Calculation of discrete retardation spectra from creep data — II. Analysis of measured creep curves

An algorithm for the calculation of discrete, logarithmic equidistant retardation spectra from creep or recovery is applied to experimental data in different regions of consistency. Spectra in the glass-rubber transition region are given for technical poly(styrene), poly(methylmethacrylate), and poly(carbonate) as well as the course of all characteristic compliance type functions. The spectrum in the terminal region of a poly(styrene) of narrow molecular weight distribution is calculated both from creep and recovery data. The course of the dynamic moduli calculated from the spectra and by direct conversion is found in excellent agreement to measurements by means of a dynamic viscometer.Dedicated to Prof. Dr. H. Janeschitz-Kriegl at the occassion of his 70th birthday.     

mPEG-b-PLGA胶束薄膜的制备及其摩擦学行为研究

采用层层组装(layer by layer,LBL)方法,以氢键结合方式,将聚乙二醇-b-聚乳酸聚乙醇酸(mPEG-b-PLGA)胶束与聚丙烯酸(PAA)层层交替沉积到硅基底上,分别用接触角测量仪,椭圆偏光测厚仪,X光电子能谱及原子力显微镜等对聚合物胶束自组装薄膜的结构进行了表征,用UMT-2对薄膜的摩擦学特性进行了表征.沉积到基底表面的胶束薄膜能够稳定附着,且具有良好的减摩效果,有望作为导尿管或体内植入器件表面的抗炎、润滑多功能涂层.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene (PSt) microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate (KPS) as initiator in ethanol-water mixed solvents.Emulsifier-free seeded emulsion copolymerization of styrene (St) with acrylonitrile (AN) was carried out in the presence of poly(ethylene glycol) monomethoxymonomethacrylate (PEGm)macromonomer as reactive stabilizer and 2,2'-azobisisobutyronitrile (AIBN) as initiator to obtain submicron-sized PEGm graft poly(styrene-co-acrylonitrile) (PEGm-g-PSAN) composite particles with unique morphology.Scanning electron microscopy (SEM) indicated that St and AN together contributed to forming the unusual morphology.The concentration of St and AN,total monomer concentration,initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

Dispersion of multi-walled carbon nanotubes in poly（p-phenylene） thin films and their electrical characteristics

Dispersion of multi-walled carbon nanotubes in poly（p-phenylene） composite exposed to toluene was experimentally investigated. 3 mg of multi-walled carbon nanotubes with nominal size of 20 nm was compounded with 30 mg of poly（p-phenylene） with the presence of terpineol as binding initiator. To investigate an optimal condition for homogenizing all constituents, ultrasonication with an output power of 750W was employed with compounding time of 3, 10, 20 and 30 min. With FTIR analyses, it could be confirmed that homogeneous composite of multi-walled carbon nanotubes and poly（p-phenylene） could be prepared. SEM analyses were also conducted to examine the dispersion of multi-walled carbon nanotubes in the polymer matrix. Then intrinsic electrical resistance of the composites after being exposed to toluene was also investigated. It was found that the composite film prepared with ultrasonication for 20 min could provide sufficiently sensitive response with respect to varied concentration of toluene.     

Direct numerical simulation of modulation of isotropic turbulence by poly‐dispersed particles

