References of "Soft Matter"
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See detailInfluence of interface stabilisers and surrounding aqueous phases on nematic liquid crystal shells
Noh, Junghyun UL; Reguengo De Sousa, Kevin; Lagerwall, Jan UL

in Soft Matter (2015), in press

We investigate the nematic–isotropic (N–I) transition in shells of the liquid crystal 5CB, surrounded by aqueous phases that conven- tionally are considered to be immiscible with 5CB. The aqueous phases ... [more ▼]

We investigate the nematic–isotropic (N–I) transition in shells of the liquid crystal 5CB, surrounded by aqueous phases that conven- tionally are considered to be immiscible with 5CB. The aqueous phases contain either sodium dodecyl sulfate (SDS) or polyvinyl alcohol (PVA) as stabiliser, the former additionally promoting homeotropic director alignment. For all shell configurations we find a depression of the clearing point compared to pure 5CB, indicating that a non-negligible fraction of the constituents of the surrounding phases enter the shell, predominantly water. In hybrid- aligned shells, with planar outer and homeotropic inner boundary (or vice versa), the N–I transition splits into two steps, with a consequent three-step textural transformation. We explain this as a result of the order-enhancing effect of a monolayer of radially aligned SDS molecules adsorbed at the homeotropic interface. [less ▲]

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See detailMobility restrictions and glass transition behaviour of an epoxy resin under confinement
Djemour, A.; Sanctuary, Roland UL; Baller, Jörg UL

in Soft Matter (2015), 11(13), 2683-2690

Confinement can have a big influence on the dynamics of glass formers in the vicinity of the glass transition. Already 40 to 50 K above the glass transition temperature, thermal equilibration of glass ... [more ▼]

Confinement can have a big influence on the dynamics of glass formers in the vicinity of the glass transition. Already 40 to 50 K above the glass transition temperature, thermal equilibration of glass formers can be strongly influenced by the confining substrate. We investigate the linear thermal expansion and the specific heat capacity c(p) of an epoxy resin (diglycidyl ether of bisphenol A, DGEBA) in a temperature interval of 120 K around the glass transition temperature. The epoxy resin is filled into controlled pore glasses with pore diameters between 4 and 111 nm. Since DGEBA can form H-bonds with silica surfaces, we also investigate the influence of surface silanization of the porous substrates. In untreated substrates a core/shell structure of the epoxy resin can be identified. The glass transition behaviours of the bulk phase and that of the shell phase are different. In silanized substrates, the shell phase disappears. At a temperature well above the glass transition, a second transition is found for the bulk phase - both in the linear expansion data as well as in the specific heat capacity. The c(p) data do not allow excluding the glass transition of a third phase as being the cause for this transition, whereas the linear expansion data do so. The additional transition temperature is interpreted as a separation between two regimes: above this temperature, macroscopic flow of the bulk phase inside the porous structure is possible to balance the mismatch of thermal expansion coefficients between DGEBA and the substrate. Below the transition temperature, this degree of freedom is hindered by geometrical constraints of the porous substrates. Moreover, this second transition could also be found in the linear expansion data of the shell phase. [less ▲]

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See detailStrong Effect ofWeak Charging in Suspensions of Anisotropic Colloids
Dorosz, Sven UL; Shegokar, Nikhilesh; Schilling, Tanja UL et al

in Soft Matter (2014)

Suspensions of hard colloidal particles frequently serve as model systems in studies on fundamental aspects of phase transitions. But often colloidal particles that are considered as ``hard'' are in fact ... [more ▼]

Suspensions of hard colloidal particles frequently serve as model systems in studies on fundamental aspects of phase transitions. But often colloidal particles that are considered as ``hard'' are in fact weakly charged. If the colloids are spherical, weak charging has a only a weak effect on the structural properties of the suspension, which can be easily corrected for. However, this does not hold for anisotropic particles. We introduce a model for the interaction potential between charged ellipsoids of revolution (spheroids) based on the Derjaguin approximation of Debye--Hückel Theory and present a computer simulation study on aspects of the system's structural properties and phase behaviour. In line with previous experimental observations, we find that even a weak surface charge has a strong impact on the correlation functions. A likewise strong impact is seen on the phase behaviour, in particular, we find stable cubatic order in suspensions of oblate ellipsoids. [less ▲]

