8.5 Surface and Interfacial Interactions of Silane Coatings on Paper Substrates
(Room 234-236)
10 Apr 18
11:30 AM
-
12:00 PM
Tracks:
Session 8: Measuring & Testing, Session 8: Measuring & Testing I
A mixture of vinyltrimethylsilane and its associated siloxane can be polymerized ‘in-situ’ and cured over cellulose substrates to produce a hydrophobic film. The rate of hydrophobic development of this film can be monitored to discern the surface and interfacial interactions responsible for the change in hydrophobicity.
Several studies were conducted in which 7 wt% solutions in n-heptane were roll-coated onto Whatman 1 cellulose substrates, and subsequently cured at 40 and 110oC. FTIR measurements were taken at various times during curing, as were contact angle measurements. Bond development was completed well before the onset of surface hydrophobicity at both curing temperatures, and superhydrophobicity was also observed with the high temperature case. Hydrophobic development appeared to be more strongly influenced by surface topology than bond development, and this was confirmed with SEM studies that showed the appearance of 300 nm-size polysiloxane beads on the fiber surface. Cassie-Baxter behavior was confirmed with both roughness and film porosity contributing to hydrophobicity under certain circumstances. Deformation studies in the form of mechanical folding action were performed on fully-cured and developed hydrophobic films at both temperatures. Results showed decreased hydrophobic performance at 40oC prepared samples, associated with a reduction in vibrational activity of the surface hydrophobic groups. At 110oC, hydrophobic performance was largely maintained despite similar damage to the chemical bonding, and it is thought that higher levels of covalent bonding to the substrate may have been responsible. Although the hydrophobic surface requires roughness and porosity to fully form, the chemical hydrophobicity created from polymerization also ultimately contributes to the overall hydrophobicity observed.
Studies currently in progress will compare different silanes with additional hydrophobic content to investigate more thoroughly the potentially competing effects of chemical hydrophobicity and mechanical roughness. Also planned are the introduction of pigment particles into the film to investigate additional interfacial and surface interactions.