Exfoliation

Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis 1-3 because strong acid sites within their uniform micropores enable size-and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations 3-5 that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion 4,5 . This has been realized by synthesizing zeolite nanocrystals 6 , by exfoliating layered zeolites 7-9 , and by introducing mesopores in the microporous material through templating strategies 10-17 or demetallation processes . But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-togasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.

A polymerizable cationic surfactant, vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for functionalization of montmorillonite (MMT) and preparation of exfoliated polystyrene-clay nanocomposites. Organophilic MMT was prepared by cationic exchange between inorganic ions of MMT and ammonium cations of VDAC in an aqueous medium. Dispersions of intercalated clay (VDAC-MMT) in styrene monomer formed gels. Shear thinning behavior of the gels was observed via rheological measurements. Polystyrene-clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in polystyrene matrix was achieved as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exfoliated nanocomposites have higher dynamic modulus and higher decomposition temperature than pure polystyrene. ᭧

The exfoliation of graphite is a phase transition involving the vaporization of the intercalate in the graphite. Exfoliated graphite is an expanded graphite with a low density. This paper reviews the process of the exfoliation of graphite and the exfoliated graphite material. It surveys the applications of exfoliated graphite, covers both reversible and irreversible exfoliation and reviews the methods and mechanism of exfoliation. Other topics include the structure and properties of exfoliated graphite, graphite foils, exfoliated carbon fibres and com-posi\es.

Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.

Exfoliation (pseudoexfoliation; PEX) syndrome is the single most common identifiable cause of open-angle glaucoma, however, very few investigators are engaged in basic research on this disease. To stimulate the field, the First International Think Tank on Exfoliation Syndrome was held in New York in July 1999, comprising clinicians and scientists. This report is a summary of the proceedings of this meeting.

Desilication of the medium-pore ferrierite zeolite in sodium hydroxide solutions was conducted to modify the porous structure and to create structural defects, resulting in enhanced accessibility and ultimately improved catalytic performance. Commercial H-ferrierite (Si/Al = 29) with the characteristic plate-like morphology was used as starting material. The attack by NaOH induces deaggregation, exfoliation, fracture, and ultimately perforation of the ferrierite crystals, resulting in mesoporosity of combined inter-and intracrystalline nature. The parent and treated samples were characterized by ICP-OES, XRD, N 2 adsorption, SEM, TEM, 27 Al and 29 Si MAS-NMR, FTIR, and NH 3 -TPD. Optimization of the treatment conditions (NaOH concentration, temperature, and time) is required to introduce substantial mesoporosity without significantly altering the micropore structure due to excessive Si leaching. Compared to other frameworks (e.g. MFI, MTW, MOR, and BEA), FER requires harsher conditions to extract silicon leading to mesoporosity. Under optimal conditions, the mesopore surface area of the NaOH-treated ferrierite increased by a factor of 3-4 with respect to the parent zeolite, while mostly preserving the native crystallinity and acidity. The ability of NaOH to induce porosity changes in FER largely exceeds conventional dealumination post-treatments. The benefit of the introduced porosity was demonstrated in the catalytic pyrolysis of low-density polyethylene.

Siliceous MCM-41-supported nickel phosphides from a precursor with a Ni/P atomic ratio of 3, 2, 1.25, 1, 0.5, or 1/3 were prepared by in situ reduction. A high heating rate and a multistep program were used to prepare the supported nickel phosphides. The in situ reduction method proved superior to the traditional reduction-passivation-rereduction method. The timely removal of local moisture from the surface during reduction is crucial to obtaining a high hydrodesulfurization (HDS) performance of the phosphide catalysts. The precursors were characterized by TPR to investigate the reactions involved in phosphide preparation, and the structures of the resulting nickel phosphides were characterized by means of 31 P NMR and XRD. Nickel phosphide formation may start with the reduction of NiO to Ni, and the Ni metal may assist phosphide formation in the reduction of nickel-rich precursors. Nickel-rich phosphides exhibited much higher HDS activity than phosphorus-rich phosphides prepared by the in situ reduction method. Reduction of the precursor with Ni/P = 2 yielded Ni 12 P 5 / MCM-41, whereas reduction of the precursor with Ni/P = 1.25 produced Ni 2 P/MCM-41. As in the traditional reduction-passivationrereduction method, a small excess of phosphorus in the precursors is also needed to obtain the desired nickel-rich phosphides by the in situ reduction method. Ni 2 P/MCM-41 was the most active catalyst in the HDS of dibenzothiophene among all of the supported nickel phosphides prepared by the in situ reduction method.

