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A high-throughput experimentation (HTE) approach is adopted for the synthesis of a special class of elastomeric polyolefins with a tailored thermomechanical response. Ethylene/hexadec-1-ene (E/C16) statistical multiblock copolymers (MBCs) are synthesized through chain shuttling copolymerization (CSC). They are characterized by alternation of crystalline (hard) and amorphous (soft) blocks consisting of E/C16 random copolymers with low (0.5 mol %) and high (22 mol %) C16 content, respectively. The MBCs have statistical block length; mass average molecular mass greater than 100 kDa; hard block content whof 20, 31, and 50 wt %; and elastomeric properties. The regulation of the mechanical properties with the temperature is triggered by the independent melting and crystallization of the side chains at low temperatures facilitated by the high C16 content in the soft blocks. DSC thermograms show two endothermic peaks at ≈10 and 122 °C and two exothermic peaks at ≈2 and 100 °C due to the melting/crystallization of the crystals formed by the side chain pendant from the soft blocks and the crystals formed by the main chain long ethylene sequences belonging to the hard blocks, respectively. Transmission electron microscopy (TEM) reveals that all of the samples show heterogeneous morphologies in the solid state due to the tendency of the hard blocks to crystallize in separated domains. For the samples with wh≈ 20 and 31 wt %, the partial miscibility of the hard blocks with short length in the soft block rich regions prevents good phase separation, resulting in pass-through morphologies characterized by lamellar crystals crossing the soft block rich region in all directions, low contrast, and diffuse boundary at domain interfaces. The pass-through morphology occurs also for the sample with wh≈ 50 wt %. However, as it includes a large fraction of long hard and soft blocks with nearly symmetric length, disordered bicontinuous morphologies develop characterized by a better microphase separation, good contrast, and sharp boundaries at domain interfaces. The presence of heterogeneities in the melt is indicated by rheology measurements in the linear viscoelastic regime by the time–temperature superposition principle failure at low frequencies. The tensile properties and X-ray fiber diffraction analysis show that the designed MBCs present elastomeric properties at 25 °C and a remarkable increase of the stiffness at low temperatures. The low-temperature reinforcement effect is caused by side chain crystallization. Upon heating to room temperature, the melting of the side chain crystals induces an almost complete recovery of the pristine dimensions of the sample. It is suggested that the regulation of thermomechanical response, that is, the melting and crystallization temperatures of the side chain crystals along with the strength of reinforcing effect, may be easily achieved for elastomeric MBCs by varying the length of the alk-1-ene counit and/or its content in the soft block.

Age-long ambition of medical scientists has always been advancement in healthcare and therapeutic medicine. Biomedical research indeed claims paramount importance in nanomedicine and drug delivery, and the development of biocompatible storage structures for delivering drugs stands at the heart of emerging scientific works. The delivery of drugs into the human body is nevertheless a nontrivial and challenging task, and it is often addressed by using amphiphilic compounds as nanosized delivery vehicles. Pluronics belong to a peculiar class of biocompatible and thermosensitive nonionic amphiphilic copolymers, and their self-assemblies are employed as drug delivery excipients because of their unique properties. We herein report on the encapsulation of diclofenac sodium within Pluronic F68 self-assemblies in water, underpinning the impact of the drug on the rheological and microstructural evolution of pluronic-based systems. The self-assembly and thermoresponsive micellization were studied through isothermal steady rheological experiments at different temperatures on samples containing 45 wt % Pluronic F68 and different amounts of diclofenac sodium. The adoption of scattering techniques, small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS), allowed for the description of the system features at the nanometer length scale, providing information about the characteristic size of each part of the micellar structures as a function of temperature and drug concentration. Diclofenac sodium is not a good fellow for Pluronic F68. The triblock copolymer aids the encapsulation of the drug, highly improving its water solubility, whereas diclofenac sodium somehow hinders Pluronic self-assembly. By using a simple empirical model and no fitting parameters, the steady viscosity can be predicted, although qualitatively, through the volume fraction of the micelles extracted through scattering techniques and compared to the rheological one. A tunable control of the viscous behavior of such biomedical systems may be achieved through the suitable choice of their composition.

