Crossover regime for the diffusion of nanoparticles in polyethylene glycol solutions: influence of the depletion layer

N. Ziębacz, S. A. Wieczorek, T. Kalwarczyk, M. Fiałkowskia and R. Hołyst

Soft Matter, 2011,7, 7181-7186

The viscosity in soft matter systems is a scale dependent quantity. In polymer solutions the viscosity of nanoprobes of size R approaches the macroscopic viscosity when R exceeds the radius of gyration of the polymer, Rg. The nano to macroviscosity crossover occurs for R ∼ Rg. Here we analyze diffusion in a polymer (polyethylene glycol) solution of nanoparticles in the crossover regime. We report a scale dependent diffusion coefficient in this regime due to non-uniform viscosity in the depletion layer around particles. The phenomenological scaling of the slow diffusion coefficient as a function of probe size is compared to the same scaling for macroscopic viscosity as a function of polymer size.

New One-Pot Technique to Introduce Charged Nanoparticles into a Lyotropic Liquid Crystal Matrix

E. Kalwarczyk, M. Paszewski, X. Xin, E. Gorecka, D. Pociecha, R. Holyst and M. Fialkowski

Langmuir 2011, 27, 7, 3937–3944

We present a new method to incorporate hydrophilic charged nanoparticles into the lyotropic liquid crystal (LLC) template. This method is based on the effect of the polymer-induced phase separation (PIPS) and consists of two steps. In the first step, the nanoparticles are mixed with a surfactant micellar solution. In the second step, upon addition of polymer, phase separation is induced and the LLC phase doped with the nanoparticles is formed. Columnar hexagonal and lamellar LLC templates are obtained with the PIPS method. The ordering of the LLC phase can be controlled by the amount of polymer added to induce phase separation. The method works both for the system of nonionic surfactants and polymers and ionic surfactants and polyelectrolytes. We demonstrate that the PIPS method enables the fabrication of the LLC templates doped with positively or negatively charged nanoparticles as well as with a mixture of oppositely charged nanoparticles in arbitrary proportions.

Self‐Assembly at Different Length Scales: Polyphilic Star‐Branched Liquid Crystals and Miktoarm Star Copolymers

G. Ungar, C. Tschierske, V. Abetz, R. Holyst, M. A. Bates, F. Liu, M. Prehm, R. Kieffer, X. Zeng, M. Walker, B. Glettner and A. Zywocinski

Advanced Functional Materials 2011, 21, 7, 296-1323

The diversity of phase morphologies observed recently in star‐branched liquid‐crystalline and polymeric compounds containing at least three immiscible segments is reviewed. Bolaamphiphiles and facial amphiphiles with rodlike aromatic cores, two end‐groups, and one (T‐shape) or two (X‐shape) chains attached laterally to the core, form numerous honeycomblike liquid‐crystal phases, as well as a variety of novel lamellar and 3D‐ordered mesophases. Molecular self‐organization is described in bulk phases and in thin films on solid and liquid surfaces, as well as in Langmuir–Blodgett films. The remarkably reversible formation of mono‐ and trilayer films is highlighted. In the bulk, T‐shaped “rod–coil” molecules without appended end‐groups form predominantly lamellar phases if the core is a straight rod, but the bent‐core variety forms hexagonal honeycombs. Furthermore, self‐assembly of “Janus”‐type molecules, is discussed. Also covered is the diversity of morphologies observed in miktoarm star terpolymers, i.e., polymers with three different and incompatible arms of well defined lengths. Similarities and differences are highlighted between the liquid‐crystal morphologies on the 3–15 nm scale and the polymer morphologies on the scale of 10–100 nm. A separate section is dedicated to computer simulations of such systems, particularly those using dissipative particle and molecular dynamics. Of special interest are the recently synthesised X‐shaped tetraphilic molecules, where two different and incompatible side‐chains are attached at opposite sides of the rodlike core. The tendency for their phase separation produces liquid‐crystal honeycombs with cells of different compositions that can be represented as a plane paved with different colored tiles. The independent variation of chain length and “color” creates the potential for developing a considerable range of complex new 2D and 3D soft nanostructures. Analogous X‐shaped rod–coil compounds with unequal side groups are also of considerable interest, forming tubular lyotropic structures capable of confining strings of guest molecules.

