Nikon S9100 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor. On the other hand, Nikon AW100 has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor .
Below you can see the S9100 and AW100 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon S9100 and Nikon AW100 Cameras
Nikon S9100 and Nikon AW100 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon S9100 has 32% larger pixel area compared to Nikon AW100, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.