Small Amplitude Oscillatory Shear Rheology Research Articles

Tuning the thermostability of GHG gels by salts at different positions on the Hofmeister scale

The influence of Hofmeister cations (NH4+, Na+, Mg2+) and anions (H2PO4−, CH3COO−, Cl−, NO3−) on the thermostability of a GHG hydrogel was investigated. The combined results of UV circular dichroism (UVCD) and Small Amplitude Oscillatory Shear Rheology experiments reveal that the addition of salt reduces the stability of the gel phase and the underlying fibrils. In line with the cationic Hofmeister hierarchy, the chaotropic Mg2+ ions caused the greatest thermal destabilization of the gel phase with the gel → sol transition temperature Tgs value lowered by 10 °C. In the absence of salt, the gel → sol transition probed by the storage modulus and microscopy is biphasic. In the presence of salt, it becomes monophasic. Contrary to expectations the presence of Hofmeister anions leads to a nearly identical reduction of the gel → sol transition temperatures. However, UVCD spectra suggest that they affect the ππ-stacking between imidazole groups to a different extent. We relate the absence of ion specificity regarding the solubility of fibrils (probed by UVCD) to the observed enthalpy-entropy compensation of the dissolution process. Our results combined show how CD spectroscopy and rheology combined yields a more nuanced picture of the processes underlying the gel → sol transition.

Preparation and Characterization of H-Shaped Polylactide.

An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter "H". Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. 1H NMR spectroscopy, size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the multigram scale with a weight-average molar mass Mw > 100 kg/mol and low dispersity Đ < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (∼93%). Small-amplitude oscillatory shear and extensional rheology measurements demonstrate the unique viscoelastic behavior associated with the H-shaped architecture.

Exploring the mechanism of amylose/amylopectin improving formation of yeast-soy protein high-moisture extrudates based on small and large amplitude oscillatory shear rheology

Yeast protein (YP) has high production efficiency and comprehensive nutritional value compared to soy protein isolate (SPI). However, relatively higher proportion of YP replaces SPI seriously affect the structure of extrudates in the production of meat analogues. This study investigated starch addition (amylose/amylopectin) on the structure of YP-SPI extrudates with higher YP proportion and formation mechanism by using closed cavity rheometer simulated the high-moisture extrusion process (mixing, melting, cooling, and extrudates). The proportions of YP:SPI:amylose:amylopectin were set as 5:5:0:0, 5:4:1:0, 5:4:0:1, and 5:4:0.5:0.5. Starch addition could improve the structure formation of extrudes, but the improvement effect varied depending on the type of starch. Compared to amylose, incorporating amylopectin significantly enhanced the fibrous degree of extrudates and improved their tensile resistance. Furthermore, small amplitude oscillatory shear (SAOS) was used to establish texture map. In the mixing and melting zones, amylose decreased the miscibility of protein and starch phase, while amylopectin had positive effect on the integrity and uniformity of protein network. Amylopectin could transform the extrudates into a “mushy” state, contributing to reconstruct protein network. Large amplitude oscillatory shear (LAOS) demonstrated amylopectin had higher energy dissipation ratio in the cooling zone, indicating the uniform “phase separation” facilitated the formation of fiber structure of extrudates. This study provides technical reference for the preparation of high-moisture extrudates using YP as a substitute for SPI based on starch type addition.

Branched copolymer surfactants impart thermoreversible gelation to LAPONITE® gels.

This investigation seeks to integrate LAPONITE® clay gels with thermoresponsive branched copolymer surfactants (BCSs) to develop advanced functional materials with temperature-induced sol-gel behaviour. It is known that a diverse range of molecules adsorb strongly to clays which may be used to control liberation of the species in healthcare applications, and as such the development of polymer/clay hybrid materials which can add function to the native clay behaviour are of great interest. BCS were synthesised with a structure that encompasses poly(ethylene glycol)methacrylate (PEGMA), ethylene glycol dimethacrylate (EGDMA), and dodecanethiol (DDT), conferring versatile and tuneable thermoresponsive attributes. Systematic modulation of the monomer : DDT/initiator ratio was used to facilitate the synthesis of BCS architectures spanning a range of molecular weights. Through application of small-amplitude oscillatory shear (SAOS) rheology and small-angle neutron scattering (SANS) in conjunction with controlled temperature variations, the sol-gel transition dynamics of these nanocomposite materials were elucidated. Complementary insights into the mechanisms underpinning this transition and temperature-induced alterations in the constituents are gleaned through the utilization of SANS techniques employing contrast-matching methodologies to mitigate clay and polymer scattering interference. It is found that heating systems from room- to body- temperature induces self-assembly of BCS in the bulk aqueous phase with concurrent structuration of clay in gel-forming samples with lower number average molecular weight (Mn). SANS study unpicks this phenomenon to find that gelation occurs with concurrent aggregation of BCS in the bulk, inducing clay-clay interactions only in lower Mn BCS systems with large nanoaggregates.

