Showing papers in "Macromolecules in 2011"

Self-Healing Materials Based on Disulfide Links

Abstract: Autonomous healing of damage is a common phenomenon in living organisms but is hardly ever encountered in synthetic materials. Disulfide chemistry is used to introduce a self-healing ability in a covalently cross-linked rubber. Autonomous healing of a cut takes place at moderate temperatures and leads to full recovery of mechanical properties. This result is achieved by introducing disulfide groups in the network that are able to exchange, leading to renewal of cross-links across the damaged surfaces. The healing process can be repeated many times. The combination of their unique self-healing properties and applicability for a large variety of polymers makes this approach ideal for coatings.

Tough and Self-Healing Hydrogels Formed via Hydrophobic Interactions

Abstract: Large hydrophobic monomers stearyl methacrylate (C18) and dococyl acrylate (C22) could be copolymerized with the hydrophilic monomer acrylamide in a micellar solution of sodium dodecyl sulfate (SDS). This was achieved by the addition of salt (NaCl) into the reaction solution. Salt leads to micellar growth and, hence, solubilization of the hydrophobes within the SDS micelles. The hydrogels thus obtained without a chemical cross-linker exhibit unique properties due to the strong hydrophobic interactions. They can only be dissolved in SDS solutions demonstrating the physical nature of cross-links. Results of dynamic light scattering, rheological and mechanical measurements show that the hydrophobic associations between the blocks of C18 or C22 units prevent water solubility and flow, while the dynamic nature of the junction zones provides homogeneity and self-healing properties together with a high degree of toughness. When fractured, the hydrogels formed using C18 associations can be repaired by bringing to...

Triggered Release from Polymer Capsules

Abstract: Stimuli-responsive capsules are of interest in drug delivery, fragrance release, food preservation, and self-healing materials. Many methods are used to trigger the release of encapsulated contents. Here we highlight mechanisms for the controlled release of encapsulated cargo that utilize chemical reactions occurring in solid polymeric shell walls. Triggering mechanisms responsible for covalent bond cleavage that result in the release of capsule contents include chemical, biological, light, thermal, magnetic, and electrical stimuli. We present methods for encapsulation and release, triggering methods, and mechanisms and conclude with our opinions on interesting obstacles for chemically induced activation with relevance for controlled release.

A New Strategy to Microporous Polymers: Knitting Rigid Aromatic Building Blocks by External Cross-Linker

Abstract: A series of microporous polymers has been obtained via a low-cost versatile strategy, which involves “knitting” rigid aromatic building blocks, such as benzene, biphenyl, 1,3,5-triphenylbenzene, methylbenzene, chlorobenzene, and phenol using an external cross-linker. These materials are predominantly microporous and exhibit high surface areas. Moreover, different building blocks can generate materials with different pore structures, functional groups and application properties, which are significant for materials design.

Block Copolymers for Fuel Cells

Abstract: Ion-containing block copolymers hold promise as next-generation proton exchange membranes in hydrogen and methanol fuel cells. These materials’ self-assembled ordered nanostructures facilitate proton transport over a wide range of conditions, a requirement for robust fuel cell performance. In this perspective, we will present an overview of the morphology and transport properties of ion-containing block copolymers that have been studied to gain insight into the fundamental behavior of these materials and, in some cases, are targeted toward applications in fuel cells and other electrochemical devices. We will discuss the challenges associated with predicting and obtaining well-ordered morphologies in block copolymers with high ion content, particularly those with chemistries that can withstand the chemical and mechanical stresses of the fuel cell, such as aromatic backbone block copolymers. New opportunities for ion-containing block copolymers in alkaline membrane fuel cells will also be reviewed.

Strong Nanocomposite Reinforcement Effects in Polyurethane Elastomer with Low Volume Fraction of Cellulose Nanocrystals

Abstract: Polyurethane/cellulose nanocrystal nanocomposites with ultrahigh tensile strength and stain-to-failure with strongly improved modulus were prepared by adding cellulose nanocrystals (CNCs) during th ...