A direct numerical simulation technique based on two‐way coupling is presented to study a particle‐laden, decaying isotropic turbulent flow. Physical characteristics of turbulence modulation because of the mono‐dispersed (i.e., particles with single Stokes number) and poly‐dispersed particles (i.e., particles with more than one Stokes number) were investigated. A scale dependent effective viscosity that summarizes the aspects of the interaction between the velocity field and particles is defined in the study. Particles of Stokes number (St) 3.2,6.4 and 12.8 were used in performing the simulations. Poly‐dispersed particles were acquired by mixing particles of two different Stokes numbers at a time. As a whole, decay of turbulence because of the poly‐dispersed particles is observed to be larger than that of the decay of turbulence because of the mono‐dispersed particles. Simulations of poly‐dispersed particle indicate nonlinear characteristics in the modification of the temporal evolution of turbulence energy and dissipation. The scale dependent effective viscosity, which correlates with the energy spectrum plot, indicates that the decay of turbulence is mostly observed at the intermediate scales of turbulence. The effective viscosity for the simulations of the poly‐dispersed particles was calculated to be higher than that of the simulations of the mono‐dispersed particles. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene （PSt） microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate （KPS） as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene （St） with acrylonitrile （AN） was carried out in the presence of poly（ethylene glycol） monomethoxymonomethacrylate （PEGm） macromonomer as reactive stabilizer and 2,2＇-azobisisobutyronitrile （AIBN） as initiator to obtain submicron-sized PEGm graft poly（styrene-coacrylonitrile） （PEGm-g-PSAN） composite particles with unique morphology. Scanning electron microscopy （SEM） indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

Linear and branched poly(butyleneisophthalate): Activation energy for melt flow

Several poly(butyleneisophthalate)s of different molecular weight, both linear and randomly branched, were synthetized by bulk polymerization and studied in the molten state with a capillary rheometer in the temperature range 190–220°C. The viscosity shift factors showed to be well correlated to temperature by an Arrhenius-type equation. The melt-flow activation energy at constant shear stressE was found to be 15±1 kcal/mol for both linear and branched samples, whereas for polydisperse poly(butyleneterephthalate) and poly(ethyleneterephthalate) it was found previously that random long-chain branching substantially increases the activation energy.An analysis of our results and of those available in the literature shows that the influence of branches on the temperature coefficient of viscosity of polymers is still a subject open to discussion.     

MOLECULAR DYNAMICS SIMULATION OF POLYMER/CARBON NANOTUBE COMPOSITES

In this paper, we present classical molecular dynamics(MD) simulations of model polymer/CNT composites constructed by embedding a single wall(10,10) CNT into two different amorphous polymer matrices: poly(methyl methacrylate) and poly{(m-phenylene-vinylene)-co-[(2,5-dioctoxy-p-phenylene) vinylene]}, respectively, with different volume fractions. The simulation results support the idea that it is possible to use CNTs to mechanically reinforce an appropriate polymer matrix, especially in the longitudinal direction of the nanotube. The comparison of the simulation results with the macroscopic rule-of-mixtures for composite systems showed that for strong interfacial interactions, there can be large deviations of the results from the rule-ofmixtures. In order to verify this study, results obtained have been compared with those given by Elliott and Han(2007).     

PREPARATION AND CHARACTERIZATION OF SUPERPARAMAGNETIC FUNCTIONAL POLYMERIC MICROPARTICLES

Superparamagnetic poly(styrene-divinylbenzene-glycidyl methacrylate) (Pst-DVB-GMA) microparticles were prepared via a modified suspension polymerization process. A magnetic fluid was first prepared by a chemical co-precipitation method. Then magnetic microparticles were produced by mixing the monomers and the magnetic fluid with water in the presence of a stabilizer poly(vinyl pyrrolidone) (PVP) to form a suspension, and finally benzoyl peroxide was added to initiate the co-polymerization. The morphology and magnetic properties of the microparticles were examined by TEM and VSM. The spherically shaped microparticles, with a size range of 4 to 7 pm, showed distinct superparamagnetic characteristics. XRD was used to investigate the structure of the magnetite particles dispersed in the polymer matrix. The microparticles with epoxy groups on their surface can be applied directly to the seoaration of biomolecules.     

Scaling theory of adsorption-induced stresses in polymer brushes grafted onto compliant structures

The lateral forces exerted on a substrate by a layer of end-grafted polymer molecules are calculated on the basis of simple scaling arguments. The results are cast in terms of an equilibrium surface stress and an elastic constant, which describes the rate of change of the surface stress upon deformation of the substrate. This allows for straightforward integration of the present results into a continuum framework describing the response of a compliant structure, which facilitates device design and analysis. The results are illustrated with calculations for end-grafted poly(styrene) and poly(ethylene oxide), and the implications for building micromechanical devices based on adsorption-induced deformation are discussed.     

