Liquid Phase Photopolymerization

The liquid phase photopolymerization process is used to photopattem polymer structures. The essence of this process is the same as the photolithography process described earlier. The main difference is that the liquid form prepol5rmer is not spin coated onto the substrate but rather is filled into a predefined cavity or channel. Like negative PRs, the prepolymers are photosensitive, and upon masked exposure to light (mostly UV), they undergo polymerization and solidify. Unexposed pre-polymer will not polymerize and can be rinsed away. 

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Liquid-phase photopolymerization was used to fabricate plastic chips [218, 219]. To create a microchannel, a UV photomask was used so that the masked channel areas were prevented from polymerization, while the exposed areas were photopo-lymerized. Subsequent suction and flushing removed the unexposed monomer mixtures [218]. 

Khoury, C., Mensing, G.A., Beebe, D.J., Ultra rapid prototyping of microfluidic systems using liquid phase photopolymerization. Labchip 2002, 2, 50-55. 

The technological requirements for designing and constructing microfluidic devices for micro- and nano-technology are expanding. A microfluidic platform for the construction of microscale components and autonomous systems consists of a combination of liquid-phase photopolymerization, lithography, and laminar flow to generate channels, valves, actuators, sensors, and systems. ... 

X. Zeng and H. Jiang, "Polydimethylsiloxane microlens arrays fabricated through liquid-phase photopolymerization and molding," Journal of Microelectromechanical Systems, vol. 17, pp. 1210-1217, Oct 2008. 

In addition to the three basic microfabrication steps discussed above, other fabrication techniques are quite useful. We will briefly discuss a few of them, namely lift-off, annealing, liquid phase photopolymerization, micromolding, soft lithography, electroplating, sacrificial processes, bonding, surface modification, laser-assisted processes, planarization, and fabrication on flexible substrates and curved surfaces. Some of these techniques do not necessarily belong to the traditional repertoire of microfabrication of ICs. However, they have proved very useful for the creation of other types of microdevices and systems such as MEMS, microfluidics, and labs on chips. 

Step 2 We will need a mold to perform the electroplating. The thickness of this mold must exceed the desired height of the electroplated Ni stirrer (100 pm). Hence we choose to utilize liquid phase photopolymerization rather than a PR since it is easier to generate structures with heights on this order. 

Step 1 The first layer of the first IBA mold for the PDMS islands is patterned using liquid phase photopolymerization. See Figure 3.19a. The IBA layer is photopatterned on a glass slide with Mask 1, which is shown on the right of Figure 3.19a. 

Step 7 Hydrogel precursor is injected into the chambers, followed by another liquid phase photopolymerization step to define the actuators. The sidewalls of the lens apertures are plasma treated to be more hydrophilic. See Figures 3.19g and h. The whole structure is now ready to be wrapped onto the target hemisphere for final assembly of the microlenses. 

Discusses many microfabrication techniques, including deposition, photolithography, etching, annealing, liquid-phase photopolymerization, micromolding, electroplating, laser-assisted processes, and more... 

The gas-phase photolysis of 2-furaldehyde in the it -n and ir <-it transitions76 proceeds with fragmentation to CO, furan and C3-hydrocarbons, but a certain amount of resinification is also noted (about 5% quantum yield with excitation of the it - n transition). The latter observation prompted a study of the vacuum liquid-phase photolysis by sunlight or by light from a medium-pressure mercury arc at room temperature24 7S. The resin obtained was submitted to fractionation and structural analysis. On the basis of the results obtained and other mechanistic evidence, the following sequence of events was postulated for the photopolymerization ... 

The photopolymerization of furfural by UV radiation has not received much attention. Although the products of heat polymerization of furfural are branched polycondensates with highly conjugated structures, the photopolymer of furfural is a linear polyaddition product (8,9). The gas-phase photolysis of furfural in the n — 7r and ir — 7r transitions (10) proceeds with fragmentation to carbon monoxide, furan, and C3 hydrocarbons, but a certain amount of resinification has also been noted (about 5% quantum yield with excitation of the n — 7r transition). Vacuum liquid-phase photolysis by UV radiation at room temperature has produced linear polymers (4) with a degree of polymerization of about... 

Finally, we consider the role of valence isomers when these do occur. The two oversimplified pathways we considered—i.e., the isomer is very reactive and leads to other products and in addition stores energy until it decays back to the Kekule ground state—clearly hold for DB in liquid phase. (This behavior is quite consistent with the high percentage of C6F6+ parent ion found (5) in the 70-e.v. mass spectrum of DB on the one hand, and with the 1849 A. photopolymerization (8) of DB on the other.)... 

The patterning of hydrogels is not a new concept and has been applied over the last 10 years to volumetric as well as thin films, the last one being the most important since many applications in sensors and actuators are based on this form. For many applications, in situ photopolymerization and photo cross-linking using UV light in the liquid phase are the most used. An alternative approach is to cross-link a prefabricated dry film of toe sensitive polymer. 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Self-standing nanostructured two-dimensional polymer films were prepared by in situ photopolymerization of ionic liquid crystalline monomer 11 that forms homeotropic monodomains of the smectic A phase on a glass plate (Figure 25.4). The film of 12 has a macroscopically oriented layered nanostructure as presented in Figure 25.5. 

The following protocols (6-10) describe the synthesis of some cholesterol-based acrylates and their photopolymerization in an aligned cholesteric phase. The protocols utilize a modification of a system previously described by Shannon. 5 6 ip ie absence of a diacrylate comonomer, the cholesteric phase produced initially on copolymerization is not stable and reverts to a smectic phase on a single cycle of heating and cooling. In the presence of the diacrylate the first-formed phase is stable. This is one example of how crosslinking can stabilise the liquid crystal phase in liquid crystalline elastomers, others include, the so-called, polymer-stabilized liquid crystals and those described in the later protocols. 

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