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See detailMolecular versus macroscopic perspective on the demixing transition of aqueous PNIPAM solutions by studying the dual character of the refractive index
Philipp, Martine UL; Aleksandrova, Ralitsa UL; Müller, Ulrich UL et al

in Soft Matter (2014), 10(37), 7297-7305

The phase separation of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions is known to strongly affect their volume expansion behaviour and the elastic moduli, as the latter are strongly coupled to ... [more ▼]

The phase separation of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions is known to strongly affect their volume expansion behaviour and the elastic moduli, as the latter are strongly coupled to the macroscopic order parameter. On the molecular scale, considerable changes in H-bonding and hydrophobic interactions, as well as in the structure govern the demixing process. However, the relationship between the molecular and macroscopic order parameters is unclear for such complex phase-separating solutions. We contribute to the clarification of this problem by relating optical to volumetric properties across the demixing transition of dilute to concentrated aqueous PNIPAM solutions. Far from the demixing temperature, the temperature dependence of the refractive index is predominantly determined by thermal expansion. In the course of phase separation, the refractive index is dominated by the anomalous behaviour of the specific refractivity, which reflects the spatio-temporally averaged changes in molecular interactions and the structural reorganization of the demixing solutions. Moreover, the presence of relaxation processes is studied by the complex expansion coefficient using the novel technique of temperature modulated optical refractometry. [less ▲]

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See detailKinetic processes at the demixing transition of PNIPAM solutions
Philipp, Martine UL; Müller, Ulrich UL; Jiménez Riobóo et al

in Soft Matter (2013), 9

Kinetic processes, which are joined with mass transport, are studied in the vicinity of the sharp LCST-type demixing transition of semi-dilute aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions ... [more ▼]

Kinetic processes, which are joined with mass transport, are studied in the vicinity of the sharp LCST-type demixing transition of semi-dilute aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions. These processes are slow as compared to the highly cooperative collapse of individual polymer chains. Purely elastic properties, that are particularly sensitive to this phase transition, are addressed depending on the temperature, space and time by Brillouin spectroscopy. Above the demixing temperature Tc, we discriminate between kinetics related to the phase separation into PNIPAM-rich and PNIPAM-poor domains and kinetics connected to the impact of gravitation on the on-going phase separation. Using shallow temperature jumps of 0.3 C, the growth of compact PNIPAM-rich agglomerates with identical gel-like mechanical consistency is provoked independently of temperature and position within the sample above Tc. Astonishingly, the transition temperature does not vary while heating or cooling the solutions across the phase transition, although the elastic properties depend strongly on space and time during the equilibration of PNIPAM concentration gradients following the re-entrance into the lowtemperature phase. [less ▲]

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See detailImmense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions
Philipp, Martine UL; Müller, Ulrich UL; Aleksandrova, Ralitsa UL et al

in Soft Matter (2013), 9

Elastic nonlinearities are particularly relevant for soft materials because of their inherently small linear elasticity. Nonlinear elastic properties may even take over the leading role for the ... [more ▼]

Elastic nonlinearities are particularly relevant for soft materials because of their inherently small linear elasticity. Nonlinear elastic properties may even take over the leading role for the transformation at mechanical instabilities accompanying many phase transitions in soft matter. Because of inherent experimental difficulties, only little is known about third order (nonlinear) elastic constants within liquids, gels and polymers. Here we show that a key concept to access third order elasticity in soft materials is the determination of mode Gr¨uneisen parameters. We report the first direct observation of third order elastic constants across mechanical instabilities accompanying the liquid–liquid demixing transition of semi-dilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions. Immense elastic nonlinearities, leading to a strong strain-softening in the phase-separating PNIPAM solutions, are observed. Molecular mechanisms, which may be responsible for these immense elastic nonlinearities, are discussed. The importance of third order elastic constants in comparison to second order (linear) elastic constants in the demixing PNIPAM solutions evidences the need to focus more on the general role played by nonlinear elasticity at phase transitions within synthetic and biological liquids and gels. [less ▲]

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See detailTowards tunable defect arrangements in smectic liquid crystal shells utilizing the nematic-smectic transition in hybrid-aligned geometries
Liang, Hsin-Ling; Zentel, Rudolf; Rudquist, Per et al

in Soft Matter (2012), 8(20), 5443-5450

We produce and investigate liquid crystal shells with hybrid alignment—planar at one boundary, homeotropic at the other—undergoing a transition between the nematic (N) and smectic-A (SmA) phases. The ... [more ▼]