Exploring opportunities for biowaste valorization, herein, humic substances (HS) were combined with gelatin, a hydrophilic biocompatible and bioavailable polymer, to obtain 3D hydrogels. Hybrid gels (Gel HS) were prepared at different HS contents, exploiting physical or chemical cross-linking, through 1-ethyl-(3-3-dimethylaminopropyl)carbodiimide (EDC) chemistry, between HS and gelatin. Physicochemical features were assessed through rheological measurements, X-ray diffraction, attenuated total reflectance (ATR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). ATR and NMR spectroscopies suggested the formation of an amide bond between HS and Gel via EDC chemistry. In addition, antioxidant and antimicrobial features toward both Gram(−) and Gram(+) strains were evaluated. HS confers great antioxidant and widespread antibiotic performance to the whole gel. Furthermore, the chemical cross-linking affects the viscoelastic behavior, crystalline structures, water uptake, and functional performance and produces a marked improvement of biocide action.

We analyzed bubble rupture and hole opening dynamics in a non-Newtonian fluid by investigating the retraction process of thin films after inflation at different blowing rates. The experiments were modeled through a dimensional analysis, with the aim of establishing a general approach on the bubble rupture dynamics and discerning the role of viscous, elastic, surface, and inertial forces on the opening velocity, according to the nature of the specific fluid. A new mathematical model, which includes all possible contributions to the hole opening dynamics, was proposed, to the best of our knowledge for the first time. The experimental evidence on the opening velocity as a function of the inflation rate was found to be in good agreement with the prediction of the model. The sensitivity of our modeling was tested by comparing our results with the existing models of retracting velocity.

In this study, a state-of-the-art high-throughput experimentation (HTE) workflow for catalytic olefin polymerization, covering an unprecedented wide part of the polymer knowledge and value chains from catalytic synthesis all the way down to “engineering” microrheology, was thoroughly assessed with respect to its ability to prepare new materials and produce large and accurate databases for the investigation of quantitative structure–property relationships (QSPRs). Olefin blocks copolymers (OBCs) produced under chain-shuttling polymerization conditions were used as a demonstration case. The results of a thorough microstructural, structural, mechanical, morphological, and rheological characterization of OBC replicas prepared with the HTE synthetic platform and a commercial sample, chosen as a benchmark, demonstrate the robustness of the approach. The proposed workflow can become a paradigm for the high-throughput synthesis and investigation of novel materials, thus reducing the time to market of new products. In our opinion, this opens the door to integrated HTE and artificial intelligence approaches to QSPR problem solving in the numerous cases for which a thorough understanding of the theory is not sufficient to deterministically unravel the complexity of practical applications.

Ethylene/hex-1-ene (E/H) statistical multiblock copolymers (MBCs) with molecular mass between 144 and 188 kDa, and segregation strength greater than that of commercially available samples, are prepared in a high-throughput parallel pressure reactor via chain shuttling copolymerization technology (CSC). They are characterized by alternation of crystalline (hard) and amorphous (soft) blocks with H content xHof ≈1 and ≈34 mol % (ΔxH≈ 33 mol %), respectively, hard block content wh≈ 20, 30, 35, and 50 wt %, and a statistical distribution of block length and the number of blocks per chain. Transmission electron microscopy shows mesophase-separated morphologies in the solid state, crystallization of hard blocks in separated domains, and only scarce inclusion of hard blocks in the alien domains rich in soft blocks. MBCs with hard block content whequal to ≈20 and 30 wt % show round-shaped and isolated worm-like domains rich in hard blocks, respectively, separated by the surrounding amorphous phase through sharp boundaries. The sample with wh≈ 35 wt % shows a disordered bicontinuous structure, whereas the sample with 50 wt % gives rise to an inverted morphology, characterized by round-shaped domains rich in soft blocks scarcely crossed by lamellar crystals and surrounded by a matrix containing sheaf-like lamellar crystal aggregates splaying in all directions. Rheological measurements carried out in a linear viscoelastic regime reveal time–temperature superposition failure in the measured frequency range, suggesting that mesophase separation occurs already in the melt. Mesophase separation in the melt and solid state is controlled by the blocks of major length that are characterized by high segregation strength. The partial solubility of the hard blocks with minor length in the soft block-rich regions is instead responsible for the sporadic crystallization of lamellar crystals in the alien domains.

