X-ray scattering study of water intercalation into thin lyotropic multilayers. II. Transitions between pure states of hydration via disordered intermediate states

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Abstract
X-ray scattering experiments are described which probe the effect of water adsorption and desorption on the lamellar, or layer ordering, in thin substrate-deposited multilayers of the phospholipid dipalmitoylphosphatidylcholine. The analysis of the lamellar or (00l) line shapes on the basis of a model of one-dimensional displacement disorder in a multilayer of finite size, resulting from the presence of two components, reveals the formation of distinct states of hydration during water uptake and release. Transitions between pure states occur via disordered intermediate states that contain at least two pure states, arranged in a variety of sequences. The commonly employed picture of a continuous ‘‘swelling’’ process does not adequately account for our observations. Instead, we propose that water adsorption be viewed as an intercalation process. Its similarities with graphite intercalation and layering transitions encountered in the context of wetting phenomena are discussed in some detail.