Plasma treatments

Polymer/ treatment Surface chemical analysis (%) by ESCA Bond strength, N  

Plasma treatment can be carried out on a variety of plastic parts, and even on powder additives such as 

The plasma used for treating material surfaces is called cold plasma, meaning its temperature is about room temperature. Cold plasma is created by introducing the desired gas into a vacuum chamber (Fig. 5.17), followed by radio frequency (13.56 MHz), or microwave (2450 MHz) excitation of the gas. The energy dissociates the gas into electrons, ions, free radicals, and metastable products. Practically any gas may be used for plasma treatment, but oxygen is the most common. The electrons and free radicals created in the plasma collide with the 

Treatment type (duration) 13-mm wide lap shear 6-mm wide lap shear 

A = adhesive failure, C = cohesive failure (see Section 5.2 for definitions of bond failure), PE = polyethylene, Al = aluminum, 

Gas plasma treatment of plastics involves exposing the plastic to a gas activated by radiofrequency energy. Materials exposed to this cocktail of ions, electrons, free radicals and UV energy are cleaned and made receptive to adhesives. Oxygen plasma treatment of PE appears to remove weak boundary layers and oxidise the surface, leading to several-fold increases in bond strength with adhesives such as urethanes and epoxies. 

Ammonia plasma treatment of PE gives strong bonds with cyanoacrylate adhesives coupled with excellent strength retention upon water immersion [41]. It is argued that covalent bonding between the surface amine groups and the cyanoacrylate is more resistant to water than physical bonding alone. 

Gas plasma is a relatively clean process with no hazardous by- 

The fluorination of polyolefins is a well-established (though expensive) batch process often used to treat containers to give resistance to hydrocarbon solvents. Authors based in Germany [43] reported that fluorination of PP and PE gives a sixfold increase in peel strength if bonded to steel with a two-part epoxy adhesive. Evidence has been presented that indicates covalent bond formation between the fluorinated surface and the amine component of the epoxy hardener. 

Other treatments that have been reported to enhance adhesion of polyolefins are contact with phosphorus trichloride in combination with UV radiation [44], electrical discharge [45] and excimer laser treatment [46, 47]. 

Low-density polyethylene (LDPE) foils are cleaned with dichloromethane to remove the impurities. The foils are then activated, imder dynamic conditions at atmospheric pressure and room temperature, with diffuse coplanar surface barrier discharge equipment. The treatment is carried out for 15 s under an air atmosphere using a 200 W power supply. Plasma is generated by two parallel banded system of electrodes (1 mm wide, 50 micron thick, with 0.5 mm spacing between the strips, made of silver-paste) embedded in 96% aluminium oxide of high purity, while the electrodes are supplied with a high frequency sinusoidal voltage (-15 kHz, Um 10 kV). 

A range of values were obtained for bond strengths with different adhesives. 

Plasma treatment is a dry process that does not utilize solvents and generates little waste compared to sodium etching. It is a more expensive process due 

D - Tensile Test Bonded Surface 1 sq. inT Treated Wafer /p —. l X Load 

Source of data Gasonics/IPC Applications Notes, Gasonics International, San Jose, California. Tetra-Etch by WL Gore Associates, Inc. Too low to measure. 

1) surface cleaning and topological and morphological changes of surfaces  

4) chemical stmcture change and free radical formation at the surfaces. 

There are a number of papers reporting the surface treatment of cellulose-based natural fibers and the property improvement of biocomposites through the surface modification of natural fibers by means of plasma treatment [96-99]. 

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R. Manory and A. GriU, Protective Coatings of Metal Sufaces by Cold Plasma Treatments, NASA Technical Memorandum 87152, National Technical Information Service, Springfield, Va., 1985. 

M. D. Smith, Suface Modfcation of High-Strength Reinforcing Fibers by Plasma Treatment, AUiedSignal Inc., Kansas City, Mo., July 1991, p. KCP-613-4369. 

W. Rakowski, Plasma Treatment of Wool, PhD. dissertation, PoUsh Textile Institute, Lodz, 1991 idem, Pr. Inst. Wlok. 36—37, 184—201 (1987) K. M. Byrne, Finishing of Wool using Plasma Technology, IWS Technical Information Bulletin CPB 109, International Wool Secretariat, Tikley, U.K., (1991). 

The principal problems for sdicone mbber as a viable lens material are the nonpolar nature, which gives Hpid deposits and wettabdity problems and the tendency to adhere to the cornea. Efforts to modify the sdicone lens surface for improved wettabdity have achieved limited success. These efforts include grafting hydrophilic monomers, such as HEMA, GM (150), and NVP (151—153), to the lens surface and plasma treatments of finished lenses. Efforts to improve the movement of sdicone lenses on the cornea with various lens designs have not been successfld, and the cause of lens—cornea adherence, which is not an exclusive problem of sdicone lenses, is an active area of research. 