Lamellar Bilayers as Reversible Sacrificial Bonds To Toughen Hydrogel: Hysteresis, Self-Recovery, Fatigue Resistance, and Crack Blunting

Abstract: We report the extraordinary toughness, hysteresis, self-recovery, and persistent fatigue resistance of an anisotropic hydrogel with single-domain lamellar structure, consisting of periodical stacking of several thousands of rigid, hydrophobic bilayers in the ductile, hydrophilic polymer matrix. The stratified lamellar bilayers not only diffract light to exhibit magnificent structural color but also serve as reversible sacrificial bonds that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. Both the molecular dissociation and lipid-like mobile nature of bilayers dramatically enhance the resistance to crack propagation by suppressing the stress concentration at the crack tip with the formation of extraordinary crack blunting. This unique toughening phenomenon could allow deep insight into the toughening mechanism of the hydrogel-like soft materials such as biological soft tissues.

Mobility of Nonsticky Nanoparticles in Polymer Liquids

Abstract: We use scaling theory to derive the time dependence of the mean-square displacement ⟨Δr2⟩ of a probe nanoparticle of size d experiencing thermal motion in polymer solutions and melts. Particles with size smaller than solution correlation length ξ undergo ordinary diffusion (⟨Δr2(t)⟩ ∼ t) with diffusion coefficient similar to that in pure solvent. The motion of particles of intermediate size (ξ < d < a), where a is the tube diameter for entangled polymer liquids, is subdiffusive (⟨Δr2(t)⟩ ∼ t1/2) at short time scales since their motion is affected by subsections of polymer chains. At long time scales the motion of these particles is diffusive, and their diffusion coefficient is determined by the effective viscosity of a polymer liquid with chains of size comparable to the particle diameter d. The motion of particles larger than the tube diameter a at time scales shorter than the relaxation time τe of an entanglement strand is similar to the motion of particles of intermediate size. At longer time scales (t...

Polymer-Grafted-Nanoparticles Nanocomposites: Dispersion, Grafted Chain Conformation, and Rheological Behavior

Abstract: We investigate the dispersion mechanisms of nanocomposites made of well-defined polymer (polystyrene, PS) grafted-nanoparticles (silica) mixed with free chains of the same polymer using a combination of scattering (SAXS/USAXS) and imaging (TEM) techniques. We show that the relevant parameter of the dispersion, the grafted/free chains mass ratio R tuned with specific synthesis process, enables to manage the arrangement of the grafted nanoparticles inside the matrix either as large and compact aggregates (R 0.24). From the analysis of the interparticles structure factor, we can extract the thickness of the spherical corona of grafted brushes and correlate it with the dispersion: aggregation of the particles is associated with a significant collapse of the grafted chains, in agreement with the theoretical models describing the free energy as a combination of a mixing entropy term between the free and the grafted chains and an elastic term of deformation ...

Impact of Filler Surface Modification on Large Scale Mechanics of Styrene Butadiene/Silica Rubber Composites

Abstract: In material science of elastomers the influence of nanoscale and nanostructured filler particles is of utmost significance for the performance of innovative rubber products, i.e., passenger car tires with ultralow rolling resistance but high wet-grip performance. A better understanding of the physical characteristics of the filler–rubber interface and the filler–rubber interphase as well is necessary to improve the overall macroscopic properties of these elastomeric nanocomposites. Therefore, the surface energies and polarities of filler particles with different modified surfaces were measured by a modified Wilhelmy technique. In all cases the rubber matrix consisted of a solution - styrene butadiene copolymers, filled with 20 or 40 phr pyrogenic or precipitated silica grades with different surface modifications by silanes, and a carbon black sample as reference. A moving die rheometer was employed to observe the filler flocculation at elevated temperatures (160 °C) in rubber mixtures containing no curati...

