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1.
Inorg Chem ; 63(18): 8180-8193, 2024 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-38652050

RESUMO

Laves phases exhibit a plethora of different structures and a multitude of physical properties. Investigations in the ternary system Hf-V-Al led to the discovery of numerous members of the solid solution Hf(V1-xAlx)2, which adopt the hexagonal MgZn2 type (C14) for medium to high amounts of Al (x = 0.2-1) and the cubic MgCu2 type (C15) for small Al amounts (x = 0.05-0.1). While all members exhibit Pauli-paramagnetic behavior due to the absence of localized magnetic moments, the V-rich cubic member Hf(V0.95Al0.05)2 additionally exhibits a superconducting state below TC = 7.6(1) K. All synthesized compounds were characterized by powder X-ray diffraction, and selected samples were furthermore investigated by 27Al solid-state magic-angle spinning (MAS) NMR. HfAl2 exhibits two Al resonances, one rather sharp and one significantly broadened signal, in line with the crystal structure and respective coordination environments. The members of the solid solution exhibit extremely broadened resonances due to the mixing of V and Al on the same crystallographic sites. For nominal Hf(V0.125Al0.875)2, however, two distinct sharp NMR signals were observed. This contrasts with the description of a solid solution. Therefore, single-crystal X-ray studies were conducted, showing that Hf(V0.125Al0.875)2 really is an ordered compound with the sum formula Hf4VAl7 (P3̅m1), which exhibits an, thus far, unknown superstructure of MgZn2.

2.
Inorg Chem ; 63(18): 8099-8108, 2024 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-38656922

RESUMO

Vanadium oxides exhibit promising characteristics for electrochemical energy storage, owing to their capability to switch between different oxidation states, in combination with the incorporation of alkali metals. Here, we report on a systematic investigation of the mechanochemical reduction of V2O5 with NaH. In contrast to conventional high-temperature synthesis methods, the mechanochemical reaction occurs already after a few minutes. We observed a mixture of different (sodium) vanadium oxides with vanadium oxidation states ranging from +III to +V. Remarkably, these highly exothermic self-propagating reactions occur even within a rudimentary pistil-mortar setup. Hereby, the hydride concentration has a greater effect on the final sample composition than the milling time. In general, higher percentages of sodium vanadates are formed instead of vanadium oxides, and the lower oxidation states of vanadium are accessible with increasing amounts of NaH. Theoretical calculations confirm these experimental observations and emphasize the central role of sodium vanadates, especially with vanadium in the +V oxidation state, in carrying out the observed exothermic reactions. This comprehensive study sheds light on the mechanochemical reduction of vanadium oxides and underlines their potential for further development of electrochemical energy storage systems.

3.
Nanoscale ; 16(15): 7396-7408, 2024 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-38445431

RESUMO

Titania nanoparticles with a diameter of 8 nm underwent an anisotropic modification using apolar 6-bromohexylphosphonic acid and cationic polar N,N,N-trimethyl-6-phosphonohexan-1-aminium bromide. The Janus modification was achieved through a straightforward one-step Pickering emulsion approach using toluene-water mixtures. The resulting Janus particles were compared with isotropically and statistically modified titania particles, where either a single coupling agent is attached to the surface or both coupling agents are assembled over the surface randomly, respectively. The covalent binding of the phosphonic acids to the titania surface was confirmed by FTIR and 31P solid-state CP-MAS NMR analyses. The grafting density was assessed using TGA, elemental analysis, and ICP-MS, revealing grafting densities of 0.1 mmol g-1 to 0.5 mmol g-1 for the cationic coupling agent and 1.2 mmol g-1 to 1.5 mmol g-1 for the apolar coupling agent, respectively. ζ-Potential titration measurements of both pristine and modified particles revealed isoelectric points at pH 4.5 to 9.3, depending on the type of modification. The ability of the particles to stabilize Pickering emulsions was tested under various conditions, with statistically and Janus-modified particles demonstrating a significant increase in stabilization compared to their isotropically modified counterparts. Furthermore, Janus particles were deposited onto glass substrates by a simple layer-by-layer approach. Through the self-assembly of these Janus particles, the glass substrate's properties could be tailored from hydrophilic to hydrophobic to hydrophilic, depending on the dipping cycle.