The effect of polar comonomers introduced into polystyrene (PS) chains on the melt intercalation into organosilicate is investigated in terms of shear and annealing time. In the case, where the interaction between polymers and silicate layers is relatively weak, e.g. PS/ organosilicate hybrids, it is difficult for the polymer chains to diffuse into interlayers of organosilicate and the hybrids are unstable under shear. For hybrids in which the interaction is enhanced by incorporating polar comonomers, e.g. acrylonitrile (AN) and methylvinyl oxzoline (OZ), their structures are stable even after a long mixing time. However, they do not show an exfoliated structure under the mixing conditions used in this study. The interaction between the comonomer and the silicate surface is investigated indirectly via both X-ray diffractional and FTIR spectral analyses. It is concluded that the structural stability of polymer/organosilicate hybrids is very dependent on the relative magnitude of the interactions between polymers, organic modifiers, and silicate layers.

The present paper analyzes the effects of the plasticizer nature on the clay exfoliation process into starchbased nano-biocomposites. The nano-hybrids have been elaborated by melt blending starch with different plasticizers, namely, glycerol, sorbitol and Polysorb Ò . In addition two types of nanofillers, natural montmorillonite (MMT-Na) and montmorillonite organo-modified with cationic starch (OMMT-CS) have been tested. Intercalated/aggregated and exfoliated morphologies were obtained with respectively MMT-Na and OMMT-CS as the nanofillers and glycerol as the plasticizer. Morphological analyses combined with uniaxial tensile tests have shown the negative effect of the sorbitol on the exfoliation extent into such nano-hybrid materials. Besides, thermo-mechanical analyses revealed the occurrence of a phase separation between domains rich and without nanofillers induced by the high plasticizer content of the starch formulations.

Layered double hydroxides (LDH) are a class of readily synthesizable layered crystals that can be used as an alternative to the commonly used silicate crystals for the preparation of polymeric nanocomposites. In this work layered double hydroxide/polyamide 6 nanocomposites (LDH/PA6) were prepared from organo-modified LDH by melt processing. The anionic exchange capacity of LDH was varied in order to investigate its influence on the degree of exfoliation. LDH were dispersed by a twin screw micro-extruder at a variety of processing conditions. The nanocomposites were characterized by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy, dynamic scanning calorimetry, and thermogravimetric analysis. It was found that exfoliated nanocomposites were successfully prepared by melt processing with a low exchange capacity LDH, whereas residue tactoids were observed with a high exchange capacity LDH. Shear, together with the exchange capacity, seems to be the key factor for the delamination in LDH/PA6. No major change in the crystalline phase or in the rate of crystallization was observed in the nanocomposite as compared to the neat polymer. A reduction in the onset of thermal decomposition temperature was observed in PA6/LDH compared to neat PA6, likely due to a nucleophilic attack mechanism. The properties of this nanocomposite system are discussed with connections to the current understanding within the broader nanocomposite field. q

With Hansen's solubility parameters, δ o 2) δ d 2 + δ p 2 + δ h 2 , the correlation between the degree of exfoliation of organically modified clays and the solvent in which the clay platelets are dispersed/mixed has been analyzed. It has been found that the dispersion force of the solvent, reflected by δ d , is the principal factor determining whether the clay platelets remain suspended in the solvent while the polar (δ p) and hydrogen-bonding (δ h) forces affect primarily the tactoid formation/structure of the suspended platelets. The organically modified clays studied in this work precipitated in any solvent with molecules with moderately strong hydrogen-bonding groups. The correlation found has been used to correctly identify a solvent, trichloroethylene, which completely exfoliates the organically modified clay studied in this work.

