• Some materials are not very compatible with ink, printing processes. Ex. Polypropylene • Surface energy is an important factor in terms of wetting behavior of the material • When material is exposed to ink, it might not spread on the material as required • We have to change the surface energy of the material so that we can modify our surface in terms of its appearence
Used for increasing the surface energy Exploits the corona effect Result of this treatment is usually better adhesion and better wettability properties Usually employed in film production Its effect degrades over time, that is why inking or printing is done after corona treatment
Corona treatment is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of high voltage to sharp electrode tips which forms plasma at the ends of the sharp tips.
Electromagnetic field is produced by magnetic field generator Film winded on a roll goes under the corona generators Excited species in the air modifies the surface Important parameters are voltage, pressure of the air, sample/electrode geometry
Again used for wetting and printing purposes Usually used for polyolefin surfaces Basic apparatus: Flame generators and mold holding the material Flames located at certain points scans the material for the time of treatment Scan time, material-flame distance, flame temperature are important in this treatment
Introduction of plasma to the surface Process resembles corona discharge Has to be done in a vacuum chamber for a better homogeneity in gaseous mixture Anode and cathode are used to form plasmas Plasmas generated modify surface via increasing surface activity in micro level
There are two types of plasma treatment Cold Plasma vs Hot Plasma Temperature of plasma is very high at atmospheric pressure This can be utilized in melting of a powder to be used as a coating.
This is called hot plasma treatment It is usually used for deposition of coatings
FUNCTIONALIZATION OF POLYMER SURFACES
Functionalization occurs by chemical interaction of plasma produced species - ions, radicals and photons with the surface.
(a) (b) (c)
Example: H abstraction by O atom enables affixing O atoms as a peroxy site.
Increase surface energy
Process treats the top few layers.
Wettability on PE film with 3 zones of treatment.
SURFACE MODIFICATION OF POLYMERS
Pulsed atmospheric filamentary discharges (coronas) routinely treat commodity polymers like poly-propylene (PP) and polyethylene (PE).
Filamentary Plasma 10s – 200
COMMERCIAL CORONA PLASMA EQUIPMENT
PRIMER ON SURFACE CHEMISTRY
Functional groups are when treated in O 2 containing plasmas: Alkyl Alkoxy Carbonyl Alcohol Peroxy Acid R
R=O R-OH R-OO
PRIMER ON SURFACE CHEMISTRY
Ratio of O, OH, O 2 and O 3 fluxes determine surface composition.
Magnitude of fluxes and residence time determines importance of surface surface reactions.
FORCED GAS FLOW AND WEB MOVEMENT Gas Flow
Polymer surfaces are continuously treated at web speeds of a few m/s with residence times in plasma of up to a few ms.
Non air gas mixtures are often “forced flowed” through gap to customize radicals to surface. EUJapan_0307_22
There are two types of ICP geometries: planar and cylindrical. In planar geometry, the electrode is a coil of flat metal wound like a spiral. In cylindrical geometry, it is like a helical spring.
When a time-varying electric current is passed through the coil, it creates a time varying magnetic field around it, which in turn induces azimuthally electric currents in the rarefied gas, leading to the formation of a plasma. Argon is one example of a commonly-used rarefied gas.
Plasma technologies in Plasma lab
Used for biocompatible materials (polymers, composites, artificial blood vessel, etc.) • sterilization • functionalization
PLASMAS USED IN PLASMA LAB
Plasmas are created in oxygen , hydrogen, nitrogen and argon
For medical purposes the inductively coupled oxygen plasma is used. Typical parameters of weakly ionized fully dissociated oxygen plasma
• Electron temperature 5 eV • Electron density 10
15 m -3
• Positive ion density 10
15 m -3
• Degree of dissociation up to 100% • Neutral gas kinetic temperature about 50C • Density of O atoms depends on pressure • Density of O atoms often over 10
21 m -3
Plasma sterilization 1μm 1μm
SEM image of Bacillus subtilis before (left) and after plasma treated.
AFM investigations of biological samples
Atomic Force Microscope (AFM) (left) and image of Staphylococcus aureus (right).
Plasma functionalization of organic materials
Reactive particles from oxygen plasma are incorporated on the surface forming O-rich functional groups.
C-OH C-O COOH C=O Surface polymer oxygen plasma Polar groups on a polymer surface cause a dramatic increase of surface wettability.
