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PDMS surface

PDMS surface

PDMS surface

Figure 8. Schematic illustration of the procedure for creation of three kinds of transferred polyelectrolyte patterns in a POPS process. Reprinted with permission from [173], H. Zheng et al., Langmuir 18, 4505 (2002). © 2002, American Chemical Society.

Figure 8. Schematic illustration of the procedure for creation of three kinds of transferred polyelectrolyte patterns in a POPS process. Reprinted with permission from [173], H. Zheng et al., Langmuir 18, 4505 (2002). © 2002, American Chemical Society.

(see Fig. 8a), the PDMS stamps were pretreated with airplasma for 20 s to render them fully wettable to a 0.02 M PDAC aqueous solution with 0.1 M NaCl, which was used as ink [172].

By tuning surface properties of the PDMS stamp—the solvents of the polymer ink and controlled POPS conditions— two kinds of new patterns—ring patterns and small-dot patterns—were created from the same patterned PDMS stamps, as well as the uniform circle-grid patterns. When the PDMS stamps were plasma treated for 5-10 s and inked with 0.02 M PDAC/0.1 M NaCl aqueous solutions, PDAC ring patterns were transferred onto the SPS surface, as shown in Figure 8b. When the stamp is not plasma treated at all, and a mixed solvent polymer ink consisting of 0.01 M PDAC water/ethanol solution (50/50, v/v) is used, the transferred pattern consists of small periodic dots as shown in Figure 8c.

Two different particles on a defined array use two different approaches—ionic attractions coupled with hydrophobic and hydrogen bonding interactions, respectively. The first set of negatively charged particles were deposited on the multilayer surface primarily through electrostatic interactions, whereas the second set of colloidal particles adsorb onto a neutral SAM surface [174].

Two component colloidal arrays on a single-patterned PDAC/EG surface, were fabricated by adding surfactant, DTAB, to tune the selective deposition of the colloidal particles. When low concentrations of DTAB are added to the colloidal suspension (10-6~10-5 M), the PSS particles are deposited primarily on the multilayer surface with small changes in their packing density [179]. As more DTAB suspension (10-4~10-3 M) is added, the surfaces of the particles become increasingly hydrophobic as the negative charge density is reduced and alkyl chains are introduced. The selectivity of the particles for the PDAC surface decreases sharply at a given degree of surfactant shielding, resulting in little or no selectivity [179]. Finally, at a high degree of shielding, the selectivity is reversed, and the deposition occurs preferentially on the neutral surface.

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