Comparative Analysis of Viscosity of Complex Liquids and Cytoplasm of Mammalian Cells at the Nanoscale

T. Kalwarczyk, N. Ziȩbacz, A. Bielejewska, E. Zaboklicka, K. Koynov, J. Szymański, A. Wilk, A. Patkowski, J. Gapiński, Hans-Jürgen Butt and R. Hołyst

Nano Lett. 2011, 11, 5, 2157–2163

We present a scaling formula for size-dependent viscosity coefficients for proteins, polymers, and fluorescent dyes diffusing in complex liquids. The formula was used to analyze the mobilities of probes of different sizes in HeLa and Swiss 3T3 mammalian cells. This analysis unveils in the cytoplasm two length scales: (i) the correlation length ξ (approximately 5 nm in HeLa and 7 nm in Swiss 3T3 cells) and (ii) the limiting length scale that marks the crossover between nano- and macroscale viscosity (approximately 86 nm in HeLa and 30 nm in Swiss 3T3 cells). During motion, probes smaller than ξ experienced matrix viscosity: ηmatrix ≈ 2.0 mPa·s for HeLa and 0.88 mPa·s for Swiss 3T3 cells. Probes much larger than the limiting length scale experienced macroscopic viscosity, ηmacro ≈ 4.4 × 10–2 and 2.4 × 10–2 Pa·s for HeLa and Swiss 3T3 cells, respectively. Our results are persistent for the lengths scales from 0.14 nm to a few hundred nanometers.

Aggregation and Layering Transitions in Thin Films of X‐, T‐, and Anchor‐Shaped Bolaamphiphiles at the Air–Water Interface

P. Nitoń, A. Żywociński J. Paczesny, M. Fiałkowski, R. Hołyst B. Glettner R. Kieffer, C. Tschierske, D. Pociecha and E. Górecka

Chemistry - A European Journal 2011, 17, 21, 5861-5873

Aggregation in Langmuir films is usually understood as being a disorderly grouping of molecules turning into chaotic three‐dimensional aggregates and is considered an unwanted phenomenon causing irreversible changes. In this work we present the studies of 11 compounds from the group of specific surfactants, known as bolaamphiphiles, that exhibit reversible aggregation and, in many cases, transition to well‐defined multilayers, which can be considered as a layering transition. These bolaamphiphiles incorporate rigid π‐conjugated aromatics as hydrophobic cores, glycerol‐based polar groups and hydrophobic lateral chains. Molecules of different shapes (X‐, T‐, and anchor) were studied and compared. The key property of these compounds is the partial fluorination of the lateral chains linked to the rigid cores of the molecules. The most interesting feature of the compounds is that, depending on their shape and degree of fluorination, they are able to resist aggregation and preserve a monolayer structure up to relatively high surface pressures (T‐shaped and some X‐shaped molecules), or create well‐defined trilayers (X‐ and anchor‐shaped molecules). Experimental studies were performed using Langmuir balance, surface potential and X‐ray reflectivity measurements.

Ionic polarization of liquid-liquid interfaces; dynamic control of the rate of electro-coalescence

T. Szymborski, P. M. Korczyk, R. Hołyst and P. Garstecki

Appl. Phys. Lett. 2011, 99, 094101

Electrostatic forces are the strongest interactions in soft matter physics, yet they are usually screened by ions present in the solutions. Here we demonstrate that the extent of ionic polarization of liquid-liquid interfaces can be dynamically controlled via appropriate choice of the strength and frequency of the external electric field. Results of microfluidic experiments on electro-coalescence of droplets of aqueous solutions of salt provide guidelines for optimization of the process.
Project operated within the Foundation for Polish Science (FPS) Team Program (2008-1/1) co-financed by the EU European Regional Development Fund. T.S. thanks the Ministry of Science for support (IP2010 042270). R.H. thanks the FPS for support within the TEAM program (2008-2/2).

