Liquid crystal phases in the aqueous colloids of size-controlled fluorinated layered clay mineral nanosheets
TL;DR: Size-controlled nanosheet colloids of fluorohectorite and fluortetrasilicic mica were prepared in high yield and their transitions to fluid liquid crystal phases with highly ordered lamellar structures were identified over a wide concentration range, which is a rare case for clay mineral systems.
About: This article is published in Chemical Communications.The article was published on 2010-06-02. It has received 61 citations till now. The article focuses on the topics: Liquid crystal & Nanosheet.
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TL;DR: Large progress of mechanical and functional properties of self-assembled polymer/nanoclay nacre-mimetics are demonstrated by using synthetic nanoclays with aspect ratios covering three orders in magnitude, and comprehensive relationships among structure formation, nanostructuration, deformation mechanisms and mechanical properties as a function of nanoclay aspect ratio are established.
Abstract: Nacre-mimetics hold great promise as high-performance, functional materials. Here, the authors use synthetic nanoclays and demonstrate tuneable mechanical properties by varying the nanoclay aspect ratio, and suggest a transparent gas barrier application.
241 citations
TL;DR: A critical outlook into the future of this fascinating field of liquid crystal research is provided.
Abstract: Combinations of liquid crystals and materials with unique features as well as properties at the nanoscale are reviewed. Particular attention is paid to recent developments, i.e., since 2007, in areas ranging from liquid crystal-nanoparticle dispersions to nanomaterials forming liquid crystalline phases after surface modification with mesogenic or promesogenic moieties. Experimental and synthetic approaches are summarized, design strategies compared, and potential as well as existing applications discussed. Finally, a critical outlook into the future of this fascinating field of liquid crystal research is provided.
185 citations
TL;DR: This Account introduces an ongoing research project that focuses on the development of molecular robotics funded by MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan), titled "Development of Molecular Robots Equipped with Sensors and Intelligence".
Abstract: ConspectusWhat we can call a molecular robot is a set of molecular devices such as sensors, logic gates, and actuators integrated into a consistent system. The molecular robot is supposed to react autonomously to its environment by receiving molecular signals and making decisions by molecular computation. Building such a system has long been a dream of scientists; however, despite extensive efforts, systems having all three functions (sensing, computation, and actuation) have not been realized yet.This Account introduces an ongoing research project that focuses on the development of molecular robotics funded by MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan). This 5 year project started in July 2012 and is titled “Development of Molecular Robots Equipped with Sensors and Intelligence”.The major issues in the field of molecular robotics all correspond to a feedback (i.e., plan–do–see) cycle of a robotic system. More specifically, these issues are (1) developing molecular sensor...
158 citations
TL;DR: Dynamic polymers were designed with low glass-transition temperature T(g) and bonded by quadruple hydrogen-bonding motifs, and subsequently assembled with high-aspect-ratio synthetic nanoclays to generate nacre-mimetic films, enabling synergistic combinations of stiffness and toughness.
Abstract: Designing the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass-transition temperature Tg and bonded by quadruple hydrogen-bonding motifs, and subsequently assembled with high-aspect-ratio synthetic nanoclays to generate nacre-mimetic films. The high dynamics and self-healing of the polymers render transparent films with a near-perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σUTS≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.
139 citations
TL;DR: An overview of the organization of colloidal charged clay particles in aqueous suspension is presented by studying different natural samples with different structural charges and charge locations through a detailed investigation of the structure factors of the various clay samples.
Abstract: In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson−Boltzmann approach for ionic strength up to 10−3 M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson−Boltzmann treatment shows differences in the repulsive poten...
134 citations
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TL;DR: In this article, it was shown that colloids in general are apt to exhibit considerable deviations from Raoult's law and that crystalline phases retaining a fair proportion of solvent may separate from concentrated solutions.
