Soft Matter Science Research Articles

Capillary interactions between anisotropic particles

Micro and nanoparticle adsorption to and assembly by capillarity at fluid–fluid interfaces are intriguing aspects of soft matter science with broad potential in the directed assembly of anisotropic media. The importance of the field stems from the ubiquitous presence of multiphase systems, the malleability of fluid interfaces, and the ability to tune the interactions of the particles adsorbed on them. While homogeneous spherical particles at interfaces have been well studied, the behavior of anisotropic particles – whether the anisotropy originates from shape or chemical heterogeneity – has been considered only very recently. We review recent advances in the field of anisotropic particles at fluid interfaces, by focusing on particles in the micron and submicron range. We discuss capillary adsorption, orientation, migration, and self-assembly, on planar and curved interfaces, and the rheology of particle-laden interfaces. Prospects for future work and outstanding challenges are also discussed.

High frequency soft phononics

Phononic crystals, the acoustic equivalents of the photonic crystals, are controlled by a larger number of material parameters. The study of hypersonic crystals imposes substantial demand on fabrication and characterization techniques. Colloid and polymer science offer methods to create novel materials that possess periodic variations of density and elastic properties at mesoscopic length scales commensurate with the wave length of hypersonic phonons and hence photons of the visible light. Polymer- and colloid-based phononics is an emerging new field at the interface of soft materials science and condensed matter physics with rich perspectives ahead. The key quantity is the dispersion of high frequency (GHz) acoustic excitations which is nowadays at best measured by high resolution spontaneous Brillouin light scattering. Depending on the components of the nanostructured composite materials, the resolved vibration eigenmodes of the individual particles sensitively depend on the particle architecture and their thermo-mechanical properties [T. Still et al., Nano Lett. 10, 3194 (2008)]. In periodic structures of polymer based colloids, the dispersion relation ω(k) between the frequency and the phonon wave vector k has revealed hypersonic phononic band gaps of different nature [T. Still et al., Phys. Rev. Lett. 106, 175505 (2011)].

Linac Coherent Light Source soft x-ray materials science instrument optical design and monochromator commissioning

We present the x-ray optical design of the soft x-ray materials science instrument at the Linac Coherent Light Source, consisting of a varied line-spaced grating monochromator and Kirkpatrick-Baez refocusing optics. Results from the commissioning of the monochromator are shown. A resolving power of 3000 was achieved, which is within a factor of two of the design goal.

Sensing membrane stress with near IR-emissive porphyrins.

Probes embedded within a structure can enable prediction of material behavior or failure. Carefully assembled composites that respond intelligently to physical changes within a material could be useful as intrinsic sensors. Molecular rotors are one such tool that can respond optically to physical environmental changes. Here, we propose to use molecular rotors within a polymersome membrane to report membrane stress. Using supermolecular porphyrin-based fluorophores as rotors, we characterize changes in the optical emission of these near-infrared (NIR) emissive probes embedded within the hydrophobic core of the polymersome membrane. The configuration of entrapped fluorophore depends on the available space within the membrane; in response to increased volume, emission is blue shifted. We used this feature to study how shifts in fluorescence correlate to membrane integrity, imparted by membrane stress. We monitored changes in emission of these porphyrin-based fluorophores resulting from membrane stress produced through a range of physical and chemical perturbations, including surfactant-induced lysis, hydrolytic lysis, thermal degradation, and applied stress by micropipette aspiration. This paper comprehensively illustrates the potential for supermolecular porphyrin-based fluorophores to detect intrinsic physical changes in a wide variety of environments, and suggests how molecular rotors may be used in soft materials science and biology as sensors.

Periodic Space Partitioners (PSP) and their relations to Crystal Chemistry

AbstractWe are looking back on 30 years development of periodic space partitioners (PSP) and their relations to their periodic relatives,i.e.minimal surfaces (PMS), zero potential surfaces (P0PS), nodal surfaces (PNS), and exponential scale surfaces. Hans-Georg von Schnering and Sten Andersson have pioneered this field especially in terms of applications to crystal chemistry. This review relates the early attempts to approximate periodic minimal surfaces which established a systematic classification of all PSP in terms space group symmetry and consecutive applications in a variety of different fields. A consistent nomenclature is outlined and different methods for deriving PSP are described. Characteristic structure factor sets which solely define PNS by can be used to discriminate structure types of a given symmetry or even to determine complicated crystal structures. The concept of PSP relates space group symmetry, topology, and chemical bonding in an intriguing way and tessellations on PSP which can be generated in a straight forward way allow to predict new framework types. Through transformation of such continuous topological forms a new entry has been found for understanding and interpreting reconstructive phase transitions. Finally we indicate the importance of PSP models for soft matter science.

