To clarify the structural changes behind the viscoelastic build-up during fast free-radical polymerization, the photopolymerization of isobornyl acrylate (IBoA) was studied in detail from a synchronized viscoelastic-conversion perspective using time-resolved FT-MIR photorheology. Before effective elasticity development, polymerization proceeds in a viscous fluid state where the polymerization rate reaches a steady value after a steep ramp within the first 10% of conversion irrespective of the initiation conditions. For soft to moderate initiation the (semi)dilute entangled polymer regime before vitrification covers the second major conversion range after elasticity sets in. Interestingly, extrapolation to full conversion of the latter regime provides an alternative means to estimate the equilibrium plateau modulus and molar mass between entanglement for the bulk IBoA polymer. Further up the conversion path vitrification takes over as characterized by a steep modulus increase of at least 3 orders of magnitude over a small conversion window. Additionally, the acceleration and deceleration processes of the polymerization are discussed along the viscoelastic-conversion path.

HypothesisHydrophilic smectite nanoclay suspensions exhibit soft glassy dynamics due to strong interparticle electrostatic interactions between the positively charged edges and negatively charged surfaces that lead to the creation of colloidal gels. These interactions drive gelation with complex rheological behavior and aging. Unlike many other parameters, the effect of high hydrostatic pressure (HHP), on the interparticle interactions and the consequent suspension microstructure, dynamics and rheology has not been much investigated. Experimental results. We report the time evolution of the slow dynamics in the sol state (2.5 wt. %) and of flow curves in the gel state (3.5 wt. %) probed experimentally using HHP dynamic light scattering and HHP rheology respectively. Both are found to speed up with increasing pressure. The mean slow relaxation time, [[EQUATION]], associated with microstructural rearrangements in the sol state, exhibits the typical super-exponential growth with waiting time, [[EQUATION]], that was found to be pressure dependent with effects similar to those observed by increasing temperature for different salt concentrations, [[EQUATION]]. The colloidal fragility index [[EQUATION]] which characterizes the super exponential behavior, depends on pressure but not on [[EQUATION]]. The increase of yield stress [[EQUATION]] with [[EQUATION]], investigated at different pressures, was found to increase exponentially with [[EQUATION]] until it saturates at long [[EQUATION]]. We also applied a fluidity model that accounts for the thixotropic behavior that captures the evolution of [[EQUATION]] with [[EQUATION]] and shows how the increase of pressure raises the saturation value of [[EQUATION]] at long [[EQUATION]].ConclusionsThis study provides new insights into the effect of pressure on the nanoclay suspensions probed through their microscopic soft glassy dynamics and their macroscopic rheological response. The clear effects observed, despite the minimal change in volume fraction, suggest a change of attraction-repulsion balance upon increasing pressure in a way that favored attraction and promoted interparticle contacts.

We investigated the effects of high hydrostatic pressure on the sol-gel transition of gelatin dispersions. We used dynamic light scattering (DLS) and DLS-based passive microrheology to monitor the evolution of the viscoelasticity during isothermal gelation. It provided easy identification of the sol-gel transition and the isothermal critical gelation time (t c) and values of viscosities of sols and shear modulus of gels. At a given temperature, t c decreased with increasing pressure. Up to 100 MPa, the temperature dependence of t c followed the established empirical rule and the critical temperature T c increased with pressure by ∼0.04 K/MPa. The critical gelation time scaled with the quench depth T-T c or equivalently with the distance from the pressure-dependent collagen denaturation temperature (∼314 K, at 0.1 MPa), which also increases by ∼0.04 K/MPa in the first 100 MPa. The pressure dependence also reflected on the time evolution of the intrinsic viscosity, η i , or elastic modulus, G p, in the sol or gel state, respectively, are reported. Both η i or G P evolution speeds up with pressure. Finally, using a reverse quenching approach, we observed a slowing of the gel melting when the pressure increases. Our results confirmed that the rheological evolution reflects the helix formation process and that pressure stabilizes the helices.

