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1.
Mixtures of dioctadecyldimethylammonium chloride (DODAC) cationic vesicle dispersions with aqueous micelle solutions of the anionic sodium cholate (NaC) were investigated by differential scanning calorimetry, DSC, turbidity and light scattering. Within the concentration range investigated (constant 1.0 mM DODAC and varying NaC concentration up to 4 mM), vesicle → micelle → aggregate transitions were observed. The turbidity of DODAC/NaC/water depends on time and NaC/DODAB molar concentration ratio R. At equilibrium, turbidity initially decreases smoothly with R to a low value (owing to the vesicle–micelle transition) when R = 0.5–0.8 and then increases steeply to a high value (owing to the micelle–aggregate transition) when R = 0.9–1.0. DSC thermograms exhibit a single and sharp endothermic peak at Tm ≈ 49 °C, characteristic of the melting temperature of neat DODAC vesicles in water. Upon addition of NaC, Tm initially decreases to vanish around R = 0.5, and the main transition peak broadens as R increases. For R > 1.0 two new (endo- and exothermic) peaks appear at lower temperatures indicating the formation of large aggregates since the dispersion is turbid. All samples are non-birefringent. Dynamic light scattering (DLS) data indicate that both DODAC and DODAC/NaC dispersions are highly polydisperse, and that the mean size of the aggregates tends to decrease as R increases. 相似文献
2.
Puertas AM Fernández-Barbero A Javier de Las Nieves F Rull LF 《Langmuir : the ACS journal of surfaces and colloids》2004,20(22):9861-9867
The structure of colloidal clusters formed by long-range attractive interactions under diluted conditions is studied by means of Monte Carlo simulations. For a not-too-long attraction range, clusters show self-similar internal structure with lower density than that typical for diffusive aggregation. For long-range interactions, low kappa, nonfractal clusters are formed (dense at short scales but open at long ones). The dependence on the volume fraction shows that more-compact clusters are grown the higher the colloidal density for diffusive aggregation and attraction-driven aggregation in the fractal regime. The whole trend is explained in terms of the interpenetration among aggregates. In attraction-driven aggregations, the interpenetration of clusters competes with aggregation in the tips of the clusters, causing low-density clusters. 相似文献
3.
Hoyos-Montilla Ary A. Puertas F. Tobón Jorge I. 《Journal of Thermal Analysis and Calorimetry》2018,131(3):2395-2410
Journal of Thermal Analysis and Calorimetry - The objective of this research is to know, through the flow of heat released, the effect of the addition of calcium hydroxide and the temperature on... 相似文献
4.
Corella Puertas Elena Dzafic Adna Coulombe Sylvain 《Plasma Chemistry and Plasma Processing》2020,40(1):145-167
Plasma Chemistry and Plasma Processing - Although the erosion of high-voltage electrodes was extensively studied in in-liquid electrical discharges, to the best of our knowledge, the erosion... 相似文献
5.
We present simulation results addressing the dynamics of a colloidal system with attractive interactions close to gelation. Our interaction also has a soft, long-range repulsive barrier that suppresses liquid-gas type phase separation at long wavelengths. The new results presented here lend further weight to an intriguing picture emerging from our previous simulation work on the same system. Whereas mode coupling theory (MCT) offers quantitatively good results for the decay of correlators, closer inspection of the dynamics reveals a bimodal population of fast and slow particles with a very long exchange time scale. This population split represents a particular form of dynamic heterogeneity (DH). Although DH is usually associated with activated hopping and/or facilitated dynamics in glasses, the form of DH observed here may be more collective in character and associated with static (i.e., structural) heterogeneity. 相似文献
6.
A number of fundamental studies on the interactions between lipid bilayers and (ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide) copolymers (PEO-PPO-PEO, Pluronics) have been carried out recently as model systems for the complex behavior of cell membranes with this class of polymers often employed in pharmaceutical formulations. We report here a study by differential scanning calorimetry (DSC) of the interactions in water between Pluronic F127 (F127), and the cationic vesicles of di-n-octadecyldimethylammonium bromide (DODAB), as a function of concentration of the two components (DODAB 0.1 and 1.0 mM; F127 0.1 to 5.0 mM) and of the sample preparation protocol. The DSC studies follow the critical micellization temperature (cmt ≈ 27 °C at 1.0 mM) of F127 and the gel-liquid crystal transition (T(m) ≈ 45 °C) of the DODAB bilayer and of F127/DODAB mixtures. Upon heating past T(m), vesicle/polymer mixtures undergo an irreversible conversion into mixed DODAB/F127 micelles and/or F127-bearing vesicles, depending on the relative amount of each component, together with, in some cases, residual intact F127 micelles or DODAB vesicles. Sample preparation protocol is shown to have little impact on the composition of mixed systems once they are heated above T(m). 相似文献
7.