Nanotechnology with Soft Matter: From Structures to Functions

Soft matter science is a multidisciplinary area of chemistry, physics, biology, and materials science. It essentially deals with matter such as functional polymers, amphiphiles, liquid crystals, colloids, and a number of biological molecules, in which the typical energies of interaction are comparable to thermal energies.[1] Nanotechnology involves understanding and controlling matter typically on the sub-100-nanometer scale, where unique phenomena enable novel and functional applications.[2] The endeavor in nanotechnology is to identify the chemical and physical consequences of the miniaturization and to develop nanoscale functional materials and devices, which differ in fundamental properties from the individual molecules or bulk matter.[2,3] When nanotechnology meets soft matter, the fi rst question that arises is how the soft building blocks can be tailored, manipulated, and assembled into nanostructures. This is one of the fundamental focuses in the materials research frontier. This focus has led to the generation of a broad range of soft nanoscale structures such as supramolecular architectures, gels, vesicles, polymer brushes, molecular aggregates, nanofi bers, and nanotubes. The goal of such soft nanomaterials is

The chiral structure of porous chitin within the wing-scales of Callophrys rubi

The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4₁32, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable example of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid-protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.

Gel electrophoresis in suspensions of charged spherical particles

Gel-electrophoresis, the migration of colloidal particles through a polymer gel in response to an applied electric field, is investigated theoretically in this study. It is a very powerful technique widely used in soft matter science. Both the short range steric effect (due to the direct contact friction between the gel and the migrating particles) and the long range hydrodynamic effect (due to the hydrodynamic force of the gel exerted upon the liquid suspension) are considered with the particle mobility calculated as the product of the predictions from these two approaches separately. Brinkman fluid is assumed to model the polymer gel and Kuwabara's unit cell model is employed to represent the suspension of particles. A pseudo-spectral method is adopted to solve the resulting general electrokinetic equations. We find, among other things, that the deformation of ion clouds surrounding the particles due to the convection flow within the porous gels deters the particle motion significantly, as an induced electric field opposite to the applied electric field is generated, an effect referred to as the polarization effect here. The higher the surface potential of the particle is, the more significant the reduction of mobility due to this polarization effect. Local extrema are observed in the mobility profiles with varying double layer thickness around κa = 1, where κ is the reciprocal of Debye length, and a is the particle radius, as the polarization effect manifests itself there in general. The presence of the gel retards the particle motion in general. The poorer the permeability is, the more severe the reduction. On the other hand, the more concentrated the particle suspension is, the slower the particle motion in general, due to the hindrance effect between neighboring particles. Moreover, the involvement of polarization and overlapping effects of the double layer further complicates the electrophoretic behavior of the particle, which is discussed in detail. Excellent agreement is obtained between the results reported here and the experimental data available in the literature for gold nanoparticles in dilute suspensions. The current study greatly extends the theoretical analysis scope of gel-electrophoresis from previous dilute suspensions only to concentrated ones as well, which are encountered frequently in practical applications in biological and biochemical fields, as well as other fields involving soft matters such as colloids and polymer gels.

BioRef – a time-of-flight neutron reflectometer combined with in-situ infrared spectroscopy at the Helmholtz Centre Berlin

The novel BioRef reflectometer currently under construction in neutron guidehall-I of the BER-2 reactor at the Helmholtz Centre Berlin is designed for applications in soft matter science at solid-liquid interfaces especially under dynamic conditions. In addition to a time-of-flight (TOF) approach to be realised with three choppers in order to adapt resolutions and wavelength bands to the needs of specific applications, the instrument will be equipped with an in-situ infrared (IR) spectrometer operating in its surface sensitive ATR-geometry for simultaneous spectroscopic and conformational studies. The instrument will become operational in 2010.