The consequences of the interfacial mobility on the coalescence process in immiscible polymer blends was studied. Blends of PIB and PDMS with 10 vol.% PIB were subjected to shear‐flow step‐down experiments under controlled conditions. The blend was initially sheared at high shear rate to obtain a fine dispersion (small drop size). The shear rate was then stepped down and the coalescence process was monitored by performing repeated SAOS experiments. In the limit of high and low viscosity ratios, the experimental results were in excellent agreement with theory predictions for IMI and FMI conditions. In the intermediate range of viscosity ratio, corresponding to PMI conditions, a smooth transition between the limiting IMI and FMI states was found.

We investigate the linear and nonlinear shear flow properties of several polystyrene solutions in the unentangled state. The solutions are made up of long (linear) polystyrene chains dissolved in oligostyrene at sufficiently small volume fractions such that the critical entanglement molar mass remains larger than that of the polymer. The use of a cone-partitioned plate fixture for nonlinear rheological measurements, coupled with the relatively small moduli and long relaxation times of the solutions, allows one to explore unprecedented large values of the Rouse–Weissenberg number in shear flow. As a result, chains are stretched close to their maximum extensibility, thus displaying shear strain hardening. Data on normal stresses indicate that the second normal stress difference is virtually zero at high Weissenberg numbers. Brownian dynamics simulations of Rouse-like chains incorporating finite extensibility and friction reduction suitably describe the nonlinear behavior of the solutions provided flow-induced changes of hydrodynamic interactions are also accounted for.

The thermoreversible gelation of hydroxypropylcellulose (HPC)/water solutions is investigated by means of rheological and optical techniques. The linear viscoelasticity of solutions at different concentrations is measured during heating ramps from room temperature. The experimental results suggest that the solution microstructure changes according to two sequential steps, i.e., precipitation and gelation. Temperature, temperature rate of change, and concentration are found to be relevant parameters controlling the phase transition.The thermoreversible gelation of hydroxypropylcellulose (HPC)/water solutions is investigated by means of rheological and optical techniques. The linear viscoelasticity of solutions at different concentrations is measured during heating ramps from room temperature. The experimental results suggest that the solution microstructure changes according to two sequential steps, i.e., precipitation and gelation. Temperature, temperature rate of change, and concentration are found to be relevant parameters controlling the phase transition.

In this paper, the quiescent crystallization of polycaprolactone (PCL) melts is studied by rheological measurements coupled to calorimetry and optical microscopy. Based on a comparison between the different techniques, we find that the increase in viscoelastic properties during crystallization starts only when a relatively high degree of crystallinity is reached, which corresponds to a much developed crystalline microstructure. Like other semicrystalline thermoplastic polymers, the crystallization of PCL can be seen as a gelation process. In this case, however, we find a peculiar critical gel behavior, as the liquid-to-solid transition takes place at a very high (~20%) relative crystallinity, and this value is independent of temperature. These facts, and the comparison with optical microscopy observations, suggest that the microstructure at the gel point is controlled by the interactions between the growing crystallites. The gel time (from rheometry) and the half-crystallization time [from differential scanning calorimetry (DSC)] both show an Arrhenius-like behavior and have the same pseudoactivation energy. A practical implication of this parallel behavior of tgeland t0.5is that the rheological measurements can be used to extend to higher temperatures the study of crystallization kinetics where DSC is not sufficiently sensitive.In this paper, the quiescent crystallization of polycaprolactone (PCL) melts is studied by rheological measurements coupled to calorimetry and optical microscopy. Based on a comparison between the different techniques, we find that the increase in viscoelastic properties during crystallization starts only when a relatively high degree of crystallinity is reached, which corresponds to a much developed crystalline microstructure. Like other semicrystalline thermoplastic polymers, the crystallization of PCL can be seen as a gelation process. In this case, however, we find a peculiar critical gel behavior, as the liquid-to-solid transition takes place at a very high (~20%) relative crystallinity, and this value is independent of temperature. These facts, and the comparison with optical microscopy observations, suggest that the microstructure at the gel point is controlled by the interactions between the growing crystallites. The gel time (from rheometry) and the half-crystallization time [from differential scanning calorimetry (DSC)] both show an Arrhenius-like behavior and have the same pseudoactivation energy. A practical implication of this parallel behavior of tgeland t0.5is that the rheological measurements can be used to extend to higher temperatures the study of crystallization kinetics where DSC is not sufficiently sensitive.

