Contact angles were measured for these liquids on unmodified elastomer, 5% LMW, 5%

HMW, 15% vinyl tris, 20% tris, 5% 50 cSt, 20% 50 cSt, 5% 5000 cSt, and 20% 5000 cSt

coated slides. For each sample, cos 0was plotted for each liquid versus the surface

tension, and linear regression was performed to determine the surface free energy where

cos = 1. The surface energy and contact angles of each substrate can be found in Table

3.5. A representative example of a Zisman plot from these data is shown in Figure 3.4.




Table 3.5 Contact angles and surface free energy of various substrates
 Average Contact Angles (degrees) Yc
 Samples Water Mel DMF ACN 1-Prop (mN/m)
 Unmodified 109 +4 67 + 4 55 + 2 47 + 4 32 + 2 19
 5% 50 cSt 110+3 66+ 1 56+2 44+3 31 1 20
 20% 50 cSt 109 1 64 2 54 +2 46 +3 25 +1 21
 5% 5000 cSt 108 +2 65 + 2 55 + 1 48 + 2 26 + 2 20
 20% 5000 cSt 103 +2 64 + 2 52 + 2 48 + 2 26 + 2 19
 20% Tris 106 +2 64 +2 56 +2 46 +2 29 + 1 19
 5% LMW 107 5 65 3 55 +2 47 +2 29 +3 19
 5% HMW 112 2 64 2 56 +2 46 +3 25 +3 21
 15% vinyl 107 +2 66 3 58 3 50 5 33 + 3 17
 Tris

 As seen by Table 3.5, there is very little difference between all the samples in

terms of surface free energy. This is an expected outcome since essentially the samples

are all made of silicone elastomer with different PDMS oligomer additives. Since the

material is the same, the surface energy should be similar. In addition, to minimize the

energy at the interface, low surface tension oligomers have been shown to migrate to the

surface.[116' 117] The fact that this does not affect a change in surface energy is supported

by the results for the 20% 5000 cSt samples of no appreciable difference in surface

energy even with a visible layer of oil on the surface.