High Polymer Concentrations Research Articles

Uniform Symmetric and Asymmetric Polymer Nanostructures via Directed Chain Organization

Polymer nanostructures can be designed with specific properties and functions, such as controlled shape, size, chemical composition, and adaptive ability to change shape or size in response to environmental cues. Precise control to organize polymer chains into uniform nonspherical symmetric and asymmetric nanostructures and at scale remains a synthetic challenge. Here, by using the temperature-directed morphology transformation (TDMT) method we show through a systematic organization of polymer chains the synthesis of well-defined asymmetric (i.e., tadpole) and symmetric (i.e., worm) nanostructures in water at high polymer concentrations. This method further allowed the production of tadpoles with controlled and uniform tail lengths, ranging from 200 to 800 nm. The organization of chains could be driven by environmental conditions to produce adaptive nanostructure systems.

The use of polyamidoamines for the conservation of iron-gall inked paper

A new approach to the conservation of paper manuscripts is proposed that leads to both deacidification and strengthening of paper. The study was carried out by using polyamidoamines (PAAOHs) functionalized with alcoholic groups, in their native form (PAAb) or neutralized with boric acid (PAAn). They were applied on model paper samples containing iron-gall ink spots through agar rigid gel or by brushing. Preliminary evaluation of the effects of polymer concentration, methods, and duration of application have been tested on model ink-free paper samples. The improvements induced by PAAOHs on paper samples was revealed by surface pH (evaluated in ink-free areas, inside ink spots and on the edges between them) and by measurements of alkaline reserve according to TAPPI T 553 pm-92. The results showed the different behaviour of ink-free and inked regions due to high acidity of iron gall ink. In fact, although a treatment with solutions having low concentration (i.e. 0.1 and 0.15 M) is sufficient for preserving ink-free paper samples from ageing, higher concentration of polymer (0.3 M) or extra brushing application are needed in order to get a complete deacidification of the ink spots. As a side-effect of deacidification treatments, PAAOHs promoted a significant reduction of thermo-hygrometric ageing effects and water smearing at the edge of iron-gall ink spots, as suggested by Raman spectroscopy and mechanical analyses.

Microfluidic-enabled bottom-up hydrogels from annealable naturally-derived protein microbeads

Naturally-derived proteins, such as collagen, elastin, fibroin, and gelatin (denatured collagen) hold a remarkable promise for tissue engineering and regenerative medicine. Gelatin methacryloyl (GelMA), synthesized from the methacryloyl modification of gelatin, mimicking the structure of extracellular matrix, has widely been used as a universal multi-responsive scaffold for a broad spectrum of applications, spanning from cell therapy to bioprinting and organoid development. Despite the widespread applications of GelMA, coupled stiffness and porosity has inhibited its applications in 3D cellular engineering wherein a stiff scaffold with large pores is demanded (e.g., at concentrations >10 wt%). Taking advantage of the orthogonal thermo-chemical responsivity of GelMA, we have developed microfluidic-assisted annealable GelMA beads, that are first stabilized by temperature-mediated physical crosslinking, flowed to form a scaffold structure, and then chemically annealed using light to fabricate novel bead-based 3D GelMA scaffolds with high mechanical resilience. We show how beaded GelMA (B-GelMA) provides a self-standing microporous environment with an orthogonal void fraction and stiffness, promoting cell adhesion, proliferation, and rapid 3D seeding at a high polymer concentration (∼20 wt%) that would otherwise be impossible for bulk GelMA. B-GelMA, decorated with methacryloyl and arginylglycylaspartic acid (RGD) peptide motifs, does not require additional functionalization for annealing and cell adhesion, providing a versatile biorthogonal platform with orthogonal stiffness and porosity for a myriad of biomedical applications. This technology provides a universal method to convert polymeric materials with orthogonal physico-chemical responsivity to modular platforms, opening a new horizon for converting bulk hydrogels to beaded hydrogels (B-hydrogels) with decoupled porosity and stiffness.

