Crystalline swell

Norrish, K. and Quirk, J.P., 1954. Crystalline swelling of montmorillonite. Use of electrolytes to control swelling. Nature (London), 173 255—256. 

Figure 8.20. Effect of NaCI concentration on the c-axis spacing of Na" -saturated smectites having different total layer charge (number labeling curves is the layer charge per unit cell) and percentage of charge in tetrahedral sites (value in brackets). (Adapted from P. G. Slade et al. 1991. Crystalline swelling of smectite samples in concentrated NaCI solutions in relation to layer charge. Clays Clay Min. 39 234-238.)...

Slade, P. G., J. P. Quirk, and K. Norrish. 1991. Crystalline swelling of smectite samples in concentrated NaCl solutions in relation to layer charge. Clays Clay Min. 39 234-238. 

Quirk, J.P. 1997. Application of double-layer theories to the extensive crystalline swelling of Li-montmorillonite. Langmuir, 13 pp.6241-6248. 

K. Nonish and J. P. Quirk, Crystalline swelling of montmorillonite, Nature 173 225 (1954). A. M. Posner and J. P. Quirk, The adsorption of water from concentrated electrolyte solutions by montmorillonite and illite, Proc. Royal Soc. 278A 35 (1964). A. M. Posner and J. P Quirk, Changes in basal spacing of montmorillonite in electrolyte solutions, /. Colloid Sci. 19 798 (1964). 

Other studies have shown that the reaction of phosphoric acid with cellulose, even at low temperatures, produces considerable inter-crystalline and intra-crystalline swelling (Porter and Rollins, 1972 Pandey and Nair, 1974). Further, Pandey and Nair (1974) examined the reaction of phosphoric acid with cotton at temperatures of 10,29 and 40 °C for 0.5 h using... 

There are many uses of solvents in polymer compounds. Soluble hydrocarbon oils are widely used with natural and synthetic rubber to gain the advantages of higher molecular weight. Polyvinyl chloride, which has a low level of crystallinity, swells extensively in polar solvents to become a rubbery material known as plasticized polyvinyl chloride . 

Solvent Resistance. At temperatures below the melting of the crystallites, the parylenes resist all attempts to dissolve them. Although the solvents permeate the continuous amorphous phase, they are virtually excluded from the crystalline domains. Consequently, when a parylene film is exposed to a solvent a slight swelling is observed as the solvent invades the amorphous phase. In the thin films commonly encountered, equilibrium is reached fairly quickly, within minutes to hours. The change in thickness is conveniently and precisely measured by an interference technique. As indicated in Table 6, the best solvents, specifically those chemically most like the polymer (eg, aromatics such as xylene), cause a swelling of no more than 3%. 

Crystallization and Melting Point. The abihty of PVA to crystallize is the single most important physical property of PVA as it controls water solubiUty, water sensitivity, tensile strength, oxygen barrier properties, and thermoplastic properties. Thus, this feature has been and continues to be a focal point of academic and industrial research (9—50). The degree of crystallinity as measured by x-ray diffraction can be directly correlated to the density of the material or the swelling characteristic of the insoluble part (Fig. 2). 

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. 

Since polyethylene is a crystalline hydrocarbon polymer incapable of specific interaction and with a melting point of about 100°C, there are no solvents at room temperature. Low-density polymers will dissolve in benzene at about 60°C but the more crystalline high-density polymers only dissolve at temperatures some 20-30°C higher. Materials of similar solubility parameter and low molecular weight will, however, cause swelling, the more so in low-density polymers Table 10.5). 

Nylons 46, 6, 66, 610, 11 and 12 are polar crystalline materials with exceptionally good resistance to hydrocarbons. Esters, alkyl halides, and glycols have little effect. Alcohols generally have some swelling action and may in fact dissolve some copolymers (e.g. nylon 66/610/6). There are few solvents for the nylons, of which the most common are formic acid, glacial acetic acid, phenols and cresols. 

As is typical for crystalline polymers incapable of specific interactions with liquids, there are no solvents at room temperature but liquids which have a similar solubility parameter (8 = 22.4 MPa ) will cause a measure of swelling, principally in the amorphous region. ... 

Adhesion development depends on diffusion of the CPO component of the primer through the crystalline boundary layers followed by swelling and entanglement with the rubber rich layer [75]. 

In the case of crystalline polymers it may be that solvents can cause cracking by activity in the amorphous zone. Examples of this are benzene and toluene with polyethylene. In polyethylene, however, the greater problem is that known as environmental stress cracking , which occurs with materials such as soap, alcohols, surfactants and silicone oils. Many of these are highly polar materials which cause no swelling but are simply absorbed either into or on to the polymer. This appears to weaken the surface and allows cracks to propagate from minute flaws. 

Because of the geometry, or morphology, of these molecules some can come closer together and more orderly than others. These are identified as crystalline and all others that behave like spagetti as amorphous. Morphology influences such properties as mechanical and thermal, swelling and solubility, specific gravity, and other properties (mechanical, physical, chemical, electric, etc.). 

Even when they have a partial crystallinity, conducting polymers swell and shrink, changing their volume in a reverse way during redox processes a relaxation of the polymeric structure has to occur, decreasing the crystallinity to zero percent after a new cycle. In the literature, different relaxation theories (Table 7) have been developed that include structural aspects at the molecular level magnetic or mechanical properties of the constituent materials at the macroscopic level or the depolarization currents of the materials. 

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