IV INTERNATIONAL CONFERENCE TIMES OF POLYMERS (TOP) AND COMPOSITES
CHAIN DYNAMICS IN SOLID POLYMERS AND POLYMERIZING SYSTEMS AS REVEALED BY BROADBAND DIELECTRIC SPECTROSCOPY1042(2008); http://dx.doi.org/10.1063/1.2989001View Description Hide Description
A number of techniques are used to study the chain‐dynamics of solid polymers, including those of dielectric relaxation [1–4], dynamic mechanical thermal analysis (DMTA) [1, 5], multinuclear NMR relaxations , quasi‐elastic dynamic light scattering  and neutron scattering  (QELS & QENS) and transient fluorescence depolarization (TFD) . Each technique has its own particular probe of the dynamics in a material. e.g. dielectric relaxation gives information on the angular motions of molecular chain‐dipoles (for dipole relaxation) and the translational motions of ions (for f‐dependent electrical conduction); NMR relaxations relate to the angular motions of chemical bonds; QELS relates to fluctuations in local refractive index; QENS to the time‐dependent van Hove correlation function (suitably‐defined) for proton‐containing groups; TFD to the angular motions of fluorescent groups in a chain. Due to its relevance to practical applications of materials, DMTA is pre‐eminent among the many physical techniques applied to solid polymers, but interpretations of behaviour in terms of molecular properties remain difficult since the direct link between an applied macroscopic stress and the molecular response of polymer chains in a bulk material remains an unsolved problem.
Of the above techniques, Broadband Dielectric Spectroscopy (BDS) offers several advantages.
(a) Materials may be studied in the frequency range to over wide ranges of temperature and applied pressure, using commercially‐available instrumentation.
(b) Since the electrical capacitance of a film is inversely proportional its thickness, free‐standing and supported films may be studied down to nm‐thicknesses, giving e.g. information on the behaviour of the dynamic Tg as sample thickness approaches molecular dimensions.
(c) Theoretical interpretations of dielectric relaxation and a.c. conduction are well‐established in terms of Fourier transforms of molecular time correlation functions (TCFs) for motions of chain dipoles and ionic species. Large scale “Molecular dynamics” simulations have been used to calculate molecular TCFs, and hence the dielectric properties, of model bulk amorphous polymer materials [10, 11].
1042(2008); http://dx.doi.org/10.1063/1.2989065View Description Hide Description
In this work, the nucleating ability of different micro and nano sized nucleating agents for the foaming of thermoplastic biodegradable semi‐crystalline polymer will be reviewed. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase will be compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semi crystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow conflicting phenomena.
1042(2008); http://dx.doi.org/10.1063/1.2989077View Description Hide Description
Broadband dielectric relaxation spectroscopy (DRS) was employed to study molecular dynamics of blends composed of generation 3 poly(amidoamine) (PAMAM) dendrimers with ethylenediamine core and amino surface groups and four linear polymers: poly(propylene oxide)—PPO, two block copolymers, poly(propylene oxide)/poly(ethylene oxide)—PPO/PEO with different mol ratios (29/6 and 10/31) and poly(ethylene oxide)—PEO. The results were generated over a broad range of frequency. Dielectric spectra of dendrimers in PPO matrix reveal slight shift of normal and segmental processes to higher frequency with increasing concentration of dendrimers. In the 29PPO/6PEO matrix, no effect of concentration on the average relaxation time for normal and segmental processes was observed. In the 10PPO/31PEO matrix the relaxation time of the segmental process increases with increasing dendrimer concentration, while in the PEO matrix, local processes in dendrimers slow down. A detailed analysis of the effect of concentration of dendrimers and morphology of polymer matrix on the dielectric properties of dendrimer nanocomposites will be presented.
