Intake of silica nanoparticles by giant lipid vesicles: influence of particle size and thermodynamic membrane state

• Florian G. Strobl,
• Florian Seitz,
• Christoph Westerhausen,
• Armin Reller,
• Adriano A. Torrano,
• Christoph Bräuchle,
• Achim Wixforth and
• Matthias F. Schneider

Beilstein J. Nanotechnol. 2014, 5, 2468–2478, doi:10.3762/bjnano.5.256

• and the release of cargo from giant vesicles was also the subject of earlier works in our group [35][36]. Due to the non-zero lateral shear resistance of gel-phase membranes, the relaxation time for the healing of defects will be much longer as compared to liquid membranes. Hence, induced pores remain

• the typical relaxation time of membrane defects. Both parameters are very important for uptake processes. The facts, that massive internalization of particles can be driven by unspecific interaction of lipid membranes and that this is dependent on the phase state of the membrane are highly relevant

Modeling viscoelasticity through spring–dashpot models in intermittent-contact atomic force microscopy

• Enrique A. López-Guerra and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 2149–2163, doi:10.3762/bjnano.5.224

• characterization with AFM. Results and Discussion Model descriptions Linear Maxwell model The Linear Maxwell model is one of the simplest spring–dashpot sets. It consists of a spring arranged in series with a dashpot (Figure 1a). This model is known for successfully describing stress relaxation (time-dependent

• existence of a single relaxation time (cd/k) which is reflected in the inflection point in Figure 1b. The existence of a single relaxation time is also considered a limitation in depicting true viscoelastic surfaces, which generally have more than one relaxation time [27]. Finally, it is worth mentioning

• may be such that they favor only a particular relaxation time of the sample or none at all. Despite the above disadvantages of the Linear Kelvin–Voigt model, it has been previously used in tapping mode AFM, both in experimental and numerical simulation approaches [16][17]. This model is also

Properties of plasmonic arrays produced by pulsed-laser nanostructuring of thin Au films

• Katarzyna Grochowska,
• Katarzyna Siuzdak,
• Peter A. Atanasov,
• Carla Bittencourt,
• Anna Dikovska,
• Nikolay N. Nedyalkov and
• Gerard Śliwiński

Beilstein J. Nanotechnol. 2014, 5, 2102–2112, doi:10.3762/bjnano.5.219

• collective electron motion and is characterized by the time constant T2, which is size-dependent and is given by the expression [31]: where Tr is the bulk-specific, purely free-electron relaxation time, vF is the Fermi velocity and A is a constant. The reported value of Tr for Au is 18 fs and can be used as

The surface properties of nanoparticles determine the agglomeration state and the size of the particles under physiological conditions

• Christoph Bantz,
• Olga Koshkina,
• Thomas Lang,
• Hans-Joachim Galla,
• C. James Kirkpatrick,
• Roland H. Stauber and
• Michael Maskos

Beilstein J. Nanotechnol. 2014, 5, 1774–1786, doi:10.3762/bjnano.5.188

• amplitude of 0.08 plus one additional component with an amplitude of 0.91, which can be assigned to agglomerates. The relaxation time of the aggregate component corresponds to a hydrodynamic radius of 91 nm. As shown, the multicomponent analysis yields not only a size that can be assigned specifically to

Probing viscoelastic surfaces with bimodal tapping-mode atomic force microscopy: Underlying physics and observables for a standard linear solid model

• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 1649–1663, doi:10.3762/bjnano.5.176

• solution of the cantilever equations of motion in the form of boundary conditions at the tip [4][5]. This model can reproduce time-dependent creep compliance (time-dependent strain relaxation under a constant stress) with high accuracy, but not stress relaxation (time dependent drop in stress under a

• for constant-indentation imaging of the sample with increasing higher mode amplitude (if such a method can be developed) the level of dissipation decreases monotonically, which is as expected, since the SLS has only one characteristic relaxation time (governed by the damper) and the sample deformation

• is transitioning from a low frequency deformation (governed by the fundamental mode) to a high frequency deformation (governed by the higher mode). However, a real sample may have more than one characteristic relaxation time, which could be probed by gradually increasing the amplitude of different

Synthesis of hydrophobic photoluminescent carbon nanodots by using L-tyrosine and citric acid through a thermal oxidation route

• Venkatesh Gude

Beilstein J. Nanotechnol. 2014, 5, 1513–1522, doi:10.3762/bjnano.5.164

• relaxation time of the solvent is lower or comparable to the fluorescence life time, which depends on the polarity of the chosen solvent [36]. This explanation contradicts the expected electron–hole pair mechanism of CNDs from earlier reports [2][5]. Therefore, further spectroscopic investigations are

Spin relaxation in antiferromagnetic Fe–Fe dimers slowed down by anisotropic Dy^III ions

• Valeriu Mereacre,
• Frederik Klöwer,
• Yanhua Lan,
• Rodolphe Clérac,
• Juliusz A. Wolny,
• Volker Schünemann,
• Christopher E. Anson and
• Annie K. Powell