We elucidate the effect of preparation conditions on the rheological properties of organophilic clays consisting of platelet-like primary particles, VG69 (trademark of SLB) dispersed in oil, by varying the homogenization rate, homogenization temperature, and amount of added water. We establish that stable, nonsedimenting gel formation requires homogenization temperatures higher than 45 °C and the addition of a small amount of water during the homogenization stage. Dried organoclay dispersions, on the other hand, do not form stable gels, independent of the homogenization rate and temperature, suggesting the existence of only weak attractions in the absence of water molecules. Water-induced attraction is necessary to form gels, probably through hydrogen bonding between the silanol group of clay particles and water molecules. Moreover, the effect of homogenization temperature is related to the extent of exfoliation during the homogenization stage as confirmed by X-ray scattering. The gel plateau modulus, G p, is found to increase with clay concentration as G P ∼ c clay 3.9, typical of fractal gel networks. More interestingly, a linear increase in the elastic modulus with water concentration is observed over a wide range of water concentrations, while analyzing the effective yield strain deduced from the yield stress and elastic modulus reveals the existence of three regimes. We finally present dynamic state diagrams that clearly indicate the required conditions for the creation of stable gels and demonstrate the importance of controlling the preparation protocols in the formulation of clay dispersions and gels with desirable structural and mechanical properties.

We provide a detailed investigation of the pressure and temperature dependence of flow curves and, in particular, of the yield stress, σy, of a model drilling fluid formulation and the parent colloidal dispersion. We carefully considered the limitations of the high-pressure cell and designed reliable protocols covering a pressure range up to 100 MPa and a temperature range up to 85 °C. For both systems, the viscosity at high shear rates increased with pressure, scaling well with the pressure dependence of the solvent viscosity. For clay dispersions, σy increases slightly with temperature at a given pressure and much more with pressure across the whole temperature range (25-85 °C). For the drilling fluid formulation, σy increases with pressure and decreases with temperature. The time evolution of σy at high pressures (aging) was found to be different for the two systems. The clay dispersions did not show any aging of σy, whereas the drilling fluid formulation shows a pressure-dependent aging of σy. The aging is well captured by phenomenological kinetic models, with the amplitude of the aging being dependent on pressure but the kinetics not being dependent on pressure. The results suggest that the pressure does not affect much the volume fraction but rather affects the interactions between clay particles and emulsion droplets in the drilling fluid formulation. These new findings are in line with our previous results on the microscopic dynamics of the drilling fluid under high pressure and provide insights into the origin of the yield stress and its evolution with pressure and temperature in these technologically relevant systems.

Clay minerals are abundant natural materials used widely in coatings, construction materials, ceramics, as well as being a component of drilling fluids. Here, we present the effect of steady and oscillatory preshear on organophilic modified clay gels in synthetic oil. Both platelet and needlelike particles are used as viscosifiers in drilling fluid formulations. For both particles, the plateau modulus exhibits a similar concentration dependence, GP∼c3.9, whereas the yield strain is γy∼c−1 for the platelets and γy∼c−1.7 for the needles. Mixtures of the two follow an intermediate behavior: at low concentrations, their elasticity and yield strain follows that of needle particles while at higher concentrations they exhibit a weaker power-law dependence. Furthermore, upon varying the preshear history, the gel viscoelastic properties can be significantly tuned. At lower (higher) clay concentrations, preshear at specific oscillatory strain amplitudes or steady shear rates may induce a hardening (softening) of the dispersions and, at all concentrations, a lowering of the shear strain. Hence, in needle dispersions preshear resulted in changes in the volume fraction dependence of the elastic modulus from GP∼c3.9 to GP∼c2.5 and of the yield strain fromγy∼c−1.7 to γy∼c−1. However, small angle x-ray scattering showed not much structural changes, within the q-range covered. Our findings indicate ways to design colloidal organoclay dispersions with a mechanical response that can be tuned at will.

Water molecules can play a striking role in dictating the structure of supramolecular polymer networks in apolar media, but the consequences on their viscoelasticity are not completely understood. Herein, we compare two synthetic supramolecular polymer networks based on hydrogen bonding motifs that coassemble with water molecules in different ways. The first is a biphenyl tetracarboxamide (BPTA) that forms three different helical structures, two of which feature intercalated water molecules. The second is 2,4-bis(2-ethylhexylureido)toluene (EHUT), for which water molecules act as chain stoppers. Networks of each motif in n-dodecane were studied by light scattering, linear viscoelasticity, and passive microrheology while controlling the environmental conditions. At low temperatures in the presence of traces of water, both motifs form networks of dynamic, "living" supramolecular polymers. At high temperatures, in striking contrast to EHUT networks, BPTA networks behave like conventional covalent polymer chains. The counterintuitive behavior of BPTA networks is proposed to originate from enhanced dynamicity enabled by intercalated water molecules at low temperatures.