4.
Chemistry ; 30(16): e202303343, 2024 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-38146778

RESUMO

Oligo- and polysiloxanes are usually prepared by condensation reactions in solvents without control of stereochemistry. Here we present a solventless thermal condensation of stable organosilanols. We investigated the condensation reactions of organosilanediols with different organic substituents, having in common at least one aromatic group. The condensation kinetics of the precursors observed by NMR spectroscopy revealed a strong dependence on temperature, time, and substitution pattern at the silicon atom. SEC measurements showed that chain length increases with increasing condensation temperature and time and lower steric demand of the substituents, which also influences the glass transition temperatures (Tg) of the resulting oligo- or polymers. X-ray diffraction studies of the crystalline silanediols and their condensation products revealed a structural correlation between the substituent location in the crystalline precursors and the formed macromolecules induced by the hydrogen bonding pattern. In certain cases, it is possible to carry out topotactic polymerization in the solid-state, which has its origin in the crystal structure.

5.
Nanomaterials (Basel) ; 13(23)2023 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-38063679

RESUMO

Self-healing nanocomposites can be generated by organic functionalization of inorganic nanoparticles and complementary functionalization of the polymer matrix, allowing reversible interactions between the two components. Here, we report on self-healing nanocomposites based on ionic interactions between anionic copolymers consisting of di(ethylene glycol) methyl ether methacrylate, sodium 4-(methacryloyloxy)butan-1-sulfonate, and cationically functionalized iron oxide nanoparticles. The materials exhibited hygroscopic behavior. At water contents < 6%, the shear modulus was reduced by up to 90%. The nanoparticle concentration was identified as a second factor strongly influencing the mechanical properties of the materials. Backscattered scanning electron microscopy and small-angle X-ray scattering measurements showed the formation of agglomerates in the size range of 100 nm to a few µm in diameter, independent of concentration, resulting in the disordering of the semi-crystalline ionic polymer blocks. These effects resulted in an increase in the shear modulus of the composite from 3.7 MPa to 5.6 MPa, 6.3 Mpa, and 7.5 MPa for 2, 10, and 20 wt% particles, respectively. Temperature-induced self-healing was possible for all composites investigated. However, only 36% of the maximum stress could be recovered in systems with a low nanoparticle content, whereas the original properties were largely restored (>85%) at higher particle contents.

6.
Dalton Trans ; 52(11): 3391-3402, 2023 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-36811669

RESUMO

The cubic Laves-phase aluminides REAl2 with RE = Sc, Y, La, Yb and Lu were prepared from the elements by arc-melting or using refractory metal ampoules and induction heating. They all crystallize in the cubic crystal system with space group Fd3̄m and adopt the MgCu2 type structure. The title compounds were characterized by powder X-ray diffraction and spectroscopically investigated using Raman and 27Al and in the case of ScAl2 by 45Sc solid-state MAS NMR. In both, the Raman and NMR spectra, the aluminides exhibit only one signal due to the crystal structure. DFT calculations were used to calculate Bader charges illustrating the charge transfer in these compounds along with NMR parameters and densities of states. Finally, the bonding situation was assessed by means of ELF calculations rendering these compounds aluminides with positively charged REδ+ cations embedded in an [Al2]δ- polyanion.

7.
Chemistry ; 29(29): e202300223, 2023 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-36762875

RESUMO

Partially or fully reduced transition metal oxides show extraordinary electronic and catalytic properties but are usually prepared by high temperature reduction reactions. This study reports the systematic investigation of the fast mechanochemical reduction of rutile-type TiO2 and H-Nb2 O5 to their partially reduced black counterparts applying NaH and LiH as reducing agents. Milling time and oxide to reducing agent ratio show a large influence on the final amount of reduced metal ions in the materials. For both oxides LiH shows a higher reducing potential than NaH. An intercalation of Li+ into the structure of the oxides was proven by PXRD and subsequent Rietveld refinements as well as 6 Li solid-state NMR spectroscopy. The products showed a decreased band gap and the presence of unpaired electrons as observed by EPR spectroscopy, proving the successful reduction of Ti4+ and Nb5+ . Furthermore, the developed material exhibits a significantly enhanced photocatalytic performance towards the degradation of methylene blue compared to the pristine oxides. The presented method is a general, time efficient and simple method to obtain reduced transition metal oxides.