Rheology and Phase Behavior of Lyotropic Cellulose Nanocrystal Suspensions

Abstract: The dispersion microstructure and rheological properties of aqueous sulfonated cellulose nanocrystal (CNC) suspensions have been investigated. Between 3.07 and 10.4 vol % the suspensions phase separated into liquid crystalline and isotropic domains. At 12.1 vol %, no isotropic phase was visible, and the samples had the fingerprint texture characteristic of a cholesteric liquid crystal. Below 35 °C, temperature had little influence on rheology and phase behavior. However, between 35 and 40 °C there was a significant change in both the fraction of isotropic phase and the rheological properties. In contrast to many lyotropic suspensions, the steady shear viscosity did not go through a maximum with increasing concentration. Maxima were observed for complex viscosity, storage modulus, and loss modulus at concentrations that appeared fully liquid crystalline. Time–concentration superposition was successful for the loss modulus but not the storage modulus. This suggests that the interface in biphasic samples aff...

Bioinspired Mechanically Adaptive Polymer Nanocomposites with Water-Activated Shape-Memory Effect

Abstract: New biomimetic, stimuli-responsive mechanically adaptive nanocomposites, which change their mechanical properties upon exposure to water and display a water-activated shape-memory effect, were investigated. These materials were produced by introducing rigid cotton cellulose nanowhiskers (CNWs) into a rubbery polyurethane (PU) matrix. A series of materials with CNW concentrations of 2–20% v/v was produced by solution blending CNWs and the PU. Films were subsequently prepared by compression molding. The introduction of CNWs led to an increase of the tensile storage moduli (E′) in the dry nanocomposites. The level of reinforcement scaled with the CNW content and followed the Halpin–Kardos model below and the percolation model above the percolation limit of ∼7% v/v. Upon exposure to water, the materials with a CNW content above the percolation limit swelled slightly and showed a decrease of E′, for example from 1 GPa to 144 MPa in the case of the material with 20% v/v CNWs. This effect is the result of compet...

Interaction of Microstructure and Interfacial Adhesion on Impact Performance of Polylactide (PLA) Ternary Blends

Abstract: Polyactide (PLA) was blended with an ethylene/n-butyl acrylate/glycidyl methacrylate (EBA-GMA) terpolymer and a zinc ionomer of ethylene/methacrylic acid (EMAA-Zn) copolymer. The phase morphology of the resulting ternary blends and its relationship with impact behaviors were studied systematically. Dynamic vulcanization of EBA-GMA in the presence of EMAA-Zn was investigated by torque rheology, and its cross-link level was evaluated by dynamic mechanical analysis. Reactive compatibilization between PLA and EBA-GMA was studied using Fourier transform infrared spectroscopy. The dispersed domains in the ternary blends displayed a “salami”-like phase structure, in which the EMAA-Zn phase evolved from occluded subinclusions into continuous phase with decrease in the EBA-GMA/EMAA-Zn ratio. An optimum range of particle sizes of the dispersed domains for high impact toughness was identified. Also, the micromechanical deformation process of these ternary blends was also investigated by observation of the impact-fra...

Effect of Nanoscale Morphology on the Conductivity of Polymerized Ionic Liquid Block Copolymers

Abstract: Polymerized ionic liquid (POIL) block copolymers represent a unique class of materials for fundamental studies of single ion conduction as a function of morphology in microphase-separated polymer electrolytes for energy storage and conversion applications. We describe the synthesis of a series of poly(styrene-b-4-vinylbenzylalkylimidazolium bis(trifluoromethanesulfonyl)imide) (PS-b-PVBn(alkyl)ImTFSI; alkyl = CH3 (Me), n-C4H9 (Bu), n-C6H13 (Hex)) diblock copolymers (2.7–17.0 mol % POIL) via exhaustive functionalization and ion exchange of relatively narrow molecular weight dispersity poly(styrene-b-4-vinylbenzyl chloride) precursors derived from nitroxide-mediated block copolymerizations. The solid-state morphology of these PS-b-PVBn(alkyl)ImTFSI copolymers were studied using a combination of temperature-dependent synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). From electrochemical impedance spectroscopy measurements, we observe that lamellar samples having simil...

