Plasma and Dry Micro/Nanotechnologies 7. Plasma Treatment Lenka Zajíčková Faculty of Science, Masaryk University, Brno & Central European Institute of Technology - CEITEC lenkaz@physics.muni.cz spring semester 2023 Central European Institute of Technology BRNO I CZECH REPUBLIC • Plasma Treatment 7.1 Introduction to Plasma Treatment 7.2 Low Pressure Plasma Treatment 7.3 Atm. Plasma Treatment for Adhesive Joints Plasma & Dry Technologies lasma Treatment ka Zajíčková 3/16 7.1 Introduction to Plasma Treatmen Plasma Treatment combination of various processes (chemistry, ions, UV) results in: > removal of material > modification of original material (especially important for polymers) > grafting of new functional groups In contrary to depositions the changes are limited to a very thin surface layer (in the order of nm) but please note that the term "surface" is a matter of definition! ageing of treated surfaces important issue of any surface treatment processes Plasma & Dry Technologies PI asma Treatment Len ka Zajíčková 4/16 Plasma generates also UV photons and this effect is often forgotten! Plasma & Dry Technologies lasma Treatment ka Zajíčková 5/16 Plasma modifications of polymers in inert gas > discharge in argon, helium: chemical bonds, such as C-H, C-C, C=C, are broken ^ generation of free radicals at or near the surface ^ radicals react with each other either directly (if polymer chain is flexible enough) or due to migration along polymer chain („cha in -transfer") ^ cross-linking, branching, removal of low molecular weight material or its conversion into high molecular weight one (no new functional groups) (cross-linking by activated species of inert gas) R. H. Hansen, H. Schonhorn, J. Polym. Sci. B 4 (1966) 203 H. Schonhorn, R. H. Hansen, J. Appl. Polym. Sci. 11 (1967) 1461 increase of surface hardness, improvement of adhesive forces at the interface Additionally, changes of surface roughness Plasma & Dry Technologies lasma Treatment ka Zajíčková 6/16 Plasma treatment in reactive gases gases > plasma containing oxygen (02, H20, C02 ...) • etching of surface carbon radicals by atomic oxygen • new functional groups, e.g. C-O, OO, O-OO, C-O-O, C03, OH 4^ hydrophilic surface, change of roughness > plasma containing nitrogen (N2, NH3...) • new functional groups such amine (N-C), imine (N=C), nitrile (N=C), amide (N-C=0) • incorporation of oxygen and its functional groups • grafting of amine groups -NH2 hydrophilization, biocompatibility, imobilization of biomolecules > plasma containing fluorine (SF6, CF4, C2F6 ...) F and CFX radicals react with surface and two different processes compete: • etching • grafting and deposition hydrophobization, change of roughness ^ Plasma & Dry Technologies lasma Treatment ka Zajíčková 7/16 7.2 Low Pressure Plasma Treatment Why Plasma Modification of Polycarbonate? Polycarbonates are attractive business article, the I V^kiJ most important PCs are based on on bisphenol A -'^M^SE (Diflon®, Macrolon®, Lexan®) MShPI Properties I^^^^HH ■ excellent breakage resistance (15-20x than acrylate, 250x than glass) ■ good transparency (3 mm thick - 90 %) ■ low inflammability, good workability, lighter than glass low hardness (0.2 GPa) low scratch resistance degradation by ultraviolet light replace glass and metals in: • automobile headlamps, stoplight lenses, • corrective lenses, • safety shields in windows, architectural glazing can be