We produce and investigate liquid crystal shells with hybrid alignment—planar at one boundary, homeotropic at the other—undergoing a transition between the nematic (N) and smectic-A (SmA) phases. The shells display a dynamic sequence of patterns, the details depending on the alignment agents and on the diameter and thickness of the shell. In shells of sufficient diameter we typically find a transient striped texture near the N–SmA transition, stabilising into a pattern of tiled, more or less regularly spaced focal conic domains in the SmA phase. The domain size and spacing decrease with reduced shell thickness. In case of strong homeotropic anchoring at one boundary and small shell size, however, the increased curvature favors homeotropic against planar alignment in the smectic phase, and the shell then tends to adapt to complete homeotropic alignment at the final stage of the transition. This is the first study of hybrid-aligned smectic shells and the results constitute a beautiful demonstration of the capacity for dynamic structure formation and reformation via self-assembly in soft matter. The new patterns extend the range of arrays of topological defects that can be realised with liquid crystals in spherical morphology and the correlation between the feature arrangements and the variable parameters of the shell and its environment opens a route towards tunability. However, the observed strong impact from increasing curvature, even for these rather large shells, indicates that the choice of alignment agents inducing planar or homeotropic alignment with varying strength will become critical when targeting the most attractive colloidal size scale of about a micron or smaller. [less ▲]

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See detailOn the elastic nature of the demixing transition of aqueous PNIPAM solutions
Phillip, M.; Müller, Ulrich UL; Aleksandrova, Ralitsa UL et al

in Soft Matter (2012), 8

Mechanical instabilities accompanying the demixing transition of semi-dilute aqueous poly(Nisopropylacrylamide) (PNIPAM) solutions are probed for the first time with Brillouin spectroscopy, densitometry ... [more ▼]

Mechanical instabilities accompanying the demixing transition of semi-dilute aqueous poly(Nisopropylacrylamide) (PNIPAM) solutions are probed for the first time with Brillouin spectroscopy, densitometry and refractometry. The particular role of the elastic moduli and the mass density at this coil-to-globule transition followed by molecular aggregation is investigated. Even though the demixing transition of PNIPAM solutions is denoted as a volume phase transition, it turns out that this transition is governed by the elastic properties, instead of the volume properties. This is consistent with earlier findings made for the demixing transition in chemically cross-linked PNIPAM hydrogels. Above the demixing temperature, Brillouin spectroscopy discriminates compact PNIPAM-rich agglomerates with sizes larger than 200 nm. Interestingly, these agglomerates possess a sharp distribution of elastic moduli, which can be attributed without any doubt to a material with gel-like mechanical consistency. Thus the phase-separated PNIPAM-rich agglomerates are not in the glassy state. [less ▲]

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See detailFilament formation in carbon nanotube-doped lyotropic liquid crystals
Schymura, Stefan; Dölle, Sarah; Yamamoto, Jun et al

in Soft Matter (2011), 7(6), 2663-2667

By introducing carbon nanotubes (CNTs) into lyotropic nematic liquid crystals, strongly enhanced viscoelastic behaviour results, allowing the extraction of very thin and long filaments in which the CNTs ... [more ▼]

By introducing carbon nanotubes (CNTs) into lyotropic nematic liquid crystals, strongly enhanced viscoelastic behaviour results, allowing the extraction of very thin and long filaments in which the CNTs are uniformly aligned. The filament formation requires the liquid crystallinity of the host phase and it does not take place for coarsely dispersed nanotubes or if their concentration is below a threshold value. The type of nanotube plays only a small role, single- as well as multiwall CNTs both trigger the filament formation, but spherical C60 fullerenes do not give rise to the phenomenon. We argue that individualized CNTs stiffen the rod-shaped micelles of the liquid crystal host and that the elongational flow then increases the nematic long-range order as well as the micelle length. If the CNTs are present at a sufficient concentration to connect in continuous linear chains of arbitrary extension, the micelle stiffening is ensured regardless of length, taking the system into a positive feedback loop between increasing orientational order and diverging micelle length. It is this percolation-like transition to aligned and quasi-infinite micelles stabilized by chains of nanotubes that makes the filament formation possible. [less ▲]

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See detailOn the interplay between matter transport and structure formation at epoxy-hardener interfaces visualized by scanning Brillouin microscopy
Philipp, Martine UL; Müller, Ulrich UL; Sanctuary, Roland UL et al

in Soft Matter (2011), 7(1), 118-124

Structural developments are investigated in network-forming reactive polymers by time- and 10 space-resolved scanning Brillouin microscopy. Hypersonic properties are probed to reveal the subtle interplay ... [more ▼]