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp2 domains of graphene nanosheets obtained after the reduction of graphite oxide.

Imaging ofbiliary strictures may suggest malignancy but cytology can provide a tissue diagnosis. The aim of this study is to compare the diagnostic value of brush cytology and bile cytology. Thirty two patients (20 males, 12 females, median age 66 years, range 31-84

The effect of high energy ball milling under different conditions on the structure of Na + -montmorillonite (Na-MMT), and the organo-montmorillonite (Cloisite 30B) was investigated. Ball milling increased the structural disorder: peeling off of layers from the particles was observed, followed by the exfoliation of the particles, indicated by the disappearance of the (001) reflection. X-ray diffraction and infrared spectra revealed that the exfoliated layers did not show deteriorated structures. The presence of the alkylammonium ions seemed to stabilize the structure by reducing exfoliation.

In recent times, the materials properties of graphene have generated ever-increasing interest across multiple scientifi c disciplines including physics, material science and chemistry. The quantity and quality of graphene produced directly impacts the performance and development of applications related to organic fi eld-effect transistors (OFETs), conductive materials, [ 2b , 5 ] and photovoltaics, not forgetting biological applications. Generally, the techniques used to prepare graphene are based on either physical processes, chemical methodologies [ 3a , 9 ] or a blend of the two. Although physical methods are able to produce high-quality graphene consistently, the amount of processable graphene produced is always limited, as well as being quite costly. Conversely, although chemical oxidation of graphite to graphene oxide (GO), followed by reduction, results in reduced graphene oxide (RGO) in large quantities, this method generates defect-laden RGO to the extent that the resultant graphene is generally of lower quality than that produced by physical methods. Despite the fact that there are some reports relating to the use of wet chemistry to exfoliate graphene from graphite, the exfoliation of graphite to graphene employing noncovalent ππ interactions with π -conjugated molecules in water is relatively unexplored. Herein, we describe the preparation of graphene by direct exfoliation of graphite through the exploitation of ππ interactions between the N,N ′ -dimethyl-2,9-diazaperopyrenium dication ( MP 2 + ) and graphene in aqueous media.

Mg-Al layered double hydroxide (LDH) intercalated with glycinate anions was synthesized through co-precipitation and exfoliated in formamide and the single-layer suspension was reacted with aqueous iron porphyrin solutions (Fe(TDFSPP) and Fe(TCFSPP)). The obtained materials were characterized by X-ray powder diffraction, UV-vis, and electron paramagnetic resonance and investigated in the oxidation reaction of cyclooctene and cyclohexane using iodosylbenzene as oxidant. The iron porphyrin seems to be immobilized at the surface of the glycinate intercalated LDH. The catalytic activities obtained in heterogeneous media for iron porphyrin, Fe(TDFSPP), was superior to the results obtained under homogeneous conditions, but the opposite effect was observed on the Fe(TCFSPP), indicating that, instead of the structural similarity of both iron porphyrins (second-generation porphyrins), the immobilization of each one produced different catalysts. The best catalytic activity of the Fe(TDFSPP)/Gly-LDH, compared to Fe(TCFSPP)/Gly-LDH, can be explained by the easy access of the oxidant and the substrate to the catalytic sites in the former, probably located at the surface of the layered double hydroxide pillared with glycinate anions. A model for the immobilization and a mechanism for the oxidation reaction will be discussed.