Molecular origin of viscoelasticity and chain orientation of glassy polymers

Dynamic birefringence and dynamic viscoelasticity of poly(4-methyl styrene) and poly(4-t-butyl styrene) were measured to investigate the molecular origin of viscoelasticity around the glass transition zone. The data were analyzed with a modified stress-optical rule: The birefringence and the stress were separated into two component functions of different molecular origins. One component is related to the orientation of the main chain axis and the other one to the rotation of the repeating units about the main chain axis. The strain dependence of the two characteristic orientation functions in the glassy zone was estimated and the orientation mechanism of repeating units was discussed.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

Enhanced bioavailability and biosafety of cannabidiol nanomicelles for effective anti-inflammatory therapy

Cannabidiol (CBD) shows great anti-inflammatory potential; however, the hydrophobicity and strong first-pass effect of CBD leads to its extremely low oral bioavailability. Poloxamer 407 (P407) is a triblock copolymer composed of (poly)ethylene oxide (PEO) and (poly)propylene oxide (PPO) sections. It has a PEO-PPO-PEO structure, which is widely used in the preparation of drug delivery systems that are highly biocompatible. When it reaches a certain concentration in water, P407 can self-assemble into a micelle structure containing a hydrophobic core and a hydrophilic shell. A potential approach to enhancing the oral bioavailability of hydrophobic drugs incorporating them into the hydrophilic carrier. We prepared CBD nanomicelles with a drug loading of 14.29% by a cosolvent evaporation method using P407 with appropriate antioxidants. Cell experiments indicated that anti-inflammatory markers (IL-4 and IL-10) increased, while inflammatory markers (TNF-α and IL-6) decreased. Moreover, animal experiments showed that inflammatory cells were inhibited by CBD nanomicelles, and the anti-inflammatory effect of micelles was better than that of CBD, while no obvious evidence indicated toxicity to the liver and kidney.     

Threshold-type shear-thickening in polymeric solutions

Threshold-type shear-thickening has been reported in the literature for relatively complex mixtures and one of the most famous is a solution of poly(vinylalcohol) in water in which a substantial amount of sodium borate is added. As far as we know, relatively few polymer solutions have been shown to be shear-thickening, even less of the threshold type. Two cases of threshold-type shear-thickening are examined. One of them is reversible [HPAM Pusher 700 or partially hydrolyzed poly(acrylamide) aqueous solution], the other one (in vitro-synthesized native dextran aqueous solution) leads to the formation of an irreversible structure provided sufficient strain is applied. In both cases, the occurrence of shear-thickening above a critical value of shear rate is related with a change in macromolecular conformation. This conformational change (reversible) can be followed by the formation of intermolecular bonds (irreversible).Presented at the 57^th Annual Meeting of the Society of Rheology, Ann Arbor, Michigan, Oct. 1985     

Ultrapermeable membranes based on connected cluster of hollow polydimethylsiloxane nanoparticles for gas separation

Mixed matrix membranes (MMMs) with the performance between the matrix and the filler is a promising strategy for membranes with excellent gas permeability-selectivity. In this study, the hollow polydimethylsiloxane nanoparticles were synthesized and then incorporated with the poly(oxide ethylene) monomer and tri-functional cross-linker to form mixed matrix membranes by in situ polymerization. The hollow nanoparticles formed the independent closed nanocavities in membranes, which enhanced the gas permeability contributed by both the improved diffusivity and solubility. At high loading, the hollow polydimethylsiloxane nanoparticle was converted into the continuous phase with the cross-linked poly(oxide ethylene) as the dispersed phase. Gases preferred to permeate through the connected cluster of hollow polydimethylsiloxane nanoparticles, finally leading to ultrahigh gas permeabilities far going beyond the instinct values of polydimethylsiloxane and the cross-linked poly(oxide ethylene). The optimized membrane with 34 wt% hollow nanoparticles loadings exhibited ultrahigh permeabilities with the values of 44186 Barrer for CO₂ and 11506 Barrer for O₂, accompanied with a CO₂/N₂ selectivity of 9.9 and an O₂/N₂ selectivity of 2.6, which exceeded the 2008 Robeson upper bound for O₂/N₂ and located at the 2008 Robeson upper bound for CO₂/N₂.     