applied to: • plastics vessels, parts of machines • in optical grades for compact discs (CDs, CD-ROMs and DVDs), optical fibers deposition of functional films (scratch resistant, reflective, ...) surface treatment for improved film adhesion Plasma & Dry Technologies lasma Treatment ka Zajíčková 8/16 Plasma treatment of polycarbonate in Ar or 02 discharges (CCP) External plasma parameters: ■f = 13.56 MHz ■ inner diameter of reactor 490 mm ■ r.f. driven bottom electrode (420 mm) ■ Ar, 02: Q = 5.7 seem , p = 1.5 Pa ■ r.f. power P = 100 and 400 W c Plasma & Dry Technologies lasma Treatment ka Zajíčková 9/16 P = 100 W, Ubias = -115 V, Qar = 5.7 seem, p = 1.5 Pa _ 25 'to I 20 h > 15 10 etching in 02 discharge sputtering in Ar discharge _i_i_i_i_i_i_i_ 100 150 200 250 300 350 400 450 rf power [W] - 5 : 4 - 3 : 2 1 (M E o CO Ö > Plasma treatment of polycarbonate -etching rate and surface free energy E E 75 70 65 60 45 time [days] 0.01 0.1 1 10 —i—i i 1111 -r i i—i t i 111- —i—i—i—111111—i—i—i—111111—i— - Or.------ a"" ' " "......."'-fl-. 1 A a —- \ '■ \ .....a..... •-•-»•-- Ar, 100 W Ar, 400 W 02, 100 W 02, 400 W ■ \ \ ■ .......,......... ■ . 10 100 1000 10000 time [min] Plasma & Dry Technologies lasma Treatment ka Zajíčková 10/16 C1 C2 C4 C3 C5 Plasma treatment of polycarbonate -surface chemistry by XPS position [eV] assigment Cl 285.0 C-C, C-H C2 286.6 C-0 C3 288/289 C-C(=0)-C / 0-C(=0)-0 C4 290.9 C-C(=0)-0 C5 292.1 shake up power [W] untreated 280 285 290 295 530 binding energy [eV] C [at. %] 84.3 76.4 76.0 74.0 72.6 O [at. %] 15.7 20.3 19.9 24.0 24.7 Si [at. %] N[at. %] Plasma & Dry Technologies Plasma Treatment Lenka Zajíčková 11/16 7.3 Atmospheric Pressure Plasma Treatment for Adhesive Joints Case study: Polypropylene (PP) adhesive joints with aluminium General problem of PP (and other syntetic polymers): low free surface energy, chemical inertness ► Surface modification is required ► Added value is low, i. e. atmospheric pressure plasma treatment Experiments: comparison of different atmospheric pressure plasma jets, water contact angle, surface chemistry and topography, adhesive joint between PP and Al strips created with the epoxide adhesive DP 190 (3M) CH3 CH-CH2— n NOy OH NH ■x Q OH \ 9" N H, Plasma & Dry Technologies Plasma Treatment Lenka Zajíčková 12/16 7.3 PT & AFS Atm. Pressure Plasma Jets Jet Principle Working gas Working gas flow rate [slm] Additive Power [W] Frequency Treated area 0 [mm] Plasmatreat rotating plasma jet (PT) Electrical arc Dry air 30 — 1000 21 kHz 33 AFS Plasmajet® (AFS) Electrical arc Dry air 5-10 — 200-500 16-31 kHz 8 SurfaceTreat gliding arc (GA) Electrical arc Dry air 11.8 Ar 550 50 Hz 27-36 RF plasma slit jet (RF) CCP/ICP Ar 50-100 N2 300-600 13.56 MHz 150-300 {HI plasmatreat Working gas (dry air) Substrátu Plasma & Dry Technologies Plasma Treatment Lenka Zajíčková 13/16 7.3 SurfaceTreat Atm. Pressure Plasma Jet Jet Principle Working gas Working gas flow rate [slm] Additive Power [W] Frequency Treated area 0 [mm] Plasmatreat rotating plasma jet (PT) Electrical arc Dry air 30 — 1000 21 kHz 33 AFS Plasmajet® (AFS) Electrical arc Dry air 5-10 — 200-500 16-31 kHz 8 SurfaceTreat gliding arc (GA) Electrical arc Dry air 11.8 Ar 550 50 Hz 27-36 RF plasma slit jet (RF) CCP/ICP Ar 50-100 N2 300-600 13.56 MHz 150-300 SurfaceTreat bubbler Plasma & Dry Technologies asma Treatment asma Je ka Zajíčková 14/16 without a cross flow 180- aj Q- O, 170-