Patterned Polymers

The advantage of this approach is not only the free choice of surface stractures which can be created, the material contrast which can be realized by the combination of chemical lithography and amplification with SIP, but also the potential to bridge the gap in structural feature sizes ranging from the microscopic to the nano-scopic scale. Since the feature sizes reported are still limited to the features of the mask used, direct writing with a focused e-beam should result in patterned polymer brushes of features matching the size of the immobilized macromolecule. 

In a series of papers, Matsuda et al. [291-295] employed RAFT-SIP with immobilized benzyl N,N-diethyldithiocarbamate to form polymer brushes from styrene, methacrylamides, acrylamides and acrylates, NIPAM and N-vinyl-2-pyrrolidone on various surfaces. The SIP is initiated by UV irradiation of the surface-bonded dithiocarbamates. Thermoresponsive polymer brushes were prepared by the polymerization of NIPAM and investigated by XPS, wetting experiments and mainly SPM [294]. Patterned polymer brush layers were also prepared. When chloro-methyl styrene was used as a comonomer, RAFT-SIP resulted in branching. By control of the branching, spatio-resolved hyperbranching of a controllable stem/ branch design was realized (Fig. 9.32) [293, 295]. 

In addition, patterns created by surface instabilities can be used to pattern polymer films with a lateral resolution down to 100 nm [7]. Here, I summarize various possible approaches that show how instabilities that may take place during the manufacture of thin films can be harnessed to replicate surface patterns in a controlled fashion. Two different approaches are reviewed, together with possible applications (a) patterns that are formed by the demixing of a multi-component blend and (b) pattern formation by capillary instabilities. 

Park, C., Yoon, J. Thomas, E. L. Enabling nanotechnology with self assembled block copolymer patterns. Polymer 44, 6725-6760 (2003). 

Fig. 7 (a) Growth of temperature-dependent, patterned polymer brushes on SAMs on gold surfaces. Images show adhesion of (b) FITC-BSA after incubation at 37°C and rinse at 12°C (c) S. mutans after incubation at 4°C for 1 h and (d) S. mutans after incubation at 37°C for 1 h. Reproduced from [112] with permission. Copyright The Royal Society of Chemistry, 2005... 

Figure C.6. Overview of the fabrication process. Two coverslips are placed at the top and bottom of a transparency (a) and prepolymer solution is dropped in the center (b). A thick glass slide is positioned on top of the prepolymer solution, allowing it to rest on the coverslips, and causing the prepolymer solution to flow and fill the gap (c). A photomask is aligned on top of the glass slide (d), a second glass slide is placed on top of the photomask to keep it in place, and the exposed photoresist is polymerized using UV light. After rinsing, an insoluble, patterned polymer results (e).

Figure 6. Interaction of a water droplet with 200 micron features of a patterned polymer brush prepared by surface-initiated polymerization. The unusual wetting profile is due to preferential interaction of the water droplet with the polymery lie acid) brush domains (light) and complete non-wetting of the hydrophobic poly(tert-butyl acrylate) domains (dark).

A variation of MIMIC for patterning polymer semicondnctor TFT arrays was recently reported by Salleo and coworkers [105]. This techniqne exploits capillary forces to pattern a solution-processable polymer semicondnctor. In this method, the polymer semiconductor solution is spin-coated onto a snbstrate. A chemically treated PDMS stamp is then placed directly on top of the substrate coated with the polymer semiconductor solution. In the regions of contact, the PDMS stamp absorbs the solvent, leaving behind a solid polymer semiconductor film between the stamp and the substrate. In the recessed regions of the PDMS stamp, the polymer semiconductor solution wicks into the stamp due to capillary forces, effectively leaving behind a clean snrface in the noncontact regions. 

While NIL and S-FIL have been shown to be effective tools for creating nanoscale patterns, it is important to keep in mind that the patterned polymer layers utilized in both techniques are sacrificial structures. Additional etchback steps are required to transfer the patterns into the substrate. Further, metal contacts and other functional materials have to be deposited separately to create functional devices. 

Finally a type of addition polymerization calling for the employment of stereospecific catalysts has recently aroused much interest in the laboratory as well as in industry. With the aid of such catalysts, an addition polymerization yields certain poljmers in which the main chain as well as tire chemical substituents are dtuated in a highly ordered spatial pattern. Polymers of physical and chemical characteristics are thus obtained which contrast markedly from those formed in normal polymerizations. 

Welch ME, Ober CK. Responsive and patterned polymer brushes. J Polym Sci B Polym Phys 2013 51(20) 1457-72. 

Farhan T, Huck WTS. Synthesis of patterned polymer brushes from flexible polymeric films. Eur Polym J 2004 40(8) 1599-604. 

Nakayama and coworkers presented two different strategies for obtaining patterned polymer brushes on PET and PS [12]. In the first approach, a styrene-based polymer with photoreactive RAFT initiators was synthesized and spincoated on PET (Figure 3.7A). Alternatively,... 

L. T. Yan, J. Sheng, Analysis of phase morphology and dynamics of immiscible PP/PAlOlO blends and its partial-miscible blends during melt mixing from SEM patterns. Polymer 2006, 47,2894. 

Figure 4. Experimental design based on the new concept of self organization to obtain a hierarchic dot or stripe pattern composed of metal nanoparticles. Here polymer is used for constructing the super-layer structure with the wavelength X that is chosen by dewetting instability. The patterned polymer islands simultaneously provide the initial and boundary conditions of sub-layer, i.e., the conditions for self-assembly of nanoparticles.

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