Mechanical, rheological, fatigue, and degradation behavior of PLLA, PGLA and PDGLA as materials for vascular implants

The biggest challenge in the treatment of arterial stenosis remains the issue of optimization of stent design. Despite continuous improvement in surgical techniques and use of intensive pharmacotherapy, the results of stent coronary interventions may be unsatisfactory, and long-term interaction of a metal implant with a blood vessel results in complications such as recurrent stenosis and thrombosis. Therefore, it is necessary to search for new materials and stent designs to obtain a stent capable of restoring flow in the vessel and disappearing after fulfilling its function. Such stent must also be compatible with the vessel wall to enable regeneration of new structure of endothelium and deeper artery layers damaged during implantation. Consequently, there is ongoing search for functional solutions with minimum effects of long-term implant-tissue interaction. In light of the above, the team investigated the possibility of using biodegradable polymers already mentioned in the literature as a construction material for vascular stent. The study used three polyhydroxyacids based on lactic acid and glycolic acid: poly(l-lactide), poly(lactide-co-glycolide) and poly(d,l-lactide-co-glycolide). The research focused on assessing changes in mechanical, thermomechanical, rheological, and fatigue properties during the process of hydrolytic degradation. The analysis also covered the rate of release of degradation products. The results of the conducted tests indicate the possibility of developing a vascular stent with biodegradable polymers.     

锂离子液体作为聚乙二醇添加剂的摩擦学性能研究

利用2-恶唑烷酮(OZO)、尿素、三乙二醇二甲醚(G3)和四乙二醇二甲醚(G4)与四氟硼酸锂(LiBF4)、六氟磷酸锂(LiPF6)、三氟甲烷磺酸锂(LiSO3CF3)和双(三氟甲烷磺酰)亚胺锂(LiTFSI)的配位作用,在聚乙二醇(PEG)中合成了一系列锂离子液体润滑油添加剂,如[Li(OZO)]BF4、[Li(OZO)] PF6、[Li(OZO)]SO3CF3和[Li(OZO)] TFSI等,并对其物理化学性质和摩擦学性能进行了研究.结果显示:这类离子液体在PEG中具有较好的溶解性,作为PEG的添加剂,显示出优于传统离子液体(1-丁基-3-甲基咪唑双三氟甲烷磺酰亚胺盐)的减磨抗磨性能;阳离子对这一系列离子液体添加剂的摩擦学性能影响不明显,以TFSI-为阴离子的离子液体表现出最好的减摩性能.     

Rheological,morphological, and interfacial properties of compatibilized PLA/PBAT blends

The focus of this paper was to gain a true understanding of the impact of a multifunctional epoxide (Joncryl®;ADR-4368) on the interfacial properties of biopolymer blends based on poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). The effect of Joncryl on the shear rheological, morphological, and interfacial properties of the blends was systematically investigated. For the deformed drop retraction experiments, different sandwich model systems (droplet/matrix), representing various scenarios of compatibilization, were prepared, aiming to probe the role of the epoxy-functionalized chains on the interface. The decrease of the interfacial tension in the modified/compatibilized PLA_PBAT and the formation of the PLA-Joncryl-PBAT copolymer were highlighted. A new relaxation peak relative to this copolymer was detected by the relaxation spectrum. Transient start-up shear and nonlinear stress relaxation experiments were carried out and confirmed the obtained results. In addition, the interface contribution was demonstrated using the Lee and Park model. The relaxation time increased with the amount of added Joncryl. Hence, the coexistence of chain extension/branching chains coupled to the PLA-Joncryl-PBAT copolymer formation had to be taken into account to explain the improved mechanical properties.     