8.
ChemSusChem ; 16(7): e202202213, 2023 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-36542465

RESUMO

Inorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C6 H10 N2 ]2 [Mo8 O26 ] ⋅ 6 H2 O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C6 H9 N2 ]4 [NH4 ]2 [Mo7 O24 ] ⋅ 3 H2 O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g-1 at 100 mA g-1 after 150 cycles. The maximum capacity was reached after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li2 MoO4 and an additional in situ polymerization of PPD. The final hybrid material is a promising material for lithium-ion battery (LIB) applications.

9.
Chemistry ; 27(66): 16461-16476, 2021 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-34545975

RESUMO

Organosilanols typically show a high condensation tendency and only exist as stable isolable molecules under very specific steric and electronic conditions at the silicon atom. In the present work, various novel representatives of this class of compounds were synthesized by hydrolysis of alkoxy- or chlorosilanes. Phenyl, 1-naphthyl, and 9-phenanthrenyl substituents at the silicon atom were applied to systematically study the influence of the aromatic substituents on the structure and reactivity of the compounds. Chemical shifts in 29 Si NMR spectroscopy in solution, correlated well with the expected electronic situation induced by the substitution pattern on the Si atom. 1 H NMR studies allowed the detection of strong intermolecular hydrogen bonds. Single-crystal X-ray structures of the alkoxides and the chlorosilanes are dominated by π-π interactions of the aromatic systems, which are substituted by strong hydrogen bonding interactions representing various structural motifs in the respective silanol structures.

10.
Molecules ; 26(4)2021 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-33562273

RESUMO

Diels-Alder reactions on the surface of nanoparticles allow a thermoreversible functionalization of the nanosized building blocks. We report the synthesis of well-defined magnetite nanoparticles by thermal decomposition reaction and their functionalization with maleimide groups. Attachment of these dienophiles was realized by the synthesis of organophosphonate coupling agents and a partial ligand exchange of the original carboxylic acid groups. The functionalized iron oxide particles allow a covalent surface attachment of a furfuryl-functionalized rhodamine B dye by a Diels-Alder reaction at 60 °C. The resulting particles showed the typical fluorescence of rhodamine B. The dye can be cleaved off the particle surface by a retro-Diels-Alder reaction. The study showed that organic functions can be thermoreversibly attached onto inorganic nanoparticles.


Assuntos
Corantes Fluorescentes/química , Nanopartículas de Magnetita/química , Maleimidas/química , Reação de Cicloadição , Compostos Inorgânicos/química , Maleimidas/síntese química , Rodaminas/química , Propriedades de Superfície/efeitos dos fármacos
11.
Nanoscale Adv ; 3(19): 5589-5604, 2021 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-36133272

RESUMO

Supramolecular interactions represent versatile, reversible, and intrinsic mechanisms for bond formation after the failure of materials. Ionic interactions excel through high flexibility and binding strength. In this study, ionic interactions between polymer matrices and inorganic nanoparticles were used to induce self-healing properties. Random, anionic polyelectrolyte copolymers consisting of di(ethylene glycol) methyl ether methacrylate and sodium-4-(methacryloyloxy)butan-1-sulfonate were synthesized by atom transfer radical polymerization. Differential scanning calorimetry measurements confirmed the adjustability of the glass transition temperature via the polymer composition. Within the glass transition temperature window of the homopolymers from -23 °C to 126 °C, the range between -18 °C to 50 °C was examined, generating suitable matrices for self-healing. Superparamagnetic iron oxide nanoparticles with a size of 8 nm were synthesized by thermal decomposition of iron(iii) acetylacetonate and used as the inorganic filler. Positive surface charges were introduced by functionalization with N,N,N-trimethyl-6-phosphonhexan-1-aminium bromide. Functionalization was confirmed with FTIR, TGA, and zeta potential measurements. Ionic interactions between filler and polymer promote a uniform particle dispersion within the material. Self-healing experiments were performed at 80 °C and without the addition of further healing agents. Utilizing the magnetic properties induced by the iron oxide nanoparticles, spatially resolved healing within an alternating magnetic field was achieved on a µm scale.

