The alternating, layer-by-layer assembly of oppositely charged polyelectrolytes, often referred to as electrostatic self-assembly (ESA), has been well-established in the past decade for the preparation of ultrathin polymer films with precise thicknesses of between 1 and 1000 nm. [1,2] The method is based on the formation of water-insoluble, nearly stoichiometric complexes of polycations and polyanions (so-called ªsymplexesº) at an interface. Characteristically, the preparation of ESA films involves the use of an appropriate substrate onto which the polymers are adsorbed layer by layer. Consequently, the ESA method results, first of all, in the surface modification of a given substrate. However, ultrathin polymer films are often desirable as freestanding films. [3,4] In fact, numerous examples have been reported in which the substrate was removed after film preparation in order to prepare substrate-free films, particularly in cases where colloidal supports have been used. [5,6] In these cases, hollow polyelectrolyte capsules dispersed in liquid are produced by the dissolution or decomposition of the substrate. [5,7] Following the same strategy, planar films without a supporting substrate have also been prepared in exceptional cases, either by removing the entire support or by dissolving a thin buffer coating between the primary substrate and the stable ESA film. [3,8±14] In all these examples, the preparation of freestanding, ultrathin polymer films required two steps: first, film growth on a substrate and second, the removal of the substrate. This twostep approach is not only cumbersome, but may also damage the ultrathin polymer films as a result of, for example, chemical and mechanical stresses during the removal of the substrate. In fact, nearly all examples of freestanding films have been made using charged colloidal particles, which have been used to improve the mechanical stability of the films. [3,10±13] Therefore, direct access to freestanding ESA films, which is suited for organic, flexible polyelectrolytes, appears very attractive. In this communication, we present a strategy to prepare ultrathin, freestanding ESA films directlyÐi.e., without using a substrateÐwith a thickness/width ratio of up to 1:10 000, by appropriately choosing the polyelectrolyte pair and conditions for self-assembly. We also investigate the response of the freestanding films to chemical stimuli before and after their stabilization by chemical crosslinking.In order to prepare freestanding films, we used electron microscopy (EM) grids, with typical hole sizes of 100 lm 100 lm, as supports. Although the formation of films which successfully span pores has been reported occasionally using supports with very small pores (< 50 nm), [15,16] so far, the use of supports with larger pores has resulted in coating of the pore walls.[8,9,17±19] Indeed, when we used the classical experimental conditions during the dipping cyclesÐ namely, washing between subsequent dipping steps and drying in ambient atmosphereÐall our attempts to obtain f...

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Spreading a hydrophobic liquid star polymer with ionic head groups and transferring the resulting monomolecular layers to solid substrates with holes provides access to ultrathin, freely suspended elastomeric membranes (see picture), which are stable for at least several months.

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“Move‐connect‐prove” is the sequence that is employed to join and shape two individual strands of dendronized polymers. A scanning force microscope is used to move and shape the strands (picture a→b); the connection is obtained by UV irradiation of the sample, and tested by pulling on the connected polymer chains.