The present work consists in the study of the modification of a nano-layered vermiculite by thermal treatment up to 900 °C. Changes in the structure and texture after thermal treatment were used for evaluation of dehydration properties of the studied material. The dehydration properties of the clay are strongly affected by the crystal structure.The Differential Thermal Analysis (DTA) allows the determination

Prevalence of oral cancer is high in Sudan and the disease is attributed to N-nitrosamine rich oral snuff consumption. As part of the development of a screening procedure for oral cancer and precancer, exfoliative cytology (EFC) was applied to a retrospective cohort to assess the presence and severity of oral epithelial atypia (ET) in 300 subjects (100 toombak dippers; 100 cigarette smokers; 100 non-tobacco users) without prior knowledge of the subjects' tobacco exposure. Five patients with oral squamous cell carcinoma (OSCC) were included as internal controls. ET was ascertained in 29 subjects and could not be ascertained in the remaining 271. Among the 29 subjects with ET, there were 11 (38%) toombak dippers, 14 (48%) cigarette smokers and 4 (14%) non-tobacco users. Among the 271 subjects without ET, there were 89 (33%) toombak dippers, 86 (32%) cigarette smokers and 96 (35%) non-tobacco users. ET was found in all the 5 control cases with OSCC. For the ET among toombak dippers...

The dispersion of clay in a polymer matrix is influenced by two factors: the choice of organic treatment for the clay and the processing or mixing method. Maximum benefits are achieved when the platelets are well dispersed or exfoliated. Exfoliated nanocomposites are formed when the individual clay layers break off the agglomerated particles or tactoids and are either randomly dispersed in the polymer (a disordered nanocomposite) or left in an ordered array. It is suggested that size reduction of clay particles and platelet delamination occur by erosion or surface peeling. A model based on the classical theories of interparticle interactions was formulated for the exfoliation of the clay platelets in a polymer matrix. The model involves the estimation of the binding energy and the adhesive force between the platelets in a clay particle, which indicate the forces required for breaking apart or delamination of clay particles. Then, the shear force required for breakup or delamination of the tactoids is estimated and compared to the hydrodynamic shear forces available during processing. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Mg-Al layered double hydroxide (LDH) intercalated with dodecylsulfate, was exfoliated in toluene, and the single-layer suspension was reacted with (3-aminopropyl)triethoxysilane (3APTS) in the same solvent. After washing with toluene and acetone to remove the excess reagent and drying procedure, the solid was reacted with neutral and anionic iron(III) porphyrins in toluene and methanol, respectively. The products were analyzed by powder X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, ultravioletvisible light, and atomic absorption spectrometric techniques. All of the data are consistent with the grafting of the LDH interlayers with 3APTS and immobilization of the iron porphyrins on the pendent terminal amino groups positioned at the top the grafted molecule. Based on these results, a schematic representation for the immobilization and preliminary catalytic oxidation reactions is presented.

Manganese oxide nanosheets were synthesized using liquid-phase exfoliation that achieved suspensions in isopropanol (IPA) with concentrations of up to 0.45 mg ml −1 . A study of solubility parameters showed that the exfoliation was optimum in N,N-dimethylformamide followed by IPA and diethylene glycol. IPA was the solvent of choice due to its environmentally friendly nature and ease of use for further processing. For the first time, a hybrid of graphene and manganese oxide nanosheets was synthesized using a single-step co-exfoliation process. The two-dimensional (2D) hybrid was synthesized in IPA suspensions with concentrations of up to 0.5 mg ml −1 and demonstrated stability against re-aggregation for up to six months. The co-exfoliation was found to be a energetically favorable process in which both solutes, graphene and manganese oxide nanosheets, exfoliate with an improved yield as compared to the single-solute exfoliation procedure. This work demonstrates the remarkable versatility of liquid-phase exfoliation with respect to the synthesis of hybrids with tailored properties, and it provides proof-of-concept ground work for further future investigation and exploitation of hybrids made of two or more 2D nanomaterials that have key complementary properties for various technological applications.

