Soft molding

We can tune the physical characteristics of polyurethanes over a wide range by careful selection of their components. Polyurethanes are used extensively as foams, which range from soft and resilient to rigid. Solid polyurethanes range from soft moldings and elastic fibers to rigid injection molded items. Other uses of polyurethanes include coatings, sealants, and adhesives. 

Martin-del-Campo, S. T., Pickque, D., Cosio-Ramlrez, R., and Corrieu, G. (2007). Evaluation of chemical parameters in soft mold-ripened cheese during ripening by mid-infrared spectroscopy. ]. Dairy Sci. 90,3018-3027. 

FIGURE 2.23 Scheme for fabrication of plastic microdevices from silicon master using an intermediate soft mold, (a) Silicon structures are fabricated using conventional photolithography and reactive ion etching, (b) PDMS is cured in situ over the silicon master, (c) Polystyrene is hot embossed onto the PDMS mold or polymerized in situ from partially polymerized styrene, (d) Polystyrene replica is separated from the mold [85]. Reprinted with permission from Springer Science and Business Media. 

A recent thorough review of nanofabrication using both hard and soft molds, as well as other forms of soft lithography, see Gates, B. D. Xu, Q. Stewart, M. Ryan, D. Willson, C. G. Whitesides, G. M. Chem. Rev. 2005,105,1171. 

Soft lithography includes a collection of lithographic methods in which a soft mold or template is used to create patterned structures in the subjeeted materials. These methods offer attractive solutions for producing well-ordered CP nanowires. For example, Beh et al have developed a micromolding in capillaries (MIMIC) process in which a poly(dimethylsiloxane) (PDMS) mold with embedded ehannels can be used for the... 

In most cases the article is removed mechanically by ejector pins, integrated into the mold. With sensitive or soft moldings, the pins are often replaced by air ejectors. Air ejectors separate and push the molding off the mold surface by compressed air. 

Y. S. Kim, H. H. Lee, P. T. Hammond, High density nanostructure transfer in soft molding using polyurethane acrylate molds and polyelectrolyte multilayers. Nanotechnology, 2003,14,1140. 

In the present paper we review some of our findings on the reversible photo-induced wettability changes of polymer surfaces doped with photochromic spiropyran molecules. We illustrate how the hydrophilicity of the surfaces is enhanced upon UV laser irradiation when the embedded non-polar spiropyran molecules convert to their polar merocyanine isomers and how this process is reversed upon irradiation with green laser pulses. Moreover, we show that, when the doped polymer surfaces are micropattemed by soft molding lithography or by interferometric... 

Sinking (bobbing) n. In mold making, pressing a hardened hob into annealed, soft mold steel or beryllium copper. 

Arrays of distributed pillars can be manufactured using a patented technology that was invented at the Fraunhofer IKTS, Germany ° .This process consists of copying a soft mold from a positive form of the final structure, filling the mold with a slip loaded with the calcined piezoceramic powder and subsequent firing of the element in PbO-controlled atmosphere. 

This soft-mold process holds many advantages over conventional die-and-flll, injection molding or dicing techniques Soft molds are reusable. There is no need for expensive cutting machinery. The process allows for free design of elements with various types of fiber shapes, sizes, and pitches, and high voliune production while maintaining superior quality at a reasonable price per unit. See Fig. 5. 

Figure 5. Ceramic pillar array imit prepared by soft molding.

Fine scaled composites can be prepared starting with molded and sintered ceramic arrays made by the soft mold process. Once the piezoceramic pillars have been formed, the remaining spaces are filled with a polymer matrix material. Next the base is removed by grinding. Metal electrodes are then bonded to the ends of the fibers and first used to polarize the piezoceramic at an elevated temperamre and then to apply an electric field or collect developed charges from the material. At this point, the active elements are ready to be used as piezoelectric transducer element. Experiments have shown that high-performance composites can be prepared . 

Fig. 3.16 Embossing or nanoimprint lithography procedure. A hard or soft mold is in contact with surface of a film (a) A pressure is accomplished on the hard mold or a conformal contact is realized for the soft one in order to transfer the features of the mold on the film surface (b) sometimes at this stage a thermal treatment is necessary in order to soften the film and allow abetter transfer of the patterning. Mold is removed (c) A final etching process can be performed to reduce the residual layers between the transferred structures (d)...

Figure 3.1 Illustration of the soft molding method, (a) An elastomeric mold is placed on a polymer film that is spin coated onto a substrate, and then slightly pressed down to form the pattern on the spin-coated polymer film, (b) After releasing the pressure, the whole structure is left undisturbed fora period of time...

To arrive at a condition under which soft molding can be effective, solvent absorption into the mold and evaporation from the polymer surface are modeled for their rates. If it is assumed that the rate of solvent evaporation is proportional to the solvent concentration, then one has Equation 3.1 ... 

In soft molding, the solvent is absorbed into the mold at the interface between the polymer film and the mold. Therefore, the value of a in the soft molding would be smaller than that of a determined in a hath of solvent. Therefore, the condition... 

Figures 3.2 and 3.3 show SEM images of several 3D structures formed by soft molding or SAMIM. The circular cones shown in Figure 3.2a have a base diameter of approximately 1 pm. Rounded triangular channels with a period of approximately 3 pm are depicted in Figure 3.2b. A three-level structure is shown in Figure 3.2c. These results demonstrate the effectiveness of solvent-assisted molding in fabricating 3D structures. SAMIM can also replicate complex relief structures over large...

Figure 3.2 Tilted SEM images of several three-dimensional structures fabricated by soft molding (a) circularcones,the enlarged parton the right showing that the base diameter of the cone is approximately 1 im (b) rounded...

A large number of review papers can already be found in literature about soft lithography techniques, [1, 2, 4, 6, 7, 9-13] and, more specifically, pCP technique [6, 9,13). This chapter focuses on the generation of topographies and is divided into two main parts the first will deal with the key features defining the soft lithography technique and its main application, p.CP the second part will report on some of the attempts to pattern polymers by using soft molds. 

Soft molding uses the elastomeric PDMS stamp instead of hard molds to obtain polymer replicas via molding processes. Using an elastomeric, flexible mold makes... 

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