Structure–function relationship during the early and long‐term hydration of one‐part alkali‐activated slag

AbstractUnderstanding the mechanisms controlling the early (fresh) and long‐term (hardened) hydration of one‐part alkali‐activated slags (AAS) is key to extend their use as low CO2 substitutes for ordinary Portland cement (OPC). Their “just add water” use makes them easier and less hazardous to manipulate than the more studied two‐part ones. This is due to the absence of liquid alkaline activators, which are environmentally and energy demanding. In this work, numerous experimental techniques have been linked to obtain a comprehensive physico‐chemical characterization of a one‐part AAS activated with Na2CO3 and Ca(OH)2 powders at several water to solid ratios (w/s). Calorimetry and pH/conductivity measurements describe the functioning of the activators immediately after contact with water. Early reactivity is characterized through in situ X‐ray powder diffraction (XRPD) and small amplitude oscillatory shear (SAOS) rheology, which reveal a rapid precipitation of nanometric hydration products (nano‐C‐A‐S‐H), which results in a continuous increase in the paste cohesivity until setting. Moreover, SAOS shows that rejuvenating the paste by means of shearing (performed externally to the rheometer in this study) is enough to restore the initial cohesion (i.e., workability) for long time spans until setting occurs. The long‐term hydration is characterized by ex situ XRPD on aged AAS pastes, in parallel with mechanical testing on AAS mortar. A correlation can be observed between the amount of nano‐C‐A‐S‐H and the increase in compressive strength. Overall, this formulation shows satisfactory fresh and solid properties, demonstrating suitability for low‐ and normal‐strength applications.

Impact of Photoactive Monomer Location in Photoresponsive Block Copolymer/Ionic Liquid Solutions

By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Previous studies have looked at situating azobenzene, a common photoresponsive molecule, along the backbone of the polymer as a pendant group, and even as part of the solvent rather than as a comonomer. Here, we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder–order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. Using small-angle X-ray scattering and ultraviolet (UV)-irradiated small-amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt %. At 35 wt %, MBsA microphase-separated at 60 °C, MBA at 100 °C, and followed by MAB at 120 °C, a trend that was repeated at 50 wt %. MBsA was the only polymer to order onto a lattice at 35 wt %, forming hexagonally close-packed spheres. Both MBsA and MBA formed hexagonally packed cylinders at 50 wt %. MBsA consistently ordered onto a lattice over the temperature range of interest, while MBA only did so at 50 wt %, and MAB remained disordered at both concentrations. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Therefore, adjusting the location of the azobenzene units within the thermo- and photoresponsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature.

Study of Morphology, Rheology, and Dynamic Properties toward Unveiling the Partial Miscibility in Poly(lactic acid)-Poly(hydroxybutyrate-co-hydroxyvalerate) Blends.

The purpose of the present work was to gain a fundamental understanding of how the composition and physico-chemical properties affect the rheology, morphology, miscibility, and thermal stability of poly(lactic acid) (PLA)-poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) biopolymer blends obtained by melt mixing. First, restricted processing conditions were chosen, due to the inherent thermal degradation of PHBV, as proven by rheological dynamic time sweep (DTS) measurements and size-exclusion chromatography (SEC). Based on this, the composition dependence of the blends was investigated using small-amplitude oscillatory shear rheology (SAOS), and the results were confirmed by scanning electron microscopy (SEM) analysis. Subsequently, the changes in glass transition temperatures (Tgs) from the molten to the solid state, as observed by DMA and DSC, were verified by coupling SAOS to dielectric relaxation spectroscopy (DRS). Herein, the thermo-rheological complexity of PLA/PHBV blends in the melt was revealed, especially for PLA-rich blends. Irregularly structured morphologies, caused by highly mismatched viscoelastic properties, illustrated the degree of partial miscibility. Moreover, the thermo-rheological complexity appeared in the molten state of the asymmetric PLA-rich phases could be correlated to the crystal-amorphous interfacial MWS polarization, because of the locally-induced phase separation and heterogeneity, and owing to the differences in their crystallization properties during cooling. The miscibility also suffered from the lower thermal stability of PLA and the even more unstable PHBV. Nevertheless, the melt-induced degradation process of the PLA/PHBV blends seemed to be responsible for some of the in situ self-compatibilization and plasticization mechanisms. As a result, the miscibility and thermo-rheological simplicity were improved for the intermediate and PHBV-rich compositions at low temperatures, since their properties were, to a large extent, governed by the significant degradation of PHBV. The present findings should increase the understanding of morphological changes in PLA/PHBV blends and help control their micro/nanostructure.