Influence of bitumen type on cracking resistance of asphalt mixtures used in pavement overlays

Cracking is one of the predominant distresses occurring in flexible pavements, especially in old pavements that were rehabilitated with an asphalt overlay. In such cases asphalt mixtures should be designed to ensure high resistance to reflective cracking because new asphalt layers are exposed to existing cracks of the old pavement. The nature of these cracks can be various (transverse, longitudinal as well as crazy cracking). One factor that minimizes this type of distress is the proper mix design process, which should involve selection of specific bitumen binder and mineral mix gradation. However, still there is no universally adopted laboratory test method that would allow to clearly assess resistance of asphalt mixtures to reflective cracking. This paper describes the usage of one of the devices developed to test asphalt mixtures in terms of such distress – Texas Overlay Tester. For this test, samples prepared in laboratory conditions (i.e. compacted with the use of Superpave Gyratory Compactor) as well as obtained in the field (by core drilling) can be used. The results are obtained not only quickly and easily, but also with sufficient repeatability. The described method characterizes both crack initiation and crack propagation properties of asphalt mixtures. In this work one type of mineral mixture was tested with 4 different types of bitumen (one neat bitumen, two ordinary polymer-modified and one polymer-modified with high polymer content). For selected cases extra additives (rubber and loose fibres) were also tested. In total, six asphalt mixtures were tested. A ranking of the used binders was created on the basis of the results in order to conclude which bitumen would ensure the best performance characteristics in terms of reflective cracking. The results have clearly shown that deliberate choice of the binder used in the asphalt mixture for the overlay will significantly improve its reflective cracking resistance or even fatigue resistance.

Surfactant enhanced drying of waterbased poly(vinyl alcohol) coatings

Coatings of the poly(vinyl alcohol)-water based system have been studied. The effect of various surfactants on drying beavior was investigated. Anionic (SDS), non- ionic (PEG) and fluoro based surfactants (CAPSTONE FS-63) were used to minimize the residual solvent. The results indicate that the anionic surfactant is not much effective in drying of these coatings whereas the non-ionic surfactant changed the drying behavior to a small extent. The fluro based surfactant showed the significant effect on drying behavior of the coatings. The drying rate in the fluoro based surfactant was moderate for a longer time which led to more solvent recovery. Solutions with high polymer concentrations need high amount of surfactant for significant change in the drying behavior.

OEGylated polypeptide bearing Y-Shaped pendants with a LCST close to body temperature: Synthesis and thermoresponsive properties

The understanding of molecular structure and thermoresponsive property relationships and development of water-soluble thermoresponsive polymers with tunable cloud point temperatures (Tcps) are crucial toward versatile practical uses. Herein, OEGylated polypeptides bearing Y-shaped pendants, namely poly(γ-4-(propoxycarbonyl)benzyl-L-glutamate)-oligo(ethylene glycol) conjugates (8-OEGx, x = 2, 3) were synthesized by the combination of ring-opening polymerization of γ-4-(allyloxycarbonyl)benzyl-L-glutamic acid based N-carboxyanhydride (4) and subsequent side-chain modifications, including bromination of poly(γ-4-(allyloxycarbonyl)benzyl-L-glutamate) (5), nucleophilic substitution of 5 in the presence of NaN3, and subsequent copper-mediated 1,3-dipolar cycloaddition. Both 1H NMR and FTIR analysis confirmed the molecular structures of the intermediates and 8-OEGx. In aqueous solutions, 8-OEGx samples showed reversible lower critical solution temperature (LCST)-type phase transitions in broad polymer concentration range (0–30 mg·mL−1). Variable-temperature UV–vis spectroscopy results revealed that the LCST-type Tcp of 8-OEG2 at high polymer concentrations (e.g., ≥10 mg∙mL−1) was in the range of 37.5–42.5 °C. 8-OEG2 showed a remarkable increase of hydrophilicity than PBLG-OEG4 with the same amount of OEG units as well as linear shaped pendants. The Tcp of OEGylated polypeptides increased by addition of NaI, yet it decreased upon addition of NaCl, NaBr, or KCl, which obeys the Hofmeister effect.