Abstract: Introdzution. The shapes of colloidal particles are often reasonably compact, so that no diameter greatly exceeds the cube root of the volume of the particle. On the other hand, we know many coiloids whose particles are greatly extended into sheets (bentonite), rods (tobacco virus), or flexible chains (myosin, various Iinear polymers). In some instances, a t least, solutions of such highly anisometric particles are known to exhibit remarkably great deviations from Raoult’s law, even to the extent that an anisotropic phase may separate from a solution in which the particles themselves occupy but one or two per cent of the total volume (tobacco virus, bentonite). We shall show in what follows how such results may arise from electrostatic repulsion between highly anisometric particles. Most colloids in aqueous solution owe their stability more or less to electric charges, so that each particle will repel others before they come into actual contact, and effectively claim for itself a greater volume than what it actuaily occupies. Thus, we can understand that colloids in general are apt to exhibit considerable deviations from Raoult’s law and that crystalline phases retaining a fair proportion of solvent may separate from concentrated solutions. However, if we tentatively increase the known size of the particles by the known range of the electric forces and multiply the resulting volume by four in order to compute the effective van der Waal’s co-volume, we have not nearly enough to explain why a solution of 2 per cent tobacco virus in 0.005 normal NaCZ forms two phases.
4,260 citations
TL;DR: In this paper, a novel nanocomposite hydrogels (NC gels) with a unique organic-inorganic (clay) network structure have been synthesized by in-situ free radical polymerization.
Abstract: Novel nanocomposite hydrogels (NC gels) with a unique organic-inorganic (clay) network structure (see Figure) have been synthesized by in-situ free radical polymerization. The resulting NC gels exhibit high structural homogeneity, superior elongation with near-complete recovery, good swellability, and rapid deswelling in response to temperature changes.
1,841 citations
TL;DR: In this article, a layered protonic titanate of lepidocrocite-type was exfoliated on the action of an aqueous solution of tetrabutylammonium (hereafter TBA) hydroxide, resulting in a stable colloidal suspension.
Abstract: A layered protonic titanate of lepidocrocite-type, HxTi2-x/4□x/4O4·H2O (x ∼ 0.7; □, vacancy), has been exfoliated on the action of an aqueous solution of tetrabutylammonium (hereafter TBA) hydroxide, which resulted in a stable colloidal suspension. A colloidal aggregate centrifuged from the suspension was examined by an in situ X-ray diffraction technique under conditions where drying speed was controlled. The diffraction immediately after separation from the liquid phase was principally amorphous except for a series of sharp reflections detected in a small angle scattering region. On the basis of the line profile analysis, the latter diffraction feature was accounted for by the fundamental intersheet interference of a spacing >10 nm, which demonstrates the existence of a novel associated pair of the titanate nanosheets accommodating a large volume of water cluster between them. These XRD data provide persuasive evidence for delamination into single layers. Upon drying, the amorphous halo disappeared and ...
749 citations
TL;DR: In this paper, it was shown that the Coulomb attraction between the micelles and the oppositely charged ions in the solution gives an excess of attractive force which must be balanced by the dispersive action of thermal agitation and another repulsive force.
