The lack of data concerning all the species and the microscopic phenomena involved in low pressure plasmas has always been the major obstacle for the complete understanding of the process mechanisms. As a matter of fact, even today, there is no gas-discharge system for which we can have, by whatever diagnostic tools, a complete picture of the concentration profiles of the species, either charged or neutral, involved in the various gas phase, gasfield, and gas-surface interactions (figure 1). This is more pronounced as we go from simpler noble or molecular gas plasmas to the more and more complex" chemical" plasmas used for the deposition of thin films. The main difference between classical chemical reactors and these plasma reactors comes from the presence of the electromagnetic field in interaction with various charged particles and surfaces. This makes the different plasma processes not easily predictable, controllable and comparable with each other. The rf power used in all these processes implies special reactor design and operation regimes which are different from the idealized plug-flow (PFR) or continuous stirred tank (CSTR) chemical reactors. Therefore, what one measures outside the reactor has no straightforward relation with what is happening inside, and there is no universal way of translating this information since, the" reacting gas volume" is not known, isotropic or homogeneous, while all the microscopic plasma quantities are also functions of space, in the specific reactor. On the other hand, a variation of one of the process parameters, like power or pressure, is not only associated with a change in the value of other macroscopic and microscopic quantities, but also with the way they interact with each other, with the electric field, and the surrounding surfaces. Two basic requirements arise from the discussion above: the need for more efficient, yet simple, non-intrusive diagnostics, and the need for more accurate process control. In fact, both requirements end up to the need for more accurate measurements. This is essential if the characterization of the discharge in a universal way is to be pursued, and it is also the main prerequisite for understanding the basic mechanisms governing the process, for building realistic mathematical models and in general for the development of the discharge theory.

In recent years, fluorocarbon plasmas have been extensively used for the treatment of polymer surfaces in an increasing number of applications. A decrease of the surface wettability is observed after exposure of the polymer to the discharge, to a degree depending on the treatment time and discharge parameters. Fluorination of the polymer surface, following exposure of the surface to the discharge, is believed to be the result of functionalization and/or polymerization, depending on the plasma composition. However, due to the complexity of the chemical reactions both in the gas phase and at surfaces, the underlying mechanisms are not yet well understood. The characterization of the reactive species formed in the discharge and the possible correlation of their behaviour to the plasma-induced modification of the surface properties is essential for understanding the role of the species and for the identification of the mechanisms of surface modification. Fluorocarbon radicals can be detected in situ by a number of diagnostic techniques, that include optical emission spectroscopy [1], laser-induced fluorescence (LIF)[2-4], UV absorption [5], infrared diode laser absorption spectroscopy (IRLAS)[6-8], and threshold ionization mass spectrometry [9-11].

According to the concept described by Langmuir in 1938 [1], the surface properties of a solid are determined by the surface-configuration (spatial arrangement of atoms at the interface) rather than the configuration of molecules which occupy the top surface region. In other words, whether a polymer surface is hydrophilic or hyrophobic cannot be predicted by the presence or absence of hydrophilic moieties in the molecules, but is determined by whether or not the hydrophilic moieties are located at the interface. In recent years, it has been recognized that the surface of a solid, particularly polymeric solid, is very different from what can be anticipated from the bulk characteristics of the same material. This discrepancy has been a focal point of the general phenomena recognized by the terms surface dynamics, surface reconstruction, etc., which deal with the change of chemical and morphological properties of polymer surface due to the change of the surrounding medium [2-14]. The surface dynamic change depends on the reference state from which the change takes place, and if one cannot define the reference state, the surface dynamics cannot be dealt in a generic sense. This problem was indeed found with moderately hydrophilic copolymer of ethylene/vinyl alcohol. The reference state depends on the history of a sample, and the change cannot be reproduced without precise knowledge of the history of a sample [15]. According to the view that a polymeric surface is an ever-changing entity depending on the surrounding medium [16], the restructured surface is not necessarily the final one to stay, ie, restructuring of once restructured surface or multiple repeated restructuring occur with highly perturbable polymeric surfaces. Therefore, the term" surface reconstruction" is intensionally avoided in the discussion of surface dynamics in this article. The change of surface is expressed by the change of surface-configuration.

