Correlation length of hydrophobic polyelectrolyte solutions

The combination of two techniques (Small Angle X-ray Scattering and Atomic Force Microscopy) has allowed us to measure in reciprocal and real space the correlation length $\xi$ of salt-free aqueous solutions of highly charged hydrophobic polyelectrolyte as a function of the polymer concentration $C_p$, charge fraction $f$ and chain length $N$. Contrary to the classical behaviour of hydrophilic polyelectrolytes in the strong coupling limit, $\xi$ is strongly dependent on $f$. In particular a continuous transition has been observed from $\xi \sim C_p^{-1/2}$ to $\xi\sim C_p^{-1/3}$ when $f$ decreased from 100% to 35%. We interpret this unusual behaviour as the consequence of the two features characterising the hydrophobic polyelectrolytes: the pearl necklace conformation of the chains and the anomalously strong reduction of the effective charge fraction.Comment: 7 pages, 5 figures, submitted to Europhysics Letter

Ultrasonic particle trapping in microfluidic devices using soft lithography

2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme

We report on a SANS investigation into the potential for these structural reorganization of complexes composed of lysozyme and small PSS chains of opposite charge if the physicochemical conditions of the solutions are changed after their formation. Mixtures of solutions of lysozyme and PSS with high matter content and with an introduced charge ratio [-]/[+]intro close to the electrostatic stoichiometry, lead to suspensions that are macroscopically stable. They are composed at local scale of dense globular primary complexes of radius ~ 100 {\AA}; at a higher scale they are organized fractally with a dimension 2.1. We first show that the dilution of the solution of complexes, all other physicochemical parameters remaining constant, induces a macroscopic destabilization of the solutions but does not modify the structure of the complexes at submicronic scales. This suggests that the colloidal stability of the complexes can be explained by the interlocking of the fractal aggregates in a network at high concentration: dilution does not break the local aggregate structure but it does destroy the network. We show, secondly, that the addition of salt does not change the almost frozen inner structure of the cores of the primary complexes, although it does encourage growth of the complexes; these coalesce into larger complexes as salt has partially screened the electrostatic repulsions between two primary complexes. These larger primary complexes remain aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary complex with a [-]/[+]intro close to 1, only slightly changes the inner structure of the primary complexes. Moreover, in contrast to the synthesis achieved in the one-step mixing procedure where the proteins are unfolded for a range of [-]/[+]intro, the native conformation of the proteins is preserved inside the frozen core

On the pearl size of hydrophobic polyelectrolytes

Hydrophobic polyelectrolytes have been predicted to adopt an unique pearl-necklace conformation in aqueous solvents. We present in this Letter an attempt to characterise quantitatively this conformation with a focus on $D_p$, the pearl size. For this purpose polystyrenesulfonate (PSS) of various effective charge fractions $f_{eff}$ and chain lengths $N$ has been adsorbed onto oppositely charged surfaces immersed in water in condition where the bulk structure is expected to persist in the adsorbed state. \emph{In situ} ellipsometry has provided an apparent thickness $h_{app}$ of the PSS layer. In the presence of added salts, we have found: $h_{app}\sim aN^{0}f_{eff}^{-2/3}$ ($a$ is the monomer size) in agreement with the scaling predictions for $D_p$ in the pearl-necklace model if one interprets $h_{app}$ as a measure of the pearl size. At the lowest charge fractions we have found $h_{app}\sim aN^{1/3}$ for the shorter chains, in agreement with a necklace/globule transition.Comment: 7 pages, 4 figures, 1 table. Published in Europhysics Letters, Vol. 62, Number 1, pp. 110-116 (2003

Nanostructures via DNA scaffold metallization

金沢大学大学院自然科学研究科物質情報解析金沢大学理学部The critical role of polymers in process of noble metals nanostructures formation is well known, however, the use of DNA chain template in this process is yet largely unknown. In this study we demonstrate different ways of silver deposition on DNA template and report the influence of silver nanostructures formation on DNA conformational state. Metallization of DNA chain proceeds by two different scenarios depending on DNA conformation. If DNA chain is unfolded (elongated) chain, silver reduction leads to the nucleation of silver nanoparticles and their growth on DNA scaffold. Silver nanoparticles assemble on negatively charged DNA template due to electrostatic interactions. During formation of silver nanoparticles, DNA chain, similarly to other polyelectrolytes, plays a role of stabilizing agent, and silver nanoparticles formed in DNA solutions are smaller and have narrower size distributions as compared to the particles formed in DNA-free solutions. Since positive change of thus formed silver nanoparticles is rather low, DNA chain remains in unfolded conformation no matter how high is a concentration of silver nanoparticles. On the other hand, when DNA molecule has been compacted into tight condensate, naturally of a toroid shape, deposition of silver on compacted DNA chain proceeds in a different manner without discretion into nanoparticles. As a result of such silver metal deposition, DNA-templated silver nanorings are formed. By comparison of UV-Vis spectra changes, the detection of transition point between unfolded and compact DNA conformations becomes possible. Metallization of unfolded DNA chain brings nanoparticles of about 30-50 nm size, while deposition of silver metal on a compact DNA condensate gives 100-150 nm metal rings that are distinguished by optical properties. The approach of different scenario of metallization can be used for detection of conformational changes in biopolymers

Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes—Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.</p