L-Arginine as a Bio-Based Curing Agent for Epoxy Resins: Glass Transition Temperature, Rheology and Latency

The need for sustainable practices in the processing chain of fiber-reinforced thermosets has led to the development of bio-based epoxy resins and curing agents. As a contribution to sustainable composites, this study focuses on the glass transition temperature (), viscosity and latency of diglycidyl ether of bisphenol a (DGEBA) cured with l-arginine in the presence of a urea-based accelerator. These characteristics are decisive features for application as a matrix in fiber-reinforced polymer composites produced via prepreg technology in which low viscosity and sufficient latency, meaning low reactivity of the one-component system, are necessary. The homogeneous mixture of amino acid and epoxy resin was prepared via three-roll milling. Two formulations, Argopox-1 with 1 accelerator and Argopox-2.5 with accelerator, were prepared and parts of each formulation were stored at 22 °C and −18 °C, respectively. Both formulations were tested via differential scanning calorimetry (DSC) and small amplitude oscillatory shear rheology (SAOS) after 0 d, 30 d, 60 d, 90 d and 180 d of storage to determine the influence of accelerator weight fraction, storage temperature and storage period on the glass transition temperature of the uncured resin system , and their viscosity. The of the thermosets is about 100 °C. The DSC and SAOS measurements show that the of Argopox-1 shifts about 5 °C in 60 d, while its viscosity is still low enough to be processed in a prepreg production line. Furthermore, Argopox-1 is storable for at least 180 d at −18 °C without significant changes in its and viscosity. Consequently, Argopox-1 possesses a sufficiently high and adequate latency, as well as a low viscosity for application as prepreg matrix material.

Chemorheological Monitoring of Cross-Linking in Slide-ring Gels Derived From α-cyclodextrin Polyrotaxanes.

Despite hundreds of studies involving slide-ring gels derived from cyclodextrin (CD)-based polyrotaxanes (PRs), their covalent cross-linking kinetics are not well characterized. We employ chemorheology as a tool to measure the gelation kinetics of a model slide-ring organogel derived from α-cyclodextrin/poly (ethylene glycol) PRs cross-linked with hexamethylenediisocyanate (HMDI) in DMSO. The viscoelastic properties of the gels were monitored in situ by small-amplitude oscillatory shear (SAOS) rheology, enabling us to estimate the activation barrier and rate law for cross-linking while mapping experimental parameters to kinetics and mechanical properties. Gelation time, gel point, and final gel elasticity depend on cross-linker concentration, but polyrotaxane concentration only affects gelation time and elasticity (not gel point), while temperature only affects gelation time and gel point (not final elasticity). These measurements facilitate the rational design of slide-ring networks by simple parameter selection (temperature, cross-linker concentration, PR concentration, reaction time).

Anomalous rheological aging of a model thermoreversible colloidal gel following a thermal quench.

We investigate the aging behavior in a well-studied model system comprised of a colloidal suspension of thermoreversible adhesive hard spheres (AHS) but thermally quenched below the gel transition to much larger depths than previously studied. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from the liquid state at 40 °C to a temperature below the gel temperature, and new, anomalous aging behaviors are observed. Shallow quenches lead to monotonic development of the elastic modulus with time, consistent with prior reports for the development of a homogeneous gel [Gordon et al., J. Rheol. 61, 23-34 (2017)]. However, for deeper quenches, a unique and new phenomenon is reported, namely, after an initial rise in the modulus, a reproducible drop in the modulus is observed, followed by a plateau in the modulus value. This drop can be gradual or sudden and the extent of the drop depends on the quench depth. After this drop in the modulus, AHS gel evolves toward a quench-path independent state over the experimental timescale. These effects of the extent of quenching on aging behavior are hypothesized to be a consequence of quenching into different underlying thermodynamic states of colloidal gels and the possible influence of the adhesive glass dynamical arrest for the deepest quenches. The research connects homogeneous gelation with heterogeneous gel formation due to phase separation and shows that the extent of quench can be used as an independent parameter to govern the rheological response of the arrested gel.

