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1.
J Colloid Interface Sci ; 541: 213-225, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-30690265

RESUMO

Disperse polymethylsiloxane (PMS) alone and in a mixture with highly disperse nanosilica A-300 was studied as a dry powder and a hydrogel located in various dispersion media (air, chloroform alone and with addition of trifluoroacetic acid) using low-temperature 1H NMR spectroscopy, cryoporometry, thermogravimetry, nitrogen adsorption, microscopy, infrared spectroscopy, and quantum chemistry. The powders of dried PMS and PMS/A-300 can be easily rehydrated upon strong stirring with added water. The slurry properties depend on mechanical treatment features due to stronger compaction of the secondary structures with increasing mechanical loading. The organization of bound water (at a constant hydration degree h = 1 g/g) depends strongly on the dispersion media (because chloroform can displace water from narrow interparticle voids into broader ones or into pores inaccessible for larger CDCl3 molecules) and mechanical loading reorganizing aggregates of PMS and A-300 nanoparticles (<1 µm in size) and agglomerates (>1 µm) of aggregates. The PMS/nanosilica blends could be of interest from a practical point of view due to additional control of the textural and structural characteristics determining efficiency of sorbents with respect to low- and high-molecular weight compounds depending on the dispersion media that is of importance, e.g., for medical applications.

2.
J Colloid Interface Sci ; 529: 273-282, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-29908403

RESUMO

Three polydimethylsiloxanes (PDMS200, PDMS1000, and PDMS12500 with numbers showing the viscosity values dependent on the molecular weight) were used for adsorption (14-95 wt% PDMS) onto unmodified and PDMS-modified (16.7 wt% PDMS using dimethyl carbonate (DMC) as a siloxane bond breaking reagent) nanosilica A-300. The materials were studied using microscopy, infrared spectroscopy, thermodesorption, calorimetry, ethanol and water/ethanol evaporation, nitrogen adsorption-desorption, and quantum chemical methods. The interfacial and temperature behaviors of a PDMS layer at a silica surface depend strongly on the type of bonding to silica particles, molecular weight and content of PDMS. Upon chemical bonding, shorter PDMS200 forms a denser coverage of the silica surface since SBET diminution is larger and residual free silanols are practically absent (the degree of free silanol substitution Θ > 0.95) in contrast to the reactions with PDMS1000/DMC or PDMS12500/DMC providing Θ = 0.60-0.63 at larger SBET values. Upon thermal decomposition of the PDMS layer, oxidation/depolymerization desorption gives a greater contribution than pure depolymerization destruction. An increase in the PDMS adsorption layer thickness leads to enhancement of the depolymerization contribution because the oxidation mainly occurs at the top of the layer, but the depolymerization can occur in the total PDMS layer. The adsorption, desorption, and evaporation processes of low-molecular weight probes at a surface of PDMS-modified nanosilica depend strongly on the type of bonding and content of PDMS. Thus, the most effective hydrophobization of nanosilica by PDMS/DMC could be carried out using the shortest polymer giving the shortest PDMS fragments upon the interaction with DMC that is of interest from a practical point of view.

3.
J Colloid Interface Sci ; 513: 809-819, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29222980

RESUMO

Interaction of doxorubicin hydrochloride (DOX) (anti-cancer drug) with hydro-compacted nanosilica A-300 (cA-300) alone or cA-300/human serum albumin (HSA) at a small content of water (h = 0.4 g per gram of dry silica) in different dispersion media (air, chloroform, and chloroform/trifluoroacetic acid) was analyzed using low-temperature 1H NMR spectroscopy, NMR cryoporometry and quantum chemistry to elucidate specific changes in the interfacial layers. Initial (bulk density ρb ≈ 0.046 g/cm3) and hydro-compacted (ρb ≈ 0.051-0.265 g/cm3 as a function of the hydration degree) nanosilicas were analyzed using nitrogen adsorption-desorption, gelatin adsorption, small angle X-ray scattering (SAXS), TEM, and infrared (FTIR) spectroscopy. Equilibrium adsorption of DOX onto cA-300 and cA-300/HSA was analyzed using ultraviolet-visible light spectroscopy. Photon correlation spectroscopy was used to analyze the particle size distribution in aqueous suspensions with various contents of components. DOX more strongly bound to HSA than silica also affects structure of interfacial water layers that depends on dispersion media because chloroform as immiscible with water changes the water organization to enlarge water structures. In aqueous media, DOX alone remains mainly in the form of nano/microparticles (50 nm-2 µm in size). However, with the presence of cA-300, cA-300/HSA, and HSA alone DOX transforms into pure nano-sized structures. These effects are explained by effective bonding of DOX to HSA having good transport properties with respect to drug molecules/ions that exceed similar properties of nanosilica alone, but cA-300/HSA can be a more effective composite as a drug carrier.


