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Rudoy, V. M.; Дементьева, О. В.; Yaminskii, I. V.; Sukhov, V. N.; Kartseva, M. E.; Ogarev, V. A.

doi:10.1023/a:1021558424276

Cited by 28 publications

(26 citation statements)

References 25 publications

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“…The analysis of obtained AFM images demonstrated that, already at 40-50 ° C, the PS surface layer 3-4 nm thick is in the devitrified state; moreover, as the temperature increases to 80 ° C, the thickness of such a layer noticeable increases [37].…”

Section: Introductionmentioning

confidence: 93%

“…Let us discuss now the results of experiments on the enlargement of gold nanoparticles in the ensembles on 2 We remind to the reader that, according to [37], the glass transition temperature of the surface layer of PS with a molecular mass of 270 000 is equal to 40-50°C. the surfaces of initial PS-234 and mixtures based on this polymer.…”

Section: The Enlargement Of Nanoparticles In Monolayer Ensembles On Tmentioning

confidence: 99%

“…The data obtained in [37] evidence that it is possible to create "continuous" nanoparticulate gold (in principle, other metals as well) films fixed in the polymer surface layer, according to the following scheme.…”

Section: Introductionmentioning

confidence: 97%

“…By now a great deal of experimental data obtained by using X-ray photoelectron spectroscopy [7], ellipsometry [32,33], atomic force microscopy (AFM) [34][35][36][37][38], and other methods [39,40] have been accumulated demonstrating that the glass transition temperature of polymer surface layer ( ) is substantially lower than its "bulk" value T g . The observed effect is explained by the presence of excess free volume in a polymer near its boundary with the air due to such effects as the segregation of end groups, constrained geometry, and the partial degradation of entanglement network.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, in our previous work [37], we studied the specific features of the vitrification of the surface layers of amorphous polymers using polystyrene (PS) with a molecular mass M ≈ 270 000 as an example. For this purpose, after the adsorption of gold hydrosol nanoparticles on the PS film, the film was stepwise annealed at temperatures lower than T g , then it was abruptly cooled (at each stage) to ambient temperature, thus freezing the structure formed during the thermal treatment, and was examined with atomic force microscope.…”

Section: Introductionmentioning

confidence: 99%

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Metal nanoparticles on polymer surfaces: 4. Preparation and structure of colloidal gold films

et al. 2005

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The process of the enlargement of gold hydrosol nanoparticles adsorbed on the surfaces of glassy polymers (polystyrene and poly(2-vinylpyridine)) in mixed aqueous solution of chloroauric acid and hydroxylamine is studied. It is established that the character of this process depends on the intensity of metal-polymer interaction and the density of nanoparticle packing in an initial monolayer. At a high coverage of a poly(2-vinylpyridine) surface by "seeding" gold particles, their rather uniform growth is observed, whereas, at low coverage, the enlargement of adsorbed particles, as well as the nucleation and growth of new particles take place. At the same time, new Au nanoparticles are not formed on the polystyrene surface in the enlargement process, even at low coverages by preliminarily deposited "seeding" hydrosol particles. Adsorbed gold particles can also be enlarged after their preliminary incorporation into the polystyrene surface layer. Such an incorporation (partial embedding) is ensured by the annealing of a system at a temperature between "surface" ( ) and "bulk" glass transition temperatures. In this case, the value can be considerably decreased (up to room temperature) by the addition of small amounts of a homologue with a much lower molecular mass in the polystyrene matrix. Lateral conductivity of colloidal Au films formed on a poly(2-vinylpyridine) surface by the enlargement of adsorbed seeding particles is measured. According to these measurements, contacts providing the formation of conductive channels are formed in the process of nanoparticle enlargement. T g 'T g ' 125

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Section: Introductionmentioning

confidence: 93%

Section: The Enlargement Of Nanoparticles In Monolayer Ensembles On Tmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Metal nanoparticles on polymer surfaces: 4. Preparation and structure of colloidal gold films

et al. 2005

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Three‐Dimensional Assembly of Polymer Microstructures at Low Temperatures