Photodegradable, Photoadaptable Hydrogels via Radical-Mediated Disulfide Fragmentation Reaction

Abstract: Various techniques have been adopted to impart a biological responsiveness to synthetic hydrogels for the delivery of therapeutic agents as well as the study and manipulation of biological processes and tissue development. Such techniques and materials include polyelectrolyte gels that swell and deswell with changes in pH, thermosensitive gels that contract at physiological temperatures, and peptide cross-linked hydrogels that degrade upon peptidolysis by cell-secreted enzymes. Herein we report a unique approach to photochemically deform and degrade disulfide cross-linked hydrogels, mitigating the challenges of light attenuation and low quantum yield, permitting the degradation of hydrogels up to 2 mm thick within 120 s at low light intensities (10 mW/cm2 at 365 nm). Hydrogels were formed by the oxidation of thiol-functionalized 4-armed poly(ethylene glycol) macromolecules. These disulfide cross-linked hydrogels were then swollen in a lithium acylphosphinate photoinitiator solution. Upon exposure to light...

Stability of Self-Assembled Polymeric Micelles in Serum.

Abstract: The stability of polymeric nanoparticles in serum is critical to their use in drug delivery where dilution after intravenous injection often results in nanoparticle disassembly and drug unloading; however, few investigate this in biologically relevant media. To gain greater insight into nanoparticle stability in blood, the stability of self-assembled polymeric micelles of poly(d,l-lactide-co-2-methyl-2-carboxytrimethylene carbonate)-g-poly(ethylene glycol), P(LA-co-TMCC)-g-PEG, were tested in both serum and individual serum protein solutions. By encapsulating Forster resonance energy transfer pairs and following their release by fluorescence, these micelles demonstrated excellent thermodynamic and kinetic stability in the presence of serum. Further analyses by fast protein liquid chromatography and dynamic light scattering confirmed these data. Moreover, these micelles are compatible with red blood cells, as shown by a hemolysis assay. The stability and compatibility demonstrated in blood suggest that the...

Drastic Control of Texture in a High Performance n-Type Polymeric Semiconductor and Implications for Charge Transport

Abstract: Control of crystallographic texture from mostly face-on to edge-on is observed for the film morphology of the n-type semicrystalline polymer {[N,N-9-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)}, P(NDI2OD-T2), when annealing the film to the polymer melting point followed by slow cooling to ambient temperature. A variety of X-ray diffraction analyses, including pole figure construction and Fourier transform peak shape deconvolution, are employed to quantify the texture change, relative degree of crystallinity and lattice order. We find that annealing the polymer film to the melt leads to a shift from 77.5% face-on to 94.6% edge-on lamellar texture as well as to a 2-fold increase in crystallinity and a 40% decrease in intracrystallite cumulative disorder. The texture change results in a significant drop in the electron-only diode current density through the film thickness upon melt annealing, while little change is observed in the in-plane transport of bott...

Enzymatic surface hydrolysis of PET : effect of structural diversity on kinetic properties of cutinases from thermobifida

Abstract: In this study cutinases from Thermobifida cellulosilytica DSM44535 (Thc_Cut1 and Thc_Cut2) and Thermobifida fusca DSM44342 (Thf42_Cut1) hydrolyzing poly(ethylene terephthalate) (PET) were successfully cloned and expressed in E.coli BL21-Gold(DE3). Their ability to hydrolyze PET was compared with other enzymes hydrolyzing natural polyesters, including the PHA depolymerase (ePhaZmcl) from Pseudomonas fluorescens and two cutinases from T. fusca KW3. The three isolated Thermobifida cutinases are very similar (only a maximum of 18 amino acid differences) but yet had different kinetic parameters on soluble substrates. Their kcat and Km values on pNP–acetate were in the ranges 2.4–211.9 s–1 and 127–200 μM while on pNP–butyrate they showed kcat and Km values between 5.3 and 195.1 s–1 and between 1483 and 2133 μM. Thc_Cut1 released highest amounts of MHET and terephthalic acid from PET and bis(benzoyloxyethyl) terephthalate (3PET) with the highest concomitant increase in PET hydrophilicity as indicated by water co...