For organically modified montmorillonite (OMM)–epoxy nanocomposites, maximal montmorillonite dispersion is found to depend synergistically on the mechanical processing history of the resin mixture and the chemistry at the OMM surface. Specifically, Cloisite 30A (quaternary ammonium OMM) and I30.E (primary ammonium OMM), each containing surfactants with different catalytic effects on the curing chemistry of Epon 862, are compared. Irrespective of the OMM, conventional solvent-free processing methodologies, including sonication, result in an inhomogeneous distribution of OMM on the micron scale. Even though the primary ammonium alkyls within I30.E enhance intragallery reactivity, this only results in extensive swelling of tactoids (interlayer distance ∼10–20 nm), and thus retention of layer–layer correlations, leading to ‘hybrid’ micron scale reinforcing particles, not nanoscale dispersion of individual layers. In contrast, sub-ambient temperature (cryo) compounding had substantial impact on the ability to reduce tactoid and agglomerate size and increase homogeneity of dispersion for Cloisite 30A. The reactivity near Cloisite 30A is similar to that in the bulk and thus localized gelation around the layer-stacks does not retard particulate refinement. In all cases, alteration of the global epoxy network structure was ruled out by FTIR and NMR measurements. For nanocomposites with similar OMM content, however, the final thermal–mechanical properties does not coherently relate to one characteristic of the morphology. The coefficient of thermal expansion (T>Tg) and hardness (T<Tg) depend only weakly on morphology, where as the glass transition temperature depends strongly on the extent of OMM dispersion and interfacial chemistry. In general, the inter-relationships between mechanical processing, OMM surface chemistry and the desired property enhancements are not linear and thus must be considered in light of a final application to evaluate the optimal ‘nanocomposite’ fabrication methodology to achieve maximal benefit.

Exfoliation of graphite was achieved using a free-base porphyrin 1 resulting in an efficient fabrication of single-layer nanographene (NG)-1 hybrid platelets that can be further functionalized with other nanomaterials. The novel nanographene-porphyrin hybrids reveal efficient charge transfer in the excited state.

Controlling the level of dispersion of silicate layers in polymer matrices through intermolecular interactions and exploiting these interactions to enhance thermomechanical behavior are key challenges in the field of polymer nanocomposites. In this investigation, unmodified Laponite platelets are dispersed in a segmented polyurethane containing polar, hydrophilic soft segment and a hydrophobic hard segment using a novel solvent exchange method and compared to polyurethane nanocomposites containing more hydrophobic hard and soft domains. It was determined that the silicate layers were preferentially, but not exclusively, attracted to the hydrophilic, polar soft domains. An apparent micro-phase segregated morphology was observed in transmission electron microscopy for this system, revealing regions of exfoliation and intercalation. According to polarizing optical microscopy, strain-induced alignment is inhibited for this polyurethane nanocomposite, which is reflected in dramatic reductions in tensile strength and ultimate extensibility. In comparison, the Laponite discs 2 appear to be preferentially, but not exclusively, embedded to the hard domains in the segmented polyurethanes containing more hydrophobic hard and soft domains. Exfoliation of the clay platelets leads to enhanced modulus and toughness without a reduction in extensibility. This study provides clues for exploiting silicate-polymer interactions to tune material properties without chemical modification.

Although it is widely accepted that clonal genetic alterations are an essential component of tumor progression, little is known of the distnbu tion of such changes in high-risk lesions or how such clones are altered overtime.Weexploredthefeasibilityofusing exfoliativecellscollectedby scraping the mucosal surface to detect allelic loss in oral lesions of 22 patients (14 squamous cell carcinomas, 2 carcinomas in situ, and 6 dys plasias). The data show that the patterns of allelic loss observed in these samples closely represent those observed In biopsies of the same region.

The microcrystalline flaked graphites SFG6 and SFG44 were evaluated with regard to their compatibility with propylene carbonate (PC) by in situ Raman microscopy and postmortem scanning electron microscopy (SEM) study. PC is employed as electrolyte component in lithium-ion batteries. However, when used with certain types of graphitic materials, exfoliation occurs. To compare the effects of exfoliation, the first lithium insertion properties of these graphitic materials were measured with in situ Raman microscopy. Lithium half-cells containing either 1 M LiClO 4 1:1 (w/w) ethylene carbonate (EC):dimethyl carbonate (DMC) or 1:1 (w/w) EC:PC were investigated. The commencement of the exfoliation process was detected in SFG44 EC:PC by the appearance of a shoulder band at 1597 cm −1 on the G-band (1584 cm −1 ) below 0.9 V versus Li/Li + . The band (assigned as the exfoliation or E-band) at higher wavenumbers (1597 cm −1 ) corresponded to solvated lithium ions intercalated into graphite. The in situ Raman spectra of SFG6 in EC:DMC or EC:PC and SFG44 in EC:DMC did not show the E-band and instead displayed regular lithium intercalation spectra.

