Equilibrium water uptake

The equilibrium water content, Moo, depends on the temperature, water concentration, and extent of cure. The temperature dependence reported by Brettle et al shows that Moo increases with increasing temperature, the plot of log Moo against 1/ T being linear. The equilibrium moisture content is a function of the relative humidity, , of the air to which the system is exposed (Eq. 2).  

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In contrast to TMC-DLLA, the mechanical properties at equilibrium water uptake of TMC-CL copolymers are not significantly different from those in the dry state as shown in Table 8.1. 

The subsequently presented model of water sorption in PEMs reconciles vapor sorption and porosity data. At sufficiently large water contents exceeding the amount of surface water, T > equilibrium water uptake is controlled by capillary forces. Deviations from capillary equilibrium arising at A < can be investigated by explicit ab initio calculations of water at dense interfacial arrays of protogenic surface groups. ° In the presented model, the problem of Schroeder s paradox does not arise and there is no need to invoke vapor in pores or hydrophobicity of internal channels. Here, we will present a general outline... 

Figure 7. Equilibrium water-uptake or isotherm curve at 30 °C. The dashed line signifies the effect of Schroeder s paradox, a change in water uptake at the same chemical potential depending on the phase of water next to the membrane liquid is at A = 22.

Figure 4. Equilibrium water uptake curve for Nafion membrane (a) measurement at 30 (b) measurement...

Fig. 6. Equilibrium water uptake of P(DEAEA-co-HEMA) samples with 30% (O) and 60% ( ) DEAEA with a crosslinking ratio of 0.003 mol EGDMA/mol monomers in a citrate-borate buffer solution as a function of pH...

The equilibrium water uptake of the homopolymers and the corresponding foams were measured at 22 °C and a relative humidity of 90%, using a quartz crystal microbalance (Table 6). The rate of water uptake was linear with RH, suggesting a Fickean diffusion process for both the homopolymers and the porous materials. The water uptake for the PMDA/4-BDAF samples was not measured,... 

Water sorption in a series of regular copolyoxamides was investigated by gravimetric determination of equilibrium water uptake at 93% relative humidity at 25°C, and by calorimetric measurement of freezing water in hydrated polymer san les. Equilibrium water uptake was determined as a function of the chemical structures of the polymers, with the following results ... 

The equilibrium water uptakes of series 2 polymers in distilled water are illustrated in Fig. 4 along with that of soluble PH PM A, (f) which was prepared by a similar method. As expected, water content of all three series increased monatonically with the HEMA content in the polymer. We were encouraged that the EWC of PHEMA appeared very similar to that of crosslinked PHEMA hydrogel. Unexpectedly, the EWC of these polymers changed dramatically in phosphate buffered saline (PBS). Some of the more hydrophilic polymers in series 1 dissolved in PBS, the EWC of hydrophilic series 2 polymers increased dramatically and that of series 3 polymers to a lesser extent. Differential Scanning Calorimetry (DSC) of hydrated polymer indicated that the content of freezable water (82, 83) in the more hydrophilic polymers increased dramatically also in PBS. We attribute these changes to ionization of trace quantities of acidic impurity in the PBS buffer. 

Fig. 7. Equilibrium water uptakes of chemically cross-linked polyampholyte hydrogel as a function of pH, compositions in mole fractions MAA/DMAEMA/ HEMA/EGDMA. Formulation A 10/10/79.5/0.5 (open squares). Formulation B 30/30/39.5/0.5 (open circles). Formulation C 49.75/49.75/0/0.5 (fitted circles)...

Equilibrium water uptake is achieved in a very short time with thin samples. An equilibrium weight gain of 3.8% was achieved after approximately 48 hours at 57 C. A 33% loss of shear strength occurs after soaking in distilled water at 57 C. The shape of the curve (Figure 6) seems to indicate that this... 

In fact, studies of water uptake with a direct comparison of water uptake in com-pomers and conventional composite resins do not show particularly large differences between the two different types of composite material. For example, when the polyacid-modified composite resin brands Dyract and Compoglass were compared with the conventional composite resin Pekafill , there were only minor differences in equilibrium water uptake in both pure water and in 0.9% saline solution (Table 4.1) [18]. Pekafill showed lowest equilibrium water uptakes in both storage media, but only by a very small amount, and one that was not statistically significant in the case of pure water. 

Figure 15.8 Tensile strength and equilibrium water uptake of TPS reinforced with Eucalyptus wood pulps (a-c) Kraft pulp (b-d) thermomechanical pulp. Reproduced with permission from Reference [147].

The introduction of diacetine in the reaction batch reduces the swelling and the water gain. While the sample prepared with an initial water content of 60% shows an equilibrium water uptake of 56.5%, the equivalent sample containing 30% of water and 30% of diacetine shows an equilibrium water uptake of 42.4% by weight. The shrinkage... 

Figure 18. Variation of equilibrium water uptake with relative humidity at 25°C for a DGEBA/DDS adhesive cured at 175°C for 50 min. Data from ref. 87.

At sufficient water contents, exceeding the amount of surface water, X > Xg, equilibrium water uptake is established by the action of capillary forces. To support this hypothesis, isopiestic vapor sorption isotherms for Nafion, in Figure 2.17a, are compared with data on pore size distributions in Figure 2.17b, obtained by standard porosimetry. In Figure 2.17a, a simple fit function. 

Inserting Equations 2.33 (or 2.34, 2.35), 2.40, and 2.41 into Equation 2.32 gives the equation of state for equilibrium water uptake by a pore with radius Re. ... 

Soles CL, Yee AF (2000) A discussion of the molecular mechanisms of moisture transput in epoxy resins. J Polym Sci B Polym Phys 38(5) 792-802 Soles CL, Chang FT, Gidley DW, Yee AF (2000) Contributions of the nanovoid structtue to the kinetics of moisture transport in epoxy resins. J Polym Sci B Polym Phys 38(5) 776-791 Suh D, Ku M, Nam J, Kim B, Yoon S (2001) Equilibrium water uptake of epoxy/carbon fiber composites in hygrothermal environmental conditions. J Compos Mater 35(3) 264—278 Taitel Y (1972) On the parabolic, hyperbolic and discrete formulation of the heat conduction equation, hit J Heat Mass Transf 15(2) 369-371... 

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