Assuntos
Antibióticos Antineoplásicos/metabolismo , Doxorrubicina/metabolismo , Portadores de Fármacos/química , Nanopartículas/química , Albumina Sérica Humana/metabolismo , Dióxido de Silício/metabolismo , Antibióticos Antineoplásicos/química , Doxorrubicina/química , Humanos , Albumina Sérica Humana/química , Dióxido de Silício/química , Suspensões
4.
Adv Colloid Interface Sci ; 235: 108-189, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27344189

RESUMO

Investigations of interfacial and temperature behaviors of nonpolar and polar adsorbates interacting with individual and complex fumed metal or metalloid oxides (FMO), initial and subjected to various treatments or chemical functionalization and compared to such porous adsorbents as silica gels, precipitated silica, mesoporous ordered silicas, filled polymeric composites, were analyzed. Complex nanooxides include core-shell nanoparticles, CSNP (50-200nm in size) with titania or alumina cores and silica or alumina shells in contrast to simple and smaller nanoparticles of individual FMO. CSNP could be destroyed under high-pressure cryogelation (HPCG) or mechanochemical activation (MCA). These treatments affect the structure of aggregates of nanoparticles and agglomerates of aggregates, resulting in their becoming more compacted. The analysis shows that complex FMO could be more sensitive to external actions than simple nanooxides such as fumed silica. Any treatment of 'soft' FMO affects the interfacial and temperature behaviors of polar and nonpolar adsorbates. Rearrangement of secondary particles and surface functionalization affects the freezing-melting point depression of adsorbates. For some adsorbates, open hysteresis loops became readily apparent in adsorption-desorption isotherms. Clustering of adsorbates bound in textural pores in aggregates of nanoparticles (i.e., voids between nanoparticles in secondary structures) causes reduced changes in enthalpy during phase transitions (freezing, fusion, evaporation). Freezing point depression and melting point elevation cause significant hysteresis freezing-melting effects for adsorbates bound to FMO in the textural pores. Relaxation phenomena for both low- and high-molecular weight adsorbates or filled polymeric composites are affected by the morphology of primary particles, structural organization of secondary particles of differently treated or functionalized FMO, content of adsorbates, co-adsorption order, and temperature.

5.
J Colloid Interface Sci ; 434: 28-39, 2014 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-25168580

RESUMO

Unmodified pyrogenic silica PS300 and partially silylated nanosilica samples at a degree of substitution of surface silanols by trimethylsilyl (TMS) groups Θ(TMS)=27.2% and 37.2% were studied to elucidate features of the interfacial behavior of water adsorbed alone, or co-adsorbed with methane, hydrogen, or trifluoroacetic acid (TFAA). In the aqueous suspension modified PS300 at Θ(TMS)=37.2% forms aggregates of 50-200 nm in size and can bind significant amounts of water (up to ∼5 g/g). Only 0.5 g/g of this water is strongly bound, while the major fraction of water is weakly bound. The presence of surface TMS groups causes the appearance of weakly associated water (WAW) at the interfaces. The adsorption of methane and hydrogen onto TMS-nanosilica with pre-adsorbed water (hydration degree h=0.05 or 0.005 g/g) increases with increasing temperature. In weakly polar CDCl3 medium, interfacial water exists in strongly (SAW, chemical shift δ(H)=4-5 ppm) and weakly (δ(H)=1-2 ppm) associated states, as well as strongly (changes in the Gibbs free energy -ΔG>0.5-0.8 kJ/mol) and weakly (-ΔG<0.5-0.8 kJ/mol) bound states. WAW does not dissolve TFAA but some fraction of SAW bound to TMS-nanosilica surface can dissolve TFAA.