Structural developments are investigated in network-forming reactive polymers by time- and 10 space-resolved scanning Brillouin microscopy. Hypersonic properties are probed to reveal the subtle interplay between molecular transport, dissolution, polymerization and network defects in the vicinity of the interface between reactants, which are either pure epoxy resin or various epoxy resin-hardener mixtures, topped by a layer of pure hardener. The trans-interfacial polymerization produces heterogeneous epoxy structures of either gelatinous or glassy nature. Interestingly, the 15 hardener can easily penetrate and swell these networks and epoxy network fragments can be transported over several millimeters by convective flow. The observed features may be used to form interpenetrating networks during self-healing procedures. [less ▲]

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See detailEffects of chain branching and chirality on liquid crystalline phases of bent-core molecules: blue phases, de Vries transitions and switching of diastereomeric states
Ocak, Hale; Bilgin-Eran, Belkiz; Prehm, Marko et al

in Soft Matter (2011), 7(18), 8266-8280

Bent-core molecules based on a resorcinol bisbenzoate core with a series of distinct substituents in different positions at the central resorcinol core have been synthesized and characterized. The focus ... [more ▼]

Bent-core molecules based on a resorcinol bisbenzoate core with a series of distinct substituents in different positions at the central resorcinol core have been synthesized and characterized. The focus is on the effect of branched terminal groups in the racemic and chiral forms on the mesomorphic properties. These were investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray diffraction, electro-optic and dielectric methods. Only bent-core mesogens derived from 4- cyanoresorcinol exhibit liquid crystalline phases and the mesophases of these compounds are strongly influenced by the branching and enantiomeric composition of the terminal chains. Depending on the structure of the rod-like wings and the enantiomeric composition, cybotactic nematic phases (NcybC), BPIII-like isotropic mesophases (BPIIIcybC*) and various polar and apolar smectic phases (SmA, SmC, SmC*, SmCsPA, SmCsPA*) are formed. For one compound, a de Vries type smectic phase is observed and it appears that with decreasing temperature, order develops in two steps. First, at the SmA to SmC transition, the tilt direction becomes long range ordered and in a second step a long range ordering in bend direction takes place. Hence, for the optically active compound a transition from chirality induced polar switching to bend induced (shape induced) antiferroelectricity takes place. In this SmCsPA* phase a homogeneous layer chirality is induced under an applied electric field which interacts with the fixed molecular chirality leading to the energetically favoured diastereomeric state and giving rise to a field direction dependent uniform tilt director orientation. Field reversal induces a flipping of the layer chirality, which first leads to the less favorable diastereomeric state, and then this slowly relaxes to the more stable one by a spontaneous reversal of the tilt direction. [less ▲]

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See detailSmart polymer surfaces: mapping chemical landscapes on the nanometre scale
Filimon, Marlena UL; Kopf, Ilona; Erik, Bründermann et al

in Soft Matter (2010)

We show that Scattering Infrared Near-field Microscopy (SNIM) allows chemical mapping of polymer monolayers that can serve as designed nanostructured surfaces with specific surface chemistry properties on ... [more ▼]

We show that Scattering Infrared Near-field Microscopy (SNIM) allows chemical mapping of polymer monolayers that can serve as designed nanostructured surfaces with specific surface chemistry properties on a nm scale. Using s-SNIM a minimum volume of 100 nm × 100 nm × 15 nm is sufficient for a recording of a “chemical” IR signature which corresponds to an enhancement of at least four orders of magnitudes compared to conventional FT-IR microscopy. We could prove that even in cases where it is essentially difficult to distinguish between distinct polymer compositions based solely on topography, nanophase separated polymers can be clearly distinguished according to their characteristic near-field IR response. [less ▲]

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See detailPolymer-induced phase separation in Escherichia coli suspensions
Schwarz-Linek, Jana; Winkler, Alexander; Wilson, Laurence G. et al

in Soft Matter (2010), 6(18), 4540-4549

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See detailSpontaneous macroscopic carbon nanotube alignment via colloidal suspension in hexagonal columnar lyotropic liquid crystals
Scalia, Giusy; von Bühler, Clemens; Hägele, Constanze et al

in Soft Matter (2008), 4(3), 570-576

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 ... [more ▼]

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. [less ▲]

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