Ionic Strength-Controlled Deposition of Charged Nanoparticles on a Solid Substrate

K. Winkler, M. Paszewski, T. Kalwarczyk, E. Kalwarczyk, T. Wojciechowski, E. Gorecka, D. Pociecha, R. Holyst and M. Fialkowski

J. Phys. Chem. C 2011, 115, 39, 19096–19103

There is experimental evidence that in solutions of low ionic strength, charged nanoparticles (NPs) adsorbing onto an oppositely charged substrate cannot form dense monolayers due to the electrostatic repulsion. Here, we investigated the adsorption onto negatively charged substrates occurring in solutions containing positively charged NPs and salt for a wide range of ionic strengths. We found that the salt added in high concentration, above 2M, stabilizes the solution and the NPs adsorb on the substrate to form dense coatings characterized by the surface coverage of about 50%. In this regime, the adsorption rate was found to grow with the square of the NP concentration. This effect of salt on the deposition process provides a facile method of coating of solid substrates with NP monolayers. The density of such monolayers depends on and can be easily controlled by the deposition time, as well as by the salt and NP concentration in the plating solution.

Gold Micro-Flowers: One-Step Fabrication of Efficient, Highly Reproducible Surface-Enhanced Raman Spectroscopy Platform

K. Winkler, A. Kaminska, T. Wojciechowski, R. Holyst and M. Fialkowski

Plasmonics volume 2011, 6, Article number: 697

We present a new method enabling simultaneous synthesis and deposition of gold micro-flowers (AuMFs) on solid substrates in a one-pot process that uses two reagents, auric acid and hydroxylamine hydrochloride, in aqueous reaction mixture. The AuMFs deposited onto the substrate form mechanically stable gold layer of expanded nanostructured surface. The morphology of the AuMFs depends on and can be controlled by the composition of the reaction solution as well as by the reaction time. The nanostructured metallic layers obtained with our method are employed as efficient platforms for chemical and biological sensing based on surface-enhanced Raman spectroscopy (SERS). SERS spectra recorded by such platforms for p-mercaptobenzoic acid and phage lambda exhibit enhancement factors above 106 and excellent reproducibility.

Crystallization of the Photosystem II core complex and its chlorophyll binding subunit CP43 from transplastomic plants of Nicotiana tabacum

D. Piano, S. El Alaoui, H. J. Korza, R. Filipek, I. Sabala, P. Haniewicz, C. Buechel, D. De Sanctis & M. Bochtler

Photosynthesis Research volume 106, pages221–226 (2010)

Photosystem II from transplastomic plants of Nicotiana tabacum with a hexahistidine tag at the N-terminal end of the PsbE subunit (α-chain of the cytochrome b559) was purified according to the protocol of Fey et al. (BBA 12:1501–1509, 2008). The protein sample was then subjected to two additional gel filtration runs in order to increase its homogeneity and to standardize the amount of detergent. Large three dimensional crystals of the core complex were obtained. Crystals of one of its chlorophyll binding subunits (CP43) in isolation grew in very similar conditions that differed only in the concentration of the detergent. Diffraction of Photosystem II and CP43 crystals at various synchrotron beamlines was limited to a resolution of 7 and 14 Å, respectively. In both cases the diffraction quality was insufficient for an unambiguous assignment of the crystallographic lattice or space group.

