Determination of Surface Free Energy and Contact Angle for Hydrolyzed Shellac

The purpose of this research was to determine surface free energy and contact angle of hydrolyzed shellac by using sessile drop technique. It is a method for determination of contact angle by placing a drop of liquid on a substrate and the surface free energy is then calculated by using the Wus equation. The substrate in this study was the hydrolyzed shellac prepared by hydrolysis of the native shellac at various times; 0, 15, 30 and 45 min using 2.0 %w/w sodium hydroxide. Water, formamide and ethylene glycol were liquids used for the investigation of the contact angle and surface free energy. The effect of hydrolysis time tended to reduce the contact angle and increase in the total surface free energy and polar force of hydrolyzed shellac. The result could be due to the breaking of the ester bonds of shellac during the hydrolysis process causing the higher free carboxyl group giving the higher polar group indicating by higher polar force and surface free energy. Therefore, the contact angle and surface free energy detected by sessile drop technique could be of benefit for the determination of hydrolysis process.

Ion Assisted Reaction In Polymer And Ceramics

AbstracrIon assisted reaction (IAR), which was firstly presented in 1995 MRS Fall meeting, has been reviewed for the surface modifications of polymer and ceramics. The reaction is assisted by energetic ions from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 0 ∼ 8 ml/min. Hydrophilic surfaces of polymers (wetting angle < 20° and surface energy 60 ∼ 70 erg/cm2) have been accomplished by the reaction, and an improvement of wettability and an increment of the surface energy are mainly due to the polar force and hydrophilic functional groups such as C=O, (C=O)-O, C-O, etc., without surface damage. The IAR was also applied on aluminum nitride in an O2 environment and AMON on AIN is formed by the Ar+ irradiation. The improvement of bond strength of Cu films on the AIN surface resulted from the interface bonds between Cu and the surface layers. Comparisons between the conventional surface treatments and the IAR are described in terms of physical bombardment, surface damage, functional group, and chain mobility in polymer.

Surface Modification of Polymer by Ion Assisted Reaction in Reactive Gases Environment

Wettable surface of polymers (advanced wetting angle ∼10° and surface energy ∼ 60 ∼ 70 erg/cm2) have been accomplished by the ion assisted reaction, in which energetic ions are irradiated on polymer with blowing oxygen gas. The energies of ions are varied from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 0 ∼ 8 ml/min. The wetting angles are increased when the wettable polymers were exposed in air, but are remained in pure water. Improvement of surface energy is mainly due to the polar force. Surface analysis shows hydrophilic functional groups such as C=O, (C=O)-O, C-O, etc., are formed without surface damage after the ion assisted reaction treatment. Comparisons between the conventional surface treatments and the ion assisted reaction are described in term of physical bombardment, surface damage, functional group, and chain mobility in polymer.

The adhesion of thermoplastic fibre composites

Fibre composites based upon thermoplastic polymeric matrices containing continuous fibres of carbon or ‘ Kevlar' are being increasingly used in engineering structures. Engineering applications frequently require that they be joined to components fabricated from similar fibre composites, or to other types of materials, and the use of structural adhesives, typically based upon epoxy resins, offers many advantages compared with other methods of joining. The present paper describes in detail the mechanics and mechanisms of the adhesion of thermoplastic fibre composites. The surface topography and chemistry of the composites have been characterized using contact angle measurements and X-ray photoelectron spectroscopy, both before and after using various surface treatments. Joints have then been prepared using epoxy adhesives and the adhesive fracture energies, Gc, of the joints have been measured. Two major aspects of the observed results, with wide applicability to many adhesion problems, have been analysed in detail. First, the need to apply a critical intensity of surface treatment to the thermoplastic fibre composite to prevent interfacial failure, and hence give relatively high values of G has been interpreted by relating the chemical composition of the surface of the composite to the corresponding value of the polar force component of the surface free energy. It is thereby shown that the fundamental requirement is that a critical value of the surface polarity has to be attained. Secondly, after this critical value is reached, it is shown that the locus of joint failure may then be accurately predicted from a knowledge of the stress field in the joint and the experimentally measured interlaminar fracture stress of the fibre composite substrates.