Recycling of Pretreated Polyolefin-Based Ocean-Bound Plastic Waste by Incorporating Clay and Rubber

Plastic waste found in oceans has become a major concern because of its impact on marine organisms and human health. There is significant global interest in recycling these materials, but their reclamation, sorting, cleaning, and reprocessing, along with the degradation that occurs in the natural environment, all make it difficult to achieve high quality recycled resins from ocean plastic waste. To mitigate these limitations, various additives including clay and rubber were explored. In this study, we compounded different types of ocean-bound (o-HDPE and o-PP) and virgin polymers (v-LDPE and v-PS) with various additives including a functionalized clay, styrene-multi-block-copolymer (SMB), and ethylene-propylene-based rubber (EPR). Physical observation showed that all blends containing PS were brittle due to the weak interfaces between the polyolefin regions and the PS domains within the polymer blend matrix. Blends containing clay showed rough surfaces and brittleness because of the non-uniform distribution of clay particles in the polymer matrix. To evaluate the properties and compatibility of the blends, characterizations using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and small-amplitude oscillatory shear (SAOS) rheology were carried out. The polymer blend (v-LDPE, o-HDPE, o-PP) containing EPR showed improved elasticity. Incorporating additives such as rubber could improve the mechanical properties of polymer blends for recycling purposes.

Effect of pH-modifiers on the rheological behaviour of clay slurries: Difference between a swelling and non-swelling clay

Owing to their anisotropic surface charge and anisometric shape aqueous clay slurries are known to exhibit rich rheological behavior with the existence of yield stress at very low solids concentrations which can be modulated using different pH modifiers. The impact of particle-particle association on the rheological behaviour of two different clays, a swelling 2:1 (bentonite) and a non-swelling 1:1 clay (kaolin) was investigated. Effect of factors such as pH, pH modifiers, and solids concentration on the rheological behaviour was studied using Small Amplitude Oscillatory Shear (SAOS) and shear rheology. For kaolin, the microstructural strength as measured using storage modulus (G′) was reflected directly in the high shear response. However, for bentonite the high shear viscosity evolved non- monotonically as a function of G′ which was connected to its swelling behaviour. Cohesive energy density increased sharply as a function of volume fraction for bentonite compared to kaolin and may provide a basis for the stark contrast in industrial unit operation response of the two clays. The results highlight the importance of using several rheological material functions to understand the true microstructure of clay dispersions.

Synthesis, Rheology, and Assessment of 3D Printability of Multifunctional Polyesters for Extrusion-Based Direct-Write 3D Printing

Three-dimensional (3D) printing offers the unprecedented ability to create medical devices with complex architectures matched to the patient’s anatomy. However, the development of 3D printable synthetic polymers for biomedical applications has been relatively slow. Here, we present the synthesis and characterization of a library of single-component, undiluted, modular multifunctional polyesters for extrusion-based direct-write 3D printing (EDP). The polyesters were synthesized using carbodiimide-mediated polyesterification of pendant functionalized diols and succinic acid and characterized using 1H NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and rheology. The rheology was characterized by using small amplitude oscillatory shear rheology and at steady-state shear flow conditions. The viscoelasticity of the polyesters was characterized by plotting master curves using the time–temperature superposition (TTS) principle, which were then validated by Van Gurp-Palmen and Cole–Cole plots. The 3D printability of the polyesters was assessed on the basis of several key parameters including the ability to extrude as continuous filaments, retain the printed shape, form multilayer constructs, and form bridge-spanning filaments without significant sagging or collapse. The rheological characterization suggests that the polyesters are unentangled melts that facilitate printing at ambient temperatures without the use of external additives or solvents. The presence of supramolecular interactions inducing pendant functional groups forms a temporary, physical cross-link-like network that enables 3D shape retention. The insights from this study will further assist in the design and characterization of 3D printable polymer melts for biomedical applications and standardizing the assessment of polymer 3D printability.