In aqueous dispersion, Na-montmorillonite swells due to absorption of water and exfoliate into smaller entities, known as tactoids, with electric double layers on their surfaces. The exfoliation rate of such tactoids in aqueous Laponite dispersion was seen to be greatly reduced at the jamming transition and was reported by this group in a recent article [Langmuir, 2013, 29, 12663-12669]. The work reported here uses ultrasound attenuation spec-troscopy experiments on Na-montmorillonite dispersions and shows that the complete exfoliation of tactoids is not achieved even below the jamming concentration. This behavior indicates that screened Coulomb repulsions between and within tactoids, as well as the osmotic pressure of hydrated Na + ions, play very important roles in the exfoliation kinetics of tactoids. In this work, the phenomenon of tactoid exfoliation is studied systematically by changing clay mineral concentration, ionic conditions and the ages of the dispersions. A signature of an irreversible process of tactoid reformation under certain ionic conditions is also observed. Finally, electroacoustic measurements and rheometry are used to assess the influence of tactoid exfoliation on the stability and viscoelas-ticity of the arrested phases formed under different ionic conditions.

Over a 70-year period, a mine near Libby, MT supplied nearly 80% of the world's vermiculite. Raw vermiculite, which was contaminated with naturally occurring amphibole in veins throughout the deposit, was shipped to processing sites throughout the United States for exfoliation. In this pilot study, tree bark samples were collected near processing facilities

Medium chain length polyhydroxyalkanoates (mcl-PHA) have been produced by fed-batch cultivation of Pseudomonas oleovorans. Using octanoic acid as the sole carbon substrate, a copolymer of 3-hydroxyoctanoate and 3-hydroxyhexanoate monomer units was accumulated up to 38 wt. % of cell mass. Mcl-PHA based nanocomposites have then been prepared using Cloisite 15A as nanofiller and characterized. Wide angle X-ray diffraction and rheological analysis of the nanocomposites highlighted their morphologies, which can be considered as well-intercalated structures. The thermal characteristics of mcl-PHA are not significantly affected by the nanofiller incorporation. On the contrary, the storage moduli of nanocomposites are greatly enhanced with increasing clay fraction due to the degree of dispersion of the nanoplatelets in the polymer matrix.

A poly(ether-block-amide) copolymer (PEBA) was successfully hybridized with montmorillonites using melt processing techniques to form nanocomposites. The organoclays used in preparation of the nanocomposites were modified with ammonium surfactants of different molecular structures to study the effect of the surfactant on the intercalation and exfoliation of the polymer by X-ray diffraction (XRD) and dynamic linear viscoelastic analysis. The polymer was found to be capable of forming intercalated composite with unmodified montmorillonite and the best intercalation and exfoliation was found in the hybrids using surfactants that possess hydroxyl group. Organoclays modified with a single tallow tail ammonium prevailed over those modified with a double tallow tail ammonium in intercalation and exfoliation of silicate layers. Higher capacity of ion exchange also led to a better intercalation for hybrids using single tail surfactants, but the hybrids with swallow tail surfactant behaved oppositely. XRD data showed that the diffraction peaks in the hybrids were narrower than those of the organoclay implying a higher order and more number of layers in the stacks of clays. The intercalation of nanocomposites was found dominated by the energetic factor and entropic factor played no role in the outcome of intercalation. Results of linear viscoelastic measurements paralleled those of XRD showing that melts of those nanocomposites with a superior intercalation or exfoliation also exhibited higher storage modulus and thus the linear viscoelasticity could be an indicator for intercalation. The composites showed an abnormal terminal behavior suggesting the existence of a network structure.

