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Hexaniobato lamelar: Estudos de esfoliação e intercalação"; Layered hexaniobate: studies of exfoliation and intercalation

Shiguihara, Ana Lucia
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/12/2004 PT
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O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0...

Investigação dos processos de intercalação e esfoliação de hexaniobato lamelar e preparação de materiais híbridos com biopolímeros; Investigation of the intercalation and exfoliation processes of layered hexaniobate and preparation of hybrid materials with biopolymers

Shiguihara, Ana Lucia
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 01/09/2010 PT
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A presente tese tem como objetivo principal a investigação do processo de intercalação e esfoliação do hexaniobato lamelar em soluções de hidróxidos de tetraalquilamônios e, também, do emprego das partículas do niobato na preparação de materiais híbridos com polissacarídeos. O material de composição H2K2Nb6O17 foi suspenso em soluções aquosas contendo diferentes concentrações dos hidróxidos de tetrametilamônio (TMA+), tetraetilamônio (TEA+) e tetrapropilamônio (TPA+). Após o tempo de reação foram separadas duas frações: o sólido depositado no recipiente e o sobrenadante turvo contendo as partículas não depositadas de características coloidais. Os resultados de difratometria de raios X, análise termogravimétrica, análise elementar, espectroscopia vibracional no infravermelho e Raman mostram que o processo de intercalação é promovido segundo a ordem: TMA+ > TEA+ > TPA+, isto é, a intercalação é facilitada para íons pouco volumosos. Já o processo de esfoliação do hexaniobato é promovido na ordem inversa: TPA+ » TEA+ > TMA+, ou seja, quanto mais volumoso o íon tetraalquilamônio, maior a extensão do processo de separação das lamelas. A formação das partículas cilíndricas, presentes em maior quantidade nas amostras tratadas com soluções de TPA+ e TBA+...

Lectin and immunohistochemical comparison of glycoconjugates in the conjunctiva of patients with and without exfoliation syndrome.

Hietanen, J; Uusitalo, M; Tarkkanen, A; Kivelä, T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1995 EN
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AIMS--The study was carried out to search for labelling similar to that of intraocular exfoliation material in the conjunctiva by light microscopy using lectin and immunohistochemistry. METHODS--Ten formalin fixed and paraffin embedded conjunctival biopsy specimens both from patients with and without exfoliation syndrome were studied with a panel of 11 lectins and with three monoclonal antibodies to the HNK-1 carbohydrate epitope, all of which react with intraocular exfoliation material. RESULTS--The lectin binding profile was essentially the same in specimens from patients with and without exfoliation syndrome. The superficial epithelium reacted similarly with Phaseolus vulgaris (PHA-E), Caragana arborescens (CAA), Helix pomatia (HPA), concanavalin A (ConA), and wheat germ (WGA) agglutinins. Binding was also detected with peanut (PNA) and Bauhinia purpurea (BPA) agglutinins, particularly in patients with exfoliation. The basement membrane generally reacted with Ricinus communis (RCA-I), PHA-E, Vicia villosa (VVA), ConA, and Lens culinaris (LCA) agglutinins. The stroma was weakly labelled with RCA-I, PHA-E, ConA, and LCA. Lectin binding to the vascular endothelium was moderate with RCA-I, PHA-E, CAA, ConA, LCA, and WGA. Inconsistent labelling was also detected with PNA...

Course of exfoliation and simplex glaucoma after primary trabeculectomy

Popovic, V.; Sjostrand, J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1999 EN
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AIM—To study the course of exfoliation and simplex glaucoma with respect to intraocular pressure (IOP) regulation and visual field survival after primary trabeculectomy.
METHODS—Postoperative IOP regulation and complications were analysed prospectively in 95 patients. Mean follow up was 46 months. Visual field survival was studied by high pass resolution perimetry (HRP) in a subsample of 28 patients.
RESULTS—Medical treatment was reinstated in 42% of exfoliation and in 36% of simplex glaucoma. In these patients, mean medicine free survival time, last untreated IOP, and mean IOP at the end of follow up were similar for both glaucoma types. Among patients with controlled postoperative IOP without added medication, mean IOP at the end of follow up was significantly lower in exfoliation glaucoma. Visual field deterioration and the pattern of complications were similar for both glaucoma types.
CONCLUSION—The effect of trabeculectomy on IOP regulation was good in both types of glaucoma, and somewhat better in exfoliation glaucoma. The magnitude of IOP lowering could not separate patients with continued visual field deterioration from those in whom visual fields remained stable. Visual field preservation was similar for both glaucoma types.

