Soft Molding Techniques

Microcontact printing in liquid media is another alternative to avoid stamp deformation and sample contamination. The incompressible liquid supports the stamp roof during printing and, at the same time, confines the inking molecules to the area of mutual contact. Xia and Whitesides [33,34] have published results to show that, by performing pCP under water, thiol transfer improves and the dimensions of the features that are subsequently etched on gold substrates can be reduced. Bessueille et al. [35] have confirmed that liquid pCP enables the use of stamps with aspect ratios unsuitable for the conventional air-based approaches. 

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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A final mention should be made of the use of polysiloxanes in the area of microfluidics.377 381 Devices of this type have to have channels or capillaries with dimensions 10-10,000 pm, and their preparation is relatively straightforward with PDMS, using the soft-lithography techniques just described to make the required molds. 

An elastomeric stamp or mold with relief structures on its surface is the key to soft lithographic techniques (see Sect. 3.2). As a result, the utility of these techniques is often limited by the availability of appropriate masters. In general, the masters are fabricated using photolithography. Chrome masks are available commercially from custom fabricators,but the time required for vendors to produce a chrome mask from a design presented in a computer aided design (CAD) file can be weeks, and they are expensive ( 300 per square inch for features larger than 20 pm, and 500 - 1000 per square inch for features between 1 and... 

Although conventional soft lithography techniques can be used to fabricate nonspherical particles, the production rate is limited by the mold size, limiting mass production due to the increased complexity in parallel configuration setup, and a possible solution involves the combined use of a microfluidic device and microscope projection lithography, so that the fabrication process for nonspherical objects could be transformed into a continuous. ... 

Blow molding is another molding technique for plastic. It is used to make things such as milk jug containers, soft drink bottles, shampoo bottles, and even hard-sided plastic cases for tools. 

Soft-template technique offers advantage of scalability [39]. In hard-template method, a porous membrane of inorganic or polymeric material serves as a rigid mold for chemical or electrochemical replication of stracture. This method provides an easy marmer for production of 1-D nanostractures, but with difficulties of scale up. Hard templates such as silica or carbon spheres are also ideal for synthesis of hollow strac-tures (11 Chen et al. 2003). Classical examples where the template enables the control of morphology of a-Fe Oj nanoparticles can be found in literature (Table 1). 

History. The Shell Chemical Corporation introduced the epoxy resin systems into the United States in 1941, and their good property profile has been utilized in a wide range of applications. The molding compounds are available in extreme soft flows and long gelation times, which make them very adaptable for encapsulation molding techniques in the encapsulation of electronic components such as integrated circuits, resistors, diode capacitors, relays, and bobbins. 

D printing can be quicker and less expensive than conventional machining of prototype parts or production of cast or molded parts by conventional hard or soft tooling techniques (9). 

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. 

Low-density polyethylene (LDPE) can be made by radical polymerization of ethylene using peroxides as radical initiators. LDPE is soft and transparent and is made into films using a blow-molding technique. 

Whitesides research groups opened a new era in microfabrication and rephcation using sol-gel method. They have explored so-called soft lithography techniques such as microcontact printing (/rCP), replica molding (REM), microtransfer molding (/ TM), and micromolding in capillaries (MIMIC), which have been described in their excellent review paper in detail (Xia, 1998). 

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