample treated with PLA after washing behave similarly to untreated CNT. Stability of suspension of CNT treated with PLA‐IL after washing was considerably higher than that of untreated CNT and the presence of polymer bound to CNT was clearly detectable in scanning electron microscopy images. Results indicate that there is indeed an interaction between end‐group derived from IL and CNT surface as postulated earlier but to observe solely this effect an excess of polymer should be removed, otherwise factors such as increase of viscosity of solution or weak interactions of PLA ester groups with CNT may obscure results. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011