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We present the monolayer phase behavior of several slightly water-soluble linear poly(ethylene glycol) alkyl ether surfactants (C i E j = CH3(CH2) i - 1−(O(CH2)2) j OH) and the relationship between the adsorbed monolayer phases, their transitions, and the rate of surface tension reduction. Surface pressure isotherms suggest a first-order phase transition between liquid expanded (L1) and liquid condensed (L2) states for the least soluble amphiphiles:  C12E0, C14E1, and C16E2, with transition surface pressures near 20 mN/m at room temperature. In addition, C14E1 isotherms show a possible vertical LS state at higher pressure but below its equilibrium spreading pressure of 46 mN/m. Fluorescence microscopy of spread C14E1 monolayers confirms L1−L2 phase coexistence and reveals coexistence between liquid expanded and gaseous (G) states at low surface pressure. The dynamic assembly of these phases from solution, induced by flow in the subphase, is visualized with fluorescence and monitored with surface tension measurements; results compare well with spread monolayers. These observations show that as surfactant adsorbs to an initially clean air−water interface and phase transitions occur, coexistence gives rise to tension plateaus consistent with those measured for spread monolayers by surface compression. We confirm these results with C14E1 pendant bubble dynamic tension measurements, where the observed pronounced induction period represents G−L1 coexistence, and the intermediate plateau results from an L1−L2 transition.

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In this paper, we describe a procedure to prepare mixed self-assembled monolayers containing nanometer to micrometer domains of a chemical functionality surrounded by another chemical functionality, using sequential adsorption. Partial monolayers of octadecyltrichlorosilane (OTS) consisting of condensed islands with controlled size are prepared by varying the deposition conditions. The area surrounding the OTS islands is backfilled with 11-bromo undecyltrichlorosilane (BrUTS) or decyltrichlorosilane (DTS) to obtain nanometer to micrometer scale domains of OTS in a monolayer of DTS or BrUTS. First, we describe in detail the methodology to form partial OTS monolayers composed of domains of a desired size. Then, we discuss the procedure and optimum conditions for successful backfilling. These monolayers were analyzed by atomic force microscopy (AFM) to obtain height and friction images in contact and tapping modes. In addition, we have studied (1) the friction properties of various phases in OTS monolayers, (2) the morphology of monolayers on silicon substrates with various degrees of hydration, and (3) in situ adsorption of OTS monolayers using AFM.

Water-swollen hydrogels characterized by hydrophobic microdomains within an aqueous polymer network have been prepared and investigated. The microdomains consist of comicelles of sodium dodecyl sulfate (SDS) and alkyl grafts from a hydrophobically modified water-soluble polymer and form at concentrations below the critical micelle concentration of the surfactant alone. These aggregates behave like pseudo-crosslinks, bridging together many polymer molecules to form a viscoelastic network. The comicelles have the ability to solubilize water-insoluble dyes; hence, these materials may be of use in separations and controlled release processes.