The development of single-ion solid polymer electrolytes with high ion conductivity holds the key to the realization of safe, long-lasting, high-energy batteries. Here we introduce the use of core-shell nanostructured polyanionic particles, composed of polyanion asymmetric miktoarm stars with a large number of glassy polystyrene-based polyanion arms that complement longer poly(ethylene oxide), PEO, arms, as additives to low molecular weight, liquid PEO. Due to the proposed macromolecular design approach, the polyanion particles are well dispersed for wt % ≤ 55 that enables the formation of a nanostructured single-ion electrolyte with highly interconnected channels composed of liquid PEO that promotes fast ion transport. Noticeably, while the ion conductivity remains fairly unaffected and close to 10-5 S/cm at room temperature with nanoparticle loading, the shear modulus monotonically increases by several order of magnitudes indicating a very strong decoupling between the antagonistic properties of mechanical modulus and ion conductivity.

We revisit the equilibrium phase diagram of the much-studied model supramolecular polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT) in nonpolar solvents and provide unambiguous evidence of a much richer behavior, characterized by four distinct regimes. Typically, two types of self-assembled structures are formed: tubes (filaments) at higher (lower) concentrations and lower (higher) temperatures. The tube structure forms viscoelastic solutions that had been characterized by rheology, however, without detailed analysis of the experimental signals. Here, we combine rheology and microrheology to establish the complete dynamic phase diagram of EHUT in dodecane. It still comprises two structures, tubes and filaments, with the transition temperature being almost constant over the examined wide concentration range, as confirmed with the help of complementary differential scanning calorimetry measurements. The tubes are found to exist in three dynamic states with increasing concentration, unentangled, partially entangled, and well entangled, which are separated by isolength lines. We present criteria for unambiguously identifying these phases and discuss their distinct concentration and temperature dependencies. The new, complete phase diagram may serve as a guide for investigating other supramolecular polymers with tunable rheology and, more importantly, providing insights into a universal description of one-dimensional self-assembled structures by linking this class of materials with the classic wormlike surfactant micelles, for which the partially and well-entangled regimes were recently elucidated.

Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.

A methodology to investigate the linear viscoelastic properties of complex fluids at elevated pressures (up to 120 MPa) is presented. It is based on a dynamic light scattering (DLS) setup coupled with a stainless steel chamber, where the test sample is pressurized by means of an inert gas. The viscoelastic spectra are extracted through passive microrheology. We discuss an application to hydrogen-bonding motif 2,4-bis(2-ethylhexylureido)toluene (EHUT), which self-assembles into supramolecular structures (tubes and filaments) in apolar solvents dodecane and cyclohexane. High levels of pressure (roughly above 20 MPa) are found to slow down the terminal relaxation process; however, the increases in the entanglement plateau modulus and the associated persistence length are not significant. The concentration dependence of the plateau modulus, relaxation times (fast and slow), and correlation length is practically the same for all pressures and exhibits distinct power-law behavior in different regimes. Within the tube phase in dodecane, the relative viscosity increment is weakly enhanced with increasing pressure and reaches a plateau at about 60 MPa. In fact, depending on concentration, the application of pressure in the tube regime may lead to a transition from a viscous (unentangled) to a viscoelastic (partially entangled to well-entangled) solution. For well-entangled, long tubes, the extent of the plateau regime (ratio of high- to low-moduli crossover frequencies) increases with pressure. The collective information from these observations is summarized in a temperature-pressure state diagram. These findings provide ingredients for the formulation of a solid theoretical framework to better understand and exploit the role of pressure in the structure and dynamics of supramolecular polymers.

Oil-continuous drilling fluids used in the oil and gas industry are formulated to be pseudoplastic with a relatively weak yield stress. These fluids are required to maintain their properties over wide temperature and pressure ranges yet there are few methods that can sensitively study the inherent structure and mechanical properties in the fluids under such conditions. Here we study a model oil-continuous drilling fluid formulation as a function of both temperature (up to 153 °C) and pressure (up to 1330 bar) with Diffusive Wave Spectroscopy (DWS). The system comprises a colloidal gel network of clay particles and trapped emulsion droplets. As a function of temperature the system undergoes local structural changes reflected in the DWS dynamics which are also consistent with macroscopic rheological measurements. On cycling to high pressure the system exhibits similar structural and dynamic changes with a strong hysteresis. Although multiple scattering in multicomponent non-ergodic samples does not directly yield self diffusion probe dynamics, the use of microrheology analysis here appears to be in good agreement with direct rheological measurements of the sample linear viscoelasticity at ambient pressure. Thus DWS microrheology succesfully probes irreversible changes in the structure and the mechanical response of the drilling fluid formulation under a high pressure cycle.

