Journal of Colloid and Interface Science 244, 336–341 (2001) doi:10.1006/jcis.2001.7920, available online at http://www.idealibrary.com on Influence of Plasma Treatment on Microstructures and Acid–Base Surface Energetics of Nanostructured Carbon Blacks: N 2 Plasma Environment Soo-Jin Park 1 and Jeong-Soon Kim Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusong, Taejon 305-600, Korea Received March 15, 2001; accepted August 17, 2001; published online November 9, 2001 In this work, the effect of N 2 plasma treatment generated by radiofrequency was investigated in the context of surface and mi- crostructure characteristics of carbon blacks. XRD measurements revealed that the interlayer spacing, d 002 and crystalline size along the c axis, L C , decrease with plasma treatment, which can result in the removal from weak or unstable microstructures of carbons. In this work, the determination of electron-acceptor (γ + S ) and -donor (γ − S ) parameters of the surface free energy of a solid was proposed by the polar testing liquids using a water, diiodomethane, and ethy- lene glycol. It was clear that the major obvious improvement of the treatment is in the London dispersive component of the surface free energy of carbon blacks. And both γ + S and γ − S for the specific component also increased with increasing treatment time, result- ing in improvement in the surface functional groups of the carbon blacks studied, together with increases in acidic and basic surface functional groups and ion-exchange properties. C  2001 Elsevier Science Key Words: plasma treatment; electron acceptor; electron donor; carbon blacks; microstructures; surface free energy. 1. INTRODUCTION Carbon materials are largely used to modify the mechanical and electrical properties of the medium in which they are dis- persed, adsorbents, and catalyst supports—perhaps the most sig- nificant applications of carbonaceous materials. Carbon blacks as fillers are one of the major inputs in tire industry and have some extraordinary features. These are due mainly to the effects of their high porosity, irregular nanoshapes, and structures in general (1–4). Carbon surfaces are often difficult to wet due to their low sur- face energy and chemical inertness (5). This statement is par- ticularly applicable to low-surface-energy carbon blacks which generally contain a very large proportion of C–C bonds, the strongest bonds found in organic compounds. Surface treatments are therefore needed to improve the wettability of carbon sur- faces by promoting the formation of hydrophilic groups, which increase surface energetics. 1 To whom all correspondence should be addressed. E-mail: psjin@pado. krict.re.kr. The most widely used surface modification techniques involve chemical treatments, electrochemical treatment, photoirradia- tion or phototreatments with ionized gases, i.e., microwave, ra- diofrequency, and glow discharge plasmas (6–12). Among these, the interaction of the plasma treatment with carbon surfaces produces highly active species, such as free radicals, ions, and metastable species, which cause ablation, crosslinking, and oxi- dation reactions, depending on the nature of the gases used in the plasma zone (6, 13–15). There are two principal advantages to mild plasma treatment method for materials: (1) the reaction takes place only on the material surface without significantly changing bulk properties, and (2) it is possible to make any at- mosphere, such as oxidative, reductive, and inactive. This has become increasingly more important owing to their very high efficiency and operational simplicity. Surface energetics are also of importance because of the possibility of exerting careful con- trol of the layer affected by the treatment, usually 0.02–50 μm in depth (6). This characterization of carbon surfaces is one of the most critical parameters considered for degree of reinforcement (2, 14). Moreover, it is believed that the surface energetics of car- bon blacks are of much greater importance than their physical and chemical elements with respect to the resulting mechanical properties of the filled polymeric matrix. An approach to the determination of the surface free energy of a solid has been de- veloped based on the theory of nonpolar and polar components, including acid–base interactions, by several researchers (16–22). It is more general where one of the most important factors is the electron-acceptor (acid) and electron-donor (base) parameters of surface free energy between the solid surfaces (23). This is recognized to provide an accurate and real description of the specific surface free energy of a solid, and has been applied to a variety of interfacial systems in many areas of surface science. The main purpose of this study is to understand the influ- ence of surface properties, such as acid–base values and ion exchange, acquired by N 2 plasma treatment on nanostructured carbon blacks. In a next step, the effect of plasma treatment of carbon blacks on microstructure and acid–base surface energet- ics is investigated in the context of XRD and contact angles, respectively. 336 0021-9797/01 $35.00 C  2001 Elsevier Science All rights reserved