Monitoring the confinement of methylene blue in pyrene labeled poly(acrylic acid)

This work was devoted to investigate the aggregation of methylene blue (MB) with pyrene labeled poly(acrylic acid) (PAA25Py3) by using the measurements of UV–vis absorption, steady-state and time-resolved fluorescence. For comparison, the effect of unlabeled poly(acrylic acid) (PAA25) on the self-association of MB was also evaluated. The spectral positions of the absorption and emission bands of MB as well as the pyrene monomer and excimer emissions were used to assess the local changes of polymer/MB microenvironment. The binding mechanism and thermodynamic analysis for the interaction between MB and pyrene labeled poly(acrylic acid) were evaluated by fluorescence quenching measurements. Moreover, the strategy of switching of pyrene excimer/monomer emission was used to manage the self-aggregation of the pH-responsive fluorescent polymer with phenothiazinium dye. The UV–vis absorption and fluorescence results showed that low amounts of polymers provoked the self-association of MB. At high concentrations of polymer, the MB monomer is stabilized. The labeling of polymer with pyrene induced a dramatic changing of optical properties suggesting that a peculiar process occurred between PAA25Py3 and MB. At low quencher concentrations, both steady-state and time-resolved fluorescence data indicated a static quenching process. The thermodynamic parameters (∆H, ∆S and ∆G) and the efficiency of pyrene excimer formation revealed that the association of MB with the fluorescent polymer occurred spontaneously due to non-covalent hetero π-π stacking, hydrophobic and electrostatic interactions. The study highlights the key contribution of the π-π stacking interactions in the capturing of methylene blue in pyrene labeled poly(acrylic acid). The outcome may be useful in biomedical applications or in wastewater treatment.

Effects of weak-alkali ASP composition on the stability of O/W emulsions

ABSTRACT The effects of weak-alkali ASP composition on the o/w emulsion-stabilizing properties of simulative produced liquid by the weak-alkali ASP flooding were analyzed by use of spinning-drop interfacial-tension (IFT) meters, microscopes, zeta-potential analyzer and Turbiscan laboratory expert stabilizer in this work. The experimental results showed that the irregular movement of the droplets in the lower and middle regions is the main cause of the instability of the emulsion system. The addition of alkali changes the movement of emulsion droplets formed by the weak-alkali ASP system and the oil. Both weak-alkali and surfactants play dual roles in the ASP system. The optimum amount can make the emulsion achieve the best stability and less or more amounts are not conducive to the stability of the emulsion. Appropriately increasing the polymer concentration is helpful to increase the stability of the emulsion. However, the addition of an excessively high concentration of polymer does not increase the stability of the emulsion, resulting in unnecessary waste. It is expected that this study will be of guiding significance for the mechanism of weak-alkali ASP flooding and the treatment of produced liquid in actual production.

Sericin Ameliorates the Properties of Poly(Vinyl Alcohol) Hydrogel Prepared by Simple Repeated Freeze-Thaw Process without the Use of Chemical Crosslinking

Hydrogel of polyvinyl alcohol (PVA) and sericin can be easily produced using a repeated freeze-thaw process. The effects of polymer concentration (4-8 %wt), blending ratio of PVA/sericin (100/0-50/50), and the number of freeze-thawing cycle (4, 8, and 12 cycles) on chemical and physical properties of the hydrogels obtained were studied. We here showed that higher polymer concentration, higher PVA ratio, and more cycles of freeze-thawing produced the hydrogels with high gel (crosslinked) fraction (>90), wall-like structure, and high compressive modulus (100-170 kPa). When the sericin ratio was increased, the hydrogels showed less gel fraction (60-80), more porous structure with highly interconnected pores, and better swelling ability (up to 8-9 times of its original state). The formation of the PVA/sericin hydrogels was occurred by the conformational changes of both PVA and sericin. The secondary structures of PVA and sericin turned to more stable crystalline conformation during the freeze-thawing process, as confirmed by fourier transform infrared (FTIR) spectroscopic results. Furthermore, all hydrogels were not toxic to human skin keratinocytes (HaCaT) cells while the anti-oxidant activity of sericin component in hydrogels was confirmed. We concluded that the freeze-thawing process was a simple and effective technique for fabrication of PVA and sericin, which both are water-soluble, into the stable hydrogels without the use of any chemical solvents or further crosslinking. More importantly, sericin enhances the biological activities of the hydrogels, allowing the use of this hydrogel in various medical applications such as wound dressing.