The involvement of nuclear inositol lipids in the processes related to DNA repair upon ionizing radiation has been investigated in Murine Erythroleukaemia cells. Early changes in the in vitro phosphatidylinositol-bisphosphate phosphorylation in isolated nuclei were found to precede transiently the marked increase in DNA synthesis occurring after irradiation. Such an increase detected by anti BrdU monoclonal antibodies has been found to be related mainly to DNA polymerase beta activity as revealed by the kinetic analysis of in vitro DNA synthesis. The results here presented allow us to speculate on a possible involvement of nuclear inositol lipids in the cascade of the early events leading to the regulation of DNA repair in the nucleus.

Dynamics light scattering (DLS) is a widely used techniques to characterize dynamics in soft phases. Evanescent Wave DLS refers to the case of total internal reflection DLS that probes near interface dynamics. We here investigate the use of EWDLS for turbid sample. Using combination of ray-tracing simulation and experiments, we show that a significant fraction of the detected photons are scattered once and has phase shifts distinct from the multiple scattering fraction. It follows that the measured correlation can be separated into two contributions: a single scattering one arising from the evanescent wave scattering, providing information on motion of the "scatterers" and the associated near wall dynamics and a multiple scattering contribution originating from scattering within the bulk of the sample. In case of turbid enough samples, the latter provides diffusive wave spectroscopy (DWS) -like correlation contribution. The validity of the approach is validated using turbid colloidal dispersion at rest and under shear. At rest we used depolarized scattering to distinguish both contributions. Under shear, the two contributions can easily be distinguished as the near wall dynamics and the bulk one are well separated. Information of both the near wall flow and the bulk flow can be retrieved from a single experiment. The simple structure of the measured correlation is opening the use of EWDLS for a large range of samples.

Light induced self-written waveguides (LISWs) with unique elongation characteristics and low optical loss are formed in a monodispersed polyisoprene solution using a low-power laser photopolymerization process, while their light transmission characteristics are exemplified in the flexible interconnection of two single-mode optical fibers operating in the visible/near infrared wavelengths. The LISWs formed exhibit rubbery properties, allowing extensibilities upon cases from 400% to 800%, while still retaining significant optical transmission. The rubber elasticity enables sustaining LISWs at stressed lengths longer than 500 µm propagation losses from 1.0 to 2.9 dB/mm.

Dendronized polymers (denpols) are thick polymers comprising a linear backbone with grafted treelike structures (dendrons). The latter give rise to a molecular thickness that is a function of dendron generation. In this work, we investigate the structure and dynamics of a series of denpols with varying degrees of polymerization and generations (up to the fifth) in the melt, using X-ray scattering, dielectric spectroscopy, and shear rheometry. These polymers are well characterized and exhibit primarily topological interactions. Our findings indicate that the molar mass needed to form entanglements depends on the dendron generation. Furthermore, regardless of their molar mass, all denpols of fourth and fifth generations remain unentangled, at least in the range of the studied backbone degrees of polymerization. Stress relaxation bears signatures of different modes associated with dendron interpenetration and backbone motion and bears analogies to that of classic bottlebrushes. Interestingly, denpols of the third generation exhibit a distinct viscoelastic relaxation spectrum, which is discussed in view of the pertinent structural information. This mode is attributed to the interdigitation of dendrons, which becomes less dominant at larger generations as backfolding prevails. This interplay of dendron interdigitation and backfolding, which can be interrogated by combining rheometry and scattering, is believed to give rise to a nonmonotonicity of the terminal relaxation time with increasing generation. The fast (segmental) dynamics of the denpols is also rich. Denpols of the second generation show two glassy modes, one reflecting local liquid crystallinity, with the overall local dynamics being broader and slower compared to higher generations. A generalized representation of normalized viscosity versus degree of polymerization for different polymers of the same class (denpols, bottlebrushes, Cayley trees) shows different scaling regimes between Rouse and reptation limits. These findings bring into focus the distinct properties of these macromolecules, and at the same time, they provide ingredients for extending the current state of the art of polymer dynamics to thick polymers.