Beilstein J. Nanotechnol. 2013, 4, 807–814, doi:10.3762/bjnano.4.92

• anisotropy using simple ligand field considerations, but also because of its huge field dependence of the relaxation time [13]. Designing the ligand field environment can help to control the magnetic anisotropy of some of the later lanthanides [2][3], but this is less useful for the DyIII ion. The

• structural aspect can prevail over the others. Here, we report how, contrary to reported Fe2Dy2 compounds [14][15], the application of an external magnetic field does not always affect the ground state of the DyIII ion and its relaxation time. Two compounds [Fe4Ln2(μ3-OH)2(L)4((CH3)3CCOO)6(N3)2]·(solv) (Ln

• spectrum. At 3 K (Figure 2), a magnetic spectrum is obtained, indicating that the spin-relaxation time is slow with respect to the Mössbauer time scale. The spectrum has been fitted with two sextets with the parameters listed in Table 1. The best fits for the zero-field spectrum at 3 K were achieved

Large-scale atomistic and quantum-mechanical simulations of a Nafion membrane: Morphology, proton solvation and charge transport

• Pavel V. Komarov,
• Pavel G. Khalatur and
• Alexei R. Khokhlov

Beilstein J. Nanotechnol. 2013, 4, 567–587, doi:10.3762/bjnano.4.65

• ) correlation functions exhibit an exponential decay at very short time (≈10 fs). The estimated relaxation time τh associated with the formation of hydronium ions is greater than the relaxation time τZ found for Zundel ions, but is considerably less than the relaxation time τE found for Eigen ions. This result

Novel composite Zr/PBI-O-PhT membranes for HT-PEFC applications

• Mikhail S. Kondratenko,
• Igor I. Ponomarev,
• Marat O. Gallyamov,
• Dmitry Y. Razorenov,
• Yulia A. Volkova,
• Elena P. Kharitonova and
• Alexei R. Khokhlov

Beilstein J. Nanotechnol. 2013, 4, 481–492, doi:10.3762/bjnano.4.57

• of PA inside the MEA and the formation of the effective boundary between the three phases (electron and proton conducting phases and gas phase) is observed during the first 1000 h. This relaxation time is noticeably higher than the typical time of about 100 hours reported in the literature as a

Growth behaviour and mechanical properties of PLL/HA multilayer films studied by AFM

• Cagri Üzüm,
• Johannes Hellwig,
• Narayanan Madaboosi,
• Dmitry Volodkin and
• Regine von Klitzing

Beilstein J. Nanotechnol. 2012, 3, 778–788, doi:10.3762/bjnano.3.87

• δ data for the indentation depth at 5–10% of the total thickness. For very thin films, this range was extended up to 20% of the total thickness, restricted to cases for which the calculated E does not change abruptly. Relaxation time measurements Measuring the viscoelastic properties of films in the

• compared to the creep-compliance function [41][46], it resembles the stress relaxation fit used for heterogeneous materials [13][14], and allows for a qualitative comparison of the cantilever relaxation time rather than giving the actual material relaxation time. Before discussing the outcome of the fits

• relaxation time τ1 and τ2 as a function of the initial indentation velocity. Error bars indicate the standard deviation from 10 measurements. Acknowledgements We thank the Deutsche Forschungsgemeinschaft (VO1716-2/1, KL 1165-11/1, KL 1165-12/1) and Alexander von Humboldt Foundation for the financial support.

Zeolites as nanoporous, gas-sensitive materials for in situ monitoring of DeNO_x-SCR

• Thomas Simons and
• Ulrich Simon

Beilstein J. Nanotechnol. 2012, 3, 667–673, doi:10.3762/bjnano.3.76

• Equation 4. The resonance frequencies determined by using the phase angle φ are slightly different (up to a factor of two) from those determined from the imaginary part of the modulus M″. This is caused by a relaxation time distribution, which is not an ideal Debye relaxation in this system. This leads to

Pulse-response measurement of frequency-resolved water dynamics on a hydrophilic surface using a Q-damped atomic force microscopy cantilever

• Masami Kageshima

Beilstein J. Nanotechnol. 2012, 3, 260–266, doi:10.3762/bjnano.3.29

• below this would require a cantilever having a longer relaxation time in water. Therefore the positive constant value of in the low-frequency regime in Figure 7b is not realistic. This is obvious also from the fact that a fluid cannot maintain finite stiffness down to zero frequency unless it is

• completely solidified. However, this positive value is maintained in the higher frequency regime, and this stiffening accounts for the observed shortening of the relaxation time. On the other hand, seems to start increasing above 10 kHz, although it substantially perturbed by noise. Similar behaviors of

• and were observed in a different data acquired in the same experimental run, apart from a irreproducible singularity around 6 kHz attributed to the influence of the residual 1st mode resonance of the cantilever. A constant value of hints at a system having only a single relaxation time. Then

Structural and magnetic properties of ternary Fe_1–xMn_xPt nanoalloys from first principles