Thermoviscosifying polymers based on polyether prepared from inverse emulsion polymerization

ABSTRACTThermoviscosifying polymers are attractive for enhancing oil recovery owing to their exceptional thickening power as temperature increases. However, the polymers reported to date show inadequacies including obligatory high polymer concentration to get the thermothickening ability because of their low molecular weight (MW), and inconvenient post‐treatment due to the high viscosity after manufacturing. To overcome these drawbacks, inverse emulsion polymerization was used here for preparing polyether‐based thermoviscosifying polymers (TVP‐Ps) by grafting acrylic monomers onto triblock copolymers PEO–PPO–PEO. It was found the MW of final products could reach 8 million Daltons, making them thermoviscosifying at 0.2 wt %. The viscosity of polymerized inverse emulsions was as low as 175 mPa·s, leading to direct dispersing. The TVP‐Ps containing Pluronic F127, F108, F68 all exhibited significant thermothickening behaviors in both aqueous solutions and brines, and the critical thermoassociative temperature could be tuned by changing the nature or amount of Pluronics. After aging at 45 °C for 60 days with equal initial viscosity, TVP‐Ps shows 21% higher viscosity retention than the reference polymer without Pluronic, PAMA, and preliminary core flooding test demonstrated TVP‐Ps can get 2.1% higher incremental oil recovery than PAMA. This work paves a new avenue for scaled‐up preparation and potential use of TVP‐Ps. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 134, 46696

Histidine and arginine conjugated starch-PEI and its corresponding gold nanoparticles for gene delivery

The high surface energy of gold nanoparticles (GNPs) along with its unique physical and chemical properties delivers it as an effective nonviral gene delivery platform for anticancer treatments. GNPs were synthesized by using starch-PEI in which PEI act as reducing agent and starch as a stabilizer. Cytocompatibility studies carried out in C6 cells revealed that gold modification significantly improved the percentage cell viability even at higher polymer concentration. Irrespective of excellent cellular internalization, the transfection efficiency studied with p53 plasmid was found to be compromised with gold modification. For better transfection efficiency, we further modified starch-PEI with amino acids (l-Arginine, l-Histidine) and synthesized the corresponding GNPs. Though starch-PEI gold nanoparticles exhibited low transfection, its amino acid modified counterparts were found to have good transfection efficiency along with low cytotoxicity. It was found that the GNPs containing l-Arginine showed improved transfection efficiency. Hence, it can be inferred that selective amino acid modification is beneficial for improving the transfection efficiency.

Experimental study of two-phase oil – Polymer flow in horizontal flow path

Two-phase flow inside the oil and gas wells and flow path lines is a usual occurrence in petroleum and petrochemical studies. Due to its complexity, flow transfer parameters such as hold up and pressure drop and their dependency on the flow regime maps are not well understood yet. This study is aimed at analyzing holdup for oil- water system and evaluation of this parameter by means of Image processing under different available flow regime conditions. In addition, different oil-polymer systems have been studied to evaluate the impact of polymer concentration on transport criteria. The experimental setup used for this study is consisted of a 12 m long Plexiglas pipe with an inner diameter of 30 mm. The results revealed that the only polymer solutions with polymer concentration below than 333 ppm behave as Newtonian fluids. The results showed that low concentration of polymer solution acts as drag reducing agent and reduces the amount of pressure gradient in comparison with oil – water system. Furthermore, the change in flow pattern map between oil-low concentration polymer solution and oil-high concentration polymer solution systems have been analyzed. The results showed that high concentration polymer solution not only leads to higher degrees of pressure drop but also impacts the flow pattern map and more specifically the Three-Layer flow regime cannot be observed in such flow systems. Therefore, a generalized model has been developed to define the flow regime map and the transition criteria between different flow regimes as well as pressure drop and hold up for oil – polymer systems.