Relaxation dynamics of selected polymer chain segments and comparison with theoretical models

Simultaneous measurement of infrared dichroism and birefringence is used to study selected polymer segment dynamics in isotopically labeled block copolymers. Two different polymers were studied: polybutadiene and poly (ethylene propylene). The first type consisted of a triblock with a short middle block labeled and a diblock with a short end block labeled, while the second type consisted of a triblock with three equal blocks and the end blocks labeled. Results of step strain experiments at –10°C for polybutadiene and at room temperature for poly(ethylene propylene) indicated that segments located at chain ends relax faster than segments located at chain centers. These experimental data were compared to the predictions of two molecular models: the bead-spring model of Rouse and the tube model of Doi and Edwards, and it was found that both models correctly predict the qualitative features of segmental relaxation. However, the tube-model predictions were closer to the experimental results. In addition, when the effects of orientational coupling interactions between segments in the melt were incorporated into this model, its predictions quantitatively agreed with the experimental results. The orientational coupling coefficient for poly(ethylene propylene) was 0.45 as measured from previous work, and for polybutadiene it was found to be 0.4.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.Dedicated to Prof. R.S. Stein, University of Massachussets at Amherst, USA, on the occasion of his 65th birthday.     

ADVANCES IN MICROEMULSION PHASE ON SELF-ASSEMBLY AND MICELLE EXTRACTION WITH BLOCK COPOLYMERS

In this paper we review our work on self-assembly of the system, poly（ethylene oxide）-poly（propylene oxide）-poly（elhylene oxide） （PEO-PPO-PEO） block copolymers, which is a kind of macromolecular complex fluids. The control of self-assembly could be obtained by adding inorganic salts or aliphatic alcohols. By self-assembly of amphiphilic block copelymers a microemulsion phase is formed which could be applied in micelle extraction, such as hollow-fiber membrane micelle extraction, magnetic micelle extraction and immobilized micelle extraction.     

Phase behavior and effects of microstructure on viscoelastic properties of a series of polylactides and polylactide/poly(ε-caprolactone) copolymers

Dynamic viscoelastic measurements were combined with differential scanning calorimetry (DSC) and atomic force microscopy (AFM) analysis to investigate the rheology, phase structure, and morphology of poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL), poly(d,l-lactide) (PDLLA) with molar composition l-LA/d-LA?=?53:47, and poly(l-lactide-co-ε-caprolactone) (PLAcoCL) with molar composition l-LA/CL?=?67:33. After melt conformation, both copolymers PDLLA and PLAcoCL were found to be amorphous whereas PLLA and PCL presented partial crystallinity. The copolymers and PCL were considered as thermorheologically simple according to the rheological methods employed. Therefore, data from different temperatures could be overlapped by a simple horizontal shift (a _T) on elastic modulus, G′, and loss modulus, G′, versus frequency graph, generating the corresponding master curves. Moreover, these master curves showed a dependency of G″≈ω and G′≈ω ² at low frequencies, which is a characteristic of homogeneous melts. For the first time, fundamental viscoelastic parameters, such as entanglement modulus G _N ⁰ and reptation time τ _d, of a PLAcoCL copolymer were obtained and correlated to chain microstructure. PLLA, by contrast, was unexpectedly revealed as a thermorheologically complex liquid according to the failure observed in the superposition of the phase angle (δ) versus the complex modulus (G*); this result suggests that the narrow window for rheological measurements, chosen to be close to the melting point centered at 180 °C thus avoiding thermal degradation, was not sufficient to assure an homogeneous behavior of PLLA melts. The understanding of the melt rheology related to the chain microstructural aspects will help in the understanding of the complex phase structures present in medical devices.