Research On Preparation Of Aligned Carbon Nanotubes Films Using Thermal CVD And Its Blood Compatibility

Carbon nanotubes（CNTs） are novel one-dimensional nano-materials with low density, high intensity and large aspect ratio.Aligned CNTs films are ordered groups of these nano-structures,which are all arranged along an identical direction,and are expected to have excellent properties implying promising applications,becoming one of the research hotspots in the world.Nickel catalyst thin films were deposited firstly on silicon substrates by K575X magnetron sputtering coater.The effects of ammonia pretreatment on the change of catalyst films from continuous one to the one with nanoscale particles were investigated. The nanostructures of the Ni thin films as a function of etching time,temperature and initial thickness of the catalyst film were discussed.The etching rules of the nickel catalyst film were summarized.Good-shape catalyst particles were obtained on the substrates.And the functional mechanism of ammonia was primarily analyzed.Aligned CNTs films were prepared secondly on nickel particles which derived from ammonia etching through thermal CVD method.Modern measuring and testing techniques such as SEM,TEM,XRD and Raman spectrum were employed to characterize the sample properties.The relationship between surface morphologies of CNTs and technological conditions were investigated to optimize the preparation parameters.Based on the morphology of catalyst and the nucleation of CNTs,the growth mechanism of aligned bamboo-shaped CNTs was studied and growth model was proposed.Contact angles（CA） of standard solution on CNTs films prepared in different conditions were measured.Then the relationship between surface-interface properties of CNTs and technological parameters was studied.Potential applications of CNTs films for blood compatibility in biomedicine were investigated.The property of prevention of platelet adhesion, anticoagulant property and damage degree to erythrocytes of CNTs films were investigated by platelet adhesion test,dynamic clotting time test and hemolysis assessment in vitro,respectively.The main factors influencing the blood compatibility of CNTs films were analyzed according to the characterization of surface-interface properties and the evaluation of blood compatibility of CNTs films in vitro.The relationship between surface-interface properties and blood compatibility of CNTs films were preliminary discussed.The principal results of this thesis were listed as follows.1、The size,density and homogenization of Ni nanoparticles on Si were adjusted through high temperature NH₃ etching.The appropriate processing time of ammonia, the processing temperature and initial film thickness are the key factors to obtain high dense.The better conditions for the fabrication of the uniform,small and high density transition metal catalyst nanoparticles on Si substrates are as follows:the etching duration of about 12min,the temperature of 800℃and initial film thickness of 10nm.2、Aligned CNTs films were prepared successfully by thermal CVD on etched Ni films. Controllable growth of CNTs films was implemented by adjusting different technogical parameters.Optimum preparation parameters of aligned CNTs films is obtained as follows:the growth temperature of 850℃,the growth time of 10min, C₂H₂ concentration of 16.7%and film thickness of 10nm.3、The results suggest that the intensity ratio I_D/I_G indicates the purity and degree of order in aligned CNTs.A lower I_D/I_G means less amorphous carbon and higher graphitization in aligned CNTs.4、A new growth mechanism based on dynamics alternation between growth-stop and steric hindrance was proposed,and it can give a qualitative explaination for the experiment results.EDX spectroscopy with non-destructive testing quickly indicated that the growth of CNTs conformed to tip-growth model,and XRD testing confirmed that Ni nanoparticles acted as the catalyst,not nickel carbide compound occurred during the CNTs growth period.5、The results obtained from surface-interface properties of CNTs films prepared in different conditions indicated that increasing the temperature could improve the wettability of CNTs surface with the contact angle ranging form 79.9°to 155.4°; contact angle increase of the time and ultimately kept steady;contact angle increased firstly and sharply decreased with the rising concentration of acetylene;contact angle changed from 95.7°to 160.2°by means of adjusting the thickness of nickel films. With the increase of contact angle for CNTs films,γ_s^d /γ_s^p and work of adhesion W_a decreased,while interfacial free energyγ_sl increased.6、Blood compatibility test for CNTs films in vitro indicated that CNTs films could improve the blood compatibility of substrate.Due to the interposition of CNTs,the number of platelets adhered and activated decreased,dynamic clotting time extended, haemolysis ratio decreased.It also improved the external environment,reduced the toxicity to erythrocyte and played an important role in maintaining the normal morphology and function of erythrocyte.In addition,CNTs films with excellent blood compatibility could be prepared via optimizing the technological parameters.7、Through investigation of the relation between surface-interface properties of CNTs and its blood compatibility,it indicated that several factors can be used to improve its blood compatibility such as strong hydrophobicity,low ratio of dispersive/polar component of the surface energyγ_s^d /γ_s^p and work of adhesion W_a,high interfacial free energyγ_sl.Moreover,the micro-nano structure is also closely related to its blood compatibility.