Many useful processes for treating solid surfaces can be carried out by plasma methods. However, most previous work was done at low pressure, usually less than a few torr. For such low pressure processes, the vacuum apparatus requires great cost and is not suitable for the treatments of large scale substrates such as long film rolls. We previously reported that surface fluorination and thin film deposition could be carried out with the atmospheric pressure glow plasma (APG) process [1]. This approach can reduce apparatus costs and can also be applied to high vapor pressure substances such as gum, textiles and biomaterials. In this article, we will discuss the mechanism of stabilization of glow plasma at atmospheric pressure and report examples of applications of this technology.

A low pressure plasma comprises a complex mixture of electrons, charged and neutral molecules and fragments in the ground state and excited states, and a broad spectrum of radiation ranging from the infrared to the far ultraviolet. The specific role of each of these components in a plasma treatment of polymers is still not understood completely. The experimental data reported in the literature seem to be contradictory.

Low-pressure plasma processing of materials can be divided into three categories, namely (A) etching (removal of material),(B) deposition (addition of new material to a surface), and (C) modification (morphological, structural, and physicochemical change of the surface or near-surface region). In industries which make extensive use of low-pressure plasmas (for example, in the manufacture of integrated circuits-IC, the treatment of polymers for improved adhesion, etc), the above-named changes are deliberate and highly beneficial. However, there exist many instances where treatment can turn into a liability, or where plasma-chemical changes occur involuntarily and are a priori detrimental. The main objective of this chapter is to sensitize the reader to the existence of circumstances where plasma effects can be deleterious, for example:(1) Corona discharges, also known as silent discharges or dielectric barrier discharges, are a form of plasma which occurs when insulating materials are exposed to an alternating source of high voltage (~ 10 kV). Corona is comprised of multitudes of ultra-rapid (~ 100 ns), narrow (~ 100 μm) filamentary micro-discharges, which impinge upon the dielectric surface. Since the 1950s corona is being used commercially for treating polymeric webs up to 8 m in width, so as to render them printable (process category (C) above). However, corona treatment (like its low-pressure counterpart) can be detrimental if" overtreatment" occurs: If the reagent gas, like ambient air, contains oxygen, low-molecular-weight oxidized materials (LMWOM) form on the surface, and these can give rise to a weak boundary layer. This laboratory has compared corona and glow discharge treatment of LDPE and PET, using peel strength and XPS measurements, and has found similar" optimum" treatment criteria for both types of processes: High treatment (oxidation) levels could be correlated with elevated concentrations of acidic (O= C-O) reaction products and low peel strength.(2)

Surfaces and interfaces exhibit a rich variety of phase transitions. While some of these phase transitions also occur in the bulk, others involve coupling between surface and bulk degrees of freedom; consequently the surface phase diagram may be rather complex even for simple Ising like systems. In these lectures I will introduce the generic 4-dimensional surface phase diagram (bulk and surface couplings, bulk and surface fields) of Ising like systems and discuss bulk vs. surface criticality. I will start with a review of surface thermodynamics and scaling of interfaces with emphasis on wetting phenomena. Then Landau mean-field theory is used to calculate the global surface phase diagram. The effects of thermal fluctuations are discussed using the capillary wave Hamiltonian: The correlation functions are calculated using Ornstein-Zernike theory for systems with short and long-range forces. Finally, I will comment on the status of the renormalization group results for 3-dimensional short-range critical wetting that are at odds with the results of simulations of the Ising model and of a recent experiment.

These lecture notes discuss some theoretical approaches for the prediction of the structure, thermodynamics, and dynamics of polymers at interfaces, with emphasis on self-consistent field (SCF) methods. We begin with simple models for the conformational statistics of unperturbed chains and derive the Edwards diffusion equation for a Gaussian thread in a field. We then describe a simple lattice-based approach for a polymer melt at a flat interface and results from its application. Next, we discuss mixing energetics in the lattice model and outline an extension of the lattice-based SCF theory to treat copolymers at interfaces. Correspondences are pointed out between lattice-based and continuous SCF approaches, the latter making use of the Edwards diffusion equation. As an example of continuous formulations we present Helfand and Tagami’s elegant analytical solution for a flat interface between two immiscible polymers in the limit of very large molecular weights. Following Fredrickson et al., we outline a general fieldtheoretic approach for the mesoscopic modelling of inhomogeneous polymer systems. Using a symmetric diblock copolymer as an example, we show how a saddle point approximation reduces this formalism to a SCF theory and discuss the phase diagram obtained through continuous SCF by Matsen and Schick. As an example of scaling considerations, we derive expressions for the chain length dependence of the long period of the lamellar phase of the diblock copolymer. The latter part of the notes focusses on applications and comparisons with experiment. We discuss the structure of polymer/polymer and solid/polymer interfaces in the presence of diblock copolymers. We then briefly review a hierarchical theoretical/simulation approach for exploring adhesion at a solid/polymer interface strengthened by chains terminally grafted to the solid.