The effect caused by dehydration and rehydration of the synthetic Na-magadiite was investigated by TGA, XRD, SEM, and 29 Si NMR. Thermal analysis of Na-magadiite presented two well-defined loss mass stages between 20 and 150 • C and another between 270 and 310 • C, both related to the removal of interlayer water. The swelling behavior of Na-magadiite was studied by thermal dehydration data obtained at 150 and 300 • C, and respective rehydration by water addition. X-ray patterns showed that the dehydration of Na-magadiite at 150 and 300 • C provoked the basal spacing decrease. The XRD also showed that only the material treated at 150 • C returned to the original structure with the rehydration. Si NMR spectra showed that after rehydration, the Q 3 /Q 4 relationship presented the same value for Na-magadiite treated at 150 • C. However, this Q 3 /Q 4 value decreased when the treatment was done at 300 • C. Kinetic studies of thermal decomposition showed that the dehydration of magadiite is based on a phase boundarycontrolled reaction, caused by contracting areas. The exfoliation of lamellas with thermal treatment can explain this behavior, as observed in SEM images.

A synthetic Li-fluorohectorite with typical aspect ratios around 1000 shows superior thermal, fire and mechanical properties. A comparison between Li-fluorohectorite and MMT underlines the crucial role of the aspect ratio in particular for flame retardancy. Furthermore, solution blending yields a better dispersion of the filler, as compared to melt compounding, which directly transforms into superior properties. Quite surprisingly, the homogenous clay surface layer built during burning of the PS fluorohectorite nanocomposite has such a high gas barrier that an intumescent-like behavior of the char is detectable.

The correlation between sorption capacity for heavy oil with a viscosity of 0.004 kg/ms and pore volume measured by a mercury porosimeter was studied on exfoliated graphite samples with different bulk densities. Pore volume measured by using the conventional dilatometer (N-type cell), which gives information on the pore size from 0.004 to 4 pm, was too low to explain the sorption capacity measured. However, pore volume measured by a special dilatometer (U-type cell) for large pore sizes up to 600 pm was very closed to sorption capacity. Pore volume measured by this U-type cell showed a linear relation to sorption capacity of exfoliated graphite samples, of which the slope was the same value as the density of heavy oil used (860 kg/m3). Therefore, large pores, which are reasonably assumed to be inter-particle pores among entangled worm-like particles of exfoliated graphite, were responsible for the large sorption capacity of heavy oils. Intra-particle pores inside and cleavage-like pores on the surface of worm-like particles were assumed to assist the capillary pumping of heavy oil.

The preparation of processable graphene oxide colloids called chemically converted graphene (CCG) involves the following steps: oxidation of graphite to form graphite oxide; exfoliation of graphite oxide to form graphene oxide (GO); and reduction of GO to form CCG. In this work, the exfoliation and reduction steps were monitored by capillary zone electrophoresis (CZE). CZE was performed in fused silica capillaries with UV absorbance at 230 nm (GO) and 270 nm (CCG) using 250 M tetrapropylammonium hydroxide (pH 10.4). The results indicate that almost complete exfoliation of graphite oxide (0.05 wt%) and higher recovery of CCG were obtained by sonication at 50% power for more than 15 h. CZE is considered a valuable tool for the fractionation and analysis of GO nanoparticles and, hence, for the control of different steps in preparation of CCG.

Twenty-four hour control of intraocular pressu re with dorzolamide and timolol maleate in exfoliation and primary open-angle glaucoma Abstract Purpose To determine the efficacy and safety of adding dorzolamide 2% twice daily to timolol maleate solution 0.5% twice daily when treating exfoliation glaucoma or primary open-angle glaucoma. Methods This was a single-centre, crossover intra-individually controlled comparison. Sixty-two consecutive patients (31 with exfoliation glaucoma and 31 with primary open angle glaucoma) chronically treated with timolol maleate twice daily were included in this trial. Patients then had added dorzolamide 2% twice daily (08:00 and 20:00), instilled approximately 10 min after timolol maleate. Patients underwent diurnal intraocular pressure (lOP) testing (six measurements over 24 h), first on timolol maleate monotherapy and 2 months later following the addition of dorzolamide 2% as adjunctive therapy.