Dynamic Supramolecular Polymers Based on Benzene‐1,3,5‐tricarboxamides: The Influence of Amide Connectivity on Aggregate Stability and Amplification of Chirality

P. J. M. Stals, J. C. Everts, R. de Bruijn, I. A. W. Filot, M. M. J. Smulders, R. Martin-Rapun, E. A. Pidko, T. F. A. de Greef, A. R. A. Palmans and E. W. Meijer

Chem. Eur. J., 2010, 16, 810-821

N‐Centred benzene‐1,3,5‐tricarboxamides (N‐BTAs) composed of chiral and achiral alkyl substituents were synthesised and their solid‐state behaviour and self‐assembly in dilute alkane solutions were investigated. A combination of differential scanning calorimetry (DSC), polarisation optical microscopy (POM) and X‐ray diffraction revealed that the chiral N‐BTA derivatives with branched 3,7‐dimethyloctanoyl chains were liquid crystalline and the mesophase was assigned as Colho. In contrast, N‐BTA derivatives with linear tetradecanoyl or octanoyl chains lacked a mesophase and were obtained as crystalline compounds. Variable‐temperature infrared spectroscopy showed the presence of threefold, intermolecular hydrogen bonding between neighbouring molecules in the mesophase of the chiral N‐BTAs. In the crystalline state at room temperature a more complicated packing between the molecules was observed. Ultraviolet and circular dichroism spectroscopy on dilute solutions of N‐BTAs revealed a cooperative self‐assembly behaviour of the N‐BTA molecules into supramolecular polymers with preferred helicity when chiral alkyl chains were present. Both the sergeants‐and‐soldiers as well as the majority‐rules principles were operative in stacks of N‐BTAs. In fact, the self‐assembly of N‐BTAs resembles closely that of their carbonyl (CO)‐centred counterparts, with the exception that aggregation is weaker and amplification of chirality is less pronounced. The differences in the self‐assembly of N‐ and CO‐BTAs were analysed by density functional theory (DFT) calculations. These reveal a substantially lower interaction energy between the monomeric units in the supramolecular polymers of N‐BTAs. The lower interaction energy is due to the higher energy penalty for rotation around the PhNH bond compared to the PhCO bond and the diminished magnitude of dipole–dipole interactions. Finally, we observed that mixed stacks are formed in dilute solution when mixing N‐BTAs and CO BTAs.

SERS Active Surface Based on Au‐Coated Porous GaN

A. Kaminska, Weyherb, J. Waluk, S. Gawinkowski and R. Holyst

AIP Conference Proceedings 2010, 1267, 954

Sınce the discovery of the surface-enhanced Raman spectroscopy SERS effect on roughened silver electrode surfaces numerous promising substrates have been explored that can be used as efficient SERS-platform. In the last decade broad interest was focused on producing and using nano-structural forms (e.g. nano-columns) as active platforms for immobilization and examination of organic substances. Such platforms, covered by nano-size metal layers (e.g. Au, Ag, Cu), constitutes very sensitive bio-sensors on which different indıvıdual organic molecules can be examıned by SERS Despite the considerable progress that have been made towards improving and optimizing SERS substrates, the fabrication of reproducible SERS platform still remains a challenging task. In this respect a promising approached was described recently, namely the use of porous GaN3 covered by gold and sılver layers.

Reversible aggregation of X-Shaped bolaamphiphiles with partially fluorinated lateral chains at the air/water interface

P. Nitoń, A. Żywociński, R. Hołyst, R. Kieffer, C. Tschierske, J. Paczesny, D. Pociechad and E. Górecka

Chem. Commun., 2010,46, 1896-1898

Langmuir films of four X-shaped bolaamphiphiles were studied using surface pressure and Kelvin potential measurements, Brewster angle microscopy and X-ray reflectivity. The partially fluorinated bolaamphiphiles exhibit an unusual reversibility and reproducibility of Langmuir isotherms, and create very stable and well defined single- or triple layers which can be transferred to solid substrates.