Viscoelastic behaviour of rapid and slow self-healing hydrogels formed by densely branched arabinoxylans from Plantago ovata seed mucilage

We report rheological characterisation of hydrogels formed by highly substituted brush-like arabinoxylans from Plantago ovata seed mucilage. Two arabinoxlyan fractions with similar molecular weight and linkage compositions are chosen to form gels with distinct rheological properties but a similar network structure. Small and large amplitude oscillatory shear rheology is used to characterise the sol-gel transition as a function of temperature and concentration. Differences in rheology and gelation of the two hydrogels are found to be associated with the different proportion of ‘slow’- and ‘fast’-dissociating junctions stabilised by hydrogen bonds, with the ‘fast’-dissociating junctions playing an important role in rapid self-healing of the gel. Based on the temperature dependence of storage modulus and time–temperature superposition principle in combination with the Arrhenius equation, the activation energies of junction zone dissociation are estimated to be 402–480 kJ/mol and 97–144 kJ/mol for the ‘slow’ and ‘fast’ junction types, respectively.

Nonlinear Viscoelastic Response of Crumb Rubber Modified Asphalt Binder Under Large Strains

Agencies have been increasing their use of polymer modified asphalt binders in recent years to address performance issues and lengthen the useful life of their pavements. When deployed these materials likely experience strain levels exceeding their linear viscoelastic (LVE) limits. The same situation exists in non-polymer modified asphalt binders as well, but the effect may be more pronounced in polymer modified systems because of their bi-phasic nature. In this study, terminally blended crumb rubber (CR-TB) modified asphalt is studied to understand and quantify the nonlinear viscoelastic response under large strains. The CR-TB binders are extensively used in pavements subjected to high vehicular loads and extreme climatic conditions; thereby, their response under large strains becomes more critical. The current standard characterization techniques are based on LVE response using small amplitude oscillatory shear rheology only and do not consider the behavior of binders under large strains. In this study, large amplitude oscillatory shear (LAOS) rheology is used as a framework to more thoroughly investigate the complete response of the CR-TB modified asphalt binder under large strains at 30°C, 40°C, 50°C, and 60°C and at the frequencies of 0.5, 1, and 5 Hz. The LAOS response is analyzed using Fourier-transform rheology and the orthogonal stress decomposition method involving Chebyshev polynomial representation. It is found that nonlinearity manifests greatly in this study material as strain levels increase and frequencies decrease. The relative nonlinearity increases with increasing strain amplitude and is more significant towards lower end of the tested temperature range. The CR-TB binder shows strain-stiffening/softening and shear-thinning/thickening behavior depending upon a specific temperature, strain level, and frequency.

Small and Medium Amplitude Oscillatory Shear Rheology of Model Branched Polystyrene (PS) Melts.

Linear and nonlinear rheological properties of model comb polystyrenes (PS) with loosely to densely grafted architectures were measured under small and medium amplitude oscillatory shear (SAOS and MAOS) flow. This comb PS set had the same length of backbone and branches but varied in the number of branches from 3 to 120 branches. Linear viscoelastic properties of the comb PS were compared with the hierarchical model predictions. The model underpredicted zero-shear viscosity and backbone plateau modulus of densely branched comb with 60 or 120 branches because the model does not include the effect of side chain crowding. First- and third-harmonic nonlinearities reflected the hierarchy in the relaxation motion of comb structures. Notably, the low-frequency plateau values of first-harmonic MAOS moduli scaled with (total molecular weight), reflecting dynamic tube dilution (DTD) by relaxed branches. Relative intrinsic nonlinearity Q0 exhibited the difference between comb and bottlebrush via no low-frequency Q0 peak of bottlebrush corresponding to backbone relaxation, which is probably related to the stretched backbone conformation in bottlebrush.

Gluten-Degrading Proteases in Wheat Infected by Fusarium graminearum-Protease Identification and Effects on Gluten and Dough Properties.

Recently, we have observed a relationship between poor breadmaking quality and protease activities related to fungal infection. This study aims to identify potential gluten-degrading proteases secreted by fungi and to analyze effects of these proteases on rheological properties of dough and gluten. Fusarium graminearum-infected grain was used as a model system. Zymography showed that serine-type proteases secreted by F. graminearum degrade gluten proteins. Zymography followed by liquid chromatography-mass spectrometry (MS)/MS analysis predicted one serine carboxypeptidase and seven serine endo-peptidases to be candidate fungal proteases involved in gluten degradation. Effects of fungal proteases on the time-dependent rheological properties of dough and gluten were analyzed by small amplitude oscillatory shear rheology and large deformation extensional rheology. Our results indicate that fungal proteases degrade gluten proteins not only in the grain itself, but also during dough preparation and resting. Our study gives new insights into fungal proteases and their potential role in weakening of gluten.

