A diblock copolymer of deuterated styrene and isoprene (dPS−PI) with a small volume fraction of isoprene was chemically modified to incorporate pendant fluorinated side chains (“fingers”). The composition distribution of the diblock copolymers within a high molecular weight polystyrene (PS) homopolymer was determined by forward recoil spectrometry. Surface segregation and interfacial segregation of the modified block copolymers from a polystyrene matrix are observed in as-spun films. Equilibrium segregation was achieved on annealing at 160 °C for several days. The segregation isotherms at the air−polymer interface are shown to be quantitatively described by a self-consistent mean field theory (SCMF), and these permit us to estimate an effective Flory parameter which describes the attraction of the fluorinated segments to the surface and their repulsion from the bulk. The change in the surface tension as a result of the adsorption of the block copolymers at the air−homopolymer interface was evaluated from the predictions of SCMF theory and compared with the changes in the water contact angle observed. Advancing water contact angle data are consistent with the presence of a nonuniform layer of PS, CF2, and CF3 segments on the surface of the segregated samples.

The JKR method measures the adhesion between two spheres or a sphere and a plane surface, all materials being elastomers. We have used this technique to study the self-adhesion of a siloxane elastomer. Our results demonstrate that there is a large difference of behavior (hysteresis) between the loading and unloading regimes when the soluble fraction of the networks has been extracted. The unloading regime is then not described by the classical application of the JKR model. We believe that the work of adhesion measured during the unloading regime is not constant along the contact area but rather decreases from its center toward its edges. This behavior may be the signature of the JKR pressure profile (compressive in the center of the contact area and tensile near its edges) the sign and magnitude of which influence the formation of hydrogen bonds across the interface. A generalization of the JKR model that includes this feature is proposed and gives a good description of the experimental data.

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The JKR technique was used to study the adhesion hysteresis between hydrolyzed poly(dimethylsiloxane), PDMS, networks. PDMS model networks were synthesized and then hydrolyzed for various lengths of time in a 0.1 M HCl aqueous solution. It was found that as the exposure time of the networks to the HCl solution increased, the adhesion hysteresis increased. This hysteresis could be reduced by up to 80% by exposing the hydrolyzed networks to hexamethyldisilazane, which replaces the silanol end-functionality with a trimethylsilyl group. This dramatic reduction of the hysteresis suggests that the bulk of the adhesion hysteresis arises from a surface reconstruction reaction between silanol groups. We have also analyzed the unloading rate dependence of the adhesion hysteresis and found that it is probably due to the rate of bond dissociation.