6.
J Colloid Interface Sci ; 426: 48-55, 2014 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-24863764

RESUMO

To control the properties of poly(dimethylsiloxane) (PDMS, Oxane 1000) as a bio-inert material, the characteristics of Oxane 1000 were compared for PDMS alone and interacting with silica gel Si-100 and nanosilica PS400. Low-temperature (1)H NMR spectroscopy, applied to static samples at 200-300 K, and differential scanning calorimetry (DSC) at 153-393 K were used to analyze the properties of PDMS and composites. The NMR study shows that liquid and solid-like fractions of PDMS co-exist over a broad temperature range. The cooling-heating cycles give hysteresis loops of intensity of (1)H NMR signals of methyl groups of a liquid fraction of PDMS vs. temperature depending on the silica type. The loop width differs for PDMS alone and bound to silicas, and the samples preheated at 420 K are characterized by much narrower loops. DSC measurements of the samples show a significant difference in the thermograms on the first and second DSC scans that depend on the silica type. For PDMS confined in pores of silica gel, 3D spatial structure of the polymers can be more ordered than that of PDMS located in thin layers at a surface of nanosilica. Therefore, both melting endotherms and crystallization exotherms are observed for PDMS/silica gel. However, for PDMS/nanosilica, both thermal features are much weaker and observed during only the first DSC scan.


Assuntos
Temperatura Baixa , Dimetilpolisiloxanos/química , Temperatura Alta , Nanoestruturas , Dióxido de Silício/química , Varredura Diferencial de Calorimetria
7.
Biofizika ; 59(3): 492-9, 2014.
Artigo em Russo | MEDLINE | ID: mdl-25715591

RESUMO

The state of water in partially destroyed dry yeast cells has been studied using low-temperature 1H NMR spectroscopy. It has been shown that the residual water is in the form of clusters of strongly and weakly associated water (SAW and WAW, respectively). Three or more types of SAW different in the chemical shift values have been found. It has been established that the interfacial water poorly dissolves hydrochloric and trifluoroacetic acids as well as DMSO and CD3CN. Hydrochloric acid on a surface of biomaterials can be separated into HCl and water. This process is stabilized by polar co-solvents (DMSO and CD3CN) added to the CDCl3 dispersion medium.


Assuntos
Dimetil Sulfóxido/química , Ácido Clorídrico/química , Saccharomyces cerevisiae/química , Água/química , Espectroscopia de Ressonância Magnética , Saccharomyces cerevisiae/citologia
8.
J Colloid Interface Sci ; 404: 140-9, 2013 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-23721830

RESUMO

Detailed analysis of the interfacial behavior of water and weakly polar or nonpolar organics adsorbed alone or co-adsorbed onto activated carbons (AC) at different temperatures is a complex problem important for practical applications of adsorbents. Interaction of water, 1-decanol, and n-decane with AC possessing highly developed porosity (pore volume Vp≈1.4-2.3 cm(3)/g, specific surface area S(BET)≈1500-3500 m(2)/g) was studied over a broad temperature range using differential scanning calorimetry (DSC), thermoporometry, (1)H NMR spectroscopy, cryoporometry, and temperature-programmed desorption with mass-spectrometry control methods. Comparison of the pore size distributions (PSD) calculated using the DSC thermoporometry, NMR cryoporometry, and nitrogen adsorption isotherms allows us to determine localization of adsorbates in different pores, as well as changes in the PSD of AC due to freezing of adsorbates in pores. Theoretical calculations (using ab initio HF/6-31G(d,p), DFT B3LYP/6-31G(d,p), and PM7 methods) explain certain aspects of the interfacial behavior of water, decane, and decanol adsorbed onto AC that appear in the experimental data. Obtained results show strong temperature dependence (above and below the freezing point, Tf, of bulk liquids) of the interfacial behavior of adsorbates on the textural characteristics and hydrophilic/hydrophobic properties of AC and the adsorbate amounts that affect the distributions of adsorbates unfrozen at T

9.
J Colloid Interface Sci ; 394: 467-74, 2013 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-23313347

RESUMO

The interfacial behavior of silicone oils Oxane 1000 and Oxane 5700 (polydimethylsiloxanes, PDMS) interacting with dried or hydrated (hydration h=0.005 or 0.1g/g) silica gels Si-60 and Si-100 or nanosilica A-400 was studied using low-temperature (1)H NMR spectroscopy over the 210-310 K range. Broadening of the melting temperature range toward both sides from the freezing point is observed for silicone oils confined in mesopores (2-15 nm in radius) of silica gel particles (0.2-0.5 mm in size) or voids (1-100 nm) between silica nanoparticles (5-10 nm in size) in their aggregates. This effect is a consequence of the phase state heterogeneity, since both liquid and solid-like fractions of adsorbed PDMS are observed over a large temperature range. The adsorbed PDMS heterogeneity depends on the pore size distribution (confined space effect), and it is lower for silica gel Si-100 possessing broader pores than Si-60. An increase in the amounts of adsorbed polymer and water diminishes the effects of confined space on PDMS because a fraction of the polymers is located in broader pores or out of pores (voids). This leads to relative decrease in interactions of PDMS with the silica surface. (1)H NMR spectra of PDMS and n-decane bound to silica gels reveal much stronger heterogenization of adsorbed PDMS (depending on the polymer length) than that of the alkane.