Relative Chemical Stability of Imidazolium-Based Alkaline Anion Exchange Polymerized Ionic Liquids

Abstract: We thoroughly investigate and quantify the chemical stability of an imidazolium-based alkaline anion exchange polymerized ionic liquid (PIL), poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium hydroxide) (poly(MEBIm-OH), over a broad range of humidities, temperatures, and alkaline concentrations using the combined techniques of electrochemical impedance spectroscopy and nuclear magnetic resonance spectroscopy. High chemical stability was observed under dry conditions (10% RH) at 30 °C, humid and saturated conditions up to 80 °C, and even in mild alkaline conditions ([KOH] 1 M). Under these conditions, we suggest an imidazolium ring-opening mechanism as the primary degradation pathway, based on a detailed analysis of the 1H NMR spectra. Similar to poly(MEBIm-OH), other alkaline anion (carbonate (CO32–) and bicarbonate (HCO3–)) exchange PILs were als...

Shape-Dependent Localization of Carbon Nanotubes and Carbon Black in an Immiscible Polymer Blend during Melt Mixing

Abstract: In melt mixed multiphase polymer blends, the mechanisms determining the spatial distribution and localization of solid particles smaller than the blend domain sizes are still not completely understood. From theoretical considerations of a previous paper of one of the authors, it was derived that the transfer dynamics as well as the stability of different solid fillers at the blend interface reveal a strong dependence on the particle’s aspect ratio. Low interfacial stabilities and high transfer speeds between the blend phases can be deduced for fillers with very high aspect ratios, entitled as the “Slim-Fast Mechanism” (SFM). The SFM appears suitable to explain in retrospect important features of several previous studies that address the localization of differently shaped nanoscaled particles in polymer blends. The SFM was evaluated by investigating the simultaneous transfer of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) from a poly(styrene acrylonitrile) (SAN) precompound into the thermody...

Diphenyl Phosphate as an Efficient Cationic Organocatalyst for Controlled/Living Ring-Opening Polymerization of δ-Valerolactone and ε-Caprolactone

Abstract: The ring-opening polymerization of δ-valerolactone (δ-VL) and e-caprolactone (e-CL) using 3-phenyl-1-propanol (PPA) as the initiator and diphenyl phosphate (DPP) as the catalyst in toluene at room temperature with the [δ-VL or e-CL]0/[PPA]0/[DPP] ratio of 50/1/1 homogeneously proceeded to afford poly(δ-valerolactone) (PVL) and poly(e-caprolactone) (PCL) with narrow polydispersity indices. The molecular weights determined from a 1H NMR analysis (PVL, Mn,NMR = 5170 g mol−1 and PCL, Mn,NMR = 5920 g mol−1) showed good agreement with those estimated from the initial ratio of [δ-VL or e-CL]0/[PPA]0 and monomer conversions (PVL, Mn,theo = 4890 g mol−1 and PCL, Mn,theo = 5680 g mol−1). The 1H NMR, SEC, and MALDI-TOF MS measurements of the obtained PVL and PCL clearly indicated the presence of the initiator residue at the chain end, confirming that the DPP-catalyzed ROP of lactones proceeded through an activated monomer mechanism. The kinetic and chain extension experiments confirmed the controlled/living nature f...