Using rheological techniques, we investigate the evolution of the microstructure evolution during the early stages of quiescent crystallization of poly(1-butene). In performing the measurements, use is made of an innovative experimental protocol, called “inverse quenching”, which allows stopping the crystallization process and producing a stable biphasic (crystalline/amorphous) system. In this way, very low frequency measurements at fixed degrees of crystallization are made possible. We find that crystallization, evidenced as a liquid-to-solid transition (LST) under isothermal conditions, with characteristics of critical gel behavior, takes place at surprisingly low degrees of crystallinity (below 1.5%). The critical gel properties, which are found to depend on both crystallization temperature and molecular weight, can be reduced to a single master curve when the gel strength is plotted as a function of the relaxation exponent. More importantly, the LST is preceded by the development of a long relaxation process. This latter process, although not fully understood, brings analogies to the slow dynamics observed in hybrid colloid−polymer systems (block copolymer micelles or multiarm star polymers) as well as the recently suggested presence of dormant nuclei. It is clear, however, that the connectivity among crystallites, apparently via the amorphous segments, plays a key role in this new process.

Flow Induced Crystallization (FIC) is the common term to indicate the acceleration in polymer crystallization kinetics due to the action of flow. When modeling FIC, two major challenges are encountered. On the one hand, the model must be able to produce quantitative reliable results, while correctly describing the coupling between the intrinsic (quiescent) crystallization kinetics and the rheological response of the polymer. On the other hand, the model must be able to describe the complex kinematics taking place in real industrial processes. In this paper, we present the predictions of a recently proposed model for FIC in the case of a mixed flow, where both shear and extensional components are present at the same time. In particular, the effects of the overall flow intensity and of relative weight between shear and extension on the enhancement in nucleation rate are presented and discussed. Some guidelines for future development are also proposed.

In this work, we present two novel methods to determine the interfacial tension of a disperse polymer blend through rheo‐optical measurements of flow‐induced single drop distortions. A counter‐rotating shearing device with transparent plates is used to measure drop distortions. The cell geometry allows for a top view of the deforming drop, i.e., along the velocity gradient direction. Such a view is the only possible option for all currently available commercial rheo‐optical instruments. Two different quantities are monitored, namely, the drop axis along the vorticity direction, and the rotation period of the drop surface. We use drops of a polyacrilamide aqueous solution (a shear thinning liquid) immersed in a polyisobutene matrix. Experimental results are interpreted in terms of theories for Newtonian liquids, where the relevant parameter is the Capillary number. If an appropriate viscosity ratio is chosen, that accounts for the shear thinning behaviour of the drop phase, good agreement is found between measurements and theoretical predictions. As a result, a robust estimate of the blend interfacial tension, that makes use only of the information acquired from top view experiments, is obtained.

Abstract. Turbidity measurements were used to characterize the effect of shear flow on the crystallization kinetics of several isotactic poly(1-butene) samples of different molecular weight (MW). Polymer melts were rapidly cooled below the nominal crystallization temperature, and subjected to a shear flow of varying shear rate but constant total deformation. While the quiescent crystallization was found to be essentially MW-independent, a strong effect of MW on the flow-induced crystallization kinetics was observed. It was shown that such an effect could be cast in terms of a characteristic Weissenberg number, which measures the ability of flow to orient the polymer chains. The proposed scaling relation was found to predict correctly the dependence of flow-induced crystallization upon molecular weight, at least when samples of similar molecular weight distribution were considered. The molecular weight scaling was also found to explain qualitatively the observed transition from a low-shear rate isotropic morphology to a high-shear rate rodlike crystalline structure.

Flow Induced Crystallization (FIC) is the common term to indicate the acceleration in polymer crystallization kinetics due to the action of flow. FIC is expected to be the result of the coupling between the intrinsic (quiescent) crystallization kinetics and the rheological response of the polymer. The choice of a suitable rheological model, therefore, is a crucial requirement for a successful FIC model. Recent work of our group[1]has demonstrated that the Doi‐Edwards rheological model (DE), based on the concept of chain reptation, can be easily incorporated into classical crystallization models to successful predict the enhancement in nucleation rate under the action of a steady shear flow. In this paper, the interaction between the rheological parameters of the DE model and the crystallization kinetics parameters is investigated in more details. In particular, the effect of the crystallization temperature, which acts on both the polymer relaxation time and the free energy jump between liquid and solid phase, is determined and discussed.

