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Zeta potential, DLC, Diamond like carbon, Carbon films, Medical applications
[Nitta et. al., Diamond & Related Materials 17 (2008) 1972-1976]
MSE 576 Thin Films & Analysis Presentation
* Diamond-like carbon thin films
* Zeta potential
* Discuss paper by Nitta et. al.
* Interesting properties:
* Low coefficient of friction
* Applications: Dies and automobile parts.
* Reason: Medical devices that are in contact with the blood, e.g., artificial hearts and blood pumps.
* Present problem: blood clotting, performance.
* Blood compatibility is not outstanding.
* Chemically stable amorphous hydrocarbon thin film.
* Problem: Not effective in all the situations.
* Account must be taken of the interactions between the cell and the DLC thin film surface.
* Important parameter: Zeta potential !!
* Theoretically, it is the electric potential in the interfacial double layer (DL) at the location of the slipping plane versus a point in the bulk fluid away from the interface.
* In simple terms, it is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.
* It indicates the degree of repulsion between adjacent, similarly charged particles (the vitamins) in a dispersion.
* A high zeta potential: Stability ! (+ or -)
* A low zeta potential: Flocculation !
* Stimulation to the cells can be reduced by controlling the zeta potential.
* Method by Nitta et. al.: Introduce functional groups such as amino (-NH2) and carboxyl groups (-COOH).
* How: Plasma surface treatment.
* Amino groups: high positive charge.
* If the quantities of these functional groups can be controlled at the DLC thin film surface, it will be possible to control the zeta potential.
* Process chamber connected to a RF power supply with an excitation frequency 13.56 MHz at power of 300W.
* RF power of 30 W was injected to generate plasmas.
* Capacitatively Couple Plasmas (CCP) was generated by means of two parallel plate electrodes.
* Gases used: O2, Ar, NH3 and C2H2 (15 seconds).
* DLC thin films used were prepared by ionization-assisted deposition using benzene.
* DLC thin film thickness: 40 nm.
* After plasma surface treatment:
* XPS: Composition ratios of the DLC samples.
Results: C2H2 followed by O2 treatment
* Comparing them with the XPS results of the DLC samples show that C-C bonds or C-H bonds were cleaved by radicals, electrons, and ions in the plasma.
* Thereby oxidation reactions such as C-O, C=O and O=C-O were promoted.
* O2 or O radicals in plasma mainly drew H from C-H bonds. Amount of C-C bonds or C-H bonds in DLC thin films were dependent on functional groups introduced to DLC surface.
* Thus, it is considered that amount of functional groups introduced to DLC thin films surface can be controlled by controlling amount of C-C bonds or C-H bonds in DLC thin films.
* The O=C-O peaks stem from the carboxyl groups and were three times more numerous than that of untreated DLC sample.
* Carboxyl groups can be introduced efficiently onto the surface of DLC thin films by plasma surface treatment.
* N1s peak was remarkable compared to that of C2H2+O2 plasma treatment.
* C-H bonds or C-C bonds were cleaved by radicals, electrons, and ions in the NH3 plasma, and nitrogen was introduced into the DLC thin films surface.
* C-NH2 peak dominated
* It is possible to generate amino groups on DLC thin films surface.
* It is possible to control the zeta potential of DLC thin films by controlling the amounts of the carboxyl groups and amino groups.
* A new method discovered to develop a biocompatible material.