Polymer Crystallization of Partially Miscible Polythiophene/Fullerene Mixtures Controls Morphology

Abstract: Mixtures of polythiophene and fullerene are intensely studied for organic photovoltaic applications. Control of nanoscale morphology of these materials is critical for device performance, but characterization and understanding of this morphology and how it arises is lacking. We use energy-filtered transmission electron microscopy (EFTEM) to obtain high-contrast images of P3HT nanocrystals in organic semiconductor mixtures. Grazing-incidence small-angle X-ray scattering correlates well with the length scales obtained from EFTEM images; we combine the two techniques to follow the morphology evolution under different material processing histories. EFTEM also measures local P3HT concentration in PCBM-rich regions, proving that these components are partially miscible. We determine the P3HT-PCBM χ parameter and Flory–Huggins phase diagram, which predicts miscibility for P3HT volume fractions above 0.42. This miscibility suppresses fullerene crystallization. The nanoscale morphology in these materials, critical ...

Interface of Grafted and Ungrafted Silica Nanoparticles with a Polystyrene Matrix: Atomistic Molecular Dynamics Simulations

Abstract: Atomistic molecular dynamics simulations of a composite consisting of an ungrafted or a grafted spherical silica nanoparticle embedded in a melt of 20-monomer atactic polystyrene chains have been performed. The structural properties of the polymer in the vicinity of a nanoparticle have been studied. The nanoparticle modifies the polymer structure in its neighborhood. These changes increase for higher grafting densities and larger particle diameters. Mass and number density profiles show layering of the polymer chains around the nanoparticle, which extends to ∼2 nm. In contrast, the increase in the polymer’s radius of gyration and other induced ordering (alignment of the chains parallel to the surface and orientation of backbone segments) are shorter-ranged. The infiltration of free polystyrene chains into the grafted chains region is reduced with increasing grafting density. Therefore, the interpenetration of grafted and free chains at high grafting densities, which is responsible for the mechanical ancho...

Sub-Tg Cross-Linking of a Polyimide Membrane for Enhanced CO2 Plasticization Resistance for Natural Gas Separation

Abstract: Decarboxylation-induced thermal cross-linking occurs at elevated temperatures (∼15 °C above glass transition temperature) for 6FDA–DAM:DABA polyimides, which can stabilize membranes against swelling and plasticization in aggressive feed streams. Despite this advantage, such a high temperature might result in collapse of substructure and transition layers in the asymmetric structure of a hollow fibers based on such a material. In this work, the thermal cross-linking of the 6FDA–DAM:DABA at temperatures much below the glass transition temperature (∼387 °C by DSC) was demonstrated. This sub-Tg cross-linking capability enables extension to asymmetric structures useful for large scale membranes. The resulting polymer membranes were characterized by swelling in known solvents for the un-cross-linked materials, TGA analysis, and permeation tests of aggressive gas feed stream at higher pressure. The annealing temperature and time clearly influence the degree of cross-linking of the membranes, and results in a sli...

A Soluble and Conductive Polyfluorene Ionomer with Pendant Imidazolium Groups for Alkaline Fuel Cell Applications

Abstract: Solvent processable polyfluorene ionomers with pendant imidazolium groups were synthesized and characterized. The synthesized polymeric membranes are transparent, flexible, and mechanically strong and exhibit hydroxide ion conductivity above 10–2 S/cm at room temperature. The membranes are soluble in polar aprotic solvents such as DMSO and DMF, while insoluble in water and aqueous methanol. The solubility properties of polyfluorene ionomers enable the use for not only alkaline anion-exchange membrane but also ionomer electrode material. 1H NMR and hydroxide ion conductivity measurements demonstrated an excellent chemical stability of the synthesized polyfluorene ionomers in high-pH solution at elevated temperatures. The results of the study suggest a feasible approach for the synthesis and practical applications of alkaline anion-exchange membranes (AEMs).

