Polymer mass transport properties

Little is known about the mass transport properties of reinforced-composite materials. Certainly, there are no new relations or concepts that govern estimations of diffusiv-ities that have not already been discussed. In most polymer-matrix composites, the transport properties of the polymer play an important role in diffusion through the composite. For example, hydrophilic polymers such as epoxy readily absorb water from the atmosphere. Thermoplastic polymers absorb relatively little moisture since they are more hydrophobic, but are more susceptible to uptake of organic solvents. 

The majority of todays membranes used in microfiitration, dialysis or ultrafiltration and reverse osmosis cire prepared from a homogeneous polymer solution by a technique referred to as phase inversion. Phase inversion can be achieved by solvent evaporation, non-solvent precipitation and thermcd gelation. Phase separation processes can not only be applied to a large number of polymers but also to glasses and metal alloys and the proper selection of the various process parameters leads to different membranes with defined structures and mass transport properties. In this paper the fundamentals of membrane preparation by phase inversion processes and the effect of different preparation parameters on membrane structures and transport properties are discussed, and problems utilizing phase inversion techniques for a large scale production of membranes are specified. 

To prepare the FRP composite, the respective fiber is embedded in a polymer matrix mostly thermoset or thermoplastic resins. The role of the matrix is (i) to bind the fibers together, (ii) to transfer stresses between fibers, and (iii) to protect them against environmental attack and damage due to mechanical abrasion. The matrix also controls the processability, the maximum service temperatures, as well as the flammability and corrosion resistance of FRP. Most FRPs are made in order to improve mechanical performances such as elastic properties (modulus of elasticity) and ultimate properties (strength, toughness). To some extent and based on the choice of constituents, preparation of composites makes it also possible to tailor other physical properties, such as electrical conductivity, mass transport properties, heat conduction, etc. [49]. 

For polymers which are in the glassy state, the removal of diluents or small molecules may cause an increase in sorption and mass transport properties of the polymer [32]. It has been found that the removal of liquids from a polymer below its Tf can increase the porosity within the polymer [32]. This would therefore result in an increase in the rate of diffusion of dUuents such as water and MeOH into PMMA. It should be noted that there was no reduction in dry weight with each successive absorption-desorption cycle of water and MeOH, which would... 

The proper representation of the thermodynamic properties of out-of-equilibrium systems such as glassy polymers is still an open question. Reliable correlations and predictive expressions for the mass transport properties in polymeric glasses as a function of temperature and concentration are also lacking. 

This work offers a contribution to the understanding of some fundamental aspects of sorption and diffusion in glassy polymers. The research focuses on an extensive experimental study of sorption and mass transport in a specific polymeric matrix. A high free volume polymer, (poly l-trimethylsilyl-l-propyne) [PTMSP], has been used here in order to emphasise aspects of sorption and transport which are peculiar to polymer/penetrant mixtures below the glass transition temperature. The discussion of the experimental data presented in this work permits a clarification of concepts which are of general validity for the interpretation of thermodynamic and mass transport properties in glassy systems. 

The experimental results are briefly discussed in terms of thermodynamic and mass transport properties in the glassy polymer mixture. The aim of the discussion is to highlight peculiarities of solubility and difiusivity in polymeric systems below the glass transition temperature and to consider possible interpretations. The focus is on the effect of swelling on the thermodynamic and transport properties in glasses. Indeed, it is well known that, contrary to the case of rubbery systems, the solute partial specific... 

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

Both share more or less the same merits but also the same disadvantages. The beneficial properties are high OCV (2.12 and 1.85 V respectively) flexibility in design (because the active chemicals are mainly stored in tanks outside the (usually bipolar) cell stack) no problems with zinc deposition in the charging cycle because it works under nearly ideal conditions (perfect mass transport by electrolyte convection, carbon substrates [52]) self-discharge by chemical attack of the acid on the deposited zinc may be ignored because the stack runs dry in the standby mode and use of relatively cheap construction materials (polymers) and reactants. 

ORR catalysis by Fe or Co porphyrins in Nation [Shi and Anson, 1990 Anson et al., 1985 Buttry and Anson, 1984], polyp5rrolidone [Wan et al., 1984], a surfactant [Shi et al., 1995] or lipid films [CoUman and Boulatov, 2002] on electrode surfaces has been studied. The major advantages of diluting a metalloporphyrin in an inert film include the abUity to study the catalytic properties of isolated molecules and the potentially higher surface loading of the catalyst without mass transport Umit-ations. StabUity of catalysts may also improve upon incorporating them into a polymer. However, this setup requires that the catalyst have a reasonable mobUity in the matrix, and/or that a mobile electron carrier be incorporated in the film [Andrieux and Saveant, 1992]. The latter limits the accessible electrochemical potentials to that of the electron carrier. 

The dynamical properties of polymer molecules in solution have been investigated using MPC dynamics [75-77]. Polymer transport properties are strongly influenced by hydrodynamic interactions. These effects manifest themselves in both the center-of-mass diffusion coefficients and the dynamic structure factors of polymer molecules in solution. For example, if hydrodynamic interactions are neglected, the diffusion coefficient scales with the number of monomers as D Dq /Nb, where Do is the diffusion coefficient of a polymer bead and N), is the number of beads in the polymer. If hydrodynamic interactions are included, the diffusion coefficient adopts a Stokes-Einstein formD kltT/cnr NlJ2, where c is a factor that depends on the polymer chain model. This scaling has been confirmed in MPC simulations of the polymer dynamics [75]. 

The polymer blend PDMS/PEMS with molar masses of Mw = 16.4 and 22.3kgmol 1, respectively, is similar to the one which has previously been used for the investigation of transport properties in the critical regime [81]. A 515nm and 20 mW laser was used for local heating. The blend with a PDMS weight fraction of c = 0.536 is almost critical with a critical temperature of Tc = 37.7°C. A minute amount of an inert dye (quinizarin) was added for optical absorption at... 

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