Design of an electron microscope phase plate using a focused continuous-wave laser

We propose a Zernike phase contrast electron microscope that uses an intense laser focus to convert a phase image into a visible image. We present the relativistic quantum theory of the phase shift caused by the laser–electron interaction, study resonant cavities for enhancing the laser intensity and discuss applications in biology, soft-materials science and atomic and molecular physics.

Shear-induced reaction-limited aggregation kinetics of Brownian particles at arbitrary concentrations

The aggregation of interacting brownian particles in sheared concentrated suspensions is an important issue in colloid and soft matter science per se. Also, it serves as a model to understand biochemical reactions occurring in vivo where both crowding and shear play an important role. We present an effective medium approach within the Smoluchowski equation with shear which allows one to calculate the encounter kinetics through a potential barrier under shear at arbitrary colloid concentrations. Experiments on a model colloidal system in simple shear flow support the validity of the model in the concentration range considered. By generalizing Kramers' rate theory to the presence of shear and collective hydrodynamics, our model explains the significant increase in the shear-induced reaction-limited aggregation kinetics upon increasing the colloid concentration.

Single Molecules as Optical Nanoprobes for Soft and Complex Matter

The optical signals of single molecules provide information about structure and dynamics of their nanoscale environment, free from space and time averaging. These new data are particularly useful whenever complex structures or dynamics are present, as in polymers or in porous oxides, but also in many other classes of materials, where heterogeneity is less obvious. We review the main uses of single molecules in studies of condensed matter at nanometer scales, especially in the fields of soft matter and materials science. We discuss several examples, including the orientation distribution of molecules in crystals, rotational diffusion in glass-forming molecular liquids, polymer studies with probes and labeled chains, porous and heterogeneous oxide materials, blinking of single molecules and nanocrystals, and the potential of surface-enhanced Raman scattering for local chemical analysis. All these examples show that static and dynamic heterogeneities and the spread of molecular parameters are much larger than previously imagined.

Multiscale simulation of soft matter systems

This paper gives a short introduction to multiscale simulation approaches in soft matter science. This paper is based on and extended from a previous review. (1. C. Peter and K. Kremer, Soft Matter, 2009, DOI:10.1039/b912027k.) It also includes a discussion of aspects of soft matter in general and a short account of one of the historically underlying concepts, namely renormalization group theory. Some different concepts and several typical problems are shortly addressed, including a (more personal) view on challenges and chances.

What Factors Determine Hierarchical Structure of Microbial Cellulose – Interplay among Physics, Chemistry and Biology –

AbstractA microbial cellulose film (pellicle), prepared by Acetorbactor xylinum, is a supramolecule system, absorbing a huge amount of water (99% by weight). To elucidate the affinity to water, we investigated the hierarchical structure in a pellicle by using ultra‐small‐angle and small‐angle neutron scattering, observing a wide range of length scales from nm to µm. We successfully determined mass fractal dimensions for the amorphous structure, which hierarchically varies local concentration fluctuations, bundle and network, appeared as the length scale increases. On a basis of these findings, we discuss to address a question what factors determine the hierarchy in the microbial cellulose. This is a new topic of soft matter science, regarded as reaction‐induced self‐assembly in a non‐equilibrium open system, therein soft matter physics, biochemistry and cell biology crucially interplay.

Multiscale Simulation of Soft Matter: From Scale Bridging to Adaptive Resolution

The relation between atomistic chemical structure, molecular architecture, molecular weight, and material properties is of basic concern in modern soft material science and includes standard properties of bulk materials and surface and interface aspects, as well as the relation between structure and function in nanoscopic objects and molecular assemblies of both synthetic and biological origin. This all implies a thorough understanding on many length and correspondingly time scales, ranging from (sub)atomistic to macroscopic. Presently, computer simulations play an increasingly important, if not central, role. Some problems do not require specific atomistic details, whereas others require them only locally. However, in many cases this strict separation is not sufficient for a comprehensive understanding of systems, and flexible simulation schemes are required that link the different levels of resolution. We here give a general view of the problem regarding soft matter and discuss some specific examples of linked simulation techniques at different resolution levels. We then discuss a recently developed flexible simulation scheme, the AdResS method, which allows one to adaptively change the resolution in certain regions of space on demand.