1042(2008); http://dx.doi.org/10.1063/1.2989088View Description Hide Description
Nanotechnology are providing tools of practical interest for many applications such as bioanalyitc, drug delivery devices. Indeed there is need to clarify molecular motion in nanometric space. We addressed this topic performing a single molecule fluorescence technique, Fluorescence Correlation Spectroscopy of polymeric particles and chains in glass etched channels characterized by having one dimension in the nanoscale range. The experimental set up was then simulated in silico trough a mesoscale modeling approach. Here the first results of molecular nano‐constrained motion are shown.
1042(2008); http://dx.doi.org/10.1063/1.2988975View Description Hide Description
Relaxation properties and adhesion of pressure‐sensitive adhesives (PSA) have been studied with the Probe Tack and Squeeze Recoil methods under the conditions corresponding to the adhesive bond formation under compressive stress and upon the removal of bonding pressure. Direct correlation has been established between the compressive stress relaxation in the course of adhesive bond formation and the mechanism of debonding. High adhesive strength requires the contribution of the longer relaxation times that vary for different PSAs in the range from 150 to 800 seconds. Relative contributions of viscous end elastic deformations into relaxation properties of pressure sensitive adhesives are assessed in the terms of Deborah number. At the stage of adhesive polymer relaxation after withdrawing of bonding pressure, the relaxation properties have been characterized in terms of retardation times. By comparison of the adhesive and relaxation behaviors of different PSAs, the relaxation criteria for pressure‐sensitive adhesion have been stated. Relaxation behavior of the PSAs examined has been shown to reveal two values of retardation time: the shorter retardation time of 10–70 sec and the longer time of 300–660 sec. The longer retardation times are associated with high adhesion.
1042(2008); http://dx.doi.org/10.1063/1.2988985View Description Hide Description
Main objective of this research work is to accurately measure and predict in‐plane micro‐deformation and bending of foil‐on‐carrier during lamination and lithographic process. It was demonstrated that lamination of foil on carrier introduced (1) an average in‐plane micro‐expansion of independently of foil orientation and (2) bending up to 300 μm, which was strongly related to the foil thickness. Besides this initial in‐plane expansion introduced by lamination, the thermal steps of lithography process introduce additional micro‐deformation to the foil. To be able to predict the micro‐deformation and also time‐dependent behaviour of foil‐on‐carrier, a multi‐mode Maxwell model was employed. The parameters of this model were identified by fitting to the storage and loss moduli measured by DMTA. It was shown that: (1) the used high resolution measurement technique was able to measure in‐plane micro‐deformation of foil fixed on carrier; (2) a classical model for linear viscoelasticity was used to predict time‐dependent behaviour of foil‐fixed on carrier. Obtained experimental data and modelling approach were used to optimize the lithography process.
1042(2008); http://dx.doi.org/10.1063/1.2988996View Description Hide Description
Three grades of polypropylene were tested in compression at room temperature, across an unusually wide range of strain rate: to The quasi‐static testing was done in a Hounsfield machine fitted with a digital image acquisition kit, while tests at the highest strain rates were carried out using a compression split Hopkinson pressure bar. The strain rate dependence of compressive yield stress was compared with the Eyring prediction, and found to be a nonlinear function of The nonlinearity is attributed to the presence of two relaxation processes in polypropylene, with differing activation volumes: the α‐ and β‐processes. According to the Bauwens two‐process model this would lead naturally to curved Eyring plots, where the apparent activation volume decreases with increasing strain‐rate. Another prominent feature in the experimental results was the increase in magnitude of post‐yield strain‐softening with increase in strain‐rate. This indicates that the dominant structural relaxation time exceeds the experimental time‐scale at the highest strain‐rates, but lies below it for the quasi‐static tests.
1042(2008); http://dx.doi.org/10.1063/1.2989009View Description Hide Description
Mesoporous silica has been added to Ultem® 1000 polyetherimide using solution casting. The mesoporous silica that was added was either uncoated or coated with polystyrene. Audio frequency dielectric relaxation studies were then carried out over the temperature range 5.5 to 550 K. Several interesting results were obtained. First, the uncoated mesoporous silica caused essentially no change in the relaxation spectrum of pure Ultem®. The polystyrene coated mesoporous silica caused rather large changes. The most striking example is the introduction of a new relaxation. This relaxation occurs at about 150 K and 1000 Hz as showing in fig. 1 via the open circles.
