Contact angle results for polymethacrylates

Atomic force microscopy (AFM) maps out the topographical features of a surface. A miniature tip (radius of curvature is 5-10 nm °), usually made of silicon or silicon nitride, taps along a prescribed area of the surface being imaged.Attractive and repulsive electrostatic forces affect the motion of the tip as it operates close to the surface. A piezoelectric scanning actuator works in a feedback loop to raise or lower the 

It has been demonstrated that chemical structure directly affects cooperativity. To simplify the research, one amorphous polymer with a high molecular weight was chosen. Polymethyl methacrylate (PMMA) was purchased from Aldrich in the powder form. Gel permeation chromatography showed a Mw of 101,300 g/mol with a polydispersity of 1.967. 

Polished silicon wafers one inch in diameter and -0.30 mm thick were purchased from Wafer World, Inc. The wafers were held isothermally at 90°C for 90 minutes in a 30/70 solution by volume of H2O2 and H2SO4 respectively. Next, they were submersed in acetone in a sonicator for 30 minutes. The wafers were then rinsed with acetone and dried in a stream of air. This treatment produced a native oxide layer on the silicon wafers that were used as the substrate for depositing thin films of PMMA. 

Solutions of PMMA in toluene were prepared at 2%, 5%, and 10% by weight. The silicon wafers were positioned on the spin coater and several drops of solution were placed on the wafer. Immediately, each sample began rotating at a constant speed to 

Samples of PMMA were heated in a vacuum oven at 120°C for 24 hours to drive off any moisture that had been absorbed. One sample of approximately 15 mg was placed in aluminum pans in a TA Instruments DSC 2920. The sample was equilibrated at 25°C and then heated from 25°C to 180°C at 10°C/min for the first run. The sample was then cooled slowly, again equilibrated at 25°C and the heating process was repeated for a second run. All of these tests used nitrogen as a purge gas. The glass transition function in TA Instrumental Analysis was used to calculate the Tg of the material by finding the inflection point in the Tg step. 

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