 Keywords: trabeculectomy; exfoliation glaucoma; simplex glaucoma; intraocular pressure; visual field survival

Scanning laser ophthalmoscopy of the optic nerve head in exfoliation glaucoma and ocular hypertension with exfoliation syndrome

Harju, M.; Vesti, E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/2001 EN
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AIMS—To study the relation between optic nerve head topography (Heidelberg retina tomograph, HRT) and disc area, visual field index mean defect (MD), and intraocular pressure (IOP), and to see whether change in HRT parameters is associated with change in MD in a prospective follow up.
METHODS—80 consecutive patients (69 patients with exfoliation glaucoma and 11 with ocular hypertension combined with exfoliation syndrome) were examined before IOP reducing intervention and prospectively followed every 6 months for 2 years.
RESULTS—At the entry point, multiple regression analysis showed significant linear association between MD and all HRT parameters, when controlling for disc area. Disc area showed significant association with cup area, cup/disc area ratio, rim area, cup volume, and mean RNFL thickness. Six months after intervention IOP had decreased significantly. Reversible changes in cup area, cup/disc area ratio, rim area, cup volume, rim volume, mean cup depth, and maximum cup depth were associated with decrease in IOP. During the follow up period from 6 month to 2 years, IOP did not change significantly, and MD was used as a measure of progression of glaucoma. During this period, only cup shape measure among HRT parameters showed significant association with subsequent change in MD.
CONCLUSION—Disc area should be taken into account when using HRT to compare patients. Any effect of change in IOP should be also taken into account when using HRT in follow up. Cup shape measure is a promising indicator of progression of glaucomatous damage.



Exfoliation syndrome angle characteristics: a lack of correlation with amount of disc damage

Cobb, C J; Blanco, G C; Spaeth, G L
Fonte: Copyright 2004 British Journal of Ophthalmology Publicador: Copyright 2004 British Journal of Ophthalmology
Tipo: Artigo de Revista Científica
Publicado em /08/2004 EN
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Background/aims: The exact pathogenesis of glaucoma in exfoliation syndrome is unclear. There has been some suggestion that narrow angles are more common in exfoliation syndrome and that this may be a component in the disease. The degree of pigmentation has also been shown to influence the intraocular pressure. The aim was to determine whether gonioscopic features of the anterior chamber angle in patients with exfoliation syndrome correlate with severity of the glaucoma.

Directed Therapy for Exfoliation Syndrome

Angelilli, Allison; Ritch, Robert
Fonte: Bentham Open Publicador: Bentham Open
Tipo: Artigo de Revista Científica
Publicado em 17/09/2009 EN
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Exfoliation syndrome (XFS) is an age-related disorder of the extracellular matrix that leads the production of abnormal fibrillar material that leads to elevated intraocular pressure and a relatively severe glaucoma. Exfoliation material is deposited in numerous ocular tissues and extraocular organs. XFS is associated with ocular ischemia, cerebrovascular disease, neurodegenerative disease and cardiovascular disease. Current modalities of treatment include intraocular pressure lowering with topical antihypertensives, laser trabeculoplasty and filtration surgery. The disease paradigm for XFS should be expanded to include directed therapy designed specifically to target the underlying disease process. Potential targets include preventing the formation or promoting the depolymerization of exfoliation material. Novel therapies targeting trabecular meshwork may prove particularly useful in the care of exfoliative glaucoma. The systemic and ocular associations of XFS underscore the need for a comprehensive search for neuroprotective agents in its treatment.