12.
Respir Res ; 21(1): 168, 2020 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-32616045

RESUMO

BACKGROUND: Titanium dioxide nanoparticles (TiO2 NPs) have a wide range of applications in several industrial and biomedical domains. Based on the evidence, the workers exposed to inhaled nanosized TiO2 powder are more susceptible to the risks of developing respiratory diseases. Accordingly, this issue has increasingly attracted the researchers' interest in understanding the consequences of TiO2 NPs exposure. Regarding this, the present study was conducted to analyze the local effects of TiO2 NPs on allergic airway inflammation and their uptake in a mouse model of ovalbumin (OVA)-induced allergic airway inflammation. METHODS: For the purpose of the study, female BALB/c mice with or without asthma were intranasally administered with TiO2 NPs. The mice were subjected to histological assessment, lung function testing, scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), and NP uptake measurement. In addition, T helper (Th) 1/Th2 cytokines were evaluated in the lung homogenate using the enzyme-linked immunosorbent assay. RESULTS: According to the results, the mice receiving OVA alone or OVA plus TiO2 NPs showed eosinophilic infiltrates and mucus overproduction in the lung tissues, compared to the controls. Furthermore, a significant elevation was observed in the circulating Th2 cytokines, including interleukin (IL)-4, IL-5, and IL-13 after NP exposure. The TiO2 NPs were taken up by alveolar macrophages at different time points. As the results of the SEM and ICP-MS indicated, TiO2 NPs were present in most of the organs in both asthmatic and non-asthmatic mice. CONCLUSION: Based on the findings of the current study, intranasally or inhalation exposure to high-dose nanosized TiO2 particles appears to exacerbate the allergic airway inflammation and lead to systemic uptake in extrapulmonary organs. These results indicate the very important need to investigate the upper limit of intranasally or inhalation exposure to nanosized TiO2 particles in occupational and environmental health policy.


Assuntos
Asma/induzido quimicamente , Asma/patologia , Nanopartículas/toxicidade , Titânio/toxicidade , Administração Intranasal , Animais , Hiper-Reatividade Brônquica/induzido quimicamente , Hiper-Reatividade Brônquica/fisiopatologia , Líquido da Lavagem Broncoalveolar/citologia , Citocinas/metabolismo , Eosinófilos/imunologia , Feminino , Exposição por Inalação , Camundongos , Camundongos Endogâmicos BALB C , Nanopartículas/administração & dosagem , Ovalbumina/imunologia , Testes de Função Respiratória , Linfócitos T Auxiliares-Indutores/metabolismo , Titânio/administração & dosagem
13.
Dalton Trans ; 49(28): 9820-9834, 2020 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-32633297

RESUMO

Al nanoparticles represent one of the most challenging classes of metal nanoparticles in synthesis and handling due to their high chemical reactivity and their affinity to oxidation. A promising wet chemical preparation route is the catalytic decomposition of alane adducts. In the current systematic study, we investigated the influence of various reaction parameters, such as precursors, catalysts, solvents, reaction temperatures, capping agents, and concentrations of the reactants on the size and morphology of the resulting Al nanoparticles. One major goal was the optimization of the reaction parameters towards short reaction times. Our studies revealed that Ti alkoxides, such as Ti(OiPr)4, are much more efficient decomposition catalysts compared to other related metal catalysts. Optimized conditions for full conversion times smaller than 15 min are temperatures between 90-100 °C and non-polar solvents such as toluene. Amine alanes containing short alkyl chains, for example H3AlNMe2Et or H3AlNEt3, were the most suitable precursors, leading to the formation of the smallest nanoparticles. The use of weakly coordinating capping agents like amines and phosphines should be preferred over the commonly employed carboxylic acids because they do not accelerate the formation of an amorphous oxide shell upon binding to the particle surface. In conclusion, the best reaction parameters for a fast synthesis of Al nanoparticles via a catalytic decomposition approach are the combination of sterically less hindered amine alanes applying a Ti catalyst in toluene solutions in the presence of amine or phosphine stabilizers at elevated temperatures.