Hydrolysis by Indigenous Plasmin: Consequences for Enzymatic Cross-Linking and Acid-Induced Gel Formation of Non-Micellar Casein

Casein is a group of milk proteins with high nutritional value, and the exploitation of its techno-functional potentials has been investigated for decades. In this study, acid casein powder was dissolved in 0.1 mol/L phosphate buffers with different pH, resulting in casein solutions with pH 5.9, 6.6 and 7.3. During preparation and storage (40 °C) of the samples, casein hydrolysis was observed in size exclusion chromatography and gel electrophoresis. The degree of hydrolysis increased with increasing pH, and treatment of casein with commercial plasmin resulted in similar polypeptides, suggesting that the hydrolysis was caused by residual indigenous plasmin present in the acid casein powder. Most polypeptides could be cross-linked by microbial transglutaminase, except for one particular fraction which appeared at constant intensity in the chromatograms. The stiffness of acid-induced gels as determined in small amplitude oscillatory shear rheology decreased with increasing degree of hydrolysis, and was also lower for cross-linked samples when the preceding casein hydrolysis was more pronounced. Enzymatic cross-linking increased the resistance of casein against plasmin-related hydrolysis, presumably because of the resulting lysine modification. However, one particular fraction of polypeptides was released by hydrolysis in spite of cross-linking, suggesting that they did not contain lysine residues that are susceptible for mTGase. The results indicate that plasmin-related hydrolysis should be taken into account for the application of acid casein or sodium caseinate as additive in food design.

Photoreversible Order-Disorder Transition in an Ionic Liquid Solvated Block Polymer.

The structure of a solution of poly(methyl methacrylate)-block-poly(benzyl methacrylate-stat-(4-phenylazophenyl methacrylate)) in the ionic liquid 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonylimide) can be controlled with light. We explored the phase behavior of this block polymer at a concentration of 30 wt % as a function of temperature. Remarkably, this solution shows ordering into hexagonally closed packed spheres (HCP) upon heating under visible light, as confirmed by small-angle X-ray scattering. Small amplitude oscillatory shear rheology was used to demonstrate that the system could readily be converted between HCP and disorder by switching between visible and UV light wavelengths at 100 °C. This switching was cycled six times, without any noticeable change in the ordered or disordered state. The dependence on illuminating wavelength arises from the changes in polarity of the azobenzene moiety, which modulates its solubility in this ionic liquid to a significant extent. This is the first example of reversible light-triggered ordering of a "coil-coil" block polymer, a phenomenon that has been previously observed only in liquid crystalline systems.

Cross-platform mechanical characterization of lung tissue.

Published data on the mechanical strength and elasticity of lung tissue is widely variable, primarily due to differences in how testing was conducted across individual studies. This makes it extremely difficult to find a benchmark modulus of lung tissue when designing synthetic extracellular matrices (ECMs). To address this issue, we tested tissues from various areas of the lung using multiple characterization techniques, including micro-indentation, small amplitude oscillatory shear (SAOS), uniaxial tension, and cavitation rheology. We report the sample preparation required and data obtainable across these unique but complimentary methods to quantify the modulus of lung tissue. We highlight cavitation rheology as a new method, which can measure the modulus of intact tissue with precise spatial control, and reports a modulus on the length scale of typical tissue heterogeneities. Shear rheology, uniaxial, and indentation testing require heavy sample manipulation and destruction; however, cavitation rheology can be performed in situ across nearly all areas of the lung with minimal preparation. The Young’s modulus of bulk lung tissue using micro-indentation (1.4±0.4 kPa), SAOS (3.3±0.5 kPa), uniaxial testing (3.4±0.4 kPa), and cavitation rheology (6.1±1.6 kPa) were within the same order of magnitude, with higher values consistently reported from cavitation, likely due to our ability to keep the tissue intact. Although cavitation rheology does not capture the non-linear strains revealed by uniaxial testing and SAOS, it provides an opportunity to measure mechanical characteristics of lung tissue on a microscale level on intact tissues. Overall, our study demonstrates that each technique has independent benefits, and each technique revealed unique mechanical features of lung tissue that can contribute to a deeper understanding of lung tissue mechanics.