Floating anterior lens capsule: an unusual case of true exfoliation

Riffle, John
Fonte: Massachusetts Eye and Ear Infirmary Publicador: Massachusetts Eye and Ear Infirmary
Tipo: Artigo de Revista Científica
Publicado em 29/11/2010 EN
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A rare case of delamination and replication of the anterior lens capsule into prominent floating folds in the anterior chamber approximately 55 years after a penetrating injury to the eye and anterior lens capsule is reported. Classically, true exfoliation of the anterior lens capsule has been reported in individuals who have been exposed to intense heat over a prolonged period. However, more recently cases of true exfoliation of the anterior lens capsule have been reported in patients who have not been occupationally exposed to high temperatures and associated infrared radiation. A brief review of the literature concerning true exfoliation of the lens capsule in the absence of intense heat exposure is included. Associations with trauma, inflammation, advanced age, hyperopia, glaucoma, and capsular protein abnormality have been reported, but the pathogenesis of this rare clinical finding remains conjectural.

Review: The role of LOXL1 in exfoliation syndrome/glaucoma

Whigham, Benjamin T.; Allingham, R. Rand
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN
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Exfoliation syndrome is a common cause of open-angle glaucoma. It is characterized by microscopic flakes of protein-rich material being deposited in both ocular and non-ocular tissues. While its mechanism is poorly understood, family- and population-based studies have established that the disorder has a strong genetic component. A further understanding of the relevant gene variants might help reveal the molecular mechanism behind exfoliation. The most-strongly associated genetic variants are found in the lysyl oxidase-like 1 (LOXL1) gene. However, two major risk alleles in the LOXL1 coding region are reversed between ethnic groups. It now appears the strong association between LOXL1 and XFS is due to non-coding variants that have not yet been identified. Such variants might alter LOXL1 expression, which is decreased in the late stages of exfoliation syndrome/glaucoma. Here we discuss LOXL1 as a risk gene for exfoliation syndrome and glaucoma.

Exfoliation and Performance Properties of Non-Oxidized Graphene in Water

Chen, I-Wen Peter; Huang, Chun-Yuan; Jhou, Sheng-Hong Saint; Zhang, Yu-Wei
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 29/01/2014 EN
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Single-layered graphene has unique electronic, chemical, and electromechanical properties. Recently, graphite exfoliation in N-methylpyrrolidone and molten salt has been demonstrated to generate monolayer exfoliated graphene sheets (EGS). However, these solvents are either high-priced or require special care and have high boiling points and viscosities, making it difficult to deposit the dispersed graphene onto substrates. Here we show a universal principle for the exfoliation of graphite in water to single-layered and several-layered graphene sheets via the direct exfoliation of highly oriented pyrolytic graphite (HOPG) using pyridinium tribromide (Py+Br3−). Electrical conductivity >5100 S/cm was observed for filtered graphene paper, and the EGS exhibited superior performance as a hole transport layer compared to the conventional material N,N-di(naphthalene-1-yl)-N,N-diphenylbenzidine at low voltage. The overall results demonstrate that this method is a scalable process for the preparation of highly conductive graphene for use in the commercial manufacture of high-performance electronic devices.

Role of Peroxide Ions in Formation of Graphene Nanosheets by Electrochemical Exfoliation of Graphite

Rao, Kodepelly Sanjeeva; Senthilnathan, Jaganathan; Liu, Yung-Fang; Yoshimura, Masahiro
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 28/02/2014 EN
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This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO−) leads to the formation of highly nucleophilic peroxide ions (O22−), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.

Ultrasound exfoliation of inorganic analogues of graphene

Štengl, Václav; Henych, Jiří; Slušná, Michaela; Ecorchard, Petra
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 05/04/2014 EN
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High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.