Microgel-Reinforced Hydrogel Films with High Mechanical Strength and Their Visible Mesoscale Fracture Structure

Abstract: The poor mechanical properties remain the largest barrier to traditional synthetic hydrogels for extensive practical applications, such as tissue scaffolds. In this work, we have synthesized the hydrogel films in the presence of microgel precursors of various chemical species with different charges. The hydrogels fabricated have a novel two-phase composite structure, where the continuous phase is a loosely cross-linked polyacrylamide (PAAm) matrix and the disperse phase is virtually double-network (DN) microgels. Named as microgel-reinforced (MR) hydrogels, they exhibited dramatic enhancement in mechanical strength and toughness, in comparison to the hydrogels with no microgels. MR hydrogels showed the comparable mechanical properties with the conventional bicontinuous DN hydrogels. By visualizing the embedded microgels before, during, and after the elongation, mesoscale fractures of the microgels phase were confirmed, which should effectively blunt the crack and enhance the fracture propagation resistanc...

Effect of Crystallization on the Electronic Energy Levels and Thin Film Morphology of P3HT:PCBM Blends

Abstract: We study thin films of semi-crystalline regioregular poly(3-hexylthiophene) (RR-P3HT) and amorphous regiorandom P3HT (RRa-P3HT) in blends with [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Ultraviolet and (angle-resolved) X-ray photoelectron spectroscopy techniques together with absorption, photoluminescence and optical microscopy were used to measure electronic energy levels, vertical chemical compositions and optical properties of these films. We find that ordering the P3HT chains raises the highest occupied molecular orbital (HOMO) energy level of P3HT thin films (reducing ionization potential) and that the ordering of P3HT chains occurs preferentially at the film−air interface in RR-P3HT:PCBM thin films. This leads to a vertical phase separation between P3HT and PCBM molecules, which may be undesirable for conventional P3HT:PCBM solar cells.

Swelling Behaviors of pH- and Salt-Responsive Cellulose-Based Hydrogels

Abstract: Ampholytic hydrogels with pH and salt responsive properties have been synthesized by cross-linking quaternized cellulose (QC) and carboxymethyl cellulose (CMC) with epichlorohydrin (ECH) in NaOH aqueous solution. The swelling behaviors of the QC/CMC hydrogels were studied as a function of the polymer composition, pH, and salt concentration. The equilibrium swelling ratio of the hydrogel in ultrapure water strongly depended on the composition, and increased dramatically from 8.6 to 498 g/g with the change of the weight ratio of QC to CMC from 3:1 to 1:3 (w/w). The hydrogel (Gel32) consisted of QC and CMC in the ratio of 3:2 (w/w) had the minimum swelling ratio, and it was electrically neutral. The results from ζ-potential experiments were in good agreement with the theoretically calculated stoichiometry for balanced charge, confirming that the weight ratio of QC and CMC was 1.5, corresponding to Gel32. Furthermore, all hydrogels exhibited excellent pH sensitivity in the range of pH from 1 to 13 and shrunk ...

Poly(vinyl alcohol) Nanocomposites with Nanodiamond

Abstract: Carbon-based nanomaterials, such as carbon nanotubes, are well-known for their unique physical properties. They have attracted interest as reinforcing fillers because of their superb mechanical properties (Young’s modulus ≥1 TPa and tensile strength = 100–150 GPa). However, the success of the reinforcement has been limited because of their tendency to form agglomerates in polymer matrices. We report the excellent reinforcement properties of polymer nanocomposites by the incorporation of nanodiamond (ND). ND has been expected to offer polymer nanocomposites optimal properties because of its smooth surface and excellent optical, mechanical, and thermal properties, which can approach the values of single diamond crystal. We prepared poly(vinyl alcohol) (PVA)/ND nanocomposites by a simple casting method from aqueous medium and achieved the high dispersibility of ND in the PVA matrices. The resulting nanocomposites had excellent properties derived both from ND and PVA. The Young’s modulus of the nanocomposites...