Simulation approaches to soft matter: Generic statistical properties vs. chemical details

The relation between atomistic structure, architecture, molecular weight and material properties is a basic concern of modern soft material science. This by now goes far beyond standard properties of bulk materials. A typical additional focus is on surface or interface aspects or on the relation between structure and function in nanoscopic molecular assemblies. This all implies a thorough understanding on many length and correspondingly time scales ranging from (sub-)atomic to macroscopic. At this point computer simulations are playing an increasingly important, if not the central role. Traditionally simulations have been separated in two main groups, namely simplified models to deal with generic or universal aspects of polymers, i.e. critical exponents, and those employing classical force field simulations with (almost) all atomistic detail, i.e. for the diffusion of small additives in a small “sample”. Still characteristic problems, which require huge systems and/or long times in combination with a chemistry specific model, cannot be tackled by these methods alone. More recently with the development of scale bridging or multiscale simulation techniques, these different approaches have been combined into an emerging rather powerful tool. It is the purpose of this contribution to give a few examples of how such an approach can be used to understand specific material properties.

Simulation studies of soft matter: generic statistical properties and chemical details

The relation between atomistic structure, architecture, molecular weight and material properties is a basic concern of modern soft material science. This by now goes far beyond standard properties of bulk materials. A typical additional focus is on surface or interface aspects or on the relation between structure and function in nanoscopic molecular assemblies. This all implies a thorough understanding on many length and correspondingly time scales ranging from (sub)-atomic to macroscopic. At this point computer simulations are playing an increasingly important, if not the central role. Traditionally simulations have been separated in two main groups, namely simplified models to deal with generic or universal aspects of polymers, i.e. critical exponents, and those employing classical force field simulations with (almost) all atomistic detail, i.e. for the diffusion of small additives in a small “sample”. Still characteristic problems, which require huge systems and/or long times in combination with a chemistry specific model, cannot be tackled by these methods alone. More recently with the development of scale bridging or multi scale simulation techniques, these different approaches have been combined into an emerging rather powerful tool. It is the purpose of this contribution to give a few examples of how such an approach can be used to understand specific material properties.

Spontaneous macroscopic carbon nanotube alignment via colloidal suspension in hexagonal columnar lyotropic liquid crystals.

The self-assembly of amphiphilic molecules in aqueous solution into lyotropic liquid crystals (LCs), characterised by soft yet long-range ordered nanoscale structures, constitutes a fascinating phenomenon at the heart of soft matter science which can be employed in a manifold of creative ways. Particularly interesting structures may arise as a result of functionalisation of the LC with appropriate guest molecules, adopting the order of their host. Here we combine cat- and anionic surfactants to form a liquid-crystalline colloidal suspension of carbon nanotubes (CNTs), which by virtue of the spontaneously formed hexagonal columnar LC structure are uniaxially aligned over macroscopic areas. The nanotube concentration can be so high, with sufficiently uniform alignment, that the mixture becomes a fluid linear polariser, the anisotropic optical properties of CNTs having been transferred to macroscopic scale by the LC. Moreover, thin and highly aligned filaments can be drawn and deposited in selected directions on arbitrary surfaces, after which the LC template can be rinsed away. Combined with recently developed methods for CNT fractionation according to chirality, the technique would yield an unprecedented degree of control in the practical realisation of carbon nanotube-based devices and materials.

グローイングポリマー

The author has been studied polymerization systems by using small-angle neutron scattering (SANS) technique in the research group of soft matter science and neutron scattering at Japan Atomic Energy Agency since 2003. SANS technique played an important role to examine a growing single polymer chain and hierarchically ordered structures in polymerization solution. The author hopes that neutron beam will give a breakthrough for the comprehension and development for the research field of polymer synthesis.

FIB/SEM for Soft Matter and Life Sciences

Focused Ion Beams (FIBs) provide a sharp ion cross-sectioning tool for soft or biological materials to etch, mill and image the sample surface and the exposed sections. The area of FIB sectioning/imaging of biomaterials is one that is sadly neglected, compared with studies on inorganic materials. In combination with a Scanning Electron Microscope (SEM), FIB makes electron and ion microscopy available at the same time, providing complementary morphological information and, sometimes, facing charge problems.