A transparent flow cell apparatus has been used to obtain quantitative information on the morphology evolution of a model polymer blend flowing in complex flow fields. A dilute emulsion of poly-dimethylsiloxane droplets immersed in a poly-isobutene matrix, both Newtonian liquids at room temperature, has been chosen as a model system. Optical microscopy coupled with image acquisition analysis allowed to monitor the behavior of droplets flowing through a sudden contraction and through a gradual converging channel followed by a sudden expansion. The experimental results indicate that drop deformation and breakup are sensitive to both shear and extensional components. A simple criterion, based on the evaluation of a local critical capillary number, is proposed to predict the morphological evolution of the flowing blend. By using computer simulations to estimate the velocity gradients in the flow field, it is shown that the proposed criterion is able to successfully predict the observed morphology.

Aqueous solutions of hydroxypropylcellulose (HPC) have been widely used as a model system to study liquid crystalline behavior in polymers. The HPC limiting concentration for mesophase formation in water is about 40% wt, quite independent of molecular weight. Most rheo-optical investigations have been carried out in the concentration range from 50% to 65% wt, on the assumption that only the liquid crystalline phase was present. In this study, by using video-enhanced contrast light microscopy, we show that an isotropic phase in form of tiny droplets is also present at concentrations up to 60% wt, both in quiescent and in sheared samples at room temperature. The isotropic phase can be made to disappear by lowering the temperature. The effects of phase separation on the rheology of the HPC/water system are studied by measuring viscosity as a function of temperature and concentration. A slope of Region I of the viscosity curve close to -0.5 is found only at low temperatures, when the sample is fully anisotropic, whereas an anomalous dependence of the viscosity on temperature is observed when phase separation is significant. This study shows that special care is needed when interpreting experimental results from the HPC/water system in terms of theories for liquid crystalline polymers.

In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a 'model' polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range-from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations.

Exploring the chance to convert biowaste into a valuable resource, this study tests the potential role of humic acids (HA), a class of multifunctional compounds obtained by oxidative decomposition of biomass, as physical agents to improve gelatin’s mechanical and thermal properties. To this purpose, gelatin–HA aqueous samples were prepared at increasing HA content. HA/gelatin concentrations changed in the range 2.67–26.67 (wt/wt)%. Multiple techniques were employed to assess the influence of HA content on the gel properties and to unveil the underlying mechanisms. HAs increased gel strength up to a concentration of 13.33 (wt/wt)% and led to a weaker gel at higher concentrations. FT-IR and DSC results proved that HAs can establish noncovalent interactions through H-bonding with gelatin. Coagulation phenomena occur because of HA–gelatin interactions, and at concentrations greater than 13.33 (wt/wt)%, HAs established preferential bonds with water molecules, preventing them from coordinating with gelatin chains. These features were accompanied by a change in the secondary structure of gelatin, which lost the triple helix structure and exhibited an increase in the random coil conformation. Besides, higher HA weight content caused swelling phenomena due to HA water absorption, contributing to a weaker gel. The current findings may be useful to enable a better control of gelatin structures modified with composted biowaste, extending their exploitation for a large set of technological applications.

The curing performance of a homogeneous set of different grades of novolac-type phenol–formaldehyde (PF) resins having different structures is analyzed. The PF resins have a statistical ortho/para substitution at aromatic rings and contain from 5 to 15 wt % hexamethylenetetramine (HMTA) as a hardener. Moreover, the different analyzed grades are PF resins differently modified by addition of boron/phosphorous compounds, or an acrylic rubber, or silicone and xylene/phenol copolymers, or introduction of aralkyl modifications. The curing behavior is compared with that of an unmodified PF resin in which the cross-linking agent (HMTA) is added into the molten polymer to guarantee a good dispersion according to the hexamine adduct phenolic (HAP) technology. The effect of the different modifications is probed by rheological measurements during curing under isothermal conditions. Under similar curing conditions, the modified resins show different curing performances and lower stiffness with respect to the unmodified Ph resin obtained by HAP technology. A method to quantify the curing performance is introduced and suggested based on two relevant parameters derived from rheological measurements, the “curing ratio” that indicates the efficiency to generate the thermal-induced three-dimensional network and a “maximum curing rate” that is related to the cross-linking reaction rate. The results allow classifying the resins as belonging to different classes, depending on the combination of the curing ratio and curing rate.