Effect of glow discharge treatment of poly(acrylic acid) preadsorbed onto poly(ethylene)

In order to introduce carboxylic acid groups at the surface of poly(ethylene) (PE) films, an attempt was made to covalently link a preadsorbed layer of poly(acrylic acid) (PAAc) on a PE film by an argon or tetrafluoromethane (CF4) plasma treatment. Surface analysis was performed by XPS (X-ray photoelectron spectroscopy) and water contact angle measurements. It was shown that by treatment of a PAAc layer preadsorbed on PE with an argon or a CF4 plasma, a small amount of carboxylic acid groups was introduced at the surface. A similar amount of these groups was obtained by plasma treatment of PE films without a preadsorbed PAAc layer. A comparison of the etching rates of PAAc and PE by either an argon or a CF4 plasma, showed that PAAc is etched much faster by both types of plasmas than PE. The preadsorbed PAAc layer on PE is etched off before it could be immobilized by either an argon or a CF4 plasma treatment. Additionally the effect of treating PE films for very short times with an argon or a CF4 plasma was studied. After an induction period of approximately 0.1 s, the oxidation during the argon plasma treatment and the fluorination during the CF4 plasma treatment were proportional to the logarithm of the treatment time for time periods up to 50 s

Introduction of functional groups on polyethylene surfaces by a carbon dioxide plasma treatment

Poly(ethylene) (PE) films were treated with a carbon dioxide (CO2) plasma to study the formation of oxygen-containing functional groups at the surface. Modified and nonmodified films were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. During the CO2 plasma treatment, the PE surface is etched and oxidized, yielding films with a very hydrophilic surface. The oxygen incorporation at the surface is fast and can be described by a combination of a zero-order incoraporation and a first-order etching process. Several oxygen functionalities such as carboxylic acid (approximately 14% of the oxygen persent), ketone/aldehyde (25%), and hydroxyl/epoxide (5-9%) groups were introduced at the surface by the plasma treatment. This was shown by using derivatization reactions for specific functional groups followed by XPS analysis. The wettability of the plasma-treated surface decreased when the films were stroed for prolonged periods of time in air. This aging process could not be completely reversed by immersion of the films in water

On the effect of treating poly(acrylic acid) with argon and tetrafluoromethane plasmas:kinetics and degradation mechanism

Poly(acrylic acid) (PAAc) films were treated with either an argon or a tetrafluoromethane (CF4) plasma and subsequently analyzed with X-ray photoelectron spectroscopy (XPS). PAAc films were decarboxylated during both types of plasma treatments. In addition, during the CF4 plasma treatment, the PAAc films became fluorinated. The plasma phase during the argon plasma treatment of PAAc films was investigated with optical emission spectroscopy. It was shown that during this plasma treatment carbon dioxide, water, and possibly hydrogen were liberated from the PAAc surface. By covering the surface of PAAc films with different materials (lithium fluoride, UV fused silica, and glass) during the plasma treatment, it was possible to differentiate between photochemically induced and particle-induced changes of the surface. This method was used to show that decarboxylation during the argon plasma treatment was caused by vacuum UV radiation (wavelength < 150 nm) and the decarboxylation/fluorination during the CF4 plasma treatment was induced by reactive fluorine-containing species from the plasma phase. Furthermore, during both processes, etching of the PAAc surface occurred. Based on these mechanisms, kinetic models were derived that could be used to describe the measured kinetic data adequately

Immobilization of Surface Active Compounds on Polymer Supports Using Glow Discharge Processes 1. Sodium Dodecyl Sulfate on Poly(propylene)

A new method has been developed in which a reversibly adsorbed layer of a surfactant (sodium dodecyl sulfate, SDS) is covalently immobilized in one step onto a hydrophobic substrate (poly(propylene), PP) by applying an argon plasma treatment. The adsorption of SDS from aqueous solutions onto PP surfaces was studied with X-ray photoelectron spectroscopy (XPS). Plateau levels of adsorbed SDS were reached within 10 s using SDS solution concentrations above the critical micelle concentration (CMC). At SDS concentrations below the CMC almost no adsorption took place, whereas at SDS concentrations above the CMC constant adsorption levels were measured. Preadsorbed SDS layers could be completely desorbed after immersion of the SDS-coated substrates in water for 90 min. If PP surfaces with preadsorbed SDS were dried and plasma-treated with an argon glow discharge and then immersed in water for 90 min, intact sulfate groups were present at the surface as shown by ion exchange and XPS measurements. This indicates that SDS preadsorbed onto PP surfaces can be immobilized by a plasma treatment. It is concluded that plasma techniques can be used to immobilize physically adsorbed surface active compounds onto substrates. This is a useful way to derivatize inert substrates with various polar or nonpolar groups

Immobilization of surface active compounds on polymer supports using glow discharge processess: 1. Sodium dodecyl sulfate on poly(propylene)

