Laser ablation polymer surfaces

D.L. Pugmire, E.A. Waddell, R. Haasch, J.J. Tarlov and L.E. Locascio, Surface characterization of laser-ablated polymers used for microfluidics. Anal. Chem., 74 (2002) 871-878. 

These criteria resulted in the design of laser ablation polymers for 308 nm as irradiation wavelength, where it is possible to separate the absorption bands of the photochemically active chromophore from the aromatic groups in the polymer. The importance of this concept was discussed previously. Irradiation of the polymers with 248 nm caused carbonization of the polymer surface, while irradiation with 308 nm did not yield carbonization. These results prove that our concept of separating the absorption bands is valid, but... 

The surface characteristics of a microfluidic channel are very important in determining the flow in electrokinetically driven systems. In electrokinetically driven systems, the bulk flow is created by movement of the mobile diffuse layer near the channel wall/solution interface that is termed electroosmotic flow (EOF). The EOF is dependent on the surface of the microchannel walls. Roberts et al. demonstrated the generation of EOF on laser-ablated polymer substrates for the first time, using the parallel processing mode with a photomask and an ArF excimer laser at 193 nm [17]. A variety of polymer substrates such as polystyrene, polycarbonate, cellulose acetate, and poly(ethylene terephthalate) (PET) were ablated to fabricate microfluidic channels. The laser ablation process alters the surface chemistry of the machined regions and produced negatively charged. 

There are differences in the surface of the laser-ablated polymer depending on the mode of operation, static and dynamic laser ablation mode. Rossier et al. investigated differences in surface states of polymer PET as a result of these two modes of ablation [18], Their studies revealed that the static ablation mode produced a homogeneous and hydrophobic surface with poor wettability, whereas the dynamic ablation mode produced an inhomogeneous and hydrophilic surface with high wettability. These differences were attributed to the redeposition of fragments. 

Pugmire DL, Waddell EA, Haasch R, Tarlov MJ, Locascio LE (2002) Surface Characterization of Laser-Ablated Polymers Used for Microfluidics. Anal Chem 74(4) 871-878... 

In this technique the pulse from a NdA AG laser ablates the surface of the polymer generating molecular fragments in the vapour phase that are representative of the target material. These vapour phase components are drawn into the ion mobility spectrometer source where they are ionised. Both positive and negative ions are formed and the spectrometer can operate in either mode. The ions are resolved into a pattern or signature characteristic of the polymer. Simpson and co-workers [42] examined polyvinyl chloride (PVC), Nylon 66, acrylonitrile - butadiene - styrene terpolymer, polyethylene terephthalate (PET) and polyethylene (PE), by this technique. 

In this technique the pulse from a Nd/YAG laser ablates the surface of the polymer generating molecular fragments in the vapour phase that are representative of the target material. These vapour phase components are drawn into the ion mobility spectrometer source where they are ionized. Both positive and negative ions are formed... 

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

Hydrophilicity of polymeric channels can also be increased by photoablation. For instance, polymeric channels (37 pm deep) were photoablated through a copper foil mask. Relative to the original polymer, the photoablated surface is rougher and has increased hydrophilicity. The EOF increases in the following order PC < PS < cellulose acetate < PET [194]. The excimer laser ablation has... 

Laser ablation is a process in which an intense btast of energy is used to remove a small amount of material fi om the surface [19]. It is the basis for excimer laser micromachining. It can be used with a variety of different materials, ranging from silicon to polymers and ceramics. Feature sizes in the low micrometer range can be realized. The advantage of laser ablation is the... 

The power of laser ablation can be extended as a popular method for trace and bulk analysis in conjunction with ICP-OES and is an invaluable tool in the study of surface behaviour particularly where sensitive surfaces are important. The common area for surface knowledge is in environment, medicines, adhesives, powders, slurries, oil-based samples and liquids. It finds application in the analysis of metallurgical samples, non-conductive polymers, ceramic materials, surface mapping, elemental migration, depth profiling, thin film coatings, biological and clinical specimens, forensic, paint chips, inks, bullets, fabrics, etc. 

The presence of titanium dioxide in the alkyd resin films is concluded to play an important role in the photocatalytic decomposition of the latter species. A number of articles have appeared on the laser ablation user of polymers and the photodecomposition products.In controlled etching the intensity of the laser is extremely important for introducing reactive surface functional groups. Intense laser pulses whilst they cause ablation do not give the polymer radicals time enough to react with oxygen. Product distributions also vary enormously depending on the polymer structure. For example, with poly(methyl methacrylate) at 193 nm, 18% of the ablated polymer is monomer while at 248 nm less than 1% monomer is produced. 

All the studies on these polymers have involved some aspect of laser ablation. The minimum fluence for a 248 nm laser pulse to etch the surface of poly(ethylene terephthalate) (polyester) film has been determined while in other work on aluminized polyester this has been found to be dependent upon the film thickness . Fresnel patterns were obtained in biaxially stretched polyester films on laser ablation while other workers have found that the shock velocities approach the blast wave theory at fluences >1 J/cro 385 ipjjg surface properties of carbon fibre filled polyester has been studied following ablation by scanning electron... 

Photochemical surface reactions of polymer systems are an important field not only from the point of view of micro-electronic materials processing, but also from a more general scientific and materials application perspective. We have reviewed our studies in this field, which include investigations of excimer laser ablation, studies of the photo-oxidation of polymer surfaces, and the use of surface cross-linking and surface polymer depositions for microlithographic applications. With the increasing miniaturization of microelectronic devices, the fundamental and the applied aspects of surface photochemistry of polymers becomes increasingly important. 

During the last decade, processing of polymers has become an important field of applied and fundamental research [48]. One of the most important fields is laser ablation involving various techniques and applications. Laser ablation is used as an analytical tool for MALDI (matrix-assisted laser de-sorption/ionization) [28, 29] and LIBS (laser-induced breakdown spectroscopy) [49] or as a preparative tool for PLD (pulsed laser deposition) of inorganic materials [37] and of synthetic polymer films [50, 51]. Another application is surface modification of polymers [52] if low fluences are applied, the polymer surface can be either chemically modified to improve adhesion... 

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