• Markus E. Gruner and
• Peter Entel

Beilstein J. Nanotechnol. 2011, 2, 162–172, doi:10.3762/bjnano.2.20

• . Probably the most severe is the so-called superparamagnetic limit. This derives from the fact that the Néel relaxation law, which relates the relaxation time τ of the magnetization to the exponential of the product of anisotropy constant Ku times the grain volume V divided by temperature: This imposes a

Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

• Bharat Bhushan

Beilstein J. Nanotechnol. 2011, 2, 66–84, doi:10.3762/bjnano.2.9

• mold (negative) were separated. After a relaxation time of 30 minutes for the molding material, the negative replicas were filled with a liquid epoxy resin (Epoxydharz L®, No. 236349, Conrad Electronics, Hirschau, Germany) with hardener (Harter S, Nr 236365, Conrad Electronics, Hirschau, Germany

Magnetic interactions between nanoparticles

• Steen Mørup,
• Mikkel Fougt Hansen and
• Cathrine Frandsen

Beilstein J. Nanotechnol. 2010, 1, 182–190, doi:10.3762/bjnano.1.22

• close to θ = 0° and θ = 180°. The superparamagnetic relaxation time is given by the Néel–Brown expression [7][8] where kB is Boltzmann’s constant and T is the temperature. τ0 is on the order of 10−13–10−9 s and is weakly temperature dependent. In experimental studies of magnetic nanoparticles, the

• timescale of the experimental technique is an important parameter. If the relaxation is fast compared to the timescale of the experimental technique one measures an average value of the magnetization, but if the relaxation time is long compared to the timescale of the experimental technique, one measures

• the instantaneous value of the magnetization. The superparamagnetic blocking temperature is defined as the temperature at which the superparamagnetic relaxation time equals the timescale of the experimental technique. In Mössbauer spectroscopy the timescale is on the order of a few nanoseconds

Magnetic nanoparticles for biomedical NMR-based diagnostics

• Huilin Shao,
• Tae-Jong Yoon,
• Monty Liong,
• Ralph Weissleder and
• Hakho Lee

Beilstein J. Nanotechnol. 2010, 1, 142–154, doi:10.3762/bjnano.1.17

• biomolecules and cells based on magnetic resonance effects. This detection platform, termed diagnostic magnetic resonance (DMR), exploits magnetic nanoparticles as proximity sensors, which modulate the spin–spin relaxation time of water molecules surrounding molecularly-targeted nanoparticles. By developing

• targets. Another technology that has achieved considerable success is diagnostic magnetic resonance (DMR). Based on nuclear magnetic resonance (NMR) as the detection mechanism, DMR exploits MNPs as proximity sensors, which modulate the spin–spin relaxation time of water molecules adjacent to the

• ), is a cooperative process in which the interacting nanoparticles become more efficient at dephasing the spins of neighboring water protons, leading to a decrease in T2 relaxation time. The phenomenon can be explained by the outer-sphere theory. For a given volume fraction of MNPs in solution, T2 of

Ultrafine metallic Fe nanoparticles: synthesis, structure and magnetism

• Olivier Margeat,
• Marc Respaud,
• Catherine Amiens,
• Pierre Lecante and
• Bruno Chaudret

Beilstein J. Nanotechnol. 2010, 1, 108–118, doi:10.3762/bjnano.1.13

• temperature dependence is characteristic of a superparamagnetic transition. The NPs, which have relaxation times (τ) longer than the measurement time (τm), give rise to a sextet (blocked NPs). The superparamagnetic NPs with a short relaxation time (τ < τm) show paramagnetic like behaviour. In the case of

• Mössbauer spectroscopy, τm is in the range of 10−8 s [33][34][35] and the superparamagnetic relaxation time is given by where ν is the volume, Keff the effective anisotropy, and τ0 is of the order of 10−11–10−9 s [36]. The blocking temperature of the material corresponds to the temperature where the blocked

• following expressions [41]: with With these equations, it is possible to extract precisely the size distribution, the magnetic parameter MS(T) and the low temperature value of Keff. We first analyse the dependence of the relaxation time on temperature. Figure 10 displays the plot of log(τm) versus 1/TB

Uniform excitations in magnetic nanoparticles

• Steen Mørup,
• Cathrine Frandsen and
• Mikkel Fougt Hansen

Beilstein J. Nanotechnol. 2010, 1, 48–54, doi:10.3762/bjnano.1.6

• magnetization direction. For a particle with a uniaxial anisotropy energy E(θ) given by the simple expression in Equation 1, the superparamagnetic relaxation time τ is given by Equation 2 [1][2]. Here K is the magnetic anisotropy constant, V is the particle volume, θ is the angle between an easy axis and the

• (sublattice) magnetization vector, kB is Boltzmann’s constant and T is the temperature. The value of τ0 is in the range 10−13–10−9 s. When the superparamagnetic relaxation time is long compared to the timescale of the experimental technique, the instantaneous magnetization is measured, but in the case of fast

• relaxation, the average value of the magnetization is measured. The superparamagnetic blocking temperature (TB) is defined as the temperature at which the superparamagnetic relaxation time equals the timescale of the experimental technique used for the study of the magnetic properties. Below TB