Surface Treatment of PDMS

Sample Preparation Spin-coating and UV Ozone Treatment [28] 

The AFM FV measurements are carried out in contact mode using 11-mercapto-1-undecanol monolayer functionalized gold-coated probe tips (these functionalized probes are commercially available, see Appendix, or can be prepared according to the literature [10]). All measurements are performed in Milli-Q water using a liquid cell without O-ring (see Sect. 3.3 in Chap. 3). The use of very soft cantilevers with a nominal spring constant of 0.06 N/m is advisable. 

the sensitivity of the optical detection system is calibrated. Hence, the setup is prepared with a neat, pre-cleaned glass slide as sample, as outlined in detail in Sect. 3.3 in Chap. 3 for mounting the dry substrate. A drop of solution is placed onto the sample and the optical head is lowered vertically into its rest position and carefully secured. Once the photodiode differential signal shows a constant value, the engagement procedure as described in hands-on example 3 is carried out. However, to avoid shear forces between tip and sample the scan size is set to 0.0 nm. 

The effect of the surface treatment for longer UV—ozone treatment times (60 min, water contact angle 30°) in terms of adherence and the laterally inhomogeneous distribution of pull-off forces provide evidence for the successful and complete oxidation of the previously hydrophobic PDMS surfaces. Upon storage in ambient conditions, one can observe that the forces gradually increase in heterogeneity with 

4 Polymer Surface and Interface Properties and (Dynamic) Processes 

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