Biosynthesis and properties of P(3HB‐co‐3HV‐co‐3H4MV) produced by using the wild‐type strain Cupriavidus eutrophus B‐10646

AbstractBACKGROUNDPolyhydroxyalkanoates (PHA) containing 3‐hydroxy‐4‐methylvalerate (3H4MV) have better processing properties than other PHA types and were not prone to ageing. The main challenge in the production of these polymers is to simultaneously achieve high cell biomass, high polymer content, and high molar fraction of 3H4MV. The aim of this study was to investigate the production of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate‐co‐3‐hydroxy‐4‐methylvalerate) [P(3HB‐co‐3 HV‐co‐3H4MV)] by Cupriavidus eutrophus B‐10646, synthesize polymers with different contents of 3H4MV and investigate their properties.RESULTSIt was shown that 4‐methylvalerate (4MV, the precursor substrate) concentration in the culture medium must not be higher than 1 g L−1, and that 4MV must be carefully dosed, with at least 10–12 h intervals between supplementations. A series of polymers with molar fractions of 3H4MV between 2.7 and 11.3 mol% was synthesized. Degrees of crystallinity, molecular weight characteristics, and thermal properties of the polymers have been investigated as dependent on proportions of monomers.CONCLUSIONThe content of 3H4MV depends on the concentration of 4MV and conditions of carbon nutrition. The molar fraction of 3H4MV had a strong effect on the crystalline to amorphous region ratio. PHA containing 3H4MV specimens synthesized in this study had a degree of crystallinity of below 50%, which remained unchanged for 2.5 years. © 2018 Society of Chemical Industry

Microwave assisted quaternization of poly(4-vinylpyridine) with 1-bromohexane

Quaternization reaction is a well-known technique and can be applied to obtain functional polycations. If quaternization agents used in this reaction contain more than 4 carbons, it can take days or weeks to reach high degrees in quaternization. In the study, microwave heating was used to increase the reaction rate. Kinetics of microwave-assisted quaternization of poly(4-vinylpyridine) with 1-bromohexane was investigated by varying the reaction conditions, such as solvent, temperature, molar ratio of components and concentrations. In less than 1 h, quaternization degree of poly(4-vinylpyridine) reached higher than 80% values in DMF and DMSO with microwave heating at 80 °C. Higher polymer concentration and molar ratio of N1-bromohexane/N4-vinylpyridine also increased the reaction rate. It was demonstrated that microwave heating can be applied to increase the quaternization reaction rate. Very short reaction times as low as minutes may allow quaternization reaction to be used in more studies for novel functional polycations.

Comparison of Carbon Based Bipolar Plate Materials for Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells can be separated into two types, the high-temperature (HT) PEM and low-temperature (LT) PEM fuel cell. As main advantages operating at higher temperatures improved tolerances to impurities like carbon monoxide, easier heat rejection and simpler water management can be mentioned. In comparison to LT-PEM fuel cells where sulfuric acid is applied polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) were used in HT-PEM fuel cells. Nevertheless, degradation and long term stability are still major challenges. Here, it is necessary to understand the degradation mechanisms regarding membrane and catalyst degradation, carbon corrosion as well as loss of phosphoric acid and degradation of bipolar plates (BPP). Titration investigations of carbon based bipolar plates after operation in PEM fuel cells showed that phosphoric acid can be found within the composite matrix [1, 2] which can lead to corrosion of the graphite material. In this work, a variety of graphite-polymer composite bipolar plate materials for PEM fuel cells were tested for their stability and compared with different methods. The electrochemical stability was investigated by means of corrosion measurements within a three-electrode cell setup. The bipolar plate material was applied as working electrode and a platinum wire with an activated felt was served as counter electrode. Potentials are shown with respect to the standard hydrogen electrode (SHE). Two different methods of aging were used: chemical storage and potentiostatic treatment. For determination of stability and corrosion rates OCP, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were evaluated. Additionally, the bipolar plate materials were compared by electrical conductivity measurements (in-plane and through-plane), contact angle measurements as well as structural changes of the surface area. Here different imaging methods like scanning electron microscopy (SEM), micro-computed tomography (µ-CT), atomic force microscopy (AFM) and confocal microscopy were applied. First results of two graphite composite bipolar plate materials with different types and amount of polymer binder show different electrochemical behavior after chemical aging for 3 and 7 days in 0.5 M H2SO4. The bipolar plate material with higher polymer content (BPP-01) reveals lower double layer capacitance and a lower amount of oxygen functional groups in the potential range between 0.5-0.7 V vs. SHE (Figure 1) in comparison to the bipolar plate with higher polymer content (BPP-02). The reason for this behavior could be the lower amount of electrochemical active graphite at the BPP/electrolyte interface from BPP-01 in comparison to BPP-02. In addition, conductivity measurements show that BPP01 has a higher sheet resistance (53.6 +/- 5.6 mOhm) compared to BPP-02 (46.2 +- 4.5 mOhm) in good agreement to the content of polymer and graphite in the composite materials. The various methods can be used to identify the difference of graphite compound materials and correlate it to degradation mechanism. Further results will be given. [1] C. Hartnig and T. J. Schmidt, Electrochim. Acta, 56 (2011), 4237-4242.[2] N. Pilinski, M. Rastedt and P. Wagner, ECS Trans., 69 (2015), 323-335. Figure 1