Assuntos
Dimetilpolisiloxanos/química , Sílica Gel/química , Dióxido de Silício/química , Óleos de Silicone/química , Adsorção , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Nanopartículas/química , Porosidade , Propriedades de Superfície , Temperatura de Transição
10.
J Colloid Interface Sci ; 368(1): 263-72, 2012 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-22138264

RESUMO

Low-temperature (1)Н NMR spectroscopy was used to study states of water bound to phosphoric and phosphonic acids (phosporus oxyacids, POA) alone or adsorbed onto nanosilica OX-50 (specific surface area S(BET)=52 m(2)/g) or A-300 (S(BET)=297 m(2)/g). Concentrated solutions or weakly hydrated solid POA or dried silica/POA powders placed in CCl(4) medium are characterized by different temperature dependences of the chemical shift of the proton resonance (δ(H)) because of partial dissociation of PO-H bonds strongly affected by water amounts and temperature. NMR cryoporometry results show that both small water clusters and nanodomains are present at the interfaces of hydrated solid POA and silica/POA powders. Quantum chemical calculations of the (1)H NMR spectra demonstrate the influence of POA/water cluster structure and dissociation of the PO-H bonds on the δ(H) values.

11.
J Colloid Interface Sci ; 355(2): 300-11, 2011 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-21227443

RESUMO

The structural, textural, and adsorption characteristics of mechanochemically activated (MCA) fumed silica A-300 as dry or water, ethanol, or water/ethanol-wetted powders (0.5 g of a solvent per gram of silica) in a ball mill for 1-6 h were studied in comparison with those of the initial powder. The MCA treatment enhances bulk density (ρ(b)) of the powder (from 0.045 g/cm(3) for the initial silica to 0.4 g/cm(3) for 6 h-MCA-treated water-wetted silica) depending on medium type and MCA time (t(MCA)). Stronger effects are observed for the MCA treatment of water-wetted silica than of dry or ethanol- or water/ethanol-wetted samples. The MCA treatment weakly affects the specific surface area (S(BET)). However, void (pore) size distribution, porosity, particle aggregation and size distribution in aqueous suspension, behavior of interfacial water, properties of poly(vinyl alcohol)/silica composites and adsorption of gelatin depend more strongly on the t(MCA) and ρ(b) values. Some of the observed changes in the characteristics (e.g., gelatin adsorption) depend on the ρ(b) value but are independent of the medium type used on the MCA. Other characteristics are nonlinear functions of both t(MCA) and ρ(b) values.


Assuntos
Gelatina/química , Nanoestruturas/química , Dióxido de Silício/química , Adsorção , Gelatina/metabolismo , Tamanho da Partícula , Porosidade , Dióxido de Silício/metabolismo , Solventes/química , Propriedades de Superfície , Suspensões , Água/química , Molhabilidade
12.
J Colloid Interface Sci ; 348(2): 546-58, 2010 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-20621822

RESUMO

Adsorption of low-molecular adsorbates (nonpolar hexane, nitrogen, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water) onto individual (silica, alumina, titania), binary (silica/alumina (SA), silica/titania (ST)), and ternary (alumina/silica/titania, AST) fumed oxides was studied to analyse the effects of morphology and surface composition of the materials. Certain aspects of the interfacial phenomena dependent on the structural characteristics of oxides were analysed using calorimetry, (1)H NMR, and Raman spectroscopies, XRD, and ab initio quantum-chemical calculations. The specific surface area S(BET,X)-to-S(BET,N(2)) ratio (X is an organic adsorbate) changes from 0.68 for hexane adsorbed onto amorphous SA8 (degassed at 200 degrees C) to 1.85 for acetonitrile adsorbed onto crystalline alumina (degassed at 900 degrees C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of molecules adsorbed onto oxide surfaces. Larger S(BET,X)/S(BET,N(2)) values are observed for mixed oxides with higher crystallinity of titania or/and alumina phases in larger primary nanoparticles with greater surface roughness and hydrophilicity. Polar adsorbates can change the structure of aggregates of oxide nanoparticles that can, in turn, affect the results of adsorption measurements.