The Frequency of Exfoliation Syndrome in the Central Anatolia Region of Turkey

Kılıç, Raşit; Sezer, Hafize; Çomçalı, Sebile Ü.; Bayraktar, Serdar; Göktolga, Gökay; Çakmak, Yasin; Çetin, Abdi B.; Cumurcu, Tongabay
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
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Aim. The aim of this study was to investigate the frequency of exfoliation syndrome in the Central Anatolia region of Turkey and to evaluate its relationship with cardiovascular and ocular diseases. Methods. Patients over the age of 45 years who presented to the clinic were included in the study. All cases underwent a comprehensive ophthalmology examination. Exfoliation syndrome was diagnosed with the presence of exfoliative material on the lens anterior capsule or iris on slit lamp examination. The patients were divided into two groups as the exfoliation syndrome group and nonexfoliation syndrome group according to the presence of exfoliative material. Results. Exfoliative material was found in one or both eyes of 212 of the 2103 patients (10.1%) evaluated within the scope of the study. A significant relationship was found between exfoliation syndrome and increasing age and male gender. A significant relationship was found between exfoliation syndrome and glaucoma, cataracts, age-related macular degeneration, and phacodonesis. While no relationship was found between exfoliation syndrome and hypertension or diabetes mellitus, a significant relationship was found with coronary artery disease. Conclusion. The unilateral or bilateral exfoliation syndrome frequency was 10.1% in this hospital-based study. A statistically significant relationship was found between exfoliation syndrome and advancing age...

A rational design of cosolvent exfoliation of layered materials by directly probing liquid–solid interaction

Halim, Udayabagya; Zheng, Chu Ran; Chen, Yu; Lin, Zhaoyang; Jiang, Shan; Cheng, Rui; Huang, Yu; Duan, Xiangfeng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Exfoliation of layered materials such as graphite and transition metal dichalcogenides into mono- or few-layers is of significant interest for both the fundamental studies and potential applications. Here we report a systematic investigation of the fundamental factors governing the liquid exfoliation process and the rational design of a cosolvent approach for the exfoliation of layered materials. We show that Young’s equation can be used to predict the optimal cosolvent concentration for the effective exfoliation of graphite and molybdenum disulphide in water mixtures with methanol, ethanol, isopropanol and t-butyl alcohol. Moreover, we find that the cosolvent molecular size has an important role in the exfoliation yield, attributed to the larger steric repulsion provided by the larger cosolvent molecules. Our study provides critical insight into the exfoliation of layered materials, and defines a rational strategy for the design of an environmentally friendly pathway to the high yield exfoliation of layered materials.

Prevalence of exfoliation syndrome in central Sri Lanka: the Kandy Eye Study

Rudkin, A.; Edussuriya, K.; Sennanayake, S.; Senaratne, T.; Selva-Nayagam, D.; Sullivan, T.; Casson, R.
Fonte: British Med Journal Publ Group Publicador: British Med Journal Publ Group
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
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Aims: To report the prevalence and correlates of exfoliation syndrome (XFS) in central, rural Sri Lanka. Methods: A population-based, cross-sectional ophthalmic survey of inhabitants 40 years of age and over from villages in the Kandy District was conducted. Selection was randomised using a cluster sampling process. 1721 eligible participants were identified, 1375 participated. A detailed ophthalmic history and examination including ocular biometry was made of each participant. Results: The prevalence of XFS was estimated to be 1.1% (95% CI 0.5 to 1.5%; 22 eyes). XFS was bilateral in eight subjects, unilateral in six subjects. Univariate analysis demonstrated a significant association between XFS and increasing age (p<0.001), increasing intraocular pressure (odds ratio 1.2; 95% CI 1.09 to 1.27; p<0.001), nuclear cataracts (odds ratio 1.92; 95% CI 1.47 to 2.51; p<0.001), visual impairment (odds ratio 9.72; 95% CI 3.01 to 31.44; p<0.001) and a history of hypertension (odds ratio 3.89; 95% CI 1.14 to 13.16; p = 0.030). Conclusion: XFS in this Sri Lankan population was associated with advanced age, raised intraocular pressure, nuclear cataracts, hypertension and visual impairment.; A. K. Rudkin, K. Edussuriya, S. Sennanayake...

Enzyme-directed pH-responsive exfoliation and dispersion of graphene and its decoration by gold nanoparticles for use as a hybrid catalyst

