Selective swelling

The amphiphilic brush displayed dynamic wetting behavior towards selective solvents such as water. If the substrate was immersed in water and then air-dried, an initial contact angle (sessile drop) of 80-75° was found, because of selective swelling... 

Fig. 12 (a) Schematic representation of the preparation of a molecularly imprinted polymer with immobilized Au nanoparticle and the detection of an analyte upon selective swelling of the MIP. Reprinted with permission from [123]. Copyright (2004) American Chemical Society, (b) Schematic representation of Au-MIP/MIP-coated SPR sensor chip. Reprinted with permission from [124]. Copyright (2005) American Chemical Society... 

Yin, J., Yao, X., Lion, J.-Y., Sun, W., Sun, Y.-S., Wang, Y. Membranes with highly ordered straight nanopores by selective swelling of fast perpendicularly aligned block copolymers. ACS Nano 7, 9961 (2013)... 

Because the chemical nature of the aliphatic junction points and the stiff aromatic segments is so different, their solubility parameters and affinity to solvents are expected to be different too. Therefore, it is expected that upon swelling in a given solvent, locally selective swelling will occur. In solvents better for the aromatic segments, segment-rich domains will preferrentially absorb more solvent and swell, and in solvents better for aliphatic units, the aliphatic junctions will preferentially swell. Large internal stresses are, hence, expected to appear in such systems. At present, however, not much is known about such systems. 

We first consider uncharged ( hydrophobic ) nanoparticles. In this case, the particle is hkely to be absorbed into the membrane, swelling it and effectively cleaving its internal hydrophobic bilayer into two. This mechanism is somewhat similar to the selective swelling of block copolymer lamellar domains by nanoparticles [83-84, 88, 91, 92]. Because of the hydrophobic nature of the particle surface, the particle breaks up the bilayer to increase its contacts with the lipophilic surfactant tails, and thereby minimize its surface tension. Such behavior is consistent with the results of recent experiments conducted Banaszak Holl, Orr et al. [17-19], which showed that charge-neutral PAMAM dendrimers G5-Ac adsorb to the existing supported lipid bilayers-the layers thicken, but no new holes are formed. 

When swelling a film in a completely selective solvent (a good solvent for one block, a nonsolvent for the other), no shift in morphology is observed. Immersion in completely selective solvents has been used to selectively swell the minor phase of polymers in thin films, causing partial pore formation, upon immersion in the solvent. Due to insolubility of the undissolved block, no change in the stmcture of the undissolved block occurs. 

Figure 55 Topographic and phase images of PS-fr-P2VP diblock copolymer film were measured by tapping-mode AFM in methanol vapor. Methanol caused selective swelling of the P2VP domains, which resulted in the enhancement of the phase contrast.

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