Electrochromic behavior and electrical percolation threshold of carbon nanotube/poly(pyridinium triflate) composites

The electrochromic composite material based on poly(4,4′-(1,4-phenylene)bis(2,6-diphenylpyridinium) triflate) (PV) and multiwall carbon nanotubes (MWCNTs) was prepared by non-covalent interaction where PV acts as a functionalizing agent for MWCNTs. The increase in electrical conductivity and improvement of electrochromic properties of PV is attributed to the formation of MWCNTs networks. The percolation threshold for PV/MWCNTs occurred at 0.3 wt% of MWCNTs. Corresponding value of critical exponent was found to be 2.8 which is far from universal values. At practically the same electrochromic contrast the coloring and bleaching time for composites with higher polymer concentration (8 mg/mL) decreased from 600 ms to 300 ms and from 500 ms to 350 ms, respectively. It was demonstrated that further increase of MWCNTs weight content did not lead to the improvement of electrochromic properties.

Microencapsulation of caffeic acid and its release using a w/o/w double emulsion method: Assessment of formulation parameters

Caffeic acid (CAF)has numerous health benefits mainly due to its antioxidant, antibacterial and fungicide properties. However, its incorporation in skin care products as anti-aging and the photoprotective agent is still limited due to its solubility and stability in oily matrices or solutions balanced with the skin pH. In this research, CAF–ethyl cellulose (EC) microparticles were produced by water-in-oil-water double emulsion solvent evaporation encapsulation technique using a biocompatible polymer, EC, as a coating material and a surfactant, polyvinyl alcohol, as a stabilizer of the double emulsion. The study assessed the influence of formulation parameters as the solubility of the polymer in organic solvents and the polymer concentration on microparticles final characteristics. CAF–EC microparticles were characterized by product yield, encapsulation efficiency, mean particle size, particle size distribution and polydispersity and imaged by scanning light microscopy. In vitro release profiles were obtained in water and octanol to mimic oily based and water-based matrices balanced with the skin pH. In vitro release kinetics studies were carried out to investigate the release pattern of CAF in simulated cosmetic formulations. Both the product yield and the encapsulation efficiency were found to be dependent on the solubility of the polymer in the organic phase. The product yield was mainly affected by operational factors such as the sticking and the agglomeration of the polymer to the walls and the magnet stirring during microparticles hardening and results from the encapsulation efficiency revealed that an increase of the polymer concentration led to an increase of the encapsulation efficiency. The usage of a water-soluble solvent contributed to a decrease in the mean particle size and reduction of polydispersity with higher polymer concentrations. The polymer concentration, the polymer solubility in the organic phase and the amount of CAF entrapped shown to affect the release in water, whereas the release in octanol was mainly independent of the amount of CAF entrapped in EC microparticles. The double emulsion solvent evaporation technique and the assessment of the selected formulation conditions have given significant and innovative insights on the microencapsulation of bioactive ingredients for cosmetics formulations.

Dynamic Behaviors of Solvent Molecules Restricted in Poly (Acryl Amide) Gels Analyzed by Dielectric and Diffusion NMR Spectroscopy.