Qu, K.; Wu, L.; Ren, J.; Qu, X.
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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A non-destructive, safe and practical strategy to produce high quality graphene in high yield is urgently required, since this would pave the way for a wide range of applications of graphene in the future. Here we present a pH-responsive water-dispersible method for the exfoliation and functionalization of graphene by using lysozyme. The pH-responsive dispersion of graphene may be useful for the reversible assembly of multicomponent/multifunctional nanohybrid materials and nanoscale electronic devices. More importantly, composites can be easily constructed through the interactions between disulphide groups in lysozyme and gold nanoparticles (AuNPs). The resulting graphene-AuNPs composites show excellent catalytic activity towards reduction of o-nitroaniline by NaBH4. Since lysozyme is low cost and has antibacterial properties, and has been widely used in food preservation, medicine and the pharmaceutical industry, our approach may open a new scalable route for the manufacture of high-quality, nondestructive graphene for practical applications.; Konggang Qu, Li Wu, Jinsong Ren, Xiaogang Qu

Directed Therapy: An Approach to the Improved Treatment of Exfoliation syndrome

Angelilli, Allison; Ritch, Robert
Fonte: Medknow Publications Publicador: Medknow Publications
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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Exfoliation syndrome (XFS) is an age-related, generalized disorder of the extracellular matrix characterized by the production and progressive accumulation of a fibrillar extracellular material in many ocular tissues and is the most common identifiable cause of open-angle glaucoma worldwide. Exfoliation syndrome plays an etiologic role in open-angle glaucoma, angle-closure glaucoma, cataract, and retinal vein occlusion. It is accompanied by an increase in serious complications at the time of cataract extraction, such as zonular dialysis, capsular rupture, and vitreous loss. It is associated systemically with an increasing number of vascular disorders, hearing loss, and Alzheimer's disease. Exfoliation syndrome appears to be a disease of elastic tissue microfibrils. Directed therapy simply means devising specific treatments for specific diseases. There was little incentive to attempt to distinguish between various open-angle glaucomas if the treatments were essentially the same. However, this view also prevented the application of directed therapy in those instances in which such was available and applicable. Pilocarpine has multiple beneficial actions in eyes with XFS. Not only does it lower IOP, but by increasing aqueous outflow, it should enable the trabecular meshwork to clear more rapidly...

Anterior chamber angle in the exfoliation syndrome.

Wishart, P K; Spaeth, G L; Poryzees, E M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1985 EN
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The gonioscopic findings of 76 patients with the exfoliation syndrome were reviewed. A high frequency of narrowness of the anterior chamber (AC) angle was found (32%). 18% had angles considered occludable, and 14% had obvious angle-closure glaucoma as shown by the presence of peripheral anterior synechias (PAS). Increased pigmentation of the posterior trabecular meshwork (PTM) was noted in all cases. When this pigmentation was markedly asymmetrical, unilateral exfoliation with glaucoma was common in the more pigmented eye. In addition heavy angle pigmentation in the absence of exfoliation was noted in the fellow eye of patients with characteristic exfoliated material in the other eye. Increased pigmentation of the PTM may be the earliest detectable sign of the exfoliation syndrome (ES). The clinical significance of our estimating PTM pigmentation at the 12 o'clock position is discussed. In view of the accelerated optic nerve damage associated with the development of glaucoma secondary to ES, routine estimation of the pigmentation of the PTM at 12 o'clock is recommended in the hope of early detection of cases of otherwise inapparent ES.

Manganese oxide nanosheets and a 2D hybrid of graphene-manganese oxide nanosheets synthesized by liquid-phase exfoliation

Coelho, Joao; Mendoza-Sanchez, Beatriz; Pettersson, Henrik; Pokle, Anuj; McGuire, Eva K.; Long, Edmund; McKeon, Lorcan; Bell, Alan P.; Nicolosi, Valeria
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/09/2014
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Manganese oxide nanosheets were synthesized using liquid phase exfoliation that achieved suspensions in isopropanol with concentrations of up to 0.45 mg/ml. A study of solubility parameters showed that the exfoliation was optimum in DMF followed by isopropanol and diethylene glycol. Isopropanol was the solvent of choice due to its environmentally friendly nature and ease of use for further processing. The 2D hybrid was synthesized in isopropanol suspensions with concentrations of up to 0.5 mg/ml and demonstrated stability against reaggregation for up to six months. The coexfoliation was found to be an 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.

Role of hydrogen in hydrogen-induced layer exfoliation of germanium

Zahler, J. M.; Fontcuberta i Morral, A.; Griggs, M. J.; Atwater, Harry A.; Chabal, Y. J.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 15/01/2007
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The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems.