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131.
Lauri A Riipinen I Ketoja JA Vehkamäki H Kulmala M 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10061-10065
The heterogeneous nucleation and condensation of water vapor onto three different surfaces (newsprint paper, Teflon, cellulose film) was studied theoretically and experimentally. The theoretical framework included the use of the classical theory of heterogeneous nucleation, diffusion theory corrected with transition regime correction factors, and the theory of heat transfer. Experiments were carried out using an environmental scanning electron microscope (ESEM). The experimental results for newsprint paper were investigated more closely. Our results show that the measured onset supersaturations were smaller than the modeled ones when the experimentally determined contact angle was used. Furthermore, the measured condensational growth rates were smaller than the modeled ones, presumably resulting from the approximations that had to be made in the calculations. 相似文献
132.
Paloniemi H Lukkarinen M Aäritalo T Areva S Leiro J Heinonen M Haapakka K Lukkari J 《Langmuir : the ACS journal of surfaces and colloids》2006,22(1):74-83
We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness. 相似文献
133.
Hellman H Laitinen RS Kaila L Jalonen J Hietapelto V Jokela J Sarpola A Rämö J 《Journal of mass spectrometry : JMS》2006,41(11):1421-1429
The hydrolysis reactions of FeCl3 in 0.1 mM aqueous solutions were monitored by electrospray ionisation time-of-flight mass spectrometry (ESI-ToF-MS). In contrast to the other ionisation techniques, electrospray ionisation provides information on the composition of the elemental cores even in water and salt cluster ions. Therefore, the technique facilitates detection of the bonding of the chloride ions in the oxo-hydroxo-iron cores. A variety of mononuclear and polynuclear iron-oxohydroxo-chloride complexes were characterised from the cationic and anionic mass spectra of iron(III) solutions. Oxidation and reduction reactions of iron, as well as competition between OH- and Cl- ions within one iron core, were also observed. 相似文献
134.
Two-dimensional (129)Xe exchange spectroscopy (EXSY) NMR measurements are presented for xenon atoms dissolved in a thermotropic nematic Liquid Crystal (LC), Merck Phase 4, confined to a mesoporous Controlled-Pore Glass (CPG) material with an average pore diameter of 81 A. Experiments were carried out as a function of mixing time at two different temperatures in which Phase 4 appears in nematic and isotropic phases. The exchange rate constants of xenon atoms between two different sites were determined utilizing the intensities of diagonal and off-diagonal signals measured in the EXSY spectra. In the studied system, the sites are: (a) xenon dissolved in the bulk LC between the CPG particles; and (b) xenon in the LC confined inside the pores. The diffusion rate of xenon atoms between the various sites was observed to be very slow. 相似文献
135.
Xenon porometry is a new method for characterization of porous materials. In this method, the material is immersed in a medium, and its properties are studied by means of 129Xe NMR spectra of xenon dissolved in the sample. The method is particularly suitable for the determination of pore size distribution of the material, since the spectra display two signals whose chemical shift is dependent on the pore size. A prerequisite for an accurate determination is the fact that the diffusion of xenon between different pores is slow enough. The diffusion is studied in this work using two-dimensional exchange spectroscopy (2-D EXSY). The spectra measured as a function of the mixing time imply that the exchange is really slow as compared with the NMR time scale, and therefore the distribution of the resonance frequencies indeed represents the pore size distribution. 相似文献
136.
Holappa J Nevalainen T Safin R Soininen P Asplund T Luttikhedde T Másson M Järvinen T 《Macromolecular bioscience》2006,6(2):139-144
Novel synthesis methods for the preparation of quaternary piperazine derivatives of chitosan were developed. Quaternary ammonium moiety can be selectively inserted into either one or both of the piperazine nitrogens, yielding structurally uniform chitosan derivative structures. Water-soluble end products were thoroughly characterized with FT-IR, 1H NMR, 13C NMR and 2D 1H-13C HSQC NMR. The molecular weights of the end products were determined by GPC with triple detection. 相似文献
137.