1042(2008); http://dx.doi.org/10.1063/1.2989017View Description Hide Description
The defect diffusion model (DDM) has been used to explain a wide variety of experimental results [1–4]. This includes the electrical relaxation time, electrical conductivity and viscosity of various materials above the glass transition temperature, In each case the pressure, temperature and volume variation of the physical property was calculated. In the present note, it is shown how the formalism can be used to account for the electrical relaxation time data of Heinrich and Stoll  for PVAc. In addition, the analysis is extended to the ratio of the isochoric activation energy to isobaric activation enthalpy known as or which elucidates the contributions of volume and temperature to the electrical relaxation time.
1042(2008); http://dx.doi.org/10.1063/1.2989030View Description Hide Description
Pressure sensitive adhesives (PSA) were microencapsulated using simple and complex coacervation and aminoplaste. The microcapsules thus prepared were characterized by FTIR spectroscopy, particle size distribution, rheological behavior and peeling tests. The microcapsules were isolated and found to be out of sticky indicating that the PSAs were indeed encapsulated. The prepared suspensions were deposited at the surface of a paper sheets and the dried labels were then pressed against each other. The ensuing complex was then characterized in terms of peeling forces and showed that the encapsulation using aminoplaste technique of a commercial PSA yielded peel energy of which constitutes the recovering of about 68% of the adhesive power of the original non encapsulated PSA.
1042(2008); http://dx.doi.org/10.1063/1.2989040View Description Hide Description
We investigate the relation between structure and viscoelasticity of model polymer nanocomposite systems based on a mixture of spherical nanoparticles and different polymer matrices. These composites exhibit a strong time‐dependence of the linear elastic and viscous moduli for filler volume fractions above a critical threshold. Despite the complexity of the rheological response, we can scale the viscoelastic properties of the hybrids by splitting their elasticity and dynamics into the independent responses of the suspending polymer melt and that of an elastic particle network. We show that the elasticity of the particle network exhibits critical behavior at the percolation threshold. Our analysis is expected to be useful for understanding the behavior of other complex fluids where the elasticity of the components may be superimposed.
ON THE MECHANISM OF MASS TRANSPORT OF LOW MOLECULAR WEIGHT COMPOUNDS IN POLYIMIDES: MODELING AND 2D‐FTIR ANALYSIS1042(2008); http://dx.doi.org/10.1063/1.2989051View Description Hide Description
Mass transport mechanism of low molecular weight compounds (water and carbon dioxide) into polyimide films has been analysed and modelled on the basis of the relevant findings of an in situ FTIR spectroscopic analysis. In particular, in the case of water, it has been assumed that concurrent diffusion occurs of single water molecules and water dimers, which display different mobilities. A non‐linear instantaneous equilibrium between the local concentrations of these two species has been imposed, based on a two layers BET theory. The proposed approach is able to give a good qualitative and quantitative interpretation of both sorption equilibrium and of sorption/desorption kinetics data.
1042(2008); http://dx.doi.org/10.1063/1.2989063View Description Hide Description
The current work focuses on the testing of a novel material used as an adhesive film in Composite Patch Repair (CPR). A series of Differential Scanning Calorimetry (DSC) results along with various curing cycles not only led to the optimum material composition but also demonstrated the compatibility to the composite pre‐impregnated patches. This in turn was subjected to mechanical testing including shear strength measurements. The substrate was chosen to be 2017 T4 aluminium alloy which is customarily used in the aerospace industry, taking into account that CPR is a technique mainly applied in this field. The subsequent surface preparation of the specimens was investigated for the specified context resulting to the selection of the Ferric Sulphate Sulphuric acid etching process. Finally, a series of specimens representing actual skin repairs were created and subjected to cyclic loading, specifying the suitability of the novel material, compared to commercially available materials.