Surface modification of a contact lens can be grouped into physical and chemical types of treatment. Physical treatments include plasma treatments with water vapor (siUcone lens) and oxygen (176) and plasma polymerization for which the material surface is exposed to the plasma in the presence of a reactive monomer (177). Surfaces are also altered with exposure to uv radiation (178) or bombardment with oxides of nitrogen (179). Ion implantation (qv) of RGP plastics (180) can greatiy increase the surface hardness and hence the scratch resistance without seriously affecting the transmission of light. 

After deposition of 0.5 nm of copper onto plasma modified polyimide, the peaks due to carbon atoms C8 and C9 and the oxygen atoms 03 and 04 were reduced in intensity, indicating that new states formed by the plasma treatment were involved in formation of copper-polyimide bonds instead of the remaining intact carbonyl groups. Fig. 28 shows the proposed reaction mechanism between copper and polyimide after mild plasma treatment. 

Negative TOF-SIMS speetra of PMDA/ODA polyimide before and after plasma treatment are shown in Fig. 53. The speetra generally show inereas-ing fragmentation as a function of plasma treatment time. This tendency was especially evident for the peak at m/z = 215 (PMDA + H ). 

Fig. 53. Negative TOF-SIMS spectra of PMDA/ODA polyimide (a) before plasma treatment and after plasma treatment for (b) 1 s and (c) 60 s. Reproduced by permission of John Wiley and Sons from Ref. 33).

While polymeric surfaces with relatively high surface energies (e.g. polyimides, ABS, polycarbonate, polyamides) can be adhered to readily without surface treatment, low surface energy polymers such as olefins, silicones, and fluoropolymers require surface treatments to increase the surface energy. Various oxidation techniques (such as flame, corona, plasma treatment, or chromic acid etching) allow strong bonds to be obtained to such polymers. 

Wertheimer, M.R., Martinu, L., Klemberg-Sapieha, J.E., and Czeremuszkin, G., Plasma treatment of polymers to improve adhesion. In Mittal, K.L. and Pizzi, A. (Eds.), Adhesion Promotion Techniques — Technological Applications. Dekker, New York, 1999, pp. 139-174. 

Gas plasma treatment operates at low pressure and relatively low temperature. While the corona treatment is applicable to substrates in sheet or film form, the gas plasma process can treat objects of virtually any shape. The gases most widely used to generate plasma by free-radical reactions include air, argon, helium, nitrogen, and oxygen. All these, with the exception of oxygen. 

Brosse et al. [41] modified isotactic polypropylene and other polyolefins by a cold plasma. In isotactic polypropylene, plasma treatment results in a polypropylene crystallization of paracrystalline or smectic form into a a-crystalline form. Further, the active films are susceptible to react with monomers in a postgrafting reaction. 

The same effects are reached by cold plasma treatment. Depending on the type and the nature of the used gases, a variety of surface modification can be achieved. 

In the presence of an inert gas, such as He or Ar, crosslinking can be introduced into the surface layer of material by plasma treatment. Hansen and Schon-horn [60] named this Crosslinking by Activated Species of Inert Gases (CASING). As a result, bond strength is enhanced because crosslinking strengthens the surface layer. 

The relatively high volatility of Tg[CH = CH2]8 has enabled it to be used as a CVD precursor for the preparation of thin films that can be converted by either argon or nitrogen plasma into amorphous siloxane polymer films having useful dielectric propertiesThe high volatility also allows deposition of Tg[CH = CH2]g onto surfaces for use as an electron resist and the thin solid films formed by evaporation may also be converted into amorphous siloxane dielectric films via plasma treatment. ... 

Some physical techniques can be classified into flame treatments, corona treatments, cold plasma treatments, ultraviolet (UV) treatment, laser treatments, x-ray treatments, electron-beam treatments, ion-beam treatments, and metallization and sputtering, in which corona, plasma, and laser treatments are the most commonly used methods to modify silicone polymers. In the presence of oxygen, high-energy-photon treatment induces the formation of radical sites at surfaces these sites then react with atmospheric oxygen forming oxygenated functions. 

Williams and coworkers utilized low-powered plasma treatment in the presence of four different gases (O2, Ar, N2, and NH3) to treat with the surface of the medical-grade silicone mbber. 

Besides the changes in wettability, they found that the hemocompatibility was significantly affected by plasma treatment. Treatment of PDMS with both Ar and O2 induced a decrease in hemocompatibility, leading to shorter clotting times. The N2 and NH3 treatments had a significantly beneficial effect on the activation of the coagulation cascade. 

Ortiz-Magan A.B., Pastor-Bias M.M., Eerrandiz-Gomez T.P., Morant-Zacares C., and Martfn-Martfnez J.M., 2001, Surface modifications produced by N2 and O2 RF-plasma treatment on a synthetic vulcanised rubber. Plasmas Polym., 6(1,2), 81-105. 

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