Phase Transition in Salt-Free Catanionic Surfactant Mixtures Induced by Temperature

H. Li, S. A. Wieczorek, Xia Xin, T. Kalwarczyk, N. Ziebacz, T. Szymborski, R. Hołyst, J. Hao, E. Gorecka and D. Pociecha

Langmuir 2010, 26, 1, 34–40

Aggregate transitions in salt-free catanionic surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/fatty acid were investigated as a function of surfactant concentration and temperature. Lauric acid (LA), myristic acid (MA), and palmitic acid (PA) were chosen for the current study. The TTAOH/LA mixture exhibited rich phase behavior at room temperature. With increasing total surfactant concentration (cT), a bluish vesicular (Lαv) phase, an isotropic micellar (L1) phase, and a birefringent lamellar (Lα) phase were observed. Between the Lαv phase and the L1 phase, a narrow Lα′/L1 two-phase region was determined. With increasing temperature, a transition from the Lα phase to the L1 phase was induced at higher cT whereas at lower cT an opposite transition from the L1 phase to the Lαv phase was noticed. Thus surprisingly, we observed bilayer-to-micelle and micelle-to-bilayer transitions in the same catanionic surfactant system, both induced by the temperature increase. Replacing LA by MA and PA caused a continuous increase in the average Krafft point of the mixture. The Lαv-phase region and phase-separated region become larger. Moreover, a single L1-phase region was absent within the investigated temperature range.

Polymer-induced ordering and phase separation in ionic surfactants

E. Kalwarczyk, M. Gołoś, R. Hołyst and M. Fiałkowski

Journal of Colloid and Interface Science 2010, 342, 1, 93-102

We present a new method to induce phase separation in solutions of ionic surfactants. In this method, the phase separation is obtained either by addition of polyelectrolytes or nonionic polymers along with inorganic salt. As a result, the system separates into polyelectrolyte-rich (or nonionic polymer-rich) and surfactant-rich phase. Four types of the mixtures were investigated: (i) anionic surfactants and anionic polyelectrolytes, (ii) cationic surfactants and cationic polyelectrolytes, (iii) cationic surfactants and nonionic polymers, and (iv) anionic surfactants and nonionic polymers. We found that the addition of polyelectrolyte with the charge of the same sign as that of surfactant can induce the phase separation in a wide range of surfactant concentrations. The addition of nonionic polymers induces the phase separation only in solutions of cationic surfactants. Moreover, the addition of nonionic polymers induces the phase separation only for relatively high total content of polymer and surfactant in the mixture. We found however that the addition of inorganic salt to the mixture of cationic surfactant and nonionic polymer triggers the phase separation even for a small concentrations of surfactant. In our experiments, water as well as mixtures of water and polar solvents were employed as solvents. Based on the optical microscopy studies we found that the surfactant-rich phase represents hexagonal ordering.

Incorporation of Carbon Nanotubes into a Lyotropic Liquid Crystal by Phase Separation in the Presence of a Hydrophilic Polymer

X. Xin, H. Li, S. A. Wieczorek, T. Szymborski, E. Kalwarczyk, N. Ziebacz, E. Gorecka, D. Pociecha and R. Hołyst

Langmuir 2010, 26, 5, 3562–3568

Single-walled carbon nanotubes (SWNTs) were incorporated into a lyotropic liquid crystal (LLC) matrix formed by n-dodecyl octaoxyethene monoether (C12E6) at room temperature through spontaneous phase separation induced by nonionic hydrophilic polymer poly(ethylene glycol) (PEG). The quality of SWNTs/LLC composite was evaluated by polarized microscopy observations and small-angle X-ray scattering (SAXS) measurements. The results obtained clearly indicated that SWNTs have been successfully incorporated into the LLC matrix up to a considerable high content without destroying the LLC matrix, although interesting changes of the LLC matrix were also induced by SWNTs incorporation. By varying the ratio of PEG to C12E6, the type of LLC matrix can be controlled from hexagonal phase to lamellar phase. Temperature was found to have a significant influence on the quality of SWNTs/LLC composite, and tube aggregation can be induced at higher temperature. When SWNTs were changed to multiwalled carbon nanotubes (MWNTs), they became difficult to be incorporated into LLC matrix because of an increase in the average tube diameter.

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