Swelling experiments

Let Lo be the length of one side of a cubic sample (volume Vb = Ao ) when it is made. We choose it as the reference state before deformation. If the sample is synthesized and 

SweUing experiments. The sample swollen by the solvent is deformed by the applied force. 

The sample is then immersed in a solvent for the swelling experiment. It is swollen to the length of one side. The volume is V = (L b)3 (i)e volume fraction 

This is taken as the initial volume fraction of the deformation experiment. 

Let Lx, Ly, Lz be the length of each side of the sample in the final state. The macroscopic deformation tensor k takes the form 

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In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

In the case of crystalline polymers better results are obtained using an amorphous density which can be extrapolated from data above the melting point, or from other sources. In the case of polyethylene the apparent amorphous density is in the range 0.84-0.86 at 25°C. This gives a calculated value of about 8.1 for the solubility parameter which is still slightly higher than observed values obtained by swelling experiments. 

Fig. 1. Solvent swelling experiments with ECA polymers crosslinked with 7.

Solvent swelling experiments, with CH2CI2 and ECA polymer crosslinked with 7, demonstrate that the addition of a difunctional cyanoacrylate monomer does improve solvent resistance [6], shown in Fig. 1. 

For small volume changes, the diffusion coefficient is constant and the D values determined by macroscopic swelling experiments are in a remarkable agreement... 

Maiti and Bhowmick also investigated the diffusion and sorption of methyl ethyl ketone (MEK) and tetrahydrofuran (THE) through fluoroelastomer-clay nanocomposites in the range of 30°C-60°C by swelling experiments [98]. A representative sorption-plot (i.e., mass uptake versus square root of time, at 45°C for all the nanocomposite systems is given in Figure 2.12. 

Resilin has a greater percentage of acidic residues than collagen, elastin, and silk fibroin and contains fewer non-polar residues (i.e., Gly, Ala, Val, He, Leu, Pro, Met, and Phe) than silk fibroin and elastin. The significant content of acidic residues might account for resilin s hydrophilicity as well as its low isoelectric point, as indicated through swelling experiments [141, 145]. Resilin contains little to no... 

Characterization. The overall structure and amphiphilic properties of the networks were characterized by DSC and swelling experiments, respectively. The Mc of the PDMAAm segments (that is the molecular weight between PIB crosslinks of the PDMAAm segment) was calculated by... 

Network Characterization. The networks were characterized by DSC (DuPont 1090 Thermal Analyzer) under nitrogen at a heating rate of 20 °C/min. Prior to the experiment the samples were preheated to 130 °C, equilibrated for 10 minutes and cooled to room temperature at 1 °C/min. Swelling experiments were conducted as described (7). 

Characterization. The structure and properties of the networks were investigated by DSC and swelling experiments. The Mc of PHEMA (i.e., the molecular weight of PHEMA sequence between PIB crosslinks) was estimated by... 

During our early experiments on chemical gels, when first observing the intermediate state with the self-similar spectrum, Eq. 1-5, we simply called it viscoelastic transition . Then, numerous solvent extraction and swelling experiments on crosslinking samples showed that the viscoelastic transition marks the transition from a completely soluble state to an insoluble state. The sol-gel transition and the viscoelastic transition were found to be indistinguishable within the detection limit of our experiments. The most simple explanation for this observation was that both phenomena coincide, and that Eqs. 1-1 and 1-5 are indeed expressions of the LST. Modeling calculations of Winter and Cham-bon [6] also showed that Eq. 1-1 predicts an infinite viscosity (see Sect. 4) and a zero equilibrium modulus. This is consistent with what one would expect for a material at the gel point. 

Fahing et al. [24] studied the modifier effects in the supercritical fluid extraction of organics from soils and clays. Swelling experiments showed that unmodified carbon dioxide did not cause swelling of the soil whereas carbon dioxide modified with water did cause rapid swelling of soil, thereby facilitating extraction of the organics. 

In a similar approach Riihe et al. [279] reported the preparation ofpoly(2-oxazoline) brushes by the grafting onto as well as grafting from method. For LCSIP of 2-ethyl-2-oxazolines silane functionalized undecane tosylate was first prepared and then immobilized on the substrate surface. SIP resulted in PEOx layers with thickness close to 30 nm. PEOx brushes were prepared by chemisorption of PEOx disulfides onto gold substrates. Preliminary static and dynamic swelling experiments are reported for these brushes. However, later observations [243] contradicted these findings. 

Swelling experiments showed that a lignin epoxide resin of 0.11 epoxy equivalents per lOOg formed a network polymer when cured with DETA, PA, or ATBN. Phase separation was observed in the rubber-toughened lignin epoxide network. Cured epoxides had lignin derivative contents of up to 95%. 

Swelling experiments are usually conducted in a solution. In this case, the isobar condition is automatically attained, i.e. II = 0. The phase diagram is then calculated from Eq. (2.12) by imposing the condition, IT = 0... 

Figures 6a, b, c show predictions of njon/RT at constant EWF = 0.7, for conditions matching those for the free swelling experiments in Figs. 3a, b, c...

Viscometric particle swelling experiments were carried out with a Cannon-Ubbelohde shear-dilution viscometer thermostated at 30 + 0.05°C. The shear rate was approximately 2000 sec-1 with flow times determined to + 0.1 sec. As in the sedimentation method, the model latexes were diluted with distilled water to a concentration of approximately 1 percent. Individual samples were adjusted with sodium hydroxide to various pH values and allowed to equilibrate at least 24 hours before measuring the viscosity. 

Figure 4. Effect of added ethyl benzene on the monomer concentration in seed particles ((O) data obtained from swelling experiments (%) data obtained from seeded emulsion polymerization at start)...

To demonstrate the capability of the presented model, a free swelling experiment on hydrogel is simulated by the FE tool PANDAS. Therefore, a 3-dimensional block is discretized with hexagonal extended Taylor-Hood elements with a quadratic approximation of us and linear approximations of p and Cm- To initiate swelling, the concentration of the external solution is decreased from 0.15 mol/l to 0.125 mol/1 within 10 sec. 

Figure 1. Qualitative comparison of a free swelling experiment on a soot-coloured hydrogel disc (experiment by J. M. Huyghe, 1999) with the 3-d FEM simulation via PANDAS...

Conventionally, cross-link density is determined by measurements of the modulus, the glass transition temperature T, and by solvent uptake in swelling experiments. In these procedures, the chemical cross-link density cannot be discriminated from network-... 

Figure 15.8 2H NMR spectra obtained in a randomly crosslinked, deuterated PB network. Precursor chain molecular weight 115700 g.mol"1, 1.2% crosslink agent, the average molecular weight between junctions is 27400 g.mol 1 (as determined by swelling experiments) or 11600 g.mol"1 (elastic measurements). The smooth curves are fits with a most probable distribution of chain lengths with number average molecular weight Mc = 11600 and with non-Gaussian chain statistics...

Critical values y and (f> are shown in Table 7.5 for various degrees of polymerisation, x. It follows that for high molar weight polymer ycrit and determined from swelling experiments of cross-linked, i.e. nonsoluble, polymers. 

The proposed theory semiquantitatively describes swelling experiments of... 

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