14.
Nanotechnology ; 31(26): 265605, 2020 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-32160597

RESUMO

Submicron Al particles can be used in energy materials, as reducing agents, or for the formation of aluminides. Their standard electrode potential and their reactivity towards oxygen makes their synthesis a challenging task. Here we present a thermal decomposition approach starting from triisobutylaluminium (TIBAL) as a precursor. This compound can be decomposed in refluxing diphenylether as a high-boiling solvent and in the presence of metallic nanoparticles of Ni, Ru or Ag acting as seeds. The resulting particles revealed sizes of around 100 nm. Passivation of the Al particles is possible in an optional second step after the synthesis by adding oleic acid resulting in the formation of organically capped Al particles. The suitability of these submicron particles for the synthesis of aluminides was studied by reacting the synthesized particles with Ru powders, resulting in the formation of the respective aluminide.

15.
Inorg Chem ; 58(22): 15021-15024, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31687822

RESUMO

Syntheses of Mn3O4 involve either high sintering temperatures to produce well crystallized products or the use of water-soluble precursors, surfactants, and organic solvents to generate nanocrystalline products. Mechanochemical approaches are known to be effective in the preparation of fine-grained or nanoscaled materials, while also being environmentally friendly because no solvents and no sintering at high temperatures are required. We report the solvent free mechanochemical synthesis of Mn3O4 nanocrystals at room temperature, from a mixture of MnO and Mn2O3. The single-phase product was characterized by Rietveld refinement and SEM images. The obtained crystallite size was 14.2(2) nm, which is among the smallest ever produced crystallite sizes of Mn3O4. The obtained product reveals an enormous increase in lithium intercalation capability, which was proven via chemical lithium intercalation at room temperature. More than 50% lithiation of nanocrystalline Mn3O4 is observed after a reaction time of 1 h, while coarse-grained material from a solid-state reaction shows no intercalation under the same reaction conditions. Therefore, the produced manganese oxide has a high potential in lithium battery applications.

16.
Langmuir ; 35(35): 11369-11379, 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31393730

RESUMO

Organophosphorus coupling agents bearing permanently charged functional groups (either cationic quaternary ammonium or anionic sulfonates) were synthesized and used for the modification of zirconia nanoparticles with a diameter <10 nm. Surface functionalization was confirmed by FTIR and solid-state NMR spectroscopy. Surface coverages up to 2.3-2.4 molecules/nm2 were achieved for modification with these charged coupling agents. The pH-dependent charge measurements of homogeneously modified particles showed stable surface charges over a wide range of pH for both ammonium- and sulfonate-functionalized particles. Surface charge measurements of particles co-functionalized with charged coupling molecules and uncharged methyl phosphonic acid revealed a decreasing charge density with increasing amount of uncharged coupling agent. Thus, an adjustment of charges by co-functionalization was obtained on the particle surface. The thus-formed surface-charged colloids were used in a second step for electrostatic-driven aggregation phenomena necessary for layer-by-layer processes. Sulfonate-modified negatively charged SiO2 submicrometer particles of 506 nm in diameter were decorated with ammonium-modified ZrO2 nanoparticles. In addition, a layer-by-layer deposition of alternating charge-modified TiO2 nanoparticles was proven by optical spectroscopy. Due to the broad applicability of organophosphorus coupling agents for surface modification, particularly for transition-metal oxides, the shown route represents a general method for the creation of almost pH-independent charges on the surface of nanoparticles.

17.
Acta Crystallogr C Struct Chem ; 75(Pt 6): 678-685, 2019 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-31166919

RESUMO

Liu et al. [Chin. J. Struct. Chem. (1996). 15, 371-373] reported the structure of 6-hydroxy-1,4-diazepane di(hydrogen bromide), C5H12N2O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6-hydroxy-1,4-diazepane-1,4-diium dibromide, C5H14N2O2+·2Br-, measured at 142 K, crystallized in the orthorhombic space group P212121. The structure displays O-H...Br and N-H...Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly-bonded H-Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br- anions and a protonated substrate such as an amine, is addressed.