The behavior of nematic liquid crystal (LC) Merck Phase 4 confined to controlled pore glass (CPG) materials was investigated using 129Xe nuclear magnetic resonance (NMR) spectroscopy of xenon gas dissolved in the LC. The average pore diameters of the materials varied from 81 to 2917 A, and the measurements were carried out within a wide temperature range (approximately 185-370 K). The spectra contain lots of information about the effect of confinement on the phase of the LC. The theoretical model of shielding of noble gases dissolved in liquid crystals on the basis of pairwise additivity approximation was applied to the analysis of the spectra. When pore diameter is small, smaller than approximately 150 A, xenon experiences on average an isotropic environment inside the pore, and no nematic-isotropic phase transition is observed. When the size is larger than approximately 150 A, nematic phase is observed, and the LC molecules are oriented along pore axis. The orientational order parameter of the LC, S, increases with increasing pore size. In the largest pores, the orientation of the molecules deviates from the pore axis direction to magnetic field direction, which implies that the size of the pores (approximately 3000 A) is close to magnetic coherence length. The decrease of magnetic coherence length with increasing temperature is clearly seen from the spectra. When the sample is cooled rapidly by immersing it in liquid nitrogen, xenon atoms do not squeeze out from the solid, as they do during gradual freezing, but they are occluded inside the solid lattice, and their chemical shift is very sensitive to crystal structure. This makes it possible to study the effect of confinement on the solid phases. According to the measured 129Xe NMR spectra, possibly three different solid phases are observed from bulk liquid crystal in the used temperature region. The same is also seen from the samples containing larger pores (pore size larger than approximately 500 A), and the solid-solid phase-transition temperatures are the same. However, no first-order solid-solid phase transitions are observed from the smaller pores. Melting point depression, that is, the depression of solid-nematic transition temperature observed from the pores as compared with that in bulk LC, is seen to be very sensitive to the pore size, and it can be used for the determination of pore size of an unknown material. 相似文献
138.
Muhammad Zakir B.D.S MSc PhD Taina Laiho Sari Granroth Edwin Kukk Chun Hung Chu James Kit-Hon Tsoi Jukka Pekka Matinlinna 《Surface and interface analysis : SIA》2022,54(7):747-758
This laboratory study aimed to compare, contrast, and evaluate the effect of a novel dual surface modification method on the adhesion strength of resin composite cement to titanium. C.p.-2 grade titanium samples were silica-coated, etched with HNO3(69vol %) or a blend of HCl (35vol %) and H3PO4 (85vol %), for 1 h at 80°C. Surface roughness was measured by surface roughness profilometry, topographic analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM), and surface analyses by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS). Silanization of all specimens was carried out after SEM, EDX, and AFM analysis, before enclosed mold microshear bond strength testing (EM-μSBS). Adhesion strengths were measured after artificial ageing: 1 day, 1 week, 4 weeks, and 8 weeks by EM-μSBS testing and failure mode analysis by optical microscopy. Polished titanium was used as a control. The highest surface roughness was observed in titanium samples treated with silica-coating + HCl-H3PO4 etching. The elemental composition confirmed the presence of Ti, O, C, with Si and Al in samples treated with silica-coating. A gradual decrease in EM-μSBS values was observed in all titanium samples with adhesive and cohesive failure modes. The novel dual surface modification method applied in this study suggests that silica-coating + HCl-H3PO4etching strongly affects titanium surface topography and roughness. The presence of Si on silica-coated surface modified titanium before silanization with an experimental silane has a positive effect on the EM-μSBS of titanium samples treated with silica-coating only or silica-coating + HNO3 etching. 相似文献
139.
140.
Surface modification of titanium with thermally treated polydimethylsiloxane coating and the effect on resin to titanium adhesion 下载免费PDF全文
Christie Y. K. Lung Markku Heinonen Edwin Kukk Jukka P. Matinlinna 《Surface and interface analysis : SIA》2015,47(1):105-112
In this study, titanium surface modification by a thermal treatment using a polydimethylsiloxane (PDMS) coating was investigated. The surfaces of four titanium samples were surface treated by polishing, sandblasting, and coating with a PDMS with a thermal treatment at 800 and 1100 °C. The titanium surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy. The effect of the surface treatments on adhesion of resin to titanium was assessed by shear adhesion strength test. XPS analysis showed that there was a change of elemental composition of titanium surfaces after surface treatment. Binding energy shifts for Si2p and O1s were observed after sandblasting and thermally treated PDMS. Therefore, chemical states of Si and O were changed. Atomic force microscopy analysis revealed that the surface topography of the Ti samples was different, and surface roughness was increased after sandblasting and thermal treatment of PDMS coating. Shear adhesion strength test results showed that the adhesion between resin and titanium is affected by the treatment temperature of PDMS coating. The highest adhesion is obtained at 1100 °C (14.7 ± 1.57 MPa). Copyright © 2014 John Wiley & Sons, Ltd. 相似文献