Yang

Zeng

Lee³

2004

Advanced Materials

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ing sphere [28] purged with flowing nitrogen and the sample was excited at 325 nm and excitation power of 0.2 mW. Photoluminescence transient decays were measured by a time-correlated singlephoton counting (TCSPC) system. Excitation was at~390 nm from a pulsed laser diode (Picoquant) giving 10 pJ pulse ±1. The apparatus response function was~350 ps (full width at half maximum) on its fastest scale. All measurements were performed at room temperature. Films were kept in a vacuum of < 10 ±3 mbar during measurements. The decay kinetics were fitted by a sum of exponential functions: I(t) = A 1 exp(±t/s 1 ) + A 2 exp(±t/s 2 ) with A and s as the pre-exponential factor and excited state lifetime respectively. The quality of the fits was confirmed by random distribution of the residuals.For EL characterization OLEDs were prepared by spin-coating the electroluminescent layers, consisting of 20 wt.-% of each dendrimer blended into CBP, onto transparent indium tin oxide (ITO) anodes (20 X/square) that had been oxygen-plasma treated in an Emitech K1050X plasma unit. The solution concentration was 20 mg mL ±1 in chloroform and the spin speed 2000 rpm for 1 min. The films formed were of good quality as determined by optical microscopy and surface profilometry. After spin-coating, the samples were placed into a high vacuum chamber and an electron transport layer (ETL) and cathode materials were sequentially evaporated. The electron transport layer was 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI), and was evaporated at 0.05 nm s ±1, and the cathode comprised lithium fluoride (0.4 nm), calcium (12 nm), and aluminum (50 nm) layers evaporated at 0.5 nm s ±1 . Electrical and optical measurements of all OLED devices were made under high vacuum (10 ±5 mbar) at room temperature. The effective area of each emitting diode was 6 mm 2 . The EL spectra were recorded with an Oriel MS125 Spectrograph coupled to a CCD detector (spectral resolution~1 nm). Current±voltage and brightness±voltage analyses were performed using a Keithley 2400 Source meter and a Keithley 2000 meter (employing a calibrated silicon photodiode), respectively. Luminance was also measured using a calibrated Minolta LS-100 luminance meter. External quantum efficiencies were calculated from the luminance, current density, and emission spectrum of each device assuming Lambertian emission.

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Low‐Temperature Fusion of Polymeric Nanostructures Using Carbon Dioxide

et al. 2006

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Low-temperature assembly techniques are desirable for further evolving polymer-based microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). Especially for systems containing biomolecules and cells, biologically benign processing techniques that meet strict design constraints (e.g., non-contaminating, non-deforming, low temperature) are necessary. Traditional solvent-based and thermal polymer processing methods have unacceptable drawbacks for these applications. Here, we propose a new and universal method for assembling polymer nanostructures. This method is based on using a low carbon dioxide (CO 2 ) pressure to significantly reduce the glass-transition temperature (T g ) of the polymer surface, thus allowing fusion of nanoscale structures at low temperatures. As a benign volatile solvent, CO 2 is a completely unregulated, non-contaminating processing aid.It has been reported that polymer properties at the free surface and near the polymer/substrate interface are different from those in the bulk, [1] as extensively demonstrated by the T g of ultrathin polymer films that are supported on a substrate [2][3][4] or freely standing. [5][6][7] For example, the T g could be significantly lowered at the surface when the substrate effect was negligible. [2,8] Based on these results, interfacial fusion of polymers at temperatures below their bulk T g has been achieved. [9,10] However, these studies showed that the adhesive strength was very low and developed very slowly below the T g , for example, 0.08 MPa after 4 h at 62°C for polystyrene (PS), making it unsuitable for practical applications. Unlike the fusion of polymers by using supercritical CO 2 in previous studies, [11,12] we have successfully demonstrated that CO 2 can enhance interfacial fusion of microstructures at low temperatures by applying a low CO 2 pressure to the polymer surface. By selecting proper processing conditions, microscale features (as small as 3.9 lm) on the polymer surface were well-preserved. The adhesive strength of poly(D,L-lactic-coglycolic acid) (PLGA) copolymer approached 1 MPa at 35°C and a CO 2 pressure of 0.79 MPa.[13]Most thin-film T g studies only record the global behavior of thin films, except for Ellison and Torkelson who measured the local T g distribution at the surface.[8] Moreover, the enhancement of the surface-chain mobility by CO 2 also needs to be explored. Here, we use atomic force microscopy (AFM) with gold nanoparticles as probes [14,15] to investigate the surface T g of polymers in a CO 2 environment. A polymer film is spincoated onto a silicon wafer with a surface roughness in the range of 1-2 nm. Gold nanoparticles are then placed onto the polymer surface as the probes. After annealing at a prespecified temperature and applying CO 2 pressure for 4 h, the system reaches an equilibrium state, [15] and the apparent height of the nanoparticles embedded into the surface is measured using AFM. From this data, the mobile surface layer at the annealing temperature can be probed. In the case of PS (M ...

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Cited by 28 publications

References 25 publications

Metal nanoparticles on polymer surfaces: 4. Preparation and structure of colloidal gold films

Metal nanoparticles on polymer surfaces: 4. Preparation and structure of colloidal gold films

Three‐Dimensional Assembly of Polymer Microstructures at Low Temperatures

Low‐Temperature Fusion of Polymeric Nanostructures Using Carbon Dioxide

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