Dynamics of solvent molecules restricted in poly (acryl amide) gels immersed in solvent mixtures of acetone–, 1,4-dioxane–, and dimethyl sulfoxide–water were analyzed by the time domain reflectometry method of dielectric spectroscopy and the pulse field gradient method of nuclear magnetic resonance. Restrictions of dynamic behaviors of solvent molecules were evaluated from relaxation parameters such as the relaxation time, its distribution parameter, and the relaxation strength obtained by dielectric measurements, and similar behaviors with polymer concentration dependences for the solutions were obtained except for the high polymer concentration in collapsed gels. Scaling analyses for the relaxation time and diffusion coefficient respectively normalized by those for bulk solvent suggested that the scaling exponent determined from the scaling variable defined as a ratio of the size of solvent molecule to mesh size of polymer networks were three and unity, respectively, except for collapsed gels. The difference in these components reflects characteristic molecular interactions in the rotational and translational diffusions, and offered a physical picture of the restriction of solvent dynamics. A universal treatment of slow dynamics due to the restriction from polymer chains suggests a new methodology of characterization of water structures.

Studying the interaction of hydrophobically modified ethoxylated urethane (HEUR) polymers with sodium dodecylsulfate (SDS) in concentrated polymer solutions

HypothesisHydrophobically modified ethoxylated urethane polymers (HEURs) are widely used to control the rheological profile of formulated particulate dispersions through associative network formation, the properties of which are perturbed by the presence of surfactants. At high polymer concentrations and in the presence of surfactants, it is hypothesised that the dominant factors in determining the rheological profile are the number and composition of the mixed hydrophobic aggregates, these being defined by the number and distribution of the hydrophobic linkers along the polymer backbone, rather than the end-group hydrophobe characteristics per se that dominate the low polymer concentration behaviour. ExperimentsThree different HEUR polymers with formulae (C6-L-(EO100-L)9-C6, C10-L-(EO200-L)4-C10 and C18-L-(EO200-L)7-C18 (where L = urethane linker, Cn = hydrophobic end-group chain length, and EO = ethylene oxide block) have been studied in the absence and presence of SDS employing techniques that quantify (a) the bulk characteristics of the polymer surfactant blend, (b) the structure and composition of the hydrophobic domains, (c) the dynamics of the polymer and surfactant, and (d) the polymer conformation. Collectively, these experiments demonstrate how molecular-level interactions between the HEURs and sodium dodecylsulfate (SDS) define the macroscopic behaviour of the polymer/surfactant mixture. FindingsBinding of the SDS to the polymer via two mechanisms – monomeric anti-cooperative and micellar cooperative – leads to surfactant-concentration-specific macroscopic changes in the viscosity. Binding of the surfactant to the polymer drives a conformational rearrangement, and an associated redistribution of the polymer end-groups and linker associations throughout the hydrophobic domains. The composition and size of these domains are sensitive to the polymer architecture. Therefore, there is a complex balance between polymer molecular weight, ethylene oxide block size, and number of urethane linkers, coupled with the size of the hydrophobic end-groups. In particular, the urethane linkers are shown to play a hitherto largely neglected but important role in driving the polymer association.

Preparation of Poly(l-lactic acid) Scaffolds by Thermally Induced Phase Separation: Role of Thermal History

Abstract Poly-L-Lactic Acid (PLLA) scaffolds for tissue engineering were prepared via thermally induced phase separation of a ternary system PLLA/dioxane/tetrahydrofurane. An extension to solution of a previously developed method for solidification from the melt was adopted, the technique being based on a Continuous Cooling Transformation (CCT) approach, consisting in recording the thermal history of rapidly cooled samples and analysing the resulting morphology. Different foams were produced by changing the thermal history, the dioxane to THF ratio (50/50, 70/30, 90/10 v/v) and the polymer concentration (2, 2.5, 4 ° wt) in the starting ternary solution. Pore size, porosity, melting and crystallization behavior were studied, together with a morphological and kinetic analysis of the foams produced. A large variety of morphologies was achieved, the largest pore size (20 μm) was achieved at the highest polymer concentration (4 ° wt) and the lowest dioxane concentration (50/50 dioxane/THF v/v), whereas the largest porosity (90 °) was attained at the highest dioxane concentration (90/10). The average pore size is related to cooling rate, with a 1/3 power law exponent at low polymer concentrations and low dioxane content for thermal histories driven by low undercoolings. At high undercoolings, the growth of the demixed domains significantly departs from the diffusive-like regime.