In this work, the effect of corona discharge treatment on surface properties of polyimide film was investigated in terms of FT-IR(Fourier Transform-IR), XPS(X-ray Photoelectron Spectroscopy) and contact angles. And the adhesion characteristics of the film were studied in peel strengths of polyimide coatings. As a result, polyimide surfaces treated by corona discharge led to an increase of oxygen-containing functional groups or polar component of the surface free energy, resulting in improving the adhesion characteristics of the polyimide/copper foil. However, the surface energy of the film was decreased as the aging time increased. These results could be discussed in the formation of surface functional groups or deterioration of reactive sites of polyimde film in the presence of corona treatment with aging time.

PTFE was treated with oxygen plasma, and the effects of treatment time were evaluated by XPS, SEM, and the contact angles of water and CH₂l₂. Advancing and receding angles were interpreted in the light of current theories on contact angle hysteresis. It was found that at short treatment time wettability reflects chemical modification of the surface, while at longer treatment times surfaces are deeply etched and contact angles are controlled by roughness. With water as the wetting liquid, the typical behavior of composite surfaces was observed.

The dynamic wetting behavior of poly(tetrafluoroethylene) (PTFE), polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), nylon 6, poly(ether urethane) (PU), poly(vinyl alcohol) (PVA), and cellulose was studied by the Wilhelmy balance technique at speeds of immersion from 1 to 50 mm/min. The Wilhelmy method was modified so as to determine contact angles without extrapolation of the loop to the zero immersion depth, employing a rectangular flat sample having a rectangular hole. This modification of the method allowed us to determine the advancing and receding contact angles on the very narrow sample area close to the lower (first) and the upper (second) sample-hole boundaries, theta1 and theta2, respectively. The interaction time of the sample part located at the lower boundary with the wetting liquid (water) was twice as long as that of the upper boundary. No difference was observed between the advancing contact angles measured at the lower and the upper parts of the sample (theta(ADV,1) = theta(ADV,2)) for all the Polymers, displaying that the dried polymer surfaces had no difference in wettability along the sample length. However, the lower part of the sample became more hydrophilic than the upper part during the wetting measurement for PET, PU, nylon 6, PVA, and cellulose, resulting in the difference between the receding contact angles (theta(REC,1) < theta(REC,2)). The effect was attributed to the time-dependent surface reorientation of hydrophilic and hydrophobic groups, occurring upon immersion of the polymer sample in water. A close correlation was observed between the hysteresis of the contact angle and the underwater surface reconstruction of polymers: the strongest hysteresis corresponds to the greatest wettability gradient generated by the time-dependent reorientation process. However, even when the effect of reorientation was zero (PTFE, PE, and PP) or very low (cellulose), the observed hysteresis was still as high as 27-degrees. The contribution of the surface reorientation of polar groups to the observed hysteresis was estimated to amount to 0-25-degrees, depending on the chemical structure of the polymer investigated. The speed of the sample immersion had no detectable effect on the wettability of PTFE, PE, and PP. On the other hand, the advancing contact angle on PET, PU, and nylon 6 increased while the receding contact angle decreased, as the immersion speed became higher. This behavior may be accounted for by referring to a model of macromolecular dynamics at the three-phase boundary.

Properties of polymer surfaces are very sensitive to minute quantities of impurity and different preparation procedures. Baier and Zisman reported that wettabilities of polypeptides and polyamides such as Nylon 2,6, and 11 are different when the polymers are cast from different solvents. They attributed this difference to the existence or absence of the surface hydrogen bonding site. They also proposed a Zisman plot split criterion for the recognition of hydrogen-bonding functionality in a polymer specimen's surface. However, we found that this criterion does not always work. We then apply our new model for acid-base interactions to interpret their data. The model fits data well. Moreover, it is noticed that cases with exposed surfacehydrogen bonding sites are all bipolar and surfaces without hydrogen bonding sites are all monobasic.