1042(2008); http://dx.doi.org/10.1063/1.2989064View Description Hide Description
The interfacial properties of the inclusion complexes (ICs), obtained from the threading of α‐cyclodextrin (α‐CD) onto poly(ethylene‐oxide)(PEO), poly(ε‐caprolactone)(PEC) and poly(tetrahydrofuran)(PTHF) and their precursor homopolymers (PHPoly), were studied at the air‐water interface. The free surface energy was determined by wettability measurements. The experimental behavior of these systems was described by an atomistic molecular dynamics simulation (MDS).
1042(2008); http://dx.doi.org/10.1063/1.2989066View Description Hide Description
Imprinting of soft biological cells to create microenvironments for cell culture has gained significant importance in studying biological processes. Developments in soft lithography techniques have caused a decrease in the size of these imprinted biological cells. Where pattern sizes were in the range of 50 um, they are now being fabricated in the range of 1 um. However, there has been very little work done to characterize the elastic properties of these imprinted gels at this scale. In this work, we attempt to use an unique technique that uses the wrinkling that occurs when a floating thin film is subject to a normal loading force. A previous study has reported the use of this metrology method to measure elastic properties of floating thin polystyrene films by counting the number and length of wrinkles that are created when subjected to radial stresses from a droplet of water. In this case, we extend this theory to study wrinkle formation in floating polystyrene films coated with biological cells, and fibronectin. Also, we attempt to study capillary wrinkling in biological films such as agarose and Matrigel™. Wrinkles are induced in thin films of these materials by applying a droplet of fluid on the film surface. Using an appropriate scaling relationship, the elastic properties of these films may be obtained. The dependence of these elastic properties on gel aspect ratios, concentration, and, film floating media will be discussed.
1042(2008); http://dx.doi.org/10.1063/1.2989067View Description Hide Description
The dynamic mean‐field density functional method was applied to the mesoscopic dynamics of block copolymer melts in three‐dimensional lattice model. The analysis of the aggregates and their temporal evolution is studied in free space (PBC) and in confined space. Comparison with experimental system will be given.
1042(2008); http://dx.doi.org/10.1063/1.2989068View Description Hide Description
We are interested in strain accumulation process in polymeric materials when exposed to periodic (cyclic) loading. Within each loading cycle material undergoes a combination of the creep and relaxation process. At certain conditions the retardation process between two loading cycles cannot be fully completed. Consequently strain starts to accumulate, which leads to hardening of the material and ultimately to the failure of polymeric product.
Taking into consideration the importance of the mechanical spectrum of polymeric material for predicting durability of dynamically loaded polymeric products (see Emri, et al., ) we present the analysis of the effect of the “shape” of material time‐dependent properties, expressed with the mechanical spectrum, on the process of strain accumulation under periodically applied loading. We analyze different spectra to set background about influence of various spectrum shape. We observe, that spectrum shape defines the intensity and the magnitude of strain accumulation process. For certain type of material the accumulated strain will almost certainly lead to the failure of the product, while material with different time‐dependent characteristics will not experience the critical limit of accumulated strain that would cause failure.
1042(2008); http://dx.doi.org/10.1063/1.2989069View Description Hide Description
The linear polymers transport through a nanometer pore in the electric field is simulated. The major effects of superimposed electric field on the polymer translocation have been proved. The polymer escape time is inversely proportional with the electric field intensity.
1042(2008); http://dx.doi.org/10.1063/1.2989070View Description Hide Description
We investigate the microscopic dynamics of compressible colloidal particles as function of concentration through dynamic light scattering and confocal microscopy experiments. In analogy with hard sphere (HS) colloidal systems, we find that the particles display liquid, supercooled liquid or glassy dynamics, depending on volume fraction. In the present case, however caging effects are observed for particle volume fractions higher than one, i.e. when the particles are compressed. We find that heterogeneous dynamics, described by a non Gaussian distribution of the displacements, play a major role in the supercooled liquid in proximity of the relaxation time.