We present a systematic investigation of static and dynamic properties of block copolymer micelles with crosslinked cores, representing model polymer-grafted nanoparticles, over a wide concentration range from dilute regime to an arrested (crystalline) state, by means of light and neutron scattering, complemented by linear viscoelasticity. We have followed the evolution of their scattering intensity and diffusion dynamics throughout the non-ergodicity transition and the observed results have been contrasted against appropriately coarse-grained Langevin Dynamics simulations. These stable model soft particles of the core-shell type are situated between ultrasoft stars and hard spheres, and the well-known star pair interaction potential is not appropriate to describe them. Instead, we have found that an effective brush interaction potential provides very satisfactory agreement between experiments and simulations, offering insights into the interplay of softness and dynamics in spherical colloidal suspensions.

Well-defined dendronized polymers (denpols) bearing high-generation dendron are attractive nano-objects as high persistency provides distinct properties, contrast to the random coiled linear polymers However, their syntheses via graft-through approach have been very challenging due to their structural complexity and steric hindrance retarding polymerization. Here, we report the first example of the synthesis of poly(norbornene) (PNB) containing ester dendrons up to the sixth generation (G6) by ring-opening metathesis polymerization. This is the highest generation ever polymerized among dendronized polymers prepared by graft-through approach, producing denpols with molecular weight up to 1960 kg/mol. Combination of size-exclusion chromatography, light scattering, and neutron scattering allowed a thorough structural study of these large denpols in dilute solution. A semiflexible cylinder model was successfully applied to represent both the static and dynamic experimental quantities yielding persistent length (lp), cross-sectional radius (Rcs), and contour length (L). The denpol persistency seemed to increase with generation, with lp reaching 27 nm (Kuhn length 54 nm) for PNB-G6, demonstrating a rod-like conformation. Poly(endo-tricycle[4.2.2.0]deca-3,9-diene) (PTD) denpols exhibited larger persistency than the PNB analogues of the same generation presumably due to the higher grafting density of the PTD denpols. As the dendritic side chains introduce shape anisotropy into the denpol backbone, future work will entail a study of these systems in the concentrated solutions and melts.

The yet virtually unexplored class of soft colloidal rods with small aspect ratio is investigated and shown to exhibit a very rich phase and dynamic behavior, spanning from liquid to nearly melt state. Instead of nematic order, these short and soft nanocylinders alter their organization with increasing concentration from isotropic liquid with random orientation to one with preferred local orientation and eventually a multi-domain arrangement with local orientational order. The latter gives rise to a kinetically suppressed state akin to structural glass with detectable terminal relaxation, which, on increasing concentration reveals features of hexagonally packed order as in ordered block copolymers. The respective dynamic response comprises four regimes, all above the overlapping concentration of 0.02 g/ml: I) from 0.03 to 0.1 g/mol the system undergoes a liquid-to-solid like transition with a structural relaxation time that grows by four orders of magnitude. II) from 0.1 to 0.2 g/ml a dramatic slowing-down is observed and is accompanied by an evolution from isotropic to multi-domain structure. III) between 0.2 and 0.6 g/mol the suspensions exhibit signatures of shell interpenetration and jamming, with the colloidal plateau modulus depending linearly on concentration. IV) at 0.74 g/ml in the densely jammed state, the viscoelastic signature of hexagonally packed cylinders from microphase-separated block copolymers is detected. These properties set short and soft nanocylinders apart from long colloidal rods (with large aspect ratio) and provide insights for fundamentally understanding the physics in this intermediate soft colloidal regime, as well as and for tailoring the flow properties of non-spherical soft colloids.

Nonlinear rheometry of interfaces is very challenging because of the limits of current day instrumentation and the intricate coupling of flows at interfaces and in the bulk. The use of time periodic flows may constitute a first step in addressing this issue. Fourier transform rheology (FTR) measurements with quasi-monolayers at the air-water interface are used in order to assess the suitability of the different devices to investigate nonlinear interfacial shear viscoelasticity. The probe material was a poly (methyl methacrylate) forming a soft glassy interface, whereas complementary measurements were performed with a polystyrene latex suspension forming a predominantly viscous interface at intermediate surface coverages. The obtained data with the magnetic rod rheometer (ISR) were compared against those obtained with the bicone and the double wall ring geometries attached to standard rotational rheometers. In particular, an unexpected appearance of even in addition to odd harmonics is discussed in terms of flow field asymmetry.