Abstract: The formation of tactoids from thixotropic sols, of Schiller layers from iron‐oxide sols, the separation of tobacco virus solutions and bentonite sols into two liquid layers and the crystallization of proteins are regarded as examples of unipolar coacervation (micelles having like charges) which must involve attractive forces.Kallmann, Willstatter, Freundlich, De Boer, Hamaker, Houwink and others have assumed that the attraction is due to van der Waals forces. They have also analyzed the stability of colloid systems by diagrams giving the potential energy as a function of the distance between micelles. It is now shown that the Coulomb attraction between the micelles and the oppositely charged ions in the solution gives an excess of attractive force which must be balanced by the dispersive action of thermal agitation and another repulsive force. Thus there is no need to assume long range van der Waals forces. The past use of energy diagrams is criticized because it has ignored the effect of the thermal agitation and the attraction of the ``gegenions'' in solution. Instead of potential energy it is proposed that osmotic pressure p be used, which includes these previously neglected factors. A maximum in p as the colloid concentration increases is the condition for the separation into two phases (coacervation).The Debye‐Huckel theory (1st approximation) for the osmotic pressure of electrolytes takes into account both these factors and permits a rough calculation of the conditions under which coacervation occurs. The 2nd approximation, which considers particle size, does not agree as well with experiment as the first approximation. The reasons for this lack of agreement are discussed.The micelles in unipolar coacervates are not in contact, but are separated by relatively large distances (10–5000A). Either a specific repulsive force or a decrease in the Coulomb attraction as the concentration increases (due to decreased charges on micelles) can account for stable coacervates. The assumption of a definite ζ‐potential, rather than a definite charge on the micelles, gives automatically just such a decrease in attraction.The general mathematical theory of coacervation presents great difficulties because the approximations of the Debye‐Huckel theory cannot be used. However, the one‐dimensional problem of the forces acting between parallel colloidal platelets can be solved rigorously in terms of elliptic integrals. For highly charged particles in sufficiently dilute solutions of electrolytes, the pressure p in the liquid between the two plates is given by p = (π/2)D(kT/eb)2 = 8.9×10—7/b2 dynes/cm2 where b is the distance in cm between the plates and D is the dielectric constant (81 for water at T = 293°K). This pressure which tends to force the plates apart is independent of the charge on the plates and on the electrolyte concentration (univalent ions only). Polyvalent ions decrease the force. This force is of the right magnitude to account for the stability of unipolar coacervates. It also furnishes a quantitative explanation of the Jones‐Ray effect, by which low salt concentrations decrease the capillary rise in surface tension experiments with water.Experimental determinations were made of the relaxation times τ for the decay of birefringence in bentonite and vanadium pentoxide sols, after stirring was stopped. In one sample of bentonite, τ varied with the 22nd power of the concentration, while in V2O5 sols the exponent was 1.8. The temperature coefficients of τ were also measured and the activation energies were calculated.A theory of the relaxation of birefringence was developed, according to which the micelles in dilute thixotropic bentonite sols are arranged normally in a cubic lattice (isotropic). Temporary shear in the liquid orients the micelles and produces birefringence although the lattice remains cubic. The experimental data confirm the theory and indicate that the energy barrier opposing reorientation of micelles in a particular bentonite sol varied with the inverse 20th power of the distance between the micelles. With V2O5 this exponent was about 4. Further support for the theory was obtained by experiments which gave ``angles of isocline'' for bentonite particles in a flowing sol that varied from 65° to 78°.In bipolar coacervates (which contain micelles of unlike polarities) the electric fields and the charges on the micelles increase as the micellar concentration increases. When a certain concentration is reached, the field rises to a value so high as to cause increased hydration which holds the micelles apart and gives stability to the coacervate.
634 citations
TL;DR: The lack of difference in the band gap energies for titania nanosheet electrodes with different numbers of layers suggests that a Nanosheet is electronically isolated in multilayer assemblies without affecting the electronic state of neighboring nanosheets.
Abstract: Electrochemical and photoelectrochemical studies were conducted on self-assembled multilayer films of titania nanosheets on a conductive ITO substrate. Cyclic voltammogram (CV) curves indicated that the titania nanosheet electrode underwent insertion/extraction of Li+ ions into/from the nanosheet galleries, associated with reduction/oxidation of Ti4+/Ti3+. These processes accompanied reversible changes in UV−vis absorption of the titania nanosheet electrodes. Applying a negative bias of −1.3 V (vs Ag/Ag+) and lower brought about absorption reduction where the wavelength is shorter than 323 nm, and vice versa, indicating a flat-band potential of (approximately) −1.3 V and a band gap energy of 3.84 eV. Photocurrents were generated from the titania nanosheet electrodes under a positive bias. The onset potential for photocurrent generation from the titania nanosheet electrodes was around −1.27 V, and the band gap energy estimated from the photocurrent action spectra was 3.82 eV, in excellent agreement with th...
493 citations