Swelling anisotropy

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

The popcom formation tendency is enhanced by addition of suitable liquids. In a system with 20 volume % butanone, the first popcom particles are visible after 16 hours at a bulk conversion of 8.5 in a mobile liquid. The optical anisotropy of these polymers disappears in dimethyl-formamide, where they swell but do not dissolve. On the contrary, when a popcom polymer is formed from a similar feed but with additional glycol dimethacrylate, this material—which contains a high amount of chemical crosslinks—retains its optical anisotropy also after swelling in dimethylformamide for a long time. 

The thin NIPAAm hydrogel layers were covalently attached to the surface, therefore the swelling was confined to one direction perpendicular to the substrate. The degree of anisotropy was calculated from ratio of l/0p and swelling ratio. This ratio was found to be between 1.2-1.3. Such a study describing the effect of hydrophilic comonomer on Tc of PNIPAAm provides an opportunity to formulate thermoresponsive hydrogel layers with desired transition temperature and swelling behavior for various applications. 

In the discussion that follows, the volumetric shrinking and swelling of the gross wood will be treated first, followed by discussion of anisotropy, and finally the effect of stress. 

Fig. 5 Excitation polarisation anisotropy histograms for more than 200 single PFO chains, a Histogram for the ( > phase, b Histogram for chains in the glassy phase subjected (shaded black bars) or not subjected (filled blue bars) to the vapour swelling treatment. Adapted from [28]...

Fig. 42 Anisotropy of swelling is characterized by two linear sizes of the swelling beads perpendicular and parallel to the direction of particle chains. The arrows represent the direction of the uniform magnetic field during preparation...

In order to characterize the measure of swelling anisotropy, the anisomet-ric quotient (AQ) has been introduced ... 

Figure 6 shows the time histories of the vertical and the horizontal stress with the experimental result for the test (d). Simulated vertical stress agrees with the monitored. On the other hand, the horizontal stress was slightly different. One reason is the initial disturbance of the experiment because of the complicatedness of the apparatus. However, the most influential reason is the anisotropy of the swelling pressure. The direction of compaction of the buffer material plays an important role for the swelling behavior. The further study on the anisotropy has to be continued. 

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