Assuntos
Óxido de Alumínio/química , Nanopartículas/química , Óxidos/química , Dióxido de Silício/química , Titânio/química , Acetonitrilas/química , Adsorção , Dietilaminas/química , Etilaminas/química , Hexanos/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Nitrogênio/química , Propriedades de Superfície , Água/química
13.
Langmuir ; 26(13): 10968-79, 2010 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-20415443

RESUMO

Interfacial interactions, chain dynamics, and glass and melting transitions were studied in well-defined core-shell nanoparticles with amorphous silica or crystalline alumina cores and noncrystallizable poly(vinyl pyrrolidone) (PVP) or crystallizable poly(ethylene glycol) (PEG) shells. Varying particle composition caused regular changes in the shell thickness from 1 to 2 nm (monomolecular layer) up to 90 nm. Far- and mid-IR spectroscopy allowed us to register hydrogen bonding and, tentatively, Lewis/Brønsted (LB) interfacial interactions as well as changes in the dynamics and conformational state of the polymer chains as a function of the nanoshell thickness. Their most pronounced peculiarities were found for the monomolecular polymer layers. The LB interactions were stronger with the alumina substrate than silica. DSC analysis was performed, and the data obtained were in agreement with the spectroscopic data. Unlike the bulk polymer, the PVP monolayer was characterized with an extraordinarily large dynamic heterogeneity within the glass transition while broadening the transition range and varying the activation energy by an order of magnitude. The PEG monolayer adsorbed on silica was totally amorphous, whereas a highly crystalline one with the anomalously thin lamellae, down to 3 nm thick, was adsorbed on an alumina surface, presumably as a result of the quasi-heteroepitaxial crystallization process.


Assuntos
Nanopartículas/química , Nanoconchas/química , Polímeros/química , Óxido de Alumínio/química , Modelos Teóricos , Nanotecnologia , Polietilenoglicóis/química , Dióxido de Silício/química , Espectrofotometria Infravermelho
14.
J Colloid Interface Sci ; 338(2): 376-88, 2009 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-19596124

RESUMO

Fe2O3/SiO2 nanocomposites based on fumed silica A-300 (S(BET)=337 m2/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)3) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)3 then oxidized in air at 400-900 degrees C. Samples with Fe(acac)3 adsorbed onto nanosilica and samples with Fe2O3/SiO2 including 6-17 wt% of Fe2O3 were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe2O3 deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)3 solution in isopropanol) treated at 500-600 degrees C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)3 solution in carbon tetrachloride only alpha-Fe2O3 phase is formed in addition to amorphous Fe2O3. The Fe2O3/SiO2 materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12-0.15 g/cm3 and S(BET)=265-310 m2/g.


Assuntos
Compostos Férricos/química , Nanocompostos/química , Dióxido de Silício/química , 2-Propanol/química , Adsorção , Tetracloreto de Carbono/química , Oxirredução , Solventes/química , Propriedades de Superfície , Temperatura , Tolueno/química
15.
J Colloid Interface Sci ; 330(1): 125-37, 2009 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-18996539

RESUMO

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.

16.
Ukr Biokhim Zh (1999) ; 80(1): 114-8, 2008.
Artigo em Russo | MEDLINE | ID: mdl-18710036

RESUMO

The effect of the weak electric current (2 mA/cm2) on structural characteristics (hydrodynamic diameter and molecular weight) of the human serum albumin (HSA) was studied using photon correlation spectroscopy (PCS). The average diameter of initial HSA globule is approximately 7 nm (66.8 kDa). After electric current treatment during 2-5 min the diameter of HSA monomer increases to 7.5 nm. The duration of electric current treatment being increased to 20 min the size of HSA monomers decreases to 6.4 nm. The behaviour of HSA oligomers is close to that of monomers. Consequently, changes in the sizes of monomers and oligomers of HSA under the electric current treatment are caused by the change in the charge density stimulating change of tertiary structure of molecules and possible addition of ions from the buffer solution to them.


Assuntos
Eletricidade , Albumina Sérica/química , Terapia por Estimulação Elétrica , Humanos , Técnicas In Vitro , Lasers , Conformação Proteica , Análise Espectral
17.
J Colloid Interface Sci ; 323(1): 6-17, 2008 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-18440015

RESUMO

The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1H NMR spectroscopy with layer-by-layer freezing-out of liquids (190-273 K), and thermally stimulated depolarization current method (90-265 K). This adsorbent is characterized by large specific surface area (approximately 1500 m2/g) and pore volume (0.83 cm3/g) with a major contribution of narrow pores (R<10 nm) of a complicated shape (long hysteresis loop is in nitrogen adsorption-desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1H NMR data.