Zhang LangTing Duan YaJuan Crespo Daniel Pineda Eloi Wang YunJiang Pelletier Jean-Marc Qiao JiChao 《中国科学:物理学 力学 天文学(英文版)》2021,64(9):1-10
Spatial frequency shift(SFS) microscopy with evanescent wave illumination shows intriguing advantages, including large field of view(FOV), high speed, and good modularity. However, a missing band in the spatial frequency domain hampers the SFS superresolution microscopy from achieving resolution better than 3 folds of the Abbe diffraction limit. Here, we propose a novel tunable large-SFS microscopy, making the resolution improvement of a linear system no longer restricted by the detection numerical aperture(NA). The complete wide-range detection in the spatial frequency domain is realized by tuning the illumination spatial frequency actively and broadly through an angle modulation between the azimuthal propagating directions of two evanescent waves. The vertical spatial frequency is tuned via a sectional saturation effect, and the reconstructed depth information can be added to the lateral superresolution mask for 3D imaging. A lateral resolution of λ/9, and a vertical localization precision of ~λ/200(detection objective NA = 0.9) are realized with a gallium phosphide(GaP) waveguide. Its unlimited resolution enhancing capability is demonstrated by introducing a designed metamaterial chip with an unusual large refractive index. Besides the great resolution enhancement, this method shows better anti-noise capability than classical structured illumination microscopy without SFS tunability. This method is chip-compatible and can potentially provide a massproducible illumination chip module achieving the fast, large-FOV, and deep-subwavelength 3D nanoscopy. 相似文献
8.
Eloi Feitosa Fernanda Rosa Alves Elisabete M. S. Castanheira M. Elisabete C. D. Real Oliveira 《Colloid and polymer science》2009,287(5):591-599
In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing
Br− or Cl− counterions) molecules assemble in water as large unilamellar vesicles. Differential-scanning calorimetry (DSC) is a suitable
technique to obtain the melting temperature (T
m) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like
bilayers. These two techniques were combined to investigate the assembly of DODAX molecules at micromolar concentrations,
from 10 to 100 μM. At 1 mM surfactant, T
m ≈ 45 °C and 49 °C, respectively, for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of
DODAX aggregates, at the surfactant concentration as low as 10 μM, whose T
m decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate
that these aggregates are organized as bilayer-like structures. 相似文献
9.
Lavilla M Moros M Puertas S Grazú V Pérez MD Calvo M de la Fuente JM Sánchez L 《Analytical and bioanalytical chemistry》2012,402(10):3219-3226
Nowadays, the reference method for the detection of Clostridium tyrobutyricum in milk is the most-probable-number method, a very time-consuming and non-specific method. In this work, the suitability
of the use of superparamagnetic beads coated with specific antibodies and peptides for bioseparation and concentration of
spores of C. tyrobutyricum has been assessed. Peptide or antibody functionalized nanoparticles were able to specifically bind C. tyrobutyricum spores and concentrate them up to detectable levels. Moreover, several factors, such as particle size (200 nm and 1 μm),
particle derivatization (aminated and carboxylated beads), coating method, and type of ligand have been studied in order to
establish the most appropriate conditions for spore separation. Results show that concentration of spore is favored by a smaller
bead size due to the wider surface of interaction in relation to particle volume. Antibody orientation, related to the binding
method, is also critical in spore recovery. However, specific peptides seem to be a better ligand than antibodies, not only
due to the higher recovery ratio of spores obtained but also due to the prolonged stability over time, allowing an optimal
recovery of spores up to 3 weeks after bead coating. These results demonstrate that specific peptides bound to magnetic nanoparticles
can be used instead of traditional antibodies to specifically bind C. tyrobutyricum spores being a potential basis for a rapid method to detect this bacterial target. 相似文献
10.
Lithiation of chloro- and methoxy-(η6-benzene)tricarbonylchromium complexes yielded, after electrophilic quench with a Weinreb amide, the corresponding benzoyl-substituted complexes. One of them has been investigated by an X-ray diffraction study. 相似文献