18.
RSC Adv ; 9(4): 2205-2216, 2019 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-35516134

RESUMO

Polysiloxanes for applications in the area of optical devices are usually based on two-component platinum catalysed cross-linked materials. Here we report the synthesis and properties of a novel one-component siloxane that can be thermally cured showing similar tailorable properties like commercially available encapsulation systems without using a noble metal catalyst. The pre-curing material is formed by an acid catalysed condensation reaction of trialkoxysilanes (TAS), dialkoxysilanes (DAS) and alkoxy-terminated polysiloxanes. NMR analysis of the formed polymeric compounds reveal that the materials are partially cross-linked gels. The obtained compounds can be thermally cured and consolidated at temperatures between 160 and 200 °C. Depending on the composition a tuneable hardness in between 50-90 Shore A, refractive indices of 1.494-1.505, as well as high temperature stabilities up to 443 °C were obtained. The high thermal- and photostability, the high transparency, as well as the tailorable refractive index makes these materials to ideal systems for optoelectronic applications. Investigations under increased temperatures and high-density illumination reveal that the material can withstand conditions, which are typical for high-performance light emitting diodes (LED).

19.
RSC Adv ; 8(32): 18128-18138, 2018 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-35542110

RESUMO

The replacement of inorganic conversion dyes with their organic counterparts in LED application bears a large potential for the reduction of rare earth elements in these devices. A major challenge of this substitution is the emission and stability of organic dyes, which is more sensitive to the composition of the polymer matrix they are embedded in than inorganic systems. In this study we systematically investigated the influence of the composition and structure of a low refractive index (LRI) polydimethylsiloxane (PDMS) and a high refractive index (HRI) polymethylphenysiloxane (PMPS) based encapsulation material on the optical properties of two different embedded perylene diimide dyes. Both dyes show low solubility in the PDMS matrix, which also fosters the heat- or light-induced degradation of the incorporated dyes. Contrary phenyl containing polysiloxane encapsulation materials enhance dye solubility, improve quantum yields, and promote heat and radiation resistance. Bulky N-aryl substituents at the dye structure decrease the probability of dye-dye interaction and increase the absolute quantum yields additionally. Increased photostability and no leaching was observed when the dye was covalently attached to the polymer matrix. Additionally covalent bonding to and improved solubility of the organic dyes in the polysiloxanes allow for a solvent free processing of such dye-matrix combinations. In conclusion a good matching between the matrix and the dye is crucial for a substitution of inorganic conversion dyes by organic ones in LED devices.

20.
RSC Adv ; 8(72): 41639-41650, 2018 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-35559272

RESUMO

Ionic liquids (ILs) are a promising class of solvents, functional fluids and electrolytes that are of high interest for both basic as well as applied research. For further fundamental understanding of ILs and a successful implementation in technical processes, a deeper insight into transport properties and their interrelations is of particular importance. In this contribution we synthesised a series of mostly novel protic and aprotic ILs based on the tetramethylguanidinium (TMG) cation that is a derivative of the superbase guanidine. Different substitution patterns and anions from acids with broadly varied pK a values were investigated. We measured general properties, such as thermal transitions and densities of these ILs, as well as their transport quantities by means of rheology, impedance spectroscopy and NMR diffusometry. Different models for the correlation of the transport properties, namely the Nernst-Einstein, Walden and Stokes-Einstein-Sutherland relations were applied. The deviation from ideal behaviour of fully dissociated electrolytes, often termed as ionicity, was quantified by the reciprocal Haven ratio, fractional Walden rule and ionicity obtained from the Walden plot. Velocity cross-correlation coefficients were calculated to gain further insight into the correlation between ion movements. Both protic and aprotic TMG ILs show transport properties comparable to other ILs with similar molecular weight and high ionicity values especially in contrast to other protic ILs. Lowest ionicity values were found for the protic ILs with smallest ΔpK a values between constituting acid and base. This can either be explained by stronger hydrogen bonding between cation and anion or lower anti-correlations between the oppositely charged ions. These results aim to provide insight into the properties of this interesting cations class and a deeper understanding of the transport properties of ILs and their interrelations in general.

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