Surface wettability is measured by water drop
untreated treated 0.5s
The contact angle of a water drop on a polymer surface versus plasma treatment time
Appearance of functional groups is best analysed by X-ray photoelectron spectroscopy (XPS = ESCA) h
Photo electrons Instrument PHI-TFA Principle
Appearance of functional groups is monitored by XPS
Survey spectra of PES (poly(ether sulfones)) polymer before (bottom) and after different plasma treatment (middle and top).
High resolution C 1s peak
A … C-C or C-H B … C-O C … C=O D … O=S=O
300 295 290 285
Binding Energy (eV)
O o c c A
D C B
300 295 290 285
Binding Energy (eV)
Plasma activated PES (1s) 280
Ion assisted vs ion implantation Ion implantation is a process in which ion beam is introduced directly to the surface Ion assisted treatment is to target species which will then form a coating on the surface Apparatus includes ion gun and closed system
Used in coatings whose material can be found in liquid form and evaporates easily. Ex. Aluminium Electron gun hits the coating material in liquid form Evaporated material is coated on the polymeric film Beam emitted has to be controlled
In surface treatment, UV, laser, X-ray could also be employed Their main impact is to maintain cross-linking on the surface Closed system is required because the process has to be precise Properties like diffusion coefficient, permeability, adhesion can be modified
In the treatment of polymeric surfaces, chemical composition of polymer surfaces can be modified either by direct chemical reaction with a given solution (wet treatment) or by the covalent bonding of suitable macromolecular chains to the sample surface (grafting).
Wet treatments were the first surface modification techniques used in order to improve surface properties of polymers.
Hot chromic acid was used to oxidize polyolefins Specific solutions were prepared in order to exploit specific liquid-polymer interaction.
The effectiveness of the treatment depends on the interaction of the different modification mechanisms
Polymer surfaces are rarely homogeneous.
When the surface composition is constant throughout the surface, amorphous and crystalline domains are present on it.
Wet treatment is not homogeneous on the surface.
Sodium etching of fluoropolymers Oxidizing treatment based on chromic acid solutions Hydrolysis of polyesters etc.
Etching is a process of preparing the surface of a fluoropolymer insulated wire or tubing for bonding to another material.
The etching process is used on PTFE, FEP and PFA fluoropolymers.
PTFE has superb thermal, electrical and chemical resistance characteristics.
PTFE the choice in applications such as coating of non stick frying pans.
The chemical structure of PTFE results in a non-polar, non-wettable surface.
The etching process strips a layer of fluorine atoms from the surface and leaves the carbon atoms with a deficiency of electrons.
When the altered surface is exposed to the atmosphere, oxygen and hydrogen restore some of the electrons forming a surface that will accept bonding.
The effectiveness of etching is measured by calculating the change in surface wettability. θ = contact angle
Surface treatment of various polymers by oxidizing solutions was developed as a result of the low metal to-polymer adhesion.
In the early studies and papers that were written, the problem was handled only in a physical manner. Later studies, mainly following the development of the surface sensitive analytical techniques, considered also the chemical side of the problem.
Removing completely, or to prevent formation of, what are often referred to as weak boundary layers.
Protecting the adherend surfaces before bonding.
Producing a specific adherend surface topography, thereby altering the surface profile, and possibly increasing the bondable surface area, that is, to roughen the surface.
The attack of a nucleophilic agent, such as a base, on an electron-deficient carbon atom, has been exploited in several different classes of polymers in order to improve their surface properties.
Hydrolysis of PET by hot sodium hydroxide attack is the oldest and most used technique which increases the number of hydrophilic groups, improves the moisture-related properties.
The aim of the functionalization of polymer surfaces is to create a surface layer of well-defined functional groups. In this way one can create polymeric surfaces of controlled properties or a rigid substrate of controlled chemical reactivity.
In surface grafting, the aim is to achieve chemical modification of the surface by the covalent bonding of new macromolecules on top of the substrate.
Fundamental step in grafting is the creation of reactive groups on the substrate surface.
It can either be done chemically or by irradiation (ionizing radiation, UV light and glow discharge). This grafting-coupling technique is sometimes followed but it is more common to contact the activated surface with a suitable monomer, so that a growing chain starts from the activated site.
html http://pubs.acs.org/cgi bin/abstract.cgi/jpchax/1994/98/i47/f pdf/f_j100098a046.pdf?sessid=6006l3 http://www.kobelco.co.jp/p108/p14/sfe05.htm