A new method has been developed in which a reversibly adsorbed layer of a surfactant (sodium dodecyl sulfate, SDS) is covalently immobilized in one step onto a hydrophobic substrate (poly(propylene), PP) by applying an argon plasma treatment. The adsorption of SDS from aqueous solutions onto PP surfaces was studied with X-ray photoelectron spectroscopy (XPS). Plateau levels of adsorbed SDS were reached within 10 s using SDS solution concentrations above the critical micelle concentration (CMC). At SDS concentrations below the CMC almost no adsorption took place, whereas at SDS concentrations above the CMC constant adsorption levels were measured. Preadsorbed SDS layers could be completely desorbed after immersion of the SDS-coated substrates in water for 90 min. If PP surfaces with preadsorbed SDS were dried and plasma-treated with an argon glow discharge and then immersed in water for 90 min, intact sulfate groups were present at the surface as shown by ion exchange and XPS measurements. This indicates that SDS preadsorbed onto PP surfaces can be immobilized by a plasma treatment. It is concluded that plasma techniques can be used to immobilize physically adsorbed surface active compounds onto substrates. This is a useful way to derivatize inert substrates with various polar or nonpolar groups

In vitro leukocyte adhesion to modified polyurethane surfaces:II. Effect of wettability

The influence of substrate wettability on leukocyte adhesion was studied using a series of polyurethane films with different surface wettabilities, prepared by a two step gas plasma modification procedure. In the first step the films were made hydrophobic by exposure to a tetrafluoromethane plasma. In the second step hydrophilicity was gradually increased by exposure to an argon plasma. XPS analysis of these films demonstrated that the first step resulted in the incorporation of fluor into the film surface (50 At.-%). In the second step fluor was almost completely removed from the surface, while the surface oxygen concentration increased from 5 to 20 At.-%. The wettability of the modified films, as characterized by water contact angle measurements, increased as a function of the argon treatment time. The advancing/receding contact angles (Wilhelmy plate method ) decreased from 128/83 to 50/2 degrees respectively. In vitro adhesion of granulocytes and lymphocytes to the modified surfaces was studied under static conditions as a function of time. For both types of leukocytes it was found that the number of cells which adhered to the surface within a certain incubation time increased when the surface became more hydrophilic. The number of adherent granulocytes was about 2-3 times higher than the number of adherent lymphocytes. The number of adherent cells which could be predicted from the relationship between leukocyte adhesion and the wettability of the substrates within the series of homologous surfaces corresponded with the number of adherent cells to control surfaces (untreated polyurethane and Teflon)

Introduction of functional groups of polyethylene surfaces by a carbon dioxide plasma treatment

Poly(ethylene) (PE) films were treated with a carbon dioxide (CO2) plasma to study the formation of oxygen-containing functional groups at the surface. Modified and nonmodified films were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. During the CO2 plasma treatment, the PE surface is etched and oxidized, yielding films with a very hydrophilic surface. The oxygen incorporation at the surface is fast and can be described by a combination of a zero-order incoraporation and a first-order etching process. Several oxygen functionalities such as carboxylic acid (approximately 14% of the oxygen persent), ketone/aldehyde (25%), and hydroxyl/epoxide (5-9%) groups were introduced at the surface by the plasma treatment. This was shown by using derivatization reactions for specific functional groups followed by XPS analysis. The wettability of the plasma-treated surface decreased when the films were stroed for prolonged periods of time in air. This aging process could not be completely reversed by immersion of the films in water

In vitro leucocyte adhesion to modified polyurethane surfaces. I. Effect of ionizable functional groups

To study the effect of ionizable functional groups on the adhesion of leucocytes to surfaces, both poly(ethyleneimine) and poly(acrylic acid) were immobilized on polyurethane films, resulting in the introduction of amine and carboxylic acid groups, respectively. This was confirmed by contact angle measurements and XPS analysis. In vitro adhesion of granulocytes and lymphocytes on untreated and modified surfaces was compared. The number of adherent cells on modified surfaces as a function of time was significantly higher than on untreated surfaces. This effect was most pronounced for the adhesion of lymphocytes to surfaces modified with amine groups. In this case, the number of adherent cells after 1 h of exposure was three times higher than on untreated surfaces. A moderate enhancement of leucocyte adhesion was observed in the case of surfaces modified with carboxylic acid groups. There is evidence that these groups were not ionized under the experimental conditions used. The modification procedures described may be used to improve polyurethane filters for the removal of leucocytes from blood

In vitro leukocyte adhesion to modified polyurethane surfaces. II. Effect of wettability

The influence of substrate wettability on leukocyte adhesion was studied using a series of polyurethane films with different surface wettabilities, prepared by a two step gas plasma modification procedure. In the first step the films were made hydrophobic by exposure to a tetrafluoromethane plasma. In the second step hydrophilicity was gradually increased by exposure to an argon plasma. XPS analysis of these films demonstrated that the first step resulted in the incorporation of fluor into the film surface (50 At.-%). In the second step fluor was almost completely removed from the surface, while the surface oxygen concentration increased from 5 to 20 At.-%. The wettability of the modified films, as characterized by water contact angle measurements, increased as a function of the argon treatment time. The advancing/receding contact angles (Wilhelmy plate method ) decreased from 128/83 to 50/2 degrees respectively. In vitro adhesion of granulocytes and lymphocytes to the modified surfaces was studied under static conditions as a function of time. For both types of leukocytes it was found that the number of cells which adhered to the surface within a certain incubation time increased when the surface became more hydrophilic. The number of adherent granulocytes was about 2-3 times higher than the number of adherent lymphocytes. The number of adherent cells which could be predicted from the relationship between leukocyte adhesion and the wettability of the substrates within the series of homologous surfaces corresponded with the number of adherent cells to control surfaces (untreated polyurethane and Teflon)