18.
J Colloid Interface Sci ; 314(1): 119-30, 2007 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-17570390

RESUMO

A variety of fumed oxides such as silica, alumina, titania, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST) were characterized. These oxides have different specific surface areas and different primary particle composition in the bulk and at the surface. These materials were studied by FTIR, NMR, Auger electron spectroscopy, one-pass temperature-programmed desorption with mass spectrometry control (OP TPDMS), microcalorimetry, and nitrogen adsorption. Nonlinear changes in the surface content of alumina in SA and AST and titania in ST and AST samples with increasing oxide content along with simultaneous changes in their specific surface area cause complex dependencies of the heat of immersion in water and desorption of water on heating on the structural parameters. Simultaneous analysis of changes in the surface phase composition, in the concentration of hydroxyls, and in the structural characteristics reveals that at a low content of the second phase the structural characteristics (e.g., S(BET)) are predominant; however, at a large content of these oxides the phase composition plays a more important role.


Assuntos
Óxido de Alumínio/química , Óxidos/química , Dióxido de Silício/química , Titânio/química , Espectroscopia de Ressonância Magnética , Teste de Materiais , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de Superfície , Termodinâmica
19.
J Colloid Interface Sci ; 312(2): 201-13, 2007 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-17482636

RESUMO

Interaction of poly(vinyl alcohol) (PVA) with fumed silica was investigated in the gas phase and aqueous media using adsorption, broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC), infrared spectroscopy, thermal analysis, and one-pass temperature-programmed desorption (OPTPD) mass-spectrometry (MS) methods. PVA monolayer formation leads to certain textural changes in the system (after suspension and drying) because of strong hydrogen bonding of the polymer molecules to silica nanoparticles preventing strong interaction between silica particles themselves. This strong interaction promotes associative desorption of water molecules at lower temperatures than in the case of silica alone. Interaction of PVA with silica and residual water leads to depression of glass transition temperature (T(g)). There are three types of dipolar relaxations at temperatures lower and higher than the T(g) value. A small amount of adsorbed water leads to significant conductivity with elevating temperature.


Assuntos
Álcool de Polivinil/química , Dióxido de Silício/química , Propriedades de Superfície , Adsorção , Ligação de Hidrogênio , Espectrometria de Massas , Espectrofotometria Infravermelho , Análise Espectral , Temperatura , Água/química
20.
Langmuir ; 23(6): 3184-92, 2007 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-17261043

RESUMO

Structural characterization of different silicas (ordered mesoporous silicas MCM-41, MCM-48, and SBA-15, amorphous silica gels Si-40, Si-60, and Si-100, and initial and wetted-dried fumed silica A-300) and bio-objects (fibrinogen solution, yeast cells, wheat seeds, and bone tissues) has been done using two versions of cryoporometry based on integral Gibbs-Thomson (IGT) equation for freezing point depression of pore liquids measured by 1H NMR spectroscopy (180-200 < T < 273 K) and thermally stimulated depolarization current (TSDC) method (90 < T < 273 K). The IGT equation was solved using a self-consisting regularization procedure including the maximum entropy principle applied to the distribution function of pore size (PSD). Comparison of the PSDs calculated by using the cryoporometry and nitrogen adsorption methods for the mentioned silicas demonstrates that IGT equation provides satisfactory fit which is better than that obtained with nonintegral Gibbs-Thomson (GT) equation (based on the GT equation) proposed by Aksnes and Kimtys. The NMR- and TSDC-cryoporometry methods applied to probe biosystems give clear pictures of changes in the structural characteristics caused, e.g., by hydration and swelling of wheat seeds and yeast cells, coagulation and interaction of fibrinogen with solid nanoparticles in the aqueous media, and human bone tissue disease.


Assuntos
Biofísica/métodos , Adsorção , Osso e Ossos/metabolismo , Físico-Química/métodos , Entropia , Fibrinogênio/química , Humanos , Espectroscopia de Ressonância Magnética/métodos , Modelos Químicos , Modelos Estatísticos , Nanopartículas , Nitrogênio/química , Termodinâmica , Triticum/metabolismo , Leveduras/metabolismo
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